WO2011161692A2

WO2011161692A2 - Reactive power management for wind turbine applications

Info

Publication number: WO2011161692A2
Application number: PCT/IN2011/000405
Authority: WO
Inventors: V. R. Raghunathan
Original assignee: Raghunathan V R
Priority date: 2010-06-21
Filing date: 2011-06-16
Publication date: 2011-12-29
Also published as: WO2011161692A3

Abstract

The present invention provides pre-determined reactive power to asynchronous generator of a wind turbine, through a feedback controlled inverter by eliminating the usage of capacitor banks and is installable in remote places where grid (G) power is not available. A novel control system with 3 phase inverter setup using power transistors or IGBT's as switching elements provides reactive power for excitation to maintain sustained generation. Negative slip is controlled based on the reference DC voltage generated through the freewheeling diodes of the IGBT's. In grid (G) connected system, better efficiency is achieved by pumping reactive power from the 3 phase inverter in synchronization with power grid (G) line frequency. The system can also be used in non-grid (G) connected wind turbines to provide electrical power to local loads and in grid (G) connected systems the generated power from the Wind Turbine is exported fully/partially after usage for local loads.

Description

Title of the Invention

REACTIVE POWER MANAGEMENT FOR WIND TURBINE APPLICATIONS

FIELD OF INVENTION

This invention relates to electrical power generation and in particular to reactive power management in an asynchronous generator wind turbine without the usage of capacitor banks for the power factor and excitation maintenance. BACKGROUND OF THE INVENTION

A Wind Turbine (WT) consists of the necessary systems needed to capture the wind's energy, point the turbine into the wind, convert mechanical rotation into electrical power, and other systems to start, stop, and control the turbine. The main energy conversion part in wind turbine is the generator. Few types of generators are named below:

❖ Synchronous Generator (SG),

❖ Asynchronous or Induction generator (IG) and

❖ DC Generators used for low power applications. The type of turbine and the type of generator are primarily important for the wind turbine which provides the efficient energy conversion part of the system. In wind turbines, synchronous generator type is generally used but with the advancement and inventions in power electronics and efficient control system, the asynchronous alternator are getting familiar which has advantages over synchronous and DC generators. The major Advantages in asynchronous alternators in wind turbine are:

❖ Cost effective due to its simple construction (don't require separating excitation coils and power supply source)

❖ Reliable working performance because of its ruggedness and non availability of brushes(low wear and tear)

❖ The ability of exchange of active and re-active energy with automatic stabilizing of frequency and amplitude of output voltage (according to the nature of such electric machine). With an asynchronous machine used as an alternator [induction generator (IG) ], the excitation of the asynchronous machine is the important phenomena in power generation. The reactive power is used to excitation. The IG wind turbine is operated in two types

❖ The IG wind turbine with grid (G) connected.

❖ The IG wind turbine with Self Excitation which is a stand alone type (remote place operative) and not necessary to connect to the power grid (G).

The grid (G) connected IG wind turbine

With the grid (G) connected, the required reactive power for the IG is drawn from the grid (G). With the wind velocity, a rotational torque is developed by the wind turbine in excess to the normal rotational speed due to the motoring effect of the IG, which is connected to the grid (G). This additional torque produces a negative slip in the IG, which generates electrical power and fed into the grid (G).

Generally these asynchronous generators are lesser efficiency due to low power factor and when wind speed is insufficient, more power is drawn from the grid (G) supply. To overcome the low power factor usually capacitor banks is connected across the supply line to improve the power factor. Different capacitor banks are switched for different load levels.

The Self excited Induction generator (SEIG) wind turbine

In the SEIG, the excitation is made using the capacitor banks which deliver required leading current to overcome the magnetizing current to induce Self excitation. The SEIG have a serious voltage regulation problem when load and/or speed changes. The remedy to this problem is associated with the need of a continuous supply of the necessary leading reactive power. To balance the lagging currents of the magnetizing field for the given load currents at different power factor, a compensating leading current to be provided. This is done by connecting a Capacitor across the supply lines. Different value capacitor banks are to be connected for different load levels to keep the power generation in control and without loosing the excitation. US 2758272 show a different and more primitive method of implementing power factor correction. Here, the induction generator (IG) is operated in parallel with the primary winding of a saturable transformer across the secondary winding of which Is connected a fixed reactive load. By varying the DC current through the transformer windings, the saturation of the magnetic core may be controlled for which in turn controls modifies tho mutual inductance, and hence in turn the value of the secondary reactance seen reflected at the primary terminals. Although this technique avoids the use of semiconductor power electronics, and thus side steps the choice between cheap but low reliability semiconductors and expensive but more reliable triacs), the expense and complexity of manufacture of a suitably bespoke saturable transformer also means that such an approach is not favored. Instead of trying to control multiple variables (torque, reactive current, voltage and/or frequency).

While patent document WO 2004/040748 describes a circuit arrangements for use in a variable speed wind turbine system comprising a double-fed induction generator (IG) and a back-to- back converter. The circuit arrangement in a grid-connected variable speed wind turbine system comprising a double-fed induction generator connected on the stator side to the grid (G) and on the rotor side to a back-to-back converter connected for transferring energy between the rotor of the double-fed induction generator and the grid (G), is provided with means for disconnecting at least one normally grid-connected terminal of the back-to-back converter from the grid (G) and means for connecting an impedance for allowing controlled power transfer from the intermediate DC circuit to said impedance. The control is performed by one or more power-switching elements of the normally grid- connected converter, which has been disconnected from the grid (G). This makes it possible to keep the generator connected to the grid (G) during grid (G) faults and take active part in the reestablishment of the grid (G) voltage. The other document US 5225712 discloses a variable speed wind turbine with reduced power fluctuation and a static VAR mode of operation with reactive power control. The wind turbine power converter herein that smoothes the output power from a variable speed wind turbine, to reduce or eliminate substantial power fluctuations on the output line is disclosed. The power converter has an AC- to-DC converter connected to a variable speed generator that converts wind energy to electric energy, a DC-to-AC inverter connected to a utility grid (G), and DC voltage link connected to an electrical energy storage device such as a battery (B) or a fuel cell, or a photovoltaic or solar cell. Also, an apparatus and method is disclosed herein for controlling the instantaneous current flowing through the active switches at the line side inverter to supply reactive power to the utility grid (G). The inverter can control reactive power output as a power factor angle, or directly as a number of VARs independent of the real power. Reactive power can be controlled in an operating mode when the wind turbine is generating power or in a static VAR mode when the wind turbine is not operating to produce real power. To control the reactive power, a voltage waveform is used as a reference to form a current control waveform for each output phase. The current control waveform for each phase is applied to a current regulator which regulates the drive circuit that controls the currents for each phase of the inverter. Means for controlling the charge/discharge ratio and the regulating the voltage on the DC voltage link is also disclosed.

Finally the patent document US 6924565 discloses a continuous reactive power support for wind turbine generators with real and reactive power control for wind turbine generator systems. The technique described herein provides the potential to utilize the total capacity of a wind turbine generator system (e.g., a wind farm) to provide dynamic VAR (reactive power support). The VAR support provided by individual wind turbine generators in a system can be dynamically varied to suit application parameters.

And the document WO 2009/083446 discloses an apparatus and method for controlling reactive power from clusters of wind turbines connected to a utility grid (G). The reactive power is generated or absorbed by at least two groups of wind turbines configured with doubly fed induction generators. Each of these groups of wind turbines are herein termed a cluster. One cluster comprises wind turbines that both generate reactive power (+Q) by operating in an overexcited mode and, if desired, also absorb reactive power in an under excited mode while the second group is adapted to only absorb reactive power (-Q).

But none of the prior art documents provide a method and a system for providing the pre determined reactive power to the asynchronous generator through a feed back controlled inverter by eliminating the usage of physical capacitor banks.

OBJECT OF INVENTION It is an object of the present invention to provide a system for providing the required reactive power to the asynchronous generator through a feed back controlled inverter from an energy source in proportion to the requirement based on power factor, RPM and load variation.

It is another object of the present invention to provide a system for eliminating the usage of physical capacitor banks for maintaining the excitation and power factor for the SEIG and IG wind turbine and for switching with the generator lines within predefined operating conditions.

It is one another object of the present invention to provide a control system for a wind turbine located at a remote place where availability of grid (G) power is very minimal.

It is yet another object of the present invention to provide a system for controlling the asynchronous machine as a self excitation induction generator (IG) by maintaining necessary slip with a closed loop feedback from DC side of the inverter control.

It is yet another object of the present invention to provide a system for maintaining the power factor to near unity by adequate control of the inverter in synchronous with the grid (G) supply voltage.

STATEMENT OF THE INVENTION

A system for providing the pre determined reactive power to the asynchronous generator through a feed back controlled inverter by eliminating the usage of physical capacitor banks comprises

(A) A Digital control system (DCS) for comparing the DC voltage, controlling the inverter, recharging the battery (B), providing unity power factor, efficient power transfer to the grid (G) and for monitoring the availability of grid (G) power, wind speed and loads to be powered.

(B) Inverters and drivers for handling the power requirements of the induction generator (IG).

(C) Battery (B) and chargers for starting up the turbine operations during no grid supply conditions and for obtaining unity power factor upon grid (G) connection. A method for providing the pre determined reactive power to the asynchronous generator through a feed back controlled inverter by eliminating the usage of physical capacitor banks during stand alone mode of turbine operation comprises the steps of

(A) Operating the turbine in stand alone mode with no grid connected or no grid power if connected.

(B) Checking for the sufficient wind speed availability for the start up of the wind turbine.

(C) Upon achieving sufficient wind speed, engaging the main contact (CN-A).

(D) Starting the Induction Generator (IG) in the motoring mode.

(E) Running the wind turbine by switching the inverter controls.

(F) Obtaining the power for start up from the battery (B).

(G) Sensing the speed of the wind turbine from the rotor RPM by the Digital control system

(DCS).

(H) Checking for the sufficient speed availability in the wind turbine.

(I) Upon achieving sufficient wind speed, controlling the inverter control signals for stator frequency ros sufficiently lower.

(J) Self exciting the IG and running it in power generation mode.

(K) Maintaining the sustained power generation by the PWM-VSI Control (1).

(L) Engaging the Pump contact (CN-P) and using the generated power in activating the local load.

SUMMARY OF INVENTION

The present invention concerns with a system for generating the required reactive power from a separate built in power source to maintain self excitation and to sustain the operation without usage of any physical capacitor banks switching with the generator lines within the predefined operation conditions (changes in wind speed, load). The system generates the required reactive power from a separate built in power source to maintain the power factor to the optimum level for higher efficiency without any separate capacitor banks switching in the generator power line. A control system which monitors whose input signals are generator's rotor speed, load, excitation voltage and provide necessary relative power to the SEIG is taken from a DC source through controlled IGBT drivers. The pulse width modulation (PWM) of the IGBT is controlled by varying the modulation index by the control system, and the feed back for the reactive power required based on the charge accumulated on the DC side of the IGBT inverter. The proposed design system monitors the wind speed, local load requirement, grid (G) availability and accordingly manages the power distribution for optimum usage of the power produced by the wind turbine,

This system is used to work as a standalone wind turbine without grid power to provide electrical power for devices like pump (P), heaters, etc or with the grid (G) power connected where the generated power is exported fully/partially after usage of the local loads like pump (P), heater, etc. or with grid (G) power connected, when there is no sufficient wind energy is available to supply power from grid (G) to the local loads like pump (P), heater, etc.

BRIEF DESCRIPTION OF THE DRAWINGS Fig.1 illustrates the various scenarios of operation of the system and their operation in each of the conditions.

Fig.2 illustrates the functional block diagram of the system during the operation condition at scenario serial numbered 4.

Fig. 3 illustrates the flow of steps involved in the system during the operation condition at scenario serial numbered 4.

Fig. 4 illustrates the functional block diagram of the system during the operation condition at scenario serial numbered 8.

Fig. 5 illustrates the flow of steps involved in the system during the operation condition at scenario serial numbered 8. Fig. 6 illustrates the functional block diagram of the system during the operation condition at scenario serial numbered 6. Fig. 7 illustrates the functional block diagram of the system during the operation condition at scenario serial numbered 7. Fig. 8 illustrates the flow of steps involved in the system during the operation condition at scenario serial numbered 6 and 7.

DETAILED DESCRIPTION OF THE INVENTION AND DRAWINGS Because of the Global crises, the unpredictability of the non-ending price fluctuations of fossil fuels and the complexities of the construction and maintenance of the nuclear power plants, wind energy and utilization of wind farms has gained an increasing importance and interest. Even though there are large amount of developments are made to provide electrical power to all places where man kind is approachable and livable, still many areas are un approachable for the power lines due to various reasons like harsh landscape, power line losses, delivery versus utilization, etc

A Wind turbine control system may have its operation in two modes of configuration. They are as a stand alone type which generates electrical energy and supply to load from wind energy at remote places where no grid power is available, the system controlling an asynchronous machine as a Self excitation Induction generator (SEIG) by maintaining necessary slip with closed loop feedback from DC side of the inverter control.

The system is capable of being connected to grid (G) power if available and supplies the generated power to local loads or to the Grid (G) line or to supply to local loads and also the excess to grid (G) line. The system controlling a power grid (G) connected asynchronous generator (IG - induction generator (IG)) and maintaining the power factor near unity by adequate control of the inverter in synchronous with the grid (G) supply voltage.

To maintain the excitation and better power factor for SEIG / IG, the normally used capacitor banks are eliminated here (no physical capacitors banks being switched), To generate power without loosing excitation within specified range of wind speed and loads, the required reactive power is supplied to the asynchronous generator / leading current to the loads through an feedback controlled inverter from an energy source in proportion to the requirement based on the power factor, turbine rpm, load variation, etc. The above operation hold good for stand-alone wind turbine without grid connection or with grid (G) connection used in farms to pump (P) water from well, to power heater and to various applications etc. The overall modes and the operation of the system in each scenario are illustrated in fig. 1. The system operation during the availability and non availability of wind and grid (G) power are taken into consideration along with the respective contacts being engaged during the availability and non availability of wind and grid (G) power. The functional status of the wind turbine and the functions of the DCS with Variable Frequency AC Drive (VFD) are illustrated in each of the said operating conditions.

When no wind and grid (G) power is available to the system, all the three contacts namely CN- A, CN-G and CN-P are disengaged and wind turbine is stopped with no necessity for the DCS. The CN- A contact alone gets engaged when the wind power alone is available to the system and the wind turbine charges the battery (B) through the alternator and the DCS and VFD rectifies the three phase to DC. This condition acts as a slow startup for the turbine. The system line diagram and the functional block diagram of the system during the scenario of si. No. 4 are illustrated in fig.2. The systems comprises of Digital control system (DCS) having micro controller units, Inverter section with transistor drivers, DC charge and pump (P) control having battery (B) to store and provide the required DC power. This system has the unique feature of operating as a stand alone type or/and operating with grid (G) connected condition. The module wise description is as follows

Digital control system (DCS)

The Digital control system (DCS) which is the core control system has

❖ Pulse Width Modulated -Voltage Source Inverter (1) control

❖ Line sync UPF Control (2)

❖ Configuration selector and driver control interface (CC) ❖ Feed back signal (GF.PFB.RF)

The Pulse Width Modulated -Voltage Source Inverter (PWM-VSI) control This section is primarily used when the turbine is operated in stand alone mode. The function of this section is that the DC voltage from the inverter DC side section is compared with the internal reference and the inverter frequency is controlled in such a way that a negative slip is maintained for sustained SEIG operation without the requirement of any physical capacitor bank switching. Line svnc UPF Control

This section is primarily used when the turbine is connected to the grid (G). The prime function of this section is to control the inverter in parallel with the power grid (G) line, to pump (P) required excess current and withdraw the available excess current from grid (G)/load in synchronization with the power grid (G) voltage level. The required instantaneous additional power is taken from the battery (B) source by the inverter and the excess power available is subsequently used to charge back and the battery (B) acts as a load to consume the additional power available. By this action the current waveform is made in sync with the voltage and thus obtaining the near unity power factor. This achievement of unity power factor ensures the efficient power transfer to grid (G) and usage by the loads.

Configuration selector and driver control interface

The objective of this section is to monitor the availability of grid (G) power, wind speed and loads to be powered. According to the prevailing inputs the mode of operation is selected and to control the turbine operation to the maximum efficiency possible.

The interface

The digital, analog and reference feedback voltage are scaled to the proper level for the controller interface.

Inverter and Driver The Insulated Gate Bipolar Transistor (IGBT) is used as the switching components in the inverter. The inverter is driven by the configuration/ Driver control section. The signals are opto-isolated and fed to the IGBT through the driver IC's. The inverter is capable of handling the power requirement s of the IG and the Load current.

Battery IB) and Charger

The Battery (B) is the DC source which is used for

❖ For the startup of the turbine when it is operated in without grid supply conditions.

❖ With Grid (G) connected condition, to supply the required power to the inverter for current control in sync with the power line voltage to obtain near unity Power factor

The charger is used to charge the batteries from the supply available at the DC side of the inverter during the standalone mode and from the excess power available during the current control in sync with the power line voltage when Grid (G) power is available.

Overall operation

Fig. 3 illustrates the flow of steps involved in the system during the operation condition at scenario serial numbered 4 of fig.1. If the turbine is stand alone mode (no grid connected or grid (G) connected but no grid power available) when sufficient wind speed is available, the CN-A contact is engaged, the IG is started in the motoring mode to run wind turbine by switching the inverter controls and the necessary power for startup is taken from the DC source say Battery (B). When sufficient speed is reached, which is sensed by the Digital control system (DCS) from the rotor rpm, the inverter control signals are controlled such that the stator frequency cos is maintained lower sufficiently so that the IG is self excited and runs in the power generation mode. The PWM Control (1) takes care of this functioning to ensure sustained power generation. The generated power is used by the local load say pump (P) by engaging the CN-P contact. A method for providing the pre determined reactive power to the asynchronous generator through a feed back controlled inverter by eliminating the usage of physical capacitor banks during stand alone mode of turbine operation comprises the following steps of operating the turbine in stand alone mode with no grid connected or no grid power if connected, checking for the sufficient wind speed availability for the wind turbine, upon achieving sufficient wind speed, engaging the CN-A contact, starting the IG in the monitoring mode, running the wind turbine by switching the inverter controls, obtaining the power for start up from the battery (B), sensing the speed of the wind turbine from the rotor RPM by the Digital control system (DCS), checking for the sufficient speed availability in the wind turbine, upon achieving sufficient speed, controlling the inverter control signals for stator frequency cos sufficiently lower, self exciting the IG and running it in power generation mode, maintaining the sustained power generation by the PWM-VSI Control (1) and engaging the CN-P contact and using the generated power to the local load.

Fig. 4 and 5 illustrates the functional block diagram of the system during the operation condition at scenario serial numbered 8 of fig.1 and the flow of steps involved in the system during the operation condition at scenario serial numbered 8 of fig.1. If the turbine is in the grid (G) connected type (also grid (G) power is available) and when sufficient wind speed is available, the CN-A contact is engaged, the IG is started in the motoring mode to run T by switching the inverter controls and the necessary power for startup is taken from the DC source say battery (B).

When sufficient speed is reached, which is sensed by the Digital control system (DCS) from the rotor rpm, the grid (G) power is connected by engaging the CN-G contact. With sufficient wind speed, the IG rotor speed cor tends to increase which makes a negative slip and the power is generated, the generated power is supplied to the local load say pump (P) by engaging CN-P or Grid (G) through CN-G or by both. To have efficient power generation the Power factor is maintained near unity. To maintain near unity, the Inverter is connected in parallel and controlled by the Line sync UPF control by pumping required current in sync to the Grid (G) voltage and draws and charges to battery (B) the excess current in sync with the grid (G) voltage.

A method for providing the pre determined reactive power to the asynchronous generator through a feed back controlled inverter by eliminating the usage of physical capacitor banks during stand alone mode of turbine operation comprises the steps of operating the turbine in the grid (G) connected mode with available grid (G) power, checking for the sufficient wind speed availability for the wind turbine, upon achieving sufficient speed, engaging the CN-A contact, starting the IG in the motoring mode, running the wind turbine by switching the inverter controls, obtaining the necessary power for start up from the DC source of battery (B), sensing the speed of the wind turbine from the rotor RPM by the DCS, checking for the sufficient speed availability in the wind turbine, upon achieving sufficient speed, engaging the CN-G contact and connecting to the grid (G) power, increasing the IG rotor speed cor, initiating a negative slip and generating the power, engaging the CN-P or CN-G or both for utilizing the generated power by the local loads, connecting the inverter in parallel for maintaining the power factor to unity and for generating efficient power, pumping the required power in sync to the grid (G) voltage and its controlling by the line sync UPF control, charging the battery (B) with excess current in sync with grid (G) voltage and maintaining the power factor to unity. Figs. 6, 7 and 8 illustrate the functional block diagram of the system during the operating condition at scenario serial numbered 6 and 7 and the flow of steps involved in the system during the operating condition at scenario serial numbered 6 and 7. If the turbine is in the grid (G) connected type (also grid (G) power is available) and when sufficient wind speed is not available, the system can be used in consumer mode, i.e. the required power to the local load say pump (P) is drawn from the Grid (G). To have effective power consumption the Power factor is maintained near unity. To maintain unity power factor, the Inverter is connected in parallel and controlled by the Line sync UPF control by pumping required current in sync to the Grid (G) voltage and draws and charges to battery (B) the excess current in sync with the grid (G) voltage. A method for providing the pre determined reactive power to the asynchronous generator through a feed back controlled inverter by eliminating the usage of physical capacitor banks during stand alone mode of turbine operation comprises the steps of operating the wind turbine in grid (G) connected mode with available grid (G) power, using the system in the consumer mode of operation during the non availability of wind power and drawing the required power for the local load from the grid (G), connecting the inverter in parallel for maintaining power factor to unity and for having effective power consumption, pumping the required current in sync to grid (G) voltage by the line sync UPF control, drawing and charging the battery (B) with the excess current in sync to the Grid (G) voltage.

The system supplies required reactive power to IG for self excitation without physical capacitor bank switching and works as a stand alone unit. For sustained operation of SEIG the system provides the required reactive power by maintaining necessary slip by driving the stator with necessary frequency for the variance of turbine rpm (rotor speed), load changes. The system generates power with optimum efficiency by monitoring the power factor and maintains the PF near unity by providing necessary reactive power to the SEIG. The necessary reactive power for the above said conditions is converted from a separate DC power source say battery (B) and the necessary reactive power produced using a PWM controlled inverter configuration using IGBT's as switching elements, whereas the input is taken from a DC source.

The DC power source is a rechargeable power source, where the excess backward voltage is used to recharge the DC source. The amount of reactive power to be provided to the SEIG is controlled with the reference based on the amount of the backward return voltage charge level. The DC power source is also necessarily charged back using a portion of the power generated. The generated power is used to drive pump (P) motors, heaters and other electrical appliances. With this turbine also connected to power grid (G), and whenever power grid (G) is present, and on necessity will directly link with power grid (G) and work as IG and uses the reactive power from grid (G) for primary functioning. With the turbine connected to power grid (G), the power generation will be done when sufficient wind energy is available and the control systems recognize this mode and controls the IG based on the load, power factor and slip. The control system switches the inverter control in synchronization with the power grid (G) frequency, phase sequence. To maintain maximum power transfer and to attain optimum power factor around unity, the leading reactive power is injected by the inverters driven by the control system based on the inputs which are taped from the power grid (G) delivery lines and Induction generator (IG). This turbine generates power as a stand alone type with SEIG as mentioned above in remote places where there is no power grid (G) is available. This turbine also generates power as a stand alone and also can be connected to the power grid (G) where there is power grid (G) available to export generated power to grid (G) or export excess power to grid (G) after delivering to the local loads.

This turbine generates power with grid (G) connected and works as stand alone mode for delivering power to the local loads whenever there is a power failure in the power grid (G) and also may be connected to the power grid (G). This turbine takes power from the power grid (G) and delivers to the local loads whenever there is not sufficient wind energy is available to harvest. This system is used to work as a standalone wind turbine without grid power to provide electrical power for devices like pump (P), heaters, etc or with grid (G) power connected where the generated power is exported fully/partially after usage of the local loads like pump (P), heater, etc. or with grid (G) power connected, when there is no sufficient wind energy is available to supply power from grid (G) to the local loads like pump (P), heater, etc.

It will be obvious to a person skilled in the art that with the advance of technology, the basic idea of the invention can be implemented in a plurality of ways. The invention and its embodiments are thus not restricted to the above examples but may vary within the scope of the claims.

Further the above-described embodiments of the present invention are intended to be examples only. Alterations, modifications and variations may be effected to the particular embodiments by those of skill in the art without departing from the scope of the invention, which is defined solely by the claims appended hereto.

Kalyan Jhabakh (Agent for Applicant )

IN/PA-830

Claims

CLAIMS:

Claim 1

(C) Battery (B) and chargers for starting up the turbine operations during no grid supply conditions and for obtaining unity power factor upon grid (G) connection.

Claim 2

The system as claimed in claim 1 wherein the said Digital control system (DCS) comprises

(A) A PWM-VSI Control (1) for controlling the inverter frequency and maintaining a negative slip for sustained SEIG operation without the requirement of any physical capacitor bank switching.

(B) A line sync UPF control (2) for controlling the inverter in parallel with the power grid (G) line for pumping the required excess current and for withdrawing the available excess current from the grid (G) / load in synchronization with power grid (G) voltage level.

(C) A configuration selector and a driver control interface for monitoring the availability of grid (G) power, wind speed and loads to be powered.

(D) An interface for scaling the digital, analog and reference feed back voltage to the pre determined level for the controller interface.

Claim 3

The system as claimed in claim 2 wherein the said

(A) PWM-VSI Control (1) operates in the stand alone mode of the wind turbine by comparing the internal reference voltage with the DC voltage from the DC side inverter.

(B) Line sync UPF control (2) operates when the turbine is connected to the grid (G) and syncs the current waveform with the voltage for obtaining near unity power factor and efficient power transfer to the grid (G) and loads. (C) Configuration selector and the said driver control interface selects the mode of operation of the turbine based on the prevailing inputs and controls the operation of the turbine for maximum efficiency.

Claim 4

The system as claimed in claim 1 wherein

(A) The said driver is an IGBT driver used for switching the inverter components and is driven by the configuration / driver control section.

(B) The signals are opto-isolated and fed into the said IGBT driver through the driver IC's.

Claim 5

The system as claimed in claim 1 wherein the said battery (B) is a DC source and said charger

(A) Charges the said batteries from the available supply at the DC side of the inverter during the stand alone mode of operation of the wind turbine.

(B) Charges from the excess power available during the current control in sync with the power line voltage during availability of grid (G) power to the wind turbine.

Claim 6

A method for providing the pre determined reactive power to the asynchronous generator through a feed back controlled inverter as claimed in claim 2 by eliminating the usage of physical capacitor banks during stand alone mode of turbine operation comprises the steps of

(A) Operating the turbine in stand alone mode with no grid connected or no grid power available if connected.

(B) Checking if sufficient wind speed is availability for the wind turbine.

(C) Upon achieving sufficient speed, engaging the CN-A contact.

(D) Starting the IG in the motoring mode.

(E) Running the wind turbine by switching the inverter controls.

(F) Obtaining the power for start up from the battery (B).

(G) Sensing the speed of the wind turbine from the rotor RPM by the Digital control system (DCS). (H) .Checking the speed of the wind turbine from the rotor RPM by the DCS. (I) Upon achieving sufficient speed, controlling the inverter control signals for stator frequency sufficiently lower.

(J) Self exciting the IG and running it in power generation mode.

(K) Maintaining the sustained power generation by the PWM-VSI Control (1).

(L) Engaging the CN-P contact and using the generated power in activating the local load.

Claim 7

A method for providing the pre determined reactive power to the asynchronous generator through a feed back controlled inverter as claimed in claim 3 by eliminating the usage of physical capacitor banks during grid (G) connected mode of turbine operation comprises the steps of

(A) Operating the turbine in the grid (G) connected mode with available grid (G) power.

(B) Checking if sufficient wind speed is availability for the wind turbine.

(C) Upon achieving sufficient speed, engaging the CN-A contact.

(D) Starting the IG in the motoring mode.

(E) Running the wind turbine by switching the inverter controls.

(F) Obtaining the necessary power for start up from the DC source of battery (B).

(G) Sensing the speed of the wind turbine from the rotor RPM by the DCS.

(H) Checking for the sufficient speed availability in the wind turbine.

(I) Upon achieving sufficient speed, engaging the CN-G contact and connecting to the grid (G) power.

(J) Increasing the IG rotor speed cor, initiating a negative slip and generating the power.

(K) Engaging the CN-P or CN-G or both for utilizing the generated power by the local loads.

(L) Connecting the inverter in parallel for maintaining the power factor to unity and for generating efficient power.

(M) Pumping the required power in sync to the grid (G) voltage and its controlling by the line sync UPF control (2).

(N) Charging the battery (B) with excess current in sync with grid (G) voltage.

(0) Maintaining the power factor to unity. Claim 8 A method for providing the pre determined reactive power to the asynchronous generator through a feed back controlled inverter as claimed in claim 2 by eliminating the usage of physical capacitor banks during grid (G) connected mode of turbine operation comprises the steps of

(A) Operating the wind turbine in grid (G) connected mode with available grid (G) power.

(B) Checking for the availability of sufficient wind power.

(C) If sufficient wind power is not obtained then using the system in consumer mode of operation.

(D) Drawing from the grid (G) the required power for the local load.

(E) Connecting the inverter in parallel for maintaining power factor to unity and for having effective power consumption.

(F) Pumping the required current in sync to grid (G) voltage by the line sync UPF control.

(G) Drawing and charging the battery (B) with the excess current in sync with the grid (G) voltage.

(H) Maintaining the power factor to near unity.

Claim 9

The method as claimed in any preceding claims wherein

(C) The said battery (B) is a DC source and said charger charges the said batteries from the available supply at the DC side of the inverter during the stand alone mode of operation of the wind turbine and

(D) The said battery (B) charges from the excess power available during the current control in sync with the power line voltage during availability of grid (G) power to the wind turbine. Claim 10

A method and a system for providing the pre determined reactive power to the asynchronous generator through a feed back controlled inverter as claimed in claim 1 and claim 2 by eliminating the usage of physical capacitor banks substantially as herein described with respect to the accompanying drawings.