Starting a variable frequency independent speed motor and performing speed control with negative slope voltage frequency

Abstract

The present disclosure relates to starting a variable frequency independent speed motor and performing speed control with negative slope voltage frequency. Specifically, a method can include the steps of transmitting an excitation signal from a stator of an electric motor to a rotor of the electric motor, wherein the excitation signal is received at a set of rotor windings, and wherein the excitation signal generates a rotating magnetic flux at the rotor that generates a first alternating current (AC) voltage at a set of stator windings. The method can also include the step of controlling the excitation signal to equalize and synchronize the first AC voltage to a second AC voltage at an AC bus. After synchronization, the method can also include the step of electrically connecting the set of stator windings to the AC bus. The method can include the step of reducing an amplitude of the excitation signal to enable current to flow from the AC bus to the set of stator windings, thereby generating a torque that causes the rotor to rotate.

Description

Technical Field

[0001] This disclosure generally relates to the field of starting variable frequency independent speed (VFIS) motors, and more specifically to systems and methods for starting VFIS and for negative-slope voltage-frequency for speed control. Background Technology

[0002] A VFIS motor is a type of motor that can operate at a rotational frequency independent of the amplitude, frequency, and phase of the alternating current (AC) power signal used to power the motor. Furthermore, a typical AC motor can achieve a rotational frequency independent of the amplitude, frequency, and phase of the driving AC power signal using a rectifier and inverter that perform a full-power stage power conversion. Alternatively, a VFIS motor can operate without performing such a full-power stage power conversion.

[0003] Starting a VFIS motor by directly connecting it to the AC bus can damage its stator windings. For example, because a stationary VFIS motor does not generate significant impedance in its stator windings, a sudden surge can cause a short circuit within the windings, resulting in significant heat and potentially breakdown. Applying a sudden starting current to a VFIS motor can also cause premature wear of its electrical components.

[0004] Furthermore, typical speed control techniques (such as variable frequency drives and field-oriented control) may not be suitable for VFIS motors because VFIS motors may have active windings in both the stator and rotor. Therefore, new starting techniques and new speed control technologies are needed in industry to accommodate VFIS motors. Other drawbacks may also exist. Summary of the Invention

[0005] This document discloses a system and method for starting a VFIS motor and for speed control. The system and method can operate in a synchronization phase and a speed regulation phase. During the synchronization phase, an excitation signal can be transmitted to the rotor of the motor and applied to a set of rotor windings. The excitation signal can generate a rotating magnetic flux at the rotor, which generates a first alternating current (AC) voltage at a set of stator windings. The first AC voltage can be made equal to and synchronized with a second AC voltage on an AC bus, after which the AC bus can be connected to the set of stator windings. Because the first AC voltage and the second AC voltage are equal, no current can flow through the set of stator windings, thus preventing rotor rotation.

[0006] During the speed regulation phase, the amplitude of the excitation signal can be gradually reduced, resulting in a gradually increasing current in the set of stator windings. The amplitude of the excitation signal can be reduced according to the negative slope voltage-frequency relationship. As the voltage decreases, the current in the stator windings can increase, thereby generating a second rotating magnetic flux that can interact with the first rotating magnetic flux to initiate rotor rotation.

[0007] In the example, a system is provided including an electric motor having a stator, a rotor, a set of stator windings, and a set of rotor windings. The system further includes a high-frequency transformer configured to transmit an excitation signal from the stator to the rotor, wherein the excitation signal is received at the set of rotor windings, and wherein the excitation signal generates a rotating magnetic flux at the rotor, the rotating magnetic flux generating a first alternating current (AC) voltage at the set of stator windings. The system also includes a switch electrically connected between the set of stator windings and an AC bus. The system includes a controller circuit configured to control the excitation signal such that a first amplitude of the first AC voltage at the set of stator windings is equal to a second amplitude of a second AC voltage at the AC bus, and to synchronize the first AC voltage with the second AC voltage. The controller circuit is further configured to close the switch after synchronizing the first AC voltage with the second AC voltage, and to reduce the amplitude of the excitation signal so that current can flow from the AC bus to the set of stator windings, thereby generating a torque that causes the rotor to rotate.

[0008] In some examples, the system includes: an excitation source circuit configured to receive an amplitude excitation source control signal, a frequency excitation source control signal, and a phase excitation source control signal from the controller circuit, and to generate the excitation signal based on the amplitude excitation source control signal, the frequency excitation source control signal, and the phase excitation source control signal. In some examples, the system includes: a first voltage signal sensor electrically connected between the switch and the set of stator windings, configured to provide the controller circuit with a measurement of a first AC voltage at the set of stator windings; and a second voltage signal sensor electrically connected between the AC bus and the switch, configured to provide a measurement of a second AC voltage. In some examples, the motor is a variable frequency independent speed (VFIS) motor. In some examples, the set of stator windings is a three-phase stator winding, and wherein the set of rotor windings is a three-phase rotor winding. In some examples, the AC bus is a three-phase AC bus.

[0009] In one example, a method is provided, comprising the steps of: transmitting an excitation signal from the stator of an electric motor to the rotor of the electric motor, wherein the excitation signal is received at a set of rotor windings, and wherein the excitation signal generates a rotating magnetic flux at the rotor, the rotating magnetic flux generating a first alternating current (AC) voltage at the set of stator windings. The method further comprises the steps of: controlling the excitation signal such that a first amplitude of the first AC voltage at the set of stator windings is equal to a second amplitude of a second AC voltage at an AC bus, and synchronizing the first AC voltage with the second AC voltage. The method further comprises the steps of: after synchronizing the first AC voltage at the set of stator windings with the second AC voltage at the AC bus, electrically connecting the set of stator windings to the AC bus. The method further comprises the steps of: reducing the amplitude of the excitation signal such that current can flow from the AC bus to the set of stator windings, thereby generating a torque that causes the rotor to rotate.

[0010] In some examples, the method includes the steps of: receiving an amplitude excitation source control signal, a frequency excitation source control signal, and a phase excitation source control signal, and generating the excitation signal based on the amplitude excitation source control signal, the frequency excitation source control signal, and the phase excitation source control signal. In some examples, the method includes the steps of: measuring a first AC voltage at a set of stator windings, measuring a second AC voltage at the AC bus, calculating the amplitude difference, frequency difference, and phase difference between the first AC voltage and the second AC voltage, and determining that the first AC voltage and the second AC voltage are synchronized when the amplitude difference decreases below a first threshold, the frequency difference decreases below a second threshold, and the phase difference decreases below a third threshold.

[0011] In some examples, the method includes the steps of: receiving a speed reference value; calculating a reference frequency value based on the speed reference value; determining an excitation reference voltage according to the reference frequency value based on data that maps a voltage value to a rotor frequency value; and setting the amplitude of the excitation signal to the excitation reference voltage to cause the rotor to rotate at the speed reference value. In some examples, the step of determining the excitation reference voltage includes: storing data that maps the voltage value to the rotor frequency value; and retrieving the excitation reference voltage from the data based on the reference frequency value. In some examples, the step of determining the excitation reference voltage includes: gradually decreasing the excitation reference voltage over a period of time.

[0012] In some examples, the method includes the steps of: determining a reference excitation frequency based on the reference frequency and a measured frequency of the second AC voltage at the AC bus, and setting the frequency of the excitation signal to the reference excitation frequency. In some examples, determining the reference excitation frequency includes: gradually changing the reference excitation frequency over a time period. In some examples, the method includes the steps of: determining a reference excitation phase, and setting the phase of the excitation signal to the reference excitation phase. In some examples, determining the reference excitation phase includes: storing a measured phase of the second AC voltage at the AC bus in a memory, and generating the reference excitation phase based on data representing the measured phase.

[0013] In the example, a system is provided that includes a synchronization control module configured to measure a first AC voltage at a set of stator windings, measure a second AC voltage at an AC bus, generate an excitation synchronization signal based on the first and second AC voltages, and generate a switch control signal based on the first and second AC voltages. The system also includes a motor speed control module configured to receive a speed reference value and the measurement results of the second AC voltage, and generate an excitation reference signal based on the measurement results of the speed reference value and the second AC voltage. The system further includes an excitation source control module configured to generate an excitation source control signal based on either the excitation synchronization signal or the excitation reference signal. The system includes a switch configured to route the excitation synchronization signal to the excitation source control module during a synchronization phase and to route the excitation reference signal to the excitation source control module during a motor speed regulation phase.

[0014] In some examples, the synchronization control module includes: a first amplitude and phase analyzer module configured to measure the first AC voltage; a second amplitude and phase analyzer module configured to measure the second AC voltage; a set of differential modules configured to calculate the amplitude difference, frequency difference, and phase difference between the first AC voltage and the second AC voltage; a set of comparison modules configured to determine whether the amplitude difference has decreased below a first threshold, the frequency difference has decreased below a second threshold, and the phase difference has decreased below a third threshold; a logic module configured to generate the switching control signal based on the output from the set of comparison modules; and a set of proportional-integral-derivative (PID) controllers configured to generate the excitation synchronization signal based on the amplitude difference, the frequency difference, and the phase difference.

[0015] In some examples, the motor speed control module includes: a constant multiplier module configured to convert the speed reference value into a reference frequency value; a negative slope voltage-frequency control module configured to receive the reference frequency value and calculate an intermediate excitation reference voltage based on the reference frequency value; a first differential circuit configured to generate an intermediate excitation reference frequency value based on the reference frequency value and a measured frequency of a second AC voltage at the AC bus; a second differential circuit, a first proportional-integral-derivative controller, and a first slope module, wherein the second differential circuit... A first proportional-integral-derivative (PI-DI) controller and a first slope module are configured together to generate an excitation reference voltage and gradually change the excitation reference voltage over a period of time to match the intermediate excitation reference voltage; and a third differential circuit, a second PI-DI controller, and a second slope module are configured together to generate an excitation reference frequency value based on the intermediate excitation reference frequency value and modify the excitation reference frequency value over a period of time to match the intermediate excitation reference frequency value, wherein the excitation reference signal includes the excitation reference voltage and the excitation reference frequency value.

[0016] In some examples, the motor speed control module further includes a memory module configured to store the measured phase values ​​and generate an excitation reference phase value that matches the measured phase values, wherein the excitation reference signal includes the excitation reference phase value. Attached Figure Description

[0017] Figure 1 This is a block diagram depicting an example of a system for starting a VFIS motor and for speed control.

[0018] Figure 2 This is a block diagram depicting an example of the controller circuitry for starting a VFIS motor and for a system used for speed control.

[0019] Figure 3A and Figure 3B This is a block diagram illustrating an example of the signal paths for the controller circuitry used to start the VFIS motor and for speed control.

[0020] Figure 4 It is a graph depicting negative slope voltage-frequency data used in systems for starting VFIS motors and for speed control.

[0021] Figure 5 It is a graph depicting the simulation results of the VFIS motor for starting and the system for speed control.

[0022] Figure 6A It is a flowchart depicting the methods for starting the VFIS motor and for speed control.

[0023] Figure 6B It is a description Figure 6A The flowchart is a continuation of the method.

[0024] Figure 6C It is a description Figure 6A The flowchart is a continuation of the method.

[0025] Figure 6D It is a description Figure 6A The flowchart is a continuation of the method.

[0026] Figure 6E It is a description Figure 6A The flowchart is a continuation of the method.

[0027] Figure 6F It is a description Figure 6A The flowchart is a continuation of the method.

[0028] While this disclosure allows for various modifications and alternatives, specific embodiments have been illustrated by way of example in the accompanying drawings and will be described in detail herein. However, it should be understood that this disclosure is not limited to the specific forms disclosed. Rather, the invention is intended to cover all modifications, equivalents, and alternatives falling within the scope of this disclosure. Detailed Implementation

[0029] Reference Figure 1 The present invention describes a system 100 for starting and speed control of an electric motor. System 100 may include an electric motor 102. Electric motor 102 may include a stator 104 and a rotor 106 configured to rotate relative to the stator 104. The stator 104 may include a set of stator windings 108, and the rotor 106 may include a set of rotor windings 110. In some examples, electric motor 102 may be a variable frequency independent speed (VFIS) motor. Notably, the VFIS motor may be operated in conjunction with a motor control unit (not shown) to control the rotational frequency of the VFIS motor independently of the frequency, amplitude, and phase of the electrical signal used to drive the VFIS motor. The rotational frequency of the VFIS motor can be controlled without performing a full power-to-power conversion of the electrical signal. Examples of electric motors that can be used with system 100 are further described in U.S. Patent Application No. 15 / 982,470, filed May 17, 2018, entitled “Variable Frequency Independent Speed ​​Motor,” the entire contents of which are incorporated herein by reference.

[0030] As used herein, "full-power rated power conversion" occurs when the power level carried by the converter is equal to the power level of the generator or motor it drives or controls. Full-power rated power conversion is typically performed by a rectifier circuit that converts approximately all the energy in the electrical signal from an AC signal to a DC signal, while the inverter circuit converts approximately all the energy in the electrical signal from a DC signal to an AC signal. Power losses during these conversions can be significant. Furthermore, the hardware used to perform the conversion can add additional weight and complexity to the power distribution system.

[0031] The high-frequency transformer 112 can be configured to transmit an excitation signal 114 from the stator 104 to the rotor 106, wherein the excitation signal 114 can be applied to the set of rotor windings 110. Based on the amplitude, frequency, and phase of the excitation signal 114, a current can be generated in the set of rotor windings 110, which can generate a rotating magnetic flux 116 rotating relative to the rotor 106. The rotating magnetic flux 116 can generate a first alternating current (AC) voltage 118 at the set of stator windings 108. The set of stator windings 108 and the set of rotor windings 110 can be three-phase stator windings and three-phase rotor windings, respectively.

[0032] System 100 may further include a switch 120, which can be configured to isolate the set of stator windings 108 from the AC bus 122 in a first state. In this way, the second AC voltage 126 at the AC bus 122 can be isolated from the first AC voltage 118. In a second state, switch 120 can be configured to electrically connect the AC bus 122 to the set of stator windings 108. The AC bus 122 may be a three-phase AC bus.

[0033] System 100 may include system controller circuit 124 and excitation source circuit 128. System controller circuit 124 may be configured to control excitation source circuit 128 by providing amplitude excitation source control signal 130, frequency excitation source control signal 131, and phase excitation source control signal 132 to excitation source circuit 128. Based on signals 130 to 132, excitation source circuit 128 may generate excitation signal 114.

[0034] The system controller circuit 124 can be implemented as a processor and memory, analog circuitry, logic circuitry, or a combination thereof. Specific modules associated with the system controller circuit 124 are further described herein and can be implemented as logic circuitry within the system controller circuit 124. Alternatively, these modules can be implemented as a processor combined with a memory storing instructions corresponding to the modules.

[0035] System 100 may include a first voltage signal sensor 134 and a second voltage signal sensor 136. The first voltage signal sensor 134 may be configured to measure a first AC voltage 118 and transmit the measurement result 138 to system controller circuitry 124. The second voltage signal sensor 136 may be configured to measure a second AC voltage 126 and transmit the measurement result 140 to system controller circuitry 124. In some examples, the first voltage signal sensor 134 and the second voltage signal sensor 136 may be part of system controller circuitry 124.

[0036] During operation, the system controller circuit 124 can be activated during the synchronization phase. During the synchronization phase, switch 120 can be opened to prevent current from flowing from AC bus 122 to the set of stator windings 108. The system controller circuit 124 can receive the measurement results 138 of the first AC voltage 118 and 140 of the second AC voltage 126. The system controller circuit 124 can transmit the amplitude excitation source control signal 130, the frequency excitation source control signal 131, and the phase excitation source control signal 132 to the excitation source circuit 128 to generate an excitation signal 114 that can be transmitted via the high-frequency transformer 112 to the set of rotor windings 110 on the rotor 106. The excitation signal 114 can generate a rotating magnetic flux 116 that can sense the first AC voltage 118. In this way, the system controller circuit 124 can control the first AC voltage 118.

[0037] System controller circuit 124 can control excitation signal 114 to make the amplitude of the first AC voltage 118 at the set of stator windings 108 equal to the amplitude of the second AC voltage 126 at the AC bus 122, and to synchronize the first AC voltage 118 with the second AC voltage 126. Synchronizing the first AC voltage 118 and the second AC voltage 126 may include adjusting the first AC voltage 118 until the frequency and phase of the first AC voltage 118 match the frequency and phase of the second AC voltage 126. After synchronizing the first AC voltage 118 with the second AC voltage 126, system controller circuit 124 can be configured to close switch 120 by sending switch control signal 142.

[0038] During the speed regulation phase, the amplitude of the excitation signal 114 can be gradually reduced, resulting in a reduction in the amplitude of the first AC voltage 118. The reduced first AC voltage 118 causes a gradually increasing current within the set of stator windings 108. The amplitude of the excitation signal 114 can be reduced according to a negative slope voltage-frequency relationship. As the amplitude decreases, the current within the set of stator windings 108 can increase, thereby generating a second rotating magnetic flux that can interact with the first rotating magnetic flux 116 to initiate rotation of the rotor 106. The system controller circuit 124 can receive a speed reference value 144 to determine the speed of the rotor 106 during the speed regulation phase, as discussed herein.

[0039] The advantage of system 100 is that the motor 102 can be started without immediately connecting it directly to the AC bus 122. This avoids damage and premature wear caused by sudden power surges. Other benefits may also exist.

[0040] Reference Figure 2 This describes a system controller circuit 124 for starting a VFIS motor and for speed control. The controller circuit 124 may include a synchronization control module 202, a motor speed control module 204, and an excitation source control module 206. Specific modules associated with the system controller circuit 124 may be implemented as logic circuits within the system controller circuit 124, or as a processor combined with a memory storing instructions corresponding to that module.

[0041] The synchronization control module 202 can be configured to receive the first AC voltage (e.g., Figure 1 The measurement result 138 of the first AC voltage 118) and the second AC voltage at the AC bus (e.g., Figure 1 The measurement result 140 of the second AC voltage 126. In some examples, the synchronization control module 202 may be configured and include circuitry for measuring each of the voltages in AC voltages 118 and AC voltage 126, instead of simply receiving measurement results 138 and 140. Based on measurement results 138 and 140, the synchronization control module 202 may be configured to generate an excitation synchronization signal 208, which may be used by the excitation source control module 206 to generate an excitation source control signal 212. The excitation source control signal 212 may include... Figure 1 The amplitude excitation source control signal 130, frequency excitation source control signal 131, and phase excitation source control signal 132 described herein can be used to synchronize AC voltage 118 and AC voltage 126. After AC voltage 118 and AC voltage 126 are synchronized, the synchronization control module 202 can be configured to generate a switch control signal 142. The switch control signal 142 can be used for closing... Figure 1 The switch 120 is used to electrically connect the AC bus 122 to the set of stator windings 108.

[0042] The motor speed control module 204 can be configured to receive a speed reference value 144 and a second AC voltage (i.e., Figure 1 The second AC voltage 126 is associated with the measurement result 216, and an excitation reference signal 210 is generated based on the speed reference value 144 and the measurement result 216.

[0043] The excitation source control module 206 can be configured to generate the excitation source control signal 212 based on the excitation synchronization signal 208 or the excitation reference signal 210. For example, the switch 214 can be configured to route the excitation synchronization signal 208 to the excitation source control module 206 during the synchronization phase and to route the excitation reference signal 210 to the excitation source control module 206 during the motor speed regulation phase.

[0044] Reference Figure 3A and Figure 3B The diagram depicts a system controller circuit 124 for starting a VFIS motor and for a speed control system. The described functions can be executed by logic circuitry, by a processor coupled to a memory containing instructions to perform the functions, or by any combination thereof.

[0045] Reference Figure 3A The controller circuit 124 may include: a first amplitude and phase analyzer module 302 configured to measure a first AC voltage 118, and a second amplitude and phase analyzer module 304 configured to measure a second AC voltage 126. The amplitude and phase analyzer modules (302, 304) may, for example, include those configured according to... Figure 1 The voltage signal sensors (134, 136) are used. The first amplitude and phase analyzer module 302 can generate a first voltage amplitude signal 306, a first voltage frequency signal 307, and a first voltage phase signal 308. Similarly, the second amplitude and phase analyzer module 304 can generate a second voltage amplitude signal 322, a second voltage frequency signal 323, and a second voltage phase value 324.

[0046] A set of differential modules 310 can be configured to calculate the amplitude difference 312, frequency difference 313, and phase difference 314 between the first AC voltage 118 and the second AC voltage 126. The amplitude difference 312, frequency difference 313, and phase difference 314 can be implemented as signals and transmitted to a set of comparison modules 316.

[0047] The set of comparison modules 316 can be configured to determine whether the amplitude difference 312 has decreased below a first threshold, whether the frequency difference 313 has decreased below a second threshold, and whether the phase difference 314 has decreased below a third threshold. In some examples, the set of comparison modules 316 can be implemented as a comparator.

[0048] The system controller circuit 124 may also include a logic module 318 configured to generate a switch control signal 142 based on the outputs from the set of comparison modules 316. In some examples, the logic module 318 may be implemented as a logic circuit and may perform a three-input AND function to generate the switch control signal 142.

[0049] The system controller circuit 124 may also include a set of proportional-integral-derivative controllers 320, which are configured to generate an excitation synchronization signal 208 based on an amplitude difference 312, a frequency difference 313, and a phase difference 314.

[0050] The amplitude and phase analyzer modules (302, 304), differential module 310, comparison module 316, logic module 318, and the set of proportional-integral-differential controllers 320 can be included in Figure 2 In the synchronization control module 202. Furthermore, it can... Figure 3A and Figure 3B Each of the components and / or modules described herein is implemented as hardware logic circuitry, or a processor and a memory storing instructions that cause the processor to execute related... Figure 3A and Figure 3B The functions associated with the components and / or modules described in the document.

[0051] Reference Figure 3B The system controller circuit 124 can receive the speed reference value 144. The speed reference value 144 can be multiplied by a constant at the constant multiplier module 330 to convert the speed reference value 144 into a reference frequency value 332.

[0052] The negative slope voltage-frequency control module 334 can be configured to receive a reference frequency value 332 and calculate an intermediate excitation reference voltage 336 based on the reference frequency value 332. See further details. Figure 4The negative slope voltage-frequency control module 334 can store data that maps voltage values ​​to rotor frequency values ​​to determine an intermediate excitation reference voltage 336, from which an excitation reference voltage 356 can be derived. For example, the negative slope voltage-frequency control module 334 can be implemented as a lookup table. The data values ​​stored in the negative slope voltage-frequency control module 334 can be predetermined and can be based on the type of motor to be started.

[0053] Based on the reference frequency value 332, the first differential circuit 344 can be configured to generate an intermediate excitation reference frequency value 346 by calculating the difference between the reference frequency value 332 and the second voltage frequency signal 323 of the second AC voltage 126.

[0054] The intermediate excitation reference voltage 336 can be received at the second differential circuit 338, the first proportional-integral-derivative controller 340, and the first slope module 342, which are positioned according to the feedback configuration, so as to convert the intermediate excitation reference voltage into an excitation reference voltage 356. The first slope module 342 can limit the rate of change of the excitation reference voltage 356. This allows the motor sufficient time to change speed due to mechanical dynamics, which may be slower than electromagnetic dynamics.

[0055] The intermediate excitation reference frequency value 346 can be received at the third differential circuit 348, the second proportional-integral-derivative controller 350, and the second slope module 352, which are configured according to feedback, so as to convert the intermediate excitation reference frequency value 346 into an excitation reference frequency 357. The second slope module 352 can limit the rate of change of the reference excitation frequency 357 to gradually change the reference excitation frequency 357 over a period of time.

[0056] The system controller circuit 124 may further include a memory module 354 configured to store the measured phase value 324 and generate a reference excitation phase 358 that matches the measured phase value 324. The excitation reference signal 210 may include an excitation reference voltage 356, a reference excitation frequency 357, and a reference excitation phase 358.

[0057] The first switch 341 can be selectively controlled according to the switch control signal 142. Figure 3A ) and the second switch 343 ( Figure 3B The first switch 341 and the second switch 343 can constitute... Figure 2Switch 214. Simultaneously, the first switch 341 and the second switch 343 can determine whether to route the excitation synchronization signal 208 to the excitation source control module 206 during the synchronization phase, or to route the excitation reference signal 210 to the excitation source control module 206 during the motor speed regulation phase. The first switch 341 can determine whether to feed the excitation synchronization signal 208 or the excitation reference signal 210 to the excitation source control module 206. The second switch 343 can selectively use the second voltage amplitude signal 322, the second voltage frequency signal 323, and the second voltage phase value 324 as inputs instead of the input based on the reference frequency value 332, inserting them respectively into the first slope module 342, the second slope module 352, and the memory module 354. During the synchronization phase, the second voltage amplitude signal 322, the second voltage frequency signal 323, and the second voltage phase value 324 can be used to determine the excitation reference signal 210. During the speed regulation phase, the intermediate excitation reference voltage 336, the intermediate excitation reference frequency value 346, and the second voltage phase value 324 (stored in the memory module 354) can be used to determine the excitation reference signal 210.

[0058] The constant multiplier module 330, the negative slope voltage-frequency control module 334, the differential circuits (344, 338, 348), the proportional-integral-derivative controllers (340, 350), the slope modules (342, 352), and the memory module 354 can correspond to the motor speed control module 204.

[0059] Based on the excitation synchronization signal 208 or the excitation reference signal 210, and according to the state of the first switch 341, the excitation source control module 206 can generate an excitation source control signal 212. As described herein, the excitation source control signal 212 may include: an amplitude excitation source control signal 130, a frequency excitation source control signal 131, and a phase excitation source control signal 132. Based on the excitation source control signal 212, the excitation source circuit 128 can generate an excitation signal (e.g., Figure 1 The excitation signal 114) is applied to a set of rotor windings (e.g., Figure 1 The set of rotor windings 110.

[0060] The advantage of system controller circuit 124 is that it allows the motor to be started using a two-stage sequence including a synchronization stage and a speed regulation stage, instead of immediately connecting the motor to the AC bus. This avoids damage and premature wear caused by sudden power surges. Other benefits may also exist.

[0061] Reference Figure 4This describes a graph depicting negative slope voltage-frequency data 400 used in systems for starting VFIS motors and for speed control. For example, data 400 can be used as part of a negative slope voltage-frequency control module 334. Figure 4 As depicted, data 400 can map voltage value 402 to rotor frequency value 404 along a negative slope line 406. Thus, data 400 (e.g., as a lookup table) can be used to determine the voltage supplied for generating an excitation signal based on the desired frequency of the motor shaft.

[0062] Reference Figure 5 This describes a graph depicting the simulation results for starting the VFIS motor and for the system used for speed control. The graph plots the change in the motor's rotating shaft speed over time.

[0063] From zero seconds to one second, system 100 operates during the synchronization phase. During this phase, switch 120 is open, and there is no electrical connection between AC bus 122 and the set of stator windings 108. Thus, no current flows into the set of stator windings 108, and the rotor does not move. Therefore, the rotational shaft speed is zero.

[0064] In the first second, switch 120 closes, and from the first second to the fourth second, the rotational shaft speed gradually increases to 3300 revolutions per minute (RPM) to match the speed reference value. To generate this gradual increase, the amplitude of the excitation signal 114 is gradually reduced, resulting in a gradual build-up of current within the set of stator windings 108. Figure 4 The negative slope voltage frequency data 400 depicted in the figure determines the gradual decrease in amplitude. With no load engaged with motor 102, the rotational shaft speed is maintained at 3300 RPM.

[0065] The load is applied to the shaft in 8 seconds. This load may cause some disturbance, but the system 100 continuously controls the motor 102 via the excitation signal 114 from 8 to 12 seconds to restore the shaft speed and maintain it at 3300 RPM.

[0066] At 12 seconds, the base speed is adjusted to 2400 RPM. The axis speed is gradually reduced to match the base speed. By 13 seconds, the axis speed has reached 2400 RPM and remains at that speed for the duration of the simulation.

[0067] By using a negative slope voltage-frequency relationship, current is gradually applied to the motor 102, thereby gradually increasing the shaft rotation speed (e.g., ...). Figure 5 As shown (indicated), this can avoid sudden current and short circuits, thereby extending the life of the motor 102. Other advantages may also exist.

[0068] Reference Figures 6A to 6FThe document describes a method 600 for starting a VFIS motor and for speed control. The method 600 may include the following steps: at 602, transmitting an excitation signal from the stator of the motor to the rotor of the motor, wherein the excitation signal is received at a set of rotor windings, and wherein the excitation signal generates a rotating magnetic flux at the rotor, which generates a first AC voltage at a set of stator windings. For example, an excitation signal 114 may be transmitted from the stator 104 to the rotor 106 and received at said set of rotor windings 110.

[0069] The method 600 may further include the following steps: at 604, controlling an excitation signal to make a first amplitude of a first AC voltage at the set of stator windings equal to a second amplitude of a second AC voltage at the AC bus, and to synchronize the first AC voltage with the second AC voltage. For example, an excitation signal 114 may be controlled to make a first AC voltage 118 equal to a second AC voltage 126.

[0070] The method 600 may further include the following step: after synchronizing the first AC voltage at the set of stator windings with the second AC voltage at the AC bus, at 606, electrically connecting the set of stator windings to the AC bus. For example, switch 120 may be closed to electrically connect AC bus 122 to the set of stator windings 108.

[0071] The method 600 may include the following steps: at 608, reducing the amplitude of the excitation signal to allow current to flow from the AC bus to the set of stator windings, thereby generating torque that causes the rotor to rotate. For example, the amplitude of the excitation signal 114 may be reduced to allow current to flow from the AC bus 122 to the set of stator windings 108.

[0072] The advantage of method 600 is that the motor 102 can be started gradually without causing a short circuit or current spike. Other advantages may also exist.

[0073] Reference Figure 6B A further portion of method 600 may include the following steps: at 610, receiving an amplitude excitation source control signal, a frequency excitation source control signal, and a phase excitation source control signal. Method 600 may further include the following step: at 612, generating the excitation signal based on the amplitude excitation source control signal, the frequency excitation source control signal, and the phase excitation source control signal.

[0074] Reference Figure 6CA further portion of method 600 may include the following steps: at 614, measuring a first AC voltage at the set of stator windings. Method 600 may also include the following steps: at 616, measuring a second AC voltage at the AC bus. Method 600 may further include the following steps: at 618, calculating the amplitude difference, frequency difference, and phase difference between the first AC voltage and the second AC voltage. Method 600 may include the following step: at 620, determining that the first AC voltage and the second AC voltage are synchronized when the amplitude difference decreases below a first threshold, the frequency difference decreases below a second threshold, and the phase difference decreases below a third threshold.

[0075] Reference Figure 6D A further portion of method 600 may include the following steps: at 622, receiving a speed reference value. Method 600 may also include the following steps: at 624, calculating a reference frequency value based on the speed reference value. Method 600 may further include the following steps: at 626, determining an excitation reference voltage based on data mapping voltage values ​​to rotor frequency values, according to the reference frequency value. Method 600 may include the following step: at 628, setting the amplitude of the excitation signal to the excitation reference voltage to cause the rotor to rotate according to the speed reference value.

[0076] The step of determining the excitation reference voltage may include: at 630, storing data mapping the voltage value to the rotor frequency value. The step of determining the excitation reference voltage may further include: at 632, retrieving the excitation reference voltage from the data based on the reference frequency value. The step of determining the excitation reference voltage may further include: at 634, gradually decreasing the excitation reference voltage over a time period.

[0077] Reference Figure 6E A further portion of method 600 may include the following step: at 636, determining a reference excitation frequency based on a reference frequency value and a measured frequency of a second AC voltage at the AC bus. Method 600 may further include the step of setting the frequency of the excitation signal to the reference excitation frequency at 638. The step of determining the reference excitation frequency may include: at 640, gradually changing the reference excitation frequency over a time period.

[0078] Reference Figure 6F A further portion of method 600 may include the following step: at 642, determining a reference excitation phase. Method 600 may also include the following step: at 644, setting the phase of the excitation signal as the reference excitation phase. The step of determining the reference excitation phase may include: at 648, storing in memory a measured phase value representing a second AC voltage at the AC bus. The step of determining the reference excitation phase may further include: at 650, generating the reference excitation phase based on the data representing the measured phase value.

[0079] Furthermore, this disclosure includes embodiments according to the following provisions:

[0080] Clause 1. A system comprising: an electric motor having a stator, a rotor, a set of stator windings, and a set of rotor windings; a high-frequency transformer configured to transmit an excitation signal from the stator to the rotor, wherein the excitation signal is received at the set of rotor windings, and wherein the excitation signal generates a rotating magnetic flux at the rotor, the rotating magnetic flux generating a first alternating current (AC) voltage at the set of stator windings; a switch electrically connected between the set of stator windings and an AC bus; and a controller circuit configured to control the excitation signal such that a first amplitude of the first AC voltage at the set of stator windings is equal to a second amplitude of a second AC voltage at the AC bus, and to synchronize the first AC voltage with the second AC voltage, the controller circuit further configured to close the switch after synchronizing the first AC voltage with the second AC voltage, and to reduce the amplitude of the excitation signal such that current can flow from the AC bus to the set of stator windings, thereby generating a torque causing the rotor to rotate.

[0081] Clause 2. The system according to Clause 1, further comprising: an excitation source circuit configured to receive an amplitude excitation source control signal, a frequency excitation source control signal, and a phase excitation source control signal from the controller circuit, and to generate the excitation signal based on the amplitude excitation source control signal, the frequency excitation source control signal, and the phase excitation source control signal.

[0082] Clause 3. The system according to Clause 1 further includes: a first voltage signal sensor electrically connected between the switch and the set of stator windings and configured to provide the controller circuit with a measurement of a first AC voltage at the set of stator windings; and a second voltage signal sensor electrically connected between the AC bus and the switch and configured to provide a measurement of a second AC voltage.

[0083] Clause 4. The system according to Clause 1, wherein the motor is a variable frequency independent speed (VFIS) motor.

[0084] Clause 5. The system according to Clause 1, wherein the set of stator windings is a set of three-phase stator windings, and wherein the set of rotor windings is a set of three-phase rotor windings.

[0085] Clause 6. The system according to Clause 1, wherein the AC bus is a three-phase AC bus.

[0086] Clause 7. A method comprising the steps of: transmitting an excitation signal from the stator of an electric motor to the rotor of the electric motor, wherein the excitation signal is received at a set of rotor windings, and wherein the excitation signal generates a rotating magnetic flux at the rotor, the rotating magnetic flux generating a first alternating current (AC) voltage at a set of stator windings; controlling the excitation signal such that a first amplitude of the first AC voltage at the set of stator windings is equal to a second amplitude of a second AC voltage at an AC bus, and synchronizing the first AC voltage with the second AC voltage; after synchronizing the first AC voltage at the set of stator windings with the second AC voltage at the AC bus, electrically connecting the set of stator windings to the AC bus; and reducing the amplitude of the excitation signal such that current can flow from the AC bus to the set of stator windings, thereby generating a torque causing the rotor to rotate.

[0087] Clause 8. The method according to Clause 7, the method further comprising the steps of: receiving an amplitude excitation source control signal, a frequency excitation source control signal, and a phase excitation source control signal; and generating the excitation signal based on the amplitude excitation source control signal, the frequency excitation source control signal, and the phase excitation source control signal.

[0088] Clause 9. The method according to Clause 7 further comprises the steps of: measuring a first AC voltage at the set of stator windings; measuring a second AC voltage at the AC bus; calculating an amplitude difference, a frequency difference, and a phase difference between the first AC voltage and the second AC voltage; and determining that the first AC voltage and the second AC voltage are synchronized when the amplitude difference decreases below a first threshold, the frequency difference decreases below a second threshold, and the phase difference decreases below a third threshold.

[0089] Clause 10. The method according to Clause 7, the method further comprising the steps of: receiving a speed reference value; calculating a reference frequency value based on the speed reference value; determining an excitation reference voltage based on the reference frequency value using data that maps a voltage value to a rotor frequency value; and setting the amplitude of the excitation signal to the excitation reference voltage to cause the rotor to rotate at the speed reference value.

[0090] Clause 11. The method according to Clause 10, wherein the step of determining the excitation reference voltage comprises: storing the data mapping the voltage value to the rotor frequency value; and retrieving the excitation reference voltage from the data based on the reference frequency value.

[0091] Clause 12. The method according to Clause 10, wherein the step of determining the excitation reference voltage further comprises: gradually decreasing the excitation reference voltage over a period of time.

[0092] Clause 13. The method according to Clause 10, the method further comprising the steps of: determining a reference excitation frequency based on the reference frequency value and based on the measured frequency of the second AC voltage at the AC bus; and setting the frequency of the excitation signal to the reference excitation frequency.

[0093] Clause 14. The method according to Clause 13, wherein the step of determining the reference excitation frequency further comprises: gradually changing the reference excitation frequency over a period of time.

[0094] Clause 15. The method according to Clause 10, the method further comprising the steps of: determining a reference excitation phase; and setting the phase of the excitation signal as the reference excitation phase.

[0095] Clause 16. The method according to Clause 15, wherein the step of determining the reference excitation phase comprises: storing data representing a measured phase value of a second AC voltage at the AC bus in a memory; and generating the reference excitation phase based on the data representing the measured phase value.

[0096] Clause 17. A system comprising: a synchronization control module configured to measure a first AC voltage at a set of stator windings, measure a second AC voltage at an AC bus, generate an excitation synchronization signal based on the first AC voltage and the second AC voltage, and generate a switch control signal based on the first AC voltage and the second AC voltage; a motor speed control module configured to receive a speed reference value and the measurement results of the second AC voltage, and generate an excitation reference signal based on the speed reference value and the measurement results of the second AC voltage; an excitation source control module configured to generate an excitation source control signal based on the excitation synchronization signal or based on the excitation reference signal; and a switch configured to route the excitation synchronization signal to the excitation source control module during a synchronization phase and to route the excitation reference signal to the excitation source control module during a motor speed regulation phase.

[0097] Clause 18. The system according to Clause 17, wherein the synchronization control module comprises: a first amplitude and phase analyzer module configured to measure the first AC voltage; a second amplitude and phase analyzer module configured to measure the second AC voltage; a set of differential modules configured to calculate an amplitude difference, a frequency difference, and a phase difference between the first AC voltage and the second AC voltage; a set of comparison modules configured to determine whether the amplitude difference decreases below a first threshold, whether the frequency difference decreases below a second threshold, and whether the phase difference decreases below a third threshold; a logic module configured to generate the switching control signal based on the output from the set of comparison modules; and a set of proportional-integral-derivative (PI-DI) controllers configured to generate the excitation synchronization signal based on the amplitude difference, the frequency difference, and the phase difference.

[0098] Clause 19. The system according to Clause 17, wherein the motor speed control module comprises: a constant multiplier module configured to convert the speed reference value into a reference frequency value; a negative slope voltage-frequency control module configured to receive the reference frequency value and calculate an intermediate excitation reference voltage based on the reference frequency value; a first differential circuit configured to generate an intermediate excitation reference frequency value based on the reference frequency value and based on a measured frequency of the second AC voltage at the AC bus; a second differential circuit, a first proportional-integral-derivative controller, and a first slope module, wherein the second... A differential circuit, a first proportional-integral-differential controller, and a first slope module are configured together to generate an excitation reference voltage and gradually change the excitation reference voltage over a period of time to match the intermediate excitation reference voltage; and a third differential circuit, a second proportional-integral-differential controller, and a second slope module are configured together to generate an excitation reference frequency value based on the intermediate excitation reference frequency value and modify the excitation reference frequency value over the period of time to match the intermediate excitation reference frequency value, wherein the excitation reference signal includes the excitation reference voltage and the excitation reference frequency value.

[0099] Clause 20. The system according to Clause 19, wherein the motor speed control module includes: a memory module configured to store measured phase values ​​and generate an excitation reference phase value matching the measured phase values, wherein the excitation reference signal includes the excitation reference phase value.

[0100] Although various embodiments have been shown and described, this disclosure is not limited thereto, but rather it should be understood that it includes all such modifications and variations as will be apparent to those skilled in the art.

Claims

1. A method (600) for starting an electric motor (102), the method comprising the steps of: An excitation signal (114) is transmitted from the stator (104) of the motor (102) to the rotor (106) of the motor (102), wherein the excitation signal (114) is received at a set of rotor windings (110), and wherein the excitation signal (114) generates a rotating magnetic flux (116) at the rotor (106), and the rotating magnetic flux (116) generates a first alternating voltage, i.e., a first AC voltage (118), at a set of stator windings (108). The excitation signal (114) is controlled so that the first amplitude of the first AC voltage (118) at the set of stator windings (108) is equal to the second amplitude of the second AC voltage (126) at the AC bus (122), and the first AC voltage (118) is synchronized with the second AC voltage (126). After synchronizing the first AC voltage (118) at the set of stator windings (108) with the second AC voltage (126) at the AC bus (122), the set of stator windings (108) is electrically connected to the AC bus (122); and The amplitude of the excitation signal (114) is reduced so that current can flow from the AC bus (122) to the set of stator windings (108), thereby generating a torque that causes the rotor (106) to rotate. The method further includes the following steps: Measure the first AC voltage (118) at the set of stator windings (108); Measure the second AC voltage (126) at the AC bus (122); Calculate the amplitude difference (312), frequency difference (313), and phase difference (314) between the first AC voltage (118) and the second AC voltage (126); and When the amplitude difference (312) decreases below the first threshold, the frequency difference (313) decreases below the second threshold, and the phase difference (314) decreases below the third threshold, it is determined that the first AC voltage (118) is synchronized with the second AC voltage (126).

2. The method according to claim 1, further comprising the following steps: Receives amplitude excitation source control signal (130), frequency excitation source control signal (131), and phase excitation source control signal (132); and The excitation signal (114) is generated based on the amplitude excitation source control signal (130), the frequency excitation source control signal (131), and the phase excitation source control signal (132).

3. The method according to claim 1, further comprising the following steps: Receive speed reference value (144); The reference frequency value (332) is calculated based on the speed reference value (144); Based on data (400) that maps the voltage value (402) to the rotor frequency value (404), the excitation reference voltage (356) is determined according to the reference frequency value (332); and The amplitude of the excitation signal (114) is set to the excitation reference voltage (356) so that the rotor (106) rotates according to the speed reference value (144).

4. The method according to claim 3, wherein, The steps for determining the excitation reference voltage (356) include: Store the data (400) that maps the voltage value (402) to the rotor frequency value (404); and Based on the reference frequency value (332), the excitation reference voltage (356) is retrieved from the data (400).

5. The method according to claim 3, wherein, The step of determining the excitation reference voltage (356) further includes: The excitation reference voltage (356) is gradually reduced over a period of time.

6. The method according to claim 3, further comprising the following step: The reference excitation frequency (357) is determined based on the reference frequency value (332) and the frequency measured based on the second AC voltage (126) at the AC bus (122); and The frequency of the excitation signal (114) is set to the reference excitation frequency (357).

7. The method according to claim 6, wherein, The step of determining the reference excitation frequency (357) further includes: The reference excitation frequency (357) is gradually changed over a period of time.

8. The method according to claim 3, further comprising the following step: Determine the reference excitation phase (358); and The phase of the excitation signal (114) is set as the reference excitation phase (358), wherein the step of determining the reference excitation phase (358) includes: The measured phase value (324) representing the second AC voltage (126) at the AC bus (122) is stored in the memory; and The reference excitation phase (358) is generated based on the data representing the measured phase value (324).

9. A system (100) for starting an electric motor (102) according to any one of claims 1-8, the electric motor having a stator (104), a rotor (106), a set of stator windings (108), and a set of rotor windings (110), the system comprising: A high-frequency transformer (112) is configured to transmit an excitation signal (114) from the stator (104) to the rotor (106), wherein the excitation signal (114) is received at a set of rotor windings (110), and wherein the excitation signal (114) generates a rotating magnetic flux (116) at the rotor (106), and the rotating magnetic flux (116) generates a first alternating voltage, i.e., a first AC voltage (118), at a set of stator windings (108). Switch (120), the switch being electrically connected between the set of stator windings (108) and the AC bus (122); and A controller circuit (124) is configured to control the excitation signal (114) to make a first amplitude of a first AC voltage (118) at the set of stator windings (108) equal to a second amplitude of a second AC voltage (126) at the AC bus (122), and to synchronize the first AC voltage (118) with the second AC voltage (126). The controller circuit (124) is also configured to close the switch (120) after synchronizing the first AC voltage (118) with the second AC voltage (126), and to reduce the amplitude of the excitation signal (114) so ​​that current can flow from the AC bus (122) to the set of stator windings (108), thereby generating a torque that causes the rotor (106) to rotate.

10. The system according to claim 9, further comprising: The excitation source circuit (128) is configured to receive an amplitude excitation source control signal (130), a frequency excitation source control signal (131), and a phase excitation source control signal (132) from the controller circuit (124), and to generate the excitation signal (114) based on the amplitude excitation source control signal (130), the frequency excitation source control signal (131), and the phase excitation source control signal (132).

11. The system of claim 9, further comprising: A first voltage signal sensor (134), electrically connected between the switch (120) and the set of stator windings (108), and configured to provide the controller circuit (124) with a measurement (138) of a first AC voltage (118) at the set of stator windings (108); and A second voltage signal sensor (136) is electrically connected between the AC bus (122) and the switch (120) and is configured to provide a measurement result (140) of the second AC voltage (126).

12. The system according to claim 9, wherein, The motor (102) is a variable frequency independent speed motor, i.e., a VFIS motor.

13. The system according to claim 9, wherein, The set of stator windings (108) is a set of three-phase stator windings, and the set of rotor windings (110) is a set of three-phase rotor windings.

14. The system according to claim 9, wherein, The AC bus (122) is a three-phase AC bus.

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