CA1302484C - Regenerative two-quadrant converter and motor drive embodying the same - Google Patents
Regenerative two-quadrant converter and motor drive embodying the sameInfo
- Publication number
- CA1302484C CA1302484C CA000592165A CA592165A CA1302484C CA 1302484 C CA1302484 C CA 1302484C CA 000592165 A CA000592165 A CA 000592165A CA 592165 A CA592165 A CA 592165A CA 1302484 C CA1302484 C CA 1302484C
- Authority
- CA
- Canada
- Prior art keywords
- current
- thyristor
- conduction
- bridge
- reactor
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
Classifications
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P7/00—Arrangements for regulating or controlling the speed or torque of electric DC motors
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
- H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
- H02M7/12—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/145—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means
- H02M7/155—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means using semiconductor devices only
- H02M7/162—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means using semiconductor devices only in a bridge configuration
- H02M7/1623—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means using semiconductor devices only in a bridge configuration with control circuit
- H02M7/1626—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means using semiconductor devices only in a bridge configuration with control circuit with automatic control of the output voltage or current
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M5/00—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases
- H02M5/40—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc
- H02M5/42—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters
- H02M5/44—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac
- H02M5/443—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a thyratron or thyristor type requiring extinguishing means
- H02M5/45—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a thyratron or thyristor type requiring extinguishing means using semiconductor devices only
- H02M5/4505—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a thyratron or thyristor type requiring extinguishing means using semiconductor devices only having a rectifier with controlled elements
Abstract
13 54, 170 ABSTRACT OF THE DISCLOSURE
In a voltage-source inverter system, wherein the commutation between static switches in the AC/DC converter in the regenerative mode is forced by a GTO or transistor device in series with an auxiliary thyristor in order to bring the current path to zero, a reactor of large induc-tance is inserted for improved operation in the forward and regenerative mode, but an additional thyristor is converted in unparallel to such reactor in order to neutralize the inductance when bringing the current to zero in the regen-erative mode, and such additional thyristor is turned OFF
by natural commutation. when the next converter static switch is coming ON.
In a voltage-source inverter system, wherein the commutation between static switches in the AC/DC converter in the regenerative mode is forced by a GTO or transistor device in series with an auxiliary thyristor in order to bring the current path to zero, a reactor of large induc-tance is inserted for improved operation in the forward and regenerative mode, but an additional thyristor is converted in unparallel to such reactor in order to neutralize the inductance when bringing the current to zero in the regen-erative mode, and such additional thyristor is turned OFF
by natural commutation. when the next converter static switch is coming ON.
Description
~L3~2~
1 54,170 IMPROVED REGENERATIVE TWO-QUADRANT CONVERTER
AND MOTOR DRIVE EMBODYING THE SAME
The invention relates to constant and variable voltage voltage-source inverter systems, and to AC motor drives embodying such a voltage-source.
In the converter supplying power to the DC-link of a voltage-source inverter, there is a need Eor an inductance both as a means of reducing the harmonic content of the mains current at the AC power supply side, and to limit the rate of rise of a fault current in the event of a shoot-through among the thyristors of the converter brid~e while in ~he regenerative mode. It is desirable to maxi-mize the amount of inductance so inserted in the DC-link in order to have its full benefit. The invention, however, involves a voltage-source converter as described in U.S.
Patent No. 4,697,131 issued September 29, 1987, wherein in the regenerative mode an interruption of current is caused to happen at the time the converter thyristors are being commutated. With this particular type, a large inductance would hinder the commutation of the converter bridge static switches. The problem arises because the inductance prevents the converter current from being rapidly reduced to zero, as required for effective commutation from one set of switches to the next in the control sequence of the bridge.
The invention is particularly applicable to the converter power supply for a voltage-source inverter such as described in the afore-mentioned U.S. Patent No.
~3~2~
1 4,697,131 which should be consulted for the purpose of a more complete understanding thereof.
SUMMARY OF THY INVENTION
The present invention assists the commutation between outgoing and incoming static ~witches in the sequence of conduction of the static switches of an AC/DC
converter of the type described in the above referenced United States patent, where a large induc~ance has been inserted in its DC-link. This i5 achieved by usinq a GTO
device, or a transistor, to interrupt the main current, and by creating with an additio~al static switch a separate bypass for the inductance energy, so as to help build-up, and minimize the duration of, a zero-current condition in the bridge at the moment of commutation.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a block diagram of a variable fre-quency, variable voltage AC output system of the prior art;
Figure 2 shows the AC-DC converter used in the system of U.S. Patent No. 4,697,131, which is part of the preferred embodiment of the invention;
Figure 3 shows the use o an inductance in the DC-link of the converter of Figure 2, such use being the cause of the problem to be solved according to the present invention;
Figure 4 illustrates the improved version of the converter of Figure 3 in accordance with the present invention;
Fiqures SA to SF illustrate the current paths involved in the successive steps of operation of the circuit of Figure 4 during commutation of two of the main thyristors;
Figure 6 illustrates with curves the operatio~ of the circuit of Figures 4 and 5A to 5F;
Figure ~ is an enlarged view of the notch shown in Eiqure 6, to illustrate the effect of ~he neutralization of the inductance during the commutation period;
~3(1~
3 54,170 Figures 8A, 88 and 8C show in block diagram a gating control circuit as can be used or effecting the operative steps of Figures 5A to 5F;
Figure 9 shows curves which indicate the timing waveforms, ~he mode selecting signals and the gating pulses used in the gating control system of Figure 8C;
Figure 10 shows with curves the generation and the timing of the pulses controlling the static switches in the preferred embodiment of the invention;
DESCRIPTION OF THE PREFERRED EMBODIMENT
Figure 1 shows a voltage-source inverter includ-ing: a 60 Hz AC power supply (mains LI, L2, L3); an AC/DC
converter CNV rectifying the AC current; a DC-link filter (including an inductor and a capacitor) FLT and a DC/AC
inverter INV generating a variable frequency, variable output voltage, which can be used, for instance, to drive an AC motor coupled to a load. This is known as the forward mode of operation. With such a system, there is the possibility that the system be in a regenerative mode, namely when the load is operating as a generator returning energy back to the AC side through the inverter, the DC-link and the AC/DC converter. PWM inverters with a constant-voltage DC-link are commonly used in AC motor drives systems. Low performance drives may not require power to be returned to the AC mains whenever the motor operates in the regenerative power quadrants. In such case, the DC-link power is supplied from a simple rectifier bridge and regenerative power is dissipated in a resistor inserted across the DC-link when necessary. However, for high-performance servo drives or drives with very high inertia, the regenerated power has to be returned to the mains in order to improve the overall efficiency of the drive. Regenerative two-quadrant power systems have been conceived to convert an AC power supply from the mains into a constant DC-link voltage. Figure 2, borrowed from U.S.
Patent No. 4,~97,131, shows such a system. In order to accommodate for the operation in the regenerative mode, a ~3~
4 54,170 1 GT0 device and an auxiliary thyristor TH7 have been con-nected between the DC terminals of the thyristor bridge of the AC/DC converter and the capacitor which is across the inverter, in such a manner as to allow control of the converter continuously in either modes of operation, and to facilitate in the second mode the return of eneryy to the AC input side under the proper voltage in the DC-link in magnitude and polarity, while exercising forced-commutation. In the regenerative mode, the GT0 device when controlled for conduction concurrently with thyristor TH7, steers the current from the DC-link, thus removing energy from the capacitor (C3 and returning it to the mains (A, B, C) through the inverted polarity terminals (TP, TN~. Then, the GT0 is turned OFF, thereby creating a zero-current period. This is the time chosen or thyristor commutation in the converter. The GT0 device and auxi}iary thyristor TH7 are triggered again with the new combination of main thyristors. This is according to nrlited States Patent 4,697,131, and it is understood that although a a GT0 device has been used in the description, any device which can be triggered for conduction and out of conduction, a transistor for instance, will do in place of the GT0 device.
It is now proposed to insert, as shown in Figure 3, a large inductance Ll as DC filter reactor, without affecting the power circuit commu~ation adversely and while affording at the same time fault protection. The insertion of inductance L1 improves the mains current waveform when the converter is operating at maximum constant voltage output, and it also works favorably in the instance of a variable output vo}tage as typi~ied by the converter to an adjustable voltage six-step inverter. The six-pulse converter bridge is shown in Figure 3 to include an induc-tance L1 in series, as desirable to reduce the harmonic content of the mains current and to limit the fault current in the event of a shoot-t~rough in the bridge while in the regenerative mode. This effect could be maximized by ~3~2~
54,170 introducing as much inductance as it is economically justifiable. Such a high inductance, however, has a negative effect on the commutation process, and with a system such as shown in Eigure 3, it would paralyze the operation in the regenerative mode. The commutation loop forms a series path through the mains with the two thyristors under conduction in the bridge, via inductance Ll, diode Dl and the auxiliary thyristor TH7. If the inductance is too large, the current i.n this path will not be reduced to zero within the predetermined time interval allowed for the commutation and for the recovery of the devices. A fault will occur upon triggering of the subse-quent combination of thyristors in the bridge. Still, a high inductance is especially desirable for high perfor-mance servo drives and variable speed drives with very highenergy inertia where the return of regenerative power to the mains supply is essential for overall efficiancy.
Power circuits operating as a regenerative two-quadrant converter to convert an AC mains supply to a constant DC-link voltage have been disclosed in the prior art, one of them is the object of the afore-mentioned U.S. Patent No. 4,697,131 and the basic circuit is as shown in Figure 2. The addition of the inductance L1 at the location shown in Figure 3 having a detrimental effect on the commutation unless Ll is limited, other locations might be considered.
They are also impractical. One location is in series with the AC supply lines. In such case, the induc~ance is still in the commutation loop for regeneration, and in addition it hinders the commutation in the forward mode while affording no extra shoot-~hrough protection and necessitat-ing additional voltage regulation under load. Another location for the inductance is in series with the DC-link capacitor. Unfortunately, this means that since the circuit branch containing the capacitor is electrically disconnected from the mains during the commutation period in the regenerative mode, the inductor current would have ~L3~2~
6 54,170 no freewheel path and overvoltages would develop with destructive effect.
The solution is illustrated by Figure 4 where a large inductance is placed in series with the output of the thyristor bridge like in Figure 3 with the provision of an additional thyristor TH8 connected in parallel with the inductance Ll and strategically triggered to remove the influence of the inductance from the commutation loop when in the regenerative mode, by providing a freewheel path for the inductance current.
Figures 5A to 5F illustrate the current paths involved in the regenerative mode during the successive steps of the commutation of thyristors TH5 and TH6 for the negative DC-link terminal TN and under thyristor THl for the other DC-link terminal TP. The operation of the GTO
with respect to thyristors THl to TH6 and to auxiliary thyristor TH7 is the same as explained in the incorporated by reference patent by reference to Figures lOA to lOD
there. The additional thyristor TH8 is triggered immedi-ately upon each turning OFF of the GTO, which initiates thecommutation. Thus, as shown in Figure 5A the GTO is passing current flowing through inductance Ll via TH7 from phase A and thyristor THl to phase B and thyristor TH5 when, at the start of the commutation, the GTO is turned OFF (Figure 5B) causing this current to rapidly divert to a new path involving inductance Ll, diode Dl and thyristor TH7. Immediately thereafter, if not concurrently, the additional thyristor TH8 is triggered (Figure SC). From then on, the polarity of the mains tends to reduce the commutation loop current while the polarity of the mains voltage biases TH8 to keep it ON, so that current starts to build up through TH8 in a freewheel action, as shown in Figure 5C. This means that inductance Ll is practically neutralized as seen from the commutation loop. The rate of change of the current in the commutation loop is not affected by the inductance. The current falls rapidly under the forced commutation effect of the GTO, the action ~3~24~84L
7 54,170 of the commutatlng mains voltage despite the remaining inductances in the loop, which are in fact very small.
Finally, the commutation loop current is reduced to zero (Figure 5D), while nearly the entire original current in the inductance Ll is freewheeling through the additional thyristor TH8 . Given some recovery time, the devices which are next in the sequence of the bridge (THl and TH6) are triggered together with the GTO and the auxiliary thyristor TH7 (Figure 5E). The supply current rises rapidly to a value matching the curren~ circulating in the inductance Ll, and exceeds it under the forcing difference between the voltage on capacitor C and the mains voltage. Now, the voltage across Ll biases TH8 OFF under natural commutation.
Inductance Ll is operative again within the bridge current loop (Figure 5F) until another commutation in the sequence repeats with the GTO and thyristor TH8 the same process, thus, for each commutation in the regenerative mode.
In the forward mode, TH8 is never trlggered and the effect of the large inductance Ll is felt all the way in the circuit. It is observed that a diode instead of a thyristor at TH8 would not do because the diode would only allow Ll to be "seen" by the power circuit under conditions where the circuit current is in the process of rising.
When the circuit current would be falling, as under the action of the converter vol~age ripple or by dynamic control action, the effect of Ll would be lost as soon as the inductance current would begin to freewheel through the diode.
Referring to Figure 6, the line-to-neutral voltages VAN, VBN and VCN applied to the converter bridge for the three input phases A, B, C, are shown under (a).
Assuming full positive voltage operation in the forward mode under zero firing angle for the thyristors, currents iA, iB and iC are shown under (b~. Ideally, assuming a constant DC current being outputted, the lnput currents have a perfect square shape. This is where the large inductance is very effective in establishing DC output ~ 3~2~84 ~ 5~,17~
current and in eliminating any ripple which could otherwise appear in the input current waveform. Under (c) are shown the voltage-to-neutral voltages and the outputted voltage at 180 firing angle for full voltage negative, as required for the re~enerative mode. Ideally the currents iA, iB and iC would be of similar shape as for the forward mode, except for the 180 phase shift. However, the effect of the large inductance L1 is neutralized during the commuta tion period which is illustrated by a notch caused in the current when the GTO is switched OFF and TH8 is switched ON. This is shown at instants such as tF and t'F for the respective opposite polarities.
The effect of an idealized notch is illustrated in Figure 7 for current iA, under ta). The notch is initiated by the interruption of the conduction of the GTO
and by the concurrent triggering of the additional thyristor TH8 as shown under (b). At that moment, as shown in dotted line, the current iA decreases very rapidly. The off-going bridge thyristor is turned OFF. At the same time, by complementary action, the freewheel current iTH8 is building up quickly, also as shown in dotted line under (c). Then, the GTO device is again triggered for conduc-tion. This occurs concurrently with the auxiliary thyristor TH7, causin~ the rising edge of the notch, turning OFE the additional thyristor TH8 by natural commu-tation, causing iTH8 to decrease rapidly as shown under (c), at the same time as firing of the subsequent thyristor in the converter bridge is triggered. As the freewheel current iTH8 is vanishing, the bridge current iA reaches quickly the level shown for iA under the idealized condi-tion assumed for the purpose of illustration. In other words, the freewheel current when it ends under natural commutation of TH8 will divert back to the mains lines and the effect of the large inductance will be restored.
Therefore, beyond the notch of the current iA, any sharp ripple will be forced by the inductanca to follow more or less closely the basic square shape o the current.
8~
1 F~igures 8A, 8B, and 8C correspond to Figures llA, llB and llC of United States patent 4,697,131, with the e~ception ~hat the generation of the triggering signal for additional thyristor THB has been added with the output line 101 thereto.
Figure 8A shows a motor drive having a static converter CNV, a DC-link DCL and an inverter INV with the commutation circuit improved as in Fiqure 4 by the provision of a large inductance Ll and a thyristor THB controlled from line 101 when the GT0 is controlled by line 39 and the auxiliary thyristor TH7 is gated by line 38. These three control lines are effective only r~hen the system is in the regenerative mode, namely when current flow sensing by circuit FDS detects the change of mode and a signal of logic F/R imposes via line 20 the corresponding control mode for line 31 to 36 to the bridge thyristors THl to TH6 and renders effective lines 101, 39 and 38. Figure 8A
otherwise is as Figure llA of the above referenced United States patent.
Figures 8B and 8C are like Figures llB and llC of the abo~e referenced United States patent, except ~hat the occurrence of the triggering pulse for thyristor T~8 and line 101 carrying such pulse, have been indicated on the respective drawings. ~5 shown in Figure 8~, a pulse generator PL6 is provided, re~ponding to the triggering pulse of line 39 for the GT0 device, which generates the pulse of line 101 triggering the additional thyristor TH8.
The controlling signals of lines 31 to 36, 38, 39 and 101 have been placed together in time relation in Figure 9 where the thyristors THl to TH7 each receive a hard pulse for triggering. The occurrence of the signa}s of line 39 (GT0), line 38 (TH7) and line 101 (TH8) and the ensuing notch of interruption for the current path are shown repeatedly applied upon ea~h commutation step after shift-ing to the regenerative mode. Figure lO is like Figure 9 showing the regenerative mode where the thyristors are ~3~
54,170 being controlled with a picket fence series of pulses rather than a mere hard pulss for gating.
The proposed scheme allows the generation of mains currents which are approaching the theoretical S optimum, or quasi-square wave form, shown in Figure 6. The additional thyristor TH8 has an extremely short duty cycle and can be rated accordingly, although it should be chosen so as to be able to handle the peak power current for sho.t periods (see Figure 7). The improved two-quadrant convert-er makes possible operation with inverters requiring avariable DC-link voltage. In such casa, the large six-pulse ripple occurring when firing the devices away from the theoretical front or backstops of phase shift make it absolutely essential that a large inductance be given the filter reactor. In situations where the equipment accepts a relatively small inductance, the improVement due to mora inductance and the additional thyristor TH8 will be felt at least in the regenerative mode.
1 54,170 IMPROVED REGENERATIVE TWO-QUADRANT CONVERTER
AND MOTOR DRIVE EMBODYING THE SAME
The invention relates to constant and variable voltage voltage-source inverter systems, and to AC motor drives embodying such a voltage-source.
In the converter supplying power to the DC-link of a voltage-source inverter, there is a need Eor an inductance both as a means of reducing the harmonic content of the mains current at the AC power supply side, and to limit the rate of rise of a fault current in the event of a shoot-through among the thyristors of the converter brid~e while in ~he regenerative mode. It is desirable to maxi-mize the amount of inductance so inserted in the DC-link in order to have its full benefit. The invention, however, involves a voltage-source converter as described in U.S.
Patent No. 4,697,131 issued September 29, 1987, wherein in the regenerative mode an interruption of current is caused to happen at the time the converter thyristors are being commutated. With this particular type, a large inductance would hinder the commutation of the converter bridge static switches. The problem arises because the inductance prevents the converter current from being rapidly reduced to zero, as required for effective commutation from one set of switches to the next in the control sequence of the bridge.
The invention is particularly applicable to the converter power supply for a voltage-source inverter such as described in the afore-mentioned U.S. Patent No.
~3~2~
1 4,697,131 which should be consulted for the purpose of a more complete understanding thereof.
SUMMARY OF THY INVENTION
The present invention assists the commutation between outgoing and incoming static ~witches in the sequence of conduction of the static switches of an AC/DC
converter of the type described in the above referenced United States patent, where a large induc~ance has been inserted in its DC-link. This i5 achieved by usinq a GTO
device, or a transistor, to interrupt the main current, and by creating with an additio~al static switch a separate bypass for the inductance energy, so as to help build-up, and minimize the duration of, a zero-current condition in the bridge at the moment of commutation.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a block diagram of a variable fre-quency, variable voltage AC output system of the prior art;
Figure 2 shows the AC-DC converter used in the system of U.S. Patent No. 4,697,131, which is part of the preferred embodiment of the invention;
Figure 3 shows the use o an inductance in the DC-link of the converter of Figure 2, such use being the cause of the problem to be solved according to the present invention;
Figure 4 illustrates the improved version of the converter of Figure 3 in accordance with the present invention;
Fiqures SA to SF illustrate the current paths involved in the successive steps of operation of the circuit of Figure 4 during commutation of two of the main thyristors;
Figure 6 illustrates with curves the operatio~ of the circuit of Figures 4 and 5A to 5F;
Figure ~ is an enlarged view of the notch shown in Eiqure 6, to illustrate the effect of ~he neutralization of the inductance during the commutation period;
~3(1~
3 54,170 Figures 8A, 88 and 8C show in block diagram a gating control circuit as can be used or effecting the operative steps of Figures 5A to 5F;
Figure 9 shows curves which indicate the timing waveforms, ~he mode selecting signals and the gating pulses used in the gating control system of Figure 8C;
Figure 10 shows with curves the generation and the timing of the pulses controlling the static switches in the preferred embodiment of the invention;
DESCRIPTION OF THE PREFERRED EMBODIMENT
Figure 1 shows a voltage-source inverter includ-ing: a 60 Hz AC power supply (mains LI, L2, L3); an AC/DC
converter CNV rectifying the AC current; a DC-link filter (including an inductor and a capacitor) FLT and a DC/AC
inverter INV generating a variable frequency, variable output voltage, which can be used, for instance, to drive an AC motor coupled to a load. This is known as the forward mode of operation. With such a system, there is the possibility that the system be in a regenerative mode, namely when the load is operating as a generator returning energy back to the AC side through the inverter, the DC-link and the AC/DC converter. PWM inverters with a constant-voltage DC-link are commonly used in AC motor drives systems. Low performance drives may not require power to be returned to the AC mains whenever the motor operates in the regenerative power quadrants. In such case, the DC-link power is supplied from a simple rectifier bridge and regenerative power is dissipated in a resistor inserted across the DC-link when necessary. However, for high-performance servo drives or drives with very high inertia, the regenerated power has to be returned to the mains in order to improve the overall efficiency of the drive. Regenerative two-quadrant power systems have been conceived to convert an AC power supply from the mains into a constant DC-link voltage. Figure 2, borrowed from U.S.
Patent No. 4,~97,131, shows such a system. In order to accommodate for the operation in the regenerative mode, a ~3~
4 54,170 1 GT0 device and an auxiliary thyristor TH7 have been con-nected between the DC terminals of the thyristor bridge of the AC/DC converter and the capacitor which is across the inverter, in such a manner as to allow control of the converter continuously in either modes of operation, and to facilitate in the second mode the return of eneryy to the AC input side under the proper voltage in the DC-link in magnitude and polarity, while exercising forced-commutation. In the regenerative mode, the GT0 device when controlled for conduction concurrently with thyristor TH7, steers the current from the DC-link, thus removing energy from the capacitor (C3 and returning it to the mains (A, B, C) through the inverted polarity terminals (TP, TN~. Then, the GT0 is turned OFF, thereby creating a zero-current period. This is the time chosen or thyristor commutation in the converter. The GT0 device and auxi}iary thyristor TH7 are triggered again with the new combination of main thyristors. This is according to nrlited States Patent 4,697,131, and it is understood that although a a GT0 device has been used in the description, any device which can be triggered for conduction and out of conduction, a transistor for instance, will do in place of the GT0 device.
It is now proposed to insert, as shown in Figure 3, a large inductance Ll as DC filter reactor, without affecting the power circuit commu~ation adversely and while affording at the same time fault protection. The insertion of inductance L1 improves the mains current waveform when the converter is operating at maximum constant voltage output, and it also works favorably in the instance of a variable output vo}tage as typi~ied by the converter to an adjustable voltage six-step inverter. The six-pulse converter bridge is shown in Figure 3 to include an induc-tance L1 in series, as desirable to reduce the harmonic content of the mains current and to limit the fault current in the event of a shoot-t~rough in the bridge while in the regenerative mode. This effect could be maximized by ~3~2~
54,170 introducing as much inductance as it is economically justifiable. Such a high inductance, however, has a negative effect on the commutation process, and with a system such as shown in Eigure 3, it would paralyze the operation in the regenerative mode. The commutation loop forms a series path through the mains with the two thyristors under conduction in the bridge, via inductance Ll, diode Dl and the auxiliary thyristor TH7. If the inductance is too large, the current i.n this path will not be reduced to zero within the predetermined time interval allowed for the commutation and for the recovery of the devices. A fault will occur upon triggering of the subse-quent combination of thyristors in the bridge. Still, a high inductance is especially desirable for high perfor-mance servo drives and variable speed drives with very highenergy inertia where the return of regenerative power to the mains supply is essential for overall efficiancy.
Power circuits operating as a regenerative two-quadrant converter to convert an AC mains supply to a constant DC-link voltage have been disclosed in the prior art, one of them is the object of the afore-mentioned U.S. Patent No. 4,697,131 and the basic circuit is as shown in Figure 2. The addition of the inductance L1 at the location shown in Figure 3 having a detrimental effect on the commutation unless Ll is limited, other locations might be considered.
They are also impractical. One location is in series with the AC supply lines. In such case, the induc~ance is still in the commutation loop for regeneration, and in addition it hinders the commutation in the forward mode while affording no extra shoot-~hrough protection and necessitat-ing additional voltage regulation under load. Another location for the inductance is in series with the DC-link capacitor. Unfortunately, this means that since the circuit branch containing the capacitor is electrically disconnected from the mains during the commutation period in the regenerative mode, the inductor current would have ~L3~2~
6 54,170 no freewheel path and overvoltages would develop with destructive effect.
The solution is illustrated by Figure 4 where a large inductance is placed in series with the output of the thyristor bridge like in Figure 3 with the provision of an additional thyristor TH8 connected in parallel with the inductance Ll and strategically triggered to remove the influence of the inductance from the commutation loop when in the regenerative mode, by providing a freewheel path for the inductance current.
Figures 5A to 5F illustrate the current paths involved in the regenerative mode during the successive steps of the commutation of thyristors TH5 and TH6 for the negative DC-link terminal TN and under thyristor THl for the other DC-link terminal TP. The operation of the GTO
with respect to thyristors THl to TH6 and to auxiliary thyristor TH7 is the same as explained in the incorporated by reference patent by reference to Figures lOA to lOD
there. The additional thyristor TH8 is triggered immedi-ately upon each turning OFF of the GTO, which initiates thecommutation. Thus, as shown in Figure 5A the GTO is passing current flowing through inductance Ll via TH7 from phase A and thyristor THl to phase B and thyristor TH5 when, at the start of the commutation, the GTO is turned OFF (Figure 5B) causing this current to rapidly divert to a new path involving inductance Ll, diode Dl and thyristor TH7. Immediately thereafter, if not concurrently, the additional thyristor TH8 is triggered (Figure SC). From then on, the polarity of the mains tends to reduce the commutation loop current while the polarity of the mains voltage biases TH8 to keep it ON, so that current starts to build up through TH8 in a freewheel action, as shown in Figure 5C. This means that inductance Ll is practically neutralized as seen from the commutation loop. The rate of change of the current in the commutation loop is not affected by the inductance. The current falls rapidly under the forced commutation effect of the GTO, the action ~3~24~84L
7 54,170 of the commutatlng mains voltage despite the remaining inductances in the loop, which are in fact very small.
Finally, the commutation loop current is reduced to zero (Figure 5D), while nearly the entire original current in the inductance Ll is freewheeling through the additional thyristor TH8 . Given some recovery time, the devices which are next in the sequence of the bridge (THl and TH6) are triggered together with the GTO and the auxiliary thyristor TH7 (Figure 5E). The supply current rises rapidly to a value matching the curren~ circulating in the inductance Ll, and exceeds it under the forcing difference between the voltage on capacitor C and the mains voltage. Now, the voltage across Ll biases TH8 OFF under natural commutation.
Inductance Ll is operative again within the bridge current loop (Figure 5F) until another commutation in the sequence repeats with the GTO and thyristor TH8 the same process, thus, for each commutation in the regenerative mode.
In the forward mode, TH8 is never trlggered and the effect of the large inductance Ll is felt all the way in the circuit. It is observed that a diode instead of a thyristor at TH8 would not do because the diode would only allow Ll to be "seen" by the power circuit under conditions where the circuit current is in the process of rising.
When the circuit current would be falling, as under the action of the converter vol~age ripple or by dynamic control action, the effect of Ll would be lost as soon as the inductance current would begin to freewheel through the diode.
Referring to Figure 6, the line-to-neutral voltages VAN, VBN and VCN applied to the converter bridge for the three input phases A, B, C, are shown under (a).
Assuming full positive voltage operation in the forward mode under zero firing angle for the thyristors, currents iA, iB and iC are shown under (b~. Ideally, assuming a constant DC current being outputted, the lnput currents have a perfect square shape. This is where the large inductance is very effective in establishing DC output ~ 3~2~84 ~ 5~,17~
current and in eliminating any ripple which could otherwise appear in the input current waveform. Under (c) are shown the voltage-to-neutral voltages and the outputted voltage at 180 firing angle for full voltage negative, as required for the re~enerative mode. Ideally the currents iA, iB and iC would be of similar shape as for the forward mode, except for the 180 phase shift. However, the effect of the large inductance L1 is neutralized during the commuta tion period which is illustrated by a notch caused in the current when the GTO is switched OFF and TH8 is switched ON. This is shown at instants such as tF and t'F for the respective opposite polarities.
The effect of an idealized notch is illustrated in Figure 7 for current iA, under ta). The notch is initiated by the interruption of the conduction of the GTO
and by the concurrent triggering of the additional thyristor TH8 as shown under (b). At that moment, as shown in dotted line, the current iA decreases very rapidly. The off-going bridge thyristor is turned OFF. At the same time, by complementary action, the freewheel current iTH8 is building up quickly, also as shown in dotted line under (c). Then, the GTO device is again triggered for conduc-tion. This occurs concurrently with the auxiliary thyristor TH7, causin~ the rising edge of the notch, turning OFE the additional thyristor TH8 by natural commu-tation, causing iTH8 to decrease rapidly as shown under (c), at the same time as firing of the subsequent thyristor in the converter bridge is triggered. As the freewheel current iTH8 is vanishing, the bridge current iA reaches quickly the level shown for iA under the idealized condi-tion assumed for the purpose of illustration. In other words, the freewheel current when it ends under natural commutation of TH8 will divert back to the mains lines and the effect of the large inductance will be restored.
Therefore, beyond the notch of the current iA, any sharp ripple will be forced by the inductanca to follow more or less closely the basic square shape o the current.
8~
1 F~igures 8A, 8B, and 8C correspond to Figures llA, llB and llC of United States patent 4,697,131, with the e~ception ~hat the generation of the triggering signal for additional thyristor THB has been added with the output line 101 thereto.
Figure 8A shows a motor drive having a static converter CNV, a DC-link DCL and an inverter INV with the commutation circuit improved as in Fiqure 4 by the provision of a large inductance Ll and a thyristor THB controlled from line 101 when the GT0 is controlled by line 39 and the auxiliary thyristor TH7 is gated by line 38. These three control lines are effective only r~hen the system is in the regenerative mode, namely when current flow sensing by circuit FDS detects the change of mode and a signal of logic F/R imposes via line 20 the corresponding control mode for line 31 to 36 to the bridge thyristors THl to TH6 and renders effective lines 101, 39 and 38. Figure 8A
otherwise is as Figure llA of the above referenced United States patent.
Figures 8B and 8C are like Figures llB and llC of the abo~e referenced United States patent, except ~hat the occurrence of the triggering pulse for thyristor T~8 and line 101 carrying such pulse, have been indicated on the respective drawings. ~5 shown in Figure 8~, a pulse generator PL6 is provided, re~ponding to the triggering pulse of line 39 for the GT0 device, which generates the pulse of line 101 triggering the additional thyristor TH8.
The controlling signals of lines 31 to 36, 38, 39 and 101 have been placed together in time relation in Figure 9 where the thyristors THl to TH7 each receive a hard pulse for triggering. The occurrence of the signa}s of line 39 (GT0), line 38 (TH7) and line 101 (TH8) and the ensuing notch of interruption for the current path are shown repeatedly applied upon ea~h commutation step after shift-ing to the regenerative mode. Figure lO is like Figure 9 showing the regenerative mode where the thyristors are ~3~
54,170 being controlled with a picket fence series of pulses rather than a mere hard pulss for gating.
The proposed scheme allows the generation of mains currents which are approaching the theoretical S optimum, or quasi-square wave form, shown in Figure 6. The additional thyristor TH8 has an extremely short duty cycle and can be rated accordingly, although it should be chosen so as to be able to handle the peak power current for sho.t periods (see Figure 7). The improved two-quadrant convert-er makes possible operation with inverters requiring avariable DC-link voltage. In such casa, the large six-pulse ripple occurring when firing the devices away from the theoretical front or backstops of phase shift make it absolutely essential that a large inductance be given the filter reactor. In situations where the equipment accepts a relatively small inductance, the improVement due to mora inductance and the additional thyristor TH8 will be felt at least in the regenerative mode.
Claims (4)
1 In an AC/DC converter system including an AC
bridge having a plurality of static-controlled switches controlled sequentially for conduction across DC-link terminals operative as a DC voltage source and connected to a load, with a capacitor across said DC-link terminals and the load, the system operating in one of a forward and a regenerative mode; the combination of:
a reactor and a GTO device in series between one terminal of the bridge and a corresponding end of said capacitor;
an auxiliary thyristor connected in series with the other end of said capacitor and the other terminal of the bridge;
a rectifying device connected between said reactor and said other end of said capacitor;
an additional thyristor connected in parallel with said reactor and in opposition to said GTO device, to said rectifying device and to the bridge thyristors of the associated terminal;
said GTO device being controlled for conduction together with the bridge thyristors under conduction in the control sequence thereof so as to form a current path via said reactor, said capacitor, the load, and via said auxiliary thyristor;
said GTO device being controlled in the regenera-tive mode for interrupting said current path and said additional thyristor being controlled concurrently for 12 54,170 conduction to create a freewheeling current path for said reactor upon commutation of successive bridge thyristors for conduction in the sequence thereof, thereby to allow a zero-current condition under regeneration from the load.
bridge having a plurality of static-controlled switches controlled sequentially for conduction across DC-link terminals operative as a DC voltage source and connected to a load, with a capacitor across said DC-link terminals and the load, the system operating in one of a forward and a regenerative mode; the combination of:
a reactor and a GTO device in series between one terminal of the bridge and a corresponding end of said capacitor;
an auxiliary thyristor connected in series with the other end of said capacitor and the other terminal of the bridge;
a rectifying device connected between said reactor and said other end of said capacitor;
an additional thyristor connected in parallel with said reactor and in opposition to said GTO device, to said rectifying device and to the bridge thyristors of the associated terminal;
said GTO device being controlled for conduction together with the bridge thyristors under conduction in the control sequence thereof so as to form a current path via said reactor, said capacitor, the load, and via said auxiliary thyristor;
said GTO device being controlled in the regenera-tive mode for interrupting said current path and said additional thyristor being controlled concurrently for 12 54,170 conduction to create a freewheeling current path for said reactor upon commutation of successive bridge thyristors for conduction in the sequence thereof, thereby to allow a zero-current condition under regeneration from the load.
2. The system of claim 1 with said rectifying device diverting the current path directly to said auxilia-ry thyristor upon current interruption by said GTO device, and said auxiliary thyristor becoming non conductive by natural commutation under said zero-current condition.
3. The system of claim 2 with said GTO device being controlled for conduction after said zero-current conduction concurrently with control of the bridge thyristors next in the conduction sequence, and said additional thyristor being concurrently turned-OFF by natural commutation.
4. The system of claim 3 with said reactor having a substantially large reactance.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US07/168,062 US4805082A (en) | 1988-03-14 | 1988-03-14 | Regenerative two-quadrant converter |
| US168,062 | 1988-03-14 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1302484C true CA1302484C (en) | 1992-06-02 |
Family
ID=22609950
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000592165A Expired - Fee Related CA1302484C (en) | 1988-03-14 | 1989-02-27 | Regenerative two-quadrant converter and motor drive embodying the same |
Country Status (6)
| Country | Link |
|---|---|
| US (1) | US4805082A (en) |
| JP (1) | JPH01274666A (en) |
| KR (1) | KR960016606B1 (en) |
| AU (1) | AU608954B2 (en) |
| BR (1) | BR8901099A (en) |
| CA (1) | CA1302484C (en) |
Families Citing this family (24)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4879639A (en) * | 1987-05-11 | 1989-11-07 | Fuji Electric Co., Ltd. | Power converter for driving an AC motor at a variable speed |
| US4805082A (en) * | 1988-03-14 | 1989-02-14 | Westinghouse Electric Corp. | Regenerative two-quadrant converter |
| WO1990001230A1 (en) * | 1988-07-20 | 1990-02-08 | Power Reflex Pty. Ltd. | Switched electrical power conversion and balancing |
| US4894763A (en) * | 1988-12-05 | 1990-01-16 | General Electric Company | AC-AC converter using switches in a DC link |
| US4942511A (en) * | 1989-09-28 | 1990-07-17 | Wisconsin Alumni Research Foundation | Static power conversion apparatus using a high frequency series resonant DC link |
| JPH0491659A (en) * | 1990-08-06 | 1992-03-25 | Tokyo Electric Power Co Inc:The | Power supply conversion device |
| US5267137A (en) * | 1990-10-19 | 1993-11-30 | Kohler, Schmid Partner | High-power power supply |
| US5309346A (en) * | 1991-09-16 | 1994-05-03 | Westinghouse Electric Corp. | Transmission line fault current dynamic inverter control |
| US5198746A (en) * | 1991-09-16 | 1993-03-30 | Westinghouse Electric Corp. | Transmission line dynamic impedance compensation system |
| JP2770099B2 (en) * | 1992-02-27 | 1998-06-25 | 株式会社日立製作所 | Gate drive circuit of series multiplex inverter |
| US5367448A (en) * | 1992-08-07 | 1994-11-22 | Carroll Lawrence B | Three phase AC to DC power converter |
| US5594636A (en) * | 1994-06-29 | 1997-01-14 | Northrop Grumman Corporation | Matrix converter circuit and commutating method |
| SE503117C2 (en) * | 1994-08-24 | 1996-03-25 | Asea Brown Boveri | Inverter coupling and installation for transmission of high voltage direct current including such inverter coupling |
| US5734256A (en) * | 1995-05-31 | 1998-03-31 | General Electric Company | Apparatus for protection of power-electronics in series compensating systems |
| US6021035A (en) * | 1995-05-31 | 2000-02-01 | General Electric Company | Apparatus for protection of power-electronics in series compensating systems |
| US5828200A (en) * | 1995-11-21 | 1998-10-27 | Phase Iii | Motor control system for variable speed induction motors |
| US5933342A (en) * | 1998-06-02 | 1999-08-03 | Ford Motor Company | Rectifier with alternative path for freewheeling current |
| US6072304A (en) * | 1999-07-21 | 2000-06-06 | Regent Lighting Corporation | Circuit and method for triggering a thyristor |
| JP5169018B2 (en) * | 2007-05-15 | 2013-03-27 | 三菱電機株式会社 | Power converter |
| DE102008020030B4 (en) * | 2008-04-21 | 2022-05-19 | Aeg Power Solutions Gmbh | Circuit arrangement with a rectifier and a circuit for protecting at least one direct-current network with direct-current loads that can be connected to the circuit arrangement against overvoltage |
| CN102263414A (en) * | 2010-05-25 | 2011-11-30 | 新能动力（北京）电气科技有限公司 | Electrical energy changer and system |
| JP5866770B2 (en) * | 2011-02-17 | 2016-02-17 | 富士電機株式会社 | Power supply |
| EP2790285B1 (en) * | 2013-04-12 | 2020-07-08 | General Electric Technology GmbH | Current limiter |
| BR102015030840B1 (en) * | 2015-12-09 | 2022-04-19 | Embraco Indústria De Compressores E Soluções Em Refrigeração Ltda | System for harmonic content reduction in electric power circuit and compressor for refrigeration |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CH589966A5 (en) * | 1974-12-03 | 1977-07-29 | Siemens Ag | |
| DE2541722C3 (en) * | 1975-09-18 | 1980-09-04 | Siemens Ag, 1000 Berlin Und 8000 Muenchen | Procedure for operating a resonant circuit converter |
| US4376296A (en) * | 1981-03-02 | 1983-03-08 | Canadian Patents & Dev. Ltd. | DC-Side commutated inverter |
| US4697131A (en) * | 1985-12-11 | 1987-09-29 | Westinghouse Electric Corp. | Voltage source inverter and variable frequency, constant voltage AC motor drive embodying the same |
| US4805082A (en) * | 1988-03-14 | 1989-02-14 | Westinghouse Electric Corp. | Regenerative two-quadrant converter |
-
1988
- 1988-03-14 US US07/168,062 patent/US4805082A/en not_active Expired - Lifetime
-
1989
- 1989-02-27 CA CA000592165A patent/CA1302484C/en not_active Expired - Fee Related
- 1989-03-09 AU AU31163/89A patent/AU608954B2/en not_active Ceased
- 1989-03-09 BR BR898901099A patent/BR8901099A/en not_active IP Right Cessation
- 1989-03-14 KR KR1019890003175A patent/KR960016606B1/en not_active IP Right Cessation
- 1989-03-14 JP JP1061994A patent/JPH01274666A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| AU608954B2 (en) | 1991-04-18 |
| BR8901099A (en) | 1989-10-31 |
| KR890015496A (en) | 1989-10-30 |
| KR960016606B1 (en) | 1996-12-16 |
| JPH01274666A (en) | 1989-11-02 |
| AU3116389A (en) | 1989-09-14 |
| US4805082A (en) | 1989-02-14 |
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