Motor variable frequency and power frequency undisturbed synchronous switching system

Abstract

The utility model discloses a motor frequency conversion and work frequency undisturbed synchronous switching system, including motor, frequency converter, work frequency power supply, the first contactor of connecting frequency converter output, the second contactor of connecting work frequency power supply, synchronous sensing and control module. Synchronous sensing and control module contain work frequency power supply parameter sensing module, frequency converter output parameter sensing module and treater, and treater compares work frequency power supply and frequency converter output's voltage, frequency and phase in real time, and control frequency converter output parameter matches work frequency power supply parameter, when satisfying the preset synchronous condition, through the control output port group output predetermined timing's control signal to first and second contactor, realize motor's undisturbed switching between two kinds of power supply, usually adopt " first close later break " strategy. The utility model through accurate synchronization and optimization switching timing, reduce switching impact significantly, improve system reliability and equipment life.

Description

Technical Field

[0001] This utility model relates to the field of motor control technology, specifically to a motor frequency conversion and power frequency synchronous switching system without disturbance. Background Technology

[0002] In modern industrial production and power systems, electric motors are widely used as primary power equipment. Variable frequency drives (VFDs) play a crucial role in energy conservation and improving process efficiency due to their ability to smoothly start, stop, and precisely control the speed of motors. However, in many applications, motors only require VFD speed control during startup or under specific operating conditions; during stable operation, direct power supply from the mains grid is more economical and efficient. Therefore, switching between VFD and mains power supplies for motors has become a common requirement.

[0003] Traditional switching methods, such as direct "disconnect-then-make" or simple contactor switching, often cause significant electrical shocks (such as overcurrent and overvoltage) and mechanical shocks (such as torque fluctuations) to the motor during switching due to differences in voltage amplitude, frequency, and phase between the inverter output and the mains power grid. This can damage the motor and its driven equipment, and also disturb the power grid, affecting the system's stability and reliability. For example, switching between power supplies of different frequencies can impact loads such as motors, leading to equipment damage and instability. While some existing technologies attempt to address these issues, there is still room for improvement in synchronization accuracy, switching smoothness, and system integration compactness. Especially for applications requiring frequent switching or sensitive to switching disturbances, existing technologies are insufficient to fully meet the requirements.

[0004] Therefore, developing a system that can achieve truly disturbance-free, fast, and reliable synchronous switching between frequency converters and power frequency power supplies has significant practical importance and application value. Summary of the Invention

[0005] Purpose of the invention: The purpose of this utility model is to overcome the problems of large impact and low reliability of motors when switching between frequency converter power supply and power frequency in the prior art, and to provide a motor frequency converter and power frequency synchronous switching system without disturbance.

[0006] Technical Solution: The motor frequency converter and power frequency synchronous switching system of this utility model includes a motor, a frequency converter, a power frequency power supply, a first contactor connected to the output terminal of the frequency converter, and a second contactor connected to the power frequency power supply. The output terminals of both the first and second contactors are connected to the motor. The system further includes a synchronous sensing and control module, which comprises a power frequency power supply parameter sensing module, a frequency converter output parameter sensing module, and a processor. The input terminal of the power frequency power supply parameter sensing module is connected to the power frequency power supply, and is used to detect the voltage, frequency and phase information of the power frequency power supply and output the corresponding power frequency parameter signal. The input terminal of the inverter output parameter sensing module is connected to the output terminal of the inverter, and is used to detect the voltage, frequency and phase information output by the inverter and output the corresponding inverter parameter signal. The signal input terminal of the processor is electrically connected to the signal output terminal of the power frequency power parameter sensing module and the signal output terminal of the inverter output parameter sensing module, respectively. The first signal output terminal of the processor is electrically connected to the control input terminal of the inverter. The second signal output terminal of the processor is connected to the control coil of the first contactor and the control coil of the second contactor. The processor is configured to process the received power frequency parameter electrical signal and frequency conversion parameter electrical signal, perform comparison calculations based on preset synchronization conditions, and output a command signal to the frequency converter through the first signal output terminal to match the parameters of the power frequency power supply. When the comparison calculation result meets the synchronization conditions, the processor outputs a set of control voltages with a predetermined timing sequence to the control coils of the first contactor and the second contactor through the second signal output terminal to realize the smooth switching of the motor between the frequency conversion power supply and the power frequency power supply.

[0007] To further improve the above technical solution, the timing logic of the control voltage output by the processor through the second signal output terminal is configured as follows: outputting a pull-in voltage to the control coil of the contactor to be connected to the power supply side; after a preset short delay or after receiving a closing confirmation signal from the status feedback port of the already pulled-in contactor, outputting a disconnect signal to the control coil of the contactor on the original power supply side; and during the short period when the two contactors are simultaneously driven to close by the pull-in voltage, the processor continuously outputs command signals to the frequency converter through the first signal output terminal to maintain the synchronization of its output parameters with the power frequency power parameters.

[0008] Furthermore, the power frequency power supply parameter sensing module and / or the inverter output parameter sensing module include: a branch consisting of a voltage transformer and a sampling resistor connected in series for detecting voltage amplitude, and a zero-crossing detection circuit for detecting phase, wherein the zero-crossing detection circuit includes an optocoupler.

[0009] Furthermore, the processor internally contains a phase-locked loop (PLL) operation logic module. The input terminal of the PLL operation logic module receives frequency and phase information from the first and second signal input port groups, and its output is used to generate and transmit frequency and phase adjustment command signals to the inverter via the first signal output terminal.

[0010] Furthermore, the processor communicates with the control input terminal of the frequency converter through its built-in communication interface module conforming to a specific communication protocol, or through its configured multi-channel analog and / or digital output ports, to precisely control its output parameters.

[0011] Furthermore, the processor is also provided with at least one fault signal input port, which is used to connect to the signal output terminal of an external fault detection sensor via a wire, or to the auxiliary contact output terminal of the first contactor and the second contactor. The processor is internally configured with a protective disconnection control logic circuit for outputting a disconnection voltage to the contactor coil through the second signal output terminal when a preset fault level signal is received from the fault signal input port.

[0012] Furthermore, it also includes a motor selection switch array, the input of which is connected to the output of the first contactor. The motor selection switch array has multiple selective outputs for connecting multiple motors to be started respectively. The processor is also configured with a control output for controlling the motor selection switch array to select a target motor, and is adapted to control the frequency converter and the first contactor to connect to another motor to be started through the motor selection switch array after the motor is started by the frequency converter and switched to stable operation of the mains power supply, and repeat the synchronous sensing and control process.

[0013] Beneficial effects: Compared with the prior art, the advantages of this utility model are: (1) achieving disturbance-free switching: through precise synchronous control and optimized contactor switching timing, the electrical and mechanical shocks generated during the switching process are effectively avoided, protecting the motor and related equipment, and improving the stability and reliability of the system.

[0014] (2) Compact structure and high integration: Synchronous sensing and control functions are integrated into the same module (such as PCB or control cabinet), making the system structure more compact and easier to install and maintain.

[0015] (3) Improve energy efficiency: Allows the motor to be driven by the frequency converter when speed regulation is required, and switches to the power frequency power supply when running stably. It combines the flexibility of frequency conversion speed regulation and the high efficiency of power frequency operation, which helps to save energy and reduce consumption.

[0016] (4) Extend equipment life: Reduces the damage to components such as motors and contactors caused by switching shocks, thereby extending the service life of the equipment.

[0017] (5) High application flexibility: It can be applied to the frequency conversion / power frequency switching of a single motor, and can also be extended to support the sequential soft start and switching of multiple motors, with a wide range of application scenarios. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the motor frequency conversion and power frequency disturbance-free synchronous switching system provided by this utility model.

[0019] Figure 2 This is a circuit diagram for detecting the amplitude of power frequency supply voltage.

[0020] Figure 3 This is a circuit diagram for phase detection of power frequency power supply.

[0021] Figure 4 This is a functional block diagram of the synchronous sensing and control module. Detailed Implementation

[0022] The technical solution of this utility model will be described in detail below with reference to the accompanying drawings, but the protection scope of this utility model is not limited to the described embodiments.

[0023] Example 1: Refer to Figure 1 The present invention provides a motor frequency converter and power frequency synchronous switching system with no disturbance, comprising a motor M, a frequency converter VFD, a power frequency power supply Power, a first contactor K1, and a second contactor K2. The input terminal of the first contactor K1 is connected to the output terminal of the frequency converter VFD, and its output terminal is connected to the motor M. The input terminal of the second contactor K2 is connected to the power frequency power supply, and its output terminal is also connected to the motor M. Optionally, a line reactor L can be connected in series between the output terminal of the frequency converter VFD and the first contactor K1 to suppress harmonics and current surges.

[0024] The core of this invention lies in the synchronous sensing and control module. This module can be physically integrated onto a printed circuit board (PCB) or within a separate control cabinet to achieve a compact structure. The module includes: Power frequency power supply parameter sensing module: This module is used to detect the voltage amplitude, frequency, and three-phase phase information of the power frequency power supply in real time. (Refer to...) Figure 2 Taking phase A as an example (phases B and C are similar), the power frequency phase A voltage is stepped down by a voltage transformer UTR (such as a miniature voltage transformer) and then passed through a current-limiting resistor UR00 (for example, limiting the 380V voltage to below 2mA), outputting an AC current proportional to the primary voltage. This current passes through a ZL7 bridge rectifier circuit, forming a pulsating DC voltage across the sampling resistor UR1. This voltage is filtered by an RC filter circuit to remove high-frequency components, yielding a DC signal UAB representing the power frequency voltage amplitude, which is then sent to the processor's analog-to-digital converter (ADC) port. UD1 is a clamping diode to prevent the UAB voltage from exceeding the processor's allowable input range (e.g., 5V).

[0025] Reference Figure 3Taking phase A as an example (phases B and C are similar), the power frequency phase A voltage (input at pin 3 of Y4) is input to the input terminal of the high-speed optocoupler UR (such as 6N139) through components such as SRR0 (e.g., SRD1 and SRR0 form a half-wave rectification or zero-crossing comparison function). During the positive half-cycle of the power supply, the optocoupler is on; during the negative half-cycle, the optocoupler may be off or have different states during the negative half-cycle through specific circuitry. The output terminal (pin 6) of the optocoupler UR generates high and low level signals representing the positive and negative half-cycles or zero-crossing points of the power supply. This signal is shaped by IC5 (such as an inverter or shaping circuit like SN74HC14D) and then input to the processor's digital input or capture pin. SRR5 and SRC3 form an RC filter to filter out high-frequency interference from the input signal. SRC1 is a high-frequency interference filtering capacitor for the optocoupler's power supply (e.g., +5V). SRR3 is a pull-up resistor, and SRR2 is the adjustment resistor for the optocoupler. By detecting the zero-crossing points or high / low level sequences of the three phases, the processor can calculate the frequency, phase sequence, and instantaneous phase of the power supply.

[0026] like Figure 4 The synchronous sensing and control module shown includes a power frequency power supply parameter sensing module, a frequency converter output parameter sensing module, and a processor. The structure and principle of the frequency converter output parameter sensing module are similar to those of the power frequency power supply parameter sensing module. Its input terminal is connected to the output terminal of the frequency converter VFD (before K1) to detect the amplitude, frequency, and three-phase phase information of the frequency converter output voltage in real time. In some embodiments, if the frequency converter VFD itself has a precise output parameter feedback interface (such as through communication or analog signals), these feedback signals can also be directly used as frequency converter parameter signals.

[0027] The processor is the core of the entire synchronous sensing and control module, typically a microcontroller (MCU) or a programmable logic controller (PLC). Its signal input terminals are connected to the output signals of the power frequency parameter sensing module and the inverter output parameter sensing module, respectively. Its control output terminals include: control input terminals connected to the inverter VFD (e.g., controlling frequency and voltage through analog signals, or sending control commands through digital communication interfaces such as Modbus or Profibus), and a group of control output ports connected to the control coils of the first contactor K1 and the second contactor K2, used to control the engagement and disengagement of K1 and K2.

[0028] Working process (taking switching from VFD to mains frequency after starting the motor as an example): Initial state: K1 and K2 are both disconnected; VFD starter motor: The processor first controls K1 to close, and then controls the VFD starter motor M to smoothly accelerate the motor to a target speed that is close to or equal to the power frequency synchronous speed. Synchronization preparation: During motor operation or after reaching the target speed, the processor continuously monitors the voltage amplitude, frequency, and phase of the power grid through the power frequency power parameter sensing module. Simultaneously, it also monitors the corresponding parameters output by the VFD through the inverter output parameter sensing module (or VFD self-feedback). Parameter synchronization control: The processor executes a synchronization algorithm (e.g., a phase-locked loop (PLL) algorithm). Frequency synchronization: Controls the VFD's output frequency to precisely match the power grid frequency; Voltage synchronization: Controls the output voltage amplitude of the VFD to precisely match the voltage amplitude of the power grid. Phase synchronization: This involves controlling the VFD's output voltage phase to accurately track and align with the mains voltage phase. The goal is to minimize the voltage difference (amplitude difference, frequency difference, phase difference) between the VFD output and the mains power supply at the moment of switching. Synchronization condition judgment: The processor sets preset synchronization conditions, such as: voltage amplitude difference less than ±5%, frequency difference less than ±0.1Hz, and phase difference less than ±5 electrical angles. When these conditions are met for a continuous period of time (e.g., 100ms-500ms), synchronization is considered complete.

[0029] Disruptive switching execution: Once the synchronization condition is met, the processor outputs a set of control signals with a predetermined timing to the control coils of K1 and K2 through its control output port group, realizing a "make-before-break" switching sequence. First, control the second contactor K2 to close, and connect the mains frequency power supply to the motor; Within a very short time after K2 closes (e.g., tens to hundreds of milliseconds, ensure reliable contact of the K2 main contacts), and during this brief parallel connection period, the processor continues to maintain the synchronization between the VFD output and the mains power supply to prevent the generation of large circulating currents; Then, control the first contactor K1 to disconnect, so that the frequency converter VFD is disconnected from the motor M; At this point, motor M has smoothly switched to mains frequency power supply. The current and torque fluctuations were minimal throughout the entire switching process.

[0030] VFD Post-Processing: After the switch is completed, the VFD can be stopped, put into standby mode, or used to control other motors.

[0031] Switching back to VFD (if speed regulation or soft stop is required): The process is similar to the above, but in the reverse direction. The VFD needs to be started first and its output synchronized to the motor being driven by the mains frequency (at this time, the motor's voltage, frequency, and phase are consistent with the mains frequency, and the VFD can "capture" the running motor). After synchronization is complete, close K1 first, then open K2.

[0032] This utility model provides a motor frequency converter and power frequency synchronous switching system without disturbance. Through an integrated synchronization sensing and control module, it accurately detects and controls the voltage, frequency and phase of the frequency converter output and the power frequency power supply. After meeting strict synchronization conditions, it adopts an optimized "close first, then disconnect" contactor switching sequence to achieve smooth and disturbance-free switching of the motor between the two power supplies.

[0033] Example 2: Based on Example 1, the system can be configured with a motor selection switch array. After the processor completes the frequency conversion start-up of one motor and switches it to the mains frequency, it can control the frequency converter to connect to the next motor to be started through the motor selection switch array, repeating the above synchronous switching process to achieve sequential soft start of multiple motors by one frequency converter.

[0034] Example 3: Based on Example 1, the processor can integrate a fault detection input port to connect to external sensors (such as overcurrent detection) or receive the auxiliary contact status of K1 and K2 as feedback. Once a switching abnormality is detected (such as the contactor not acting as instructed, the synchronization parameter exceeding the tolerance time for too long, or excessive current occurring during the switching process), the preset protection logic is executed, such as emergency disconnection of all contactors and issuance of an alarm signal.

[0035] As described above, although the present invention has been shown and described with reference to specific preferred embodiments, it should not be construed as limiting the present invention itself. Various changes in form and detail may be made to the present invention without departing from the spirit and scope of the appended claims.

Claims

1. A system for seamless synchronous switching of motor frequency conversion and mains frequency, comprising a motor, a frequency converter, a mains frequency power supply, a first contactor connected to the output terminal of the frequency converter, and a second contactor connected to the mains frequency power supply, wherein the output terminals of both the first and second contactors are connected to the motor, characterized in that, The system also includes a synchronous sensing and control module, which comprises a power frequency power supply parameter sensing module, a frequency converter output parameter sensing module, and a processor, wherein: The input terminal of the power frequency power supply parameter sensing module is connected to the power frequency power supply, and is used to detect the voltage, frequency and phase information of the power frequency power supply and output the corresponding power frequency parameter signal. The input terminal of the inverter output parameter sensing module is connected to the output terminal of the inverter, and is used to detect the voltage, frequency and phase information output by the inverter and output the corresponding inverter parameter signal. The signal input terminal of the processor is electrically connected to the signal output terminal of the power frequency power parameter sensing module and the signal output terminal of the inverter output parameter sensing module, respectively. The first signal output terminal of the processor is electrically connected to the control input terminal of the inverter, and the second signal output terminal of the processor is connected to the control coil of the first contactor and the control coil of the second contactor.

2. The motor frequency conversion and power frequency disturbance-free synchronous switching system according to claim 1, characterized in that, The power frequency power supply parameter sensing module and / or the inverter output parameter sensing module include: a branch consisting of a voltage transformer and a sampling resistor connected in series for detecting voltage amplitude, and a zero-crossing detection circuit for detecting phase, wherein the zero-crossing detection circuit includes an optocoupler.

3. The motor frequency conversion and power frequency disturbance-free synchronous switching system according to claim 1, characterized in that, The processor has a built-in phase-locked loop (PLL) operation logic module. The input terminal of the PLL operation logic module receives frequency and phase information from the signal input terminal of the processor, and its output is used to generate and transmit frequency and phase adjustment command signals to the inverter via the first signal output terminal.

4. The motor frequency conversion and power frequency disturbance-free synchronous switching system according to claim 1, characterized in that, The processor communicates with the control input terminal of the frequency converter through its built-in communication interface module conforming to a specific communication protocol, or through its configured multi-channel analog and / or digital output ports, to precisely control its output parameters.

5. The motor frequency conversion and power frequency disturbance-free synchronous switching system according to claim 1, characterized in that, The processor is also provided with at least one fault signal input port, which is used to connect to the signal output terminal of an external fault detection sensor via a wire, or to the auxiliary contact output terminal of the first contactor and the second contactor. The processor is internally configured to output a disconnect voltage to the contactor coil through a second signal output terminal when a preset fault level signal is received from the fault signal input port.

6. The motor frequency conversion and power frequency disturbance-free synchronous switching system according to claim 1, characterized in that, It also includes a motor selection switch array, the input of which is connected to the output of the first contactor, and the motor selection switch array has multiple selective outputs for connecting multiple motors to be started respectively; the processor is also configured with a control output for controlling the motor selection switch array to select the target motor.

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