Non-linear control of the exciter stage of a three-stage synchronous generator

Abstract

A system and method for providing nonlinear control of a generator, comprising: a linear voltage controller and a nonlinear current controller, wherein the linear voltage controller is implemented on a microcontroller to perform: determining a reference angle for an output voltage from a first generator using a phase-locked loop; converting the reference angle and the generator output voltage from the time domain to an orthogonal reference system to generate two rotating coordinate system reference voltages; calculating the root mean square voltages of the two rotating coordinate system reference voltages and converting the root mean square voltages into an output current IfSet1; providing IfSet1 to the nonlinear current controller; and wherein the nonlinear current controller determines a control action based on the difference between IfSet1 and the output current IfFBK of a second generator.

Description

Technical Field

[0001] This invention relates to a control system for controlling the AC output of a three-stage synchronous generator, particularly a three-stage synchronous generator integrated into vehicles such as aircraft. Background Technology

[0002] Controllers and control systems are designed to suit the intended use of a system. Depending on the intended use of the control system, designers may prefer a control system with higher precision rather than one with higher gain (speed). For example, a control system using linear proportional control is designed to distribute proportional control actions at a given gain (speed). When the goal of the controller is to drive the generator's excitation current to a specific level more quickly, a linear proportional controller is not a faster way to achieve this goal. For generators used to power or assist in the control of aircraft, a faster controller is required. Summary of the Invention

[0003] The terms “invention” and “this invention” as used in this patent are intended to broadly refer to all subject matter of this patent and the following claims. The inclusion of these terms should not be construed as limiting the subject matter described herein or limiting the meaning or scope of the following claims. The inventive embodiments covered by this patent are defined by the following claims, not the summary of the invention. The summary of the invention is a high-level overview of various aspects of the invention and introduces some concepts that will be further described in the detailed description section below. The summary of the invention is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used to independently determine the scope of the claimed subject matter. The subject matter should be understood by referring to appropriate portions of the entire specification of this patent, any or all of the drawings, and each claim.

[0004] The present invention relates to a control system for controlling the three-phase AC output of a generator using a nonlinear current controller cascaded with a linear voltage controller, wherein the nonlinear current controller is a software solution implemented on a microcontroller, and the linear voltage controller is executed in an analog controller circuit.

[0005] Some embodiments of this control system technology include: a linear voltage controller and a nonlinear current controller, wherein the linear voltage controller is implemented on a microcontroller to perform: determining a reference angle for the output voltage from a first generator using a phase-locked loop; converting the reference angle and the generator output voltage from the time domain to an orthogonal reference system to generate two rotating coordinate system reference voltages; calculating the root mean square (RMS) voltages of the two rotating coordinate system reference voltages and converting the RMS voltages into an output current IfSet1; and providing IfSet1 to the nonlinear current controller; wherein the nonlinear current controller includes: an RMS-DC converter for calculating the real-time RMS voltage based on the output voltage of the first generator; a first circuit, for... The system calculates the root mean square (RMS) voltage of the output voltage of the first generator and outputs the average RMS voltage to a second circuit, wherein the second circuit compares the average RMS voltage with the higher phase RMS voltage of the output voltage of the first generator and outputs the higher voltage; a proportional-integral (PI) control module is used to convert the output of the second circuit into a current signal IfSet2; a switching component is configured to select one of outputs IfSet1 and IfSet2 to determine a control action; and an arctangent nonlinear control component is configured to use the output current IfFBK of the second generator and the selected IfSet1 or IfSet2 signal to determine the control action.

[0006] Some embodiments of this technology relate to a method of operating a control system, the method comprising: receiving a three-phase voltage Vabc_MGmeas from a three-phase generator via a linear voltage controller; determining a reference angle for Vabc_MGmeas by applying Vabc_MGmeas to a phase-locked loop of the linear voltage controller; performing a Park-Clarke transformation on the reference angle and Vabc_MGmeas to determine a first rotating coordinate system reference voltage Vq_MGmeas and a second rotating coordinate system reference voltage Vd_MGmeas; and using Vq_MGmeas and Vd_MGmeas to determine the root-mean-square voltage as follows: ; convert VRMSi into a first signal IfSet1; receive a second signal IfFBK from the exciter via a nonlinear current controller; and use the nonlinear current controller to determine a control action, wherein the control action is a function of IfSet1 and IfFBK. Attached Figure Description

[0007] Figure 1 is a block diagram representation of a nonlinear control system according to various embodiments.

[0008] Figure 2 is a flowchart of the operation method of a nonlinear control system.

[0009] Figure 3 is a block diagram representation of a cascaded linear voltage controller and a nonlinear current controller.

[0010] Figure 4 is a block diagram of the nonlinear control system, which is connected to the bipolar bridge in the power stage circuit of the generator regulator. The output of the power stage drives the excitation current of the excitation generator.

[0011] Figures 5A and 5B are block diagrams representing the approximate control of actions by applying and / or superimposing triangular wave signals. Detailed Implementation

[0012] The subject matter of embodiments of the present invention is specifically described herein to satisfy legal requirements, but this description is not necessarily intended to limit the scope of the claims. The claimed subject matter may be implemented in other ways, may include different elements or steps, and may be used in conjunction with other existing or future technologies. Unless the order of the steps or the arrangement of the elements is explicitly described, this description should not be construed as implying any particular order or arrangement between the steps or elements.

[0013] The embodiments described herein provide a nonlinear control system for controlling a three-phase generator. While the discussion of nonlinear control systems pertains to the use of three-phase generators in controlling aircraft, their applications are by no means limited to this. Rather, embodiments of the nonlinear control system can be used in other vehicles or any type of structure or for other purposes as needed. For example, embodiments can be used in trains, buses, private cars, commercial or residential buildings, or any other application where a nonlinear control system might be applicable.

[0014] In various embodiments, the nonlinear control system includes a linear voltage controller and a nonlinear current controller. The nonlinear control system provides nonlinear control for regulating the voltage output of a three-stage synchronous generator with bipolar action on a power amplifier. The control system includes a linear voltage PI loop cascaded with a nonlinear current loop that controls the excitation current of the excitation generator stage, thereby controlling the output voltage of the main generator. Either controller in the nonlinear control system can be implemented in analog hardware or in software digitally executed on a microcontroller. This control system is suitable for nonlinear dynamic loads, particularly where fast and precise control is required. Furthermore, the nonlinear current controller provides fault protection for the generator control by being configured to operate synchronously with the linear voltage controller and to provide nonlinear control in the event of linear voltage controller failure.

[0015] In this example, the linear voltage controller is digitally implemented as computer instructions on a microcontroller, while the nonlinear current controller is implemented in analog hardware with various circuits.

[0016] A linear voltage controller may include a microcontroller for executing computer instructions. The microcontroller can be connected to a main generator and a nonlinear current controller. The microcontroller receives three-phase voltages from the main generator, denoted as Vabc_MGmeas, and performs calculations on the three-phase voltages to determine reference angles for the three-phase voltages, for example, by applying phase-locked loops to the three-phase voltages. The microcontroller can measure the three-phase voltages in real-time or near real-time with a sampling rate of at least 2 kHz.

[0017] The microcontroller can perform Clark and Park transformations on the three-phase voltages and reference angles to transform them from the time domain to an orthogonal reference frame, generating two rotating coordinate system reference voltages, Vq_MGmeas and Vd_MGmeas. The microcontroller then calculates the root-mean-square voltage based on these two rotating coordinate system reference voltages.

[0018] The microcontroller appends an error setpoint output voltage to the root-mean-square (RMS) voltage, denoted as VRMS_meas, where the error setpoint output voltage represents the offset signal used to compensate for the error. It compares the RMS voltage calculated by the microcontroller with the RMS voltage of the three-phase voltage Vabc_MGmeas calculated by the nonlinear current controller. In some examples, the microcontroller can use VRMS_meas as another error setpoint output to identify and compensate for errors in the microcontroller's calculated RMS voltage. When the microcontroller detects that its calculated RMS voltage does not contain errors, such as distortion or other errors, it provides the calculated RMS voltage, including the error setpoint output, to the proportional-integral (PI) control module. The PI control module can be implemented in the microcontroller via computer instructions, or it can be a peripheral device or a separate hardware controller. The PI control module uses the error setpoint output and the RMS voltage to correct the error between the error setpoint output and the RMS voltage, and converts the corrected RMS voltage into a signal IfSet1. The microcontroller provides this IfSet1 signal to the switching module of the nonlinear current controller.

[0019] Nonlinear current controllers include various circuits, including conversion circuits for converting three-phase voltages to RMS and DC outputs, averaging circuits, circuits for identifying high-phase RMS voltages, comparator circuits, PI control modules, switching modules, zero-crossing phase-locked loops, nonlinear control modules, and pulse-width modulation amplifiers. Nonlinear current controllers can be connected to one or more drivers of linear voltage controllers, exciter generators, main generators, permanent magnet generators (PMGs), and power stage circuits.

[0020] The nonlinear current controller receives three-phase voltage from the main generator, as does the linear voltage controller, denoted as Vabc_MGmeas. The nonlinear current controller receives the three-phase voltage at a root-to-middle-direction (DC) converter circuit, which calculates the root-to-middle voltage of Vabc_MGmeas. This converter circuit provides its output to a circuit for identifying the high-phase RMS voltage and an averaging circuit for determining the average RMS voltage of the converter circuit's output. The outputs of the averaging circuit and the circuit for identifying the high-phase RMS voltage are compared in a comparator circuit, and the higher of the two outputs is provided to the PI modules of both the linear voltage controller and the nonlinear current controller as VRMS_meas, which includes an additional error setpoint output. The PI module of the nonlinear current controller uses the error setpoint output and the RMS voltage to correct for the error between the error setpoint output and the RMS voltage, and converts the corrected RMS voltage into an IfSet2 signal. The PI module provides the IfSet2 signal to the switching module of the nonlinear current controller. This switching module is configured to allow selection between the IfSet1 and IfSet2 signals. This selection can be based on the internal logic of the control system. For example, when the control system detects an error in the IfSet1 signal, it can configure the switch module to receive the IfSet2 signal. In some examples, the switch module is configured to receive the IfSet1 signal by default and can be switched when the control system detects an error. In other examples, IfSet2 can be the default signal.

[0021] The control system provides the selected signal IfSet1 or IfSet2 to the nonlinear control module. This nonlinear control module can be an arctangent (ATAN) nonlinear control module, which applies its output as a function of the current error magnitude according to the following equation: . PMG represents the available voltage of a permanent magnet generator.

[0022] Nonlinear current controllers may include sliding mode control mechanisms, which can be functions of the current error, as expressed by the following equation: Therefore, the control action can be represented by the following equation: A nonlinear current controller can provide control actions to a pulse width modulation amplifier to amplify the output, and also provide control actions to the driver of the power stage circuit to control the driver's power output.

[0023] The nonlinear current controller can also receive voltage from a permanent magnet generator (PMG), apply that voltage to a zero-crossing phase-locked loop circuit, and provide the output of the zero-crossing phase-locked loop for initializing the phase-locked loop of the linear voltage controller.

[0024] Example of a nonlinear control system Now refer to the attached diagram, Figure 1 An example of a nonlinear control system 100 according to certain embodiments is shown.

[0025] The nonlinear control system 100 includes a linear voltage controller 112 and a nonlinear current controller 111. The linear voltage controller 112 and the nonlinear current controller 111 can be cascaded. The nonlinear control system 100 is connected to a generator arrangement and other circuits, which are connected to a permanent magnet generator (PMG) 102, a power stage circuit 104, an excitation generator 106, and a main generator 108. Any of the listed generators 102, 106, and 108 can be a three-phase generator, such as... Figure 1 As shown. Figure 1 Other circuits included are rotor rectifier stage circuit 107 and load 110. The nonlinear control system 100 uses voltages from permanent magnet generator (PMG) 102, exciter generator 106 and main generator 108 to control the output voltage of main generator 108 through bipolar nonlinear control of the excitation current of exciter generator 106.

[0026] The linear voltage controller 112 may be or include a microcontroller for executing computer instructions, such as... Figure 1 As shown. The linear voltage controller 112 includes connections to the main generator 108 and the nonlinear current controller 111. The linear voltage controller 112 receives three-phase voltages from the main generator 108, denoted as Vabc_MGmeas, and performs calculations on the three-phase voltages to determine reference angles for the three-phase voltages. For example, the linear voltage controller 112 can apply Vabc_MGmeas to the phase-locked loop 114. The linear voltage controller 112 can measure instantaneous three-phase voltages in real-time or near real-time at a sampling rate of at least 2 kHz.

[0027] Phase-locked loop 114 can be initialized by zero-crossing phase-locked loop 142 of nonlinear current controller 111. Zero-crossing phase-locked loop 142 can be connected to permanent magnet generator (PMG) 102 to receive voltage signals.

[0028] Phase-locked loop 114 generates a reference angle for the three-phase voltage Vabc_MGmeas. Linear voltage controller 112 performs a Clark and Park transformation on the reference angle and the three-phase voltages, as shown in block 116, to transform the three-phase voltages and reference angles from the time domain to an orthogonal reference frame. This transformation generates two rotating coordinate system reference voltages, denoted as Vq_MGmeas and Vd_MGmeas, respectively.

[0029] The linear voltage controller 112 calculates the root mean square voltage based on two rotating coordinate system reference voltages, as shown in the following equation.

[0030] To compensate for errors during the operation of the linear voltage controller, the linear voltage controller 112 introduces an error setpoint output 120 to the root mean square voltage, denoted as VRMS1. The error setpoint output 120 represents an offset signal used to compensate for the error and is compared with the root mean square voltage calculated by the linear voltage controller 112. For example, Figure 1 The voltage of the error setpoint output 120 is listed as +115. The linear voltage controller 112 can also receive an additional RMS voltage calculated by the nonlinear current controller 111, denoted as slow VRMS_meas, as another offset signal. The linear voltage controller 112 can use this offset signal to identify and compensate for errors. The linear voltage controller 112 transmits the offset signal, including slow VRMS_meas, and Vabc_MGmeas from the error setpoint output 120, to the proportional-integral (PI) control module 122. The PI control module 122 uses the error setpoint output and the RMS voltage to correct the error between the error setpoint output 120 and the RMS voltage VRMS1, and converts the corrected RMS voltage into a signal IfSet1. The microcontroller provides this signal IfSet1 to the switching module 124 of the nonlinear current controller 111.

[0031] The nonlinear current controller includes various circuits, including a conversion circuit 126 for converting the three-phase voltage Vabc_MGmeas to a root-mean-square (RMS) and direct current (DC) output, an averaging circuit 128, a circuit 130 for identifying the high-phase RMS voltage, a comparator circuit 132, a PI control module 136, a switching module 124, a zero-crossing phase-locked loop 142, a nonlinear control module 138, and a pulse-width modulation amplifier (PWM) 140. The nonlinear current controller 111 may include connections to one or more drivers for a linear voltage controller 112, an exciter generator 106, a main generator 108, a permanent magnet generator (PMG) 102, and a power stage circuit 104.

[0032] The nonlinear current controller 111 receives three-phase voltage from the main generator 108, and the linear voltage controller also receives three-phase voltage from the main generator 108, denoted as Vabc_MGmeas. The nonlinear current controller 111 uses the three-phase voltage at the RMS-DC conversion circuit 126 to calculate the root-mean-square voltage of Vabc_MGmeas. The conversion circuit 126 provides its output to a circuit 130 for identifying the high-phase RMS voltage and an averaging circuit 128 for determining the average RMS voltage of the output of the conversion circuit 126. The outputs of the averaging circuit 128 and the circuit 130 for identifying the high-phase RMS voltage are compared at a comparator circuit 132, and the higher of the two outputs is provided to the PI control module 136 of the linear voltage controller 112 and the nonlinear current controller 111 as VRMS_meas, which includes an additional error setpoint output 134. The PI control module 136 of the nonlinear current controller uses the additional error setpoint output 134 and the root mean square voltage (represented as slowVRMS_meas) to correct the error between the additional error setpoint output 134 and the root mean square voltage, and converts the corrected root mean square voltage into a signal IfSet2. The PI control module 136 provides this signal IfSet2 to the switching module 124 of the nonlinear current controller 111. The hardware implementation loop of the nonlinear current controller 111 is used to determine the root mean square voltage and generate a true root mean square measurement. This measurement can be used to compensate the digital signal processing-based loop of the linear voltage controller 112 to improve accuracy in the presence of waveform distortion (e.g., distortion caused by a nonlinear load). The switching module 124 is configured to allow selection between the IfSet1 and IfSet2 signals according to the internal logic of the control system. For example, when the nonlinear control system 100 detects an error in the IfSet1 signal, the nonlinear control system 100 can set the switching module 124 to receive the IfSet2 signal. In some examples, the switch module 124 is set by default to receive IfSet1, and switches to receive IfSet2 when the nonlinear control system 100 detects an error.

[0033] The nonlinear control system provides the selected signal IfSet1 or IfSet2 to the nonlinear control module 138. The nonlinear control module 138 can be an arctangent (ATAN) nonlinear control module, which applies its output as a function of the current error magnitude according to the following formula: . PMG represents the available voltage of a permanent magnet generator.

[0034] The nonlinear current controller 111 may include a sliding mode control mechanism, which can be used as a function of the current error, as expressed by the following equation: Therefore, the control action can be represented by the following equation: The nonlinear current controller 111 provides control action via pulse width modulation amplifier (PWM) 140 to amplify the output and provide control action to bipolar power stage circuit 104 to directly control the magnitude of the excitation current of exciter generator 106, thereby controlling the output voltage of main generator 108. The output of exciter generator 106 is rectified by rotor rectifier stage circuit 107 and used to excite main generator 108, which supplies power to load 110.

[0035] Example of operation method for nonlinear control system Figure 2 It shows Figure 1 An example of the operation method of a nonlinear control system 100.

[0036] At block 202, method 200 may include receiving a three-phase voltage from a three-phase generator. This three-phase voltage may be received by a linear voltage controller, such as... Figure 1 As shown.

[0037] At block 204, method 200 may include determining a reference angle by applying a three-phase voltage to a phase-locked loop (PLL). The PLL may be part of a linear voltage controller or peripheral circuitry of the linear voltage controller. In other examples, the PLL is digitized as computer instructions executed by a processor of the linear voltage controller.

[0038] At block 206, method 200 may include a transformation of the reference angle and the three-phase voltage to determine a first rotating coordinate system reference voltage and a second rotating coordinate system reference voltage. For example, the transformation may be the Parker-Clark transformation.

[0039] At box 208, method 200 may include determining the root mean square voltage using first and second rotating coordinate system reference voltages, for example... Figure 1 The root mean square voltage (RMS) is VRMS1. This step can be performed at the linear voltage controller, either using circuitry for calculating the RMS voltage or as computer instructions executed on the processor of the linear voltage controller. The RMS voltage can be an instantaneous voltage or a near-instantaneous voltage. For example, the sampling rate of the linear voltage controller can be 2 kHz.

[0040] At block 210, method 200 may include converting the root mean square voltage into a first current signal, for example... Figure 1 IfSet1 in the code. For example, a control system may include... Figure 1The proportional-integral (PI) control module 122 shown is used to convert the root mean square voltage and any offset voltage or error setpoint output into a current signal. The control system can provide the first current signal to the nonlinear current controller 111 shown in Figure 1.

[0041] At box 212, method 200 may further include receiving a second current signal from an excitation generator, for example... Figure 1 IfFBK in the code. The nonlinear current controller 111 can receive this second current signal, for example... Figure 1 The further details are provided at the nonlinear control module 138.

[0042] At block 214, method 200 further includes determining a control action, wherein the control action is a function of the first current signal and the second current signal. For example, the function of the control action may be as follows: In some examples, the control action is approximated by superimposing a triangular carrier wave onto the excitation current setpoint. In some examples, the amplitude of the triangular carrier wave waveform does not exceed 1% of the maximum range of the excitation current of the excitation generator or main generator. The triangular carrier wave can be set to the maximum value of both the frequency and the current error. This is possible because of the transfer function... It is a minimum phase system.

[0043] Example of cascaded arrangement of linear voltage controller and nonlinear current controller Figure 3 This is a block diagram representation of the various parts of the nonlinear current controller 304 and the linear voltage controller 302 in the cascaded arrangement 300. Therefore, Figure 3 This shows that for a given IfSet1, the nonlinear controller is capable of... Figure 1 The PMG 102 permanent magnet generator provides seamless automatic duty cycle adjustment for voltage variations. For example... Figure 3 As shown, the cascaded arrangement 300 may include a signal IfSet1, a PI control module, an error setpoint output, and a nonlinear control module, all of which are in Figure 1 Further descriptions are provided in the text. The cascaded arrangement 300 uses IfSet1 as the setpoint for the nonlinear current controller.

[0044] The nonlinear current controller 302 utilizes available energy to make IfFBK = IfSet1. This provides the required current much faster than the linear voltage controller 304 can change the current. The linear voltage controller 304 can, according to... Figure 1The impedance characteristics of the excitation time constant of the main generator 108 are tuned, and this time constant may be greater than the excitation constant of the exciter 106. When the voltage of the permanent magnet generator (PMG) 102 changes, this change will adjust IfFBK to equal IfSet1, thereby also adjusting... Figure 1 The width of the pulse width modulation pulse of the medium pulse width modulator (PWM) 140. Adjusting IfFBK to change at a rate equal to IfSet1 can be an order of magnitude faster than the voltage loop.

[0045] Example of a control system that allows bipolar control without the need for excitation current sign reversal Figure 4 yes Figure 1 The block diagram of the nonlinear control module 138 has been rearranged to achieve bipolar control by adding a bipolar bridge 400, without requiring excitation current sign reversal. Existing high-side / low-side control (e.g., unipolar) is slower but has the advantage of not causing excitation current sign reversal. During control operation, sign reversal can generate two pairs of... and Air gap flux It may produce the same power at the reset output voltage, leading to oscillations and errors in control action. Figure 4 The rearrangement in the circuit allows for the application of bipolar control, which may reverse the excitation voltage but eliminates oscillations that could be caused by the reversal of the excitation current. A bipolar bridge can be implemented by executing computer instructions on the processor of the nonlinear current controller, or it can be an additional circuit and analog component of the nonlinear current controller.

[0046] Bipolar control allows the excitation current to vary between positive, negative, and zero states. To achieve these states, a full bipolar bridge is used. This bipolar bridge can be... Figure 1 This is part of the nonlinear current controller 111 or power stage circuit 104. The ability to use positive and negative excitation voltages enables more precise current control and faster convergence when the excitation current decreases.

[0047] The bipolar bridge 400 receives currents IfFBK and IfSet1,2. IfSet1,2 is appended to the triangular carrier signal shown in block 410, for example, set to a frequency of 20 kHz, and is 1% of the maximum range of the excitation current of the indicated exciter or main generator. The current signal of the triangular carrier signal is denoted by If,max. The bipolar bridge includes comparator circuits 402 and 404. At comparator circuit 404, the bipolar bridge compares the combination of IfSet1,2 and If,max with IfFBK and outputs the larger current signal input. The bipolar bridge 400 further compares IfFBK with a zero signal at comparator circuit 402 and outputs the larger current signal. The outputs of comparator circuits 402 and 404 are then combined at circuits 406 and 408 and provided to the driver of power stage circuit 412, for example... Figure 1 The power stage circuit 104.

[0048] An example of approximating motion control by applying a triangular wave signal. Figure 5A This is a block diagram representation of the implementation of applying and / or superimposing triangular waves on IfSet1,2. Figure 5B This represents the graphical result of applying and / or superimposing triangular waves on IfSet1,2 to approximate the arctangent (ATAN) nonlinear control module, for example... Figure 1 The nonlinear control module 138 in the middle.

[0049] For analog or digital hardware circuits, a triangular wave can be superimposed onto a surface such as... Figure 5A The excitation current setting shown is used to obtain an approximation of the ATAN function. For example, the amplitude of the triangular carrier waveform does not exceed... Figure 1 The maximum range of excitation current for the intermediate excitation generator or main generator is 1%.

[0050] For numerical errors within the amplitude range of the triangular wave, this control will provide small gain and linear action; however, for larger errors exceeding the triangular wave range, the control will provide large gain. This control method will also be based on... Figure 1 During implementation, the duty cycle of the permanent magnet generator (PMG) 102 is automatically adjusted according to voltage changes. The ultimate effect is to reach the target current faster or slower depending on the voltage of the permanent magnet generator (PMG) 102.

[0051] Figure 5B A graphical comparison of the ATAN function and the triangular carrier implementation is shown.

[0052] Example A series of exemplary embodiments, at least some of which are explicitly listed as "examples," are provided to provide additional description of various types of examples according to the concepts described herein. These examples are not intended to be mutually exclusive, exhaustive, or limiting; and the invention is not limited to these examples, but is covered by all possible modifications and variations within the scope of the claims and their equivalents.

[0053] Example 1: A system comprising: a linear voltage controller and a nonlinear current controller, wherein the linear voltage controller is implemented on a microcontroller to perform: determining a reference angle for an output voltage from a first generator using a phase-locked loop; converting the reference angle and the generator's output voltage from the time domain to an orthogonal reference system to generate two rotating coordinate system reference voltages; calculating the root mean square voltage of the two rotating coordinate system reference voltages and converting the root mean square voltage into an output current IfSet1; providing IfSet1 to the nonlinear current controller; and wherein the nonlinear current controller determines a control action based on the difference between IfSet1 and the output current IfFBK of the second generator.

[0054] Example 2: A system according to any one of the foregoing or subsequent examples or combinations thereof, wherein the linear voltage controller and the nonlinear current controller are cascaded.

[0055] Example 3: A system according to any one of the foregoing or subsequent examples or combinations thereof, wherein the control action is output to a bipolar bridge.

[0056] Example 4: A system according to any one of the foregoing or subsequent examples or combinations of examples, wherein the control action is a voltage VF defined by the following equation: VF = ATAN(IfSet1 - IfFBK).

[0057] Example 5: A system according to any one of the foregoing or subsequent examples or combinations thereof, wherein the phase-locked loop of the linear voltage controller is initialized by the zero-crossing phase-locked loop of the nonlinear current controller.

[0058] Example 6: A system according to any one of the foregoing or subsequent examples or combinations thereof, wherein the transformation is the Clark and Park transformation.

[0059] Example 7: A system according to any one of the foregoing or subsequent examples or combinations thereof, wherein the first generator is a three-phase generator and the second generator is an excitation generator.

[0060] Example 8: A system according to any one of the foregoing or subsequent examples or combinations thereof, wherein the nonlinear current controller approximates the control action by superimposing a triangular wave on IfSet1.

[0061] Example 9: A system according to any one of the foregoing or subsequent examples or combinations thereof, wherein the nonlinear current controller comprises: a root-mean-square (RMS) to DC converter for calculating a real-time root-mean-square (RMS) voltage based on the output voltage of the first generator; a first circuit for averaging the RMS voltage of the output voltage of the first generator and outputting the average RMS voltage to a second circuit, wherein the second circuit compares the average RMS voltage with the high-phase RMS voltage of the output voltage of the first generator and outputs the higher voltage therein; and a proportional-integral (PI) control module for converting the output of the second circuit into a current signal IfSet2.

[0062] Example 10: A system according to any one of the foregoing or subsequent examples or combinations thereof, wherein the amplitude of the triangular wave does not exceed 1% of IfFBK.

[0063] Example 11: A system according to any one of the foregoing or subsequent examples or combinations thereof, wherein the frequency of the triangular wave is at least 20 kHz, and the output frequency of the phase-locked loop is at least 2 kHz.

[0064] Example 12: A system according to any one of the foregoing or subsequent examples or combinations thereof, further comprising: a switching component configured to switch between outputs IfSet1 and IfSet2 to apply IfSet1 or IfSet2 to the control action.

[0065] Example 13: A system according to any one of the foregoing or subsequent examples or combinations thereof, wherein when an error is detected in the linear voltage controller, the switching component switches from IfSet1 to IfSet2.

[0066] Example 14: A method comprising: receiving a three-phase voltage Vabc_MGmeas from a three-phase generator via a linear voltage controller; determining a reference angle for Vabc_MGmeas by applying Vabc_MGmeas to a phase-locked loop of the linear voltage controller; performing a Parker-Clark transformation on the reference angle and Vabc_MGmeas to determine a first rotating coordinate system reference voltage Vq_MGmeas and a second rotating coordinate system reference voltage Vd_MGmeas; and using Vq_MGmeas and Vd_MGmeas to determine a root-mean-square voltage as follows: ; convert VRMSi into a first signal IfSet1; receive a second signal IfFBK from the exciter via a nonlinear current controller; and determine a control action using the nonlinear current controller, wherein the control action is a function of IfSet1 and IfFBK.

[0067] Example 15: The method according to any one of the foregoing or subsequent examples or combinations of examples, wherein the function is VFEG = ATAN(IfSet1-IfFBK).

[0068] Example 16: A method according to any one of the foregoing or subsequent examples or combinations thereof, wherein the phase-locked loop of the linear voltage controller is initialized using the zero-crossing phase-locked loop of the nonlinear current controller.

[0069] Example 17: The method according to any one of the foregoing or subsequent examples or combinations thereof, wherein the nonlinear current controller and the linear voltage controller are cascaded.

[0070] Example 18: According to the method of any of the foregoing or subsequent examples or combinations thereof, wherein determining the control action includes approximating the control action by superimposing a triangular wave on IfSet1.

[0071] Example 19: The method according to any of the foregoing or subsequent examples or combinations thereof, wherein the frequency of the triangular wave is at least 20 kHz, and the output frequency of the phase-locked loop is at least 2 kHz.

[0072] Example 20: A system comprising: a linear voltage controller and a nonlinear current controller, wherein the linear voltage controller is implemented on a microcontroller to perform: determining a reference angle for the output voltage of a first generator using a phase-locked loop; converting the reference angle and the generator output voltage from the time domain to an orthogonal reference system to generate two rotating coordinate system reference voltages; calculating the root mean square (RMS) voltages of the two rotating coordinate system reference voltages and converting the RMS voltages into an output current IfSet1; and providing IfSet1 to the nonlinear current controller; and wherein the nonlinear current controller includes: an RMS-DC converter for calculating a real-time RMS voltage based on the output voltage of the first generator; a first circuit. The system includes: a first circuit for averaging the root mean square voltage of the output voltage of the first generator and outputting the average root mean square voltage to a second circuit, wherein the second circuit compares the average root mean square voltage with the high-phase root mean square voltage of the output voltage of the first generator and outputs the higher voltage; a proportional-integral (PI) control module for converting the output of the second circuit into a current signal IfSet2; a switching component configured to select a signal from outputs IfSet1 and IfSet2 to determine a control action; and an arctangent nonlinear control component configured to determine the control action using the output current IfFBK of the second generator and the selected current IfSet1 or IfSet2.

[0073] The components shown in the figures or described above may have different arrangements, and components and steps not shown or described in the figures are also feasible. Similarly, certain features and sub-combinations are useful and can be used without referring to other features and sub-combinations. Embodiments of the invention have been described for illustrative and not restrictive purposes, and alternative embodiments will be readily apparent to the reader of this patent. Therefore, the invention is not limited to the embodiments described above or shown in the figures, and various embodiments and modifications can be made without departing from the scope of the following claims.

Claims

1. A system comprising: A linear voltage controller and a nonlinear current controller, wherein the linear voltage controller is implemented on a microcontroller to perform: A phase-locked loop is used to determine the reference angle of the output voltage from the first generator; The reference angle and the generator's output voltage are transformed from the time domain to an orthogonal reference system to generate two rotating coordinate system reference voltages; Calculate the root mean square voltage of the two rotating coordinate system reference voltages, and convert the root mean square voltage into an output current IfSet1; IfSet1 is provided to the nonlinear current controller; and The nonlinear current controller determines the control action based on the difference between IfSet1 and the output current IfFBK of the second generator.

2. The system according to claim 1, wherein, The linear voltage controller and the nonlinear current controller are arranged in a cascaded configuration.

3. The system according to claim 1, wherein, The control action is output to the bipolar bridge.

4. The system according to claim 1, wherein, The control action is defined by the voltage VF as follows: VF = ATAN(IfSet1 - IfFBK).

5. The system according to claim 1, wherein, The phase-locked loop of the linear voltage controller is initialized by the zero-crossing phase-locked loop of the nonlinear current controller.

6. The system according to claim 1, wherein, The transformation is the Clark and Park transformation.

7. The system according to claim 2, wherein, The first generator is a three-phase generator, and the second generator is an excitation generator.

8. The system according to claim 7, wherein, The nonlinear current controller approximates the control action by superimposing a triangular wave on IfSet1.

9. The system according to claim 7, wherein, The nonlinear current controller includes: A root-mean-square (RMS) to DC converter for calculating the real-time root-mean-square voltage based on the output voltage of the first generator; A first circuit is configured to average the root mean square (RMS) voltage of the output voltage of the first generator and output the average RMS voltage to a second circuit, wherein the second circuit compares the average RMS voltage with the higher-phase RMS voltage of the output voltage of the first generator and outputs the higher voltage; and A proportional-integral (PI) control module is used to convert the output of the second circuit into a current signal IfSet2.

10. The system according to claim 8, wherein, The amplitude of the triangular wave does not exceed 1% of IfFBK.

11. The system according to claim 8, wherein, The frequency of the triangular wave is at least 20 kHz, and the output frequency of the phase-locked loop is at least 2 kHz.

12. The system according to claim 9, further comprising: A switching component is configured to switch between outputs IfSet1 and IfSet2 to apply either IfSet1 or IfSet2 to the control action.

13. The system according to claim 12, wherein, When an error is detected in the linear voltage controller, the switching component switches from IfSet1 to IfSet2.

14. A method comprising: The three-phase voltage Vabc_MGmeas is received from the three-phase generator by a linear voltage controller; The reference angle of Vabc_MGmeas is determined by applying Vabc_MGmeas to the phase-locked loop of the linear voltage controller; Perform Parker and Clarke transformations on the reference angle and Vabc_MGmeas to determine the first rotating coordinate system reference voltage Vq_MGmeas and the second rotating coordinate system reference voltage Vd_MGmeas; Use Vq_MGmeas and Vd_MGmeas to determine the root mean square voltage as follows: ； Convert VRMSi to the first signal IfSet1; The second signal IfFBK is received from the exciter generator by the nonlinear current controller; as well as The control action is determined using the nonlinear current controller, wherein the control action is a function of IfSet1 and IfFBK.

15. The method of claim 14, wherein, The function is VFEG = ATAN(IfSet1-IfFBK).

16. The method of claim 14, wherein, The phase-locked loop of the linear voltage controller is initialized using the zero-crossing phase-locked loop of the nonlinear current controller.

17. The method of claim 14, wherein, The nonlinear current controller and the linear voltage controller are arranged in a cascaded configuration.

18. The method according to claim 14, wherein, Determining the control action includes approximating the control action by superimposing a triangular wave on IfSet1.

19. The method of claim 18, wherein, The frequency of the triangular wave is at least 20 kHz, and the output frequency of the phase-locked loop is at least 2 kHz.

20. A system comprising: A linear voltage controller and a nonlinear current controller, wherein the linear voltage controller is implemented on a microcontroller to perform: A phase-locked loop is used to determine the reference angle of the output voltage from the first generator; The reference angle and the generator's output voltage are transformed from the time domain to an orthogonal reference system to generate two rotating coordinate system reference voltages; Calculate the root mean square (RMS) voltages of the two rotating coordinate system reference voltages, and convert the RMS voltages into an output current IfSet1; and IfSet1 is provided to the nonlinear current controller. The nonlinear current controller includes: A root-mean-square (RMS) to DC converter for calculating the real-time root-mean-square voltage based on the output voltage of the first generator; The first circuit is used to calculate the average root mean square voltage of the output voltage of the first generator and output the average root mean square voltage to the second circuit, wherein the second circuit compares the average root mean square voltage with the high phase root mean square voltage of the output voltage of the first generator and outputs the higher voltage. A proportional-integral (PI) control module is used to convert the output of the second circuit into a current signal IfSet2; A switching component is configured to select a signal from outputs IfSet1 and IfSet2 to determine a control action; and An arctangent nonlinear control component is configured to determine the control action using the output current IfFBK of the second generator and a selected current IfSet1 or IfSet2.

Images