Control circuit and control method for achieving power balance of multiple synchronous motors

Abstract

The present invention provides a control circuit and a control method for achieving power balance of multiple synchronous motors, including one industrial frequency synchronous motor, n variable frequency synchronous motors and n frequency converters. The n frequency converters are connected via a communication bus to form a control loop. Current and voltage sampling circuits are respectively provided between the n frequency converters and the corresponding n variable frequency synchronous motors. The industrial frequency synchronous motor is provided with a voltage and current sampling loop connected to the frequency converter, and is connected to the power grid via an industrial frequency switch to form an industrial frequency drive loop. The industrial frequency synchronous motor and the drive shafts of the n variable frequency synchronous motors are interconnected by a transmission shaft, a gearbox and a belt to achieve power coupling transmission. The present invention obtains the voltage and current sampling signals of the industrial frequency synchronous motor by the frequency converter, and then controls the output power of each corresponding variable frequency synchronous motor to be consistent with that of the industrial frequency synchronous motor, thereby achieving starting and power balance control of n+1 synchronous motors by n frequency converters.

Description

Technical Field

[0001] The present invention relates to an electrical control circuit, and in particular discloses a control circuit and a control method for achieving power balance of multiple synchronous motors, belonging to the technical field of electrical device control. Background Art

[0002] With the rapid development of industry, industrial control systems have become increasingly sophisticated and mature, and frequency converters (VFDs) have been widely used in various industrial control systems. In particular, multi-motor drive systems with mechanical connections are often encountered in production. Multi-motor drives involve multiple motors operating synchronously within a single production machine or process section. Their motion is constrained, meaning they operate non-independently and are physically connected. For example, in a grinding mill system, two motors drive the system coaxially, typically through a gearbox or by meshing the motors' gears with the mill's external gears. Current production processes typically utilize two VFDs driving two synchronous motors. Due to specific production process requirements, motor speed regulation is rarely performed in actual applications. The primary purpose of using two VFDs is to achieve soft starting and balanced power distribution between the two motors. The need for two VFDs for two motors increases not only the initial investment cost of the VFD equipment but also ongoing maintenance costs. Summary of the Invention

[0003] The purpose of the present invention is to solve the defects of the prior art and design a control circuit and control method for achieving power balance of multiple synchronous motors. The starting and power balance distribution functions of n+1 synchronous motors can be realized through n inverters, reducing the investment cost and maintenance workload of inverter equipment in industrial control systems.

[0004] The present invention is achieved in that:

[0005] The present invention provides a control circuit and a control method for achieving power balance of multiple synchronous motors. The control circuit for achieving power balance of multiple synchronous motors includes one industrial frequency synchronous motor Ms, n variable frequency synchronous motors, and n frequency converters. The n variable frequency synchronous motors are sequentially recorded as a first variable frequency synchronous motor M1, a second variable frequency synchronous motor M2, ..., an nth variable frequency synchronous motor Mn. The n frequency converters are sequentially recorded as a first frequency converter VFD1, a second frequency converter VFD2, ..., an nth frequency converter VFDn, wherein n is a positive integer and n is greater than or equal to 1. The n frequency converters are respectively provided with a frequency converter control system and are connected to each other via a communication bus to form a control loop. The n frequency converters are connected to the corresponding frequency converters. A current and voltage sampling circuit is respectively provided between the n variable-frequency synchronous motors to form a sampling loop. A corresponding inverter power supply switch QF is respectively provided on the connection circuit between the n inverters and the variable-frequency synchronous motor connection bus. The industrial frequency synchronous motor Ms is provided with a voltage and current sampling circuit connected to the first inverter VFD1 to form a sampling loop. The industrial frequency synchronous motor Ms is connected to the industrial frequency synchronous motor connection bus through the industrial frequency switch QFs to form an industrial frequency drive loop. At the same time, the industrial frequency synchronous motor Ms and the drive shafts of the n variable-frequency synchronous motors are interconnected using conventional physical connectors and connection methods such as drive shafts, gearboxes, and belts to achieve power coupling transmission. The load 12 is driven by the drive shafts of each synchronous motor.

[0006] The control method for a control circuit for achieving power balancing of multiple synchronous motors includes n inverter control systems, where n is a positive integer and n is greater than or equal to 1. The inverter control systems exchange data via a communication bus. The n inverter control systems are sequentially recorded as: a first inverter VFD1 control system, a second inverter VFD2 control system, ..., an nth inverter VFDn control system. The first inverter VFD1 control system includes an average value calculator, a power frequency synchronous motor observer, a first variable frequency synchronous motor observer, a first speed regulator, a first torque current regulator, and a first inverter execution unit. The second inverter VFD2 control system includes a second variable frequency synchronous motor observer, a second speed regulator, a second torque current regulator, and a second inverter execution unit. The nth inverter VFDn control system includes an nth variable frequency synchronous motor observer, an nth speed regulator, an nth torque current regulator, and an nth inverter execution unit.

[0007] After the industrial frequency synchronous motor Ms and the variable frequency synchronous motor are started, the first frequency converter VFD1 samples the voltage and current of the industrial frequency synchronous motor Ms and obtains the real-time power of the industrial frequency synchronous motor Ms through the industrial frequency synchronous motor observer. Power_s and real-time torque Torque_s , real-time speedSpeed_s The real-time torque of the power frequency synchronous motor is directly measured by the speed measuring device or obtained by the power frequency synchronous motor observer. Torque_s The system average torque is calculated by the average value calculator based on the reference torque of each variable frequency synchronous motor. T_Average , the reference torque given by each variable frequency synchronous motor and the system average torque T_Average The difference between the torque difference and the proportional coefficient Ks After multiplication, the torque difference compensation value of each variable frequency synchronous motor is obtained. Similarly, the real-time speed of each variable frequency synchronous motor is directly measured by a speed measuring device or obtained by each frequency converter through sampling the voltage and current of each variable frequency synchronous motor and the variable frequency synchronous motor observer. Speed_s As the speed reference signal of each inverter, the corresponding speed difference signal is obtained by subtracting the real-time speed of each variable frequency synchronous motor and the torque difference compensation value of each variable frequency synchronous motor. The reference torque reference of each variable frequency synchronous motor is obtained by each speed regulator. The reference torque reference is adjusted and output by each torque current regulator and then driven by the corresponding inverter execution unit. Finally, the power balance of n+1 synchronous motors is achieved through n inverters under the control of each inverter control system. The torque difference adjustment proportional coefficient is: Ks It is a constant with a default value of 0.5, which can be adjusted according to actual application scenarios.

[0008] When the power balancing control circuit of the present invention uses a mechanical interlocked rotation method to start a power-frequency excitation synchronous motor, the power-frequency synchronous motor is an excitation synchronous motor, and the variable-frequency synchronous motor is an excitation synchronous motor or a permanent magnet synchronous motor. During startup, the power-frequency switch QFs is in the open state, and no excitation current is supplied. The inverter power supply switches QF, respectively provided in the connection circuit between the n inverters and the busbar connecting the variable-frequency synchronous motor, are closed, and the variable-frequency synchronous motor is driven by the inverter to operate until it reaches the power-frequency speed. Because the power-frequency synchronous motor Ms is mechanically connected, it is driven by power transmitted through the coupling, and the power-frequency synchronous motor Ms runs to the power-frequency speed. At this time, the power-frequency switch QFs is closed, and excitation current is gradually supplied through the excitation device provided in the power-frequency synchronous motor Ms, and the power-frequency synchronous motor Ms completes power-frequency drive operation. The first frequency converter VFD1 obtains the voltage and current sampling signals of the industrial frequency synchronous motor Ms, and controls the output power of the corresponding variable frequency synchronous motors (the first variable frequency synchronous motor M1 ... the nth variable frequency synchronous motor Mn) to be consistent with that of the industrial frequency synchronous motor Ms through the control system of each frequency converter (the first frequency converter VFD1 ... the nth frequency converter VFDn) using the power balancing control method of the present invention.

[0009] The power balancing control circuit described in the present invention first uses a frequency converter to drive an industrial frequency synchronous motor and then switches to industrial frequency operation. The industrial frequency synchronous motor is an excitation synchronous motor or a permanent magnet synchronous motor. A first switch KM1 is provided between the first frequency converter VFD1 and the first variable frequency synchronous motor M1. A synchronous switching reactor and a second switch KMs are sequentially provided in the connection circuit between the output line of the first frequency converter VFD1 and the first switch KM1, and are connected to the industrial frequency synchronous motor Ms. During startup, the industrial frequency switch QFs is in the open state. A voltage sampling circuit s is connected above the switch QFs and connected to the first frequency converter VFD1. The frequency, amplitude, and phase of the three-phase voltage of the bus connecting the industrial frequency synchronous motor are collected in real time. The corresponding frequency converter power switches of each frequency converter (the first frequency converter power switch QF1 ... the nth frequency converter power switch QFn) are closed. The second switch KMs is closed, and the first switch KM1 is opened. The circuit for the first frequency converter VFD1 to drive the industrial frequency synchronous motor Ms is connected, and the first frequency converter VFD1 is connected to the first frequency converter VFD1. 1. Drive the power-frequency synchronous motor Ms to the power-frequency speed. If the power-frequency synchronous motor Ms is an excitation synchronous motor, the first inverter first controls the excitation output. Each variable-frequency synchronous motor (the first variable-frequency synchronous motor M1 ... the nth variable-frequency synchronous motor Mn) is constrained by mechanical connectors to rotate synchronously with the power-frequency synchronous motor Ms. When the first inverter VFD1 drives the power-frequency synchronous motor Ms to the rated speed, the first inverter VFD1 adjusts the output voltage so that the output voltage of the first inverter VFD1 is consistent with the frequency, amplitude, and phase of the three-phase voltage of the power-frequency synchronous motor connection bus to which the power-frequency synchronous motor Ms will be connected. Then, the power-frequency switch QFs is closed, and the second switch KMs is opened, connecting the power-frequency drive circuit. If the power-frequency synchronous motor Ms is an excitation synchronous motor, the excitation device switches to power-frequency automatic control, and the power-frequency synchronous motor Ms is driven by the power frequency. Then, closing the first switch KM1 connects the circuit through which the first inverter VFD1 drives the variable-frequency synchronous motor M1. Each inverter (first inverter VFD1…nth inverter VFDn) synchronously tracks the speed and drives its corresponding variable-frequency synchronous motor (first variable-frequency synchronous motor M1…nth variable-frequency synchronous motor Mn). Closing the first switch KM1 connects the circuit through which the first inverter VFD1 drives the first variable-frequency synchronous motor M1. Each inverter (VFD1…VFDn) synchronously tracks the speed and drives its corresponding variable-frequency synchronous motor (first variable-frequency synchronous motor M1…nth variable-frequency synchronous motor Mn).The first frequency converter VFD1 obtains the voltage and current sampling signals of the industrial frequency synchronous motor Ms and controls the output power of each corresponding variable frequency synchronous motor (the first variable frequency synchronous motor M1 ... the nth variable frequency synchronous motor Mn) to be consistent with that of the industrial frequency synchronous motor Ms through the control system of each frequency converter (the first frequency converter VFD1 ... the nth frequency converter VFDn) using the power balancing control method of the present invention.

[0010] When the power balance control circuit described in the present invention uses a mechanical interlocked rotation method to start the industrial frequency synchronous motor and achieve phase synchronization with the bus connecting the industrial frequency synchronous motor, the industrial frequency synchronous motor adopts an excitation synchronous motor or a permanent magnet synchronous motor. A voltage sampling circuit connected to the first frequency converter VFD1 is also provided in the connection circuit between the industrial frequency switch QFs and the bus connecting the industrial frequency synchronous motor, and a voltage sampling circuit for connecting to the bus connecting the industrial frequency synchronous motor is formed. At startup, the power frequency switch QFs is in the open state. The power supply switches QF respectively provided on the connection circuits between the n frequency converters and the variable frequency synchronous motor connection bus 11 are closed, and the variable frequency synchronous motor is driven by the frequency converter to operate until it reaches the power frequency speed. If the power frequency synchronous motor Ms is an excitation synchronous motor, the excitation cabinet outputs a no-load excitation current. Since the power frequency synchronous motor Ms is mechanically connected, the power transmitted through the coupling drives the power frequency synchronous motor Ms to operate to the power frequency speed. Then, the first frequency converter VFD1 gradually adjusts the speed of the power frequency synchronous motor Ms by comparing the grid voltage sampling results with the power frequency motor voltage sampling results, so that the generated voltage of the power frequency synchronous motor is consistent with the frequency and phase of the grid voltage of the power frequency synchronous motor. At this time, the power frequency switch QFs is closed, and the excitation current is gradually input through the excitation device provided by the power frequency synchronous motor Ms, and the power frequency synchronous motor Ms completes the power frequency drive operation. The first frequency converter VFD1 obtains the voltage and current sampling signals of the industrial frequency synchronous motor Ms and controls the output power of each corresponding variable frequency synchronous motor (the first variable frequency synchronous motor M1 ... the nth variable frequency synchronous motor Mn) to be consistent with that of the industrial frequency synchronous motor Ms through the control system of each frequency converter (the first frequency converter VFD1 ... the nth frequency converter VFDn) using the power balancing control method of the present invention.

[0011] The average value calculator uses the following formula to calculate the system average torque T_Average :

[0012] Formula (1)

[0013] If the powers of the variable frequency synchronous motors are different, the reference torques of the variable frequency synchronous motors ( T 1 … Tn ) and the real-time torque of the industrial frequency synchronous motor Torque_s The torque can be proportionally distributed according to their respective rated powers, that is, the torque can be calibrated as a percentage of the rated torque.

[0014] In each of the synchronous motor observers, the synchronous motor three-phase current sampling signal Current Use 、 and Indicates that the three-phase voltage sampling signal Voltage Use 、 and The real-time power is calculated using the following formula Power , real-time torque Torque And real-time speed Speed :

[0015] Formula (2)

[0016] Formula (3)

[0017] Formula (4)

[0018] Torque =K m × I ｑ Formula (5)

[0019] where K m is a fixed proportional constant determined by the synchronous motor parameters.

[0020] Power = Torque × Speed Formula (6)

[0021] Ms voltage sampling signal of industrial frequency synchronous motor Ms _ Voltage and current sampling signal Ms _ Current The real-time power can be calculated by the synchronous motor observer Power_s , real-time torque Torque_s And real-time speed Speed_s .

[0022] Similarly, the voltage sampling signal of each variable frequency synchronous motor (M1…Mn) M1 _ Voltage... Mn _ Voltage ) and current sampling signal ( M1 _ Current... Mn _Current ) can be calculated by the synchronous motor observer to obtain the real-time power ( Power_1... Power_n ), real-time torque ( Torque_1...Torque_n ) and real-time speed ( Speed_1... Speed_n ).

[0023] The speed regulator adjusts the speed difference Speeddiff As the input signal, the torque reference value is calculated according to the following formula T :

[0024] Formula (7)

[0025] In formula (7), t is the integration time, Kp and Ki are the proportional coefficient and the integration coefficient respectively. The specific values ​​of Kp and Ki are determined by the parameters of the synchronous motor.

[0026] Each inverter will speed difference ( Speeddiff_1... Speeddiff_n ) as the input signal, the reference torque of each variable frequency synchronous motor is calculated by each speed regulator (1…n) T 1 …T n ).

[0027] The torque current regulator is based on the reference torque of the synchronous motor T With real-time torque Torque , the reference torque voltage V is calculated according to the following formula : Formula (8)

[0028] In formula (8), t is the integration time, Kp and Ki are the proportional coefficient and the integration coefficient respectively. The specific values ​​of Kp and Ki are determined by the parameters of the synchronous motor.

[0029] The values ​​of Kp and Ki in formula (7) and formula (8) are calculated as follows:

[0030] Formula (9)

[0031] Formula (10)

[0032] in: is the motor leakage inductance, is the rated current of the motor, is the rated voltage of the motor, is the regulator execution cycle, is the motor stator resistance.

[0033] Each inverter converts the reference torque of the variable frequency synchronous motor ( T 1 …T n and real-time torque ( Torque_1...Torque_ n ) as the input signal, the reference torque voltage of each variable frequency synchronous motor is calculated by the torque current regulator (1…n) V 1 …V n ).

[0034] The present invention has the following beneficial effects: by providing a voltage and current sampling circuit and a power frequency drive circuit, the frequency converter acquires the voltage and current sampling signals of the power frequency synchronous motor, and then controls the output power of each corresponding frequency converter synchronous motor to be consistent with that of the power frequency synchronous motor. This enables n frequency converters to start n+1 synchronous motors and achieve power balance control. Compared with existing technologies, this reduces the cost and maintenance of frequency converter equipment. Taking a mill drive system as an example, if the frequency converter equipment costs 300 yuan per kilowatt, a 10MW mill system can save 1.5 million yuan in frequency converter equipment investment. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 The present invention is a schematic diagram of the equipment connection for starting a power frequency excitation synchronous motor by adopting a mechanical interlock rotation method.

[0036] Figure 2 This is a schematic diagram of the equipment connection in which the present invention uses a frequency converter to drive an industrial frequency synchronous motor and then switches to industrial frequency.

[0037] Figure 3 This is a schematic diagram of the equipment connection for starting a power frequency synchronous motor and achieving phase synchronization with the power grid by using a mechanical interlocked rotation method according to the present invention.

[0038] Figure 4 It is a schematic block diagram of the working process of the power balance control method of the present invention.

[0039] Figure 5 It is a flow chart of power balance control in the present invention.

[0040] In the picture:

[0041] 1. Power frequency synchronous motor voltage sampling circuit;

[0042] 2. Power frequency synchronous motor current sampling circuit;

[0043] 3. Voltage sampling circuit of variable frequency synchronous motor;

[0044] 4. Current sampling circuit of variable frequency synchronous motor;

[0045] 9. Communication bus;

[0046] 10. Power frequency synchronous motor connected to busbar;

[0047] 11. Variable frequency synchronous motor connected to busbar;

[0048] 12. Load;

[0049] 13. Connectors;

[0050] 14. Excitation device;

[0051] 15. Synchronous switching reactor;

[0052] 16. Grid voltage sampling circuit;

[0053] 50. First frequency converter VFD1 control system; 60. Second frequency converter VFD2 control system; 70. Nth frequency converter VFDn control system. DETAILED DESCRIPTION

[0054] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0055] According to the attached Figure 1 ~Attached Figure 3The present invention is a control circuit and a control method for achieving power balance of multiple synchronous motors. The control circuit for achieving power balance of multiple synchronous motors described in the present invention includes one industrial frequency synchronous motor Ms, n variable frequency synchronous motors (M1...Mn) and n frequency converters (VFD1...VFDn) (n is a positive integer, and n≥1). The n frequency converters are connected to each other via a communication bus 9 to form a control loop. Current and voltage sampling circuits are respectively provided between the n frequency converters and the corresponding n variable frequency synchronous motors to form a sampling loop, namely, a voltage sampling loop 3 of the variable frequency synchronous motor and a current sampling loop 4 of the variable frequency synchronous motor. The n frequency converters are connected to the variable frequency synchronous motors. The connection circuit connected to the bus 11 is respectively provided with a corresponding inverter power supply switch QF. The industrial frequency synchronous motor Ms is provided with a voltage and current sampling circuit connected to the first inverter VFD1 and forming a sampling circuit, namely, the industrial frequency synchronous motor voltage sampling circuit 1 and the industrial frequency synchronous motor current sampling circuit 2. The industrial frequency synchronous motor Ms is connected to the industrial frequency synchronous motor connection bus 10 through the industrial frequency switch QFs to form an industrial frequency drive circuit. At the same time, the industrial frequency synchronous motor Ms and the driving shafts of the n variable frequency synchronous motors are connected to each other using conventional physical connectors 13 and connection methods such as transmission shafts, gearboxes and belts to realize power coupling transmission. The load 12 is driven by the transmission shafts of each synchronous motor.

[0056] According to the attached Figure 1 The equipment for starting a power-frequency excitation synchronous motor using a mechanical interlocked rotation method includes one power-frequency synchronous motor Ms, n variable-frequency synchronous motors (M1…Mn), and n frequency converters (VFD1…VFDn) (n is a positive integer, and n ≥ 1). The power-frequency synchronous motor is an excitation synchronous motor, and the variable-frequency synchronous motor is an excitation synchronous motor or a permanent magnet synchronous motor. The n frequency converters are connected via a communication bus 9 to form a control circuit. The n frequency converters are respectively connected to the corresponding n variable-frequency synchronous motors and are each provided with a voltage sampling circuit 3 and a current sampling circuit 4 for the variable-frequency synchronous motors, forming a sampling circuit with the corresponding n variable-frequency synchronous motors. The circuit connecting the n frequency converters to the variable-frequency synchronous motor connection bus 11 is provided with a corresponding frequency converter power supply switch QF. The industrial frequency synchronous motor Ms is provided with an industrial frequency synchronous motor voltage sampling circuit 1 and an industrial frequency synchronous motor current sampling circuit 2 which are connected to the first frequency converter VFD1 and form a sampling circuit. The industrial frequency synchronous motor Ms is connected to the industrial frequency synchronous motor connection bus 10 through the industrial frequency switch QFs to form an industrial frequency drive circuit. At the same time, the industrial frequency synchronous motor Ms and the driving shafts of the n variable frequency synchronous motors are connected to each other using conventional physical connectors 13 and connection methods such as transmission shafts, gearboxes and belts to realize power coupling transmission.

[0057] At startup, the power frequency switch QFs is in the open state and the excitation current is not applied. The inverter power supply switches QF respectively provided on the connection circuit between the n inverters and the variable frequency synchronous motor connection bus 11 are closed, and the variable frequency synchronous motor is driven by the inverter to operate until it reaches the power frequency speed. Since the power frequency synchronous motor Ms adopts a mechanical connection, it is driven by the power transmitted through the coupling and runs to the power frequency speed. At this time, the power frequency switch QFs is closed, and the excitation current is gradually applied through the excitation device 14 provided for the power frequency synchronous motor Ms, and the power frequency synchronous motor Ms completes the power frequency drive operation.

[0058] According to the attached Figure 2 This control circuit employs a frequency converter to first drive a commercial frequency synchronous motor and then switches to commercial frequency operation. A first switch KM1 is provided between the first frequency converter VFD1 and the first variable frequency synchronous motor M1. A synchronous switching reactor 15 and a second switch KMs are sequentially provided in the circuit connecting the output line of the first frequency converter VFD1 to the first switch KM1, and are connected to the commercial frequency synchronous motor Ms. The remaining equipment connections are consistent with those described above for starting a commercial frequency excitation synchronous motor using mechanical interlocking rotation. The commercial frequency synchronous motor described in this circuit is either an excitation synchronous motor or a permanent magnet synchronous motor.

[0059] During startup, the power frequency switch QFs is in the disconnected state. The voltage sampling s is connected above the switch QFs and connected to the first frequency converter VFD1. The frequency, amplitude and phase of the three-phase voltage of the power frequency synchronous motor connected to the bus 10 are collected in real time. The power supply switches (QF1…QFn) corresponding to each frequency converter are closed. The second switching switch KMs is closed and the first switching switch KM1 is opened. The circuit of the power frequency synchronous motor Ms driven by the first frequency converter VFD1 is connected. 1 drives the power-frequency synchronous motor Ms to the power-frequency speed. If the power-frequency synchronous motor Ms is an excitation synchronous motor, the first inverter first controls the excitation output. Each variable-frequency synchronous motor (M1...Mn) is constrained by mechanical connectors and rotates synchronously with the power-frequency synchronous motor Ms. When the first inverter VFD1 drives the power-frequency synchronous motor Ms to the rated speed, the first inverter VFD1 adjusts the output voltage so that the output voltage of the first inverter VFD1 is consistent with the frequency, amplitude, and phase of the three-phase voltage of the power-frequency synchronous motor connecting bus 10 to which the power-frequency synchronous motor Ms is to be connected. Then, the power-frequency switch QFs is closed and the second switch KMs is opened, connecting the power-frequency drive circuit. If the power-frequency synchronous motor Ms is an excitation synchronous motor, the excitation device switches to power-frequency automatic control, and the power-frequency synchronous motor Ms is driven by the power frequency. Then, the first switch KM1 is closed, and the circuit for the first frequency converter VFD1 to drive the variable frequency synchronous motor M1 is connected. Each frequency converter (VFD1 ... VFDn) drives the corresponding variable frequency synchronous motor (M1 ... Mn) to operate after synchronously tracking the speed.

[0060] According to the attached Figure 3 This circuit uses mechanical interlocked rotation to start a power-frequency synchronous motor and achieve phase synchronization with the power grid (i.e., busbar). A voltage sampling circuit connected to a first frequency converter VFD1 is also provided in the circuit connecting the power-frequency switch QFs to the power-frequency synchronous motor busbar 10, forming a power-grid voltage sampling loop 16. Other device connections are consistent with those described above for starting a power-frequency excitation synchronous motor using mechanical interlocked rotation. The power-frequency synchronous motor described in this circuit is either an excitation synchronous motor or a permanent magnet synchronous motor.

[0061] At startup, the power frequency switch QFs is in the open state. The power supply switches QF respectively provided on the connection circuits between the n frequency converters and the variable frequency synchronous motor connection bus 11 are closed, and the variable frequency synchronous motor is driven by the frequency converter to operate until it reaches the power frequency speed. If the power frequency synchronous motor Ms is an excitation synchronous motor, the excitation cabinet outputs a no-load excitation current. Since the power frequency synchronous motor Ms is mechanically connected, the power transmitted through the coupling drives the power frequency synchronous motor Ms to operate to the power frequency speed. Then, the first frequency converter VFD1 gradually adjusts the speed of the power frequency synchronous motor Ms by comparing the grid voltage sampling results with the power frequency motor voltage sampling results, so that the generated voltage of the power frequency synchronous motor is consistent with the frequency and phase of the grid voltage of the power frequency synchronous motor. At this time, the power frequency switch QFs is closed, and the excitation current is gradually input through the excitation device provided by the power frequency synchronous motor Ms, and the power frequency synchronous motor Ms completes the power frequency drive operation.

[0062] The control method for realizing power balance of multiple synchronous motors by the control circuit of the present invention is specifically as follows:

[0063] According to the attached Figure 4 and attached Figure 5 The control method for achieving power balancing among multiple synchronous motors described in the present invention includes a control system for n frequency converters (VFD1...VFDn) (n is a positive integer, and n ≥ 1) (represented in this order: first frequency converter VFD1 control system 50, second frequency converter VFD2 control system 60, ..., nth frequency converter VFDn control system 70). Data is exchanged between the frequency converter control systems via a communication bus. The first frequency converter VFD1 control system 50 includes an average value calculator, a power frequency synchronous motor observer, a first variable frequency synchronous motor observer, a first speed regulator, a first torque current regulator, and a first frequency converter execution unit. The second frequency converter VFD2 control system 60 includes a second variable frequency synchronous motor observer, a second speed regulator, a second torque current regulator, and a second frequency converter execution unit. The nth frequency converter VFDn control system 70 includes an nth variable frequency synchronous motor observer, an nth speed regulator, an nth torque current regulator, and an nth frequency converter execution unit.

[0064] When the power frequency synchronous motor Ms and the variable frequency synchronous motor (M1…Mn) are started, the first frequency converter VFD1 samples the voltage and current of the power frequency synchronous motor Ms and obtains the real-time power of the power frequency synchronous motor Ms through the power frequency synchronous motor observer. Power_s and real-time torque Torque_s , real-time speed Speed_s It can be measured directly by the speed measuring device s, or it can be obtained by the power frequency synchronous motor observer. The real-time torque of the power frequency synchronous motor is Torque_s The reference torque of each variable frequency synchronous motor (T1 …T n ) The average torque of the system is calculated by the average value calculator T_Average , the reference torque of each variable frequency synchronous motor is given ( T 1 …T n ) and the system average torque T_Average The difference between the torque difference and the proportional coefficient Ks After multiplication, the torque difference compensation value of each variable frequency synchronous motor is obtained ( Terrork_1… Terrork_n ). The torque difference adjustment proportional coefficient Ks It is a constant with a default value of 0.5, which can be adjusted according to actual application scenarios.

[0065] Similarly, the real-time speed of each variable frequency synchronous motor ( Speed_1…Speed_n ) can be directly measured by the corresponding speed measuring device, or can be obtained by each frequency converter (VFD1...VFDn) by sampling the voltage and current of each variable frequency synchronous motor (M1...Mn) and then obtained through each variable frequency synchronous motor observer.

[0066] The real-time speed of the industrial frequency synchronous motor Ms Speed_s As the speed given signal of each inverter, it is consistent with the real-time speed of each variable frequency synchronous motor ( Speed_1…Speed_n ) and the torque difference compensation value of each variable frequency synchronous motor ( Terrork_1… Terrork_n ) and then subtract the speed difference signal ( Speeddiff_1... Speeddiff_n ), the reference torque of each variable frequency synchronous motor is obtained through each speed regulator (1…n) ( T 1 …T n ), reference torque given ( T 1 …T n ) is outputted through each torque current regulator (1…n) and then driven by each inverter execution unit (1…n) to achieve power balance of n+1 synchronous motors.

[0067] The average value calculator uses the following formula to calculate the system average torque T_Average :

[0068] Formula (1)

[0069] If the powers of the variable frequency synchronous motors are different, the reference torques of the variable frequency synchronous motors ( T 1 … T n ) and the real-time torque of the industrial frequency synchronous motor Torque_s The torque can be proportionally distributed according to their respective rated powers, that is, the torque can be calibrated as a percentage of the rated torque.

[0070] In each of the synchronous motor observers, the synchronous motor three-phase current sampling signal Current Use 、 and Indicates that the three-phase voltage sampling signal Voltage Use 、 and The real-time power is calculated using the following formula Power , real-time torque Torque And real-time speed Speed :

[0071] Formula (2)

[0072] Formula (3)

[0073] Formula (4)

[0074] Torque =K m × I ｑ Formula (5)

[0075] where K m is a fixed proportional constant determined by the synchronous motor parameters.

[0076] Power = Torque × Speed Formula (6)

[0077] Ms voltage sampling signal of industrial frequency synchronous motor Ms _ Voltage and current sampling signal Ms _ Current The real-time power can be calculated by the synchronous motor observer Power_s , real-time torque Torque_s And real-time speed Speed_s .

[0078] Similarly, the voltage sampling signal of each variable frequency synchronous motor (M1…Mn) M1 _ Voltage... Mn _ Voltage ) and current sampling signal ( M1 _ Current... Mn _ Current ) can be calculated by the synchronous motor observer to obtain the real-time power ( Power_1... Power_n ), real-time torque ( Torque_1...Torque_n ) and real-time speed ( Speed_1... Speed_n ).

[0079] The speed regulator adjusts the speed difference Speeddiff As the input signal, the torque reference value is calculated according to the following formula T :

[0080] Formula (7)

[0081] In formula (7), t is the integration time, Kp and Ki are the proportional coefficient and the integration coefficient respectively. The specific values ​​of Kp and Ki are determined by the parameters of the synchronous motor.

[0082] Each inverter will speed difference ( Speeddiff_1... Speeddiff_n ) as the input signal, the reference torque of each variable frequency synchronous motor is calculated by each speed regulator (1…n) T 1 …T n ).

[0083] The torque current regulator is based on the reference torque of the synchronous motor T With real-time torque Torque , the reference torque voltage V is calculated according to the following formula :

[0084] Formula (8)

[0085] In formula (8), t is the integration time, Kp and Ki are the proportional coefficient and the integration coefficient respectively. The specific values ​​of Kp and Ki are determined by the parameters of the synchronous motor.

[0086] The values ​​of Kp and Ki in formula (7) and formula (8) are calculated as follows:

[0087] Formula (9)

[0088] Formula (10)

[0089] in: is the motor leakage inductance, is the rated current of the motor, is the rated voltage of the motor, is the regulator execution cycle, is the motor stator resistance.

[0090] Each inverter converts the reference torque of the variable frequency synchronous motor ( T 1 …T n ) and real-time torque ( Torque_ 1...Torque_n ) as the input signal, the reference torque voltage of each variable frequency synchronous motor is calculated by the torque current regulator (1…n) V 1 …V n ).

[0091] The inverter execution unit is based on the reference torque voltage ( V 1 …V n ) generates three SPWM (Sinusoidal Pulse Width Modulation) waves. The inverter's execution unit is a three-phase inverter composed of power switching tubes. These power switching tubes use switching devices such as MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors), IGBTs (Insulated Gate Bipolar Transistors), and IGCTs (Integrated Gate Commutated Thyristors).

[0092] Example 1:

[0093] This embodiment refers to the attached Figure 1 , Attachment Figure 4 and attached Figure 5 In this embodiment, the industrial frequency synchronous motor adopts an excitation synchronous motor, and the variable frequency synchronous motor adopts an excitation synchronous motor or a permanent magnet synchronous motor.

[0094] The power balance control working process and control principle of the present invention are as follows:

[0095] Phase 1: The power frequency switch QFs is disconnected, and the excitation current of the power frequency synchronous motor Ms is not input. The inverter power supply switch (QF1...QFn) is closed, and the inverter drive circuit is connected. Each inverter (VFD1...VFDn) is started to drive the corresponding variable frequency synchronous motor (M1..Mn) to run. Since it is mechanically connected to the power frequency synchronous motor Ms, the power frequency synchronous motor Ms rotates synchronously with other variable frequency synchronous motors.

[0096] Phase 2: When the power frequency synchronous motor Ms reaches the rated speed, the power frequency switch QFs is closed, the power frequency drive circuit is connected, and the excitation current is gradually input, and the power frequency synchronous motor Ms realizes power frequency drive operation.

[0097] Phase 3: The first frequency converter VFD1 obtains the voltage and current sampling signals of the industrial frequency synchronous motor Ms, and controls the output power of the corresponding variable frequency synchronous motors (M1…Mn) to be consistent with that of the industrial frequency synchronous motor Ms through the control system of each frequency converter (VFD1…VFDn) using the power balancing control method of the present invention.

[0098] Example 2:

[0099] This embodiment refers to the attached Figure 2 , Attachment Figure 4 and attached Figure 5 .

[0100] The power balance control working process and control principle of the present invention are as follows:

[0101] Phase 1: Open the power frequency switch QFs, close the inverter power supply switch (QF1...QFn), close the second transfer switch KMs, and open the first transfer switch KM1. The circuit of the power frequency synchronous motor Ms driven by the first inverter VFD1 is connected. The power frequency synchronous motor Ms is driven by the first inverter VFD 1 to the power frequency speed. The variable frequency synchronous motor (M1...Mn) is constrained by the mechanical connector and rotates synchronously with the power frequency synchronous motor Ms.

[0102] Phase 2: When the first inverter VFD1 drives the industrial frequency synchronous motor Ms to reach the rated speed, the first inverter VFD1 adjusts the output voltage so that the output voltage of the first inverter VFD1 is consistent with the frequency, amplitude and phase of the grid voltage of the industrial frequency synchronous motor Ms. Then the industrial frequency switch QFs is closed and the second switch KMs is opened. The industrial frequency drive circuit is connected, and the industrial frequency synchronous motor Ms is driven by industrial frequency.

[0103] Phase 3: Close the first switch KM1, the first inverter VFD1 drives the first variable-frequency synchronous motor M1, and the circuit is connected. Each inverter (VFD1...VFDn) drives the corresponding variable-frequency synchronous motor (M1...Mn) to operate after synchronously tracking the speed.

[0104] Phase 4: The first frequency converter VFD1 obtains the voltage and current sampling signals of the industrial frequency synchronous motor Ms, and controls the output power of each corresponding variable frequency synchronous motor (M1…Mn) to be consistent with that of the industrial frequency synchronous motor Ms through the control system of each frequency converter (VFD1…VFDn) using the power balancing control method of the present invention.

[0105] Example 3:

[0106] This embodiment refers to the attached Figure 3 , Attachment Figure 4 and attached Figure 5 .

[0107] The power balance control working process and control principle of the present invention are as follows:

[0108] Phase 1: Disconnect the power frequency switch QFs, close the inverter power supply switch (QF1...QFn), connect the inverter drive circuit, start each inverter (VFD1...VFDn) to drive the corresponding variable frequency synchronous motor (M1...Mn) to operate. Since the power frequency synchronous motor Ms is mechanically connected and rotates synchronously with other variable frequency synchronous motors, when the power frequency synchronous motor Ms reaches the rated speed, if the power frequency synchronous motor is an excitation synchronous motor, the first inverter VFD1 controls the excitation equipment of the power frequency synchronous motor to output the no-load excitation current.

[0109] Phase 2: The first frequency converter VFD1 adjusts the speed of the driven variable-frequency synchronous motor by comparing the grid voltage sampling with the power-frequency synchronous motor voltage sampling, so that the generated voltage of the power-frequency synchronous motor is consistent with the frequency and phase of the grid voltage of the power-frequency synchronous motor. If the power-frequency synchronous motor is an excitation synchronous motor, the first frequency converter VFD1 can control the magnitude of its excitation current output so that the generated voltage amplitude of the excitation synchronous motor is consistent with the grid voltage amplitude. Then, the power-frequency switch QFs is closed, the power-frequency drive circuit is connected, and the power-frequency synchronous motor Ms is driven by power frequency.

[0110] Phase 3: The first frequency converter VFD1 obtains the voltage and current sampling signals of the industrial frequency synchronous motor Ms, and controls the output power of each corresponding variable frequency synchronous motor (M1…Mn) to be consistent with that of the industrial frequency synchronous motor Ms through the control system of each frequency converter (VFD1…VFDn) using the power balancing control method of the present invention.

[0111] The control circuit and control method for achieving power balance of multiple synchronous motors provided by the present invention are applicable to transmission systems of multiple synchronous motors with mechanical connections, such as grinding mill applications. Soft starting and power balance distribution of n+1 synchronous motors can be achieved through n inverters, reducing the cost investment and maintenance workload of inverter equipment.

[0112] The foregoing description is merely a preferred embodiment of the present invention, intended to explain the present invention in detail, and is not intended to limit the present invention. It is apparent to those skilled in the art that various equivalent modifications, variations, or equivalent substitutions may be made to the specific embodiments based on the disclosure of the present invention, and such equivalent modifications, variations, or equivalent substitutions shall fall within the scope of protection of the present invention. The scope of protection of the present invention shall be determined by the description of the claims of this case.

Claims

1. A control circuit for achieving power balance of multiple synchronous motors, characterized by: The system comprises a power frequency synchronous motor Ms, n variable frequency synchronous motors and n frequency converters, wherein the n variable frequency synchronous motors are sequentially recorded as a first variable frequency synchronous motor M1, a second variable frequency synchronous motor M2 ... an nth variable frequency synchronous motor Mn, and the n frequency converters are sequentially recorded as a first frequency converter VFD1, a second frequency converter VFD2 ... an nth frequency converter VFDn, wherein n is a positive integer and n is greater than or equal to 1, and the n frequency converters are respectively provided with a frequency converter control system and are connected to each other via a communication bus to form a control loop, and the n frequency converters are connected to the corresponding n frequency converters. Current and voltage sampling circuits are respectively provided between the synchronous motors to form a sampling loop. Corresponding inverter power supply switches QF are respectively provided on the connection circuits between the n inverters and the variable-frequency synchronous motor connection busbar. The industrial frequency synchronous motor Ms is provided with a voltage and current sampling circuit connected to the first inverter VFD1 to form a sampling loop. The industrial frequency synchronous motor Ms is connected to the industrial frequency synchronous motor connection busbar through the industrial frequency switch QFs to form an industrial frequency drive loop. At the same time, the industrial frequency synchronous motor Ms and the driving shafts of the n variable-frequency synchronous motors are interconnected using connectors to realize power coupling transmission.

2. The control circuit for achieving power balance of multiple synchronous motors according to claim 1, characterized in that: The connecting parts include a transmission shaft, a gearbox and a belt.

3. The control circuit for achieving power balance of multiple synchronous motors according to claim 1, characterized in that: When the power balance control circuit starts the industrial frequency excitation synchronous motor in a mechanical interlocking rotation mode, the industrial frequency synchronous motor is an excitation synchronous motor, and the variable frequency synchronous motor is an excitation synchronous motor or a permanent magnet synchronous motor.

4. The control circuit for achieving power balance of multiple synchronous motors according to claim 1, characterized in that: The power balancing control circuit adopts a method of first driving the industrial frequency synchronous motor with a frequency converter and then switching to industrial frequency operation. The industrial frequency synchronous motor adopts an excitation synchronous motor or a permanent magnet synchronous motor, and a first switching switch KM1 is provided between the first frequency converter VFD1 and the first variable frequency synchronous motor M1. A synchronous switching inductor and a second switching switch KMs are sequentially provided on the connection circuit between the output line of the first frequency converter VFD1 and the first switching switch KM1, and are connected to the industrial frequency synchronous motor Ms.

5. The control circuit for achieving power balance of multiple synchronous motors according to claim 1, characterized in that: When the power balance control circuit uses a mechanical interlocking rotation method to start the industrial frequency synchronous motor and achieve phase synchronization with the bus connecting the industrial frequency synchronous motor, the industrial frequency synchronous motor uses an excitation synchronous motor or a permanent magnet synchronous motor. A voltage sampling circuit connected to the first frequency converter VFD1 is also provided on the connection circuit between the industrial frequency switch QFs and the bus connecting the industrial frequency synchronous motor, forming a voltage sampling circuit for the bus connecting the industrial frequency synchronous motor.

6. The control circuit for achieving power balance of multiple synchronous motors according to claim 1, characterized in that: At startup, the power frequency switch QFs is in the off state. The frequency converter first drives the variable frequency synchronous motor to run until it reaches the power frequency speed. Since the power frequency synchronous motor Ms adopts mechanical connection, it is driven by the power transmitted through the coupling and runs to the power frequency speed. At this time, the power frequency switch QFs is closed, and the power frequency synchronous motor Ms completes the power frequency drive operation.

7. The control circuit for achieving power balance of multiple synchronous motors according to claim 1, characterized in that: The first frequency converter VFD1 is provided with a frequency converter control system to obtain the voltage and current sampling signals of the industrial frequency synchronous motor Ms, and controls the output power of each corresponding variable frequency synchronous motor to be consistent with the industrial frequency synchronous motor Ms through the frequency converter control system of each frequency converter.

8. A control method for a control circuit for achieving power balance of multiple synchronous motors according to any one of claims 1 to 7, characterized in that: The system comprises n inverter control systems, where n is a positive integer and n is greater than or equal to 1. The inverter control systems exchange data via a communication bus. After the industrial frequency synchronous motor Ms and the variable frequency synchronous motor are started, the first inverter VFD1 samples the voltage and current of the industrial frequency synchronous motor Ms and obtains the real-time power of the industrial frequency synchronous motor Ms through the industrial frequency synchronous motor observer. Power_s and real-time torque Torque_s , real-time speed Speed_s The real-time torque of the power frequency synchronous motor is directly measured by the speed measuring device or obtained by the power frequency synchronous motor observer. Torque_s The system average torque is calculated by the average value calculator based on the reference torque of each variable frequency synchronous motor. T_Average , the reference torque given by each variable frequency synchronous motor and the system average torque T_Average The difference between the torque difference and the proportional coefficient Ks After multiplication, the torque difference compensation value of each variable frequency synchronous motor is obtained. Similarly, the real-time speed of each variable frequency synchronous motor is directly measured by a speed measuring device or obtained by each frequency converter through sampling the voltage and current of each variable frequency synchronous motor and the variable frequency synchronous motor observer. Speed_s As the speed given signal of each frequency converter, the corresponding speed difference signal is obtained by subtracting the real-time speed of each variable-frequency synchronous motor and the torque difference compensation value of each variable-frequency synchronous motor. The reference torque given of each variable-frequency synchronous motor is obtained through each speed regulator. The reference torque given is adjusted and output by each torque current regulator and then driven by the corresponding variable-frequency synchronous motor through each frequency converter execution unit. Finally, the power balancing work of n+1 synchronous motors is realized through the control system of each frequency converter through n frequency converters.

9. The control method for a control circuit for achieving power balance of multiple synchronous motors according to claim 8, characterized in that: The control systems of the n frequency converters are sequentially recorded as: a first frequency converter VFD1 control system, a second frequency converter VFD2 control system, ..., an nth frequency converter VFDn control system. The first frequency converter VFD1 control system includes an average value calculator, a power frequency synchronous motor observer, a first variable frequency synchronous motor observer, a first speed regulator, a first torque current regulator, and a first frequency converter execution unit. The second frequency converter VFD2 control system includes a second variable frequency synchronous motor observer, a second speed regulator, a second torque current regulator, and a second frequency converter execution unit. The nth frequency converter VFDn control system includes an nth variable frequency synchronous motor observer, an nth speed regulator, an nth torque current regulator, and an nth frequency converter execution unit. The average value calculator calculates the system average torque T_Average The formula is: Formula (1), At the same time, when the powers of the variable frequency synchronous motors are different, the reference torque of each variable frequency synchronous motor is the same as the real-time torque of the power frequency synchronous motor. Torque_s The motors are proportionally distributed according to their rated powers, and the torques are calibrated as a percentage of the rated torques. The reference torques of the variable frequency synchronous motors are recorded as follows: T 1 …T n ; In each of the synchronous motor observers, the synchronous motor three-phase current sampling signal Current Use 、 and Indicates that the three-phase voltage sampling signal Voltage Use 、 and Indicates real-time power Power , real-time torque Torque And real-time speed Speed The following formula is used for calculation: Formula (2), Formula (3), Formula (4), Torque =K m × I ｑ Formula (5), where K m is a fixed proportional constant determined by the synchronous motor parameters, Power = Torque × Speed Formula (6), Ms voltage sampling signal of industrial frequency synchronous motor Ms _ Voltage and current sampling signal Ms _ Current The real-time power is calculated by the synchronous motor observer Power_s , real-time torque Torque_s And real-time speed Speed_s Similarly, the voltage sampling signals and current sampling signals of each variable frequency synchronous motor are calculated by the variable frequency synchronous motor observer to obtain real-time power, real-time torque and real-time speed. The voltage sampling signal sequence is recorded as: M1 _ Voltage... Mn _ Voltage , the current sampling signal sequence is recorded as: M1 _ Current... Mn _ Current , the real-time power sequence is recorded as: Power_1...Power_n, the real-time torque sequence is recorded as: Torque_1...Torque_n, and the real-time speed sequence is recorded as: Speed_1...Speed_n; The speed regulator uses the speed difference Speeddiff as the input signal and calculates the torque reference value T according to the following formula: : Formula (7), Among them, t is the integration time, Kp and Ki are the proportional coefficient and the integration coefficient respectively. The specific values ​​of Kp and Ki are determined by the parameters of the synchronous motor. Each inverter uses the speed difference as input signal, and the corresponding speed regulator calculates the reference torque of each variable frequency synchronous motor, which is recorded as: T1 …Tn , the speed differences corresponding to each inverter are recorded in the order of: Speeddiff_1... Speeddiff_n; The torque current regulator is based on the reference torque T of the synchronous motor The reference torque voltage V is calculated based on the following formula: : Formula (8) Among them, t is the integration time, Kp and Ki are the proportional coefficient and the integration coefficient respectively. The specific values ​​of Kp and Ki are determined by the parameters of the synchronous motor. Each inverter takes the reference torque and real-time torque of the variable frequency synchronous motor as input signals, and calculates the reference torque voltage of each variable frequency synchronous motor through the corresponding torque current regulator. The reference torque sequence of the variable frequency synchronous motor is recorded as: T1 …Tn , the real-time torque sequence is recorded as: Torque_1...Torque_n, and the reference torque voltage sequence of each variable frequency synchronous motor is recorded as: V1 …Vn .

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