A control circuit for a low voltage synchronous machine

Abstract

This application relates to a control circuit for a low-voltage synchronous machine. The circuit includes: a rectifier module with a first terminal for receiving a first operating AC current, the rectifier module rectifying the first operating AC current to obtain a motor reference voltage; an inverter module inverting the motor reference voltage into a stator operating current to enable the stator windings to operate; a rotor excitation module converting a second high-voltage AC current into a DC excitation current to enable the rotor windings to operate; a voltage monitoring module acquiring the operating status parameters of the low-voltage synchronous machine; and a motion control module generating a stator current adjustment command and a rotor current adjustment command based on the status parameters, wherein the stator current adjustment command controls the inverter module to generate the stator operating current; and the rotor current adjustment command controls the rotor excitation module to generate the DC excitation current. Using this circuit can improve the control accuracy of the transmission system.

Description

Technical Field

[0001] This invention belongs to the field of motor drive control, and in particular relates to a control circuit for a low-voltage synchronous machine. Background Technology

[0002] With the development of motor drive control technology, the drive scheme of asynchronous motors combined with general frequency converters or permanent magnet synchronous motors has gradually replaced DC drives as the preferred solution for main drives of rolling mills and coilers due to its advantages such as wide speed range, fast dynamic response and significant energy saving effect. It is widely used in the metallurgical steel rolling industry.

[0003] In existing methods, asynchronous motor drive systems mainly rely on frequency converters to adjust the stator frequency to achieve speed regulation. The rotor magnetic field is generated by stator current induction, and the dynamic response is limited by the rotor time constant, making it difficult to output rated torque at zero speed. Although permanent magnet synchronous motors eliminate the excitation device, the rotor magnetic field is fixed by permanent magnets and cannot be adjusted online. The range of field weakening speed increase is limited, and the torque response capability is insufficient when the load changes abruptly.

[0004] However, when faced with the harsh conditions of frequent steel biting, throwing, acceleration and deceleration, and tension control during the rolling process, the aforementioned traditional transmission methods generally suffer from problems such as lag in dynamic response, insufficient zero-speed torque, and limited speed range. In particular, when it is necessary to quickly establish tension and cope with impact loads, the control accuracy and stability are difficult to meet the requirements of the rolling process. Summary of the Invention

[0005] Therefore, it is necessary to provide a control circuit for a low-voltage synchronous machine that can improve the control accuracy and stability of the transmission system, addressing the aforementioned technical problems.

[0006] In a first aspect, this application provides a control circuit for a low-voltage synchronous machine, comprising: a motion control module, a rectifier module, an inverter module, a rotor excitation module, and a voltage monitoring module, wherein:

[0007] The first terminal of the rectifier module is used to connect to the first working AC power, and the rectifier module is used to rectify the first working AC power to obtain the motor reference voltage;

[0008] The first end of the inverter module is connected to the second end of the rectifier module. The second end of the inverter module is used to connect to the stator winding of the low-voltage synchronous machine. The inverter module is used to invert the motor reference voltage into the stator operating current to enable the stator winding to work.

[0009] The first end of the rotor excitation module is used to connect to the second high-voltage AC power, and the second end of the rotor excitation module is used to connect to the rotor winding of the low-voltage synchronous machine. The rotor excitation module is used to convert the second high-voltage AC power into DC excitation current to make the rotor winding work.

[0010] The first terminal of the voltage monitoring module is connected to the third terminal of the inverter module. The voltage monitoring module is used to monitor the DC excitation current of the rotor excitation module and calculate the state parameters of the rotor winding based on the DC excitation current.

[0011] The first terminal of the motion control module is connected to the fourth terminal of the inverter module, the second terminal of the motion control module is connected to the third terminal of the rotor excitation module, and the third terminal of the motion control module is connected to the second terminal of the voltage monitoring module. The motion control module is used to generate stator current adjustment commands and rotor current adjustment commands based on the status parameters. The stator current adjustment command is used to control the inverter module to generate stator operating current, and the rotor current adjustment command is used to control the rotor excitation module to generate DC excitation current.

[0012] Furthermore, the rectifier module includes:

[0013] The line reactor unit has its first end being the first end of the rectifier module, which is used to connect to the first working AC power.

[0014] The first end of the coordinated rectifier unit is connected to the second end of the line reactor unit, and the second end of the coordinated rectifier unit is the second end of the rectifier module, which is used to output the motor reference voltage.

[0015] An insulation monitoring unit, the first end of which is connected to the first end of the coordinating rectifier unit and the second end of the line reactor unit;

[0016] The rectifier control unit has its first terminal connected to the third terminal of the coordinating rectifier unit.

[0017] Among them, the line reactor unit is used to filter the first working AC current to obtain the first filtered AC current;

[0018] The coordinated rectifier unit is used to rectify the first filtered AC power to obtain the motor reference voltage;

[0019] The insulation monitoring unit is used to protect the line reactor unit and coordinate the rectifier unit;

[0020] The rectifier control unit is used to instruct and coordinate the rectifier unit to generate the motor reference voltage.

[0021] Furthermore, the rotor excitation module includes:

[0022] The excitation voltage transformer unit has its first end connected to the first end of the rotor excitation module, so as to be connected to the second high-voltage AC power.

[0023] The excitation current generating unit has its first end connected to the second end of the excitation voltage transformer unit, the second end of the excitation current generating unit being the second end of the rotor excitation module, and the third end of the excitation current generating unit being the third end of the rotor excitation module.

[0024] Among them, the excitation voltage transformer unit is used to step down the second high-voltage AC power to obtain the operating voltage of the rotor excitation module;

[0025] The excitation current generation unit is used to convert the operating voltage of the rotor excitation module into DC excitation current according to the rotor current adjustment command.

[0026] Furthermore, the excitation current generation unit includes:

[0027] The ground fault detector has its first terminal as the first terminal of the excitation current generation unit.

[0028] A current transformer, with its first terminal connected to the first terminal of a ground fault detector;

[0029] The fuse switch has its first terminal connected to the first terminal of the ground fault detector and the first terminal of the current transformer.

[0030] A disconnecting switch, the first end of which is connected to the second end of a fuse switch;

[0031] The digital DC speed control device has its first terminal connected to the second terminal of the disconnecting switch, its second terminal being the second terminal of the excitation current generating unit, and its third terminal being the third terminal of the excitation current generating unit.

[0032] A voltage monitoring relay, the first terminal of which is connected to the second terminal of a digital DC speed control device.

[0033] Furthermore, the motion control module is also used to generate fan start / stop commands, brake start / stop commands, and heating start / stop commands based on status parameters. The control circuit also includes a motor auxiliary operation module, which includes:

[0034] The fan working unit has a first end for connecting to a first working low-voltage AC power supply, a second end for connecting to the fourth end of the motion control module, and a third and fourth end for connecting to the fan motor of the low-voltage synchronous machine.

[0035] The brake unit has a first end for connecting to the first working low-voltage AC power supply, a second end for connecting to the fifth end of the motion control module, and a third end for connecting to the brake of the low-voltage synchronous machine.

[0036] The heating unit has a first end for connecting to a second working low-voltage AC power supply, a second end for connecting to the sixth end of the motion control module, and a third end for connecting to the heater of the low-voltage synchronous machine.

[0037] The fan operating unit is used to connect or disconnect the power supply circuit of the fan motor according to the fan start / stop command;

[0038] The brake unit is used to connect or disconnect the power supply circuit of the brake according to the brake start / stop command;

[0039] The heating unit is used to connect or disconnect the power supply circuit of the heater according to the heating start / stop command.

[0040] The control circuit of the aforementioned low-voltage synchronous machine includes a motion control module, a rectifier module, an inverter module, a rotor excitation module, and a voltage monitoring module. Specifically: the first terminal of the rectifier module is connected to a first working AC current, and the rectifier module rectifies the first working AC current to obtain a motor reference voltage; the first terminal of the inverter module is connected to the second terminal of the rectifier module, and the second terminal of the inverter module is connected to the stator winding of the low-voltage synchronous machine, and the inverter module inverts the motor reference voltage into a stator operating current to enable the stator winding to operate; the first terminal of the rotor excitation module is connected to a second high-voltage AC current, and the second terminal of the rotor excitation module is connected to the rotor winding of the low-voltage synchronous machine, and the rotor excitation module converts the second high-voltage AC current into a DC excitation current to enable the rotor winding to operate; the first terminal of the voltage monitoring module is connected to the third terminal of the inverter module, and the voltage monitoring module monitors the rotor excitation module. The DC excitation current is used to calculate the state parameters of the rotor winding. The first terminal of the motion control module is connected to the fourth terminal of the inverter module, the second terminal of the motion control module is connected to the third terminal of the rotor excitation module, and the third terminal of the motion control module is connected to the second terminal of the voltage monitoring module. The motion control module is used to generate stator current adjustment commands and rotor current adjustment commands based on the state parameters. The stator current adjustment command is used to control the inverter module to generate stator operating current, and the rotor current adjustment command is used to control the rotor excitation module to generate DC excitation current. This realizes central coordinated control based on full-state feedback of the low-voltage synchronous machine, and dynamic decoupling and millisecond-level collaborative optimization of stator-side electromagnetic torque and rotor-side excitation magnetic field, thereby ensuring that the synchronous motor can maintain excellent dynamic performance, steady-state accuracy and operating efficiency under various working conditions such as starting, speed regulation, loading and braking. Attached Figure Description

[0041] To more clearly illustrate the technical solutions in the embodiments or related technologies of this application, the accompanying drawings used in the description of the embodiments or related technologies will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0042] Figure 1 This is a circuit diagram of the control circuit of a low-voltage synchronous machine in one embodiment;

[0043] Figure 2 This is a circuit diagram of the control circuit of a low-voltage synchronous machine in one embodiment;

[0044] Figure 3 This is a circuit diagram of the control circuit of a low-voltage synchronous machine in one embodiment;

[0045] Figure 4 This is a circuit diagram of the control circuit of a low-voltage synchronous machine in one embodiment;

[0046] Figure 5 This is a circuit diagram of the control circuit of a low-voltage synchronous machine in one embodiment.

[0047] In the picture:

[0048] 10: A control circuit for a low-voltage synchronous machine; 20: Stator winding; 30: Rotor winding; 40: Fan motor; 50: Holding brake; 60: Heater; 110: Motion control module; 120: Rectifier module; 130: Inverter module; 140: Rotor excitation module; 150: Voltage monitoring module; 160: Motor auxiliary working module; 121: Line reactor unit; 122: Coordinated rectification unit; 123: Insulation monitoring unit; 124: Rectifier control unit; 141: Excitation voltage transformer unit; 142: Excitation current generation unit; A1: Ground fault detector; T1: Current transformer T1; F1: Fuse switch F1; Q1: Disconnect switch Q1; U1: Digital DC speed control device U1; K1: Voltage monitoring relay K1. Detailed Implementation

[0049] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings, which illustrate embodiments of the present application. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of this application will be thorough and complete.

[0050] It is understood that the terms "first," "second," etc., used herein may be used to describe various elements, but these elements are not limited by these terms. These terms are only used to distinguish one element from another. For example, without departing from the scope of this application, a first resistor may be referred to as a second resistor, and similarly, a second resistor may be referred to as a first resistor. Both the first resistor and the second resistor are resistors, but they are not the same resistor.

[0051] It is understood that the term "connection" in the following embodiments should be understood as "electrical connection," "communication connection," etc., if the connected circuits, modules, units, etc., have electrical signal or data transmission with each other.

[0052] It is understandable that "at least one" refers to one or more, and "multiple" refers to two or more. "At least a part of an element" refers to part or all of an element.

[0053] When used herein, the singular forms of “a,” “an,” and “the” may also include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprising / including” or “having,” etc., specify the presence of the stated features, wholes, steps, operations, components, parts, or combinations thereof, but do not preclude the possibility of the presence or addition of one or more other features, wholes, steps, operations, components, parts, or combinations thereof. Meanwhile, the term “and / or” as used in this specification includes any and all combinations of the associated listed items.

[0054] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0055] In one embodiment, such as Figure 1 As shown, a control circuit 10 for a low-voltage synchronous machine includes: a motion control module 110, a rectifier module 120, an inverter module 130, a rotor excitation module 140, and a voltage monitoring module 150.

[0056] In this embodiment, the first terminal of the rectifier module 120 is used to connect to the first working AC power, and the rectifier module 120 is used to rectify the first working AC power to obtain the motor reference voltage.

[0057] Specifically, the first operating AC power is a three-phase AC power supply, with voltage levels such as 380V, 400V, 460V, or 690V (low voltage levels). It can be obtained by stepping down the 10kV / 50Hz high-voltage AC power from the factory's power distribution system through a high-voltage circuit breaker and a phase-shifting transformer. The first terminal of the rectifier module 120 is connected to the first operating AC power supply. The rectifier module 120 rectifies and filters the first operating AC power supply to obtain the motor reference voltage. The motor reference voltage is DC power, used to provide a stable DC power supply to the subsequent inverter module. For example, multiple (e.g., two) rectifier modules can be connected in parallel. The first terminal of each rectifier module is connected to the first operating AC power supply, while the second terminal is connected together to output the motor reference voltage. Connecting multiple rectifier modules in parallel can achieve a doubling of power supply capacity and N+1 redundancy, improving the power supply reliability of the control circuit.

[0058] In this embodiment, the first end of the inverter module 130 is connected to the second end of the rectifier module 120, and the second end of the inverter module 130 is used to connect to the stator winding 20 of the low-voltage synchronous machine. The inverter module 130 is used to invert the motor reference voltage into the stator operating current so that the stator winding 20 can work.

[0059] Specifically, the first terminal of the inverter module 130 is directly connected to the second terminal of the rectifier module 120 to obtain the motor reference voltage. The inverter module 130 inverts the motor reference voltage into a stator operating current with controllable frequency, amplitude, and phase, and outputs it to the stator winding inside the low-voltage synchronous machine through the second terminal of the inverter module 130. The stator winding of the low-voltage synchronous machine consists of three-phase symmetrical coils embedded in the stator core slots of the motor, which generate a rotating magnetic field when three-phase AC power is applied. The core of the inverter module 130 can be a high-performance power conversion and drive unit (such as the SINAMICS S120 series Motor Module). Its function is to invert the motor reference voltage into a three-phase AC power, i.e., the stator operating current, whose frequency, voltage amplitude, and phase can be independently and precisely adjusted, based on the received real-time control commands through the high-frequency switching action of the three-phase full-bridge circuit composed of internal IGBTs, according to the received real-time control commands.

[0060] In this embodiment, the first end of the rotor excitation module 140 is used to connect to the second high-voltage AC power, the second end of the rotor excitation module 140 is used to connect to the rotor winding 30 of the low-voltage synchronous machine, and the rotor excitation module 140 is used to convert the second high-voltage AC power into DC excitation current to make the rotor winding 30 work.

[0061] Specifically, the second high-voltage AC power is a 10kV / 50Hz industrial power supply, which can be obtained from the factory's power distribution system. The first terminal of the rotor excitation module 140 is used to connect to the second high-voltage AC power. The rotor excitation module 140 precisely rectifies and regulates the current of the second high-voltage AC power, and outputs a DC excitation current to the excitation winding of the low-voltage synchronous machine rotor through the second terminal of the rotor excitation module 140. The rotor winding of the low-voltage synchronous machine is a DC coil mounted on the motor rotor, which can be connected to an external power source through brushes and slip rings. The rotor excitation module 140 provides DC excitation current to the rotor winding, causing the rotor to generate a constant magnetic field, which interacts with the stator's rotating magnetic field to produce electromagnetic torque.

[0062] In this embodiment, the voltage monitoring module 150 is used to monitor the DC excitation current of the rotor excitation module 140 and calculate the state parameters of the rotor winding based on the DC excitation current.

[0063] Specifically, the first terminal of the voltage monitoring module 150 is connected to the third terminal of the inverter module 130, and the stator operating current signal output by the inverter module 130 is obtained through this connection. The voltage monitoring module 150 includes at least an encoder unit and a voltage monitoring unit: the first terminal of the voltage monitoring unit is the first terminal of the voltage monitoring module 150, used to acquire and sample the DC excitation current output by the inverter module 130 and convert it into an operating voltage; the voltage monitoring unit can be a VSM10 voltage detection module. The encoder unit is used to parse the rotor position parameters and rotor speed parameters based on the operating voltage obtained by the voltage monitoring unit. The rotor position parameters and rotor speed parameters are spliced ​​together to form the state parameters of the rotor winding; the encoder can be an SMC30 incremental encoder. This encoder unit is coaxially connected to the motor rotor, and its grating disk rotates with the rotor, generating a pulse sequence that strictly corresponds to the rotor angle. By decoding these pulses, the rotor position parameters and rotor speed, which characterize the precise spatial electrical angle of the rotor, can be calculated in real time.

[0064] In this embodiment, the first terminal of the motion control module 110 is connected to the fourth terminal of the inverter module 130, the second terminal of the motion control module 110 is connected to the third terminal of the rotor excitation module 140, and the third terminal of the motion control module 110 is connected to the second terminal of the voltage monitoring module 150. The motion control module 110 is used to generate stator current adjustment commands and rotor current adjustment commands according to the state parameters. The stator current adjustment commands are used to control the inverter module 130 to generate stator operating current, and the rotor current adjustment commands are used to control the rotor excitation module 140 to generate DC excitation current.

[0065] Specifically, the motion control module 110 is the core of the control circuit 10 and its command center, and can be implemented by a high-performance multi-axis motion controller, such as the SIMOTION D445-2. Its first terminal is connected to the fourth terminal of the inverter module 130, its second terminal is connected to the third terminal of the rotor excitation module 140, and its third terminal is connected to the second terminal of the voltage monitoring module 150. The motion control module 110 continuously receives status parameters from the voltage monitoring module 150 through its third terminal, including rotor position parameters and rotor speed parameters. Based on these status parameters, external process settings (including target speed and torque), and an internally stored motor model, the motion control module 110 executes real-time control algorithms, such as Field Oriented Control (FOC) or Direct Torque Control (DTC), and outputs stator current adjustment commands and rotor current adjustment commands. The stator current adjustment command indicates the amplitude, phase, and frequency of the stator current vector required to generate the target torque and magnetic field. The stator current adjustment command is sent to the inverter module 130 through the first terminal of the motion control module 110, instructing the inverter module 130 to accurately generate the required stator operating current. The rotor current adjustment command is the optimal DC excitation current setpoint calculated in real time based on the current motor speed, load, and field weakening control strategy. This command is sent to the rotor excitation module 140 through the second terminal of the motion control module 110, instructing it to precisely adjust the strength of the output excitation current. For example, the connection lines between the motion control module 110, the inverter module 130, and the voltage monitoring module 150 can use a Drive-Cliq bus, and the connection line between the motion control module 110 and the rotor excitation module 140 can use a Profibus bus.

[0066] This embodiment provides a control circuit for a low-voltage synchronous motor, including a motion control module, a rectifier module, an inverter module, a rotor excitation module, and a voltage monitoring module. It realizes central coordinated control based on full-state feedback of the low-voltage synchronous motor, and achieves dynamic decoupling and millisecond-level collaborative optimization of the stator-side electromagnetic torque and the rotor-side excitation magnetic field. This ensures that the synchronous motor can maintain excellent dynamic performance, steady-state accuracy, and operating efficiency under various operating conditions such as starting, speed regulation, loading, and braking.

[0067] In one embodiment, such as Figure 2 As shown, the rectifier module 120 includes a line reactor unit 121, a coordinated rectifier unit 122, an insulation monitoring unit 123, and a rectifier control unit 124.

[0068] In this embodiment, the first end of the line reactor unit 121 is the first end of the rectifier module 120, which is used to connect to the first working AC power; the line reactor unit 121 is used to filter the first working AC power to obtain the first filtered AC power.

[0069] Specifically, the first terminal of the line reactor unit 121 is the first terminal of the rectifier module 120, used to connect to the first operating AC current. The core component inside the line reactor unit 121 can be an AC reactor with a large inductance value, which filters the input first operating AC current to suppress high-order harmonics in the current waveform, reduce pollution to the power grid, and limit the rate of change of current, providing protection for downstream power devices. After processing by the line reactor unit 121, a first filtered AC current with a smoother sinusoidal current waveform is obtained and output from the second terminal of the line reactor unit 121.

[0070] In this embodiment, the first end of the coordinated rectifier unit 122 is connected to the second end of the line reactor unit 121, and the second end of the coordinated rectifier unit 122 is the second end of the rectifier module 120, which is used to output the motor reference voltage. The coordinated rectifier unit 122 is used to rectify the first filtered AC power to obtain the motor reference voltage.

[0071] Specifically, the first terminal of the coordinated rectifier unit 122 receives the first filtered AC power output from the second terminal of the line reactor unit 121. The coordinated rectifier unit 122 is the core of the power conversion in the rectifier module 120 and can employ an IGBT-based intelligent power module, such as the SLM or ALM module from the Siemens SINAMICS series. This unit integrates a three-phase rectifier bridge, a pre-charge control circuit, a DC support capacitor, and corresponding drive protection circuits. Its core function is to perform AC-DC conversion. It rectifies the input first operating AC power into stable DC power, i.e., the motor reference voltage, through the switching control of its internal power devices. This motor reference voltage is output from its second terminal. The coordinated rectifier unit 122 can also achieve bidirectional energy flow; when the motor is in generator mode, it can invert the circuit energy into AC power and feed it back to the grid, achieving energy savings.

[0072] In this embodiment, the first end of the insulation monitoring unit 123 is connected to the first end of the coordinating rectifier unit 122 and the second end of the line reactor unit 121; the insulation monitoring unit 123 is used to protect the line reactor unit 121 and the coordinating rectifier unit 122.

[0073] Specifically, the first terminal of the insulation monitoring unit 123 is connected to the node where the first terminal of the coordinated rectifier unit 122 and the second terminal of the line reactor unit 121 are connected. The insulation monitoring unit 123 can be an insulation monitor, whose function is to continuously monitor the insulation resistance to ground of the DC bus system and related AC feeder lines. The entire rectifier module 120 is designed as an ungrounded system, i.e., an IT system. The insulation monitoring unit 123 assesses the insulation condition by injecting a weak detection signal between the tested line and ground or by measuring its voltage to ground. When the insulation resistance is detected to drop below a safe threshold, indicating a possible ground fault, the insulation monitoring unit will immediately issue an alarm signal to alert maintenance personnel, thereby protecting the line reactor unit, the coordinated rectifier unit, and the entire DC power supply system, preventing more serious short-circuit accidents caused by insulation deterioration.

[0074] In this embodiment, the first end of the rectifier control unit 124 is connected to the third end of the coordinating rectifier unit 122, and the rectifier control unit 124 is used to instruct the coordinating rectifier unit 122 to generate a motor reference voltage.

[0075] Specifically, the rectifier control unit 124 is the intelligent control core of the rectifier module, and can employ a drive controller CU320-2. The first terminal of the rectifier control unit 124 is connected to the third terminal of the coordinating rectifier unit 122 via a high-speed drive bus, such as Drive-CLiQ, forming a direct control link. The function of the rectifier control unit 124 is to drive and manage the coordinating rectifier unit. Based on received instructions and real-time signals acquired by itself, such as motor reference voltage and current, the rectifier control unit 124 generates precise pulse width modulation signals through internal algorithms to control the on / off switching of the IGBT-based intelligent power module inside the coordinating rectifier unit 122. Specific control functions may include managing the system's power-on pre-charging process to avoid inrush current, maintaining the stability of the DC bus voltage during steady-state operation, and controlling energy feedback to the grid in regenerative braking mode, thereby ensuring that the coordinating rectifier unit 122 safely, efficiently, and accurately outputs the required motor reference voltage.

[0076] In the control circuit of the low-voltage synchronous machine provided in this embodiment, the rectifier module includes a line reactor unit, a coordinated rectifier unit, an insulation monitoring unit, and a rectifier control unit. This achieves purification, controllable rectification, and system insulation safety monitoring of the high-voltage AC input power. The line reactor unit is responsible for input filtering and current limiting; the coordinated rectifier unit, as the actuator, completes the core AC / DC conversion and can achieve energy feedback; the insulation monitoring unit provides continuous insulation safety protection; and the rectifier control unit acts as the local brain, receiving overall control commands and precisely driving the coordinated rectifier unit. All units work together to provide a stable and reliable DC power supply for the subsequent inverter module.

[0077] In one embodiment, such as Figure 3 As shown, the rotor excitation module 140 includes an excitation voltage transformer unit 141 and an excitation current generation unit 142.

[0078] In this embodiment, the first end of the excitation voltage transformer unit 141 is the first end of the rotor excitation module 140, so as to connect to the second high voltage AC power. The excitation voltage transformer unit 141 is used to step down the second high voltage AC power to obtain the operating voltage of the rotor excitation module.

[0079] Specifically, the first terminal of the excitation voltage transformer unit 141 is the first terminal of the rotor excitation module 140, used to connect to a second high-voltage AC power supply from an external power distribution system. This second high-voltage AC power supply is typically 10 kV 50 Hz industrial power. The core component of the excitation voltage transformer unit 141 can be an excitation transformer, which consists of an iron core and three-phase windings. The primary winding is connected in a delta (Δ) configuration, and the secondary winding is connected in a star (Y) configuration. The function of the excitation voltage transformer unit 141 is to perform voltage transformation and electrical isolation, stepping down the 10 kV high-voltage AC power to a voltage suitable for the operating voltage of the excitation current generation unit, i.e., the operating voltage of the rotor excitation module. The operating voltage of the rotor excitation module can be set according to actual operation, such as 400V, 690V, or other lower voltage levels. The excitation voltage transformer unit 141 outputs the operating voltage of the rotor excitation module through its second terminal.

[0080] In this embodiment, the first end of the excitation current generating unit 142 is connected to the second end of the excitation voltage transformer unit 141, the second end of the excitation current generating unit 142 is the second end of the rotor excitation module 140, and the third end of the excitation current generating unit 142 is the third end of the rotor excitation module 140. The excitation current generating unit 142 is used to convert the working voltage of the rotor excitation module according to the rotor current adjustment command to obtain DC excitation current.

[0081] Specifically, the excitation current generation unit 142 is the core execution part of the rotor excitation control. Its first terminal is electrically connected to the second terminal of the excitation voltage transformer unit 141, thereby receiving the operating voltage of the rotor excitation module. Its second terminal, serving as the second terminal of the rotor excitation module 140, is connected to the excitation winding of the low-voltage synchronous motor rotor via a dedicated cable, used to output the final DC excitation current. Its third terminal, serving as the third terminal of the rotor excitation module 140, is connected to the motion control module 110, used to receive rotor current adjustment commands issued by the motion control module 110. The excitation current generation unit 142 can internally utilize a fully digital DC speed controller. A digital DC speed controller is a fully digitally controlled DC speed controller that receives AC power at its input, converts the AC power to DC power internally through a thyristor rectifier circuit, and precisely adjusts the magnitude of the output DC current according to the rotor current adjustment commands. For example, a SINAMICS DCM 6RA80 can be used as the core. This device integrates a digital controller and power conversion circuit. Its function is to controllably rectify and precisely adjust the AC operating voltage input from the first terminal based on the rotor current adjustment command received through the third terminal. This command includes the optimal excitation current setpoint required in real time. Through internal fast closed-loop control, the AC power is converted into DC power with stable amplitude, fast adjustment, and excellent dynamic response, namely the DC excitation current, and continuously and accurately supplied to the motor rotor windings from the second terminal, thereby establishing a controllable rotor DC magnetic field. The unit can integrate protection and monitoring devices such as fuses, disconnect switches, and voltage and current detection relays to ensure the safe and reliable operation of the excitation circuit.

[0082] In the control circuit of the low-voltage synchronous motor provided in this embodiment, the rotor excitation module includes an excitation voltage transformer unit and an excitation current generation unit, realizing independent, controllable, and highly dynamic DC excitation for the synchronous motor rotor. The excitation voltage transformer unit is responsible for safely reducing the high-voltage input to the applicable voltage, while the excitation current generation unit, based on central control commands, accurately converts this voltage into a controlled DC current. The two work together to ensure that the rotor magnetic field can be quickly and accurately established and adjusted according to the motor's operating conditions.

[0083] refer to Figure 4 , Figure 4 This is a schematic diagram of the control circuit of a low-voltage synchronous machine in one embodiment.

[0084] In this embodiment, the excitation current generation unit includes:

[0085] Ground fault detector A1, the first end of ground fault detector A1 is the first end of excitation current generation unit 142.

[0086] Specifically, the first terminal of the ground fault detector A1 is the first terminal of the excitation current generation unit 142, used to connect to the second terminal of the excitation voltage transformer unit 141 to receive the operating voltage of the rotor excitation module. The ground fault detector A1 can also be an insulation monitor, its function being to monitor the insulation resistance to ground of the rotor excitation module 140 online. When the insulation of cables or equipment in the rotor excitation module 140 decreases, the ground fault detector A1 can promptly detect the change in insulation resistance and issue an alarm signal or trip command when the insulation resistance falls below a set threshold, thereby protecting the rotor excitation module 140 from damage by insulation faults and ensuring the safe operation of the rotor excitation module 140.

[0087] Current transformer T1, the first terminal of current transformer T1 is connected to the first terminal of ground fault detector A1.

[0088] Specifically, the first terminal of current transformer T1 is connected in parallel with the first terminal of ground fault detector A1, and together they are connected to the second terminal of excitation voltage transformer unit 141 to receive the operating voltage of rotor excitation module. Current transformer T1 is used to detect the AC input current in excitation current generation unit 142, converting the large current into a small signal (such as 4-20mA or 0-10V) for measurement, protection, or display. The current signal detected by current transformer T1 can be transmitted to digital DC speed control device or motion control module for closed-loop control of excitation current, overload protection, and operation status monitoring.

[0089] The first terminal of the fuse switch F1 is connected to the first terminal of the ground fault detector A1 and the first terminal of the current transformer T1.

[0090] Specifically, the first terminal of the fuse switch F1 is connected to the first terminal of the ground fault detector A1 and the first terminal of the current transformer T1, which are then connected to the second terminal of the excitation voltage transformer unit 141. The fuse switch F1 may contain a fuse element. When a short circuit or severe overload fault occurs in the excitation current generation unit 142, the fuse element melts due to excessive current, cutting off the fault circuit and providing short-circuit and overload protection. This prevents the fault from escalating and protects the safety of downstream equipment.

[0091] Disconnecting switch Q1, the first end of disconnecting switch Q1 is connected to the second end of fuse switch F1.

[0092] Specifically, the first terminal of the disconnecting switch Q1 is connected to the second terminal of the fuse switch F1, and is used to manually disconnect the electrical connection between the excitation current generating unit 142 and the power supply during maintenance or fault isolation of the excitation current generating unit 142. The disconnecting switch does not have arc-extinguishing capability and is typically operated only under no-load or low-load current conditions. Its main function is to provide a clear disconnection point to ensure the safety of maintenance personnel. In the excitation circuit, the disconnecting switch is usually used in conjunction with the fuse switch; the fuse switch is responsible for fault protection, and the disconnecting switch is responsible for safety isolation.

[0093] The digital DC speed control device U1 has its first terminal connected to the second terminal of the disconnecting switch Q1, the second terminal of the digital DC speed control device U1 being the second terminal of the excitation current generating unit 142, and the third terminal of the digital DC speed control device U1 being the third terminal of the excitation current generating unit 142.

[0094] Specifically, the first terminal of the digital DC speed controller U1 is connected to the second terminal of the disconnecting switch Q1. The second terminal of the digital DC speed controller U1 is the second terminal of the excitation current generation unit 142, and the third terminal of the digital DC speed controller U1 is the third terminal of the excitation current generation unit 142. The digital DC speed controller U1 is a SINAMICS DCM 6RA80 fully digital DC speed controller. Its first terminal is electrically connected to the second terminal of the disconnecting switch, receiving the rotor excitation module operating voltage after passing through the fuse switch and the disconnecting switch. The second terminal of the digital DC speed controller U1 serves as the second terminal of the excitation current generation unit 142, used to connect to the rotor winding of the low-voltage synchronous machine, and outputting an adjustable DC excitation current. The third terminal of the digital DC speed controller U1 serves as the third terminal of the excitation current generation unit 142, used to communicate with the third terminal of the motion control module 110, and to receive rotor current adjustment commands from the motion control module 110. The digital DC speed control device U1 may contain a thyristor rectifier circuit, a current closed-loop controller, and a protection circuit. Its core function is to precisely control the magnitude of the output DC excitation current according to the received rotor current adjustment command, so as to realize constant flux control or field weakening control of the rotor magnetic field, and has overcurrent, overvoltage, and overheat protection functions.

[0095] Voltage monitoring relay K1, the first terminal of voltage monitoring relay K1 is connected to the second terminal of digital DC speed control device U1.

[0096] Specifically, the first terminal of the voltage monitoring relay K1 is connected to the second terminal of the digital DC speed control device U1 to monitor the DC excitation current output by the excitation current generation unit 142. The voltage monitoring relay K1 has an internal voltage threshold setting. When the voltage corresponding to the DC excitation current exceeds the set value, the voltage monitoring relay K1 can issue an alarm signal or control signal (such as triggering bypass protection, closing the discharge circuit, etc.) to prevent damage to the rotor winding or excitation equipment due to overvoltage.

[0097] In the control circuit of the low-voltage synchronous machine provided in this embodiment, the excitation current generation unit constructs a complete excitation current generation circuit with multiple protection functions by setting up a ground fault detector, a current transformer, a fuse switch, a disconnect switch, a digital DC speed controller, and a voltage monitoring relay. Specifically, the ground fault detector monitors the insulation to ground, the current transformer provides the current detection signal, the fuse switch provides short-circuit protection, the disconnect switch provides safety isolation, the digital DC speed controller enables precise adjustment of the excitation current, and the voltage monitoring relay provides overvoltage protection. This allows the excitation current generation unit to not only accurately output a controllable DC excitation current according to the instructions of the motion control module, but also to promptly protect the safety of the excitation circuit and rotor windings under various fault conditions, achieving high precision and high reliability in excitation control.

[0098] In one embodiment, such as Figure 5 As shown, the motion control module is also used to generate fan start / stop commands, brake start / stop commands, and heating start / stop commands based on state parameters. The control circuit 10 also includes a motor auxiliary working module 160, which includes a fan working unit 161, a brake unit 162, and a heating unit 163.

[0099] In this embodiment, the first end of the fan working unit 161 is used to connect to the first working low-voltage AC power, the second end of the fan working unit 161 is connected to the fourth end of the motion control module 110, the third and fourth ends of the fan working unit 161 are used to connect to the fan motor 40 of the low-voltage synchronous machine, and the fan working unit 161 is used to connect or disconnect the power supply circuit of the fan motor 40 according to the fan start and stop command.

[0100] Specifically, the first terminal of the fan operating unit 161 is used to connect to a first operating low-voltage AC power supply, which is AC 380V three-phase AC power, typically introduced from the plant's low-voltage power distribution system. The second terminal of the fan operating unit 161 can communicate with the fourth terminal of the motion control module 110 via a PROFIBUS bus and a distributed I / O module (such as ET200SP), receiving fan start / stop commands generated by the motion control module 110 based on status parameters such as the synchronous motor's operating temperature. The third and fourth terminals of the fan operating unit 161 are three-phase AC output terminals used to connect to the fan motor of the low-voltage synchronous machine. The fan operating unit may contain control and protection components such as contactors and circuit breakers. When the motion control module 110 issues a fan start / stop command to start, the contactor coil in the fan working unit is energized, its main contacts close, connecting the AC 380V power supply to the fan motor, causing the fan motor to run and providing forced air cooling for the synchronous motor; when the motion control module 110 issues a fan start / stop command to stop, the contactor coil is de-energized, the main contacts open, cutting off the power supply circuit to the fan motor, and the fan motor stops running.

[0101] In this embodiment, the first end of the brake unit 162 is used to connect to the first working low-voltage AC power, the second end of the brake unit 162 is connected to the fifth end of the motion control module 110, the third end of the brake unit 162 is used to connect to the brake 50 of the low-voltage synchronous machine, and the brake unit 162 is used to connect or disconnect the power supply circuit of the brake 50 according to the brake start and stop command.

[0102] Specifically, the brake unit 162 is connected to the first operating low-voltage AC power supply (AC 380V). The second terminal of the brake unit 162 can communicate with the fifth terminal of the motion control module 110 via a PROFIBUS bus and a distributed I / O module (such as ET200SP), receiving braking start / stop commands generated by the motion control module 110 based on the synchronous motor's operating status. The third terminal of the brake unit 162 is used to connect to the brake of the low-voltage synchronous motor. The brake unit 162 may internally contain control elements such as contactors or relays. When the braking start / stop command issued by the motion control module 110 is "start", the contactor coil inside the brake unit 162 is energized, its main contacts close, connecting the AC 380V power supply to the electromagnetic coil of the brake, the brake opens, and the motor shaft can rotate freely; when the braking start / stop command issued by the motion control module 110 is "close", the contactor coil is de-energized, the main contacts open, cutting off the power supply circuit of the brake, the brake closes under the action of spring force, holding the motor shaft to prevent the motor from rotating or sliding due to inertia under the action of external force.

[0103] In this embodiment, the first end of the heating unit 163 is used to connect to the second working low-voltage AC power, the second end of the heating unit 163 is connected to the sixth end of the motion control module 110, the third end of the heating unit 163 is used to connect to the heater 60 of the low-voltage synchronous machine, and the heating unit is used to connect or disconnect the power supply circuit of the heater 60 according to the heating start / stop command.

[0104] Specifically, the first terminal of the heating unit 163 is used to connect to a second working low-voltage AC power supply, which is AC 230V single-phase AC power, and can be introduced from the plant's low-voltage power distribution system. The second terminal of the heating unit 163 is connected to the sixth terminal of the motion control module 110 via a PROFIBUS bus and a distributed I / O module (such as ET200SP) to communicate and receive heating start / stop commands generated by the motion control module 110 based on status parameters such as ambient temperature or synchronous motor winding temperature. The third terminal of the heating unit 163 is used to connect to the heater of the low-voltage synchronous motor. The heating unit 163 may contain control elements such as contactors or solid-state relays. When the motion control module 110 issues a heating start / stop command to start, the contactor coil inside the heating unit 163 is energized, its main contacts close, connecting the AC 230V power supply to the heater, and the heater starts working to preheat or provide moisture-proof heating for the synchronous motor; when the motion control module 110 issues a heating start / stop command to stop, the contactor coil is de-energized, the main contacts open, cutting off the power supply circuit to the heater, and the heater stops working.

[0105] This embodiment provides a control circuit for a low-voltage synchronous motor. The control circuit includes a motor auxiliary working module, which comprises a fan working unit, a brake unit, and a heating unit. This module enables centralized control and automatic management of the peripheral auxiliary equipment (cooling fan, mechanical brake, preheater) of the synchronous motor. The motion control module generates corresponding start / stop commands based on status parameters and transmits them to each execution unit via the PROFIBUS bus and distributed I / O module. The fan working unit automatically adjusts the cooling airflow according to the motor temperature, the brake unit provides safe and reliable mechanical braking based on the motor's operating status, and the heating unit automatically preheats and prevents moisture damage based on the ambient temperature. The coordinated operation of these auxiliary units not only ensures the stable operation of the synchronous motor under various working conditions but also achieves multiple beneficial effects, including energy saving, reduced consumption, extended equipment lifespan, and improved system safety.

[0106] To further illustrate the solution of the application embodiment in this embodiment, a specific example is provided below:

[0107] This application provides a control circuit for a low-voltage synchronous machine, specifically including:

[0108] (1) Stator-side power supply and control equipment (S120 rectifier and inverter section):

[0109] Rectifier unit (Smart Line Module - SLM or Active Line Module - ALM):

[0110] Function: Rectifies the three-phase AC grid voltage into a stable DC bus voltage.

[0111] Topology: Based on the motor power rating, a rack-mounted design is typically used.

[0112] ALM (Active Power Management): Supports four-quadrant operation, allows energy to be fed back to the grid, has low grid-side current harmonics (THD < 5%), and a power factor close to 1, significantly reducing interference to the grid and meeting stringent power quality standards. Suitable for applications with high requirements for power quality and energy feedback.

[0113] SLM (Smart Rectifier): Includes basic rectification and feedback functions, with a compact structure and optimized cost. Suitable for applications with relatively low grid compatibility requirements and those requiring energy feedback.

[0114] The rectifier unit controller, CU320-2, is connected to the rectifier unit via a Drive-cliq network cable.

[0115] The CU320-2 is a powerful multi-axis controller platform that supports multiple communication protocols (PROFIBUS, PROFINET, Ethernet / IP) and a rich library of process functions. The CU320-2 independently manages the control functions of the rectifier unit, including: grid-side rectification control (ensuring sinusoidal grid-side current and power factor control), precise establishment and stabilization control of the DC bus voltage, and energy feedback control.

[0116] Inverter unit (Motor Module – MM):

[0117] Function: Converts DC bus voltage into three-phase AC power with controllable frequency, amplitude, and phase to supply the stator windings of a synchronous motor.

[0118] Topology: Based on the motor power rating, a cabinet-mounted power module is typically used.

[0119] Inverter Unit (S120MM): High-performance power module with optimized heat dissipation design, supports high switching frequency, and provides excellent output current waveform quality.

[0120] Inverter controller: SIMOTION D445-2 motion controller, which connects to the inverter unit via a Drive-cliq network cable.

[0121] The D445-2, as the core processor of the system, is responsible for:

[0122] Field-oriented control (FOC) or direct torque control (DTC) on the stator side of the synchronous motor.

[0123] High-precision speed and torque control.

[0124] The main drives of rolling mills and coilers require complex speed / torque setpoints and actual value processing, transmission system protection interlock logic control, and complex process function calculations.

[0125] Key Coordination: Real-time communication and coordinated control with the excitation controller (DCM's ADVANCE CUD) ensures precise synchronization of the stator current vector and the rotor excitation magnetic field (synchronous motor rotor positioning) to achieve optimal motor performance.

[0126] (2) Rotor-side (excitation-side) power supply and control equipment:

[0127] Excitation unit: SINAMICS DCM 6RA80 DC speed control device.

[0128] Function: To provide a controllable DC excitation current to the excitation winding of a synchronous motor.

[0129] Controller: The excitation current control function of the SINAMICS DCM 6RA80 output is controlled by its own current closed controller, but the set value of the excitation current is coordinated by the SIMOTION D445-2 controller.

[0130] Coordinated Control: The SIMOTION D445-2 (master controller) communicates at high speed with the ADVANCECUD control unit of the DCM 6RA80 via PROFIBUS DP.

[0131] The D445-2 calculates and sends precise excitation current settings to the DCM based on the motor's operating status (speed, load, field weakening requirements, etc.).

[0132] The DCM receives the set value and quickly and accurately adjusts the actual excitation current.

[0133] It enables automatic adjustment of the excitation current, ensuring optimal efficiency and stability of the motor under various operating conditions such as starting, acceleration, deceleration, constant speed, and field weakening speed increase.

[0134] To ensure that the excitation system can respond quickly to sudden load changes or grid disturbances, maintain constant air gap flux or adjust it as needed, and support the dynamic stability of the system.

[0135] (3) Network topology devices:

[0136] Drive-Cliq Network: SIMOTION D445-2 communicates at high speed with the S120 power unit MotorModule, voltage monitoring module VSM10, encoder module SMC30, and terminal expansion module TM31 via Drive-Cliq network cable;

[0137] PROFIBUS Network: SIMOTION D445-2 communicates at high speed with the ADVANCECUD control unit of DCM 6RA80, auxiliary cabinet ET200SP, and field motor ET200SP via PROFIBUS DP network cable;

[0138] Ethernet Network: The SIMOTION D445-2 communicates at high speed with the TP900 drive control panel via an Ethernet cable;

[0139] Profinet Network: SIMOTION D445-2 communicates at high speed with a primary automation PLC via a Profinet network cable.

[0140] (4) VSM voltage monitoring equipment:

[0141] Rectifier Unit: Accurately measures and monitors the amplitude, frequency, and phase of the AC voltage input to the rectifier unit, and provides overvoltage / undervoltage / phase imbalance protection;

[0142] Inverter unit: Installed on the output side of the inverter, it is used to monitor the voltage change generated at the moment of synchronous motor excitation establishment and to calibrate the synchronous motor rotor positioning.

[0143] (5) SMC30 encoder monitoring equipment:

[0144] It receives and processes encoder signals to achieve accurate measurement and monitoring of motor speed and position, providing necessary data support for closed-loop control and having motor temperature detection function.

[0145] In the description of this specification, references to terms such as "some embodiments," "other embodiments," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative descriptions of the above terms do not necessarily refer to the same embodiments or examples.

[0146] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0147] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these modifications and improvements all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A control circuit for a low-voltage synchronous machine, characterized in that, The control circuit includes a motion control module, a rectifier module, an inverter module, a rotor excitation module, and a voltage monitoring module, wherein: The first terminal of the rectifier module is used to connect to the first working AC power, and the rectifier module is used to rectify the first working AC power to obtain the motor reference voltage; The first end of the inverter module is connected to the second end of the rectifier module, and the second end of the inverter module is used to connect to the stator winding of the low-voltage synchronous machine. The inverter module is used to invert the motor reference voltage into the stator operating current so that the stator winding can work. The first end of the rotor excitation module is used to connect to the second high-voltage AC power, and the second end of the rotor excitation module is used to connect to the rotor winding of the low-voltage synchronous machine. The rotor excitation module is used to convert the second high-voltage AC power into DC excitation current to make the rotor winding work. The first end of the voltage monitoring module is connected to the third end of the inverter module. The voltage monitoring module is used to monitor the DC excitation current of the rotor excitation module and calculate the state parameters of the rotor winding based on the DC excitation current. The first end of the motion control module is connected to the fourth end of the inverter module, the second end of the motion control module is connected to the third end of the rotor excitation module, and the third end of the motion control module is connected to the second end of the voltage monitoring module. The motion control module is used to generate stator current adjustment commands and rotor current adjustment commands according to the state parameters. The stator current adjustment commands are used to control the inverter module to generate the stator operating current, and the rotor current adjustment commands are used to control the rotor excitation module to generate the DC excitation current.

2. The control circuit according to claim 1, characterized in that, The rectifier module includes: A line reactor unit, wherein the first end of the line reactor unit is the first end of the rectifier module, and is used to connect to the first working AC power; A coordinated rectifier unit, wherein the first end of the coordinated rectifier unit is connected to the second end of the line reactor unit, and the second end of the coordinated rectifier unit is the second end of the rectifier module, used to output the motor reference voltage; An insulation monitoring unit, wherein the first end of the insulation monitoring unit is connected to the first end of the coordinated rectifier unit and the second end of the line reactor unit; A rectification control unit, wherein a first terminal of the rectification control unit is connected to a third terminal of the coordinated rectification unit; The line reactor unit is used to filter the first working AC current to obtain the first filtered AC current. The coordinated rectification unit is used to rectify the first filtered AC power to obtain the motor reference voltage; The insulation monitoring unit is used to protect the line reactor unit and the coordinated rectifier unit; The rectifier control unit is used to instruct the coordinated rectifier unit to generate the motor reference voltage.

3. The control circuit according to claim 1, characterized in that, The rotor excitation module includes: An excitation voltage transformer unit, wherein the first end of the excitation voltage transformer unit is the first end of the rotor excitation module, and is connected to a second high-voltage AC power supply; An excitation current generating unit, wherein the first end of the excitation current generating unit is connected to the second end of the excitation voltage transformer unit, the second end of the excitation current generating unit is the second end of the rotor excitation module, and the third end of the excitation current generating unit is the third end of the rotor excitation module; The excitation voltage transformer unit is used to step down the second high-voltage AC power to obtain the operating voltage of the rotor excitation module. The excitation current generation unit is used to convert the operating voltage of the rotor excitation module according to the rotor current adjustment command to obtain the DC excitation current.

4. The control circuit according to claim 3, characterized in that, The excitation current generating unit includes: A ground fault detector, wherein the first end of the ground fault detector is the first end of the excitation current generating unit; A current transformer, wherein the first end of the current transformer is connected to the first end of the ground fault detector; A fuse switch, the first end of which is connected to the first end of the ground fault detector and the first end of the current transformer; A disconnecting switch, wherein the first end of the disconnecting switch is connected to the second end of the fuse switch; A digital DC speed control device, wherein the first end of the digital DC speed control device is connected to the second end of the disconnecting switch, the second end of the digital DC speed control device is the second end of the excitation current generating unit, and the third end of the digital DC speed control device is the third end of the excitation current generating unit; A voltage monitoring relay, wherein the first terminal of the voltage monitoring relay is connected to the second terminal of the digital DC speed control device.

5. The control circuit according to claim 1, characterized in that, The motion control module is further configured to generate fan start / stop commands, brake start / stop commands, and heating start / stop commands based on the state parameters. The control circuit also includes a motor auxiliary operating module, which comprises: A fan working unit, wherein the first end of the fan working unit is used to connect to a first working low-voltage AC power supply, the second end of the fan working unit is connected to the fourth end of the motion control module, and the third and fourth ends of the fan working unit are used to connect to the fan motor of the low-voltage synchronous machine. A brake unit, wherein the first end of the brake unit is used to connect to the first working low-voltage AC power supply, the second end of the brake unit is connected to the fifth end of the motion control module, and the third end of the brake unit is used to connect to the brake of the low-voltage synchronous machine. A heating unit, wherein the first end of the heating unit is used to connect to a second working low-voltage AC power supply, the second end of the heating unit is connected to the sixth end of the motion control module, and the third end of the heating unit is used to connect to the heater of the low-voltage synchronous machine; The fan operating unit is used to connect or disconnect the power supply circuit of the fan motor according to the fan start / stop command; The brake unit is used to connect or disconnect the power supply circuit of the brake according to the brake start / stop command; The heating unit is used to connect or disconnect the power supply circuit of the heater according to the heating start / stop command.

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