A large synchronous motor rotor excitation device and control method

Abstract

The application provides a large synchronous motor rotor excitation device and a control method, comprising: a main control unit, which is used for collecting operation parameters of the synchronous motor and calculating a silicon-controlled trigger angle according to a control law; a power unit, which is used for receiving a double-pulse trigger signal and generating an adjustable direct-current excitation voltage; a starting loop, which is used for connecting a starting resistor across both ends of a rotor excitation winding when the motor is started asynchronously; a slip measurement module, which is used for performing AC sampling, digital filtering and slip calculation on a rotor induced voltage signal in an asynchronous starting stage to obtain a rotor speed; a field excitation control module, which is used for sending a field excitation trigger signal to the power unit when the rotor speed reaches a set field excitation speed and a field excitation angle condition is met, so that a three-phase full-bridge rectifier circuit outputs a direct-current excitation current to the rotor winding; a monitoring unit, which is used for parameter setting, state display and fault alarm; an external excitation transformer and an external starting resistor box, which are used for power supply to the power unit and starting current limiting.

Description

Technical Field

[0001] This invention relates to the field of motor excitation technology, and more particularly to a rotor excitation device and control method for a large synchronous motor. Background Technology

[0002] Synchronous motors, widely used in industrial and mining enterprises, are crucial electrical devices whose operating characteristics are closely related to their excitation systems. Synchronous motors achieve electromechanical energy conversion through the interaction between the magnetic field generated by the rotor excitation current and the rotating magnetic field of the stator, offering significant advantages such as constant speed and adjustable power factor. Specifically, the excitation system, by adjusting the magnitude and phase of the DC current in the rotor windings, not only maintains stable motor operation but also improves the power factor of the power grid, achieving energy-saving performance. With the development of power electronics technology and control theory, modern excitation systems have gradually evolved from early analog control towards digitalization and intelligence, which is of great significance for improving the overall performance of synchronous motors.

[0003] Currently, traditional excitation devices mostly employ analog control, which suffers from low adjustment accuracy and slow response speed. While some excitation systems using thyristor rectification improve adjustment performance, they still face drawbacks such as high harmonic interference and simplistic control algorithms. Existing technologies often focus only on single-parameter adjustments of voltage or current, lacking a comprehensive assessment of the motor's operating status. This leads to issues like loss of synchronization or oscillations during sudden load changes or grid fluctuations. Furthermore, conventional excitation devices have inadequate fault detection and protection functions, making it difficult to respond promptly to abnormalities such as rotor winding overheating and excitation loss, thus affecting the reliability of motor operation. These technological limitations make existing excitation systems unable to meet the requirements of modern industrial production for efficient and stable equipment operation. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a rotor excitation device and control method for a large synchronous motor. Through reverse polarity end-excitation, AC sampling digital filtering, and dual-CPU fully digital control, this invention achieves precise excitation and stable operation of the rotor excitation for a large synchronous motor.

[0005] The technical means employed in this invention are as follows:

[0006] A large synchronous motor rotor excitation device includes: The main control unit is used to collect the operating parameters of the synchronous motor and calculate the thyristor firing angle based on the control law. ; The power unit includes a three-phase fully controlled bridge rectifier circuit, which is composed of six thyristor units, and each thyristor unit has an RC snubber circuit for receiving the dual-pulse trigger signal output by the main control unit to generate an adjustable DC excitation voltage. The starting circuit includes a starting resistor and a starting thyristor, wherein the starting resistor is connected across the rotor excitation winding during asynchronous motor starting; The slip measurement module is used to perform AC sampling, digital filtering, and slip calculation on the rotor induced voltage signal during the asynchronous start-up phase to obtain the rotor speed. The excitation control module is used to send an excitation trigger signal to the power unit when the rotor speed reaches the set excitation speed and the excitation angle condition is met, so that the three-phase fully controlled bridge rectifier circuit outputs DC excitation current to the rotor winding. The monitoring unit communicates with the main control unit and is used for parameter setting, status display, and fault alarm. The external excitation transformer and the external starting resistor box are located outside the excitation cabinet and are used to supply power to the power unit and complete the starting current limiting.

[0007] Furthermore, the main control unit has a dual-CPU structure, including a CPU module and an I / O module. The CPU module completes data acquisition, control law calculation and pulse generation, while the I / O module completes digital / analog input / output, trigger pulse driving, temperature measurement and fan control.

[0008] Furthermore, the slip measurement module uses an AC sampling plus digital filtering algorithm to replace the traditional square wave comparator in order to improve the measurement accuracy under harmonic interference.

[0009] Furthermore, the excitation control module adopts a reverse polarity end-excitation strategy, which enables the DC excitation current after excitation to quickly enter the rotor winding, thereby improving the success rate of heavy-load start-up and re-synchronization.

[0010] Furthermore, the trigger pulse of the power unit is a double pulse with a phase difference of 60° electrical angle, and the α-angle phase shift range is 7° to 145° to adapt to different excitation voltage requirements.

[0011] Furthermore, the monitoring unit communicates with the main control unit via the Modbus protocol and has Ethernet, RS485, Profibus or CAN bus expansion interfaces.

[0012] The present invention also provides a method for controlling the rotor excitation of a large synchronous motor based on the above-mentioned large synchronous motor rotor excitation device, comprising: During the asynchronous start-up phase, the starting resistor is connected to the rotor circuit, and the rotor induced voltage is collected in real time. The induced voltage is AC sampled and digitally filtered to calculate the slip and obtain the rotor speed. When the rotor speed exceeds the set excitation speed, select the reverse polarity end excitation angle and issue an excitation command; The power unit is based on the firing angle Output DC excitation voltage to enable the motor to enter the synchronous operation stage; During the synchronous operation phase, the excitation current and power factor are monitored in real time, and the system switches to constant excitation current control mode when the excitation current is lower than the minimum excitation current limit to prevent loss of synchronization.

[0013] Furthermore, the trigger angle α is obtained in real time by collecting terminal voltage, terminal current, active power, reactive power and power factor, and calculated according to a predetermined control law.

[0014] Furthermore, the control method also includes a system self-test step to detect faults in the memory, power supply, and thyristor. Once a fault is detected, a hardware fault signal is issued and the cause of the fault is located.

[0015] Furthermore, the minimum excitation current limit, the excitation multiple, the low voltage range, and the excitation time are all set online through the monitoring unit.

[0016] Compared with the prior art, the present invention has the following advantages: 1. This invention comprehensively utilizes modern excitation control theory of synchronous motors, making up for the deficiencies in control theory and design concepts of existing similar equipment in China.

[0017] 2. This invention designs the excitation transformer and starting resistor box outside the excitation cabinet, saving space in the device and eliminating the safety hazards of overheating and burning of the excitation transformer and starting resistor, which could endanger the main body of the excitation device.

[0018] 3. This invention adopts the internationally popular all-digital control technology and semiconductor controllable rectification technology. Its main control unit optimizes the operating parameters, operating curves and characteristic curves of the synchronous motor to achieve the best control of the synchronous motor operation.

[0019] 4. This invention adopts open communication and network interfaces, and has Ethernet Modbus / TCP, Modbus / RS485, Profibus and CAN bus communication functions, which can be easily connected to other devices or networks to realize the automation and informatization of equipment control and management. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is the electrical schematic diagram of the main circuit of the excitation device of the present invention.

[0022] Figure 2 This is an electrical schematic diagram of the control circuit of the excitation device of the present invention.

[0023] Figure 3 This is the wiring diagram of the main control unit of the present invention.

[0024] Figure 4 This is the slip rate measurement and excitation control angle selection curve of the present invention.

[0025] Figure 5 This is the electrical schematic diagram of the monitoring unit of the present invention.

[0026] Figure 6 This is a diagram showing the location of the external excitation transformer and the starting resistor in this invention. Detailed Implementation

[0027] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0028] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0029] This invention provides a large synchronous motor rotor excitation device, comprising: The main control unit is used to collect the operating parameters of the synchronous motor and calculate the thyristor firing angle based on the control law. ; The power unit includes a three-phase fully controlled bridge rectifier circuit, which is composed of six thyristor units, and each thyristor unit has an RC snubber circuit for receiving the dual-pulse trigger signal output by the main control unit to generate an adjustable DC excitation voltage. The starting circuit includes a starting resistor (RF) and a starting thyristor (KQ), wherein the starting resistor is connected across the rotor excitation winding during asynchronous motor starting; The slip measurement module is used to perform AC sampling, digital filtering, and slip calculation on the rotor induced voltage signal during the asynchronous start-up phase to obtain the rotor speed. The excitation control module is used to send an excitation trigger signal to the power unit when the rotor speed reaches the set excitation speed and the excitation angle condition is met, so that the three-phase fully controlled bridge rectifier circuit outputs DC excitation current to the rotor winding. The monitoring unit communicates with the main control unit and is used for parameter setting, status display, and fault alarm. The external excitation transformer and the external starting resistor box are located outside the excitation cabinet and are used to supply power to the power unit and complete the starting current limiting.

[0030] In this embodiment, as Figure 1 The diagram shows the electrical schematic of the main circuit of the excitation device. The three-phase AC power supply is stepped down by an external excitation transformer and then fed into a three-phase fully controlled bridge rectifier circuit composed of six thyristors. The DC output of the rectifier bridge is connected in series with a fast-acting fuse and a shunt, and then directly connected to the synchronous motor rotor excitation winding. A varistor and RC absorption circuit are provided between the positive and negative buses to suppress overvoltage. The starting resistor (RF) is connected in parallel across the rotor winding via a starting thyristor (KQ) to achieve short-circuit current limiting during asynchronous starting. Figure 2 The diagram shows the electrical schematic of the excitation device control circuit. The main control unit's dual-CPU module outputs six dual-pulse trigger signals with a 60° phase difference through high-speed optocouplers. After isolation by a pulse transformer, these signals drive six thyristors respectively. The rotor induced voltage is sent to the sampling channel via an isolation transformer and a filter circuit for slip calculation. Switching signals such as start-up, excitation, and fault protection are entered into the IO module through opto-isolation. The monitoring unit is interconnected with the main control board via a Modbus bus to complete parameter setting, real-time monitoring, and fault alarm display.

[0031] In a preferred embodiment of the present invention, the main control unit has a dual-CPU structure, including a CPU module and an I / O module. The CPU module performs data acquisition, control law calculation, and pulse generation, while the I / O module performs digital / analog input / output, trigger pulse driving, temperature measurement, and fan control. In this embodiment, as... Figure 3The diagram shows the wiring diagram of the main control unit. The main control unit adopts a dual-CPU plug-in board structure: the CPU board on the left is connected to the A / D sampling module through a parallel bus to receive the voltage, current, excitation current and rotor induced voltage signals at the receiver end; the IO board on the right is equipped with 24 optocoupler isolated digital inputs, 8 relay outputs and 2 RS485 interfaces; six trigger pulses are output to the gate of the power unit thyristor via onboard high-speed optocouplers and pulse transformer terminal blocks; the power supply terminals are connected to dual power supplies of DC 24 V and AC 220 V, and the board is equipped with fuses, common mode inductors and status LEDs to complete the signal acquisition, calculation, pulse generation and external communication of the entire excitation control.

[0032] In a preferred embodiment of this invention, the slip measurement module uses AC sampling plus digital filtering algorithm instead of a traditional square wave comparator to improve measurement accuracy under harmonic interference. In this embodiment, when the synchronous motor starts asynchronously, an alternating induced current is induced in the rotor circuit. This induced current is converted into a voltage signal through the starting resistor. After isolation, the voltage signal is sent to the main control unit. By measuring the frequency of the voltage signal, i.e., the slip, the rotor speed can be measured. The traditional slip measurement method converts this voltage signal into a square wave signal through a comparator and measures the slip by measuring the width of the square wave. The disadvantage of this method is poor anti-interference capability; it is prone to misjudgment when the voltage signal contains harmonics. This device performs AC sampling and digital filtering on the voltage signal, and calculates the pulse width of the voltage signal using an AC algorithm, greatly improving anti-interference capability and making the hardware circuit simpler and more reliable.

[0033] In a specific implementation, as a preferred embodiment of the present invention, the excitation control module adopts a reverse polarity end-excitation strategy, enabling the DC excitation current after excitation to quickly enter the rotor winding, thereby improving the success rate of heavy-load starting and re-synchronization. In this embodiment, as... Figure 4 The figure shows the slip measurement and excitation control angle selection curves. Generally, excitation devices use same-polarity end-excitation, where the direction of the rotor induced current is opposite to the direction of the DC excitation current If generated after excitation, causing only a small portion of If to be fed into the excitation winding, or even none at all. This device uses near-reverse-polarity end-excitation, allowing the DC excitation current to be fed into the excitation winding more quickly. While the excitation angle selection is not critical during no-load motor startup, it plays a crucial role during re-synchronization, especially for units with large rotational inertia and small steady-state slip when losing synchronization, due to heavy starting loads. An improper excitation angle selection can lead to failure of synchronization or re-synchronization.

[0034] In a specific implementation, as a preferred embodiment of the present invention, the fully controlled bridge requires six identical phase-shifting trigger pulses. To ensure the reliability of the triggering, the trigger pulses of the power unit are double pulses with a phase difference of 60° electrical angle. Angular phase shift range 7° 145°, to accommodate different excitation voltage requirements. In this embodiment, for resistive and inductive loads, different... The DC voltage output at angle is: ,in, This represents the DC voltage output by the rectifier bridge. This represents the AC line voltage input to the rectifier bridge; In a preferred embodiment of this invention, the monitoring unit communicates with the main control unit via the Modbus protocol and has Ethernet, RS485, PROFIBUS, or CAN bus expansion interfaces. In this embodiment, the monitoring unit is controlled by an independent CPU, displays on an LCD, and communicates with the main control unit via Modbus. Users can set parameters and monitor variables through the monitoring unit. Figure 5 The diagram shows the electrical schematic of the monitoring unit. The independent CPU board is connected to the main control unit via an isolated RS485 interface and a Modbus bus. The onboard LCD screen driver circuit and 4×4 membrane keyboard form a human-machine interface for local display of excitation voltage, current, power factor, and fault information. The EEPROM memory stores the setting parameters, and the RTC circuit provides fault record timestamps. Two relay outputs drive the "device fault" and "excitation ready" indicator lights respectively, and another passive contact is used for external DCS data acquisition. The power supply circuit uses AC 220 V, which is converted to DC 5 V and 3.3 V by a switching power supply. It has a self-resetting fuse and TVS overvoltage protection to achieve independent and reliable operation of the monitoring unit.

[0035] The present invention also provides a method for controlling the rotor excitation of a large synchronous motor based on the above-mentioned large synchronous motor rotor excitation device, comprising: During the asynchronous start-up phase, the starting resistor (RF) is connected to the rotor circuit, and the rotor induced voltage is collected in real time. The induced voltage is AC sampled and digitally filtered to calculate the slip and obtain the rotor speed. When the rotor speed exceeds the set excitation speed, the reverse polarity end excitation angle is selected and an excitation command is issued. In this embodiment, when the motor speed exceeds a certain speed, for a synchronous motor with reduced voltage start, the main control unit issues a control signal to disconnect the reduced voltage reactor and apply full voltage to accelerate the motor start-up. When the motor speed reaches the given excitation speed, the main control unit issues an excitation signal to excite the motor.

[0036] The power unit outputs DC excitation voltage based on the firing angle α, enabling the motor to enter the synchronous operation stage; During synchronous operation, the excitation current and power factor are monitored in real time. When the excitation current falls below the minimum excitation current limit, the system switches to constant excitation current control mode to prevent loss of synchronization. In this embodiment, the synchronous motor generally operates with a leading power factor. When the excitation is insufficient, the power factor of the motor stator current changes from leading to lagging, absorbing inductive reactive power from the grid. The motor can operate stably with a light load, but with a heavy load, reducing the excitation current lowers the motor's static stability coefficient, potentially leading to loss of synchronization, necessitating limitation. By using a minimum excitation current limit, protection is activated after a delay when the excitation current reaches the minimum limit, switching to constant excitation current control, with the excitation current set to a predetermined value.

[0037] In this embodiment, as Figure 6 The diagram shows the location of the external excitation transformer and starting resistor. The excitation cabinet itself only houses the main control unit, power unit, and monitoring unit, while the excitation transformer and starting resistor box are located in separate compartments on the left and right sides outside the cabinet. The high-voltage side of the excitation transformer is connected to the 6kV busbar in the plant area via a cable, and the low-voltage side enters the power unit inside the cabinet through a shielded busbar. The starting resistor box is forced air-cooled, and its output line is connected to the terminal block at the bottom of the cabinet via a quick connector, allowing it to be pulled out for maintenance without shutting down the system. The external design of both significantly reduces the temperature rise inside the cabinet, eliminates the risk of excitation cabinet fire caused by overheating of the transformer and resistor, and saves cabinet space.

[0038] In a specific implementation, as a preferred embodiment of the present invention, the trigger angle The data is obtained in real time by collecting terminal voltage, terminal current, active power, reactive power, and power factor, and then calculating them according to a predetermined control law.

[0039] In a specific implementation, as a preferred embodiment of the present invention, the control method of the present invention further includes a system self-test step to detect faults in the memory, power supply and thyristor. Once a fault is detected, a hardware fault signal is issued and the cause of the fault is located.

[0040] In a specific implementation, as a preferred embodiment of the present invention, the minimum excitation current limit, the excitation multiple, the low voltage range, and the excitation time are all set online by the monitoring unit.

[0041] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A rotor excitation device for a large synchronous motor, characterized in that, include: The main control unit is used to collect the operating parameters of the synchronous motor and calculate the thyristor firing angle based on the control law. ; The power unit includes a three-phase fully controlled bridge rectifier circuit, which is composed of six thyristor units, and each thyristor unit has an RC snubber circuit for receiving the dual-pulse trigger signal output by the main control unit to generate an adjustable DC excitation voltage. The starting circuit includes a starting resistor and a starting thyristor, wherein the starting resistor is connected across the rotor excitation winding during asynchronous motor starting; The slip measurement module is used to perform AC sampling, digital filtering, and slip calculation on the rotor induced voltage signal during the asynchronous start-up phase to obtain the rotor speed. The excitation control module is used to send an excitation trigger signal to the power unit when the rotor speed reaches the set excitation speed and the excitation angle condition is met, so that the three-phase fully controlled bridge rectifier circuit outputs DC excitation current to the rotor winding. The monitoring unit communicates with the main control unit and is used for parameter setting, status display, and fault alarm. The external excitation transformer and the external starting resistor box are located outside the excitation cabinet and are used to supply power to the power unit and complete the starting current limiting.

2. The large synchronous motor rotor excitation device according to claim 1, characterized in that, The main control unit has a dual-CPU structure, including a CPU module and an I / O module. The CPU module completes data acquisition, control law calculation and pulse generation, while the I / O module completes digital / analog input / output, trigger pulse driving, temperature measurement and fan control.

3. The rotor excitation device for a large synchronous motor according to claim 1, characterized in that, The slip measurement module uses an AC sampling plus digital filtering algorithm to replace the traditional square wave comparator in order to improve the measurement accuracy under harmonic interference.

4. The large synchronous motor rotor excitation device according to claim 1, characterized in that, The excitation control module adopts a reverse polarity end excitation strategy, which enables the DC excitation current after excitation to quickly enter the rotor winding, thereby improving the success rate of heavy-load start-up and re-synchronization.

5. A large synchronous motor rotor excitation device according to claim 1, characterized in that, The trigger pulse of the power unit is a double pulse with a 60° electrical angle phase difference. Angular phase shift range 7° 145°, to adapt to different excitation voltage requirements.

6. The rotor excitation device for a large synchronous motor according to claim 1, characterized in that, The monitoring unit communicates with the main control unit via the Modbus protocol and has Ethernet, RS485, Profibus or CAN bus expansion interfaces.

7. A method for controlling the rotor excitation of a large synchronous motor based on the rotor excitation device of any one of claims 1-6, characterized in that, include: During the asynchronous start-up phase, the starting resistor is connected to the rotor circuit, and the rotor induced voltage is collected in real time. The induced voltage is AC sampled and digitally filtered to calculate the slip and obtain the rotor speed. When the rotor speed exceeds the set excitation speed, select the reverse polarity end excitation angle and issue an excitation command; The power unit outputs DC excitation voltage based on the firing angle α, enabling the motor to enter the synchronous operation stage; During the synchronous operation phase, the excitation current and power factor are monitored in real time, and the system switches to constant excitation current control mode when the excitation current is lower than the minimum excitation current limit to prevent loss of synchronization.

8. The rotor excitation control method for a large synchronous motor according to claim 7, characterized in that, The trigger angle The data is obtained in real time by collecting terminal voltage, terminal current, active power, reactive power, and power factor, and then calculating them according to a predetermined control law.

9. The rotor excitation control method for a large synchronous motor according to claim 7, characterized in that, It also includes a system self-test step, which detects faults in the memory, power supply and thyristor. Once a fault is detected, a hardware fault signal is issued and the cause of the fault is located.

10. The rotor excitation control method for a large synchronous motor according to claim 7, characterized in that, The minimum excitation current limit, excitation multiple, low voltage range, and excitation time are all set online through the monitoring unit.

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