WO2019147323A1

WO2019147323A1 - Wind turbine power conversion system and method

Info

Publication number: WO2019147323A1
Application number: PCT/US2018/060226
Authority: WO
Inventors: Anthony Dellapenna
Original assignee: Ajax Tocco Magnethermic Corporation
Priority date: 2018-01-26
Filing date: 2018-11-10
Publication date: 2019-08-01

Abstract

Methods and controllers to operate a wind turbine system, including generating control signals to operate a boost converter and an inverter according to a setpoint, increasing the setpoint, sampling a feedback value after increasing the setpoint, further increasing the setpoint in response to the feedback value indicating that the output power delivered is increasing following an increase in the setpoint, decreasing the setpoint in response to the feedback value indicating that the output power is not increasing following the increase in the setpoint, or that the output power delivered is greater than a demanded output power value following a decrease in the setpoint, and increasing the setpoint in response to the feedback value indicating that the output power is less than the demanded output power value following the decrease in the setpoint.

Description

WIND TURBINE POWER CONVERSION SYSTEM AND METHOD

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to, and the benefit of, U.S. Provisional Patent Application No. 62/622,284, filed January 26, 2018, entitled WIND TURBINE POWER CONVERSION SYSTEM AND METHOD, the entirety of which is hereby incorporated by reference as if fully set forth herein.

BACKGROUND

[0002] The described subject matter relates to wind energy conversion systems. Wind turbine power conversion typically uses a user input table of setpoints for a specific wind turbine power generation curve. The generator stores these in a lookup table (LUT) and uses these setpoints to control how much power is available to be sourced from the turbine. This method is limited to the amount of setpoints available for the user to enter. Possible power generation between setpoints is lost due to the resolution of the look up table.

BRIEF DESCRIPTION

[0003] Disclosed examples include systems, control circuitry and methods to operate a wind turbine based power conversion system. Described example methods include generating control signals to operate a boost converter and an inverter of the power conversion system according to a setpoint, increasing the setpoint, sampling a feedback value of the power conversion system after increasing the setpoint, and further increasing the setpoint in response to the feedback value indicating that the output power delivered by the power conversion system is increasing following an increase in the setpoint. Example methods further include decreasing the setpoint where the feedback value indicates that the output power delivered by the power conversion system is not increasing following the increase in the setpoint, or where the feedback value indicates that the output power is greater than a demanded output power value following a decrease in the setpoint. Described methods also include increasing the setpoint in response to the feedback value indicating that the output power delivered by the power conversion system is less than the demanded output power value following a decrease in the setpoint. BRffiF DESCRIPTION OF THE DRAWINGS

[0004] FIG. 1 is a schematic diagram showing a turbine-based wind energy system with a power conversion system to convert power from the turbine and generator to deliver power to a grid.

[0005] FIG. 2 is a flow diagram of a method to operate a power conversion system.

[0006] FIG. 3 is a graph of demanded current, feedback current, DC bus voltage and power feedback in the system of FIG. 1.

[0007] FIG. 4 is a graph of demanded current, feedback current, DC bus voltage and power feedback in the system of FIG. 1.

[0008] FIG. 5 is a graph of power as a function of time for operation according to the method of FIG. 2, and for use of a lookup table.

DETAILED DESCRIPTION

[0009] Referring now to the figures, several embodiments or implementations are hereinafter described in conjunction with the drawings, wherein like reference numerals are used to refer to like elements throughout, and wherein the various features are not necessarily drawn to scale.

[0010] FIG. 1 shows a turbine-based wind energy system 100 that includes a turbine 102 with blades to transfer wind energy to rotational motion of a rotor. The turbine rotor drives a rotor of a generator 104. The generator 104 converts mechanical rotation into AC electrical power. The illustrated generator provides a three phase output. In other examples, the generator 104 can provide a single phase AC output or other multi-phase AC output. A power conversion system 106 (e.g., and AC-DC-AC converter) converts AC input power from the generator 104 to AC output power. In the illustrated system, the power conversion system 106 generates a three phase output to provide AC power to a grid 108 (labeled GRID in FIG. 1). In other examples, the power conversion system 106 can provide a single phase AC output or other multi-phase output.

[0011] The power conversion system 106 includes a rectifier 110 with an input to receive an AC input signal from a turbine driven generator 104, and an output to provide a first DC output signal. In the illustrated example, the rectifier 110 is a three phase passive rectifier with rectifier diodes D1-D6 converting a three phase AC input voltage signal VR, VS, VT from input lines R, S and T to provide a rectified first DC output voltage VDC1 across a capacitor Cl. A discharge resistor Rl is connected across the capacitor Cl. In other possible examples, the resistor Rl can be omitted. In further examples, a single phase passive rectifier can be provided to rectify a single phase AC input signal. In other examples a single or multiphase active rectifier can be used to convert an input AC signal to provide the first DC signal VDC 1.

[0012] The power conversion system 106 further includes a boost converter 1 12 to convert the first DC output signal VDC1 to a second DC output signal VDC2. In one example, VDC2 is greater than or equal to VDC1. The boost converter 1 12 includes an inductor L, a low side switch SB and a high side diode D7. In another example, the high side diode D7 can be replaced by a high side switch. In the illustrated example, the low side switch SB is an IGBT. Other types of switches can be used in other implementations (e.g., bipolar transistors, field-effect transistors, etc.). The switch SB operates according to a first switching control signal SCB with a duty cycle controlling the on time of the switch SB in each of a plurality of switching cycles to convert the first DC signal VDC1 to the second DC signal VDC2.

[0013] A DC bus circuit 1 14 is coupled between the boost converter 1 12 and an inverter 1 16. The DC bus circuit 1 14 includes a first node DC+ connected between the cathode of the diode D7 and a first input of the inverter 1 16, a second node DC-, and a DC bus capacitor C2 connected between the nodes DC+ and DC-. The inverter 1 16 converts the second DC output signal VDC2 to an AC output signal VU, VV, VW to deliver output power to the grid 108. The inverter 1 16 includes six IGBT switches S 1-S6 individually connected between one of the DC bus nodes DC+ or DC- and a corresponding one of three inverter output nodes U, V and W. The inverter output delivers phase currents IU, IV and IW to the grid 108.

[0014] The power conversion system 106 includes a controller or control circuit 1 18. The illustrated controller 1 18 includes a setpoint controller 120 that advantageously controls an operating point or setpoint of the converter 106 as described further below. The controller 1 18 can be a single processor-based system or can be implemented in distributed fashion. In one example, the conversion system 100 can include an integrated inverter 116 with an included processor-based control circuit that is operatively coupled with a central processor-based controller that provides setpoints to the inverter and to a separate boost converter controller. In the illustrated example, the controller 1 18 includes a boost converter 122 with an output 124 that provides a boost converter switching control signal SCB to operate the switch SB of the boost converter 1 12. The controller 1 18 further includes an inverter controller 126 with one or more outputs 128 that provide inverter switching control signals to operate the inverter switches S 1-S6. In one example, the boost converter control signal SCB and the inverter switching control signals are pulse width modulated (PWM) signals that control the respective boost conversion and DC-AC inverter functions of the boost converter 1 12 and the inverter 1 16. The boost controller 122 and the inverter controller 126 include suitable driver circuitry to generate the switching control signals at suitable amplitudes to selectively turn the associated switches SB and S 1-S6 on and off to implement the power conversion functions of the converters 1 12 and 1 16.

[0015] The controller controls operation of the boost converter 112 and/or the inverter 1 16 according to a setpoint 130. In one example, the setpoint 130 is an output power setpoint 130 that represents a demanded output power value of the conversion system 106 (e.g., the amount of power provided to the grid 108). The example controller 118 implements closed loop feedback control of the output power according to the output power setpoint 130 and an output power feedback value 132 (labeled PFB in FIG. 1). The controller 1 18 can implement one or more inner control loops to control various additional operating parameters of the power conversion system 106. For instance, the boost controller 122 controls a duty cycle of the boost converter control signal SCB according to a feedback signal received at an input 134 that represents the second DC voltage VDC2. The controller 1 18 also includes inputs 136 to receive current feedback sense signals IFB representing the inverter output currents IU, IV and IW, as well as inputs 138 to receive inverter output voltage feedback sense signals VFB representing the inverter output voltages VU, VV and VW. In one example, the controller 1 18 computes the output power feedback value 132 (PFB) according to the current and voltage feedback sense signals IFB and VFB.

[0016] The illustrated controller 118 includes a processor 140 to execute instructions stored in an electronic memory 142. One, some or all of the setpoint controller 120, the inverter controller and the boost controller 122 can be implemented in hardware circuits, processor-executed program instructions stored in the memory 142 (e.g., software, firmware, etc.) or combinations thereof.

[0017] Referring also to FIG. 2, the processor 140 in one example executes program instructions stored in the memory 142 to implement the setpoint controller 120, the inverter controller and the boost controller 122. In one example, the control processor 140 executes program instructions to implement a process or method 200 shown in FIG. 2 in order to operate the power conversion system 106. The processor 140 implements the boost converter controller 122 to generate control signals SCB to operate the boost converter 1 12, and implements the inverter controller 126 to operate the inverter 1 16 of the power conversion system 106 according to the setpoint 130.

[0018] The controller 1 18 in FIG. 1 and the process or method 200 in FIG. 2 advantageously implement setpoint control to facilitate higher output power delivery to the grid 108 compared to previous power setpoint lookup table (LUT) implementations. At 202, the processor 140 increases the setpoint 130, and samples a feedback value of the power conversion system 106 at 204 after the setpoint 130 was increased (e.g., samples one or more of the feedback values VU, VV, VW, IU, IV, IW, VDC2 and/or PFB).

[0019] At 206, the processor 140 determines whether and how the feedback (e.g., the system 106) is responding to the setpoint increase. In the illustrated example, the processor 140 determines whether the feedback is increasing at 206 following the setpoint increase at 202. In response to the feedback value indicating that the output power delivered by the power conversion system 106 is increasing (YES at 206), the control processor 140 continues increasing the setpoint 130 by returning to 202. Otherwise (NO at 206), the processor 140 decreases the setpoint 130 at 208 in response to the feedback value indicating that the output power delivered by the power conversion system 106 is not increasing following the increase in the setpoint 130. In one example, the setpoint decrease at 208 is a rapid decrease, e.g., faster than the setpoint increase at 202. Following the decrease at 208, the processor 140 samples the feedback at 210 (e.g., one or more of the feedback values VU, VV, VW, IU, IV, IW, VDC2 and/or PFB). At 212, the processor 140 determines whether the output power feedback is less than the output power setpoint (e.g., whether the feedback 132 in FIG. 1 is less than the setpoint 130). If not (NO at 212), the processor 140 again decreases the setpoint at 208 in response to the feedback indicating that the output power delivered by the power conversion system 106 is greater than a demanded output power value following the previous setpoint decrease. Otherwise (YES at 212), the processor 140 returns to 202 to again increase the setpoint in response to the feedback value indicating that the output power delivered by the power conversion system 106 is less than the demanded output power value after the setpoint decrease.

[0020] By this operation, the converter controller 1 18 advantageously attempts to continue increasing the output power setpoint 130 to the extent that the sampled feedback signal or signals indicate that the system is capable of following the increased setpoint, and then backs off when the system does not follow the increased setpoint. As further shown in FIG. 1, various implementations can implement the selectively increased setpoint operation of the setpoint controller 120 by one or more control parameters used in operating the power conversion system 106. In one example, the setpoint controller 120 uses the setpoint 130 to control the duty cycle (labeled DUTY CYCLE) of the boost converter switching control signal SCB of the boost converter 1 12. In another possible example, the support controller 120 uses the setpoint 132 control a modulation index (labeled MI) of inverter switching control signals of the inverter 1 16. In other possible implementations, the setpoint controller 120 uses the setpoint 130 to control both the boost converter duty cycle (signal SCB) and the inverter modulation index (inverter switching control signals provided to S I -S 6).

[0021] FIGs. 3-5 show example operation of the power conversion system 106 and illustrate power delivery advantages of the method 200. A graph 300 in FIG. 3 illustrates a demanded current curve 302 (labeled CURRENT DEMAND), along with a current feedback curve 304 (IFB), a power feedback curve 306 (PFB), and a DC bus voltage curve 308 (VDC2) in the system 106 of FIG. 1. In this example, the current demand curve 302 is generated according to the output power setpoint 130. The setpoint controller 120 in this example generates a modulation index value (MI in FIG. 1) according to the current demand shown in curve 302. The inverter controller 126 in FIG. 1 generates the PWM inverter switching control signals at the output 128 according to the modulation index value. As seen in FIG. 3, the setpoint controller 120 operates according to the process 200 in FIG. 2 as described above to preferentially attempt to increase the demanded current 302. The increases in the demanded current curve 302 continue until the current feedback curve 304 stops following the increased setpoint. When this occurs, the setpoint controller 120 rapidly decreases the setpoint (current demand curve 302) until the reduced setpoint 130 is satisfied by the subsequently sampled feedback signal or signals. As shown in the power feedback curve 306, the output power correspondingly increases with increased setpoint current demand curve 302, and then backs off in response to the setpoint decreases. A graph 400 in FIG. 4 illustrates another example in a reduced timescale. The graph 400 illustrates the preferential setpoint increases in the current demand curve 304 and the corresponding current feedback curve 304. As in the example of FIG. 3, the power feedback curve 306 follows accordingly. [0022] A graph 500 in FIG. 5 illustrates an example power feedback curve 306 using the above- described power conversion system 106 with the setpoint controller 120 operating generally according to the process 200 of FIG. 2. The graph 500 also includes a curve 502 illustrating comparative operation of a wind turbine system using a lookup table (LUT) form of setpoint control having discrete set point values for system output power. The curve 306 in this example shows the preferential increase in the power output setpoint while the feedback shows the system is following the setpoint increases, and subsequent setpoint decreases when the system is unable to follow. In comparison, the curve 502 in FIG. 5 shows the corresponding system power output using lookup table setpoint value generation, including transitions between two discrete values in the table. The area between the curse 306 and 502 represents increased power generation of the system 106 achieved using the presently described concepts compared to the lookup table approach.

[0023] As seen in FIG. 5, the disclosed control systems and techniques provide increased power generation for the system. The described examples actively control power without the use of a lookup table or user input data. The controller continuously increases its output power setpoint while sampling feedback variables. As long as the feedback variables increase with the increase in setpoint, the controller is allowed to continue trying to increase the output setpoint. The point at which the feedback variables do not increase with the increase of the output power setpoint, the controller starts to rapidly decrease the output power setpoint until the feedback variables are again equal to or greater than the output power setpoint. As show in in FIGs. 3 and 4, the auto regulating demand signal continuously tries to increase the output as long as the control variable follows. As soon as it does not the auto regulating demand signal decreases until the control variable is satisfied. As seen in FIG. 5, the described examples facilitate production of more watt hours due to the generated energy that would normally be lost due to the finite resolution of the lookup table approach.

[0100] In the preceding specification, various embodiments have been described with reference to the accompanying drawings. It will be evident that various modifications and changes may be made thereto, and additional embodiments may be implemented, without departing from the broader scope of the invention as set forth in the claims that follow. The specification and drawings are accordingly to be regarded in an illustrative rather than restrictive sense.

Claims

CLAIMS The following is claimed:

1. A power conversion system, comprising:

a rectifier, including an input to receive an AC input signal from a turbine driven generator, and an output to provide a first DC output signal;

a boost converter to convert the first DC output signal to a second DC output signal according to a first switching control signal;

an inverter to convert the second DC output signal to an AC output signal to deliver output power to a connected grid;

a DC bus circuit coupled between the boost converter and the inverter; and

a controller to control operation of the boost converter and/or the inverter according to a setpoint, the controller configured to:

increase the setpoint,

sample a feedback value of the power conversion system after increasing the setpoint,

continue increasing the setpoint in response to the feedback value indicating that the output power delivered by the power conversion system is increasing following an increase in the setpoint,

decrease the setpoint in response to the feedback value indicating that (1) the output power delivered by the power conversion system is not increasing following the increase in the setpoint, or (2) that the output power delivered by the power conversion system is greater than a demanded output power value following a decrease in the setpoint, and increase the setpoint in response to the feedback value indicating that the output power delivered by the power conversion system is less than the demanded output power value following the decrease in the setpoint.

2. The power conversion system of claim 1, wherein the setpoint is an output power setpoint representing the demanded output power value.

3. The power conversion system of claim 2, wherein the setpoint is used to control a duty cycle of a boost converter switching control signal of the boost converter.

4. The power conversion system of claim 3, wherein the setpoint is used to control a modulation index of inverter switching control signals of the inverter.

5. The power conversion system of claim 4, wherein the feedback value is selected from the group consisting of: an output voltage of the inverter, an output current of the inverter, an output power of the inverter, and a voltage of the DC bus circuit.

6. The power conversion system of claim 2, wherein the setpoint is used to control a modulation index of inverter switching control signals of the inverter.

7. The power conversion system of claim 2, wherein the feedback value is selected from the group consisting of: an output voltage of the inverter, an output current of the inverter, an output power of the inverter, and a voltage of the DC bus circuit.

8. The power conversion system of claim 1, wherein the feedback value is selected from the group consisting of: an output voltage of the inverter, an output current of the inverter, an output power of the inverter, and a voltage of the DC bus circuit.

9. A controller for controlling a power conversion system, comprising:

an electronic memory; and

a processor to execute instructions stored in the memory to:

generate control signals to operate a boost converter and an inverter of the power conversion system according to a setpoint,

increase the setpoint,

sample a feedback value of the power conversion system after increasing the setpoint, continue increasing the setpoint in response to the feedback value indicating that the output power delivered by the power conversion system is increasing following an increase in the setpoint,

10. The controller of claim 9, wherein the setpoint is an output power setpoint representing the demanded output power value.

1 1. The controller of claim 10, wherein the setpoint is used to control a duty cycle of a boost converter switching control signal.

12. The controller of claim 11, wherein the setpoint is used to control a modulation index of inverter switching control signals of the inverter.

13. The controller of claim 10, wherein the setpoint is used to control a modulation index of inverter switching control signals of the inverter.

14. The controller of claim 10, wherein the feedback value is selected from the group consisting of: an output voltage of the inverter, an output current of the inverter, an output power of the inverter, and a voltage of a DC bus circuit.

15. The controller of claim 9, wherein the feedback value is selected from the group consisting of: an output voltage of the inverter, an output current of the inverter, an output power of the inverter, and a voltage of a DC bus circuit.

16. A method of operating a power conversion system, the method comprising: generating control signals to operate a boost converter and an inverter of the power conversion system according to a setpoint;

increasing the setpoint;

sampling a feedback value of the power conversion system after increasing the setpoint; further increasing the setpoint in response to the feedback value indicating that an output power delivered by the power conversion system is increasing following an increase in the setpoint;

decreasing the setpoint in response to the feedback value indicating that (1) the output power delivered by the power conversion system is not increasing following the increase in the setpoint, or (2) that the output power delivered by the power conversion system is greater than a demanded output power value following a decrease in the setpoint; and

increasing the setpoint in response to the feedback value indicating that the output power delivered by the power conversion system is less than the demanded output power value following the decrease in the setpoint.

17. The method of claim 16, wherein the setpoint is an output power setpoint representing the demanded output power value.

18. The method of claim 17, wherein the setpoint is used to control a duty cycle of a boost converter switching control signal.

19. The method of claim 17, wherein the setpoint is used to control a modulation index of inverter switching control signals of the inverter.

20. The method of claim 16, wherein the feedback value is selected from the group consisting of: an output voltage of the inverter, an output current of the inverter, an output power of the inverter, and a voltage of a DC bus circuit.