Excitation circuit for synchronous machine

Abstract

An excitation circuit for a synchronous machine, the excitation circuit comprising: at least one charge storage device configured to supply energy to a DC output coupled to the synchronous machine; and a control circuit configured to receive a first signal indicative of an operating state of the synchronous machine, receive a second signal indicative of a control request of the synchronous machine, and supply at least a portion of the energy stored by the at least one charge storage device to satisfy the control request indicated by the second signal when the control request indicated by the second signal exceeds a threshold capacity of the synchronous machine that would be present in the absence of the at least one charge storage device and the synchronous machine is in a suitable operating state as derived from the first signal.

Description

[Technical Field]

[0001] The present disclosure relates to excitation circuits for synchronous machines (which may also be referred to as synchronous machine systems, but in either case are typically synchronous generators, synchronous motors, or synchronous condensers), and more particularly to excitation circuits configured generally to discharge at least one charge storage device to a DC output for the synchronous machine in response to power system demand requirements. [Background technology]

[0002] Generator excitation systems typically operate to maintain the generator terminal voltage at a specific set point. Thus, the terminal voltage is automatically maintained as the load changes over time, a control technique known as steady-state control. Additionally, the control system responds to system disturbances, such as short-circuit faults, that may occur in the power system to which the generator is connected. During such disturbances, the power system voltage may drop below normal, causing the excitation system to take strong forcing action to increase the generator field current. Furthermore, with low voltage disturbances, while the mechanical power from the turbine remains unchanged in the short term, the generator rotor, along with any connected turbine rotor, experiences acceleration forces due to the reduced power produced by the voltage drop. High-speed forcing by the excitation system helps improve generator rotor stability, thereby reducing deviations in rotor speed and benefiting the broader power system. Summary of the Invention [Problem to be solved by the invention]

[0003] Therefore, it is beneficial for a synchronous machine, such as a synchronous generator, to have a fast response time to changes in power demand.

[0004] The listing or discussion of a prior-published document or any background in this specification should not necessarily be construed as an admission that the document or background is part of the state of the art or within common general knowledge. One or more aspects / embodiments of the present disclosure may or may not address one or more of the background issues.

[0005] According to a first aspect, there is provided an excitation circuit for a synchronous machine, the excitation circuit comprising: at least one charge storage device configured to be discharged to a DC output; A control circuit comprising: receiving a first signal indicative of an electrical output of the synchronous machine; receiving a second signal indicative of an electrical demand from a load device connected to the synchronous machine; and a control circuit configured to discharge the at least one charge storage device when the electrical demand indicated by the second signal exceeds the electrical output indicated by the first signal.

[0006] The excitation circuit may further comprise a rectifier circuit configured to convert an AC input to a DC output.

[0007] The control circuit is receiving a third signal indicative of an amount of charge stored by the at least one charge storage device; The device may be configured to initiate charging of the at least one charge storage device when the amount of stored charge indicated by the third signal falls below a predetermined threshold and the voltage output indicated by the first signal meets the voltage demand indicated by the second signal.

[0008] The control circuit may be configured to initiate charging of the at least one charge storage device by the AC input.

[0009] The control circuit may be configured to initiate charging of the at least one charge storage device by the load device.

[0010] The control circuit may be configured to discharge the at least one charge storage device when the electrical demand indicated by the second signal exceeds the electrical output indicated by the first signal by a predetermined amount, which may be an absolute amount or a relative amount.

[0011] The control circuit may be configured to discharge the at least one charge storage device when the electrical demand indicated by the second signal exceeds the electrical output indicated by the first signal for a predetermined period of time.

[0012] The control circuit may be configured to electrically isolate the at least one charge storage device from the DC output when the electrical output indicated by the first signal meets the electrical demand indicated by the second signal.

[0013] The DC output may be a positive or negative voltage, and the AC input may be a three-phase or single-phase signal.

[0014] The first signal may include one or more of a voltage output, a current output, and a power output of the synchronous machine, and the second signal may include one or more of a voltage demand, a current demand, a power demand, an exciter field voltage demand, an inductance demand, and a power factor from a load device connected to the synchronous machine, and the load device may include an electrical load device or a mechanical load device.

[0015] The control circuit may comprise one or more transistors and an automatic voltage regulator configured to control the one or more transistors to discharge the at least one charge storage device to the DC output.

[0016] One or more of the transistors may be insulated gate bipolar transistors.

[0017] The control circuit may comprise a capacitor configured to protect the insulated gate bipolar transistor from circuit inductance when the insulated gate bipolar transistor is switched from an on state to an off state by the automatic voltage regulator.

[0018] The automatic voltage regulator may be configured to apply pulse width modulation to control the DC output.

[0019] The at least one charge storage device may include one or more capacitors, batteries, or battery-capacitor hybrids.

[0020] According to a second aspect, there is provided an exciter machine for a synchronous machine comprising the excitation circuit of the first aspect or the fourth aspect, wherein the DC output is coupled to an exciter field coil of the exciter machine.

[0021] The exciter may be a brushless AC exciter or a DC exciter.

[0022] According to a third aspect, there is provided a synchronous machine (or synchronous electric machine) comprising the exciter machine of the second aspect. The synchronous machine may be a synchronous generator, a synchronous motor or a synchronous condenser.

[0023] The synchronous machine may further include a main generator and a pilot exciter coupled to a rotor shaft of the main generator configured to provide an AC input.

[0024] The sub-exciter may include a permanent magnet generator.

[0025] According to a fourth aspect, there is provided an excitation circuit for a synchronous machine, the excitation circuit comprising: at least one charge storage device configured to provide energy to a DC output coupled to the synchronous machine; A control circuit comprising: receiving a first signal indicative of an operating state of the synchronous machine; receiving a second signal indicative of a control request for the synchronous machine; the control demand indicated by the second signal exceeds a threshold capacity of the synchronous machine that would be present if the at least one charge storage device were not present; and a control circuit configured to provide at least a portion of the energy stored by the at least one charge storage device to satisfy a control demand indicated by the second signal when the synchronous machine is in a suitable operating condition as derived from the first signal.

[0026] The control circuit is The DC output may be configured to initiate charging of the at least one charge storage device when the control request indicated by the second signal is associated with removing energy from the synchronous machine.

[0027] The control circuit is receiving a third signal indicative of an amount of charge stored by the at least one charge storage device; The control circuit may be configured to initiate charging of the at least one charge storage device when the amount of accumulated charge indicated by the third signal is less than a predetermined threshold and the operating condition indicated by the first signal satisfies the control requirement indicated by the second signal. Initiating charging may include charging with an AC input or a DC output.

[0028] The first signal may be indicative of a measured parameter of an operating condition of the synchronous machine, and the control circuit may be configured to provide at least a portion of the energy stored by the at least one charge storage device when the operating condition indicated by the first signal does not satisfy the control requirement indicated by the second signal by a predetermined amount.

[0029] The first signal may be indicative of a measured parameter of an operating condition of the synchronous machine, and the control circuit may be configured to supply at least a portion of the energy stored by the at least one charge storage device when the operating condition indicated by the first signal does not satisfy the control requirement indicated by the second signal for a predetermined period of time.

[0030] The control circuit may be configured to electrically isolate the at least one charge storage device from the DC output to provide a predetermined voltage upper limit at the DC output when the operating condition indicated by the first signal satisfies the control requirement indicated by the second signal.

[0031] The first signal may indicate measured parameters of the operating state of the synchronous machine, the measured parameters including at least one of a voltage output, a current output, and a power output of the synchronous machine, and one or more of a voltage demand, a current demand, a power demand, an inductance demand, and a power factor from a load device connected to the synchronous machine, and the second signal may indicate parameter requirements of control demands of the synchronous machine, the parameter requirements including at least one of a field voltage and / or a field current of an exciter machine of the synchronous machine, an input, an output, and / or one or more internal values ​​of an automatic voltage regulator configured to control the synchronous machine, a voltage and / or a current provided by a generator of the synchronous machine, a real inductance demand or a complex inductance demand of the synchronous machine, and a power factor from a load device connected to the synchronous machine.

[0032] The control circuit is Modulates the DC output based on the modulation signal, It may be configured to set the polarity of the DC output.

[0033] The automatic voltage regulator may comprise a pulse width modulation unit configured to generate a pulse width modulated signal.

[0034] One or more transistors a transistor configured to receive a pulse width modulated signal from the pulse width modulation unit to modulate the DC output; and a plurality of further transistors configured to set the polarity of the DC output.

[0035] The excitation circuit may further comprise a rectifier circuit configured to convert the AC input to a DC output, and the control circuit may a first current path connecting a first terminal of the rectifier circuit to a corresponding first terminal of the DC output section via a first transistor; a second current path connecting a second terminal of the rectifier circuit to a corresponding second terminal of the DC output section via a second transistor; a third current path coupling a first point along the first current path to a first terminal of the DC output through a third transistor; a fourth current path coupling a second point along the first current path to the first terminal of the DC output via a fourth transistor; At least one charge storage device is disposed in parallel with the fourth transistor.

[0036] The automatic voltage regulator providing at least a portion of the energy stored by the at least one charge storage device to provide a positive voltage at the DC output; by switching on the first transistor and the fourth transistor, switching off the third transistor, and providing a pulse width modulation signal to the second transistor via a pulse width modulation unit; or supplying a positive voltage by switching on the first transistor and the second transistor, switching off the third transistor, and supplying a pulse width modulation signal to the fourth transistor via a pulse width modulation unit; or providing at least a portion of the energy stored by the at least one charge storage device to provide a negative voltage at the DC output; by switching off the first transistor, the third transistor, and the fourth transistor and providing a pulse width modulation signal to the second transistor via a pulse width modulation unit; or The negative voltage may be provided by switching off the first transistor, the second transistor, and the fourth transistor, and providing a pulse width modulated signal to the third transistor via the pulse width modulation unit.

[0037] The automatic voltage regulator may be configured to charge the at least one charge storage device by switching on the first transistor and switching off the second transistor, the third transistor, and the fourth transistor.

[0038] The automatic voltage regulator isolating at least one charge storage device and providing a positive voltage at a DC output; providing a positive voltage by switching on the first transistor and the third transistor, switching off the fourth transistor, and providing a pulse width modulated signal to the second transistor via a pulse width modulation unit; or isolating at least one charge storage device and providing a negative voltage at a DC output; The negative voltage may be provided by switching off the first transistor and the fourth transistor, switching on the third transistor, and providing a pulse width modulated signal to the second transistor via the pulse width modulation unit.

[0039] The synchronous machine may comprise an exciter and a generator; The DC output may be coupled to a field coil of an exciter; The operating state may reflect an operating state of the generator; The control demand may represent a demand value of a field voltage generated by the exciter, and the generator is powered by the exciter based on the field voltage; The control circuit may be configured to provide at least a portion of the energy stored by the at least one charge storage device to increase the voltage across the exciter field coil and the corresponding rate of change of current in the exciter field coil when operating conditions of the generator do not meet the required value of the field voltage.

[0040] The operating conditions of the generator may not meet the required value of the field voltage when the measured voltage provided by the generator deviates from the predicted voltage supplied by the generator, which predicted voltage is based on the field current generated by the field coil of the exciter.

[0041] The control circuit may be configured to determine the deviation.

[0042] The corresponding rate of change of current may be proportional to the voltage increase in the exciter field circuit and inversely proportional to the inductance of the exciter field circuit.

[0043] Supplying at least a portion of the energy stored by the at least one charge storage device may include gradual or immediate release of energy from the at least one charge storage device and / or complete discharge of the at least one charge storage device.

[0044] The control circuit may be configured to temporarily increase the voltage upper limit at the DC output to boost the output of the synchronous machine when the control demand indicated by the second signal exceeds a threshold capacity of the synchronous machine that would be present in the absence of the at least one charge storage device and the synchronous machine is in a suitable operating condition as derived from the first signal.

[0045] The first signal may be configured to indicate that the synchronous machine is in a proper operating state, or the control circuit is configured to derive the proper operating state from the first signal.

[0046] A suitable operating state may be a state that allows for use of at least one charge storage device.

[0047] The threshold capacitance may be based on an output voltage of an automatic voltage regulator configured to control the synchronous machine. The automatic voltage regulator may include a smoothing capacitor, and the threshold capacitance may be limited by a voltage of the smoothing capacitor.

[0048] According to a fifth aspect, there is provided a method of using the excitation circuit of the first aspect, the method comprising: receiving a first signal indicative of an electrical output of a synchronous machine; receiving a second signal indicative of an electrical demand from a load device connected to the synchronous machine; discharging the at least one charge storage device when the electrical demand indicated by the second signal exceeds the electrical output indicated by the first signal.

[0049] According to a sixth aspect, there is provided a method of using the excitation circuit of the fourth aspect, the method comprising: receiving a second signal indicative of a control request for the synchronous machine; the control demand indicated by the second signal exceeds a threshold capacity of the synchronous machine that would be present if the at least one charge storage device were not present; and providing at least a portion of the energy stored by the at least one charge storage device to satisfy a control demand indicated by the second signal when the synchronous machine is in a suitable operating condition as derived from the first signal.

[0050] According to a seventh aspect, there is provided an apparatus comprising a processor and a memory containing computer program code, the memory and the computer program code being configured by the processor to enable the apparatus to perform at least the method of the fourth aspect.

[0051] According to an eighth aspect, there is provided apparatus substantially as herein described with reference to and as illustrated by the accompanying drawings.

[0052] Optional features described in relation to the excitation circuit of the first aspect or the fourth aspect are also applicable, where compatible, to the exciter machine of the second aspect, the synchronous machine of the third aspect, the method of the fifth aspect or the sixth aspect, and / or the apparatus of the eighth aspect.

[0053] The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated or understood by one of ordinary skill in the art.

[0054] Corresponding computer programs for implementing one or more steps of the methods disclosed herein are also within the present disclosure and may be encompassed by one or more of the described embodiments.

[0055] One or more of the computer programs, when executed on a computer, may cause the computer to configure any apparatus, including a battery, circuit, controller, or device disclosed herein, or to perform any method disclosed herein. One or more of the computer programs may be implemented in software, and the computer may be considered to be any suitable hardware, including, by way of non-limiting example, a digital signal processor, a microcontroller, and a read-only memory (ROM), an erasable programmable read-only memory (EPROM), or an electronically erasable programmable read-only memory (EEPROM). The software may also be an assembly program.

[0056] One or more of the computer programs may be provided on a computer-readable medium, which may be a physical computer-readable medium such as a disk or memory device, or may be embodied as a transient signal, which may be a network download, including an internet download.

[0057] The present disclosure includes one or more corresponding aspects, embodiments, or features, whether or not that combination or combination is specifically set forth (including claimed), singly or in various combinations. Corresponding means for carrying out one or more of the discussed functions are also within the scope of the present disclosure.

[0058] Throughout this specification, position, orientation, or motion descriptors such as "left," "right," "up," "down," "horizontal," and "vertical," as well as any adjective and adverbial derivatives thereof, are used to refer to the position, orientation, or motion of the devices as depicted in the drawings. However, such descriptors are not intended to be limiting in any way to the intended use of the invention as described or claimed.

[0059] The above summary is intended to be illustrative only and not limiting. [Brief explanation of the drawings]

[0060] The following description, by way of example only, refers to the accompanying schematic drawings, in which: [Figure 1a] FIG. 1a shows a different arrangement of a synchronous generator system. [Figure 1b] FIG. 1b shows a different arrangement of the synchronous generator system. [Figure 2] FIG. 2 illustrates, in schematic form, an exemplary excitation circuit. [Figure 3] FIG. 3 shows an exemplary excitation circuit. [Figure 4] FIG. 4 illustrates, in schematic form, another exemplary excitation circuit. [Figure 5a] FIG. 5a shows another exemplary excitation circuit. [Figure 5b] FIG. 5b shows another exemplary excitation circuit. [Figure 6] FIG. 6 shows a synchronous generator system including the excitation circuit of FIG. [Figure 7a] FIG. 7a shows the excitation circuit of FIG. 5 in a first mode of operation. [Figure 7b]FIG. 7b shows the excitation circuit of FIG. 5 in a second mode of operation. [Figure 7c] FIG. 7c shows the excitation circuit of FIG. 5 in a third mode of operation. [Figure 7d] FIG. 7d shows the excitation circuit of FIG. 5 in a fourth mode of operation. [Figure 7e] FIG. 7e shows the excitation circuit of FIG. 5 in a fifth mode of operation. [Figure 8] FIG. 8 shows the simulated response of the excitation circuits of FIGS. [Figure 9] FIG. 9 shows the measured response of the excitation circuits of FIGS. [Figure 10] FIG. 10 shows a further measured response of the excitation circuits of FIGS. [Figure 11] FIG. 11 shows a method of operating the excitation circuit of FIG. [Figure 12] FIG. 12 shows another exemplary excitation circuit. [Figure 13a] FIG. 13a shows the excitation circuit of FIG. 12 in a first mode of operation. [Figure 13b] FIG. 13b shows the excitation circuit of FIG. 12 in a second mode of operation. [Figure 13c] FIG. 13c shows the excitation circuit of FIG. 12 in a third mode of operation. [Figure 13d] FIG. 13d shows the excitation circuit of FIG. 12 in a fourth mode of operation. [Figure 13e] FIG. 13e shows the excitation circuit of FIG. 12 in a fifth mode of operation. [Figure 14] Figure 14 shows a simple exciter model. [Figure 15] FIG. 15 shows an exemplary arrangement of a synchronous generator system with a brushless excitation system. [Figure 16a] FIG. 16a shows in schematic form another exemplary excitation circuit. [Figure 16b] FIG. 16b shows the load characteristics of the exemplary excitation circuit of FIG. 16a. [Figure 17a]FIG. 17a shows in schematic form another exemplary excitation circuit. [Figure 17b] FIG. 17b shows the load characteristics of the exemplary excitation circuit of FIG. 17a. [Figure 18] FIG. 18 shows the output characteristic curve of the exemplary excitation circuit of FIG. 17a. [Figure 19a] FIG. 19a illustrates a portion of the exemplary excitation circuit of FIG. 17a in a first mode of operation. [Figure 19b] FIG. 19b shows a portion of the exemplary excitation circuit of FIG. 17a in a first mode of operation. [Figure 20a] FIG. 20a illustrates a portion of the exemplary excitation circuit of FIG. 17a in a second mode of operation. [Figure 20b] FIG. 20b illustrates a portion of the exemplary excitation circuit of FIG. 17a in a second mode of operation. [Figure 21a] FIG. 21a illustrates a portion of the exemplary excitation circuit of FIG. 17a in a third mode of operation. [Figure 21b] FIG. 21b illustrates a portion of the exemplary excitation circuit of FIG. 17a in a third mode of operation. [Figure 21c] FIG. 21c illustrates a portion of the exemplary excitation circuit of FIG. 17a in a third mode of operation. [Figure 21d] FIG. 21d illustrates a portion of the exemplary excitation circuit of FIG. 17a in a third mode of operation. [Figure 22a] FIG. 22a illustrates a portion of the exemplary excitation circuit of FIG. 17a in a fourth mode of operation. [Figure 22b] FIG. 22b illustrates a portion of the exemplary excitation circuit of FIG. 17a in a fourth mode of operation. [Figure 23a] FIG. 23a illustrates a portion of the exemplary excitation circuit of FIG. 17a in a fifth mode of operation. [Figure 23b] FIG. 23b shows a portion of the exemplary excitation circuit of FIG. 17a in a fifth mode of operation. [Figure 23c] FIG. 23c illustrates a portion of the exemplary excitation circuit of FIG. 17a in a fifth mode of operation. [Figure 23d] FIG. 23d illustrates a portion of the exemplary excitation circuit of FIG. 17a in a fifth mode of operation. DETAILED DESCRIPTION OF THE INVENTION

[0061] 1a-1b show in schematic form different arrangements of a synchronous generator system (synchronous generator excitation system).

[0062] 1a, a synchronous generator system 100 is shown comprising a generator 102 and an excitation circuit 104. The excitation circuit 104 is configured to sense and receive a signal indicative of the electrical output of the generator 102 (e.g., the power output or voltage output of the generator 102). In addition, the excitation circuit 104 is configured to receive a signal indicative of the electrical demand (e.g., the voltage demand) for the synchronous generator system and to provide a rectified output to a field winding of the generator 102 to provide a magnetizing current for the rotor of the generator 102, where the rectified output is based on the sensed electrical output of the generator 102 and the signal indicative of the electrical demand. In this manner, the excitation circuit 104 may regulate the electrical output of the generator 102.

[0063] 1b, a synchronous generator system 100 is shown comprising a generator 102, an excitation circuit 104, a sub-exciter 106, and a main exciter 108. The generator 102, excitation circuit 104, sub-exciter 106, and main exciter 108 are arranged and configured such that the sub-exciter 106 can serve as a power source for the main exciter 108, which serves as a power source for exciting the rotor of the generator 102.

[0064] More specifically, the excitation circuit 104 is configured to sense the electrical output of the generator 102 and receive power from the secondary exciter 106. Further, the excitation circuit 104 is configured to provide a rectified output to the primary exciter 108, where the rectified output is based on the sensed electrical output of the generator 102 and a signal indicative of electrical demand. In this manner, the excitation circuit 104 may regulate the electrical output of the generator 102.

[0065] The auxiliary exciter 106 is implemented as a dedicated AC generator with a permanent magnet generator mounted on the shaft 110 of the synchronous generator system 100. The main exciter 108 is an AC exciter that includes an armature (rotor) mounted on the shaft 110 of the synchronous generator system 100 and a stator. The rectified output of the excitation circuit 104 is provided to an exciter field winding on the stator of the main exciter 108 to generate electrical power. This electrical power is rectified by diodes 112 on the shaft of the synchronous generator system 100 to provide the excitation current for the generator 102.

[0066] The synchronous generator system 100 of Figure 1a may use a static excitation system, and the synchronous generator system 100 of Figure 1b may use a brushless excitation system.

[0067] 2 illustrates in schematic form an exemplary excitation circuit 204 for a synchronous machine, such as the synchronous generator system of FIG. 1a or 1b. The exemplary excitation circuit 204 includes a rectifier circuit 214 configured to convert an AC input to a direct current (DC) output, and a control circuit 216 configured to receive a first signal indicative of the electrical output of the synchronous machine, receive a second signal indicative of an electrical demand from a load device connected to the synchronous machine, and control the DC output based on the electrical demand indicated by the second signal and the electrical output indicated by the first signal.

[0068] Thus, the excitation circuit 204 is configured to regulate the electrical output of the synchronous machine, as can be appreciated from the previous discussion of Figures 1a-1b.

[0069] In some embodiments, the rectifier circuit 214 and the control circuit 216 may be implemented as modules of the excitation circuit 200. Referring to Figures 1a-1b, the excitation circuit 200 may include or be implemented as an automatic voltage regulator (AVR).

[0070] Figure 3 illustrates an exemplary excitation circuit 304 for a synchronous machine, corresponding to the excitation circuit of Figure 2. In particular, the excitation circuit 300 includes a rectifier circuit 314 configured to convert an alternating current (AC) input to a direct current (DC) output, and a control circuit 316 configured to receive a first signal indicative of the electrical output of the synchronous machine, receive a second signal indicative of an electrical demand from a load device connected to the synchronous machine, and adjust the DC output based on the electrical demand indicated by the second signal and the electrical output indicated by the first signal.

[0071] The control circuit 316 further comprises one or more insulated-gate bipolar transistors (IGBTs) 318a-318e and an automatic voltage regulator 320 configured to control the one or more IGBTs 318a-318e to regulate the DC output of the rectifier circuit 314.

[0072] Control circuit 316 further includes a capacitor 322 configured to protect one or more IGBTs 318a-318e from circuit inductance when the IGBTs are switched from an on state to an off state by automatic voltage regulator 320. That is, capacitor 322 allows one or more IGBTs 318a-318e to be turned off, or "commutated," without damage. Capacitor 322 is selected to be able to withstand the applied voltage and store the charge necessary to provide commutation.

[0073] The layout of the excitation circuit 304 may therefore represent an IGBT H-bridge.

[0074] As previously mentioned, the electrical output of a synchronous machine is regulated to meet the electrical demands of the load devices. In situations where the electrical output exceeds the electrical demands of the load devices, the synchronous machine should be responsive enough to quickly reduce its electrical output to avoid overload and damage to the load devices. Similarly, when the electrical demands of the load devices exceed the electrical output, the synchronous machine should be responsive enough to quickly increase its electrical output to avoid the load devices functioning incorrectly (or, more seriously, a brownout or blackout).

[0075] Such responsiveness may be hindered by inherent characteristics of synchronous generator systems, including the circuit inductance of the main exciter, which can result in a relatively long time constant for the response.

[0076] FIG. 4 illustrates, in schematic form, another exemplary excitation circuit 404 for a synchronous machine. The synchronous machine (or synchronous electric machine) may be a synchronous generator, a synchronous motor, or a synchronous condenser. Similar to the excitation circuits of FIGS. 2 and 3, the excitation circuit 404 of FIG. 4 includes, as an optional feature, a rectifier circuit 414 configured to convert an AC input to a DC output coupled to the synchronous machine, and a control circuit 416. Unlike the previous excitation circuits, the excitation circuit of FIG. 4 includes at least one charge storage device 424 configured to provide energy to the DC output, and the control circuit 416 is configured to receive a first signal indicative of an operating state of the synchronous machine, receive a second signal indicative of a control request for the synchronous machine, and provide at least a portion of the energy stored by the at least one charge storage device 424 to satisfy the control request indicated by the second signal when the control request indicated by the second signal exceeds a threshold capacity of the synchronous machine that would exist in the absence of the at least one charge storage device, and the synchronous machine is in an appropriate operating state as derived from the first signal.

[0077] The first signal may indicate a measured parameter of the operating state of the synchronous machine or a control or command signal for the excitation circuit (e.g., to enable the use of at least one charge storage device), and the second signal may indicate a parameter requirement of a control request for the synchronous machine.

[0078] The excitation circuit may or may not include a rectifier circuit configured to convert the AC input to a DC output. For example, in an abnormal situation where the AC input (supply signal) from a permanent magnet generator is unavailable, the system may operate from a DC input (supply signal), thereby eliminating the need for a rectifier circuit. In another embodiment, the system may include a DC power source and an AC power source, and the excitation circuit may include a rectifier circuit. In this scenario, the DC power source may be used as standby power if the AC power source (e.g., from a permanent magnet generator) becomes unavailable.

[0079] Thus, an excitation circuit for a synchronous machine comprises at least one charge storage device configured to supply energy to a DC output coupled to the synchronous machine; and a control circuit configured to receive a first signal indicative of an operating state of the synchronous machine, receive a second signal indicative of a control request for the synchronous machine, and supply at least a portion of the energy stored by the at least one charge storage device to satisfy the control request indicated by the second signal when the control request indicated by the second signal exceeds a threshold capacity of the synchronous machine that would be present in the absence of the at least one charge storage device and the synchronous machine is in a suitable operating state as derived from the first signal.

[0080] In one example, an excitation circuit for a synchronous machine may include at least one charge storage device configured to be discharged to a DC output; and a control circuit configured to receive a first signal indicative of an electrical output of the synchronous machine, receive a second signal indicative of an electrical demand from a load device connected to the synchronous machine, and discharge the at least one charge storage device when the electrical demand indicated by the second signal exceeds the electrical output indicated by the first signal.

[0081] The electrical output may be a voltage output, a current output, or a power output of the synchronous machine. The electrical demand may be a voltage demand, a current demand, a field voltage demand of an exciter machine, a power demand, or a demand characterized by the inductance (real or complex) of a load device coupled to the synchronous machine. The electrical demand may be expressed as a parameter indicative of the electrical demand (e.g., a power factor). The load may include an electrical load or a mechanical load. When the load includes a mechanical load, the exciter circuit and / or the synchronous machine may include means for converting the mechanical load into a signal indicative of the electrical demand.

[0082] As discussed in more detail below, with at least one charge storage device 422 and control circuit 416, excitation circuit 404 of Figure 4 may advantageously achieve a higher, more dynamic DC output ceiling compared to the excitation circuits of Figures 2-3. Thus, excitation circuit 404 of Figure 4 may improve the ability of the synchronous machine to respond to changes in load demand.

[0083] In at least one embodiment, the control circuit 404 may be further configured to receive a third signal indicative of an amount of charge stored by the at least one charge storage device 424, and to initiate charging of the at least one charge storage device 424 when the amount of stored charge indicated by the third signal falls below a predetermined threshold and the power output indicated by the first signal meets the power demand indicated by the second signal. The power output indicated by the first signal may be a generator power output. In this manner, the control circuit 404 may know to prepare the at least one charge storage 424 for discharge without placing undue demands on the synchronous machine.

[0084] The control circuit may be configured to initiate charging of the at least one charge storage device by an AC input and / or a load device (in this example, an exciter field winding). The AC input may be provided by an AC power source, such as a sub-exciter (e.g., a permanent magnet generator) of a synchronous generator system.

[0085] In at least one embodiment, the first signal may be indicative of a measured parameter of the operating state of the synchronous machine, and the control circuitry 404 may be further configured to discharge the at least one charge storage device 424 when the electrical demand indicated by the second signal exceeds the electrical output indicated by the first signal by a predetermined amount, which may be an absolute amount or a relative amount. Similarly, in at least one embodiment, the first signal may be indicative of a measured parameter of the operating state of the synchronous machine, and the control circuitry 404 may be configured to discharge the at least one charge storage device 424 when the electrical demand indicated by the second signal exceeds the electrical output indicated by the first signal for a predetermined period of time, e.g., 0.05 seconds, 0.1 seconds, 0.5 seconds, or 1 second.

[0086] Thus, the control circuit 404 may be configured to prevent transient load changes (and / or small variations in load magnitude) from causing the at least one charge storage device 424 to discharge.

[0087] In at least one embodiment, the control circuit 404 may be configured to electrically isolate the at least one charge storage device 424 from the DC output when the electrical output indicated by the first signal meets the electrical demand indicated by the second signal.

[0088] In at least one embodiment, the DC output may be a positive or negative voltage, and the AC input may be a three-phase or single-phase signal.

[0089] In at least one embodiment, the first signal includes a voltage output, a current output, and / or a power output of the synchronous machine, and the second signal includes a voltage demand, a current demand, a power demand, and / or an inductance (real or complex) demand and / or reflects a power factor from a load device connected to the synchronous machine, the load including an electrical load or a mechanical load.

[0090] Figures 5a-5b illustrate an exemplary excitation circuit 504 for a synchronous machine corresponding to the excitation circuit of Figure 4. Figure 5a illustrates the excitation circuit 504 including a rectifier circuit 514 configured to convert an AC input to a DC output, at least one charge storage device 524 configured to provide energy to the DC output, and a control circuit 516 configured to receive a first signal indicative of an operating state of the synchronous machine, receive a second signal indicative of a control request for the synchronous machine, and provide at least a portion of the energy stored by the at least one charge storage device 524 to satisfy the control request indicated by the second signal when the control request indicated by the second signal exceeds a threshold capacity of the synchronous machine that would be present in the absence of the at least one charge storage device and when the synchronous machine is in a suitable operating state as derived from the first signal.

[0091] Control circuit 516 further comprises one or more IGBTs 518a-518g and an automatic voltage regulator 520 configured to control the one or more IGBTs 518a-518g to provide a DC output from the voltage on capacitor 522, optionally in combination with a voltage from at least one charge storage device 524. More generally, automatic voltage regulator 520 is configured to control one or more insulated gate bipolar transistors 518a-518g to adjust the polarity (positive or negative) of the DC output.

[0092] The control circuit 516 further comprises a capacitor 522 configured to protect the IGBT from circuit inductance when the IGBT is switched from an on state to an off state by the automatic voltage regulator 520 .

[0093] The transistor and capacitor examples shown in Figure 5a are not intended to limit the scope of the present disclosure. That is, one or more IGBTs 518a-518g may, in some embodiments, be implemented as one or more transistor devices, with or without a capacitor configured to protect the one or more transistors from circuit inductance during switching. For example, the one or more transistor devices may be field-effect transistor amplifiers or metal-oxide-semiconductor field-effect transistors. Alternatively, one or more thyristors may be used.

[0094] In at least one embodiment, the at least one charge storage device 524 includes one or more capacitors, batteries, or battery-capacitor hybrids 322. Suitable component ratings for the at least one charge storage device 524 may include a capacitance of 50 mF, a maximum operating voltage of 500 V, a maximum rated leakage current of 6 mA, and a maximum ripple current of 20 A. The use of a limited energy reservoir, such as a capacitor, across a continuous energy source reduces the risk of voltage overload, which may prevent damage to the generator or main exciter of a synchronous generator system.

[0095] 5a shows AC input terminals 526a-526c and DC output terminals 528a-528b, which may be included in excitation circuit 504. Respectively, AC input terminals 526a-526c and DC output terminals 528a-528b may be configured to receive a portion of the alternating current (AC) power output of the sub-exciter and provide a DC output to an exciter field winding on the stator of the main exciter, as described above with respect to FIG. 1b.

[0096] 5b shows an optional implementation of at least one charge storage device 524 in an expanded view, in which four charge storage devices 524a-524d are connected in parallel. Whether all four charge storage devices (or one, two, or three charge storage devices) 524a-524d are present in the excitation circuit 504 depends on the specifications and requirements of the synchronous machine with which the excitation circuit is used. All four charge storage devices 524a-524d may be required in a larger synchronous machine, while a smaller synchronous machine may require only one or two charge storage devices, for example. Of course, alternative applications may require five or more charge storage devices.

[0097] Figure 6 shows a synchronous generator system 600 including the excitation circuit of Figure 5 as an example of a synchronous machine. The synchronous generator system 600 includes a generator 602, an excitation circuit 604, a sub-exciter 606, a main exciter 608, a shaft 610, and one or more diodes (e.g., diode rectifiers) 612 attached to the shaft 610. The synchronous generator system 600 further includes a current sensor 626 and a voltage sensor 628 coupled to the generator 602 and the excitation circuit 604.

[0098] The excitation circuit 604 includes a rectifier circuit 614 and a control circuit 616, which includes one or more insulated gate bipolar transistors 618a-618g, an automatic voltage regulator 620, a capacitor 622, and at least one charge storage device 624.

[0099] The general principles of operation of the synchronous generator system 600 and excitation circuit 604 are as described with respect to Figures 1b and 5. In additional detail, the control circuit 616 may be understood to receive a first signal indicative of the electrical output of the synchronous generator system via a current sensor 626 and / or a voltage sensor 628. Similarly, the automatic voltage regulator 620 may be understood to control one or more insulated gate bipolar transistors 618a-618g with control signals, for example, control signals 630a-630b.

[0100] To further understand the operating principles of the excitation circuit of Figure 5, Figures 7a-7e illustrate a portion of the control circuit according to five modes of operation. More specifically, Figures 7a-7e focus on the operating modes of one or more insulated gate bipolar transistors (IGBTs) 718a-718e, a capacitor 722, and at least one charge storage device 724, as well as DC output terminals 728a-728b. The presence of the remaining components of the excitation circuit of Figure 5 is implicit.

[0101] FIG. 7a shows a portion of the control circuit 716 in a first operating mode, which provides a positive DC output voltage to the main exciter field via DC output terminals 728a-728b. This is the mode in which the excitation circuit operates during steady-state operation of the generator, i.e., normal mode. The DC output voltage can vary between zero and the rectified input supply voltage. In this mode, V1, V3, and V7 (i.e., IGBTs 718a, 718c, and 718g) are permanently on, and V5 (i.e., IGBT 718e) is permanently off. V2 (i.e., IGBT 718b) is driven by a pulse width modulation (PWM) signal from the automatic voltage regulator to control the DC output voltage to the exciter field. The current flow through the control circuit follows a yellow / orange (first / second hatching) path when V2 (i.e., the IGBT with reference number 718b) is on, and follows a pink / orange (third / second hatching) path when V2 (i.e., the IGBT with reference number 718b) is off.

[0102] 7b shows a portion of the control circuit 716 in a second operating mode, which provides a positive DC voltage to the main exciter field via DC output terminals 728a-728b. In this mode, the at least one charge storage device 724 is switched by the control circuit to discharge to the DC output to provide a greater positive voltage than possible in the first operating mode (i.e., a higher DC voltage limit is achieved even after accounting for capacitor 722). The voltage provided to the DC output terminals 728a-728b can vary between zero voltage and the input supply voltage plus the voltage provided by the at least one charge storage device 724.

[0103] In the second mode, V1, V5, and V7 (i.e., the IGBTs with reference numbers 718a, 718e, and 718g) are permanently on, and V3 (i.e., the IGBT with reference number 718c) is permanently off. V2 (i.e., the IGBT with reference number 718b) is driven by a PWM signal to control the voltage to the exciter field. The current in the exciter field follows a yellow / orange (first / second hatching) path when V2 (i.e., the IGBT with reference number 718b) is on, and follows a pink / orange (third / second hatching) path when V2 (i.e., the IGBT with reference number 718b) is off.

[0104] FIG. 7c shows a portion of the control circuit 716 in a third operating mode, which provides a positive DC voltage to the main exciter field via DC output terminals 728a-728b. This mode provides the same voltage range to the exciter field as the first operating mode. That is, the provided voltage can vary between zero and the input supply voltage. However, the freewheeling current when V2 (i.e., the IGBT with reference number 718b) is off is switched to charge at least one charge storage device 724. That is, a path for current decay through the inductive load device is provided elsewhere through the control circuit 716. The voltage to which the at least one charge storage device 724 is charged may be determined by a programmable setting within the control circuit, which may be implemented via an automatic voltage regulator.

[0105] In the third mode, V1 and V7 (i.e., IGBTs 718a and 718g) are permanently on, and V3 and V5 (i.e., IGBTs 718c and 718e) are permanently off. V2 (i.e., IGBT 718b) is driven by a PWM signal to control the voltage to the exciter field via DC output terminals 728a-728b. Current in the exciter field follows a yellow / orange (first / second hatching) path when V2 (i.e., IGBT 718b) is on, and follows a pink / orange (third / second hatching) path when V2 (i.e., IGBT 718b) is off. Thus, in at least one embodiment, the control circuit 716 is configured to charge at least one charge storage device 724 using a load device (in this embodiment, the exciter field winding) connected to the synchronous machine.

[0106] 7d shows a portion of the control circuit 716 in a fourth operating mode, which provides a negative DC voltage to the main exciter field via DC output terminals 728a-728b. The provided voltage can vary between zero volts and the negative input supply voltage. In this mode, capacitor 722 is charged via the path highlighted in yellow (first hatching).

[0107] In the fourth mode, V3 and V7 (i.e., IGBTs 718c and 718g) are permanently on, and V1 and V5 (i.e., IGBTs 718a and 718e) are permanently off. V2 (i.e., IGBT 718b) is driven by a PWM signal to control the voltage to the exciter field. Current in the exciter field follows a pink / orange (third / second hatching) path when V2 (i.e., IGBT 718b) is on, and follows a yellow / orange path (first / second hatching) when V2 (i.e., IGBT 718b) is off.

[0108] 7e shows a portion of the control circuit 716 in a fifth operating mode, which provides a negative DC boost voltage to the main exciter field via DC output terminals 728a-728b. In this mode, at least one charge storage device 724 is switched to a DC output by the control circuit to provide a greater negative voltage than was possible in the fourth operating mode (i.e., even after accounting for capacitor 722). The voltage provided to the DC output terminals 728a-728b can vary between zero volts and the negative input supply voltage (provided by capacitor 722) plus the negative voltage provided by the at least one charge storage device 724. In this mode, capacitor 722 and at least one charge storage device 724 are charged via the path highlighted in yellow (first hatching).

[0109] In the fifth mode, V7 (i.e., the IGBT with reference number 718g) is permanently on, and V1, V3, and V5 (i.e., the IGBTs with reference numbers 718a, 718c, and 718e) are permanently off. V2 (i.e., the IGBT with reference number 718b) is driven by a PWM signal to control the voltage to the exciter field. Current in the exciter field follows a pink / orange (third / second hatching) path when V2 (i.e., the IGBT with reference number 718b) is on, and follows a yellow / orange path (first / second hatching) when V2 (i.e., the IGBT with reference number 718b) is off.

[0110] Thus, in at least one embodiment, the automatic voltage regulator may be configured to apply pulse width modulation to control the DC output of the excitation circuit.

[0111] Thus, the first normal operating mode, as introduced above, corresponds to the control circuit electrically isolating the at least one charge storage device 724 from the DC output when the electrical output indicated by the first signal meets the electrical demand indicated by the second signal. Similarly, the second operating mode corresponds to the control circuit discharging the at least one charge storage device 724 to the DC output when the electrical demand indicated by the second signal exceeds the electrical output indicated by the first signal, thereby providing a DC output "boost." The third operating mode corresponds to the control circuit receiving a third signal indicative of the amount of charge stored by the at least one charge storage device 724 and beginning to charge the at least one charge storage device 724 when the amount of stored charge indicated by the third signal is below a predetermined threshold and the electrical output indicated by the first signal meets the electrical demand indicated by the second signal.

[0112] The negative DC voltage provided by the fourth and fifth operating modes allows the control circuit to reduce the "forced" positive DC voltage to the synchronous machine (see first and second modes) to prevent current spikes from overloading the system. Like the second operating mode, the fifth operating mode provides a larger DC voltage upper limit, albeit of negative polarity, to provide a faster reduction in the forced positive voltage.

[0113] Figure 8 shows the simulated response of an exciter with the excitation circuit of Figure 3 or Figure 5. The response was simulated by LTspice® under a DC supply voltage of 300V, a load of 7Ω, and an inductance of 14H to represent the resistance and inductance, respectively, of the brushless exciter field winding. For the excitation circuit of Figure 5, a capacitance of 10mF was assumed for the at least one charge storage device 724.

[0114] In the top panel of Figure 8a, the voltage response of the excitation circuit of Figure 3 (trace 830 shown by a red or solid line) is compared to the voltage response of the excitation circuit of Figure 5 (trace 832 shown by a cyan or dashed line) under the simulation conditions shown above. The bottom panel of Figure 8b shows the corresponding current responses, i.e., the voltage response of the excitation circuit of Figure 3 (trace 834 shown by a green or solid line) and the excitation circuit of Figure 5 (trace 836 shown by a blue or dashed line). As can be seen, the excitation circuit of Figure 5 provides a voltage "boost" when switched compared to the excitation circuit of Figure 3, providing faster rise and fall times to steady-state current.

[0115] FIG. 9 shows the measured response of an exciter with the excitation circuit of FIG. 3 or FIG. 5 under conditions consistent with those considered for the simulation (requested exciter field current step from 6.5 A to 13 A at time 1 second and from 13 A to 0 A at 3.5 seconds). The top panel of FIG. 9a shows the voltage response 930 of the excitation circuit of FIG. 3 (shown by a red or dashed line) and the voltage response 932 of the excitation circuit of FIG. 5 (shown by a blue or solid line). The bottom panel of FIG. 9b shows the current response, i.e., the excitation circuit of FIG. 3 (trace 934 shown by a red or dashed line) and the current response of the excitation circuit of FIG. 5 (trace 936 shown by a blue or solid line).

[0116] Figure 10 shows further measured responses of the excitation circuits of Figures 3 and 5 under conditions corresponding to those considered for the simulations. The top panel of Figure 10a shows the voltage response 1032 of the excitation circuit of Figure 5. The bottom panel of Figure 10b shows the current response, i.e., the current response of the excitation circuit of Figure 3 (trace 1034 shown by a red or solid line) and the excitation circuit of Figure 5 (trace 1036 shown by a blue or dashed line).

[0117] The measured responses shown in FIGS. 9 and 10 are close to the simulated response shown in FIG. 8, demonstrating the advantageous properties of the excitation circuit of FIG. 5 over the excitation circuit of FIG.

[0118] Figure 11 illustrates a method 1140 of operating the excitation circuit of Figure 5. The method, which is also applicable to operating excitation circuits according to Figures 4, 7, 12, 13, and 17, includes receiving 1142 a first signal indicative of an operating state of the synchronous machine, receiving 1144 a second signal indicative of a control request of the synchronous machine, and, when the control request indicated by the second signal exceeds a threshold capacity of the synchronous machine that would exist in the absence of the at least one charge storage device and the synchronous machine is in a suitable operating state as derived from the first signal, providing 1146 at least a portion of the energy stored by the at least one charge storage device to satisfy the control request indicated by the second signal.

[0119] The first signal may indicate measured parameters of the operating state of the synchronous machine, the measured parameters including at least one of a voltage output, a current output, and a power output of the synchronous machine, and one or more of a voltage demand, a current demand, a power demand, an inductance demand, and a power factor from a load device connected to the synchronous machine, and the second signal may indicate parameter requirements of control demands of the synchronous machine, the parameter requirements including at least one of a field voltage and / or a field current of an exciter machine of the synchronous machine, an input, an output, and / or one or more internal values ​​of an automatic voltage regulator configured to control the synchronous machine, a voltage and / or a current provided by a generator of the synchronous machine, a real inductance demand or a complex inductance demand of the synchronous machine, and a power factor from a load device connected to the synchronous machine.

[0120] Figure 12 shows an example excitation circuit 1204 for a synchronous machine, corresponding to the excitation circuits shown in Figures 4-6 and 7a-7e. In particular, excitation circuit 1204 includes a rectifier circuit 1214, at least one charge storage device 1224 (illustrated as capacitor "C2" and may otherwise be referred to as a boost capacitor), and a control circuit 1216, which includes one or more transistors 1218a-1218f and a capacitor 1222 (illustrated as capacitor "C1"). As shown, excitation circuit 1204 further includes input terminals 1226a-1226c and DC output terminals 1228a-1228b, which may be connected to an inductive load device 1250.

[0121] The excitation circuit 1204 (which may also be called a converter) may be supplied with an AC three-phase voltage or a single-phase voltage. As a standby power supply, AC voltage and DC voltage may be used.

[0122] The rectifier circuit 1214 feeds the capacitor 1222. The at least one charge storage device 1224 is used for voltage boosting and is charged by switching off the transistors V2, V3 (i.e., the transistors having reference numerals 1218b and 1218c) and the inductive load device 1250. The at least one charge storage device 1224 is used only temporarily when it is necessary to increase the electrical output of the synchronous machine to its maximum electrical output and when a rapid increase in electrical output is required. The capacitor 1222 is charged to a predetermined value during normal operating mode.

[0123] One or more of the transistors 1218a-1218f may include IGBT transistors, although one skilled in the art will recognize that other types of switching devices may be used if desired.

[0124] One or more of the transistors 1218a-1218f may be controlled by an AVR (not shown) that implements (or includes) the excitation circuit 1204. Based on voltage measurements and other quantities, the AVR may control one or more of the transistors 1218a-1218f via the control circuit 1216.

[0125] The excitation circuit 1204 is applicable to the excitation system of a brushless synchronous generator, a synchronous motor, or a synchronous compensator, where a high initial electrical output response is required. Nevertheless, the excitation circuit 1204 may also be used in alternative applications with similar requirements. The excitation circuit 1204 discharges at least one charge storage device 1224 to temporarily increase the electrical output of the excitation system. This allows for a significantly accelerated increase in electrical output to the inductive load compared to existing solutions. The excitation circuit 1204 may also charge the at least one charge storage device 1224 without using any additional power source to the synchronous machine. The excitation circuit 1204 may also facilitate fast de-excitation of the inductive load.

[0126] 4-6, 7a-7e, or 12 may improve the dynamic behavior of the entire circuit (i.e., the synchronous machine with the exemplary excitation circuit and inductive load device). A further advantage of using at least one charge storage device rather than a dedicated charge source is that the latter is self-limiting and, once discharged, there is no longer any risk of overloading the synchronous machine.

[0127] For example, an excitation circuit such as that described in Figures 4-6, 7a-7e, or 12 may be included in a synchronous generator system that includes a main generator and a secondary exciter (e.g., a permanent magnet generator) coupled to the rotor shaft of the main generator and configured to provide an AC input. The output terminals of the permanent magnet generator, or any other component of the synchronous machine capable of providing an AC input, may be coupled to the input terminals of the rectifier circuit, thereby providing an AC power source for charging at least one charge storage device. Advantageously, this avoids the need for any separate external power source for charging the at least one charge storage device.

[0128] To further understand the operating principles of the excitation circuit of Figure 12, Figures 13a-13e illustrate a portion of control circuit 1316 through five modes of operation. More specifically, Figures 13a-13e focus on the operating modes of one or more transistors 1318a-1318e, capacitor 1322, at least one charge storage device 1324, DC output terminals 1328a-1328b, and inductive load device 1350. The presence of the remaining components of the excitation circuit of Figure 12 is implicit.

[0129] 13a shows a portion of control circuit 1316 in a first excitation mode of operation, which provides a positive output voltage ranging from zero to a positive voltage determined by capacitor 1322. The output voltage at DC output terminals 1328a-b may be steady-state (i.e., conceptually "permanent" during normal operation).

[0130] The operation of one or more transistors 1318a-1318e in the first mode of operation is as follows: V1 (i.e., the transistor having reference number 1318a and represented schematically as a switch) is switched on, V2 (transistor having reference number 1318b) is used for PWM to determine the output voltage, V3 (i.e., the transistor having reference number 1318c and represented schematically as a switch) is switched on, and V5 (not shown) is switched off.

[0131] The predicted output voltage over time at DC output terminals 1328a-1328b during the first operating mode is shown by red or solid trace 1340 representing the steady state output voltage (at DC output terminal designated by reference numeral 1328b) and green or dashed trace 1342 representing the pulse width modulated output voltage (at DC output terminal designated by reference numeral 1328a).

[0132] 13b shows a portion of the control circuit 1316 in a second, energized, mode of operation, which provides a positive output voltage ranging from zero to a voltage determined by a capacitor 1322. This output voltage may be steady-state, as described in connection with the first mode of operation. Additionally, at least one charge storage device 1324 is charged. After the at least one charge storage device 1324 is charged to a required level, it is left in this state.

[0133] The operation of one or more transistors 1318a-1318e in the second mode of operation is as follows: V1 (i.e., the transistor having reference number 1318a and represented schematically as a switch) is switched on, V2 (transistor having reference number 1318b) is used for PWM to determine the output voltage, V3 (not shown) is switched off, and V5 (not shown) is switched off.

[0134] The predicted output voltage over time at DC output terminals 1328a-1328b during the second operating mode is shown by red or solid trace 1344 representing the steady state output voltage (at DC output terminal designated by reference numeral 1328b) and green or dashed trace 1346 representing the pulse width modulated output voltage (at DC output terminal designated by reference numeral 1328a).

[0135] 13c shows a portion of the control circuit 1316 in a third excitation with boost mode of operation, which provides an output voltage ranging from zero to a voltage determined by the capacitor 1322 and the at least one charge storage device 1324. This output voltage may be supplied only during periods when the at least one charge storage device 1324 is being discharged.

[0136] The operation of one or more transistors 1318a-1318e in the third mode of operation is as follows: V1 (i.e., the transistor having reference numeral 1318a and represented schematically as a switch) is switched on, V2 (i.e., the transistor having reference numeral 1318b) is used for PWM to determine the output voltage, V3 (not shown) is switched off, and V5 (i.e., the transistor having reference numeral 1318e and represented schematically as a switch) is switched off.

[0137] The predicted output voltage over time at DC output terminals 1328a-1328b during the third operating mode is shown by red or solid trace 1348, which represents the steady-state output voltage (at DC output terminal designated by reference numeral 1328b), and by green or dashed trace 1350, which represents the pulse-width modulated output voltage (at DC output terminal designated by reference numeral 1328a).

[0138] FIG. 13d shows a portion of the control circuit 1316 in a fourth de-energizing mode of operation, which provides a negative output voltage as long as positive current flows through the inductive load device 1350. The output voltage ranges from zero to a negative voltage determined by the capacitor 1322. When the voltage across the capacitor 1322 reaches the maximum allowable voltage, the transistor V4 (compare the transistor having reference designation 1218d in FIG. 12) is switched on to provide an additional path for current flow (e.g., via a resistor connected in parallel with the capacitor 1322). Thus, switching on the transistor V4 facilitates reducing the voltage across the capacitor 1322.

[0139] The operation of one or more transistors 1318a-1318e in the fourth mode of operation is as follows: V1 (not shown) is switched off, V2 (i.e., transistor with reference numeral 1318b) is used for PWM to determine the output voltage, V3 (i.e., transistor with reference numeral 1318c and represented schematically as a switch) is switched on, V5 (not shown) is switched off, and V4 (not shown) is switched on when the voltage across capacitor 1322 reaches the maximum allowed voltage.

[0140] The predicted output voltage over time at DC output terminals 1328a-1328b during the fourth operating mode is shown by a red or solid trace 1352 representing the steady state output voltage (at the DC output terminal designated by reference numeral 1328b) and a green or dashed trace 1354 representing the pulse width modulated output voltage (at the DC output terminal designated by reference numeral 1328a).

[0141] FIG. 13e shows a portion of the control circuit 1316 in a fifth fast de-energization mode of operation, which also provides a negative output voltage as long as positive current flows through the inductive load 1350. The output voltage ranges from zero to a negative voltage determined by the capacitor 1322 and the at least one charge storage device 1324. If the voltage across the capacitor 1322 or the at least one charge storage device 1324 reaches the maximum allowable voltage, transistor V4 (compare transistor having reference number 1218d in FIG. 12) or transistor V6 (compare transistor having reference number 1218f in FIG. 12) is switched on to provide an additional path for current flow (e.g., via a resistor connected in parallel with the capacitor 1322 or the at least one charge storage device 1324). Thus, switching on transistor V4 or transistor V6 facilitates reducing the voltage across the capacitor 1322 or the at least one charge storage device 1324, respectively.

[0142] The operation of one or more transistors 1318a-1318e in the fifth mode of operation is as follows: V1 (not shown) is switched off, V2 (i.e., transistor 1318b) is used for PWM to determine the output voltage, V3 (not shown) is switched on, V5 (not shown) is switched off, V4 (not shown) is switched on when the voltage across capacitor 1322 reaches the maximum allowed voltage, and V6 (not shown) is switched on when the voltage across at least one charge storage device 1324 reaches the maximum allowed voltage.

[0143] The predicted output voltage over time at DC output terminals 1328a-1328b during the fourth operating mode is shown by a red or solid trace 1356 representing the steady state output voltage (at the DC output terminal designated by reference numeral 1328b) and a green or dashed trace 1358 representing the pulse width modulated output voltage (at the DC output terminal designated by reference numeral 1328a).

[0144] Transistors V4 and V6 (compare transistors having reference numbers 1218d and 1218f in FIG. 12) may be referred to as or otherwise function as "chopper" transistors. In at least one embodiment, the control circuit may include a seventh transistor (compare IGBT having reference number 518g in FIG. 5a) configured to function as a soft switch for the excitation circuit to reduce peak currents at start-up.

[0145] 14 illustrates a simplified exciter model 1460 to aid in understanding the technical effect of one or more example exciter circuits disclosed herein. The simplified exciter model 1460 includes an inductor L, which represents the inductance of the exciter's field circuit, and a resistance of the exciter's field circuit, respectively. f 1462 and resistor R f 1464. The exciter field current is I d , 1466, and the exciter output voltage is U i , 1468. Exciter output voltage U i 1448 is the exciter field current I d It is roughly proportional to 1466.

[0146] The time constant of the exciter is τ f =L f / R f and is physically associated with the exciter field winding. DC voltage U d is applied to the exciter field winding, the exciter field current 1466 (and therefore also the exciter output voltage 1468) is d / dt=Ud / L f Therefore, the applied voltage U d An increase in θ will increase the corresponding rate of change of current in the exciter's field coil.

[0147] Thus, the exemplary excitation circuits as described with reference to FIGS. 4, 7, 12, 13, and 17 provide an excitation voltage U dThe first signal may provide a temporary increase in the exciter voltage, with a corresponding shortening (or improvement) of the exciter response. For example, the temporary increase may be followed by (or achieved by) a control circuit configured to provide at least a portion of the energy stored by the at least one charge storage device when the generator operating condition indicated by the first signal does not meet the required value indicated by the second signal, which increases the voltage across the exciter field coil and the corresponding rate of change of current in the exciter field coil. The first signal and the second signal may be voltage signals.

[0148] Further understanding of this technical effect can be found in "IEEE Recommended Practice for Excitation System Models for Power System Stability Studies," IEEE Std 421.5-2016 (a revision of IEEE Std 421.5-2005), pp. 1-207, August 26, 2016, specifically the discussion of excitation system model type AC5A and automatic voltage regulator model AC7.

[0149] 15 shows an exemplary arrangement of a synchronous generator system 1500 with a brushless excitation system. The synchronous generator system 1500 includes a permanent magnet generator (PMG) 1572, a brushless exciter with an exciter field winding (stator) 1574a, an exciter armature winding (rotor) 1574b, and a rotating rectifier 1574c, a synchronous generator with a synchronous generator armature 1576a and a synchronous generator field winding 1576b, a current sense transformer 1578 and a voltage sense transformer 1580 (located at the generator power output in this example), and a generator switch 1582. In this example, the synchronous generator system 1500 is connected to a power grid 1584 via the generator switch 1582.

[0150] The synchronous generator system 1500 further includes an excitation circuit, which may also be referred to as an excitation circuit 1586, which is typically powered by a permanent magnet generator 1572. The excitation circuit includes an automatic voltage regulator 1530 with a pulse power converter control 1588, a current shunt 1590, and a power converter 1592.

[0151] Automatic voltage regulator 1530 is configured to receive signals indicative of generator quantity (via current sense transformer 1578 and voltage sense transformer 1580) and signals indicative of exciter field current (via shunt 1590). Based on the received signals, automatic voltage regulator 1530 controls power converter 1592 to maintain the appropriate voltage on the generator field winding.

[0152] The synchronous generator system 1500 shown in Figure 15 may have a wide range of applications. The excitation system may be provided as a rotary exciter (e.g., a brushless exciter as described above), a system with a DC exciter, or a system with an AC exciter and a fixed diode rectifier.

[0153] In an excitation system that includes a rotating exciter, the rotating exciter is located between the power converter 1592 and the synchronous generator field winding 1576b and has a non-negligible time constant (defined with reference to a simple exciter model shown in FIG. 14). As a result, the rotating exciter may introduce a significant delay in the time between a change in the output voltage of the power converter 1592 and a change in the voltage on the synchronous generator field winding 1576b.

[0154] When the generator switch 1582 is in the "on" position, it is important for generator stability that the generator field voltage respond to the voltage demand from the load devices coupled to the generator not only in steady state operation but also during transient conditions caused by disturbances in electrical demand.

[0155] FIG. 16a illustrates, in schematic form, another exemplary excitation circuit 1604. The excitation circuit 1616 is based on a two-quadrant power converter half-controlled IGBT H-bridge and includes input terminals 1626a-1626b and a control circuit 1616 including a rectifier 1694, a smoothing capacitor 1622, and an overvoltage protection circuit 1614. The input terminals 1626a-1626b are configured to receive a supply voltage from, for example, a permanent magnet generator, a transformer powered by a generator armature, an auxiliary bus, or a station battery. The supply voltage is rectified by the rectifier 1694 and smoothed by the smoothing capacitor 1622. The overvoltage protection circuit 1614 is disposed in parallel with the smoothing capacitor 1622 and configured to protect the smoothing capacitor 1622 from overvoltages or reverse polarity voltages.

[0156] The control circuit 1616 further comprises electronic switches (IGBT transistors, MOSFET transistors) 1618a-1618b and diodes 1696a-1696b that determine the internal voltage across the smoothing capacitor 1622 by control signals from a pulse width modulation (PWM) unit 1698. Specifically, the PWM unit 1698 is configured to control the internal voltage through control signals to the electronic switches 1618a-1618b that are delivered via PWM unit outputs 16002, 16004.

[0157] The excitation circuit 1604 further comprises output terminals 1628a-1628b and an AVR 16006. In use, the voltage across the output terminals is coupled to the field winding of the exciter 16008, and is used to generate the supply voltage and the output voltage U r Proportional to 16010.

[0158] Figure 16b shows the load characteristics of the exemplary excitation circuit of Figure 16a. According to these load characteristics, the output current varies from 0 A to a voltage U across the smoothing capacitor 1622. C1 is divided by the resistance of the exciter field winding 16008 along with any interconnecting wiring to obtain the limited value I dmax is limited to only one polarity.

[0159] The output voltage, i.e. the voltage across the output terminals 1628a-1628b, may have a positive or negative polarity. The maximum possible average value of the output voltage corresponds approximately to the voltage on the smoothing capacitor 1622.

[0160] A load characteristic with a positive output voltage corresponds to the normal operating mode of the excitation circuit 16012. A load characteristic with a negative output voltage corresponds to the transient operating mode of the excitation circuit 16014, which is used when the current through the exciter field winding is decreasing, i.e., when energy is removed from the exciter field winding.

[0161] Further aspects of providing at least a portion of the energy stored by at least one charge storage device to satisfy the control demand indicated by the second signal will now be described with reference to FIG. 11, it being understood that these aspects may be realized in various combinations thereof by the exemplary excitation circuits shown schematically in FIGS. 4, 5, 7, 12, and 13.

[0162] Figure 17a illustrates in schematic form another exemplary excitation circuit 1704 that corresponds to the exemplary excitation circuits illustrated generally in Figures 4, 5, 7, 12, and 13. Description of similar features to the exemplary excitation circuit illustrated generally in Figure 16 is omitted for the sake of brevity.

[0163] Additional features of control circuit 1716 relative to the control circuit shown in FIG. 16 are electronic switches 1718c, 1718e, diodes 1796c-1796d, at least one charge storage device 1724, and diode 17140 configured to provide additional overvoltage protection to the excitation circuit.

[0164] Additional features of the PWM unit include outputs 17016, 17018 that provide control signals to additional electronic switches 1718c, 1718e, and inputs 17020, 17022, respectively, for sensing the voltage across a smoothing capacitor and at least one charge storage device 1724. The PWM unit is also further configured to receive a control signal HDC ENABLE 17024.

[0165] The control signal 17024 may indicate the operating state of the generator and may be used to enhance the control function of the PWM unit to provide an additional (boost) operating mode of the excitation circuit 1704. The inputs 17020, 17022 of the PWM unit are used for linearizing the control characteristic and for smooth switching between these operating modes.

[0166] The control signal 17024 may be derived from the position of a generator switch (e.g., corresponding to the generator being connected to the grid) or from a minimum level of generator output, or may be independent of the generator's operating state (i.e., the control signal 17024 is always active).

[0167] The output voltage 16010 and the control signal 17024 are both voltage signals. The control signal 17024 enables the boost function of the excitation circuit 1716, but any requirements of the excitation circuit 1716 on input power (determined by the power provided by the PMG) remain the same as the exemplary excitation circuit shown in FIG.

[0168] The output voltage 16010 may indicate the desired value of the field voltage generated by the exciter field coil. The output voltage 16010 is the output of the automatic voltage regulator and may depend on the desired generator voltage, the actual generator voltage, the generator output current, the exciter field current gain, and the integral gain of the automatic voltage regulator, and may be affected by the output of the power system stabilizer and / or the activity of the limiters included in the automatic voltage regulator.

[0169] FIG. 17b shows load characteristics 17012, 17014, 17026-17030 of the exemplary excitation circuit of FIG. 17a. Similar to the load characteristics of the exemplary excitation circuit shown in FIG. 16, the output current varies from 0 A to a value I dmax limited to one polarity within the range (I dmax (where ω is as defined above). The output voltage may have a positive or negative polarity. Also, when control signal 17024 is not used (i.e., is "off"), the maximum possible average value of the output voltage corresponds approximately to the voltage on the smoothing capacitor.

[0170] In contrast to the load characteristics of the exemplary excitation circuit shown in FIG. 16, when the control signal 17024 is in use (i.e., “on”), the maximum possible average value of the output voltage corresponds approximately to the voltage on the smoothing capacitor and the voltage on the at least one charge storage device 1724.

[0171] In other words, the excitation circuit 1704 can operate in the following modes: - A normal operating mode 17012 (first mode) with a positive output voltage. A charging mode of operation 17028 (second mode) similar to the normal mode of operation 17012 but including simultaneous pre-charging of at least one charge storage device 1724 to a preset value. - A short-time operating mode 17026 (third mode) with an increased (boosted) positive output voltage. - A transient operating mode 17014 (fourth mode) with a negative output voltage, which is used when the current through the exciter field winding is decreasing, i.e. when energy is removed from the exciter field winding. A short-time operating mode 17030 (fifth mode) having a boosted (more negative) negative output voltage used to reduce the current through the exciter field winding at a faster rate than in the second operating mode.

[0172] According to this numbering scheme, the second and third modes correspond to the third and second modes described with reference to Figures 7c and 7b, respectively.

[0173] Thus, the third and fifth modes reflect exemplary operating states of the excitation circuits according to Figures 4, 5, 7, 12, 13 and 17, which follow from providing at least a portion of the energy stored by the at least one charge storage device to satisfy the control demand indicated by the second signal when the control demand indicated by the second signal exceeds the threshold capacity of the synchronous machine that would exist in the absence of the at least one charge storage device, and when the synchronous machine is in an appropriate operating state as derived from the first signal.

[0174] For example, if the synchronous machine includes an exciter machine and a generator, the DC output may be coupled to a field coil of the exciter machine, the operating state (indicated by the first signal) may reflect an operating state of the generator, and the control request (indicated by the second signal) may represent a desired value of a field voltage generated by the exciter machine (which powers the generator based on the field voltage). Further, the control circuit may be configured to provide at least a portion of the energy stored by the at least one charge storage device to increase a voltage across the field coil of the exciter machine and a corresponding rate of change of current in the field coil of the exciter machine when the operating state of the generator indicated by the first signal does not satisfy the desired value indicated by the second signal. Here, the corresponding rate of change of current may be proportional to the voltage increase on the field circuit of the exciter machine and inversely proportional to the inductance of the field circuit of the exciter machine.

[0175] The generator operating condition indicated by the first signal may fail to meet the requirement indicated by the second signal if a measured voltage provided by the generator deviates from a predicted voltage provided by the generator, the predicted voltage being based on a field current generated by a field coil of the exciter. The measured voltage may deviate from the predicted voltage if a difference between the measured voltage and the predicted voltage satisfies a threshold condition (e.g., if the difference meets or exceeds one or more of a threshold voltage difference, a threshold voltage difference for a threshold time period, and predetermined characteristics in the voltage difference data). The control circuit (e.g., an automatic voltage regulator included in the control circuit) may be configured to determine the deviation.

[0176] FIG. 18 shows an output characteristic curve of the exemplary excitation circuit of FIG. 17a. When the control signal 17024 is "off," the output characteristic 18032 corresponds to the output characteristic of the exemplary excitation circuit shown in FIG. 16a. When the control signal 17024 is "on," second, third, and fifth modes of operating the excitation circuit are available, and the output characteristic 18034 is extended, thereby enabling improved excitation response. However, because the extended output characteristic remains linear throughout the range of the output voltage Ur, well-known techniques for tuning automatic voltage regulators remain applicable.

[0177] The five modes of operation of the excitation circuit of Figure 17a are further discussed with reference to the following figures: For clarity and brevity, similar features from the exemplary excitation circuit of Figure 17a are either omitted or represented by outlines.

[0178] 19a-19b show portion 1916a of the control circuit of FIG. 17a in a first mode of operation, which provides a positive DC output voltage to the exciter field winding 19008 of the main exciter via DC output terminals 1928a-1928b.

[0179] The first operating mode corresponds to the normal mode in which the excitation circuit operates during steady-state operation of the generator, i.e., at least one charge storage device is electrically isolated and a positive voltage is provided to the DC output. The DC output voltage is determined by a ratio between zero and the rectified input supply voltage U. C1 (i.e., the voltage on the smoothing capacitor 1922). In this first mode, V1, V3 (i.e., the IGBTs having reference numbers 1918a and 1918c) are permanently on, and V5 (i.e., the IGBT having reference number 1918e) is permanently off. V2 (i.e., the IGBT having reference number 1918b) is driven by a pulse-width modulation (PWM) signal from the PWM unit to control the DC output voltage to the exciter field winding. The current flowing through the excitation circuit follows the path represented by the dotted line. When V2 (i.e., the IGBT having reference number 1918b) is on, the path is designated by a black arrow; when V2 (i.e., the IGBT having reference number 1918b) is off, the path is designated by a white arrow; and when this path is not relevant in the on state of V2 (i.e., the IGBT having reference number 1918b), the path is designated by a black arrow / white arrow.

[0180] Alternatively, in the first mode of operation, V2 (ie, the IGBT with reference number 1918b) is permanently on and V1 (ie, the IGBT with reference number 1918a) is driven by PWM modulation.

[0181] 19b shows the output voltage over time at DC output terminals 1928a-1928b during the first mode of operation. The trace with reference label 1954 represents the instantaneous voltage value (i.e., the pulse width modulated output voltage), while the trace with reference label 1952 represents the steady state output voltage.

[0182] 20a-20b show the portion 2016a of the control circuit of FIG. 17a in a second operating mode, which provides a positive DC output voltage to the main exciter field winding 20008 via DC output terminals 2028a-2028b. This mode provides the same voltage range to the exciter field as the first operating mode; that is, the voltage provided is between zero and the rectified input supply voltage U. C1 (i.e., the voltage on the smoothing capacitor 2022). However, the freewheeling current when V2 (i.e., the IGBT having reference number 2018b) is off is switched to charge at least one charge storage device 2024. That is, a path for the decay of the current through the inductive load device is provided differently, as will be explained with reference to the control circuit shown in FIG. 7c.

[0183] In this second mode, V1 (i.e., the IGBT with reference number 2018a) is permanently on, and V3 and V5 (i.e., the IGBTs with reference numbers 2018c and 2018e) are permanently off. V2 (i.e., the IGBT with reference number 2018b) is driven by a pulse-width modulation (PWM) signal from the PWM unit to control the DC output voltage to the exciter field winding. Current flowing through the control circuit follows the path represented by the dotted line. When V2 (i.e., the IGBT with reference number 1918b) is on, the path is designated by a black arrow; when V2 (i.e., the IGBT with reference number 1918b) is off, the path is designated by a white arrow; and when this path is not relevant in the on state of V2 (i.e., the IGBT with reference number 1918b), the path is designated by a black / white arrow.

[0184] Figure 20b shows the output voltage over time at DC output terminals 2028a-1928b during the second mode of operation. The trace with reference label 2054 represents the instantaneous voltage (i.e., the pulse width modulated output voltage), while the trace with reference label 2052 represents the average output voltage.

[0185] 21a-21d show the portion 2116a of the control circuit of FIG. 17a in a third mode of operation, which provides a boosted positive DC voltage to the main exciter field winding 21008 via DC output terminals 2128a-2128b (i.e., at least a portion of the energy stored by the at least one charge storage device is provided to the DC output to provide a larger positive voltage at the DC output). In this mode, the at least one charge storage device 2124 is switched by the control circuit to provide energy to the DC output to provide a larger positive voltage than would be possible in the first mode of operation (i.e., a higher DC voltage limit is achieved even after taking into account the smoothing capacitor 2122). The voltage provided to the DC output terminals 2128a-2128b is a function of the zero voltage and the rectified input supply voltage U. C1 (i.e., the voltage on the smoothing capacitor 2122) and voltage U C3 (i.e., the voltage on the at least one charge storage device 2124).

[0186] In the third mode, V1 and V5 (i.e., the IGBTs with reference numbers 2118a and 2118e) are permanently on, and V3 (i.e., the IGBT with reference number 2118c) is permanently off. V2 (i.e., the IGBT with reference number 2118b) is driven by a PWM signal to control the voltage to the exciter field. The current flowing through the control circuit follows the path represented by the dotted line. When V2 (i.e., the IGBT with reference number 2118b) is on, the path is designated by a black arrow, when V2 (i.e., the IGBT with reference number 2118b) is off, the path is designated by a white arrow, and when this path is not an issue in the on state of V2 (i.e., the IGBT with reference number 2118b), the path is designated by a black / white arrow.

[0187] 21b shows the output voltage over time at DC output terminals 2128a-2128b during the third mode of operation. The trace with reference label 2154 represents the instantaneous voltage (i.e., the pulse-width modulated output voltage), while the trace with reference label 2152 represents the average output voltage.

[0188] 21c-21d show portion 2116a of the control circuit of FIG. 17a in an alternative configuration for a third mode of operation, which reduces ripple in the instantaneous (i.e., pulse-width modulated output voltage) voltage.

[0189] An alternative configuration for the third operating mode is realized as follows: V1 and V2 (i.e., the IGBTs with reference numbers 2118a and 2118b) are permanently on, and V3 (i.e., the IGBT with reference number 2118c) is permanently off. V5 (i.e., the IGBT with reference number 2118e) is driven by a PWM signal to control the voltage to the exciter field. The current flowing through the control circuit follows the path represented by the dotted line. When V5 (i.e., the IGBT with reference number 2118e) is on, the path is designated by a black arrow; when V5 (i.e., the IGBT with reference number 2118e) is off, the path is designated by a white arrow; and when this path is not an issue in the on state of V5 (i.e., the IGBT with reference number 2118e), the path is designated by a black / white arrow.

[0190] With respect to the output voltage over time shown in Figure 21b, the trace with reference numeral 2154 (see Figure 21d) represents the instantaneous voltage value (i.e., the pulse width modulated output voltage), while the trace with reference numeral 2152 represents the average value of the output voltage. A comparison of the output voltages shown in Figures 21b and 21d clearly demonstrates the reduced ripple achieved by the alternative configuration.

[0191] 22a-22b show portion 2216a of the control circuit of FIG. 17a in a fourth mode of operation, which provides a negative DC voltage to the main exciter field winding 22008 via DC output terminals 2228a-2228b (i.e., at least one charge storage device is electrically isolated and a negative voltage is provided at the DC output). The provided output voltage is a function of zero and the rectified negative input supply voltage U. C1 (i.e., the voltage on smoothing capacitor 2022). In this mode, smoothing capacitor 2222 is charged via the path designated by the dotted line with the white arrow.

[0192] In this fourth mode, V3 (i.e., the IGBT with reference number 2218c) is permanently on, and V1 and V5 (i.e., the IGBTs with reference numbers 2218a and 2218e) are permanently off. V2 (i.e., the IGBT with reference number 2218b) is driven by a pulse-width modulation (PWM) signal from a PWM unit to control the DC output voltage to the exciter field winding. Current flowing through the control circuit follows the path represented by the dotted line. When V2 (i.e., the IGBT with reference number 2218b) is on, the path is designated by a black arrow, when V2 (i.e., the IGBT with reference number 2218b) is off, the path is designated by a white arrow, and when this path is not an issue in the on state of V2 (i.e., the IGBT with reference number 2218b), the path is designated by a black / white arrow.

[0193] 22b shows the output voltage over time at DC output terminals 2228a-2228b during the fourth mode of operation. The trace with reference label 2254 represents the instantaneous voltage (i.e., the pulse width modulated output voltage), while the trace with reference label 2252 represents the average output voltage.

[0194] 23a-23d show the portion 2316a of the control circuit of FIG. 17a in a fifth mode of operation, which provides a boosted negative DC voltage to the main exciter field winding 23008 via DC output terminals 2328a-2328b (i.e., at least a portion of the energy stored by the at least one charge storage device is provided to the DC output to provide a larger negative voltage at the DC output). In this mode, the at least one charge storage device 2324 is switched to a DC output by the control circuit to provide a larger negative voltage than would be possible in the fourth mode of operation (i.e., even after accounting for the smoothing capacitor 2322). The voltage provided to the DC output terminals 2328a-2328b is a voltage between zero volts and the rectified input supply voltage U C1 (i.e., the voltage on the smoothing capacitor 2322) and voltage U C3 (i.e., the voltage on the at least one charge storage device 2324). The smoothing capacitor 2322 and the at least one charge storage device 2324 are charged via the path designated by the dotted line with white arrows.

[0195] In the fifth mode, V1, V3, and V5 (i.e., IGBTs 2318a, 2318c, and 2318e) are permanently off. V2 (i.e., IGBT 2318b) is driven by a PWM signal to control the voltage to the exciter field. The current flowing through the control circuit follows the path represented by the dotted line. When V2 (i.e., IGBT 2318b) is on, the path is designated by a black arrow, when V2 (i.e., IGBT 2318c) is off, the path is designated by a white arrow, and when this path is not an issue in the on state of V2 (i.e., IGBT 2318b), the path is designated by a black / white arrow.

[0196] 23b shows the output voltage over time at DC output terminals 2228a-2228b during the fifth mode of operation. The trace with reference label 2354 represents the instantaneous voltage (i.e., the pulse width modulated output voltage), while the trace with reference label 2352 represents the average output voltage.

[0197] 23c-23d show portion 2316a of the control circuit of FIG. 17a in an alternative configuration for a fifth mode of operation, which reduces ripple in the instantaneous (i.e., pulse-width modulated output voltage) voltage.

[0198] An alternative configuration for the fifth operating mode is realized as follows: V1, V2, and V5 (i.e., IGBTs 2318a, 2318b, and 2318e) are permanently off. V3 (i.e., IGBT 2318c) is driven by a PWM signal to control the voltage to the exciter field. Current through the control circuit follows the path represented by the dotted line. When V3 (i.e., IGBT 2318c) is on, the path is designated by a black arrow; when V3 (i.e., IGBT 2318c) is off, the path is designated by a white arrow; and when this path is not an issue in the on state of V3 (i.e., IGBT 2318c), the path is designated by a black / white arrow.

[0199] With respect to the output voltage over time shown in Figure 23b, the trace with reference numeral 2354 (see Figure 23d) represents the instantaneous voltage value (i.e., the pulse width modulated output voltage), while the trace with reference numeral 2352 represents the average value of the output voltage. A comparison of the output voltages shown in Figures 23b and 23d clearly demonstrates the reduced ripple achieved by the alternative configuration.

[0200] One or more IGBTs may be replaced by alternative transistors or electronic switches to achieve the same functionality in each operating mode. Alternative excitation circuit designs (particularly the layout and selection of auxiliary components included in the control circuit) may also be used to achieve the same overall objective, i.e., to supply energy from at least one charge storage device, subject to the rules and conditions described herein.

[0201] The response characteristics of an exciter with the excitation circuit of Figure 16a or Figure 17a mirrors that shown in Figure 9 (which shows the measured response of the excitation circuits of Figures 3 and 5). Thus, the excitation circuit of Figure 17a also provides a voltage "boost" compared to the excitation circuit of Figure 16a, but with it faster rise and fall times of the exciter field current which determines the generator field voltage.

[0202] Advantages of the example excitation circuits according to FIGS. 4, 5, 7, 12, 13, and 17 may include one or more of the following: 1) The preference for excitation systems with rotating exciters, because in these systems the rotating exciters are located between the power converter and the generator field winding and have a significant (i.e., relatively long) time constant. Rotating exciters slow down the rate of regulation compared to static excitation systems in which the power converter is directly coupled to the generator field winding. Systems with rotating exciters typically use brushless excitation systems. By enabling a reduction in the effect of the rotating exciter's time constant, excitation system response is improved as a result. 2) Compared to conventional power converters, higher positive and negative DC output voltages can be provided to achieve higher generator upper limit voltages (positive or negative) in a relatively short time (sub-second, typically 10 ms to 100 ms) while relying on the same power source (PMG). Using the -HDC power converter, the synchronous machine generator can still be equipped with the same standard PMG and still provide a better excitation response. -HDC power converters can also be used to improve the response of existing synchronous machines without the need for specific modifications (the synchronous machine itself does not need to be modified). 3) The energy required to improve exciter response is stored in at least one charge storage device and is therefore limited, thus limiting potential damage to the synchronous machine in the unlikely event of an HDC power converter failure. 4) When PWM modulation is used, the standard method of AVR regulation is to use PWM modulation so that the control of the HDC power converter output voltage is controlled by the AVR output signal (U r ), so remains applicable.

[0203] Furthermore, The power converter output current level is controlled by the automatic voltage regulator (AVR). Max C1 / R f where U C1 is the voltage on the smoothing capacitor supplied by the rectified PMG output voltage, and R f is the resistance of the exciter field winding, including the interconnecting wiring. Under this condition, the energy stored in the at least one charge storage device is used for a relatively short (sub-second) time period to provide a boosted voltage to reduce the time constant of the rotating exciter. No additional power supply is used for precharging the at least one charge storage device; rather, precharging is performed by the power converter itself using its inductive load (exciter field winding). Even with PMGs that have significant internal reactance, the voltage level is maintained by a pulse-width modulation (PWM) unit control. This voltage level is set by programmable parameters. ​PWM modulation may be used to add energy from at least one charge storage device in a controlled manner to increase the positive output voltage above the value available from the PMG's own supply. PWM modulation may be used to transfer energy from the load device to at least one charge storage device in a controlled manner to decrease the negative output voltage below the value available from the PMG's own supply.

[0204] The applicant discloses each individual feature and any combination of two or more such features described herein alone to the extent that such feature or combination can be implemented based on the specification as a whole in light of the common general knowledge of those skilled in the art, without limiting the scope of the claims, regardless of whether such feature or combination of features solves any problem disclosed herein. The applicant indicates that the disclosed aspects / embodiments can consist of any such individual feature or combination of features. In view of the foregoing description, it will be apparent to those skilled in the art that various modifications can be made within the scope of the present disclosure.

Claims

1. 1. An excitation circuit for a synchronous machine, the excitation circuit comprising: at least one charge storage device configured to provide energy to a DC output coupled to the synchronous machine; A control circuit comprising: receiving a first signal indicative of an electrical output of the synchronous machine; receiving a second signal indicative of a control request for the synchronous machine; the control demand indicated by the second signal exceeds a threshold capacity of the synchronous machine; a control circuit configured to supply at least a portion of the energy stored by the at least one charge storage device when the electrical output derived from the first signal does not satisfy the control demand indicated by the second signal by a predetermined amount; the control circuit comprises one or more transistors and an automatic voltage regulator configured to control the one or more transistors to discharge the at least one charge storage device to the DC output; the threshold capacitance is based on the output voltage of the automatic voltage regulator; The control circuit an excitation circuit that, when the automatic voltage regulator controls one transistor of the one or more transistors using pulse width modulation, controls another transistor of the one or more transistors so that the at least one charge storage device is not charged during an on period of the pulse width modulation and the at least one charge storage device is charged during an off period of the pulse width modulation.

2. The excitation circuit of claim 1 , further comprising a rectifier circuit configured to convert an AC input to a DC output.

3. The control circuit 3. The excitation circuit of claim 1, configured to initiate charging of the at least one charge storage device by the DC output when the control request indicated by the second signal is associated with removing energy from the synchronous machine.

4. The control circuit receiving a third signal indicative of an amount of charge stored by the at least one charge storage device; 4. The excitation circuit of claim 3 when dependent on claim 2, configured to initiate charging of the at least one charge storage device by the AC input when the amount of stored charge indicated by the third signal is below a predetermined threshold and the electrical output indicated by the first signal satisfies the control request indicated by the second signal.

5. 5. The excitation circuit of claim 4, wherein the predetermined amount is an absolute amount or a relative amount.

6. 6. The excitation circuit of claim 1, wherein the first signal is indicative of a measured parameter of the electrical output of the synchronous machine, and the control circuit is configured to supply at least a portion of the energy stored by the at least one charge storage device when the electrical output indicated by the first signal does not satisfy the control requirement indicated by the second signal for a predetermined period of time.

7. 7. The excitation circuit of claim 1, wherein the control circuit is configured to electrically isolate the at least one charge storage device from the DC output to provide a predetermined upper voltage limit at the DC output when the electrical output indicated by the first signal satisfies the control requirement indicated by the second signal.

8. 8. The excitation circuit according to claim 1, wherein the DC output is a positive voltage or a negative voltage.

9. 9. The excitation circuit according to claim 2 or any one of claims 3 to 8 depending thereon, wherein the AC input is a three-phase signal or a single-phase signal.

10. 10. The excitation circuit of claim 1, wherein the first signal indicates measured parameters of the electrical output of the synchronous machine, the measured parameters comprising at least one of a voltage output, a current output, and a power output of the synchronous machine, and one or more of a voltage demand, a current demand, a power demand, an inductance demand, and a power factor from a load device connected to the synchronous machine; and the second signal indicates parameter requirements of the control request of the synchronous machine, the parameter requirements comprising at least one of a field voltage and / or a field current of an exciter machine of the synchronous machine, an input, an output, and / or one or more internal values ​​of the automatic voltage regulator configured to control the synchronous machine, a voltage and / or a current provided by a generator of the synchronous machine, a real inductance demand or a complex inductance demand of the synchronous machine, and a power factor from a load device connected to the synchronous machine.

11. 2. The excitation circuit of claim 1, wherein the one or more transistors are insulated gate bipolar transistors.

12. 12. The excitation circuit of claim 11, wherein the control circuit comprises a capacitor configured to protect the insulated gate bipolar transistor from circuit inductance when the insulated gate bipolar transistor is switched from an on state to an off state by the automatic voltage regulator.

13. The control circuit modulating the DC output based on a modulation signal; The excitation circuit of claim 1 configured to set the polarity of the DC output.

14. 14. The excitation circuit of claim 13, wherein the automatic voltage regulator is configured to apply the pulse width modulation to control the DC output.

15. 15. The excitation circuit of claim 14, wherein the automatic voltage regulator comprises a pulse width modulation unit configured to generate a pulse width modulated signal.

16. the one or more transistors a transistor configured to receive the pulse width modulation signal from the pulse width modulation unit and modulate the DC output; and a plurality of further transistors configured to set the polarity of the DC output.

17. a rectifier circuit configured to convert an AC input to the DC output, the control circuit comprising: a first current path connecting a first terminal of the rectifier circuit to a corresponding first terminal of the DC output section through a first transistor; a second current path connecting a second terminal of the rectifier circuit to a corresponding second terminal of the DC output section through a second transistor; a third current path coupling a first point along the first current path to the first terminal of the DC output through a third transistor; a fourth current path coupling a second point along the first current path to the first terminal of the DC output through a fourth transistor; 17. The excitation circuit of claim 16, wherein the at least one charge storage device is disposed in parallel with the fourth transistor.

18. The automatic voltage regulator providing at least a portion of the energy stored by the at least one charge storage device to provide a positive voltage at the DC output; by switching on the first transistor and the fourth transistor, switching off the third transistor, and providing a pulse width modulated signal to the second transistor via the pulse width modulation unit; or providing a positive voltage by switching on the first transistor and the second transistor, switching off the third transistor, and providing a pulse width modulated signal to the fourth transistor via the pulse width modulation unit; or providing at least a portion of the energy stored by the at least one charge storage device to provide a negative voltage at the DC output; by switching off the first transistor, the third transistor, and the fourth transistor and providing a pulse width modulated signal to the second transistor via the pulse width modulation unit; or 18. The excitation circuit of claim 17, configured to provide a negative voltage by switching off the first transistor, the second transistor, and the fourth transistor and providing a pulse-width modulated signal to the third transistor via the pulse-width modulation unit.

19. 19. The excitation circuit of claim 18 when dependent on claim 3, wherein the automatic voltage regulator is configured to charge the at least one charge storage device by switching on the first transistor and switching off the second transistor, the third transistor, and the fourth transistor.

20. The automatic voltage regulator isolating the at least one charge storage device and providing a positive voltage at the DC output, providing a positive voltage by switching on the first transistor and the third transistor, switching off the fourth transistor, and providing a pulse width modulated signal to the second transistor via the pulse width modulation unit; or isolating the at least one charge storage device and providing a negative voltage at the DC output, 20. The excitation circuit of claim 18 or 19, configured to provide a negative voltage by switching off the first transistor and the fourth transistor, switching on the third transistor, and supplying a pulse width modulated signal to the second transistor via the pulse width modulation unit.

21. the synchronous machine comprises an exciter and a generator, the DC output is coupled to a field coil of the exciter; the electrical output reflects the electrical output of the generator; the control request represents a required value of a field voltage generated by the exciter, the generator is powered by the exciter based on the field voltage; 21. The excitation circuit of claim 1, wherein the control circuit is configured to provide at least a portion of the energy stored by the at least one charge storage device to increase the voltage across the field coil of the exciter machine and the corresponding rate of change of current in the field coil of the exciter machine when the electrical output of the generator does not meet the required value of field voltage.

22. 22. The excitation circuit of claim 21, wherein the electrical output of the generator does not meet the required value for field voltage if a measured voltage provided by the generator deviates from a predicted voltage provided by the generator, the predicted voltage being based on a field current generated by the field coil of the exciter machine.

23. 23. An excitation circuit as claimed in claim 21 or 22, wherein the corresponding rate of change of current is proportional to the voltage increase on the field circuit of the exciter machine and inversely proportional to the inductivity of the field circuit of the exciter machine.

24. 24. The excitation circuit of claim 1, wherein supplying at least a portion of the energy stored by the at least one charge storage device comprises a gradual or immediate release of energy from the at least one charge storage device and / or a complete discharge of the at least one charge storage device.

25. 25. The excitation circuit of claim 1, wherein the control circuit is configured to temporarily increase an upper voltage limit at the DC output to boost an output of the synchronous machine when the control demand indicated by the second signal exceeds a threshold capacity of the synchronous machine that would be present in the absence of the at least one charge storage device.

26. 2. The excitation circuit of claim 1, wherein the automatic voltage regulator comprises a smoothing capacitor, and the threshold capacitance is limited by the voltage on the smoothing capacitor.

27. 27. An excitation circuit according to any preceding claim, wherein the at least one charge storage device comprises one or more capacitors, batteries, or battery-capacitor hybrids.

28. An exciter for a synchronous machine comprising an excitation circuit according to any one of claims 1 to 27, wherein the DC output is coupled to an exciter field coil of the exciter.

29. 29. The exciter of claim 28, wherein the exciter is a brushless AC exciter or a DC exciter.

30. A synchronous machine comprising an exciter machine according to claim 28 or 29.

31. 31. The synchronous machine of claim 30, wherein the synchronous machine is a synchronous generator, a synchronous motor, or a synchronous condenser.

32. 32. A synchronous machine according to claim 30 or 31, comprising the excitation circuit of claim 2, further comprising a main generator and a secondary exciter coupled to a rotor shaft of the main generator and configured to provide an AC input.

33. The synchronous machine of claim 32 wherein the co-exciter comprises a permanent magnet generator.

34. 10. A method of using the excitation circuit of claim 1, said method comprising: receiving a first signal indicative of an electrical output of the synchronous machine; receiving a second signal indicative of a control request for the synchronous machine; the control demand indicated by the second signal exceeds a threshold capacity of the synchronous machine; providing at least a portion of the energy stored by the at least one charge storage device when the electrical output derived from the first signal does not satisfy the control demand indicated by the second signal by a predetermined amount; a control circuit for the excitation circuit comprising one or more transistors and an automatic voltage regulator configured to control the one or more transistors to discharge the at least one charge storage device to the DC output; the threshold capacitance is based on the output voltage of the automatic voltage regulator; The method comprises: and when the automatic voltage regulator controls one of the one or more transistors using pulse width modulation, controlling another of the one or more transistors to not charge the at least one charge storage device during an on period of the pulse width modulation and to charge the at least one charge storage device during an off period of the pulse width modulation.

35. 35. A computer program comprising computer code configured to perform the method of claim 34.

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