Title of Invention	A DEVICE FOR SENSORLESS TORQUE CONTROL OF INDUCTION GENERATOR IN THE WIND TURBINE, USING BI-DIRECTIONAL IGBT INVERTER
Abstract	A device for sensorless torque control of induction generator in the wind turbine, using bi-directional IGBT inverter, comprises first and second IGBT based 4 quadrant power converters sharing a common DC bus, the three phase AC terminals of the first converter (generator controller) being connected to the induction generator, the three phase AC terminals of the second converter (grid controller) being connected to the 3 phase grid through a 3 phase choke, die operation of the first an second converters being controlled in a coordinated manner by two controllers which are realised by Digital Signal Processors (DSPs) working on software, such that the generator controller converts the AC power generated by the induction generator into DC quantities, making this power available in the DC bus, and the grid controller faithfully converts this DC power into 3 phase AC quantities and feeds the same to the grid, matching the frequency and phases such that the power factor is always unity, whereby the ratio of rotor feed and wind speed is maintained constant at an optimum value, for maximising the power generated by the turbine and the generator for any wind speed, without directly measuring or sensing the rotor speed.

Title of Invention

A DEVICE FOR SENSORLESS TORQUE CONTROL OF INDUCTION GENERATOR IN THE WIND TURBINE, USING BI-DIRECTIONAL IGBT INVERTER

Abstract

A device for sensorless torque control of induction generator in the wind turbine, using bi-directional IGBT inverter, comprises first and second IGBT based 4 quadrant power converters sharing a common DC bus, the three phase AC terminals of the first converter (generator controller) being connected to the induction generator, the three phase AC terminals of the second converter (grid controller) being connected to the 3 phase grid through a 3 phase choke, die operation of the first an second converters being controlled in a coordinated manner by two controllers which are realised by Digital Signal Processors (DSPs) working on software, such that the generator controller converts the AC power generated by the induction generator into DC quantities, making this power available in the DC bus, and the grid controller faithfully converts this DC power into 3 phase AC quantities and feeds the same to the grid, matching the frequency and phases such that the power factor is always unity, whereby the ratio of rotor feed and wind speed is maintained constant at an optimum value, for maximising the power generated by the turbine and the generator for any wind speed, without directly measuring or sensing the rotor speed.

Full Text	Most of the conventional wind turbines use induction generators, for converting mechanical power generated by the wind turbine into electrical power These generators are directly connected across the three-phase supply in the grid This method, although very simple, is not an efficient one The reason can be explained as follows. The power generated by the wind turbine is maximum, if it operates at its maximum power coefficient This is possible only if a specified tip speed ratio is maintained throughout the operation range To maintain this tip speed ratio, the rotor speed of the machine has to be varied according to the wind speed In the existing method, the rotor speed is determined by frequency of the grid supply, which is more or less constant. Therefore variable speed operation of wind turbine needs to be implemented to overcome the above limitation. For the variable speed control of wind turbine the basic inputs required are the wind speed, rotor speed and electrical parameters of the generator viz, three line voltages and three line currents A block diagram of the variable speed, induction generator based wind electric generator is shown in Fig. 1. In this scheme an induction generator is coupled to the wind turbine through gearbox The generator output is connected to a three-phase frequency converter, which converts the electrical power from three-phase AC voltage to DC voltage. A second converter converts the DC power into three-phase AC power with a constant frequency matching the grid frequency The controller modules will decide the frequency of operation and thus the rotor speed of the induction generator will be in such a way that maximum power is extracted from the wind turbine by maximising the turbine power coefficient In these already known schemes, the controller needs to read the rotor speed signal using a high-resolution speed sensor, to decide the operating point of the turbine The accommodation of high-resolution speed sensor on the generator rotor and transmitting the signal down to the control panel at the bottom is a complicated and expensive measure. A simple, wired connection cannot transmit the high-resolution high-speed signals over such a distance, the tower height being of the order of 30 metres. More complicated serial communication technique with adequate isolation and non-attenuation circuits are often used. This increases cost and reduces reliability of the system. Here, a novel scheme has been developed, which does not require a high-resolution speed sensor for the variable speed control of the induction generator based wind electric generator The rotor speed is computed on-line using a DSP processor based controller This scheme not only makes the scheme simple by eliminating complicated wiring/ transmission of speed signal from the nacelle (on the top of tower) to the bottom controller, also reduces the cost of the controller Reliability of the system is improved by a large extent by the elimination of the flimsy speed sensor. The detailed schematic diagram of the new controller is shown in Fig 2. The new controller only reads / senses generator currents and the DC link voltage of the power converter. From these parameters the rotor speed and machine terminal voltages are calculated using machine modeling and converter modeling, with an on-line computer- DSP processor and supporting software The turbine model, which is also run in the same computer, helps to run the turbine at a speed in which the power generated is a maximum for any wind speed, without measuring the actual wind speed or the actual rotor speed Actually the controller develops necessary torque at the generator shaft by controlling the flux and the currents of the generator to settle at the required speed to produce maximum power. The device for sensorless torque control of induction generator in the wind turbine, using bi-directional IGBT inverter, comprises first and second IGBT based 4 quadrant power converters sharing a common DC bus, die three phase AC terminals of the first converter (generator controller) being connected to the induction generator, the three phase AC terminals of the second converter (grid controller) being connected to the 3 phase grid through a 3 phase choke, the operation of the first and second converters being controlled in a coordinated manner by two controllers which are realised by Digital Signal Processors (DSPs) working on software, such that die generator controller converts the AC power generated by the induction generator into DC quantities, making this power available in the DC bus, and the grid controller faithfully converts this DC power into 3 phase AC quantities and feeds the same to the grid, matching the frequency and phases such that the power factor is always unity, whereby the ratio of rotor feed and wind speed is maintained constant at an optimum value, for maximising the power generated by the turbine and the generator for any wind speed, without directly measuring or sensing the rotor speed. This invention will now be described with reference to the accompanying drawings which illustrate In Fig.l a block diagram of a typical known variable speed wind electric generator In Fig.2 a block diagram of one of possible embodiments of the device according to this invention And in Fig 3 a block diagram of generator side controller according to the said embodiment. Construction of the sensorless torque control and variable speed operation of the induction generator for the wind turbine is as follows. The system consists of two IGBT based 4-quadrant Power Converters A block schematic of the system is shown in fig.2 These Converters are sharing a common DC bus The 3-phase AC terminals of the first converter, which is also called as the Generator Controller, is connected to the induction generator of the wind turbine. AC terminals of the second converter, which is called as the Grid controller, is connected to the 3-phase grid through a 3-phase choke. The operation of the two converters are controlled in a coordinated manner by two controllers which are realised by Digital Signal Processors and the software developed exclusively for this application. The Generator Controller converts the AC power generated by the induction generator into DC quantities and the power is available in the DC bus The Grid Controller faithfully converts this DC power into 3-phase AC quantities and feeds to the grid, matching the frequency and phases, such a way that the power factor is always unity The coordination between the two controllers is essential to make sure that the power generated by the wind turbine-induction generator assembly is fully evacuated to the grid Another important feature of the control is that the speed of the generator is appropriately controlled to match the wind speed By making the ratio between rotor speed and the wind speed, constant at an optimum value, the power generated by the turbine and the generator can be maximised for any wind speed For this the controller senses the electrical parameters namely 3-phase line currents of the generator and DC link voltage The online computing software computes the rotor speed It also maximises the power hy virtually controlling speed of the rotor without sensing the wind speed either Incrementally increasing or decreasing the torque using vector control technique, and observing for power maximisation in the event of speed variation as the result of change in the wind speed achieves the power maximising. This control results in variable speed of operation as the rotor speed will follow the wind speed keeping a definite relation between the wind speed and rotor speed Tt may be noted that sensing of wind speed accurately is a very difficult task due to the turbulence introduced by the blades of the turbine in the vicinity Sensing of rotor speed accurately and transmitting the data down to ground station is also extremely difficult and expensive measure. Whereas this novel idea works without the speed sensing signals thus the error associated with this signal is totally eliminated. Fig 3 shows the flow diagram for the implementation of the generator controller The diagram shows the control flow form the input side (feed back signals Vdc, Isl, Is2, Is3) to the output side (pulse pattern to the IGBT switches SK S2, S3) Estimation of the speed and torque from the feed back signals using the equations given above is clearly indicated in the above diagram The system is implemented through DSP based hardware, with a sampling period of 50 microseconds. The calculations and the updating of data on speed and torque are achieved in this time period It is noteworthy that: • Speed of the wind-electric generator and the torque developed is estimated from the values of the electrical signal namely the DC voltage and the generator line current signals (Vdc, Isl, Is2, Is3). This scheme eliminates the necessity of the measurement of wind speed and generator speed using speed sensors, which are flimsy, complex and costly By not using the speed sensors, reliability of the system is considerably improved. This novel scheme simplifies the implementation of variable speed operation of wind electric generators and makes it viable The implementation of the control flow diagram for sensorless estimation of speed and torque of the wind electric generator as shown in figure 3 We Claim: LA device for sensorless torque control of induction generator in the wind turbine, using bi-directional IGBT inverter, comprising first and second IGBT based 4 quadrant power converters (CI, C2) sharing a common DC bus (B) the three phase AC terminals of the first converter(Cl) (generator controller) being connected to the induction generator (G), the three phase AC terminals of the second converter (grid controller) being connected to the 3 phase grid (P) through a 3 phase choke (C), the operation of the first and second converters being controlled in a coordinated manner by two controllers which are realised by Digital Signal Processors (DSPs) working on software, such that the generator controller converts the AC power generated by die induction generator into DC quantities, making this power available in the DC but, and the grid controller faithfully converts this DC power into 3 phase AC quantities and feeds die same to the grid, matching the frequency and phases such that the power factor is always unity, whereby the ratio of rotor feed and wind speed is maintained constant at an optimum value, for maximising the power generated by the turbine and the generator for any wind speed, without directly measuring or sensing the rotor speed. 2. A device for sensorless torque control of induction generator in the wind turbine, using bi-directional IGBT inverter substantially as herein described with reference to, and as illustrated by, Figs. 2 and 3 of the accompanying drawings.

Full Text

Most of the conventional wind turbines use induction generators, for converting mechanical power generated by the wind turbine into electrical power These generators are directly connected across the three-phase supply in the grid This method, although very simple, is not an efficient one The reason can be explained as follows. The power generated by the wind turbine is maximum, if it operates at its maximum power coefficient This is possible only if a specified tip speed ratio is maintained throughout the operation range To maintain this tip speed ratio, the rotor speed of the machine has to be varied according to the wind speed In the existing method, the rotor speed is determined by frequency of the grid supply, which is more or less constant. Therefore variable speed operation of wind turbine needs to be implemented to overcome the above limitation.
For the variable speed control of wind turbine the basic inputs required are the wind speed, rotor speed and electrical parameters of the generator viz, three line voltages and three line currents A block diagram of the variable speed, induction generator based wind electric generator is shown in Fig. 1. In this scheme an induction generator is coupled to the wind turbine through gearbox The generator output is connected to a three-phase frequency converter, which converts the electrical power from three-phase AC voltage to DC voltage. A second converter converts the DC power into three-phase AC power with a constant frequency matching the grid frequency The controller modules will decide the frequency of operation and thus the rotor speed of the induction generator will be in such a way that maximum power is extracted from the wind turbine by maximising the turbine power coefficient In these already known schemes, the controller needs to read the rotor speed signal using a high-resolution speed sensor, to decide the operating point of the turbine
The accommodation of high-resolution speed sensor on the generator rotor and transmitting the signal down to the control panel at the bottom is a complicated and expensive measure. A simple, wired connection cannot transmit the high-resolution high-speed signals over such a distance, the tower height being of the order of 30 metres. More complicated serial communication technique with adequate isolation and non-attenuation circuits are often used. This increases cost and reduces reliability of the system.
Here, a novel scheme has been developed, which does not require a high-resolution speed sensor for the variable speed control of the induction generator based wind electric generator The rotor speed is computed on-line using a DSP processor based controller This scheme not only makes the scheme simple by eliminating complicated wiring/ transmission of speed signal from the nacelle (on the top of tower) to the bottom controller, also reduces the cost of the controller Reliability of the system is improved by a large extent by the elimination of the flimsy speed sensor. The detailed schematic diagram of the new controller is shown in Fig 2.

The new controller only reads / senses generator currents and the DC link voltage of the power converter. From these parameters the rotor speed and machine terminal voltages are calculated using machine modeling and converter modeling, with an on-line computer- DSP processor and supporting software The turbine model, which is also run in the same computer, helps to run the turbine at a speed in which the power generated is a maximum for any wind speed, without measuring the actual wind speed or the actual rotor speed Actually the controller develops necessary torque at the generator shaft by controlling the flux and the currents of the generator to settle at the required speed to produce maximum power.

The device for sensorless torque control of induction generator in the wind turbine, using bi-directional IGBT inverter, comprises first and second IGBT based 4 quadrant power converters sharing a common DC bus, die three phase AC terminals of the first converter (generator controller) being connected to the induction generator, the three phase AC terminals of the second converter (grid controller) being connected to the 3 phase grid through a 3 phase choke, the operation of the first and second converters being controlled in a coordinated manner by two controllers which are realised by Digital Signal Processors (DSPs) working on software, such that die generator controller converts the AC power generated by the induction generator into DC quantities, making this power available in the DC bus, and the grid controller faithfully converts this DC power into 3 phase AC quantities and feeds the same to the grid, matching the frequency and phases such that the power factor is always unity, whereby the ratio of rotor feed and wind speed is maintained constant at an optimum value, for maximising the power generated by the turbine and the generator for any wind speed, without directly measuring or sensing the rotor speed.
This invention will now be described with reference to the accompanying drawings which illustrate
In Fig.l a block diagram of a typical known variable speed wind electric generator
In Fig.2 a block diagram of one of possible embodiments of the device according to this invention
And in Fig 3 a block diagram of generator side controller according to the said embodiment.

Construction of the sensorless torque control and variable speed operation of the induction generator for the wind turbine is as follows.
The system consists of two IGBT based 4-quadrant Power Converters A block schematic of the system is shown in fig.2 These Converters are sharing a common DC bus The 3-phase AC terminals of the first converter, which is also called as the Generator Controller, is connected to the induction generator of the wind turbine. AC terminals of the second converter, which is called as the Grid controller, is connected to the 3-phase grid through a 3-phase choke. The operation of the two converters are controlled in a coordinated manner by two controllers which are realised by Digital Signal Processors and the software developed exclusively for this application. The Generator Controller converts the AC power generated by the induction generator into DC quantities and the power is available in the DC bus The Grid Controller faithfully converts this DC power into 3-phase AC quantities and feeds to the grid, matching the frequency and phases, such a way that the power factor is always unity The coordination between the two controllers is essential to make sure that the power generated by the wind turbine-induction generator assembly is fully evacuated to the grid
Another important feature of the control is that the speed of the generator is appropriately controlled to match the wind speed By making the ratio between rotor speed and the wind speed, constant at an optimum value, the power generated by the turbine and the generator can be maximised for any wind speed For this the controller senses the electrical parameters namely 3-phase line currents of the generator and DC link voltage The online computing software computes the rotor speed It also maximises the power hy virtually controlling speed of the rotor without sensing the wind speed either Incrementally increasing or decreasing the torque using vector control technique, and observing for power maximisation in the event of speed variation as the result of change in the wind speed achieves the power maximising. This control results in variable speed of operation as the rotor speed will follow the wind speed keeping a definite relation between the wind speed and rotor speed Tt may be noted that sensing of wind speed accurately is a very difficult task due to the turbulence introduced by the blades of the turbine in the vicinity Sensing of rotor speed accurately and transmitting the data down to ground station is also extremely difficult and expensive measure. Whereas this novel idea works without the speed sensing signals thus the error associated with this signal is totally eliminated.
Fig 3 shows the flow diagram for the implementation of the generator controller
The diagram shows the control flow form the input side (feed back signals Vdc, Isl, Is2, Is3) to the output side (pulse pattern to the IGBT switches SK S2, S3) Estimation of the speed and torque from the feed back signals using the equations

given above is clearly indicated in the above diagram The system is implemented through DSP based hardware, with a sampling period of 50 microseconds. The calculations and the updating of data on speed and torque are achieved in this time period
It is noteworthy that:
• Speed of the wind-electric generator and the torque developed is estimated from the values of the electrical signal namely the DC voltage and the generator line current signals (Vdc, Isl, Is2, Is3).
This scheme eliminates the necessity of the measurement of wind speed and generator speed using speed sensors, which are flimsy, complex and costly By not using the speed sensors, reliability of the system is considerably improved.
This novel scheme simplifies the implementation of variable speed operation of wind electric generators and makes it viable
The implementation of the control flow diagram for sensorless estimation of speed and torque of the wind electric generator as shown in figure 3

We Claim:
LA device for sensorless torque control of induction generator in the wind turbine, using bi-directional IGBT inverter, comprising first and second IGBT based 4 quadrant power converters (CI, C2) sharing a common DC bus (B) the three phase AC terminals of the first converter(Cl) (generator controller) being connected to the induction generator (G), the three phase AC terminals of the second converter (grid controller) being connected to the 3 phase grid (P) through a 3 phase choke (C), the operation of the first and second converters being controlled in a coordinated manner by two controllers which are realised by Digital Signal Processors (DSPs) working on software, such that the generator controller converts the AC power generated by die induction generator into DC quantities, making this power available in the DC but, and the grid controller faithfully converts this DC power into 3 phase AC quantities and feeds die same to the grid, matching the frequency and phases such that the power factor is always unity, whereby the ratio of rotor feed and wind speed is maintained constant at an optimum value, for maximising the power generated by the turbine and the generator for any wind speed, without directly measuring or sensing the rotor speed.
2. A device for sensorless torque control of induction generator in the wind turbine, using bi-directional IGBT inverter substantially as herein described with reference to, and as illustrated by, Figs. 2 and 3 of the accompanying drawings.

Documents:

0351-mas-2000 abstract-duplicate.pdf

0351-mas-2000 claims-duplicate.pdf

0351-mas-2000 description (complete)-duplicate.pdf

0351-mas-2000 drawings-duplicate.pdf

351-mas-2000-abstract.pdf

351-mas-2000-claims.pdf

351-mas-2000-correspondnece-others.pdf

351-mas-2000-correspondnece-po.pdf

351-mas-2000-description(complete).pdf

351-mas-2000-drawings.pdf

351-mas-2000-form 1.pdf

351-mas-2000-form 19.pdf

351-mas-2000-form 26.pdf

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Patent Number

228529

Indian Patent Application Number

351/MAS/2000

PG Journal Number

10/2009

Publication Date

06-Mar-2009

Grant Date

05-Feb-2009

Date of Filing

05-May-2000

Name of Patentee

ELECTRONICS RESEARCH & DEVELOPMENT CENTRE

Applicant Address

VELLAYAMBALAM, THIRUVANANTHAPURAM 695 033,

Inventors:

#	Inventor's Name	Inventor's Address
1	GAUTAM PODAR	ELECTRONICS RESEARCH & DEVELOPMENT CENTRE, VELLAYAMBALAM, THIRUVANANTHAPURAM 695 033,
2	AAMANTHRA KELOTH UNNIKRISHNAN	ELECTRONICS RESERACH & DEVELOPMENT CENTRE, VELLAYAMBALAM, THIRUVANANTHAPURAM 695 033,

PCT International Classification Number

H02P25/08

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA