Active filter based long cable motor overvoltage suppression circuit and control method

Abstract

The application provides a long cable motor overvoltage suppression circuit based on an active filter and a control method, the circuit comprising a power circuit and a driving signal circuit; the power circuit comprising a bus capacitor, a voltage clamping switch, a freewheeling diode and an energy storage inductor; the driving signal circuit comprising a voltage dividing resistor, a comparator, a trigger circuit and a driving circuit; the power circuit being connected in series between an inverter output side and a long cable, at the same time, an inverter output voltage being connected with an input end of the driving signal circuit, an output end of the driving signal circuit being connected with a power circuit of an active dv / dt filter, and the working mode of the power circuit being controlled. The application forces the output voltage to be clamped to zero level through the active dv / dt filter, so that the reflected voltage of the first stage of the ladder wave and the reflected voltage of the second stage of the ladder wave are offset to each other, and the reflected voltage at the motor end is suppressed.

Description

Technical Field

[0001] This invention relates to the field of motor control technology, specifically to an overvoltage suppression circuit and control method for long cable motors based on active filters. Background Technology

[0002] In applications where the inverter and motor are far apart, they need to be connected by a long cable, such as... Figure 1 As shown. Typically, the inverter output voltage waveform has a high dv / dt characteristic, such as... Figure 2 As shown. Due to the impedance mismatch between the cable and the motor, and the high dv / dt characteristic of the output voltage, a transmission line effect occurs in the cable, leading to reflected voltage at the motor terminals and causing overvoltage in the motor windings, such as... Figure 3 As shown. The voltage at the motor terminals is U. mot =(1+Γ L )U in Where Umot is the motor terminal voltage, Uin is the inverter output voltage, and Γ L The reflection coefficient;

[0003]

[0004] Z L Zc is the motor impedance, Zc is the cable impedance, and typically, Zc is the motor impedance. L >>Zc, therefore Γ L ≈1.

[0005] The traditional method for suppressing motor overvoltage is to use a passive dv / dt filter, the scheme of which is as follows: Figure 4 As shown. Its principle is to use LCR devices to slow down the rising and falling edges of the inverter output voltage, thereby reducing overvoltage at the motor terminals. However, passive dv / dt filters are large in size and have high losses. Especially the resistive losses, which are directly proportional to the inverter's switching frequency; the faster the inverter's switching frequency, the higher the losses. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide an overvoltage suppression circuit and control method for long cable motors based on active filters, so as to solve the problem of motor load overvoltage in the overvoltage suppression circuit for long cable motors based on active filters mentioned in the background art.

[0007] To solve the above technical problems, embodiments of the present application provide the following technical solutions: an active dv / dt filter circuit for inhibiting overvoltage of a long cable motor, the circuit comprising a power circuit and a driving signal circuit; the power circuit comprising a bus capacitor, a voltage clamping switch, a freewheeling diode and an energy storage inductor; the driving signal circuit comprising a voltage dividing resistor, a comparator, a trigger circuit and a driving circuit; the power circuit being connected in series between an inverter output side and the long cable, while the inverter output voltage is connected to an input end of the driving signal circuit, an output end of the driving signal circuit is connected to the power circuit of the active dv / dt filter, and the working mode of the power circuit is controlled.

[0008] The power circuit of the active dv / dt filter comprises a first bus capacitor C1, a second bus capacitor C2, a first voltage clamping switch T1, a second voltage clamping switch T2, a first freewheeling diode D1, a second freewheeling diode D2 and an energy storage inductor L1, wherein:

[0009] The first bus capacitor C1 and the second bus capacitor C2 are connected in series to provide voltage for the active dv / dt filter and to provide zero voltage level for the active dv / dt filter;

[0010] The first voltage clamping switch T1 and the second voltage clamping switch T2 are connected in reverse series to clamp voltage to zero voltage level when each rising edge and falling edge of the inverter output voltage arrives, so as to realize the form of two-stage step wave of the output voltage;

[0011] The first freewheeling diode D1 and the second freewheeling diode D2 are connected in same direction to provide freewheeling for the energy storage inductor L1 when the voltage clamping switch is not working;

[0012] The energy storage inductor L1 is composed of a power inductor, and when the first voltage clamping switch T1 and the second voltage clamping switch T2 are working, a part of energy is stored to reduce the current stress of the voltage clamping switch.

[0013] Further, the driving signal circuit comprises a voltage dividing resistor, a comparator, a trigger circuit and a driving circuit, the voltage dividing resistor comprising a first voltage dividing resistor R11 and a second voltage dividing resistor R12, wherein one end of the first voltage dividing resistor R11 is connected to the inverter output side, the other end of the first voltage dividing resistor R11 is connected to one end of the second voltage dividing resistor R12 and the non-inverting input end of the comparator, the inverting input end of the comparator is connected to the positive electrode of a direct current power supply, the other end of the second voltage dividing resistor R12 is connected to the negative electrode of the direct current power supply and grounded, the output end of the comparator is connected to the input of the trigger circuit, the output of the trigger circuit is connected to the input end of the driving circuit, and the output end of the driving circuit is connected to the gate of the first voltage clamping switch T1 and the second voltage clamping switch T2.

[0014] Further, an input end of the energy storage inductor L1 is connected with an output end of the inverter, and an output end of the energy storage inductor L1 is connected with the long cable; two ends of the first bus capacitor C1 and the second bus capacitor C2 connected in series are respectively connected with the inverter bus voltage output end.

[0015] Further, each phase output end of the inverter is connected with the power circuit and the driving signal circuit.

[0016] Further, the first voltage clamping switch T1 and the second voltage clamping switch T2 are switch tubes, wherein a drain of the first voltage clamping switch T1 is connected with a connection end of the first bus capacitor C1 and the second bus capacitor C2, a source of the first voltage clamping switch T1 is connected with a source of the second voltage clamping switch T2, a drain of the second voltage clamping switch T2 is connected with a series connection end of the first freewheeling diode D1 and the second freewheeling diode D2, the series connection end of the first freewheeling diode D1 and the second freewheeling diode D2 is further connected with an output end of the energy storage inductor L1, and two ends of the first freewheeling diode D1 and the second freewheeling diode D2 connected in series are respectively connected with the inverter bus voltage output end.

[0017] The application further provides a control method of the active dv / dt filter circuit, comprising the following steps:

[0018] The first bus capacitor C1 and the second bus capacitor C2 are connected in series, providing voltage for the active dv / dt filter and providing zero level for the active dv / dt filter; the first voltage clamping switch T1 and the second voltage clamping switch T2 are connected in reverse series, clamping voltage to zero level when each rising edge and falling edge of the inverter output voltage arrives, so that the output voltage forms two-stage staircase wave form, and the reflected voltage of the first-stage staircase wave and the reflected voltage of the second-stage staircase wave offset each other; the first freewheeling diode D1 and the second freewheeling diode D2 are connected in same direction, providing freewheeling current for the energy storage inductor L1 when the voltage clamping switch does not work; the energy storage inductor L1 stores part of energy when the first voltage clamping switch T1 and the second voltage clamping switch T2 work, reducing current stress of the voltage clamping switch.

[0019] Further, the flip-flop controls the conduction time of the voltage clamping switch, and the conduction time td of the voltage clamping switch is twice the cable transmission time t t , wherein:

[0020]

[0021] l ca is the cable length, v ca is the transmission speed of the cable.

[0022] The application has the following beneficial effects.

[0023] The present application forces the output voltage to be clamped to zero level when each rising edge and falling edge of the inverter output voltage comes by active dv / dt filter, so that the output voltage forms two-stage staircase wave form. The reflected voltage of the first stage staircase wave and the reflected voltage of the second stage staircase wave are counteracted to each other, so that the reflected voltage at the motor end is suppressed. In the specific control, the microprocessor controls the on time of the voltage clamping switch, and the on time td of the voltage clamping switch is twice of the cable transmission time t t wherein:

[0024]

[0025] wherein, l ca is the cable length, v ca is the transmission speed of the cable. When t d = 2t t , the reflected voltage at the motor end can be counteracted to each other, so that the overvoltage at the motor end is suppressed. BRIEF DESCRIPTION OF DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description only show some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained based on these drawings without any creative effort.

[0027] Figure 1 It is a circuit schematic diagram of the traditional inverter and the motor connected through long cable;

[0028] Figure 2 It is a waveform diagram of the traditional inverter output voltage;

[0029] Figure 3 It is a waveform diagram of the inverter output voltage waveform after the transmission line effect occurs in the long cable;

[0030] Figure 4 It is a circuit schematic diagram of the passive dv / dt filter used in the traditional method for suppressing the overvoltage of the motor;

[0031] Figure 5 It is a circuit schematic diagram of the active dv / dt filter used in the present application for suppressing the overvoltage of the motor;

[0032] Figure 6 It is a circuit schematic diagram of the active dv / dt filter used in the present application;

[0033] Figure 7 It is a circuit schematic diagram of the signal driving circuit used in the present application;

[0034] Figure 8 This is a waveform of the output voltage after filtering by an active dv / dt filter according to the present invention.

[0035] Figure 9 This is a waveform diagram of the motor end after the signal is filtered by an active dv / dt filter and passes through a long cable. Detailed Implementation

[0036] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] In applications where the inverter and motor are far apart, they need to be connected by a long cable, such as... Figure 1 As shown. Typically, the inverter output voltage waveform has a high dv / dt characteristic, such as... Figure 2 As shown. Due to the impedance mismatch between the cable and the motor, and the high dv / dt characteristic of the output voltage, a transmission line effect occurs in the cable, leading to reflected voltage at the motor terminals and causing overvoltage in the motor windings, such as... Figure 3 As shown.

[0038] The voltage at the motor terminal is

[0039] U mot =(1+Γ L )U in

[0040] Where Umot is the motor terminal voltage, Uin is the inverter output voltage, and Γ L The reflection coefficient;

[0041]

[0042] Z L Zc is the motor impedance, Zc is the cable impedance, and typically, Zc is the motor impedance. L >>Zc, therefore Γ L ≈1

[0043] The traditional method for suppressing motor overvoltage is to use a passive dv / dt filter. The solution is as follows: Figure 4 As shown. Its principle is to use an LCR device to slow down the rising and falling edges of the inverter output voltage, thereby reducing the overvoltage at the motor end.

[0044] However, the passive dv / dt filter has large volume and high loss. Especially the resistance loss, which is proportional to the switching frequency of the inverter. The faster the switching frequency, the higher the loss.

[0045] As shown in Figure 5 The application provides an active dv / dt filter circuit for suppressing overvoltage of a long cable motor. The circuit comprises a power circuit and a driving signal circuit. The power circuit comprises a bus capacitor, a voltage clamping switch, a freewheeling diode and an energy storage inductor. The driving signal circuit comprises a voltage dividing resistor, a comparator, a trigger circuit and a driving circuit. The power circuit is connected in series between an inverter output side and a long cable. Meanwhile, the inverter output voltage is connected to the input end of the driving signal circuit, the output end of the driving signal circuit is connected to the power circuit of the active dv / dt filter, and the working mode of the power circuit is controlled.

[0046] The power circuit of the active dv / dt filter comprises a first bus capacitor C1, a second bus capacitor C2, a first voltage clamping switch T1, a second voltage clamping switch T2, a first freewheeling diode D1, a second freewheeling diode D2 and an energy storage inductor L1, wherein:

[0047] The first bus capacitor C1 and the second bus capacitor C2 are connected in series to provide voltage for the active dv / dt filter and provide zero voltage level for the active dv / dt filter.

[0048] The first voltage clamping switch T1 and the second voltage clamping switch T2 are connected in reverse series to clamp the voltage to zero voltage level when each rising edge and falling edge of the inverter output voltage arrives, so as to realize the form of two-stage step wave of the output voltage.

[0049] The first freewheeling diode D1 and the second freewheeling diode D2 are connected in the same direction to provide freewheeling for the energy storage inductor L1 when the voltage clamping switch is not working.

[0050] The energy storage inductor L1 is composed of a power inductor, which stores part of energy when the first voltage clamping switch T1 and the second voltage clamping switch T2 are working, so as to reduce the current stress of the voltage clamping switch.

[0051] In the embodiment, the drive signal circuit comprises a voltage dividing resistor, a comparator, a trigger circuit and a drive circuit, the voltage dividing resistor comprises a first voltage dividing resistor R11 and a second voltage dividing resistor R12, one end of the first voltage dividing resistor R11 is connected with the output side of the inverter, the other end of the first voltage dividing resistor R11 is connected with one end of the second voltage dividing resistor R12 and the non-inverting input terminal of the comparator, the inverting input terminal of the comparator is connected with the positive pole of a direct current power supply, the other end of the second voltage dividing resistor R12 is grounded, the output terminal of the comparator is connected with the input of the trigger circuit, the output of the trigger circuit is connected with the input terminal of the drive circuit, and the output terminal of the drive circuit is connected with the gate of the first voltage clamping switch T1 and the second voltage clamping switch T2.

[0052] In the embodiment, the input end of the energy storage inductor L1 is connected with the output end of the inverter, and the output end of the energy storage inductor L1 is connected with the long cable; the two ends of the series connection of the first bus capacitor C1 and the second bus capacitor C2 are respectively connected with the output end of the inverter bus voltage.

[0053] In the embodiment, the output end of each phase of the inverter is connected with the power circuit and the drive signal circuit.

[0054] In the embodiment, the first voltage clamping switch T1 and the second voltage clamping switch T2 are switch tubes, which can be traditional silicon-based MOS, Si C MOS or GaN devices; the drain of the first voltage clamping switch T1 is connected with the connection end of the first bus capacitor C1 and the second bus capacitor C2, the source of the first voltage clamping switch T1 is connected with the source of the second voltage clamping switch T2, the drain of the second voltage clamping switch T2 is connected with the series connection end of the first freewheeling diode D1 and the second freewheeling diode D2, the series connection end of the first freewheeling diode D1 and the second freewheeling diode D2 is further connected with the output end of the energy storage inductor L1, and the two ends of the series connection of the first freewheeling diode D1 and the second freewheeling diode D2 are respectively connected with the output end of the inverter bus voltage.

[0055] The application further provides a control method of the active dv / dt filter circuit, which comprises the following steps:

[0056] The first bus capacitor C1 and the second bus capacitor C2 are connected in series to provide voltage for the active dv / dt filter and provide zero level for the active dv / dt filter; the first voltage clamping switch T1 and the second voltage clamping switch T2 are connected in reverse series to clamp the voltage to zero level when each rising edge and falling edge of the inverter output voltage arrives, so that the output voltage forms a two-stage staircase wave form, and the reflected voltage of the first-stage staircase wave and the reflected voltage of the second-stage staircase wave are offset each other; the first freewheeling diode D1 and the second freewheeling diode D2 are connected in same direction to freewheel for the energy storage inductor L1 when the voltage clamping switch is not working; the energy storage inductor L1 stores part of energy when the first voltage clamping switch T1 and the second voltage clamping switch T2 are working, so as to reduce the current stress of the voltage clamping switch.

[0057] In the embodiment, the flip-flop controls the conduction time of the voltage clamping switch, and the conduction time td of the voltage clamping switch is twice the cable transmission time t t , wherein:

[0058]

[0059] l ca is the cable length, and v ca is the transmission speed of the cable.

[0060] The above design forces the output voltage to clamp to zero level through the active dv / dt filter when each rising edge and falling edge of the inverter output voltage arrives, so that the output voltage forms a two-stage staircase wave form. The reflected voltage of the first-stage staircase wave and the reflected voltage of the second-stage staircase wave are offset each other, so as to suppress the reflected voltage at the motor end.

[0061] The active dv / dt filter is installed between the inverter output side and the long cable, as shown in Figure 5 . Taking the U phase as an example, the circuit of the active dv / dt filter includes bus capacitors (C1, C2), voltage clamping switches (T1, T2), freewheeling diodes (D1, D2) and energy storage inductors (L1), as shown in Figure 6 . The bus capacitors are composed of two capacitors connected in series to provide voltage for the active dv / dt filter and provide zero level for the active dv / dt filter; the voltage clamping switches are composed of two power devices connected in reverse series, and the function is to clamp the voltage to zero level when each rising edge and falling edge of the inverter output voltage arrives, so as to realize the two-stage staircase wave form of the output voltage; the freewheeling diodes are composed of two diodes connected in series, and the function is to freewheel for the energy storage inductor when the voltage clamping switch is not working; the energy storage inductor is composed of a power inductor, and the function is to store part of energy when the voltage clamping switch is working, so as to reduce the current stress of the voltage clamping switch;

[0062] Connection mode: the Ui n of the energy storage inductor is connected with the output end of the inverter, the Uout of the energy storage inductor is connected with the long cable; the bus capacitor is connected with the bus voltage of the inverter.

[0063] As shown in Figure 7 The schematic diagram of the signal driving circuit used in the application comprises an operational amplifier, a flip-flop circuit and a driving circuit connected in sequence. The voltage dividing resistors R11 and R12 are used to divide the high voltage of the inverter, so as to obtain a smaller voltage. The divided voltage is compared with the direct current power supply, so as to eliminate the influence of the oscillation of the rising edge and the falling edge of the output voltage of the inverter on the subsequent output. The output voltage of the comparator passes through the flip-flop circuit to generate the required control signal, and then the driving circuit drives the voltage clamping switch in the power circuit.

[0064] Then, after passing through the active dv / dt filter, the output voltage waveform is as shown in Figure 8 Each rising edge and falling edge becomes a two-stage staircase wave form.

[0065] Among them, the time td of the voltage clamping switch conduction should be twice the cable transmission time tt;

[0066]

[0067] Among them, l ca is the cable length, v ca is the transmission speed of the cable;

[0068] When t d = 2t t , the reflected voltages at the motor end can be offset to each other, so as to suppress the overvoltage at the motor end, and the waveform is as shown in Figure 9 .

[0069] The above is the preferred embodiment of the application, it should be pointed out that, for the ordinary skilled in the art, without departing from the principles of the application described, can also make a number of improvements and refinements, these improvements and refinements should also be considered as the protection scope of the application.

Claims

1. An overvoltage suppression circuit for long cable motors based on an active filter, characterized in that, It includes a power circuit and a drive signal circuit. The power circuit is connected in series between the inverter output side and the long cable. At the same time, the inverter output is connected to the input of the drive signal circuit, and the output of the drive signal circuit is connected to the power circuit to control the working mode of the power circuit. The power circuit includes a first bus capacitor C1, a second bus capacitor C2, a first voltage clamping switch T1, a second voltage clamping switch T2, a first freewheeling diode D1, a second freewheeling diode D2, and an energy storage inductor L1. The first voltage clamping switch T1 and the second voltage clamping switch T2 are switching transistors. The drain of the first voltage clamping switch T1 is connected to the connection terminals of the first bus capacitor C1 and the second bus capacitor C2. The source of the first voltage clamping switch T1 is connected to the source of the second voltage clamping switch T2. The drain of the second voltage clamping switch T2 is connected to... The series connection of the first freewheeling diode D1 and the second freewheeling diode D2 is also connected to the output terminal of the energy storage inductor L1. The two ends of the series connection of the first freewheeling diode D1 and the second freewheeling diode D2 are respectively connected to the inverter bus voltage output terminal. The input terminal of the energy storage inductor L1 is connected to the output terminal of the inverter, and the output terminal of the energy storage inductor L1 is connected to a long cable. The two ends of the series connection of the first bus capacitor C1 and the second bus capacitor C2 are respectively connected to the inverter bus voltage output terminal. The drive signal circuit includes voltage divider resistors, a comparator, a trigger circuit, and a drive circuit. The voltage divider resistors include a first voltage divider resistor R11 and a second voltage divider resistor R12. One end of the first voltage divider resistor R11 is connected to the output side of the inverter. The other end of the first voltage divider resistor R11 is connected to one end of the second voltage divider resistor R12 and the non-inverting input of the comparator. The inverting input of the comparator is connected to the positive terminal of the DC power supply. The other end of the second voltage divider resistor R12 is grounded to the negative terminal of the DC power supply. The output of the comparator is connected to the input of the trigger circuit. The output of the trigger circuit is connected to the input of the drive circuit. The output of the drive circuit is connected to the gates of the first voltage clamp switch T1 and the second voltage clamp switch T2.

2. The overvoltage suppression circuit for long cable motors based on an active filter according to claim 1, characterized in that, Each phase output terminal of the inverter is connected to the power circuit and the drive signal circuit.

3. A control method for an overvoltage suppression circuit of a long cable motor based on an active filter as described in claim 1, characterized in that, include: The first bus capacitor C1 and the second bus capacitor C2 are connected in series to provide voltage for the active dv / dt filter and at the same time provide zero level for the active dv / dt filter; The first voltage clamping switch T1 and the second voltage clamping switch T2 are connected in reverse series. When each rising and falling edge of the inverter output voltage arrives, the voltage is clamped to zero level, so that the output voltage forms a two-stage stepped wave. The reflected voltage of the first-stage stepped wave cancels out the reflected voltage of the second-stage stepped wave. The first freewheeling diode D1 and the second freewheeling diode D2 are connected in the same direction. When the voltage clamping switches are not working, they provide freewheeling for the energy storage inductor L1. When the first voltage clamping switch T1 and the second voltage clamping switch T2 are activated, the energy storage inductor L1 stores a portion of energy, reducing the current stress on the voltage clamping switches.

4. The control method for overvoltage suppression circuit of long cable motor based on active filter according to claim 3, characterized in that, The trigger circuit controls the conduction time of the voltage clamping switch, and the conduction time td of the voltage clamping switch is twice the cable transmission time. ,in: ； l ca For cable length, v ca This refers to the transmission speed of the cable.

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