A protective device for a motor frequency conversion drive circuit and a motor frequency converter

Abstract

The present invention discloses a protection device for a motor's variable frequency drive circuit and a motor inverter. The device includes: a sampling unit, disposed at the output end of a rectifier circuit and connected to the input ends of an overvoltage comparison unit and an undervoltage comparison unit, respectively; an overvoltage comparison unit, disposed between the output end of the sampling unit and a switch protection unit; an undervoltage comparison unit, disposed between the output end of the sampling unit and the switch protection unit; and a switch protection unit, disposed at the output ends of the overvoltage comparison unit and the undervoltage comparison unit, and located between the output end of a busbar and the input end of an inverter circuit. This solution implements dual overvoltage and undervoltage protection for the input voltage of the motor's variable frequency drive circuit by providing both hardware overvoltage and undervoltage protection circuits and software overvoltage and undervoltage protection logic in the motor's variable frequency drive circuit, thereby improving the safety of load component operation.

Description

Technical Field

[0001] The present invention belongs to the technical field of motors, and specifically relates to a protection device for a motor's variable frequency drive circuit and a motor's frequency converter, and more particularly to a busbar over- and under-voltage dual shutdown protection circuit for a motor's variable frequency drive circuit, and a motor's frequency converter having the busbar over- and under-voltage dual shutdown protection circuit. Background Art

[0002] In the variable frequency drive circuit of the motor of the related solution, the bus voltage value is generally detected by voltage sampling, and then the bus voltage is determined to be overvoltage or undervoltage (i.e., overvoltage or undervoltage) based on the detected bus voltage value. When the bus voltage is determined to be overvoltage or undervoltage, it is considered that the bus has an overvoltage or undervoltage fault and a fault output is performed. However, in actual applications, due to the existence of grid fluctuations or spike voltages caused by some surges, as well as user misoperation resulting in the provision of an incorrect power supply voltage (for example, the power supply adjusts the voltage incorrectly when supplying power, such as providing a three-phase 380V voltage but providing another voltage), etc., bus overvoltage or undervoltage may occur.

[0003] The variable frequency drive circuit of the motor in the related solution determines whether the bus voltage is over-voltage or under-voltage (i.e., overvoltage or undervoltage) by detecting the value of the bus voltage. This cannot solve the bus over-voltage or under-voltage (i.e., overvoltage or undervoltage) caused by grid fluctuations or spike voltages caused by some surges, user misoperation, and providing incorrect power supply voltage. However, in this case, the bus over-voltage or under-voltage (i.e., overvoltage or undervoltage) problem will affect the safety of the operation of load components (such as electrical components at the rear end of the bus in the variable frequency drive circuit of the motor).

[0004] The above content is only used to assist in understanding the technical solution of the present invention and does not constitute an admission that the above content is prior art. Summary of the Invention

[0005] The object of the present invention is to provide a protection device for a variable frequency drive circuit of a motor and a frequency converter for the motor, so as to solve the problem that the variable frequency drive circuit of the motor in the related solution determines whether the bus voltage is over-voltage or under-voltage by detecting the value of the bus voltage, but cannot solve the problem that the bus voltage is over-voltage or under-voltage caused by spike voltage caused by grid fluctuations or some surges, user misoperation and providing incorrect power supply voltage, etc., which affects the safety of the operation of load components (such as electrical components at the rear end of the bus in the variable frequency drive circuit of the motor). By setting a hardware over-voltage and under-voltage protection circuit and a software over-voltage and under-voltage protection logic in the variable frequency drive circuit of the motor, the input voltage of the bus of the variable frequency drive circuit of the motor is dually protected against over-voltage and under-voltage, thereby improving the safety of the operation of load components (such as electrical components at the rear end of the bus in the variable frequency drive circuit of the motor).

[0006] The present invention provides a protection device for a variable frequency drive circuit of a motor, wherein a rectifier circuit, a bus capacitor unit, and an inverter circuit are provided on the power supply side of the motor; the rectifier circuit, the bus capacitor unit, and the inverter circuit are sequentially provided between the power grid and the motor; the protection device for the variable frequency drive circuit of the motor is provided between the rectifier circuit and the inverter circuit, and between the rectifier circuit and the bus capacitor unit; the protection device for the variable frequency drive circuit of the motor comprises: a sampling unit, an overvoltage comparison unit, an undervoltage comparison unit, and a switch protection unit; The sampling unit is provided at the output end of the rectifier circuit and is connected to the input end of the overvoltage comparison unit and the input end of the undervoltage comparison unit respectively, and is used to sample the input voltage of the bus at the output end of the rectifier circuit, recorded as the bus voltage; and input the bus voltage to the overvoltage comparison unit and the undervoltage comparison unit respectively; the overvoltage comparison unit is provided between the output end of the sampling unit and the switch protection unit, and is used to compare the bus voltage with a preset bus overvoltage protection threshold value, so as to detect the bus voltage when the bus voltage is higher than the bus overvoltage protection threshold value. The bus voltage is outputted as a parameter indicating that the bus voltage is higher than the bus overvoltage protection threshold value when the bus voltage is lower than the bus overvoltage protection threshold value, which is recorded as the bus overvoltage parameter; the undervoltage comparison unit is provided between the output end of the sampling unit and the switch protection unit, and is used to compare the bus voltage with a preset bus undervoltage protection threshold value, so as to outputted as a parameter indicating that the bus voltage is lower than the bus undervoltage protection threshold value when the bus voltage is lower than the bus undervoltage protection threshold value, which is recorded as the bus undervoltage parameter; the switch protection unit is provided at the output end of the overvoltage comparison unit and the output end of the undervoltage comparison unit, It is located between the output end of the bus and the input end of the inverter circuit, and is used to disconnect the switch protection unit itself when the bus overvoltage parameter or the bus undervoltage parameter is received, so as to disconnect the power circuit between the bus and the inverter circuit, thereby protecting the bus capacitor unit, the inverter circuit and the motor at the rear end of the bus; and to connect the switch protection unit itself when the bus overvoltage parameter and the bus undervoltage parameter are not received, so as to connect the power circuit between the bus and the inverter circuit, thereby energizing the motor to operate normally.

[0007] In some embodiments, the sampling unit includes: a first voltage-dividing resistor module and a second voltage-dividing resistor module; wherein the first voltage-dividing resistor module and the second voltage-dividing resistor module are arranged in series between the positive and negative poles of the output end of the rectifier circuit; the common end of the first voltage-dividing resistor module and the second voltage-dividing resistor module serves as the output end of the sampling unit; the output end of the sampling unit is respectively connected to the input end of the overvoltage comparison unit and the input end of the undervoltage comparison unit.

[0008] In some embodiments, the overvoltage comparison unit includes: a first comparison module and a first threshold setting module; the undervoltage comparison unit includes: a second comparison module and a second threshold setting module; wherein, the output end of the sampling unit is connected to the inverting input end of the first comparison module; the first threshold setting module is connected to the non-inverting input end of the first comparison module; the output end of the first comparison module is connected to the first input end of the switch protection unit; the output end of the sampling unit is also connected to the non-inverting input end of the second comparison module; the second threshold setting module is connected to the inverting input end of the second comparison module; and the output end of the second comparison module is connected to the second input end of the switch protection unit.

[0009] In some embodiments, the first threshold setting module includes: a first adjustable resistance module; the second threshold setting module includes: a second adjustable resistance module; wherein, the first adjustable resistance module is arranged between a DC power supply and ground; the adjustment end of the first adjustable resistance module is connected to the non-inverting input end of the first comparison module; the second adjustable resistance module is arranged between a DC power supply and ground; the adjustment end of the second adjustable resistance module is connected to the inverting input end of the second comparison module.

[0010] In some embodiments, the switch protection unit includes: an AND logic module, a switch tube module and a relay module; wherein the first input end of the AND logic module serves as the first input end of the switch protection unit; the second input end of the AND logic module serves as the second input end of the switch protection unit; the output end of the AND logic module is connected to the control end of the switch tube module; the coil of the relay module is connected between the second DC power supply and the first connection end of the switch tube module; the contacts of the relay module are located between the output end of the bus and the bus capacitor unit, and connected between the output end of the bus and the input end of the inverter circuit; the second connection end of the switch tube module is grounded.

[0011] In some embodiments, the switch protection unit further includes: a voltage follower module and a filter module; wherein the voltage follower module is arranged between the output end of the AND logic module and the control end of the switch tube module; the output end of the voltage follower module is connected to the control end of the switch tube module; the output end of the voltage follower module is also grounded after passing through the filter module.

[0012] In some embodiments, the switch protection unit further includes: a current limiting module and a pull-down module; wherein the current limiting module is arranged between the output end of the voltage follower module and the control end of the switch tube module; the pull-down module is arranged between the control end of the switch tube module and the ground.

[0013] In some embodiments, it further includes: a control unit; the control unit is arranged between the output end of the sampling unit and the control end of the drive chip of the inverter circuit; the drive chip of the inverter circuit is arranged between the drive signal control end of the control unit and the drive end of the inverter circuit; wherein the control unit is used to determine whether the bus voltage is higher than the bus overvoltage protection threshold or the bus voltage is lower than the bus undervoltage protection threshold based on the bus voltage sampled by the sampling unit during the operation of the motor after it is powered on, and if it is determined that the bus voltage is higher than the bus overvoltage protection threshold or the bus voltage is lower than the bus undervoltage protection threshold, stop outputting the drive control signal to the drive chip of the inverter circuit to turn off the drive signal of the inverter circuit and stop the motor.

[0014] In some embodiments, it further includes: at least one of a display unit, an indication unit and an alarm unit; when the protection device of the variable frequency drive circuit of the motor also includes a display unit, an indication unit and an alarm unit, the display unit, the indication unit and the alarm unit are respectively connected to the control unit; wherein, the display unit is used to display the bus voltage sampled by the sampling unit; the alarm unit is used to remind when the bus voltage is higher than the bus overvoltage protection threshold or when the bus voltage is lower than the bus undervoltage protection threshold; the indication unit is used to indicate when the bus voltage is higher than the bus overvoltage protection threshold or when the bus voltage is lower than the bus undervoltage protection threshold.

[0015] Matching the above device, the present invention further provides a frequency converter for a motor, comprising: the protection device for the variable frequency drive circuit of the motor described above.

[0016] Therefore, the solution of the present invention sets a hardware over-voltage and under-voltage protection circuit and a software over-voltage and under-voltage protection logic in the variable frequency drive circuit of the motor by targeting the variable frequency drive circuit between the rectifier circuit and the inverter circuit on the power supply side of the motor. When the motor is powered on, the hardware over-voltage and under-voltage protection circuit detects whether the input voltage of the bus is over-voltage or under-voltage. If the input voltage of the bus is present, the bus and the subsequent load of the bus are disconnected to protect the subsequent load of the bus; if the input voltage of the bus is not over-voltage or under-voltage, the bus and the subsequent load of the bus are connected, and the motor works normally. During the normal operation of the motor, The software's overvoltage protection logic is used to detect whether the bus input voltage is overvoltage or undervoltage. If the bus input voltage is overvoltage or undervoltage, the output of the inverter circuit's driver chip is shut down to stop outputting the drive signal to the inverter circuit, control the motor to stop, and protect the motor. Thus, by setting a hardware overvoltage and undervoltage protection circuit and software overvoltage and undervoltage protection logic in the motor's variable frequency drive circuit, dual overvoltage and undervoltage protection can be implemented for the input voltage of the bus of the motor's variable frequency drive circuit, thereby improving the safety of the operation of load components (such as electrical components at the rear end of the bus in the motor's variable frequency drive circuit).

[0017] Other features and advantages of the present invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the present invention.

[0018] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the structure of an embodiment of a protection device for a variable frequency drive circuit of a motor according to the present invention;

[0020] Figure 2 The present invention is a schematic structural diagram of an embodiment of a busbar over-voltage and under-voltage dual shutdown protection circuit of a variable frequency drive circuit of a motor. DETAILED DESCRIPTION

[0021] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments of the present invention and corresponding drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0022] Considering that the variable frequency drive circuit of the motor in the related solutions determines whether the bus voltage is overvoltage or undervoltage by detecting the bus voltage value, it cannot solve the bus voltage overvoltage or undervoltage caused by voltage spikes caused by grid fluctuations or surges, user misoperation and providing incorrect power supply voltage, etc. For example, in the related solutions, the variable frequency drive circuit generally uses software to identify overvoltage or undervoltage and then reports a fault, but the actual circuit voltage remains the actual voltage, and generally no protective measures are taken. In this case, the problem of overvoltage or undervoltage (i.e., overvoltage or undervoltage) still exists on the bus, but since the overvoltage or undervoltage (i.e., overvoltage or undervoltage) of the bus cannot be solved, the bus still has the corresponding input voltage conversion value, and the load components behind the bus (such as the electrical components at the rear end of the bus in the variable frequency drive circuit of the motor, etc.) are subjected to the corresponding voltage value. This voltage value may exceed the load components (such as the electrical components at the rear end of the bus in the variable frequency drive circuit of the motor, etc.) themselves The tolerance range may cause the load components to fail or even cause the load components (such as the electrical components at the rear end of the bus in the variable frequency drive circuit of the motor, etc.) to be damaged. Therefore, the present invention proposes a protection device for a motor's variable frequency drive circuit, specifically a busbar overvoltage and undervoltage protection circuit for the motor's variable frequency drive circuit, and more specifically a busbar overvoltage and undervoltage dual-shutoff protection circuit for the motor's variable frequency drive circuit. This device protects the motor's variable frequency drive circuit and load components, ensuring the safety of the motor's variable frequency drive circuit and improving the safety of load components (such as electrical components at the rear end of the busbar in the motor's variable frequency drive circuit). The variable frequency drive circuit (or variable frequency drive inverter circuit) in the motor's inverter is a drive circuit that is disposed between the rectifier circuit and the inverter circuit in the motor's inverter and includes the inverter circuit.

[0023] According to an embodiment of the present invention, a protection device for a variable frequency drive circuit of a motor is provided. Figure 1 The structure diagram of an embodiment of the device of the present invention is shown in FIG. On the power supply side of the motor, a rectifier circuit, a bus capacitor unit and an inverter circuit are provided; the rectifier circuit, the bus capacitor unit and the inverter circuit are sequentially provided between the power grid and the motor; the protection device of the variable frequency drive circuit of the motor is provided between the rectifier circuit and the inverter circuit, and is located between the rectifier circuit and the bus capacitor unit; Figure 2The busbar over- and under-voltage dual shutdown protection circuit of the motor's variable frequency drive circuit is shown, and is arranged between the power grid (i.e., AC power supply) and the motor's power supply terminal, specifically between the rectifier circuit (e.g., rectifier bridge) and the inverter circuit (e.g., six-way inverter bridge). The power grid is sequentially transmitted through the rectifier circuit (e.g., rectifier bridge), the variable frequency drive circuit, and the inverter circuit (e.g., six-way inverter bridge) before being output to the motor's power supply terminal. The variable frequency drive circuit has the function of busbar over- and under-voltage dual shutdown protection. The protection device of the motor's variable frequency drive circuit includes: a sampling unit, an overvoltage comparison unit, an undervoltage comparison unit, and a switch protection unit.

[0024] In which, the sampling unit is arranged at the output end of the rectifier circuit and is respectively connected to the input end of the overvoltage comparison unit and the input end of the undervoltage comparison unit, and is used to sample the input voltage of the bus at the output end of the rectifier circuit, which is recorded as the bus voltage; and input the bus voltage into the overvoltage comparison unit and the undervoltage comparison unit respectively.

[0025] In some embodiments, the sampling unit includes: a first voltage-dividing resistor module and a second voltage-dividing resistor module; wherein the first voltage-dividing resistor module and the second voltage-dividing resistor module are arranged in series between the positive and negative poles of the output end of the rectifier circuit; the common end of the first voltage-dividing resistor module and the second voltage-dividing resistor module serves as the output end of the sampling unit; the output end of the sampling unit is respectively connected to the input end of the overvoltage comparison unit and the input end of the undervoltage comparison unit.

[0026] like Figure 2 As shown, the first voltage-dividing resistor module is such as resistor R1 and resistor R2, and the second voltage-dividing resistor module is such as resistor R3. Resistors R1, R2 and R3 are bus voltage-dividing resistors for sampling the bus voltage. Because the voltage across the sampling resistor R3 is generally much larger than the resistance of the lower resistor, resistors R1, R2 and R3 are set here to perform voltage-dividing sampling of the bus voltage. The three-phase electricity (i.e., three-phase AC power supply) provided by the power grid is input to the input end of the rectifier bridge. The output end of the rectifier bridge has a terminal P (i.e., a positive terminal) and a terminal N (i.e., a negative terminal). The terminal P at the output end of the rectifier bridge is connected to the terminal N at the output end of the rectifier bridge after passing through resistors R1, R2 and R3.

[0027] The overvoltage comparison unit is arranged between the output end of the sampling unit and the switch protection unit, and is used to compare the bus voltage with a preset bus overvoltage protection threshold, so as to output a parameter indicating that the bus voltage is higher than the bus overvoltage protection threshold when the bus voltage is higher than the bus overvoltage protection threshold, which is recorded as the bus overvoltage parameter.

[0028] The undervoltage comparison unit is arranged between the output end of the sampling unit and the switch protection unit, and is used to compare the bus voltage with a preset bus undervoltage protection threshold, so as to output a parameter indicating that the bus voltage is lower than the bus undervoltage protection threshold when the bus voltage is lower than the bus undervoltage protection threshold, which is recorded as the bus undervoltage parameter.

[0029] In some embodiments, the overvoltage comparison unit includes: a first comparison module and a first threshold setting module, the first comparison module being such as comparator U1 and the first threshold setting module being such as resistor R4; and the undervoltage comparison unit includes: a second comparison module and a second threshold setting module, the second comparison module being such as comparator U2 and the second threshold setting module being such as resistor R5. The output of the sampling unit is connected to the inverting input of the first comparison module; the first threshold setting module is connected to the non-inverting input of the first comparison module; and the output of the first comparison module is connected to the first input of the switch protection unit. The output of the sampling unit is also connected to the non-inverting input of the second comparison module; the second threshold setting module is connected to the inverting input of the second comparison module; and the output of the second comparison module is connected to the second input of the switch protection unit.

[0030] See also Figure 2 In the example shown, resistor R4 is used to set the voltage threshold of the reference terminal of comparator U1, and resistor R5 is used to set the voltage threshold of the reference terminal of comparator U2. The sampling input terminal of comparator U1 is connected to the negative terminal of comparator U1 (i.e., the inverting input terminal of comparator U1), and the reference terminal of comparator U1 is connected to the positive terminal of comparator U1 (i.e., the non-inverting input terminal of comparator U1). The sampling input terminal of comparator U2 is connected to the positive terminal of comparator U2 (i.e., the non-inverting input terminal of comparator U2), and the reference terminal of comparator U2 is connected to the negative terminal of comparator U2 (i.e., the inverting input terminal of comparator U2).

[0031] In some embodiments, the first threshold setting module includes a first adjustable resistor module; the second threshold setting module includes a second adjustable resistor module. The first adjustable resistor module is disposed between a DC power supply and ground; the adjustment terminal of the first adjustable resistor module is connected to the non-inverting input terminal of the first comparison module. The second adjustable resistor module is disposed between a DC power supply and ground; the adjustment terminal of the second adjustable resistor module is connected to the inverting input terminal of the second comparison module.

[0032] See also Figure 2In the example shown, resistors R4 and R5 are adjustable resistors. By adjusting the resistance values ​​of resistors R4 and R5, the comparison voltage thresholds for bus high voltage and bus undervoltage can be adjusted accordingly. The common terminal of resistors R2 and R3 is connected to the inverting input of comparator U1; the non-inverting input of comparator U1 is connected to the resistance adjustment terminal of resistor R4. Resistor R4 is connected between a 3.3V power supply and ground. The power supply terminal of comparator U1 is connected to the 3.3V power supply, and the ground terminal of comparator U1 is grounded. The common terminal of resistors R2 and R3 is also connected to the non-inverting input of comparator U2; the inverting input of comparator U2 is connected to the resistance adjustment terminal of resistor R5. Resistor R5 is connected between a 3.3V power supply and ground. The power supply terminal of comparator U2 is connected to the 3.3V power supply, and the ground terminal of comparator U2 is grounded.

[0033] The switch protection unit is arranged at the output end of the overvoltage comparison unit and the output end of the undervoltage comparison unit, and is located between the output end of the bus and the input end of the inverter circuit. It is used to disconnect the switch protection unit itself when receiving the bus overvoltage parameter or the bus undervoltage parameter, so as to disconnect the power circuit between the bus and the inverter circuit, thereby protecting the bus capacitor unit, the inverter circuit and the motor at the rear end of the bus; and to connect the switch protection unit itself when not receiving the bus overvoltage parameter and the bus undervoltage parameter, so as to connect the power circuit between the bus and the inverter circuit, thereby enabling the motor to be energized and operate normally.

[0034] The solution of the present invention proposes a bus over-voltage and under-voltage dual shutdown protection circuit for a motor's variable frequency drive circuit, which can disconnect the bus and the load when the input voltage is incorrect, thereby protecting the motor's variable frequency drive circuit and the load components (such as the electrical components at the rear end of the bus in the motor's variable frequency drive circuit, etc.); thereby, it can protect the motor's variable frequency drive circuit and load components, ensure the safety of the motor's variable frequency drive circuit, and also improve the safety of the load components (such as the electrical components at the rear end of the bus in the motor's variable frequency drive circuit, etc.).

[0035] In some embodiments, the switch protection unit includes: an AND logic module, a switch module, and a relay module. The first input terminal of the AND logic module serves as the first input terminal of the switch protection unit; the second input terminal of the AND logic module serves as the second input terminal of the switch protection unit; the output terminal of the AND logic module is connected to the control terminal of the switch module; and the second connection terminal of the switch module is grounded. The coil of the relay module is connected between the second DC power supply and the first connection terminal of the switch module; the contacts of the relay module are located between the output terminal of the busbar and the busbar capacitor unit, and are connected between the output terminal of the busbar and the input terminal of the inverter circuit.

[0036] See also Figure 2 In the example shown, the AND logic module is an AND gate U3, the switch module is a transistor Q1, and the relay module is a relay K1. AND gate U3 is a logic component, and relay K1 is a relay on the busbar. The output of comparator U1 is connected to the first input of AND gate U3, the output of comparator U2 is connected to the second input of AND gate U3, and transistor Q1 is located between AND gate U3 and relay K1.

[0037] The busbar capacitor module C2 is composed of six electrolytic capacitors for busbar energy storage and filtering. The number of electrolytic capacitors in busbar capacitor module C2 can be adjusted according to actual needs. Resistors R8 and R9 serve as voltage-equalizing resistors for the six electrolytic capacitors in busbar capacitor module C2. In busbar capacitor module C2, the six electrolytic capacitors are divided into two groups, each with three electrolytic capacitors connected in parallel. One group of electrolytic capacitors is connected in series with the other group, and the common terminal between the two groups serves as the midpoint of busbar capacitor module C2. Terminal P at the output of the rectifier bridge is also connected to the first connection terminal of busbar capacitor module C2 via the contacts of relay K1. The first connection terminal of busbar capacitor module C2 is connected to the first connection terminal of resistor R8. The first connection terminal of resistor R8 is connected to the first input terminal of the six-way inverter bridge. The second connection terminal of resistor R8 is connected to the first connection terminal of resistor R9. The midpoint of busbar capacitor module C2 is connected to the second connection terminal of resistor R8. The second connection end of resistor R8 is also connected to the midpoint of the six-way inverter bridge. The output terminal N of the rectifier bridge is connected to the second connection end of busbar capacitor module C2. The second connection end of busbar capacitor module C2 is connected to the second connection end of resistor R9. The second connection end of resistor R9 is connected to the second input end of the six-way inverter bridge.

[0038] In some embodiments, the switch protection unit further includes a voltage follower module and a filter module. The voltage follower module is disposed between the output terminal of the AND logic module and the control terminal of the switch module; the output terminal of the voltage follower module is connected to the control terminal of the switch module; and the output terminal of the voltage follower module is grounded after passing through the filter module.

[0039] See also Figure 2 In the example shown, the voltage follower module is a comparator U4, and the filter module is a capacitor C1. Comparator U4 functions as a voltage follower. Capacitor C1 is a filter capacitor. The output of AND gate U3 is connected to the non-inverting input of comparator U4. The inverting input of comparator U4 is connected to the output of comparator U4. The output of comparator U4 is connected to ground via capacitor C1.

[0040] In some embodiments, the switch protection unit further includes a current limiting module and a pull-down module. The current limiting module is provided between the output terminal of the voltage follower module and the control terminal of the switch module; the pull-down module is provided between the control terminal of the switch module and ground.

[0041] See also Figure 2 In the example shown, the current limiting module is resistor R6, and the pull-down module is resistor R7. Resistor R6 is a current limiting resistor, and resistor R7 is a pull-down resistor. Transistor Q1 is an NPN transistor element. The control terminal of the switch module is the base of transistor Q1, the first connection terminal of the switch module is the collector of transistor Q1, and the second connection terminal of the switch module is the emitter of transistor Q2. The output of comparator U4 is connected to the base of transistor Q1 through resistor R6. The 12V power supply is connected to the collector of transistor Q1 through the coil of relay K1. The collector of transistor Q1 is also connected to the anode of diode D1, and the cathode of diode D1 is connected to the 12V power supply. The base of transistor Q1 is connected to the emitter of transistor Q1 through resistor R7, and the emitter of transistor Q1 is grounded.

[0042] In some embodiments, the protection device for the variable frequency drive circuit of a motor according to the solutions of the present invention further includes: a control unit; the control unit is arranged between the output terminal of the sampling unit and the control terminal of the drive chip of the inverter circuit; the drive chip of the inverter circuit is arranged between the drive signal control terminal of the control unit and the drive terminal of the inverter circuit. The control unit is configured to determine, based on the bus voltage sampled by the sampling unit, whether the bus voltage is higher than the bus overvoltage protection threshold or lower than the bus undervoltage protection threshold during the operation of the motor after it is powered on, and if it is determined that the bus voltage is higher than the bus overvoltage protection threshold or lower than the bus undervoltage protection threshold, stop outputting the drive control signal to the drive chip of the inverter circuit, thereby shutting down the drive signal of the inverter circuit and stopping the motor. Of course, the control unit is also used to continue to output a drive control signal to the drive chip of the inverter circuit if it is determined that the bus voltage is not higher than the bus overvoltage protection threshold and the bus voltage is not lower than the bus undervoltage protection threshold, so that the inverter circuit continues to operate based on the drive signal provided by the drive chip, and the motor continues to operate.

[0043] See also Figure 2 In the example shown, a control unit, such as an MCU, has the common terminal of resistors R2 and R3 connected to the MCU's sampling signal input. The MCU's drive signal control terminal is connected to a driver chip, and the driver chip's drive signal output terminal is connected to the drive signal input terminal of the six-way inverter bridge. The driver chip can be a model such as NCD57001DWR2G.

[0044] In some embodiments, the protection device for the variable frequency drive circuit of the motor described in the solution of the present invention further includes: at least one of a display unit, an indicator unit, and an alarm unit; when the protection device for the variable frequency drive circuit of the motor further includes a display unit, an indicator unit, and an alarm unit, the display unit, the indicator unit, and the alarm unit are respectively connected to the control unit. The display unit is used to display the bus voltage sampled by the sampling unit; the alarm unit is used to remind when the bus voltage is higher than the bus overvoltage protection threshold or when the bus voltage is lower than the bus undervoltage protection threshold; the indicator unit is used to indicate when the bus voltage is higher than the bus overvoltage protection threshold or when the bus voltage is lower than the bus undervoltage protection threshold.

[0045] like Figure 2As shown, the busbar over-voltage and under-voltage dual shutdown protection circuit of the motor variable frequency drive circuit includes: resistors R1, R2, R3, R4, R5, R6, R7, R8 and R9, comparators U1, U2 and U4, AND gate U3, relay K1, transistor Q1, busbar capacitor module C2, MCU and display module, indicator light module, and driver chip. Figure 2 In the example shown, the MCU and display module include an MCU and a display module, wherein the display module is connected to the MCU. The MCU's alarm signal control terminal is connected to the alarm. The MCU's display signal control terminal is connected to the display module. The MCU's indication signal control terminal is connected to an indicator light. The indicator light is composed of three light-emitting diodes, with the cathode of each light-emitting diode connected to the MCU's indication signal control terminal and the anode of each light-emitting diode connected to ground.

[0046] See also Figure 2 In the example shown, the three-phase power provided by the power grid serves as the power supply, typically a three-phase 380V input power source. After this input power passes through the rectifier bridge, the DC bus voltage across the bridge (i.e., the positive terminal P and the negative terminal N) is approximately 540V. For example, if the bus overvoltage protection threshold is set to 800V and the bus undervoltage protection threshold is set to 250V, the operation of the bus overvoltage and undervoltage dual shutdown protection circuit of the motor's variable frequency drive circuit can be seen in the following exemplary description.

[0047] The first scenario, overvoltage protection, occurs when power is initially applied and the DC bus input voltage exceeds the bus overvoltage protection threshold. The voltage at the sampling input of comparator U1 exceeds the reference voltage at its reference terminal, and comparator U1 outputs a low level. The voltage at the sampling input of comparator U2 exceeds the voltage at its reference terminal, and comparator U2 outputs a high level. The two output signals from comparator U1 and comparator U2 (i.e., the low-level signal at the output of comparator U1 and the high-level signal at the output of comparator U2) are respectively input to the first input and second input of AND gate U3. After the AND logic operation of AND gate U3, a low level is output from the output of AND gate U3. The low-level signal output from the output end of the AND gate U3 is input to the non-inverting input end of the comparator U4, and after the voltage following processing of the follower (that is, the comparator U4 is used as a follower), it is output to the base of the transistor Q1 after passing through the resistor R6, so that the base of the transistor Q1 is at a low level, the transistor Q1 is not conducting, and the contacts of the relay K1 are disconnected. At this time, the bus is not conducting, and the electrical components at the back end of the bus have no voltage. At this time, the MCU displays the corresponding voltage value of the collected bus voltage value, and at the same time prompts the implementation of the corresponding overvoltage protection function through the indicator light. At the same time, the alarm alarm prompts that an overvoltage protection failure has occurred.

[0048] The second situation is the normal working situation: when the power is just turned on, when the input voltage of the DC bus is in the middle value of the high and low voltage (that is, the normal voltage input value between the bus overvoltage protection threshold and the bus undervoltage protection threshold), the voltage value of the sampling input terminal of the comparator U1 is lower than the voltage value of the reference terminal, and the output terminal of the comparator U1 outputs a high level. The voltage value of the sampling input terminal of the comparator U2 is higher than the voltage value of the reference terminal of the comparator U2, and the output terminal of the comparator U2 outputs a high level. The two signals output by the comparator U1 and the comparator U2 (i.e., the high level signal output by the output terminal of the comparator U1 and the low level signal output by the output terminal of the comparator U2) are respectively input to the first input terminal and the second input terminal of the AND gate U3. After the AND logic operation of the AND gate U3, a high level is output from the output terminal of the AND gate U3. After the voltage following processing of the follower (i.e., the comparator U4 is used as a follower), it is output to the base of the transistor Q1 after passing through the resistor R6, so that the base of the transistor Q1 is high level, the transistor Q1 is turned on, and the contacts of the relay K1 are attracted. At this time, the bus is turned on, and the power-consuming components at the back end of the bus obtain voltage. The variable frequency drive circuit of the motor works normally. At this time, the MCU displays the corresponding voltage value of the collected bus voltage value.

[0049] The third case, undervoltage protection, occurs when power is initially applied and the DC bus input voltage is at an undervoltage level (i.e., the voltage input is lower than the bus undervoltage protection threshold). The voltage at the sampling input of comparator U1 is lower than the voltage at the reference terminal, and the output of comparator U1 outputs a high level. The voltage at the sampling input of comparator U2 is lower than the voltage at the reference terminal, and the output of comparator U2 outputs a low level. The two output signals from comparator U1 and comparator U2 (i.e., the low-level signal output from the output of comparator U1 and the low-level signal output from the output of comparator U2) are respectively input to the first input and second input of AND gate U3. After the AND logic operation of AND gate U3, a low level is output from the output of AND gate U3. The low-level signal output from the output end of the AND gate U3 is input to the non-inverting input end of the comparator U4, and after the voltage following processing of the follower (that is, the comparator U4 is used as a follower), it is output to the base of the transistor Q1 after passing through the resistor R6, so that the transistor Q1 is not conducting and the contacts of the relay K1 are disconnected. At this time, the bus is not conducting, and the power-consuming components at the back end of the bus do not receive voltage. At this time, the MCU displays the corresponding voltage value of the collected bus voltage value, and at the same time prompts the implementation of the corresponding undervoltage protection function through the indicator light. At the same time, the alarm alarm prompts that an undervoltage protection fault has occurred.

[0050] The fourth situation is the occurrence of overvoltage or undervoltage faults during normal operation: When the variable frequency drive circuit of the motor suddenly experiences overvoltage and undervoltage during operation, refer to the protection trigger mechanism in the first and third situations. On the basis of the first and third situations, the MCU controls the driver chip at the same time to stop the output of the PWM signal sent by the driver chip to the six-way inverter bridge, so that the driver chip performs shutdown control, so that the IGBT in the six-way inverter bridge is turned off and stops working, so as to avoid damage to the components in the six-way inverter bridge and damage to the motor. Double shutdown protection is performed, and normal operation can be resumed when the voltage returns to normal.

[0051] The present invention proposes a busbar over- and undervoltage dual shutdown protection circuit for a motor's variable frequency drive circuit. The circuit has a dual shutdown function and can disconnect the busbar from the load when the input voltage is incorrect, thereby protecting the motor's variable frequency drive circuit and load components (such as the electrical components at the rear end of the busbar in the motor's variable frequency drive circuit). This circuit can thus protect the motor's variable frequency drive circuit and load components, ensuring the safety of the motor's variable frequency drive circuit and improving the safety of load components (such as the electrical components at the rear end of the busbar in the motor's variable frequency drive circuit). Furthermore, the circuit also has functions such as displaying busbar voltage values, displaying faults, and providing alarms, allowing users to immediately alert the user to the occurrence of a corresponding fault, thereby reducing troubleshooting time and improving troubleshooting efficiency. The circuit can also be used in conjunction with displayed information during troubleshooting, further reducing troubleshooting time and improving troubleshooting efficiency.

[0052] The technical solution of the present invention is adopted, by setting a hardware over-voltage and under-voltage protection circuit and a software over-voltage and under-voltage protection logic in the variable frequency drive circuit of the motor, and detecting whether the input voltage of the bus is over-voltage or under-voltage by the hardware over-voltage and under-voltage protection circuit when the motor is powered on. If the input voltage of the bus is present, the bus and the subsequent load of the bus are disconnected to protect the subsequent load of the bus; if the input voltage of the bus is not over-voltage or under-voltage, the bus and the subsequent load of the bus are connected, and the motor works normally; during the normal working process of the motor, The software's overvoltage protection logic is used to detect whether the bus input voltage is overvoltage or undervoltage. If the bus input voltage is overvoltage or undervoltage, the output of the inverter circuit's driver chip is shut down to stop outputting the drive signal to the inverter circuit, control the motor to stop, and protect the motor. Thus, by setting a hardware overvoltage and undervoltage protection circuit and software overvoltage and undervoltage protection logic in the motor's variable frequency drive circuit, dual overvoltage and undervoltage protection can be implemented for the input voltage of the bus of the motor's variable frequency drive circuit, thereby improving the safety of the operation of load components (such as electrical components at the rear end of the bus in the motor's variable frequency drive circuit).

[0053] According to an embodiment of the present invention, a motor frequency converter corresponding to the protection device of the motor's variable frequency drive circuit is also provided. The motor frequency converter may include: the motor frequency converter protection device described above.

[0054] Since the processing and functions implemented by the frequency converter of the motor in this embodiment basically correspond to the embodiments, principles and examples of the device, for any details not described in this embodiment, please refer to the relevant descriptions in the aforementioned embodiments and will not be repeated here.

[0055] The technical solution of the present invention is adopted, by setting a hardware over-voltage and under-voltage protection circuit and a software over-voltage and under-voltage protection logic in the variable frequency drive circuit of the motor through the variable frequency drive circuit between the rectifier circuit and the inverter circuit on the power supply side of the motor. When the motor is powered on, the hardware over-voltage and under-voltage protection circuit detects whether the input voltage of the bus is overvoltage or undervoltage. If the input voltage of the bus exists, the bus and the subsequent load of the bus are disconnected to protect the subsequent load of the bus; if the input voltage of the bus does not exist, the bus and the subsequent load of the bus are connected, and the motor is normally Work; During the normal operation of the motor, the overvoltage protection logic of the software is used to detect whether the input voltage of the bus is overvoltage or undervoltage. If the input voltage of the bus is overvoltage or undervoltage, the output of the driver chip of the inverter circuit is turned off to stop outputting the drive signal to the inverter circuit, control the motor to stop, and protect the motor. It can protect the motor's variable frequency drive circuit and load components, ensure the safety of the motor's variable frequency drive circuit, and improve the safety of load components (such as the electrical components at the rear end of the bus in the motor's variable frequency drive circuit).

[0056] In summary, it is easy for those skilled in the art to understand that, under the premise of no conflict, the above-mentioned advantageous methods can be freely combined and superimposed.

[0057] The foregoing description is merely an embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of the claims.

Claims

1. A protection device for a variable frequency drive circuit of a motor, characterized in that: On the power supply side of the motor, a rectifier circuit, a bus capacitor unit, and an inverter circuit are provided; the rectifier circuit, the bus capacitor unit, and the inverter circuit are sequentially provided between the power grid and the motor; a protection device for the variable frequency drive circuit of the motor is provided between the rectifier circuit and the inverter circuit, and between the rectifier circuit and the bus capacitor unit; The protection device of the variable frequency drive circuit of the motor includes: a sampling unit, an overvoltage comparison unit, an undervoltage comparison unit and a switch protection unit; wherein, The sampling unit is provided at the output end of the rectifier circuit and is connected to the input end of the overvoltage comparison unit and the input end of the undervoltage comparison unit, respectively, for sampling the input voltage of the bus at the output end of the rectifier circuit, recorded as the bus voltage; and inputting the bus voltage into the overvoltage comparison unit and the undervoltage comparison unit, respectively; The overvoltage comparison unit is provided between the output end of the sampling unit and the switch protection unit, and is used to compare the bus voltage with a preset bus overvoltage protection threshold value, and output a parameter indicating that the bus voltage is higher than the bus overvoltage protection threshold value when the bus voltage is higher than the bus overvoltage protection threshold value, which is recorded as a bus overvoltage parameter; The undervoltage comparison unit is provided between the output end of the sampling unit and the switch protection unit, and is used to compare the bus voltage with a preset bus undervoltage protection threshold value, and output a parameter indicating that the bus voltage is lower than the bus undervoltage protection threshold value when the bus voltage is lower than the bus undervoltage protection threshold value, which is recorded as a bus undervoltage parameter; The switch protection unit is arranged at the output end of the overvoltage comparison unit and the output end of the undervoltage comparison unit, and is located between the output end of the bus and the input end of the inverter circuit. It is used to disconnect the switch protection unit itself when receiving the bus overvoltage parameter or the bus undervoltage parameter, so as to disconnect the power circuit between the bus and the inverter circuit, thereby protecting the bus capacitor unit, the inverter circuit and the motor at the rear end of the bus; and to connect the switch protection unit itself when not receiving the bus overvoltage parameter and the bus undervoltage parameter, so as to connect the power circuit between the bus and the inverter circuit, thereby enabling the motor to be energized and operate normally.

2. The protection device for the variable frequency drive circuit of the motor according to claim 1, characterized in that: The sampling unit includes: a first voltage-dividing resistor module and a second voltage-dividing resistor module; Among them, the first voltage-dividing resistor module and the second voltage-dividing resistor module are arranged in series between the positive and negative electrodes of the output end of the rectifier circuit; the common end of the first voltage-dividing resistor module and the second voltage-dividing resistor module serves as the output end of the sampling unit; the output end of the sampling unit is respectively connected to the input end of the overvoltage comparison unit and the input end of the undervoltage comparison unit.

3. The protection device for the variable frequency drive circuit of the motor according to claim 1, characterized in that: The overvoltage comparison unit includes: a first comparison module and a first threshold setting module; the undervoltage comparison unit includes: a second comparison module and a second threshold setting module; wherein, The output end of the sampling unit is connected to the inverting input end of the first comparison module; the first threshold setting module is connected to the non-inverting input end of the first comparison module; the output end of the first comparison module is connected to the first input end of the switch protection unit; The output end of the sampling unit is also connected to the non-inverting input end of the second comparison module; the second threshold setting module is connected to the inverting input end of the second comparison module; the output end of the second comparison module is connected to the second input end of the switch protection unit.

4. The protection device for the variable frequency drive circuit of the motor according to claim 3, characterized in that: The first threshold setting module includes: a first adjustable resistance module; the second threshold setting module includes: a second adjustable resistance module; wherein, The first adjustable resistance module is provided between the DC power supply and the ground; the adjustment terminal of the first adjustable resistance module is connected to the non-inverting input terminal of the first comparison module; The second adjustable resistance module is arranged between the DC power supply and the ground; the adjustment end of the second adjustable resistance module is connected to the inverting input end of the second comparison module.

5. The protection device for the variable frequency drive circuit of the motor according to claim 1, characterized in that: The switch protection unit includes: a logic module, a switch tube module and a relay module; wherein, The first input end of the AND logic module serves as the first input end of the switch protection unit; the second input end of the AND logic module serves as the second input end of the switch protection unit; the output end of the AND logic module is connected to the control end of the switch tube module; The coil of the relay module is connected between the second DC power supply and the first connection end of the switch tube module; the contact of the relay module is located between the output end of the bus and the bus capacitor unit, and connected between the output end of the bus and the input end of the inverter circuit; the second connection end of the switch tube module is grounded.

6. The protection device for the variable frequency drive circuit of the motor according to claim 5, characterized in that: The switch protection unit further includes: a voltage follower module and a filter module; wherein, The voltage follower module is arranged between the output end of the AND logic module and the control end of the switch tube module; the output end of the voltage follower module is connected to the control end of the switch tube module; the output end of the voltage follower module is also grounded after passing through the filter module.

7. The protection device for the variable frequency drive circuit of the motor according to claim 6, characterized in that: The switch protection unit further includes: a current limiting module and a pull-down module; wherein, The current limiting module is provided between the output end of the voltage follower module and the control end of the switch tube module; the pull-down module is provided between the control end of the switch tube module and the ground.

8. The protection device for the variable frequency drive circuit of a motor according to any one of claims 1 to 7, characterized in that: Also includes: control unit; The control unit is arranged between the output terminal of the sampling unit and the control terminal of the driving chip of the inverter circuit; the driving chip of the inverter circuit is arranged between the driving signal control terminal of the control unit and the driving terminal of the inverter circuit; wherein, The control unit is used to determine, during the operation of the motor after it is powered on, whether the bus voltage is higher than the bus overvoltage protection threshold or the bus voltage is lower than the bus undervoltage protection threshold based on the bus voltage sampled by the sampling unit; if it is determined that the bus voltage is higher than the bus overvoltage protection threshold or the bus voltage is lower than the bus undervoltage protection threshold, stop outputting the drive control signal to the drive chip of the inverter circuit to turn off the drive signal of the inverter circuit and stop the motor.

9. The protection device for the variable frequency drive circuit of a motor according to claim 8, characterized in that: Also includes: At least one of a display unit, an indicator unit, and an alarm unit; in the case where the protection device for the variable frequency drive circuit of the motor further includes a display unit, an indicator unit, and an alarm unit, the display unit, the indicator unit, and the alarm unit are connected to the control unit respectively; wherein, The display unit is used to display the bus voltage sampled by the sampling unit; The alarm unit is used to remind when the bus voltage is higher than the bus overvoltage protection threshold or the bus voltage is lower than the bus undervoltage protection threshold; The indicating unit is used to indicate a situation where the bus voltage is higher than the bus overvoltage protection threshold or a situation where the bus voltage is lower than the bus undervoltage protection threshold.

10. A frequency converter for a motor, characterized in that: include: A protection device for a variable frequency drive circuit of a motor according to any one of claims 1 to 9.

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