Power-on self-starting reverse-filling self-discharging system for frequency converter

Abstract

The invention discloses a power-on self-starting reverse-flowing self-discharging system for a frequency converter, and the system is characterized in that a flyback power module outputs + 15V control voltage to a DC / AC controller and a sequential logic control circuit after three-phase alternating current is powered on; after the DC / AC controller is powered on by the flyback power supply module, a switching tube in the DC / AC power module is controlled to be in a closed state; the sequential logic control circuit is electrified by the flyback power supply module and then controls a thyristor in the pre-charging / discharging circuit to be conducted; the AC / DC rectifier module converts three-phase alternating current into direct current, is connected with the pre-charging / discharging circuit and charges an energy storage capacitor in the pre-charging / discharging circuit; the DC / AC power module inputs backward flowing current to an energy storage capacitor in the pre-charging / discharging circuit; on one hand, the pre-charging / discharging circuit rectifies direct current input by the AC / DC rectifier module and then pre-charges an energy storage capacitor in the circuit, and on the other hand, the pre-charging / discharging circuit receives backward flowing current input by the DC / AC power module. According to the invention, the generation of surge current can be inhibited, and the power-on time sequence of first power-on control power and then power-on power power can be realized at the same time.

Description

Technical Field

[0001] The invention relates to a power-on self-starting back-injection self-discharge system for a frequency converter, belonging to the technical field of frequency converters. Background Art

[0002] The frequency converter is a power control device that uses frequency conversion technology and microelectronics technology to control AC motors by changing the frequency of the motor's working power supply. It is mainly composed of rectification (AC to DC), filtering, inversion (DC to AC), braking unit, drive unit, detection unit and processor unit. At present, most rectifiers use diode converters, which convert industrial frequency power into DC power. In order to suppress the surge current generated by the charging of energy storage capacitors when power is turned on, a pre-charging circuit is usually added to the rectifier circuit. After the AC power is turned on, the current charges the energy storage capacitor through the current limiting resistor. After the capacitor is fully charged, the control circuit controls the switch connected in parallel with the current limiting resistor to turn on.

[0003] In the prior art, patent CN112467969B of Zhuhai Gree Electric Appliances Co., Ltd. discloses a starting control device, method and magnetic levitation system for a frequency converter. The device samples the voltage at the bus capacitor on the output side of the rectifier module. When the voltage reaches the set voltage value, the control module outputs a control signal to control the closing circuit in the electric operating mechanism to close.

[0004] Although this patent achieves the goal of inverter power-on self-start, this method has the following main problems:

[0005] 1. Connecting the current limiting resistor in series on the AC side of the three-phase input terminal undoubtedly increases the number of resistors and switches connected in parallel with them, and also increases the complexity of wiring.

[0006] 2. The bus voltage sampling and control signal output are completed through the DSP processor. Since the DSP requires many peripheral circuits, the circuit complexity will inevitably increase. In addition, since the digital circuit and the analog circuit share the same ground, there may be a risk of generating erroneous control signals due to ground interference.

[0007] 3. In the process of charging the energy storage capacitor through the three-phase current through the pre-charging resistor, the voltage across the switching tube of the inverter module also increases with the voltage on the energy storage capacitor. Since the power and control power are powered on at the same time, the controller chip of the inverter module may be out of control when the switch is reset, resulting in an output short circuit, which in turn causes the pre-charging resistor to burn out due to overpower.

[0008] 4. Since the voltage of three-phase electricity fluctuates, using the voltage value on the detection capacitor to close the switch on the pre-charging resistor may cause a risk of a large surge current due to premature switch closure. There may also be a risk of the switch not being closed due to the voltage setting value being too high, and then the current flowing through the pre-charging resistor is too large when the inverter is working, causing the resistor to burn out. Summary of the invention

[0009] The technical problem solved by the present invention is: to overcome the shortcomings of the prior art and provide a power-on self-starting and backfeeding self-discharging system for a frequency converter, which controls the conduction sequence of thyristors during the power-on process through a timing logic control circuit, thereby suppressing the generation of surge current and realizing a power-on sequence of first turning on the control power and then turning on the power power.

[0010] The technical solution of the present invention is: a power-on self-starting, reverse charging and self-discharging system for a frequency converter, comprising: an AC / DC rectifier module, a pre-charging / discharging circuit, a DC / AC power module, a flyback power supply module, a DC / AC controller and a sequential logic control circuit; wherein:

[0011] After the three-phase AC power is powered on, the flyback power module outputs a +15V control voltage to the DC / AC controller and the timing logic control circuit;

[0012] After the DC / AC controller is powered on by the flyback power module, it outputs a low-level driving signal to the DC / AC power module. After the DC bus of the DC / AC power module reaches a stable voltage, the DC / AC controller outputs a PWM pulse to the DC / AC power module.

[0013] After the flyback power module is powered on, the sequential logic control circuit controls the operation of the pre-charge / discharge circuit;

[0014] The AC / DC rectifier module converts the three-phase AC power into DC power, connects the pre-charging / discharging circuit and charges the energy storage capacitor therein;

[0015] On the one hand, the DC / AC power module receives the PWM pulses output by the DC / AC controller to control the voltage magnitude and polarity of the U-phase, V-phase, and W-phase of the external three-phase motor; on the other hand, it receives the reverse current generated by the three-phase motor to charge the energy storage capacitor in the pre-charging / discharging circuit;

[0016] On the one hand, the pre-charge / discharge circuit rectifies the DC power input by the AC / DC rectifier module to pre-charge the energy storage capacitor in the circuit. On the other hand, it accepts the feedback current input by the DC / AC power module to provide a discharge path for the feedback energy to avoid breakdown of the switch tube in the DC / AC power module due to excessive feedback energy.

[0017] Preferably, the DC / AC controller is composed of a DC / DC isolation module and a control drive module. The DC / DC isolation module realizes the ground isolation function, and the control drive module controls the duty cycle of the switch tube in the DC / AC power module.

[0018] Preferably, the sequential logic control circuit comprises: a first delay / switch module, a second delay module and a third delay module; wherein:

[0019] The first delay / switch module includes: a resistor R2, a capacitor C3, a resistor R4, a transistor T2, a resistor R5, and a transistor T1; specifically:

[0020] The input +15V control voltage is connected to one end of the resistor R2, the other end of the resistor R2 is connected to one end of the capacitor C3, the other end of the capacitor C3 is grounded, and the resistor R3 is connected in parallel with the capacitor C3; one end of the capacitor C3 is connected to the cathode of the voltage zener diode ZD1, the anode of the voltage zener diode ZD1 is connected to the base of the NPN transistor T1, the emitter of the transistor T1 is grounded, the collector of the transistor T1 is connected to one end of the resistor R5, the other end of the resistor R5 is connected to the base of the PNP transistor T2, the emitter of the transistor T2 is connected to one end of the resistor R4, the other end of the resistor R4 is connected to the +15V control voltage, and the collector of the transistor T2 is connected to the second delay module;

[0021] The second delay module includes: a resistor R6 and a capacitor C4; specifically:

[0022] One end of the resistor R6 is connected to the collector of the transistor T2 in the first delay / switch module, and the other end is connected to one end of the capacitor C4, and outputs the first thyristor input voltage VCC1 to the pre-charge / discharge circuit, the other end of the capacitor C4 is connected to the ground, and one end of the capacitor C4 is connected to the third delay module;

[0023] The third delay module includes: a resistor R7, a diode ZD2, and a capacitor C5; specifically:

[0024] One end of the resistor R7 is connected to the capacitor C4 of the second delay module, and the other end is connected to the cathode of the voltage-stabilizing diode ZD2. The anode of the voltage-stabilizing diode ZD2 is connected to one end of the capacitor C5. When the voltage across the voltage-stabilizing diode ZD2 reaches the breakdown voltage, the second thyristor input voltage VCC2 is output to the pre-charging / discharging circuit, and the other end of the fifth capacitor C5 is grounded.

[0025] Preferably, the pre-charging / discharging circuit includes: a thyristor Q1, a thyristor Q2, a diode D1, a diode D2, a diode D3, a capacitor C1 and an energy storage capacitor C2, wherein:

[0026] The first thyristor input voltage VCC1 is connected to the anode of the diode D1, the cathode of the diode D1 is connected to the gate of the thyristor Q1, the second thyristor input voltage VCC2 is connected to the anode of the diode D2, the cathode of the diode D2 is connected to the gate of the thyristor Q2; the cathode of the thyristor Q1 and the cathode of the thyristor Q2 are connected to the common ground of the first thyristor input voltage VCC1 and the second thyristor input voltage VCC2; the anode of the diode D3 is connected to the cathode of the thyristor Q1, and the cathode of the diode D3 is connected to the anode of the thyristor Q1;

[0027] The capacitor C1 is connected in parallel to the output end of the AC / DC rectifier module to play a filtering role, and the energy storage capacitor C2 is connected in parallel to the DC bus terminal of the DC / AC power module.

[0028] Preferably, in the pre-charge / discharge circuit:

[0029] As the voltage at the capacitor C1 end gradually increases, the voltages at both ends of the thyristor Q1 and the thyristor Q2 also increase accordingly. When the first thyristor input voltage VCC1 reaches the turn-on voltage of the thyristor, the thyristor Q1 is turned on, and the positive voltage of the capacitor C1 flows through the resistor R1 and the thyristor Q1 to the energy storage capacitor C2 to charge the energy storage capacitor C2. When the second thyristor input voltage VCC2 reaches the turn-on voltage of the thyristor, the thyristor Q2 is turned on, thus completing the slow power-on function.

[0030] When the DC / AC power module generates a reverse current, the voltage across the energy storage capacitor C2 increases accordingly. When the voltage is greater than the voltage across the capacitor C1, the thyristor Q1 and the thyristor Q2 are turned off, the diode D3 is turned on, and the positive electrode of the energy storage capacitor C2 flows through the third diode D3 and the resistor R1 to the capacitor C1. Part of the reverse energy is consumed by the resistor R1, and the capacitor C1 and the energy storage capacitor C2 store part of the reverse energy. When the DC / AC power module is loaded, the energy stored in the energy storage capacitor C2 is consumed, and the voltage across it decreases. The voltage on the capacitor C1 is greater than the voltage across the energy storage capacitor C2, and the thyristor Q1 and the thyristor Q2 are turned on accordingly. Due to the existence of the resistor R1, the resistor R1 and the thyristor Q1 branch are bypassed and restored to the state after slow power-on, achieving normal load working conditions.

[0031] Preferably, the AC / DC rectifier module includes: a diode D4, a diode D5, a diode D6, a diode D7, a diode D8, and a diode D9, wherein:

[0032] The diode D4 and the diode D7 are connected in series, the diode D5 and the diode D8 are connected in series, and the diode D6 and the diode D9 are connected in series; the diode D4, the diode D5, and the diode D6 are connected to a common cathode, and the connection point is used as the positive pole of the DC bus to input to the pre-charge / discharge circuit; the diode D7, the diode D8, and the diode D9 are connected to a common anode, and the connection point is used as the negative pole of the DC bus to input to the pre-charge / discharge circuit;

[0033] The three-phase alternating current R terminal is connected to the anode of diode D4 and the cathode of diode D7; the three-phase alternating current S terminal is connected to the anode of diode D5 and the cathode of diode D8; the three-phase alternating current T terminal is connected to the anode of diode D6 and the cathode of diode D9.

[0034] Preferably, the DC / AC power module includes six switch tubes, specifically:

[0035] The switch tubes Q4, Q5, and Q6 are connected to a common drain and connected to the positive electrode of the pre-charge / discharge circuit output; the switch tubes Q7, Q8, and Q9 are connected to a common source and connected to the negative electrode of the pre-charge / discharge circuit output; the source of the switch tube Q4 is connected to the drain of the switch tube Q7 and connected to the U phase of the three-phase motor, the source of the switch tube Q5 is connected to the drain of the switch tube Q8 and connected to the V phase of the three-phase motor; the source of the switch tube Q6 is connected to the drain of the switch tube Q9 and connected to the W phase of the three-phase motor.

[0036] Preferably, in the DC / AC power module: the switch tube uses MOSFET or IGBT;

[0037] When IGBT is used as the switching tube, each switching tube should be connected to a diode in reverse parallel, that is, the collector is connected to the cathode of the diode and the emitter is connected to the anode of the diode.

[0038] Preferably, when the three-phase motor is in an acceleration state, the DC / AC power module receives the PWM pulse output by the control drive module to control the voltage magnitude and polarity of the U-phase, V-phase and W-phase of the three-phase motor; when the three-phase motor is in a deceleration state, the DC / AC power module receives the reverse current generated by the three-phase motor to charge the energy storage capacitor in the pre-charge / discharge circuit.

[0039] Compared with the prior art, the present invention has the following advantages:

[0040] (1) The present invention uses a sequential logic control circuit to realize the power-on self-start function, without the need for single-chip microcomputer or DSP processor digital control, which greatly reduces the complexity of the control circuit and avoids the problem of mutual interference between analog ground and digital ground. This circuit not only effectively improves the reliability of the system, but also uses passive components with low prices, which has certain cost advantages;

[0041] (2) The present invention adopts a hierarchical delay control strategy in the sequential logic control circuit, that is, the thyristor in the pre-charge / discharge circuit is controlled to be turned on only after the switch tube in the DC / AC power module is in a controllable state, which effectively avoids the DC / AC controller chip being turned on when the system is reset or when the ends of the switch tube are too large. The problem of the switch tube being turned on incorrectly due to the interference generated by the system is greatly improved.

[0042] (3) The thyristors in the pre-charging / discharging circuit of the present invention adopt a common cathode design, which can be controlled by the gate voltage of the common ground, thereby reducing the number of floating grounds. Therefore, the control circuit of the pre-charging / discharging circuit does not need to adopt a multi-channel isolation design, which reduces the difficulty of circuit design and improves the accuracy of the control delay time.

[0043] (4) The present invention does not need to sample the capacitor voltage on the DC bus, nor does it need to consider the fluctuation range of the input three-phase AC voltage, which greatly simplifies the control circuit. Moreover, by slightly adjusting the parameters in the timing logic control circuit, it can be transformed and applied to other topological structures with timing requirements, which has the advantage of universality.

[0044] (5) The resistor in the pre-charge / discharge circuit of the present invention serves as both a current limiting resistor for charging the energy storage capacitor and a discharge resistor for absorbing the reverse current of the DC / AC power module. By adopting a multifunctional composite design method, the volume and weight of the system are effectively reduced. In addition, the system uses the reverse current to store energy for the capacitor to improve energy utilization and increase the peak energy output capacity of the system.

[0045] (6) The present invention makes full use of the respective characteristics of thyristors and diodes in the pre-charging / discharging circuit to achieve bidirectional flow of energy. When reverse current is generated, there is no need to detect the DC bus voltage or open the switch of the discharge branch to achieve reverse energy flow. After the energy discharge stops, there is no need for switch control to achieve normal load operation of the inverter. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 This is an overall block diagram of a power-on self-starting, back-injection and self-discharging system for a frequency converter of the present invention;

[0047] Figure 2 It is the principle diagram of the sequential logic control circuit of the present invention. DETAILED DESCRIPTION

[0048] The purpose of the present invention is achieved through the following technical solutions:

[0049] like Figure 1As shown, a power-on self-starting, reverse charging and self-discharging system for a frequency converter is provided, which mainly includes: an AC / DC rectifier module, a pre-charging / discharging circuit, a DC / AC power module, a flyback power supply module, a DC / AC controller and a timing logic control circuit.

[0050] After the three-phase AC power is powered on, the flyback power module outputs a +15V control voltage to the DC / AC controller and the timing logic control circuit;

[0051] After the DC / AC controller is powered on by the flyback power module, it outputs a low-level driving signal to the DC / AC power module to control the switch tube in the DC / AC power module to be in the off state; after the DC bus of the DC / AC power module reaches a stable voltage, the DC / AC controller outputs a PWM pulse to the DC / AC power module;

[0052] After the flyback power module is powered on, the sequential logic control circuit controls the thyristor in the pre-charge / discharge circuit to turn on;

[0053] The AC / DC rectifier module converts the three-phase AC power into DC power, connects the pre-charging / discharging circuit and charges the energy storage capacitor therein;

[0054] When the motor is in the acceleration state, the DC / AC power module receives the PWM pulse output by the control drive module to control the voltage magnitude and polarity of the U phase, V phase, and W phase of the three-phase motor; when the motor is in the deceleration state, the DC / AC power module receives the reverse current generated by the motor to charge the energy storage capacitor in the pre-charge / discharge circuit;

[0055] On the one hand, the pre-charge / discharge circuit rectifies the DC power input by the AC / DC rectifier module to pre-charge the energy storage capacitor in the circuit. On the other hand, it accepts the feedback current input by the DC / AC power module to provide a discharge path for the feedback energy to avoid breakdown of the switch tube in the DC / AC power module due to excessive feedback energy.

[0056] After the three-phase AC power is turned on, the flyback power supply outputs a control voltage of +15V to the DC / AC controller and the sequential logic control circuit. After the DC / AC controller is powered on, the switch tube in the DC / AC power module is controlled to be in the off state. After the sequential logic control circuit is powered on, Figure 2As shown, the +15V control voltage is output to the second delay module after passing through the first delay / switch module. When the control voltage VCC1 output by the second delay module reaches the turn-on voltage of the thyristor, the thyristor Q1 in the pre-charge / discharge circuit is controlled to be turned on; the three-phase AC power is converted into DC power by the AC / DC rectifier module, and the DC power charges the energy storage capacitor C2 through the pre-charge resistor R1 and the thyristor Q1. At the same time, the second delay module outputs to the third delay module, and waits for it to break through the voltage regulator ZD2 and after a period of delay, the thyristor Q2 in the pre-charge / discharge circuit is controlled to be turned on.

[0057] The DC / AC controller is composed of a DC / DC isolation module and a control drive module. The DC / DC isolation module realizes the ground isolation function, and the control drive module controls the duty cycle of the switch tube in the DC / AC power module.

[0058] The sequential logic control circuit includes a first delay / switch module, a second delay module and a third delay module. The first delay / switch module controls the switch to turn on after delaying the input +15V control voltage. After the switch is turned on, the +15V control voltage is output to the second delay module. The +15V control voltage is connected to one end of the resistor R2, and the other end of the resistor R2 is connected to one end of the capacitor C3. The other end of the capacitor C3 is grounded, and the resistor R3 is connected in parallel with the capacitor C3. One end of the capacitor C3 is connected to the cathode of the voltage-stabilizing diode ZD1, the anode of the voltage-stabilizing diode ZD1 is connected to the base of the NPN transistor T1, the emitter of the transistor T1 is grounded, the collector of the transistor T1 is connected to one end of the resistor R5, the other end of the resistor R5 is connected to the base of the PNP transistor T2, the emitter of the transistor T2 is connected to one end of the resistor R4, the other end of the resistor R4 is connected to the +15V control voltage, the collector of the transistor T2 is connected to one end of the resistor R6 in the second delay module, and the other end of the resistor R6 is connected to the collector of the transistor R6. The first end of the capacitor C4 is connected to one end of the capacitor C4 (and outputs the first thyristor input voltage VCC1 to the pre-charge / discharge circuit), the other end of the capacitor C4 is connected to the ground, one end of the capacitor C4 is connected to the resistor R7 in the third delay module, the other end of the resistor R7 is connected to the cathode of the Zener diode ZD2, the anode of the Zener diode ZD2 is connected to one end of the capacitor C5 (after the voltage across the Zener diode ZD2 reaches the breakdown voltage, the second thyristor input voltage VCC2 is output to the pre-charge / discharge circuit), and the other end of the capacitor C5 is grounded.

[0059] The pre-charge / discharge circuit is connected to the output end of the AC / DC rectifier module to realize the function of pre-charging the energy storage capacitor after rectification. Capacitor C1 is connected in parallel to the output end of the AC / DC rectifier module to play a filtering role, and energy storage capacitor C2 is connected in parallel to the DC bus terminal of the DC / AC power module; as the voltage at the capacitor C1 end gradually increases, the voltage at both ends of thyristor Q1 and thyristor Q2 also increases accordingly. After the VCC1 voltage reaches the turn-on voltage of the thyristor, thyristor Q1 is turned on, and the positive voltage of capacitor C1 flows through resistor R1 and thyristor Q1 to energy storage capacitor C2 to charge energy storage capacitor C2. After the VCC2 voltage reaches the turn-on voltage of the thyristor, thyristor Q2 is turned on, and the slow power-on function is completed.

[0060] The gates of the thyristor Q1 and the thyristor Q2 in the pre-charge / discharge circuit are controlled by VCC1 and VCC2 respectively, VCC1 is connected to the anode of the diode D1, the cathode of the diode D1 is connected to the gate of the thyristor Q1, VCC2 is connected to the anode of the diode D2, the cathode of the diode D2 is connected to the gate of the thyristor Q2. The cathode of the thyristor Q1 and the cathode of the thyristor Q2 are connected to the common ground of VCC1 / VCC2.

[0061] The anode of the diode D3 in the pre-charge / discharge circuit is connected to the cathode of the thyristor Q1, and the cathode of the diode D3 is connected to the anode of the thyristor Q1. When the DC / AC power module generates a reverse current, the voltage across the energy storage capacitor C2 increases accordingly. When the voltage is greater than the voltage across the capacitor C1, the thyristor Q1 and the thyristor Q2 are closed, the diode D3 is turned on, and the positive electrode of the energy storage capacitor C2 flows through the diode D3 and the resistor R1 to the capacitor C1, and part of the reverse energy is consumed by the resistor R1. The capacitor C1 and the energy storage capacitor C2 store part of the reverse energy. When the DC / AC power module is loaded, the energy stored in the energy storage capacitor C2 is consumed, and the voltage across it decreases. The voltage on the capacitor C1 is greater than the voltage across the energy storage capacitor C2, and the thyristor Q1 and the thyristor Q2 are turned on accordingly. Since the resistor R1 is used as a current limiting resistor, the resistor R1 and the thyristor Q1 branch are bypassed and restored to the state after slow power-on, thereby achieving normal load working conditions.

[0062] In the AC / DC rectifier module:

[0063] The three-phase AC input terminal R is connected to the anode of the diode D4 and the cathode of the diode D7; the three-phase AC input terminal S is connected to the anode of the diode D5 and the cathode of the diode D8; the three-phase AC input terminal T is connected to the anode of the diode D6 and the cathode of the diode D9; the diodes D4, D5 and D6 are connected in common cathode, and the connection point is used as the positive pole of the DC bus to input to the pre-charging / discharging circuit; the diodes D7, D8 and D9 are connected in common anode, and the connection point is used as the negative pole of the DC bus to input to the pre-charging / discharging circuit.

[0064] In DC / AC power modules:

[0065] The switch tube is a MOSFET (metal-oxide semiconductor field effect transistor). If it is an IGBT (insulated gate bipolar transistor), a diode should be connected in reverse parallel, that is, the collector is connected to the cathode of the diode, and the emitter is connected to the anode of the diode; the switch tubes Q4, Q5, and Q6 are connected to a common drain, connected to the positive electrode of the pre-charge / discharge circuit output, and the switch tubes Q7, Q8, and Q9 are connected to a common source, connected to the negative electrode of the pre-charge / discharge circuit output; the source of the switch tube Q4 is connected to the drain of the switch tube Q7, connected to the U phase of the motor, the source of the switch tube Q5 is connected to the drain of the switch tube Q8, connected to the V phase of the motor; the source of the switch tube Q6 is connected to the drain of the switch tube Q9, connected to the W phase of the motor.

[0066] The contents not described in detail in the specification of the present invention belong to the prior art known to the professional and technical personnel in this field.

Claims

1. A power-on self-starting back-injection self-discharge system for a frequency converter, characterized in that include: AC / DC rectifier module, pre-charge / discharge circuit, DC / AC power module, flyback power module, DC / AC controller and sequential logic control circuit; wherein: After the three-phase AC power is powered on, the flyback power module outputs a +15V control voltage to the DC / AC controller and the timing logic control circuit; After the DC / AC controller is powered on by the flyback power module, it outputs a low-level driving signal to the DC / AC power module. After the DC bus of the DC / AC power module reaches a stable voltage, the DC / AC controller outputs a PWM pulse to the DC / AC power module. After the flyback power module is powered on, the sequential logic control circuit controls the operation of the pre-charge / discharge circuit; The AC / DC rectifier module converts the three-phase AC power into DC power, connects the pre-charging / discharging circuit and charges the energy storage capacitor therein; On the one hand, the DC / AC power module receives the PWM pulses output by the DC / AC controller to control the voltage magnitude and polarity of the U-phase, V-phase, and W-phase of the external three-phase motor; on the other hand, it receives the reverse current generated by the three-phase motor to charge the energy storage capacitor in the pre-charging / discharging circuit; On the one hand, the pre-charge / discharge circuit rectifies the DC power input by the AC / DC rectifier module to pre-charge the energy storage capacitor in the circuit. On the other hand, it accepts the feedback current input by the DC / AC power module to provide a discharge path for the feedback energy to avoid breakdown of the switch tube in the DC / AC power module due to excessive feedback energy.

2. A power-on self-starting back-injection self-discharge system for a frequency converter according to claim 1, characterized in that: The DC / AC controller consists of a DC / DC isolation module and a control drive module. The DC / DC isolation module realizes the ground isolation function, and the control drive module controls the duty cycle of the switch tube in the DC / AC power module.

3. The power-on self-starting back-injection self-discharge system for a frequency converter according to claim 1, characterized in that: The sequential logic control circuit includes: a first delay / switch module, a second delay module and a third delay module; wherein: The first delay / switch module includes: a resistor R2, a capacitor C3, a resistor R4, a transistor T2, a resistor R5, and a transistor T1; specifically: The input +15V control voltage is connected to one end of the resistor R2, the other end of the resistor R2 is connected to one end of the capacitor C3, the other end of the capacitor C3 is grounded, and the resistor R3 is connected in parallel with the capacitor C3; one end of the capacitor C3 is connected to the cathode of the voltage zener diode ZD1, the anode of the voltage zener diode ZD1 is connected to the base of the NPN transistor T1, the emitter of the transistor T1 is grounded, the collector of the transistor T1 is connected to one end of the resistor R5, the other end of the resistor R5 is connected to the base of the PNP transistor T2, the emitter of the transistor T2 is connected to one end of the resistor R4, the other end of the resistor R4 is connected to the +15V control voltage, and the collector of the transistor T2 is connected to the second delay module; The second delay module includes: a resistor R6 and a capacitor C4; specifically: One end of the resistor R6 is connected to the collector of the transistor T2 in the first delay / switch module, and the other end is connected to one end of the capacitor C4, and outputs the first thyristor input voltage VCC1 to the pre-charge / discharge circuit, the other end of the capacitor C4 is connected to the ground, and one end of the capacitor C4 is connected to the third delay module; The third delay module includes: a resistor R7, a diode ZD2, and a capacitor C5; specifically: One end of the resistor R7 is connected to the capacitor C4 of the second delay module, and the other end is connected to the cathode of the voltage-stabilizing diode ZD2. The anode of the voltage-stabilizing diode ZD2 is connected to one end of the capacitor C5. When the voltage across the voltage-stabilizing diode ZD2 reaches the breakdown voltage, the second thyristor input voltage VCC2 is output to the pre-charging / discharging circuit, and the other end of the fifth capacitor C5 is grounded.

4. The power-on self-starting back-injection self-discharge system for a frequency converter according to claim 1, characterized in that: The pre-charge / discharge circuit includes: thyristor Q1, thyristor Q2, diode D1, diode D2, diode D3, capacitor C1 and energy storage capacitor C2, wherein: The first thyristor input voltage VCC1 is connected to the anode of the diode D1, the cathode of the diode D1 is connected to the gate of the thyristor Q1, the second thyristor input voltage VCC2 is connected to the anode of the diode D2, the cathode of the diode D2 is connected to the gate of the thyristor Q2; the cathode of the thyristor Q1 and the cathode of the thyristor Q2 are connected to the common ground of the first thyristor input voltage VCC1 and the second thyristor input voltage VCC2; the anode of the diode D3 is connected to the cathode of the thyristor Q1, and the cathode of the diode D3 is connected to the anode of the thyristor Q1; The capacitor C1 is connected in parallel to the output end of the AC / DC rectifier module to play a filtering role, and the energy storage capacitor C2 is connected in parallel to the DC bus terminal of the DC / AC power module.

5. A power-on self-starting back-injection self-discharge system for a frequency converter according to claim 4, characterized in that: In the pre-charge / bleed circuit: As the voltage at the capacitor C1 end gradually increases, the voltages at both ends of the thyristor Q1 and the thyristor Q2 also increase accordingly. When the first thyristor input voltage VCC1 reaches the turn-on voltage of the thyristor, the thyristor Q1 is turned on, and the positive voltage of the capacitor C1 flows through the resistor R1 and the thyristor Q1 to the energy storage capacitor C2 to charge the energy storage capacitor C2. When the second thyristor input voltage VCC2 reaches the turn-on voltage of the thyristor, the thyristor Q2 is turned on, thus completing the slow power-on function. When the DC / AC power module generates a reverse current, the voltage across the energy storage capacitor C2 increases accordingly. When the voltage is greater than the voltage across the capacitor C1, the thyristor Q1 and the thyristor Q2 are turned off, the diode D3 is turned on, and the positive electrode of the energy storage capacitor C2 flows through the third diode D3 and the resistor R1 to the capacitor C1. Part of the reverse energy is consumed by the resistor R1, and the capacitor C1 and the energy storage capacitor C2 store part of the reverse energy. When the DC / AC power module is loaded, the energy stored in the energy storage capacitor C2 is consumed, and the voltage across it decreases. The voltage on the capacitor C1 is greater than the voltage across the energy storage capacitor C2, and the thyristor Q1 and the thyristor Q2 are turned on accordingly. Due to the existence of the resistor R1, the resistor R1 and the thyristor Q1 branch are bypassed and restored to the state after slow power-on, achieving normal load working conditions.

6. The power-on self-starting back-injection self-discharge system for a frequency converter according to claim 1, characterized in that: The AC / DC rectifier module includes: diode D4, diode D5, diode D6, diode D7, diode D8, diode D9, wherein: The diode D4 and the diode D7 are connected in series, the diode D5 and the diode D8 are connected in series, and the diode D6 and the diode D9 are connected in series; the diode D4, the diode D5, and the diode D6 are connected to a common cathode, and the connection point is used as the positive pole of the DC bus to input to the pre-charge / discharge circuit; the diode D7, the diode D8, and the diode D9 are connected to a common anode, and the connection point is used as the negative pole of the DC bus to input to the pre-charge / discharge circuit; The three-phase alternating current R terminal is connected to the anode of diode D4 and the cathode of diode D7; the three-phase alternating current S terminal is connected to the anode of diode D5 and the cathode of diode D8; the three-phase alternating current T terminal is connected to the anode of diode D6 and the cathode of diode D9.

7. The power-on self-starting back-injection self-discharge system for a frequency converter according to claim 1, characterized in that: The DC / AC power module includes six switching tubes, specifically: The switch tubes Q4, Q5, and Q6 are connected to a common drain and connected to the positive electrode of the pre-charge / discharge circuit output; the switch tubes Q7, Q8, and Q9 are connected to a common source and connected to the negative electrode of the pre-charge / discharge circuit output; the source of the switch tube Q4 is connected to the drain of the switch tube Q7 and connected to the U phase of the three-phase motor, the source of the switch tube Q5 is connected to the drain of the switch tube Q8 and connected to the V phase of the three-phase motor; the source of the switch tube Q6 is connected to the drain of the switch tube Q9 and connected to the W phase of the three-phase motor.

8. A power-on self-starting back-injection self-discharge system for a frequency converter according to claim 7, characterized in that: In DC / AC power modules: MOSFET or IGBT is used as the switch tube; When IGBT is used as the switching tube, each switching tube should be connected to a diode in reverse parallel, that is, the collector is connected to the cathode of the diode and the emitter is connected to the anode of the diode.

9. The power-on self-starting back-injection self-discharge system for a frequency converter according to claim 1, characterized in that: When the three-phase motor is in the acceleration state, the DC / AC power module receives the PWM pulse output by the control drive module to control the voltage magnitude and polarity of the U-phase, V-phase and W-phase of the three-phase motor; when the three-phase motor is in the deceleration state, the DC / AC power module receives the reverse current generated by the three-phase motor to charge the energy storage capacitor in the pre-charging / discharging circuit.

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