Method and system for voltage regulation of a power system based on an independent speed variable frequency generator

Abstract

The present invention relates to a method and system for regulating the voltage of a power system based on an independent speed variable frequency generator. A system may include an independent speed variable frequency (ISVF) generator and an excitation source configured to provide an excitation signal to the rotor field winding of the ISVF generator to generate a rotating magnetic flux independent of the shaft speed of the ISVF generator. The system may include a bus configured to receive the output voltage of the ISVF generator. A generator control unit may be configured to generate a first excitation voltage reference component based on the shaft frequency of the ISVF generator, generate a second excitation voltage reference component based on the difference between a reference voltage and the measured output voltage of the ISVF generator, and generate an excitation voltage control signal based on a combination of the first excitation voltage reference component and the second excitation voltage reference component, and the excitation voltage control signal may be used to control the voltage magnitude of the excitation signal.

Description

Technical Field

[0001] The present disclosure generally relates to the field of voltage regulation, and more particularly, to voltage regulation of a power system based on an independent speed variable frequency (ISVF) generator. Background Art

[0002] Voltage regulation can ensure that a power distribution system (e.g., within an aircraft or another vehicle) operates within defined limits without damaging or destroying any load devices powered by the system. For example, some electronic devices electrically connected to the system may be vulnerable to electrical surges and other electrical phenomena. In the aircraft industry, power distribution standards can be defined by various standards organizations. For example, power distribution standards in an aircraft may include DO-160 "Environmental Conditions and Test Procedures for Airborne Equipment" (available from the Radio Technical Commission for Aeronautics in Washington, D.C., USA), MIL-STD-704 "Aircraft Electrical Power Characteristics" (available from EverySpec.com in Gibsonsia, Pennsylvania, USA), etc.

[0003] Unlike a typical generator, the output voltage amplitude of an ISVF generator can be based on a combination of a first magnetic flux generated by the rotation of a main magnetic field winding and a second magnetic flux generated by an excitation signal applied to the main magnetic field winding. The interaction of these two magnetic fields can result in voltage behavior different from that of a conventional generator. Due to the uniqueness of the ISVF generator, typical power regulation methods may not be sufficient to meet voltage regulation standards. For example, typical power regulation methods may not consider the frequency and phase angle of the excitation signal relative to the shaft speed. Summary of the Invention

[0004] The disclosed examples describe a method and system for regulating the voltage of a power system based on an ISVF generator while considering load disturbances, changes in the excitation signal, and shaft speed variations. In an example, a generator control unit device includes a frequency-to-voltage converter configured to generate a first excitation voltage reference component based on the shaft frequency of the ISVF generator. The device also includes a proportional-integral-derivative controller (PID) configured to generate a second excitation voltage reference component based on the difference between a reference voltage and the measured output voltage of the ISVF generator. The device also includes an excitation source controller configured to generate an excitation voltage control signal based on a combination of the first excitation voltage reference component and the second excitation voltage reference component, the excitation voltage control signal being usable to control the voltage magnitude of an excitation signal generated by an excitation source associated with the ISVF generator.

[0005] In some examples, the frequency-to-voltage converter includes a look-up table that maps shaft frequency values to an excitation voltage reference that, when applied to an ISVF generator, causes the output voltage at the ISVF generator to have a constant voltage magnitude for each shaft frequency value when the ISVF generator is in a no-load state. In some examples, the device includes a differential circuit configured to generate an excitation frequency reference based on a reference frequency and a shaft frequency, wherein an excitation source controller is configured to generate an excitation frequency control signal based on the excitation frequency reference, the excitation frequency control signal being usable to control the frequency of an excitation signal generated by an excitation source. In some examples, the excitation source controller is configured to generate an excitation phase angle control signal based on an excitation phase angle reference, the excitation phase angle control signal being usable to control the phase angle of an excitation signal generated by an excitation source.

[0006] In some examples, the device includes: a root mean square (RMS) circuit configured to generate the magnitude of the measured output voltage of the ISVF generator; and a differential circuit configured to generate a difference between the reference voltage and the measured output voltage based on the magnitude of the measured output voltage and the reference voltage. In some examples, the device includes a multiplier circuit configured to generate a shaft frequency based on a shaft speed. In some examples, the ISVF generator is a polyphase generator and the excitation signal includes a plurality of phases, wherein the plurality of phases have equal voltage magnitudes based on a combination of a first excitation voltage reference component and a second excitation voltage reference component, wherein the plurality of phases have equal frequencies based on the excitation frequency reference, and wherein the plurality of phases have phase angles offset by a constant value relative to each other.

[0007] In an example, a system includes an independent speed variable frequency (ISVF) generator. The system further includes an excitation source configured to supply an excitation signal to a field winding of a rotor of the ISVF generator to generate a rotating magnetic flux independent of the shaft speed of the ISVF generator. The system further includes a bus configured to receive the output voltage of the ISVF generator. The system includes a generator control unit configured to generate a first excitation voltage reference component based on the shaft frequency of the ISVF generator. The generator control unit is further configured to generate a second excitation voltage reference component based on a difference between a reference voltage and the measured output voltage of the ISVF generator. The generator control unit is further configured to generate an excitation voltage control signal based on a combination of the first excitation voltage reference component and the second excitation voltage reference component, the excitation voltage control signal being usable to control the voltage magnitude of the excitation signal.

[0008] In some examples, the generator control unit is further configured to: determine a first excitation voltage reference component from the shaft frequency using a look-up table that maps shaft frequency values to an excitation voltage reference, the excitation voltage reference when applied to the ISVF generator causing the output voltage at the ISVF generator to have a constant magnitude for each shaft frequency value when the ISVF generator is in a no-load state. In some examples, the generator control unit is further configured to generate an excitation frequency reference based on a reference frequency and the shaft frequency and generate an excitation frequency control signal based on the excitation frequency reference, the excitation frequency control signal being usable to control the frequency of the excitation signal.

[0009] In some examples, the generator control unit is configured to generate an excitation phase angle control signal based on an excitation phase angle reference, the excitation phase angle control signal being usable to control the phase angle of the excitation signal. In some examples, the generator control unit is configured to generate the magnitude of the output voltage of the measured ISVF generator and generate a difference between the reference voltage and the measured output voltage based on the magnitude of the measured output voltage and the reference voltage. In some examples, the generator control unit is further configured to generate a shaft frequency based on the shaft speed of the ISVF generator. In some examples, the ISVF generator is a polyphase generator and the excitation signal includes a plurality of phases, the plurality of phases having equal voltage magnitudes based on a combination of a first excitation voltage reference component and a second excitation voltage reference component, the plurality of phases having equal frequencies based on the excitation frequency reference, and the plurality of phases having phase angles offset by a constant value relative to each other.

[0010] In an example, a method includes generating a first excitation voltage reference component based on the shaft frequency of an ISVF generator using a data set that maps shaft frequency values to an excitation voltage reference, the excitation voltage reference when applied to the ISVF generator causing the output voltage at the ISVF generator to have a constant magnitude for each shaft frequency value when the ISVF generator is in a no-load state. The method further includes generating a second excitation voltage reference component based on a difference between the reference voltage and the measured output voltage of the ISVF generator. The method further includes generating an excitation voltage control signal based on a combination of the first excitation voltage reference component and the second excitation voltage reference component, the excitation voltage control signal being usable to control the voltage magnitude of an excitation signal generated by an excitation source associated with the ISVF generator.

[0011] In some examples, the method includes determining a data set that maps shaft frequency values to an excitation voltage reference using an ISVF generator or an ISVF generator of the same type experimentally. In some examples, the data set is a look-up table. In some examples, the method includes generating an excitation frequency reference based on a reference frequency and a shaft frequency and generating an excitation frequency control signal based on the excitation frequency reference, the excitation frequency control signal being usable to control the frequency of an excitation signal. In some examples, the method includes generating an excitation phase angle control signal based on an excitation phase angle reference, the excitation phase angle control signal being usable to control the phase angle of the excitation signal. In some examples, the method includes generating a magnitude of the output voltage of the measured ISVF generator and generating a difference between the reference voltage and the measured output voltage based on the magnitude of the measured output voltage and the reference voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 is a block diagram depicting an example of a power system based on an ISVF generator.

[0013] Figure 2 is a functional block diagram depicting an example of a generator control system for a power system based on an ISVF generator.

[0014] Figure 3 is a graph depicting a function that maps shaft frequency values to an excitation voltage reference value.

[0015] Figure 4 is a graph depicting a Figure 3 portion of a function that maps shaft frequency values to an excitation voltage reference value.

[0016] Figure 5 is a graph depicting a simulated generator output voltage over time.

[0017] Figure 6 is a graph depicting a simulated shaft speed and excitation frequency reference over time.

[0018] Figure 7 is a graph depicting a simulated excitation voltage reference and an excitation voltage reference value based on the output of a frequency-to-voltage converter.

[0019] Figure 8 is a flowchart depicting an example of a voltage regulation method.

[0020] Figure 9 is a flowchart depicting an example of a method for generating a look-up table for voltage regulation.

[0021] Although the present disclosure is susceptible to various modifications and alternative forms, specific examples have been shown by way of illustration in the drawings and will be described in detail herein. However, it should be understood that the present disclosure is not intended to be limited to the particular forms disclosed. On the contrary, the present invention is to cover all modifications, equivalents, and alternatives falling within the scope of the present disclosure. Detailed Description

[0022] Referring Figure 1 , an example of a power system 100 based on an ISVF generator is depicted. The system 100 may include an ISVF generator 110. The ISVF generator 110 may include a rotor 112 and a stator 114. The rotor may be fixed to a shaft 116. During operation of the ISVF generator 110, an excitation signal 132 may be sent from the stator 114 to the rotor 112 via a set of high-frequency transformers 118. The excitation signal 132 may be used to generate a rotating magnetic flux 122 around the rotor 112 that rotates independently of the shaft speed 124. Thus, the frequency of the output voltage 142 of the ISVF generator 110 may be independent of the shaft speed 124. A non-limiting example of the ISVF generator 110 is described in U.S. Patent Application No. 15 / 819,919, filed on November 21, 2017, which was published as U.S. Patent Application Publication No. 2019 / 0158002 and is entitled "Independent Speed Variable Frequency Alternating Current Generator", the content of which is incorporated herein by reference in its entirety.

[0023] As Figure 1 depicted therein, the ISVF generator 110 may be a polyphase generator (e.g., a three-phase generator). In this case, the excitation signal 132 may include multiple three-phases. Similarly, the output voltage 142 may include three phases. Although Figure 1 a three-phase is depicted, the ISVF generator 110 may be configured to generate more or fewer than three phases.

[0024] System 100 may also include an excitation source 130 configured to provide an excitation signal 132 to the field winding 119 of the rotor 112 of the ISVF generator 110 to generate a rotating magnetic flux 122. The frequency and magnitude of the rotating magnetic flux 122 may directly depend on the frequency and magnitude of the excitation signal 132. To ensure that the output voltage 142 of the ISVF generator 110 has a constant frequency, the frequency of the excitation signal 132 may increase and decrease inversely with the frequency of the shaft 116. For example, if the desired frequency of the output voltage 142 is 400 Hz and the frequency of the shaft 116 is also 400 Hz, the frequency of the rotating magnetic flux 122 will be zero. In other words, the shaft alone can generate the entire desired frequency independently of the rotating magnetic flux 122. However, if the frequency of the shaft 116 is 500 Hz, then to generate an output voltage 142 with a frequency of 400 Hz, the rotating magnetic flux 122 and its corresponding excitation signal 132 may have a frequency of negative (-) 100 Hz. The relationship between the frequency of the excitation signal 132 and the frequency of the shaft 116 is described further with reference to Figure 6 is further described.

[0025] The magnitude of the output voltage 142 may be based on a combination of the power generated by the rotation of the shaft 116 and the power generated by the rotating magnetic flux 122. When the frequency of the shaft 116 is operating at the desired frequency (e.g., 400 Hz), most of the power may be generated via the rotation of the shaft 116. To generate an output voltage 142 of the desired magnitude, the voltage of the excitation signal 132 may be relatively low (relying on the rotation of the shaft 116 to generate power). When the frequency of the shaft 116 is higher or lower than the desired frequency, more power may be generated via the rotating magnetic flux 122. In this case, the voltage of the excitation signal may be relatively high in order to maintain the desired output voltage level. The role of the voltage of the excitation signal in maintaining a constant magnitude of the output voltage 142 is described further with reference to Figure 7 is further described.

[0026] The bus 140 may be configured to receive the output voltage 142 of the ISVF generator 110. The bus 140 may form part of a power distribution system. In some examples, the power distribution system may supply power to systems of a vehicle (e.g., an aircraft). Due to the sensitive nature of the circuits that may be coupled to the bus 140, it may be desirable to condition the output voltage 142 as described herein.

[0027] System 100 may include a generator control unit (GCU) 150, which includes a frequency-to-voltage converter 152, a proportional-integral-derivative (PID) controller 154, and an excitation source controller 156. The frequency-to-voltage converter 152 may be configured to generate a first excitation voltage reference component based on the shaft frequency derived from the shaft speed 124 of the ISVF generator 110. The first excitation voltage reference component may be used to ensure a constant output voltage 142 under no-load conditions. The PID controller 154 may be configured to generate a second excitation voltage reference component based on the difference between the reference voltage 158 and the measured output voltage 142a (e.g., a single phase of the output voltage 142 of the ISVF generator 110). The second excitation component may be used to compensate for the effect of varying loads on the output voltage 142. Based on the combination of the first excitation voltage reference component and the second excitation voltage reference component, the excitation source controller 156 may generate an excitation voltage control signal 164. The excitation voltage control signal 164 may be used to control the voltage magnitude of the excitation signal 132. The excitation source controller 156 may also generate an excitation frequency control signal 166 (which may be based on the reference frequency 160) and an excitation phase angle control signal 168. The excitation voltage control signal 164, the excitation frequency control signal 166, and the excitation phase angle control signal 168 may together constitute an excitation source control signal 162.

[0028] As described herein, the generator control unit 150 may be configured to determine the first excitation voltage reference component from the shaft frequency using a look-up table that maps shaft frequency values to an excitation voltage reference, the excitation voltage reference when applied to the ISVF generator 110 causing the output voltage 142 at the ISVF generator 110 to have a constant magnitude for each shaft frequency value when the ISVF generator 110 is in a no-load state.

[0029] The benefit of system 100 is that the frequency-to-voltage converter 152 may enable the generator control unit 150 to control the excitation signal 132 to maintain a constant amplitude and frequency of the output voltage 142 under no-load conditions. Then, the PID controller 154 may fine-tune the excitation signal 132 to compensate for the varying loads imposed by the devices attached to the bus 140. There may be other benefits.

[0030] Referring Figure 2 to Figure 1 is an example of a generator control system 200 for a power system based on an ISVF generator. The generator control system 200 may correspond to Figure 2 the generator control unit 150. Although system 200 is depicted as discrete modules, one or more of the modules may be combined. Additionally, depending on the specific application, system 200 may be implemented as hardware or software. In some examples, the various functions described

[0031] System 200 may include a multiplier circuit 212 configured to generate a shaft frequency 214 (i.e., f shaft ) based on a shaft speed 124 (i.e., ω shaft ). Then, a frequency-to-voltage converter 152 may convert the shaft frequency 214 into a first field voltage reference component 218. In some examples, the frequency-to-voltage converter 152 includes a frequency-to-voltage (F / V) look-up table 216. The look-up table 216 maps shaft frequency values to field voltage references that, when applied to the ISVF generator 110, cause the output voltage 142 at the ISVF generator 110 to have a constant voltage magnitude for each shaft frequency value when the ISVF generator 110 is in a no-load state. In other words, the look-up table 216 may indicate what voltage the field voltage control signal 164 should have to ensure that the output voltage 142 of the ISVF generator 110 is constant.

[0032] System 200 may include a root mean square (RMS) circuit 202 configured to generate a magnitude 204 (i.e., |V sa ) of a measured output voltage 142a (i.e., V sa ) of the ISVF generator 110. In some examples, the measured output voltage 142a (i.e., V sa ) may correspond to a single phase of a polyphase output. A first difference circuit 206 may be configured to generate a difference 208 between a reference voltage 158 (i.e., V sa ) and the measured output voltage 142a based on the magnitude 204 (i.e., |V sa |) of the measured output voltage 142a (i.e., V ref ). A PID controller 154 may be configured to generate a second field voltage reference component 210 based on the difference 208.

[0033] The first field voltage reference component 218 may be used to ensure that the output voltage 142 is constant under no-load conditions. The second field voltage reference component 210 may be used to compensate for the effects of a varying load. A summing circuit 219 may be configured to generate a combination 220 (i.e., V ref-EX ) of the first field voltage reference component 218 and the second field voltage reference component 210. An excitation source controller 156 may use the combination 220 to generate an excitation voltage control signal 164, which may be used to control Figure 1 the voltage magnitude of the excitation signal 132 depicted in Figure 2 . As EX-a EX-b EX-c ref-EX shown, for a three-phase system, the magnitudes |V ​​​

[0034] System 200 may include a second differential circuit 222 configured to receive the shaft frequency 214 and the reference frequency 160 and calculate the difference therebetween to obtain an excitation frequency reference 224 (i.e., f EX ). The excitation frequency control signal 166 may be generated by the excitation source controller 156 based on the excitation frequency reference 224. The excitation frequency control signal 166 may be used to control the frequency of the excitation signal 132. As Figure 2 shown, for a three-phase system, the frequency of each phase of the excitation frequency control signal 166 |f EX-a |, |f EX-b |, |f EX-c | may be equal to the excitation frequency reference 224 (i.e., f EX ).

[0035] The excitation source controller 156 may be configured to generate an excitation phase angle control signal 168 based on an excitation phase angle reference 226 (i.e., θ EX ). The excitation phase angle control signal 168 may be used to control the phase angle of the excitation signal 132 generated by the excitation source 130. For a polyphase system, multiple phases (θ EX-a , θ EX-b , θ EX-c ) may have phase angles offset by a constant value (i.e., 120°, 240°) relative to each other.

[0036] Referring to Figure 3 , graph 300 depicts shaft frequency values 302 along the x-axis and excitation voltage reference values 304 along the y-axis. Function 306 maps the shaft frequency values 302 to the excitation voltage reference values 304 such that the resulting excitation voltage reference values 304, when applied to the ISVF generator 110, cause the output voltage at the ISVF generator 110 to have a constant voltage magnitude for each shaft frequency value 302 when the ISVF generator 110 is in a no-load state. The data in graph 300 may be determined experimentally and may vary between different ISVF generators. Additionally, the data may correspond to a specific desired output frequency. In Figure 3 the example, the desired output frequency is 400 Hz.

[0037] The data shown in graph 300 may be incorporated into Figure 2 the look-up table 216, or used to determine the first excitation voltage reference component 218. Although the PID controller 154 may be sufficient for minor adjustments to the excitation voltage control signal 164, as shown by the data in graph 300, the major adjustments may be based on Figure 2The shaft frequency 214 depicted performs on the excitation voltage control signal 164. Since these changes are predictable, it may be more efficient to use a look-up table 216 to generate the first excitation voltage reference component 218 rather than relying on the PID controller 154. Then, the PID controller 154 can be used to make minor adjustments to compensate for the load conditions.

[0038] Referring to Figure 4 , graph 400 depicts a scaled portion of graph 300. For example, graph 400 depicts the shaft frequency value 302a along the x-axis and the excitation voltage reference value 304a along the y-axis, and the function 306a maps the shaft frequency value 302a to the excitation voltage reference value 304a. Applying Figure 4 to Figure 1 and Figure 2 , when the shaft frequency 214 is at 400 Hz, the excitation signal 132 supplied to the ISVF generator can be zero. In this state, contrary to the excitation signal 132, most of the power can be generated by the rotation of the shaft 116. Therefore, in order to maintain a constant output voltage 142, the voltage of the excitation signal 132 can be minimized at 400 Hz. As the shaft frequency 214 moves away from 400 Hz, more output voltage of the ISVF generator 110 can be obtained from the excitation signal 132. Therefore, in order to maintain a constant output voltage 142, the voltage of the excitation signal 132 increases.

[0039] Referring to Figures 5 to 7 , the simulation results of the power system based on the ISVF generator are depicted over time. Figure 5 Depicts the simulated generator output voltage 502 over time. Figure 6 Depicts the simulated shaft speed 602 and excitation frequency reference 604 over time. Figure 7 Depicts the simulated excitation voltage reference 704 and the excitation voltage reference value 702 based on the output of the frequency-to-voltage converter 152.

[0040] Figures 5 to 7 The simulation can correspond to a generator output frequency of 400 Hz and a line-to-neutral voltage root mean square (RMS) value of 220 V. As Figure 6 shown, the simulated shaft speed changes from 240 Hz at t = 0 to 560 Hz at t = 4.5 and then returns to 240 Hz at t = 10. At t = 4, a 50% rated load is applied, which can be seen from the small perturbation 504 in the output voltage 502 of Figure 5 .

[0041] Figure 5Shows the RMS value of the generator output voltage 502. The generator output voltage 502 increases from 0 and stabilizes at 220V in about 1 second. At T = 4, a 50% load is applied, and the output voltage 502 undergoes a dynamic transient and remains at 220V. At T = 2.5 and T = 7.5, the output voltage 502 shows small fluctuations. This change is due to the shaft speed being equal to 400Hz at those time instants. When the shaft speed is at 400Hz, a small voltage amplitude change in the excitation signal can cause a large deviation in the generator output voltage.

[0042] Figure 6 Shows the shaft speed 602 and the excitation frequency reference 604 of the excitation source. The sum of the two values is equal to 400Hz (corresponding to the desired generator output frequency).

[0043] Figure 7 Shows the simulated excitation voltage reference 704 and the excitation voltage reference value 702 based on the output of the frequency-to-voltage converter 152. When Figure 7 is applied to Figure 2 , the excitation voltage reference value 702 can correspond to the first excitation voltage reference component 218, while the excitation voltage reference value 704 can correspond to the combination 220 of the first excitation voltage reference component 218 and the second excitation voltage reference component 210. The difference between the two curves may be attributed to the PID output, which compensates for the voltage drop caused by the load change.

[0044] Refer to Figure 8 , the flowchart depicts an example of the voltage regulation method 800. The method 800 may include, at 802, generating a first excitation voltage reference component based on the shaft frequency of the ISVF generator using a dataset that maps the shaft frequency value to the excitation voltage reference, the excitation voltage reference which when applied to the ISVF generator causes the output voltage at the ISVF generator to have a constant magnitude for each shaft frequency value when the ISVF generator is in the no-load state. For example, the first excitation voltage reference component 218 may be generated by the frequency-to-voltage converter 152 using the look-up table 216.

[0045] The method 800 may further include, at 804, generating the magnitude of the output voltage of the measured ISVF generator. For example, the magnitude 204 may be generated by the RMS circuit 202.

[0046] The method 800 may further include, at 806, generating the difference between the reference voltage and the measured output voltage based on the magnitude of the measured output voltage and the reference voltage. For example, the first difference circuit 206 may generate the difference 208 between the reference voltage 158 and the measured output voltage 142a based on the magnitude 204.

[0047] Method 800 may include, at 808, generating a second excitation voltage reference component based on a difference between a reference voltage and an output voltage of the measured ISVF generator. For example, the PID controller 154 may generate the second excitation voltage reference component 210.

[0048] Method 800 may further include, at 810, generating an excitation voltage control signal based on a combination of the first excitation voltage reference component and the second excitation voltage reference component, where the excitation voltage control signal may be used to control a voltage magnitude of an excitation signal generated by an excitation source associated with the ISVF generator. For example, the excitation source controller 156 may generate the excitation voltage control signal 164 based on the combination 220 of the first excitation voltage reference component 218 and the second excitation voltage reference component 210.

[0049] Method 800 may further include, at 812, generating an excitation frequency reference based on a reference frequency and an axis frequency. For example, the second difference circuit 222 may generate the excitation frequency reference 224 based on the reference frequency 160 and the axis frequency 214.

[0050] Method 800 may include, at 814, generating an excitation frequency control signal based on the excitation frequency reference, where the excitation frequency control signal may be used to control a frequency of the excitation signal. For example, the excitation source controller 156 may generate the excitation frequency control signal 166 based on the excitation frequency reference 224.

[0051] Method 800 may further include, at 816, generating an excitation phase angle control signal based on an excitation phase angle reference, where the excitation phase angle control signal may be used to control a phase angle of the excitation signal. For example, the excitation source controller 156 may generate the excitation phase angle control signal 168 based on the excitation phase angle reference 226.

[0052] Referring Figure 9 , the flowchart depicts an example of a method 900 for generating a look-up table for voltage regulation. Method 900 may include, at 902, experimentally determining, using the ISVF generator, a data set that maps axis frequency values to excitation voltage references. For example, Figure 3 and Figure 4 the data depicted in

[0053] may be experimentally determined.

[0054] Clause 1. A generator control unit device, the device comprising: a frequency-to-voltage converter configured to generate a first excitation voltage reference component based on the shaft frequency of an independent speed variable frequency (ISVF) generator; a proportional integral derivative (PID) controller configured to generate a second excitation voltage reference component based on the difference between a reference voltage and the measured output voltage of the ISVF generator; and an excitation source controller configured to generate an excitation voltage control signal based on a combination of the first excitation voltage reference component and the second excitation voltage reference component, the excitation voltage control signal being usable to control the voltage magnitude of an excitation signal generated by an excitation source associated with the ISVF generator.

[0055] Clause 2. The device according to Clause 1, wherein the frequency-to-voltage converter includes a look-up table that maps shaft frequency values to excitation voltage reference values, the excitation voltage reference values causing the output voltage at the ISVF generator to have a constant voltage magnitude for each shaft frequency value when the ISVF generator is in a no-load state when applied to the ISVF generator.

[0056] Clause 3. The device according to any one of Clauses 1 to 2, the device further comprising: a differential circuit configured to generate an excitation frequency reference based on a reference frequency and the shaft frequency, wherein the excitation source controller is configured to generate an excitation frequency control signal based on the excitation frequency reference, the excitation frequency control signal being usable to control the frequency of the excitation signal generated by the excitation source.

[0057] Clause 4. The device according to any one of Clauses 1 to 3, wherein the excitation source controller is configured to generate an excitation phase angle control signal based on an excitation phase angle reference, the excitation phase angle control signal being usable to control the phase angle of the excitation signal generated by the excitation source.

[0058] Clause 5. The device according to any one of Clauses 1 to 4, the device further comprising: a root mean square (RMS) circuit configured to generate the magnitude of the measured output voltage of the ISVF generator; and a differential circuit configured to generate the difference between the reference voltage and the measured output voltage based on the magnitude of the measured output voltage and the reference voltage.

[0059] Clause 6. The device according to any one of Clauses 1 to 5, the device further comprising: a multiplier circuit configured to generate a shaft frequency based on a shaft speed.

[0060] Clause 7. The apparatus according to any one of Clauses 1 to 6, wherein the ISVF generator is a polyphase generator and the excitation signal includes a plurality of phases, wherein the plurality of phases have equal voltage magnitudes based on a combination of a first excitation voltage reference component and a second excitation voltage reference component, wherein the plurality of phases have equal frequencies based on an excitation frequency reference, and wherein the plurality of phases have phase angles offset by a constant value relative to each other.

[0061] Clause 8. A system comprising: an independent speed variable frequency (ISVF) generator; an excitation source configured to supply an excitation signal to a field winding of a rotor of the ISVF generator to generate a rotating magnetic flux independent of the shaft speed of the ISVF generator; a bus configured to receive an output voltage of the ISVF generator; and a generator control unit configured to: generate a first excitation voltage reference component based on the shaft frequency of the ISVF generator; generate a second excitation voltage reference component based on a difference between a reference voltage and the measured output voltage of the ISVF generator; and generate an excitation voltage control signal based on a combination of the first excitation voltage reference component and the second excitation voltage reference component, the excitation voltage control signal being usable to control the voltage magnitude of the excitation signal.

[0062] Clause 9. The system according to Clause 8, wherein the generator control unit is further configured to: determine the first excitation voltage reference component from the shaft frequency using a look-up table that maps shaft frequency values to excitation voltage reference values, the excitation voltage reference values causing the output voltage at the ISVF generator to have a constant magnitude for each shaft frequency value when the ISVF generator is in a no-load state when applied to the ISVF generator.

[0063] Clause 10. The system according to any one of Clauses 8 to 9, wherein the generator control unit is further configured to: generate an excitation frequency reference based on a reference frequency and the shaft frequency; and generate an excitation frequency control signal based on the excitation frequency reference, the excitation frequency control signal being usable to control the frequency of the excitation signal.

[0064] Clause 11. The system according to any one of Clauses 8 to 10, wherein the generator control unit is further configured to: generate an excitation phase angle control signal based on an excitation phase angle reference, the excitation phase angle control signal being usable to control the phase angle of the excitation signal.

[0065] Clause 12. The system according to any one of Clauses 8 to 11, wherein the generator control unit is further configured to: generate the magnitude of the measured output voltage of the ISVF generator; and generate a difference between the reference voltage and the measured output voltage based on the magnitude of the measured output voltage and the reference voltage.

[0066] Clause 13. The system according to any one of Clauses 8 to 12, wherein the generator control unit is further configured to: generate a shaft frequency based on the shaft speed of the ISVF generator.

[0067] Clause 14. The system according to any one of Clauses 8 to 13, wherein the ISVF generator is a polyphase generator and the excitation signal includes a plurality of phases, wherein the plurality of phases have equal voltage magnitudes based on a combination of a first excitation voltage reference component and a second excitation voltage reference component, wherein the plurality of phases have equal frequencies based on an excitation frequency reference, and wherein the plurality of phases have phase angles offset by a constant value relative to each other.

[0068] Clause 15. A method, the method comprising: generating a first excitation voltage reference component based on the shaft frequency of an independently variable speed frequency (ISVF) generator using a data set that maps shaft frequency values to excitation voltage reference values, the excitation voltage reference values causing an output voltage at the ISVF generator to have a constant magnitude for each shaft frequency value when the ISVF generator is in a no-load state when applied to the ISVF generator; generating a second excitation voltage reference component based on a difference between a reference voltage and the measured output voltage of the ISVF generator; and generating an excitation voltage control signal based on a combination of the first excitation voltage reference component and the second excitation voltage reference component, the excitation voltage control signal being usable to control a voltage magnitude of an excitation signal generated by an excitation source associated with the ISVF generator.

[0069] Clause 16. The method according to Clause 15, the method further comprising: experimentally determining, using the ISVF generator or an ISVF generator of the same type, the data set that maps shaft frequency values to the excitation voltage reference.

[0070] Clause 17. The method according to any one of Clauses 15 to 16, wherein the data set is a look-up table.

[0071] Clause 18. The method according to any one of Clauses 15 to 17, the method further comprising: generating an excitation frequency reference based on a reference frequency and the shaft frequency; and generating an excitation frequency control signal based on the excitation frequency reference, the excitation frequency control signal being usable to control the frequency of the excitation signal.

[0072] Clause 19. The method according to any one of Clauses 15 to 18, the method further comprising: generating an excitation phase angle control signal based on an excitation phase angle reference, the excitation phase angle control signal being usable to control the phase angle of the excitation signal.

[0073] Clause 20. The method according to any one of Clauses 15 to 19, the method further comprising: generating a magnitude of the output voltage of the measured ISVF generator; and generating a difference between the reference voltage and the measured output voltage based on the magnitude of the measured output voltage and the reference voltage.

[0074] Clause 21. The method according to any one of Clauses 15 to 20, the method further comprising: generating a shaft frequency based on the shaft speed of the ISVF generator.

[0075] Clause 22. The method according to any one of Clauses 15 to 21, wherein the ISVF generator is a polyphase generator and the excitation signal comprises a plurality of phases, wherein the plurality of phases have equal voltage magnitudes based on a combination of a first excitation voltage reference component and a second excitation voltage reference component, wherein the plurality of phases have equal frequencies based on an excitation frequency reference, and wherein the plurality of phases have phase angles offset by a constant value relative to each other.

[0076] Although various examples have been shown and described, the present disclosure is not limited thereto and will be understood to include all such modifications and variations as will be apparent to those skilled in the art.

Claims

1. A system for power system voltage regulation based on an independent speed variable frequency (ISVF) generator, the system comprising: An independent speed variable frequency (ISVF) generator (110); An excitation source (130) configured to provide an excitation signal (132) to a field winding (119) of a rotor (112) of the ISVF generator (110) to generate a rotating magnetic flux (122) independent of the shaft speed (124) of the ISVF generator (110); A bus (140) configured to receive an output voltage (142) of the ISVF generator (110); and A generator control unit (150) configured to: Generate a first excitation voltage reference component (218) based on the shaft frequency (214) of the ISVF generator (110); Generate a second excitation voltage reference component (210) based on a difference (208) between a reference voltage (158) and a measured output voltage (142a) of the ISVF generator (110); Generate an excitation voltage control signal (164) based on a combination (220) of the first excitation voltage reference component (218) and the second excitation voltage reference component (210), the excitation voltage control signal (164) being capable of being used to control the voltage magnitude of the excitation signal (132); And Generate an excitation phase angle control signal (168) based on an excitation phase angle reference (226), the excitation phase angle control signal (168) being capable of being used to control the phase angle of the excitation signal (132), wherein the generator control unit (150) is further configured to determine the first excitation voltage reference component (218) from the shaft frequency (214) using a look-up table (216) that maps shaft frequency values (302) to excitation voltage reference values (304), the excitation voltage reference values causing the output voltage (142) at the ISVF generator (110) to have a constant magnitude for each of the shaft frequency values when the ISVF generator (110) is in a no-load state when applied to the ISVF generator (110), and the generator control unit (150) is further configured to determine the second excitation voltage reference component to compensate for load conditions.

2. The system according to claim 1, wherein, the generator control unit (150) is further configured to: Generate an excitation frequency reference (224) based on a reference frequency (160) and the shaft frequency (214); and Generate an excitation frequency control signal (166) based on the excitation frequency reference (224), the excitation frequency control signal (166) being capable of being used to control the frequency of the excitation signal (132).

3. The system according to claim 1, wherein, the generator control unit (150) is further configured to: Generate a magnitude (204) of the measured output voltage (142a) of the ISVF generator (110); and Generate a difference (208) between the reference voltage (158) and the measured output voltage (142a) based on the magnitude (204) of the measured output voltage (142a) and the reference voltage (158).

4. The system according to claim 1, wherein, the generator control unit (150) is further configured to: generate the shaft frequency (214) based on the shaft speed (124) of the ISVF generator (110).

5. The system according to claim 1, wherein, the ISVF generator (110) is a polyphase generator and the excitation signal (132) includes a plurality of phases, wherein the plurality of phases have equal voltage magnitudes based on the combination (220) of the first excitation voltage reference component (218) and the second excitation voltage reference component (210), wherein the plurality of phases have equal frequencies based on the excitation frequency reference (224), and wherein the plurality of phases have phase angles offset by a constant value relative to each other.

6. A method for regulating the voltage of a power system based on an independent speed variable frequency (ISVF) generator, the method comprises the following steps: generate a first excitation voltage reference component (218) based on the shaft frequency (214) of an independent speed variable frequency (ISVF) generator (110) using a data set that maps shaft frequency values (302) to excitation voltage reference values (304), the excitation voltage reference values causing the output voltage (142) at the ISVF generator (110) to have a constant magnitude for each of the shaft frequency values when the ISVF generator (110) is in a no-load state when applied to the ISVF generator (110); generate a second excitation voltage reference component (210) based on the difference (208) between the reference voltage (158) and the measured output voltage (142a) of the ISVF generator (110); generate an excitation voltage control signal (164) based on the combination (220) of the first excitation voltage reference component (218) and the second excitation voltage reference component (210), the excitation voltage control signal (164) being capable of being used to control the voltage magnitude of the excitation signal (132) generated by an excitation source (130) associated with the ISVF generator (110); and generate an excitation phase angle control signal (168) based on an excitation phase angle reference (226), the excitation phase angle control signal (168) being capable of being used to control the phase angle of the excitation signal (132), the data set that maps the shaft frequency values to the excitation voltage reference being determined experimentally using the ISVF generator (110) or an ISVF generator of the same type, wherein the data set is a look-up table (216), and wherein the first excitation voltage reference component is determined by the look-up table associated with the no-load state, the second excitation voltage reference component being generated to compensate for load conditions.

7. The method according to claim 6, the method further comprises the following steps: Generate an excitation frequency reference (224) based on a reference frequency (160) and the shaft frequency (214); and Generate an excitation frequency control signal (166) based on the excitation frequency reference (224), the excitation frequency control signal (166) being capable of being used to control the frequency of the excitation signal (132).

8. The method according to claim 6, the method further comprises the steps of: Generate a magnitude (204) of the output voltage (142a) of the measured ISVF generator (110); and Generate the difference (208) between the reference voltage (158) and the measured output voltage (142a) based on the magnitude (204) of the measured output voltage (142a) and the reference voltage (158).

9. The method according to claim 6, the method further comprises the steps of: Generate the shaft frequency (214) based on the shaft speed (124) of the ISVF generator (110).

10. The method according to claim 6, wherein the ISVF generator (110) is a polyphase generator and the excitation signal (132) comprises a plurality of phases, wherein the plurality of phases have equal voltage magnitudes based on the combination (220) of the first excitation voltage reference component (218) and the second excitation voltage reference component (210), wherein the plurality of phases have equal frequencies based on the excitation frequency reference (224), and wherein the plurality of phases have phase angles offset by a constant value relative to each other.

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