Non-linear control through an exciter stage of a three-stage synchronous generator

Abstract

Systems and method for providing non-linear control of a generator including: a linear voltage controller and a non-linear current controller, wherein the linear voltage controller is executed on a microcontroller to perform: determining a reference angle of an output voltage from a first generator using a phase lock loop; converting the reference angle and the generator output voltage from a time domain to an orthogonal reference frame to produce two rotating frame reference voltages; calculating a root mean square voltage of the two rotating frame reference voltages and converting the root mean square voltage to an output current IfSet1; providing IfSet1 to the non-linear current controller; and wherein the non-linear current controller determines a control action based on a difference of IfSet1 and an output current of a second generator IfFBK.

Description

NON-LINEAR CONTROL THROUGH AN EXCITER STAGE OF A THREE-STAGE SYNCHRONOUS GENERATORFIELD OF THE INVENTION

[0001] The field of the invention relates to a control system for controlling the alternating current (AC) output of a three-stage synchronous generator, in particular a three- stage synchronous generator integrated into a vehicle such as an aircraft.BACKGROUND

[0002] Controllers and control systems are designed to tailor to a system’s expected use. Depending on the control system’s expected use, designers may favor control systems with greater precision over control systems with greater gains (speed). For example, control systems using linear and proportional control by design allocate a proportional control action at a given gain (speed). When the objective of the controller is to drive a field current of a generator to a particular level faster, a linear and proportional controller would not be a faster way to achieve this goal. For generators that are used to power or assist in control of aircraft, faster controllers are desired.SUMMARY

[0003] The terms “invention,” “the invention,” “this invention” and “the present invention” used in this patent are intended to refer broadly to all of the subject matter of this patent and the patent claims below. Statements containing these terms should be understood not to limit the subject matter described herein or to limit the meaning or scope of the patent claims below. Embodiments of the invention covered by this patent are defined by the claims below, not this summary. This summary is a high-level overview of various aspects of the invention and introduces some of the concepts that are further described in the Detailed Description section below. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used in isolation to determine the scopeof the claimed subject matter. The subject matter should be understood by reference to appropriate portions of the entire specification of this patent, any or all drawings and each claim.

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

[0005] Some embodiments of the present technology for the control system includes: a linear voltage controller and a non-linear current controller, wherein the linear voltage controller is executed on a microcontroller to perform: determining a reference angle of an output voltage from a first generator using a phase lock loop; converting the reference angle and the generator output voltage from a time domain to an orthogonal reference frame to produce two rotating frame reference voltages; calculating a root mean square voltage of the two rotating frame reference voltages and converting the root mean square voltage to an output current IfSetl; and providing IfSetl to the non-linear current controller; wherein the non-linear current controller comprises: a root mean square to direct current converter to compute a real time root mean square voltage from the output voltage of the first generator; a first circuit to average the root mean square voltage of the output voltage of the first generator and output an average root mean square voltage to a second circuit, wherein the second circuit compares the average root mean square voltage to a hi phase root mean square voltage of the output voltage of the first generator, and outputs the higher of the voltages; a proportional and integral (PI) control module to convert the output of the second circuit to a current signal IfSet2; a switching component configured to select a signal from outputs IfSetl and IfSet2, to use in determining a control action; and an inverse tangent non-linear controlcomponent configured to the control action using an output current IfFBK of a second generator, and the selected current of either IfSetl or IfSet2.

[0006] Some embodiments of the present technology relate to a method of operation of the control system, the method including: receiving, by a linear voltage controller, a three- phase voltage Vabc MGmeas from a three-phase generator; determining a reference angle of Vabc MGmeas by applying Vabc MGmeas to a phase lock loop of the linear voltage controller; performing a Park and Clarke transformation on the reference angle and Vabc MGmeas to determine a first rotating frame reference voltage Vq MGmeas and a second rotating frame reference voltage Vd MGmeas; determining a root mean square voltage using Vq MGmeas and Vd MGmeas as follows: VRMSi = , converting VRMSi to a first signal IfSetl; receiving, by anon-linear current controller, a second signal IfFBK from an exciter generator; and determining, using the non-linear current controller, a control action, wherein the control action is a function of IfSetl and IfFBK.BRIEF DESCRIPTION OF THE DRAWINGS

[0007] FIG. 1 is a block diagram representation of a non-linear control system, according to various embodiments.

[0008] FIG. 2 is a flow chart of a method of operating a non-linear control system.

[0009] FIG. 3 is a block diagram representation of a cascaded linear voltage controller and non-linear current controller.

[0010] FIG. 4 is a block diagram representation of the non-linear control system connected to a bipolar bridge in the power stage circuit of a generator regulator. The output of the power stage drives the field current of the exciter generator.

[0011] FIG. 5A and FIG. 5B are block diagrams representing approximating a control action by applying and / or superimposing a triangle signal.DETAILED DESCRIPTION

[0012] The subject matter of embodiments of the present invention is described here with specificity to meet statutory requirements, but this description is not necessarily intended to limit the scope of the claims. The claimed subject matter may be embodied in other ways, may include different elements or steps, and may be used in conjunction with other existing or future technologies. This description should not be interpreted as implying any particular order or arrangement among or between various steps or elements except when the order of individual steps or arrangement of elements is explicitly described.

[0013] Embodiments herein may provide for a non-linear control system for controlling a three-phase generator. While the non-linear control system is discussed for use in relation to controlling a three-phase generator of an aircraft, they are by no means so limited. Rather, embodiments of the non-linear control system may be used in other vehicles or structures of any type or otherwise as desired. For example, embodiments may be used in trains, buses, personal vehicles, commercial or residential buildings, or any other instance when a non-linear control system may be useful.

[0014] In various embodiments, the non-linear control system includes a linear voltage controller and non-linear current controller. The non-linear control system provides non-linear control for the regulation of 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 to a non-linear current loop that controls a field current of an exciter generator stage as to control the output voltage of a main generator. Either controllers of the non-linear control system may be implemented in analogue hardware or in software digitally executed on a microcontroller. The utilization of this control system is suitable for dynamicloads of non-linear nature, in particular for situations requiring fast and accurate control. Further, the non-linear current controller provides a fail-safe to control of the generators by being configured to operate concurrently with the linear voltage controller and able to provide non-linear control in the absence of the linear voltage controller.

[0015] For purposes of this example, the linear voltage controller is implemented digitally as computer instructions executed on a microcontroller, and the non-linear current controller is implemented in analogue hardware with various circuits.

[0016] The linear voltage controller may include a microcontroller for executing computer instructions. The microcontroller may include connections to a main generator, the non-linear current controller. The microcontroller receives a three-phase voltage from the main generator, represented by Vabc MGmeas, and performs operations on the three-phase voltage to identify the reference angle of the three-phase voltage, such as by applying a phase lock loop to the three-phase voltage. The microcontroller may take measurements of the three-phase voltage in real time or near real time, with a sampling rate of at least 2 kHz.

[0017] The microcontroller may perform Clarke and Park transformations on the three-phase voltage and the reference angle to convert the three-phase voltage and the reference from a time domain to an orthogonal reference frame, which produces two rotating frame reference voltages, Vq MGmeas and Vd MGmeas. The microcontroller calculates the root mean square voltage from the two rotating frame reference voltages.

[0018] The microcontroller adds an error setpoint output voltage to the root mean square voltage, where the error setpoint output represents an offset signal to compensate for error and compares the root mean square voltage calculated by the microcontroller to a rootmean square voltage of the three-phase voltage Vabc MGmeas calculated by the non-linear current controller, represented as VRMS meas. In some examples, the microcontroller may use VRMS meas as another error setpoint output to identify and compensate for errors in the root mean square voltage calculated by the microcontroller. When the microcontroller identifies that the microcontroller calculated root mean square voltage is not including errors, such as distortions or other errors, the root mean square voltage calculated by the microcontroller with the error setpoint output is provided to a proportional and integral control (PI) module, which may be implemented in the microcontroller as computer instructions, or may be a peripheral or separate hardware controller. The PI control module uses the error setpoint output and root mean square voltage to correct for errors between the error setpoint output and the root mean square voltage, and converts the corrected root mean square voltage to a signal IfSetl, which the microcontroller provides to a switching module of the non-linear current controller.

[0019] The non-linear current controller includes various circuits including a converting circuit for converting a three-phase voltage into a root mean square and direct current (DC) output, an averaging circuit, a circuit for identifying a hi phase root mean square voltage, a comparator circuit, a PI control module, a switching module, a zero cross phase lock loop, a non-linear control module, and a pulse width modulation amplifier. The nonlinear current controller may include connections to the linear voltage controller, an exciter generator, a main generator, a permanent magnet generator (PMG), and one or more drivers of a power stage circuit.

[0020] The non-linear current controller may receive the three-phase voltage also received by the linear voltage controller from the main generator, represented byVabc MGmeas. The non-linear current controller receives the three-phase voltage at the root mean square to direct current (DC) converting circuit, which calculates the root mean squarevoltage of Vabc MGmeas. The converting circuit provides its output to a circuit for identifying a hi phase root mean square voltage and an averaging circuit for determining the average root mean square voltage of the converting circuit output. The outputs of the averaging circuit and the circuit for identifying the hi phase root mean square voltage are compared at the comparator circuit, and the higher of the two outputs is provided to the linear voltage controller and a PI module of the non-linear current controller as VRMS meas with an added error setpoint output. The PI module of the non-linear current controller uses the error setpoint output and root mean square voltage to correct for errors between the error setpoint output and the root mean square voltage, and converts the corrected root mean square voltage to a signal IfSet2, which the PI module provides to the switching module of the non-linear current controller. The switching module is configured to allow selection between IfSetl and IfSet2 signals. The selection may be based on internal logic of the control system. For example, when the control system detects an error in the IfSetl signal, the control system may set the switching module to receive the IfSet2 signal. In some examples, the switching module is by default set to receive IfSetl and may switch when the control system detects an error. In other examples, IfSet2 may be the default.

[0021] The control system provides the selected signal, IfSetl or IfSet2 to a nonlinear control module. The non-linear control module may be an inverse tangent (ATAN) non-linear control module which may apply its output as a function of a current error magnitude as represented by the following equation:VfEG= PMG * ATAN ( IfSetl, 2 - IfFBKf

[0022] PMG represents available voltage of the permanent magnetic generator.

[0023] The non-linear current controller may include a sliding control mechanism which may be a function of current error as represented by the following equations:e / / FG= / fSetl,2 - / fFBK

[0024] Thus, control actions may be represented by the following equation:FFEC= AT AN ( / fSetl,2 - I fFBK)

[0025] The non-linear current controller may provide the control action a pulse width modulation amplifier to amplify the output and provide the control action to drivers of a power stage circuit to control power output of the drivers.

[0026] The non-linear current controller may also receive a voltage from the permanent magnet generator (PMG), apply the voltage to a zero cross phase lock loop circuit, and provide the output of the zero cross phase lock loop to initialize a phase lock loop of the linear voltage controller.Example Non-linear Control System

[0027] Referring now to the figures, an example non-linear control system 100, according to certain embodiments, is shown in FIG. 1.

[0028] The non-linear control system 100 includes a linear voltage controller 112 and non-linear current controller 111. The linear voltage controller 112 and non-linear current controller 111 may be connected in a cascade arrangement. The non-linear control system 100 is connected to an arrangement of generators and other circuits with connections to a permanent magnet generator (PMG) 102, a power stage circuit 104, an exciter generator 106, and a main generator 108. Any of the listed generators 102 106 and 108 may be three-phase generators, as depicted in FIG. 1. Various other circuits included in FIG. 1 are a rotor rectifying stage circuit 107 and a load 110. The non-linear control system 100 uses voltages from the permanent magnet generator (PMG) 102, exciter generator 106, and main generator108, to control the main generator 108 output voltage through the bipolar non-linear control of the exciter generator 106 field current.

[0029] The linear voltage controller 112 may be or include a microcontroller for executing computer instructions, as depicted in FIG. 1. The linear voltage controller 112 includes connections to the main generator 108 and non-linear current controller 111. The linear voltage controller 112 receives a three-phase voltage from the main generator 108, represented by Vabc MGmeas and performs operations on the three-phase voltage to identify the reference angle of the three-phase voltage. For example, the linear voltage controller 112 may apply Vabc MGmeas to a phase lock loop 114. The linear voltage controller 112 may take measurements of instantaneous three-phase voltage in real time or near real time, with a sampling rate of at least 2 kHz.

[0030] The phase lock loop 114 may be initialized by a zero cross phase lock loop 142 of the non-linear current controller 111. The zero cross phase lock loop 142 may be connected to the permanent magnet generator (PMG) 102 to receive voltage signals.

[0031] The phase lock loop 114 produces a reference angle of the three-phase voltage Vabc MGmeas. The linear voltage controller 112 performs Clarke and Park transformations, represented by box 116, on the reference angle and the three-phase voltage to convert the three-phase voltage and the reference angle from a time domain to an orthogonal reference frame. The transformation produces two rotating frame reference voltages, represented by Vq MGmeas and Vd MGmeas.

[0032] The linear voltage controller 112 calculates the root mean square voltage from the two rotating frame reference voltages as shown in the equation below.

[0033] To compensate for errors during operation of the linear voltage controller, the linear voltage controller 112 introduces an error setpoint output 120 to the root mean square voltage, the root mean square voltage represented by VRMS1. The error setpoint output 120 represents an offset signal to compensate for error and compares the root mean square voltage calculated by the linear voltage controller 112. By way of example, FIG. 1 lists the error setpoint output 120 voltage to +115. The linear voltage controller 112 may also receive an additional root mean square voltage calculated by the non-linear current controller 111, represented by slow VRMS meas, as another offset signal which the linear voltage controller 112 may use to identify and compensate for errors. The linear voltage controller 112 transmits Vabc MGmeas including the offset signals from slow VRMS meas and the error setpoint output 120 to a proportional and integral (PI) control module 122. The proportional and integral (PI) control module 122 uses the error setpoint output and root mean square voltage to correct for errors between the error setpoint output 120 and the root mean square voltage VRMS1, and converts the corrected root mean square voltage to a signal IfSetl, which the microcontroller provides to a switching module 124 of the non-linear current controller 111.

[0034] The non-linear current controller includes various circuits including a converting circuit 126 for converting the three-phase voltage Vabc MGmeas into a root mean square and direct current (DC) output, an averaging circuit 128, a circuit for identifying a hi phase root mean square voltage 130, a comparator circuit 132, a PI control module 136, a switching module 124, a zero cross phase lock loop 142, a non-linear control module 138, and a pulse width modulation amplifier (PWM) 140. The non-linear current controller 111 may include connections to the linear voltage controller 112, the exciter generator 106, the main generator 108, a permanent magnet generator (PMG) 102, and one or more drivers of a power stage circuit 104.

[0035] The non-linear current controller 111 may receive the three-phase voltage also received by the linear voltage controller from the main generator, represented by Vabc MGmeas. The non-linear current controller 111 uses the three-phase voltage at the root mean square to direct current (DC) converting circuit 126 to calculate the root mean square voltage of Vabc MGmeas. The converting circuit 126 provides its output to a circuit for identifying a hi phase root mean square voltage 130 and an averaging circuit 128 for determining the average root mean square voltage of the converting circuit 126 output. The outputs of the averaging circuit 128 and the circuit for identifying the hi phase root mean square voltage 130 are compared at the comparator circuit 132, and the higher of the two outputs is provided to the linear voltage controller 112 and a PI control module 136 of the non-linear current controller 111 as VRMS meas with an additional error setpoint output 134. The PI control module 136 of the non-linear current controller uses the additional error setpoint output 134 and root mean square voltage, represented by slow VRMS meas, to correct for errors between the additional error setpoint output 134 and the root mean square voltage, and converts the corrected root mean square voltage to a signal IfSet2, which the PI control module 136 provides to the switching module 124 of the non-linear current controller 111. The hardware-implemented loop of the non-linear current controller for determining the root mean square generates a true root mean square measurement. This measurement may be used to offset a digital signal processing-based loop of linear voltage controller 112 to improve accuracy where there is waveform distortion, such as distortions due to non-linear loads. The switching module 124 is configured to allow selection between IfSetl and IfSet2 signals based on internal logic of the control system. For example, when the non-linear control system 100 detects an error in the IfSetl signal, the non-linear control system 100 may set the switching module 124 to receive the IfSet2 signal. In some examples, theswitching module 124 set to receive IfSetl by default and may switch to receive IfSet2 when the non-linear control system 100 detects an error.

[0036] The non-linear control system 100 provides the selected signal, IfSetl or IfSet2 to a non-linear control module 138. The non-linear control module 138 may be an inverse tangent (ATAN) non-linear control module which applies its output as a function of a current error magnitude as represented by the following equation:VfEG= PMG * ATAN ( IfSetl, 2 - IfFBKf

[0037] PMG represents available voltage of the permanent magnetic generator.

[0038] The non-linear current controller 111 may include a sliding control mechanism which may be a function of current error as represented by the following equations:e / / FG= IfSetl, 2 - / fFBK

[0039] Thus, control actions may be represented by the following equation:(IfSetl, 2 - I fFBK)

[0040] The non-linear current controller 111 may provide the control action through a pulse width modulation amplifier (PWM) 140 to amplify the output and provide control action to the bipolar power stage circuit 104 to directly control the exciter generator 106 field current magnitude and consequently the main generator 108 output voltage. The exciter generator 106 output is rectified at the rotor rectifier stage circuit 107 and is used to excite the main generator 108, which provides power to the load 110.Example Method of Operating a Non-Linear Control System

[0041] An example of a method for operating the non-linear control system 100 ofFIG. 1 is depicted in FIG. 2.

[0042] The method 200 at block 202 may include receiving a three-phase voltage from a three-phase generator. This three-phase voltage may be received by the linear voltage controller described in FIG. 1.

[0043] The method 200 at block 204 may include determining a reference angle by applying the three-phase voltage to a phase lock loop. The phase lock loop may be a circuit that is part of the linear voltage controller or may be a peripheral of the linear voltage controller. In other examples, the phase lock loop is performed digitally, as computer instructions executed by a processor of the linear voltage controller.

[0044] The method 200 at block 206 may include a transformation on the reference angle and the three-phase voltage to determine a first rotating frame reference voltage and a second rotating frame reference voltage. For example, the transformation may be a Park and Clarke transformation.

[0045] The method 200 at block 208 may include determining a root mean square voltage using the first and second rotating frame reference voltage, such as the root mean square voltage VRMS1 of FIG. 1. This step may occur at the linear voltage controller using either a circuit for calculating root mean square voltage or as computer instructions executed on a processor of the linear voltage controller. The root mean square voltage may be an instantaneous voltage, or near instantaneous voltage. For example, the linear voltage controller may have a sampling rate of 2 kHz.

[0046] The method 200 at block 210 may include converting the root mean square voltage to a first current signal, such as IfSetl of FIG. 1. For example, the control system may include a proportional and integral (PI) control module 122 as shown in FIG. 1, to convert the root mean square voltage, in addition to any offset voltages or error setpoint outputs, to a current signal. The control system may provide the first current signal to the non-linear current controller 111, as shown in FIG. 1.

[0047] The method 200 at block 212 may further include receiving a second current signal from an exciter generator, such as IfFBK of FIG. 1. The second current signal is received by the non-linear current controller 111, such as at the non-linear control module 138, further described in FIG. 1.

[0048] The method 200 at block 214 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:VFEG= AT AN ( / fSetl,2 - IfFBK)

[0049] In some examples, the control action is approximated by superimposing a carrier triangular wave to a field current set point. In some examples, the carrier triangular waveform with an amplitude of up to 1% of the field current maximum range of the exciter generator or main generator. The carrier triangular wave may set the frequency and theVs EG maximum value of the current error. This may be possible because the transfer function — — If EG is a minimum phase system.Example Cascaded Arrangement of a Linear Voltage Controller and a Non-Linear Current Controller

[0050] FIG. 3 is a block diagram representation of portions of the non-linear current controller 304 and portions of the linear voltage controller 302 in a cascaded arrangement 300. Thus, FIG 3 shows that for a given IfSetl, the non-linear controller provides seamless automatic duty cycle adjustment to changes in the permanent magnet generator (PMG) 102 voltages of FIG. 1. As shown in FIG. 3, the cascaded arrangement 300 may include signal IfSetl, a PI control module, an error setpoint output, and a non-linear control module, all further described in FIG. 1. The cascaded arrangement 300 uses IfSetl as a set point of the non-linear current controller.

[0051] The non-linear current controller 302 uses available energy to make IfFBK=IfSetl. This provides the demanded current faster than the speed of what the linear voltage controller 304 can change. The linear voltage controller 304 may be tuned to the impedance of the main generator 108 field time constant of FIG. 1, which may be larger than the exciter generator 106 field constant. When there is variation of the permanent magnet generator (PMG) 102 voltage this variation would adjust the speed of adjusting IfFBK to equal IfSetl, and therefore also adjusts the width of pulse width magnitude pulses of the pulse width modulation amplifier (PWM) 140 from FIG. 1. The change in speed in adjusting IfFBK to equal IfSetl may be an order of magnitude faster than the voltage loop.Example Control System Allowing Bipolar Control without Field Current Sign Reversal

[0052] FIG. 4 is a block diagram showing a rearrangement of the non-linear control module 138 from FIG. 1 to allow bipolar control without field current sign reversal by adding a bipolar bridge 400. Existing high side / low side control (e.g., unipolar) control is slow but have the benefit of not having the possibility of field current sign reversal. A sign reversal during a control action could produce two pairs ( fEG> and (—IfEG’ - An airgap flux [webers] may produce the same power on reset output voltage and cause oscillation and errors in the control action. The rearrangement in FIG. 4 allows for the application of bipolar control with the possibility of reverse the field voltage but removes potential oscillations that could be caused by field current reversals. The bipolar bridge may be performed by executing computer instructions on a processor of the non-linear current controller or may be additional circuits and analogue components of the non-linear current controller.

[0053] Bipolar control allows the field current to range positively, negatively and in a zero state. To achieve these states, a full bipolar bridge is included. The bipolar bridge may be part of the non-linear current controller 111 or the power stage circuit 104 from FIG. 1.Having the ability to use positive and negative field voltages allows for more precise control of the current and faster convergences when the field current is decreased.

[0054] The bipolar bridge 400 receives currents IfFDBK and IfSetl,2. IfSetl,2 is added to a triangular wave carrier signal shown at block 410, and by way of example is set at 20 kHz frequency and is 1% of the field current maximum range of the exciter generator or main generator represented. The current signal of the triangular wave carrier signal is represented by If, max. The bipolar bridge includes comparator circuits 402 and 404. The bipolar bridge compares the combined IfSetl,2 and If, max to IfFDBK at comparator circuit 404 and outputs the greater of the current signal inputs. The bipolar bridge 400 further compares IfFDBK to a zero signal at comparator circuit 402, and outputs the greater of the current signals. The outputs of the comparator circuits 402 and 404 are then combined at circuits 406 and 408 and provided to drivers of the power stage circuit 412, such as the power stage circuit 104 of FIG. 1.An Example of Approximating a Control Action by Applying a Triangle Signal.

[0055] FIG. 5A is a block diagram representing the implementation of applying and / or superimposing a triangular wave on IfSetl,2 and FIG. 5B represents graphical results of applying and / or superimposing a triangular wave on IfSetl,2 to approximate an inverse tangent (AT AN) non-linear control module, such as the non-linear control module 138 of FIG. 1.

[0056] For an analog or digital hardware circuit, an approximation of the ATAN function may be obtained by superimposing a triangular wave to the field current set point as shown in FIG. 5 A. By way of example, the carrier triangular waveform includes an amplitude of up to 1% of the field current maximum range of the exciter generator or main generator from FIG. 1.

[0057] For errors of a magnitude within the amplitude of the triangular wave, the control will provide a small gain and act linearly but for larger errors outside of the triangular wave the control will provide a large gain. This control method will also automatically adjust duty cycle for variations in permanent magnet generator (PMG) 102 voltage from when implemented in FIG. 1. The net effect is achieving the target current faster or slower depending on permanent magnet generator (PMG) 102 voltage.

[0058] Figure 5B shows a graphical comparison of the ATAN function and the triangular carrier implementation.Examples

[0059] A collection of exemplary embodiments, including at least some explicitly enumerated as “Examples” providing additional description of a variety of example types in accordance with the concepts described herein are provided below. These examples are not meant to be mutually exclusive, exhaustive, or restrictive; and the invention is not limited to these examples but rather encompasses all possible modifications and variations within the scope of the issued claims and their equivalents.

[0060] Examples 1 : A system comprising: a linear voltage controller and a non-linear current controller, wherein the linear voltage controller is executed on a microcontroller to perform: determining a reference angle of an output voltage from a first generator using a phase lock loop; converting the reference angle and the generator output voltage from a time domain to an orthogonal reference frame to produce two rotating frame reference voltages; calculating a root mean square voltage of the two rotating frame reference voltages and converting the root mean square voltage to an output current IfSetl; providing IfSetl to the non-linear current controller; and wherein the non-linear current controller determines a control action based on a difference of IfSetl and an output current of a second generatorIfFBK.

[0061] Example 2: The system of any of the preceding or subsequent examples or combination of examples, wherein the linear voltage controller and the non-linear current controller are in a cascaded arrangement.

[0062] Example 3: The system of any of the preceding or subsequent examples or combination of examples, wherein the control action is output to a bipolar bridge.

[0063] Example 4: The system of any of the preceding or subsequent examples or combination of examples, wherein the control action is a voltage VF defined by the following equation: VF = ,4T.4 l(IfSetl-IfFBK).

[0064] Example 5: The system of any of the preceding or subsequent examples or combination of examples, wherein the phase lock loop of the linear voltage controller is initialized by a zero-crossing phase lock loop of the non-linear current controller.

[0065] Example 6: The system of any of the preceding or subsequent examples or combination of examples, wherein the conversion is a Clarke and Park transform.

[0066] Example 7: The system of any of the preceding or subsequent examples or combination of examples, wherein the first generator is a three-phase generator, and the second generator is an exciter generator.

[0067] Example 8: The system of any of the preceding or subsequent examples or combination of examples, wherein the non-linear current controller approximates the control action by superimposing a triangular wave on IfSetl .

[0068] Example 9: The system of any of the preceding or subsequent examples or combination of examples, wherein the non-linear current controller comprises: a root mean square to direct current converter to compute a real time root mean square voltage from the output voltage of the first generator; a first circuit to average the root mean square voltage of the output voltage of the first generator and output an average root mean square voltage to asecond circuit, wherein the second circuit compares the average root mean square voltage to a hi phase root mean square voltage of the output voltage of the first generator, and outputs the higher of the voltages; and a proportional and integral (PI) control module to convert the output of the second circuit to a current signal IfSet2.

[0069] Example 10: The system of any of the preceding or subsequent examples or combination of examples, wherein the triangular wave has an amplitude of up to 1% of IfFBK.

[0070] Example 11 : The system of any of the preceding or subsequent examples or combination of examples, wherein the triangular wave has a frequency of at least 20 kHz and the phase lock loop outputs at a frequency of at least 2 kHz.

[0071] Example 12: The system of any of the preceding or subsequent examples or combination of examples, further comprising: a switching component configured to switch between outputs IfSetl and IfSet2 to apply to IfSetl or IfSet2 to the control action.

[0072] Example 13: The system of any of the preceding or subsequent examples or combination of examples, wherein the switching component switches from IfSetl to IfSet2 when an error is detected with the linear voltage controller.

[0073] Example 14: A method comprising: receiving, by a linear voltage controller, a three-phase voltage Vabc MGmeas from a three-phase generator; determining a reference angle of Vabc MGmeas by applying Vabc MGmeas to a phase lock loop of the linear voltage controller; performing a Park and Clarke transformation on the reference angle and Vabc MGmeas to determine a first rotating frame reference voltage Vq MGmeas and a second rotating frame reference voltage Vd MGmeas; determining a root mean square voltage using Vq MGmeas and Vd MGmeas as follows: VRMSi = , converting VRMSi to a first signal IfSetl; receiving, by anon-linear current controller, a second signal IfFBK from an exciter generator; and determining, using the non-linear current controller, a control action, wherein the control action is a function of IfSetl and IfFBK.

[0074] Example 15: The method of any of the preceding or subsequent examples or combination of examples, wherein the function is VFEG= AT AN (IfSetl-IfFBK).

[0075] Example 16: The method of any of the preceding or subsequent examples or combination of examples, wherein the phase lock loop of the linear voltage controller is initialized using a zero cross phase lock loop of the non-linear current controller.

[0076] Example 17: The method of any of the preceding or subsequent examples or combination of examples, wherein the non-linear current controller and the linear voltage controller are in a cascaded arrangement.

[0077] Example 18: The method of any of the preceding or subsequent examples or combination of examples, wherein determining the control action includes approximating the control action by superimposing a triangular wave on IfSetl.

[0078] Example 19: The method of any of the preceding or subsequent examples or combination of examples, wherein the triangular wave has a frequency of at least 20 kHz and the phase lock loop outputs at a frequency of at least 2 kHz.

[0079] Example 20: A system comprising: a linear voltage controller and a non-linear current controller, wherein the linear voltage controller is executed on a microcontroller to perform: determining a reference angle of an output voltage from a first generator using a phase lock loop; converting the reference angle and the generator output voltage from a time domain to an orthogonal reference frame to produce two rotating frame reference voltages; calculating a root mean square voltage of the two rotating frame reference voltages and converting the root mean square voltage to an output current IfSetl; and providing IfSetl to the non-linear current controller; and wherein the non-linear current controller comprises: aroot mean square to direct current converter to compute a real time root mean square voltage from the output voltage of the first generator; a first circuit to average the root mean square voltage of the output voltage of the first generator and output an average root mean square voltage to a second circuit, wherein the second circuit compares the average root mean square voltage to a hi phase root mean square voltage of the output voltage of the first generator, and outputs the higher of the voltages; a proportional and integral (PI) control module to convert the output of the second circuit to a current signal IfSet2; a switching component configured to select a signal from outputs IfSetl and IfSet2, to use in determining a control action; and an inverse tangent non-linear control component configured to the control action using an output current IfFBK of a second generator, and the selected current of either IfSetl or IfSet2.

[0080] Different arrangements of the components depicted in the drawings or described above, as well as components and steps not shown or described are possible. Similarly, some features and sub-combinations are useful and may be employed without reference to other features and sub-combinations. Embodiments of the invention have been described for illustrative and not restrictive purposes, and alternative embodiments will become apparent to readers of this patent. Accordingly, the present invention is not limited to the embodiments described above or depicted in the drawings, and various embodiments and modifications may be made without departing from the scope of the claims below.

Claims

CLAIMSWhat is claimed is:

1. A system comprising: a linear voltage controller and a non-linear current controller, wherein the linear voltage controller is executed on a microcontroller to perform: determining a reference angle of an output voltage from a first generator using a phase lock loop; converting the reference angle and the generator output voltage from a time domain to an orthogonal reference frame to produce two rotating frame reference voltages; calculating a root mean square voltage of the two rotating frame reference voltages and converting the root mean square voltage to an output current IfSetl; providing IfSetl to the non-linear current controller; and wherein the non-linear current controller determines a control action based on a difference of IfSetl and an output current of a second generator IfFBK.

2. The system of claim 1, wherein the linear voltage controller and the non-linear current controller are in a cascaded arrangement.

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

4. The system of claim 1, wherein the control action is a voltage VF defined by the following equation: VF = AT AN (IfSetl -IfFBK).

5. The system of claim 1, wherein the phase lock loop of the linear voltage controller is initialized by a zero-crossing phase lock loop of the non-linear current controller.

6. The system of claim 1, wherein the conversion is a Clarke and Park transform.

7. The system of claim 2, wherein the first generator is a three-phase generator, and the second generator is an exciter generator.

8. The system of claim 7, wherein the non-linear current controller approximates the control action by superimposing a triangular wave on IfSetl.

9. The system of claim 7, wherein the non-linear current controller comprises: a root mean square to direct current converter to compute a real time root mean square voltage from the output voltage of the first generator; a first circuit to average the root mean square voltage of the output voltage of the first generator and output an average root mean square voltage to a second circuit, wherein the second circuit compares the average root mean square voltage to a hi phase root mean square voltage of the output voltage of the first generator, and outputs the higher of the voltages; and a proportional and integral (PI) control module to convert the output of the second circuit to a current signal IfSet2.

10. The system of claim 8, wherein the triangular wave has an amplitude of up to 1% of IfFBK.

11. The system of claim 8, wherein the triangular wave has a frequency of at least 20 kHz and the phase lock loop outputs at a frequency of at least 2 kHz.

12. The system of claim 9, further comprising: a switching component configured to switch between outputs IfSetl and IfSet2 to apply to IfSetl or IfSet2 to the control action.

13. The system of claim 12, wherein the switching component switches from IfSetl to IfSet2 when an error is detected with the linear voltage controller.

14. A method comprising: receiving, by a linear voltage controller, a three-phase voltage Vabc MGmeas from a three-phase generator; determining a reference angle of Vabc MGmeas by applying Vabc MGmeas to a phase lock loop of the linear voltage controller; performing a Park and Clarke transformation on the reference angle and Vabc MGmeas to determine a first rotating frame reference voltage Vq MGmeas and a second rotating frame reference voltage Vd MGmeas; determining a root mean square voltage using Vq MGmeas and Vd MGmeas as follows.converting VRMSi to a first signal IfSetl; receiving, by a non-linear current controller, a second signal IfFBK from an exciter generator; and determining, using the non-linear current controller, a control action, wherein the control action is a function of IfSetl and IfFBK.

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

16. The method of claim 14, wherein the phase lock loop of the linear voltage controller is initialized using a zero cross phase lock loop of the non-linear current controller.

17. The method of claim 14, wherein the non-linear current controller and the linear voltage controller are in a cascaded arrangement.

18. The method of claim 14, wherein determining the control action includes approximating the control action by superimposing a triangular wave on IfSetl.

19. The method of claim 18, wherein the triangular wave has a frequency of at least 20 kHz and the phase lock loop outputs at a frequency of at least 2 kHz.

20. A system comprising: a linear voltage controller and a non-linear current controller, wherein the linear voltage controller is executed on a microcontroller to perform: determining a reference angle of an output voltage from a first generator using a phase lock loop; converting the reference angle and the generator output voltage from a time domain to an orthogonal reference frame to produce two rotating frame reference voltages; calculating a root mean square voltage of the two rotating frame reference voltages and converting the root mean square voltage to an output current IfSetl; and providing IfSetl to the non-linear current controller; wherein the non-linear current controller comprises:a root mean square to direct current converter to compute a real time root mean square voltage from the output voltage of the first generator; a first circuit to average the root mean square voltage of the output voltage of the first generator and output an average root mean square voltage to a second circuit, wherein the second circuit compares the average root mean square voltage to a hi phase root mean square voltage of the output voltage of the first generator, and outputs the higher of the voltages; a proportional and integral (PI) control module to convert the output of the second circuit to a current signal IfSet2; a switching component configured to select a signal from outputs IfSetl and IfSet2, to use in determining a control action; and an inverse tangent non-linear control component configured to the control action using an output current IfFBK of a second generator, and the selected current of eitherIfSetl or IfSet2.

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