A motor rotor energy discharge circuit for a frequency converter

Abstract

The present application discloses a motor rotor energy discharge circuit for a frequency converter, which includes a double-contact switch, a freewheeling diode, and an energy discharge branch; the energy discharge branch includes a discharge resistor and A-phase, B-phase, and C-phase rotor energy discharge diodes; the first contact end of the double-contact switch is connected to the output end of the rectifier in the frequency converter power supply circuit, the moving end is connected to the first end of the bus filter capacitor and the braking resistor, and the second contact end is connected to the first end of the discharge resistor; the second end of the discharge resistor is respectively connected to the anodes of the A-phase, B-phase, and C-phase rotor energy discharge diodes, and the cathodes of the A-phase, B-phase, and C-phase rotor energy discharge diodes are correspondingly connected to the A, B, and C-phase windings of the three-phase AC motor; the cathode of the freewheeling diode is connected to the second end of the braking resistor and the collector of the IGBT tube, and the anode is connected to the emitter of the IGBT tube and the second end of the bus filter capacitor; the present invention can improve the energy discharge capacity of the system and at the same time reduce the consumption of grid energy.

Description

Technical Field

[0001] This application relates to the technical field of electronic circuits, and more specifically, to a motor rotor energy discharge circuit for a frequency converter. Background Art

[0002] Due to the mature and excellent speed regulation performance of frequency converters, their applications in the speed regulation field are becoming more and more widespread. However, the resulting braking problems have attracted increasing attention. In a variable frequency speed regulation system, when the frequency converter drives the load motor to decelerate instantaneously or stop quickly, due to inertia, the rotational speed of the motor rotor will not suddenly become zero in a short time. At this time, the motor is in a regenerative power generation state, thus generating a feedback current, which is fed back to the intermediate DC circuit through the antiparallel diodes of the IGBTs in the inverter bridge of the frequency converter. Although capacitors are connected in parallel in the DC circuit of a general frequency converter, the capacitance of the capacitors is limited and cannot absorb all the feedback electrical energy. Moreover, when the load inertia is particularly large or the braking is frequent, the feedback electrical energy is even greater. At this time, the built-in capacitor of the frequency converter is difficult to store this part of electrical energy, causing the built-in capacitor to be damaged due to exceeding the withstand voltage, resulting in damage to the frequency converter.

[0003] Currently, the method of externally connecting a braking resistor to the frequency converter is often used to solve this problem. This part of electrical energy is consumed through external energy consumption braking. However, this method has the following disadvantages: First, while consuming the feedback electrical energy of the electronic rotor through the externally connected braking resistor, it also consumes the built-in capacitor of the frequency converter and the electrical energy of the power grid, resulting in energy waste. Second, when the requirement for discharging the energy of the motor rotor is relatively high, a single braking resistor cannot achieve rapid discharge of the energy of the motor rotor, and the discharge capacity of the system is limited. Summary of the Invention

[0004] In view of at least one defect or improvement requirement of the prior art, the present invention provides a motor rotor energy discharge circuit for a frequency converter, which can improve the energy discharge capacity of the system, while reducing the consumption of electrical energy from the power grid, and only consumes the rotational energy of the motor rotor to the greatest extent.

[0005] To achieve the above object, according to one aspect of the present invention, there is provided a motor rotor energy discharge circuit for a frequency converter, which includes a double-contact switch, a freewheeling diode, and an energy discharge branch;

[0006] The energy discharge branch includes a discharge resistor, an A-phase rotor energy discharge diode, a B-phase rotor energy discharge diode, and a C-phase rotor energy discharge diode;

[0007] The first contact end of the double-contact switch is connected to the output end of the rectifier in the inverter power supply circuit, the moving end is connected to the first end of the bus filter capacitor and the braking resistor in the inverter power supply circuit, and the second contact end is connected to the first end of the discharge resistor; the second end of the discharge resistor is respectively connected to the anodes of the A-phase rotor energy discharge diode, the B-phase rotor energy discharge diode, and the C-phase rotor energy discharge diode, and the cathodes of the A-phase rotor energy discharge diode, the B-phase rotor energy discharge diode, and the C-phase rotor energy discharge diode are correspondingly connected to the A, B, and C phase windings in the three-phase AC motor;

[0008] The cathode of the freewheeling diode is connected to the second end of the braking resistor and the collector of the IGBT tube, and the anode is connected to the emitter of the IGBT tube and the second end of the bus filter capacitor.

[0009] Preferably, the above-mentioned motor rotor energy discharge circuit for the inverter has two working modes:

[0010] Partial working mode: The IGBT tube is turned off, and the moving end of the double-contact switch is connected to the second contact, so that the freewheeling diode, the braking resistor, the discharge resistor, and the A-phase, B-phase, and C-phase rotor energy discharge diodes form a first discharge loop, and the rotor energy of the three-phase AC motor is released through the series-connected braking resistor and discharge resistor; the energy of the bus filter capacitor is released through the discharge resistor;

[0011] Full working mode: The moving end of the double-contact switch is connected to the second contact, so that the freewheeling diode, the braking resistor, the discharge resistor, and the A-phase, B-phase, and C-phase rotor energy discharge diodes form a first discharge loop, and the rotor energy of the three-phase AC motor is released through the series-connected braking resistor and discharge resistor; the energy of the bus filter capacitor is released through the discharge resistor; and the IGBT tube is turned on, so that the braking resistor, the IGBT tube, and the bus filter capacitor form a second discharge loop, and the energy of the bus filter capacitor is released through the braking resistor.

[0012] Preferably, when the above-mentioned motor rotor energy discharge circuit for the inverter is not working, the moving end of the double-contact switch is connected to the first contact, and the inverter power supply circuit charges the bus filter capacitor and provides kinetic energy for the three-phase AC motor.

[0013] Preferably, the above-mentioned motor rotor energy discharge circuit for the inverter includes multiple energy discharge branches arranged in parallel.

[0014] Preferably, the above-mentioned motor rotor energy discharge circuit for the inverter further includes a soft charging resistor, and the soft charging resistor is arranged between the output end of the rectifier and the bus filter capacitor.

[0015] Preferably, in the motor rotor energy discharge circuit for the frequency converter, the frequency converter power supply circuit includes a three-phase AC bus of the power grid, a three-phase autotransformer, and a three-phase diode uncontrolled rectifier connected in sequence.

[0016] Preferably, in the motor rotor energy discharge circuit for the frequency converter, the double-contact switch can be a single-pole double-throw switch or a double-contact travel switch.

[0017] Generally speaking, compared with the prior art through the above technical solutions conceived by the present invention, the following beneficial effects can be achieved:

[0018] (1) The motor rotor energy discharge circuit for the frequency converter provided by the present invention adds a loop for directly discharging energy from the motor phase line, thereby increasing the energy discharge capacity of the frequency converter system. And compared with the original structure, when the energy discharge requirement is relatively low, only the energy discharge branch provided by this solution can be used, reducing the energy from the power grid provided by the rectifier and transformer system at the DC bus. When the energy discharge requirement is relatively high, the conventional braking circuit and the energy discharge branch in this solution are used simultaneously to quickly release the excess energy, improving the energy discharge capacity and ensuring the safety of the bus filter capacitor to the greatest extent when the motor rotor energy storage is large. Description of the Drawings

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0020] Figure 1 It is a schematic circuit diagram of a frequency converter system with a conventional energy discharge branch;

[0021] Figure 2 It is a schematic diagram of the energy flow when the braking circuit is working;

[0022] Figure 3 It is a schematic circuit diagram of the motor rotor energy discharge circuit for the frequency converter provided by the embodiment of the present application;

[0023] Figure 4 It is an energy flow diagram of the motor rotor energy discharge circuit for the frequency converter provided by the embodiment of the present application when it is not working;

[0024] Figure 5 It is an energy flow diagram of the motor rotor energy discharge circuit for the frequency converter provided by the embodiment of the present application when it is partially working;

[0025] Figure 6It is the energy flow diagram when the motor rotor energy discharge circuit provided by the embodiment of the present application is fully operating;

[0026] Figure 7 It is the schematic structural diagram of the parallel connection of multiple energy discharge branches in the motor rotor energy discharge circuit provided by the embodiment of the present application. Detailed implementation manners

[0027] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application.

[0028] The terms "first", "second", "third", etc. in the specification and claims of the present application and the above-mentioned accompanying drawings are used to distinguish different objects, rather than to describe a specific order. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device that includes a series of steps or units is not limited to the listed steps or units, but optionally further includes steps or units not listed, or optionally further includes other steps or units inherent to these processes, methods, products or devices.

[0029] Figure 1 It is the schematic circuit diagram of a frequency converter system with a conventional energy discharge branch; as Figure 1 shown, the system includes a frequency converter power supply circuit, a bus filter capacitor soft charging circuit, a direct-to-alternating conversion inverter circuit, and a braking circuit;

[0030] Among them, the frequency converter power supply circuit includes a 380V three-phase AC bus of the power grid, a three-phase autotransformer, a three-phase diode uncontrolled rectifier, and a bus filter capacitor C1; the 380V three-phase AC bus of the power grid, the three-phase autotransformer, and the three-phase diode uncontrolled rectifier are electrically connected in sequence, and the bus filter capacitor C1 is connected to the output end of the three-phase diode uncontrolled rectifier.

[0031] The bus filter capacitor soft charging circuit includes a soft charging resistor R1 and a soft charging travel switch SW1. Among them, the soft charging resistor R1 is arranged between the output end of the three-phase diode uncontrolled rectifier and the bus filter capacitor C1, and the soft charging travel switch is arranged in parallel with the soft charging resistor R1; the soft charging resistor R1 mainly plays a current limiting role when the power grid discharges, reducing the impact current on the bus filter capacitor C1 during energization, and the instantaneous voltage drop is dropped on the charging resistor, avoiding the impact on the power grid.

[0032] The direct - orthogonal transformation inverter circuit includes the upper IGBT (IG1) of the A - phase inverter power switch, the lower IGBT (IG2) of the A - phase inverter power switch, the upper IGBT (IG3) of the B - phase inverter power switch, the lower IGBT (IG4) of the B - phase inverter power switch, the upper IGBT (IG5) of the C - phase inverter power switch, and the upper IGBT (IG6) of the C - phase inverter power switch.

[0033] In this embodiment, the three - phase AC motor in the conventional frequency converter system is simplified to a three - phase equivalent conversion circuit. Specifically, the three - phase AC motor is equivalent to a controlled voltage source corresponding to the inductance, resistance, and phase - rotating back - electromotive force of each phase. See Figure 1 , the A - phase winding of the three - phase AC motor is equivalent to the A - phase inductance Lm1, the A - phase resistance Rm1, and the A - phase back - electromotive force Vm1; the B - phase winding of the three - phase AC motor is equivalent to the B - phase inductance Lm2, the B - phase resistance Rm2, and the B - phase back - electromotive force Vm2; the C - phase winding of the three - phase AC motor is equivalent to the C - phase inductance Lm3, the C - phase resistance Rm3, and the C - phase back - electromotive force Vm3.

[0034] Generally, the load motor operates "under the constraint" of the output frequency of the frequency converter, and its speed is equal to or close to the output frequency of the frequency converter. However, for some large - inertia loads, during the deceleration or stop process, the motor speed may exceed the given frequency of the frequency converter and be in an overspeed operation state. At this time, the rotor speed of the motor exceeds the stator magnetic field speed, generating capacitive current and entering the dynamic - electric (generating) state from the electric state. The generating energy of the load motor is fed back to the DC circuit of the frequency converter through the three - phase bridge rectifier circuit composed of diodes connected in parallel across the IGBTs, which may cause abnormal increase in the DC voltage and endanger the safety of the energy - storage capacitor and the IGBT module.

[0035] Currently, the most commonly used method is to adopt a braking circuit (or braking circuit), connect the braking circuit to the DC circuit, and convert the voltage increment in the DC circuit into the power consumption of the braking resistor (the braking current flows through the braking resistor). When the frequency converter starts the braking action, it can quickly dissipate the generating energy of the motor and achieve the effect of accelerating the stop. Therefore, the braking circuit is also called the braking circuit.

[0036] Please continue to refer to Figure 1, a common braking circuit includes a braking resistor R2 and an energy dissipation IGBT tube IG7 that controls the opening / closing of the braking circuit; the first end of the braking resistor R2 is respectively connected to the first end of the bus filter capacitor C1 and the collectors of the upper IGBTs of the A-phase inverter power switch IG1, the B-phase inverter power switch IG3, and the C-phase inverter power switch IG5. The second end is connected to the collector of the energy dissipation IGBT tube IG7. The emitter of the energy dissipation IGBT tube IG7 is respectively connected to the second end of the bus filter capacitor C1 and the emitters of the lower IGBTs of the A-phase inverter power switch IG2, the B-phase inverter power switch IG4, and the upper IGBT of the C-phase inverter power switch IG6. The gate of the energy dissipation IGBT tube IG7 receives an external control signal to trigger the conduction or closing of the energy dissipation IGBT tube.

[0037] The schematic diagram of the energy flow when the above braking circuit is working is as Figure 2 shown. When the energy dissipation IGBT tube IG7 is controlled to conduct, the energy of the electronic rotor is dissipated through the braking resistor R2; however, the energy of the power grid and the bus filter capacitor C1 will also be dissipated through the braking resistor R2, resulting in energy waste.

[0038] In order to improve the problem that the braking circuit of a conventional frequency converter consumes the energy of the power grid and the bus filter capacitor C1, this embodiment provides a more optimized motor rotor energy dissipation circuit for a frequency converter. The specific circuit structure is as Figure 3 shown. The circuit includes a double-contact switch SW2, a freewheeling diode D4, and an energy dissipation branch; the energy dissipation branch includes a dissipation resistor R3, an A-phase rotor energy dissipation diode D1, a B-phase rotor energy dissipation diode D2, and a C-phase rotor energy dissipation diode D3;

[0039] Among them, the first contact end 1 of the double-contact switch SW2 is connected to the output end of the rectifier in the frequency converter power supply circuit. The moving end is connected to the first end of the bus filter capacitor C1 and the braking resistor R2 in the frequency converter power supply circuit. The second contact end 2 is connected to the first end of the dissipation resistor R3; the second end of the dissipation resistor R3 is respectively connected to the anodes of the A-phase rotor energy dissipation diode D1, the B-phase rotor energy dissipation diode D2, and the C-phase rotor energy dissipation diode D3. The cathodes of the A-phase rotor energy dissipation diode D1, the B-phase rotor energy dissipation diode D2, and the C-phase rotor energy dissipation diode D3 are correspondingly connected to the A, B, and C phase windings in the three-phase AC motor;

[0040] The freewheeling diode D4 is arranged in reverse parallel with the energy dissipation IGBT tube IG7. The cathode of the freewheeling diode D4 is connected to the second end of the braking resistor R2 and the collector of the IGBT tube, and the anode is connected to the emitter of the IGBT tube and the second end of the bus filter capacitor C1.

[0041] The energy direct discharge circuit provided in this embodiment has three working modes: non-working, partial working mode, and full working mode;

[0042] See Figure 4 , when the energy discharge circuit is not working, that is, when the motor is running normally, the moving end of the double-contact switch SW2 is connected to the first contact end 1, and the grid energy charges the bus filter capacitor C1 normally through the inverter power supply circuit. The grid energy and the energy stored in the bus filter capacitor C1 provide kinetic energy to the motor rotor and the load driven by the rotor through the power switches IG1, IG4, and IG6.

[0043] See Figure 5 , when the energy discharge circuit is in the partial working mode: the energy discharge IGBT tube IG7 is turned off, and the moving end of the double-contact switch SW2 is connected to the second contact end 2, so that the freewheeling diode D4, the braking resistor R2, the discharge resistor R3, and the A-phase, B-phase, and C-phase rotor energy discharge diodes D1, D2, D3, and the A-phase, B-phase, and C-phase inverter power switch IGBT lower tubes IG2, IG4, and IG6 form a first discharge loop. The rotor energy of the three-phase AC motor is released through the series-connected braking resistor R2 and discharge resistor R3; the energy of the bus filter capacitor C1 is slowly released through the discharge resistor R3; this mode is applicable when the generated energy of the load motor is small and the requirement for the system discharge capacity is small. At this time, the grid energy cannot be released through the braking resistor R2 or the discharge resistor R3, and the voltage of the bus filter capacitor C1 is clamped by the braking resistor R2 and the energy discharge IGBT tube IG7. Since the energy discharge IGBT tube IG7 is in the off state, the energy of the bus filter capacitor C1 cannot be discharged through the braking resistor R2 and can only be slowly released through the discharge resistor R3, thereby reducing the consumption of the grid and the energy of the bus filter capacitor C1, and directly consuming the motor rotor energy.

[0044] See Figure 6, when the energy discharge circuit is in the full working mode: the moving end of the double-contact switch SW2 is connected to the second contact end 2, enabling the freewheeling diode D4, the braking resistor R2, the discharge resistor R3, and the A-phase, B-phase, and C-phase rotor energy discharge diodes D1, D2, D3, as well as the A-phase, B-phase, and C-phase inverter power switch IGBT lower tubes IG2, IG4, and IG6 to form the first discharge loop. The rotor energy of the three-phase AC motor is released through the series-connected braking resistor R2 and discharge resistor R3, and the energy of the bus filter capacitor C1 is released through the discharge resistor R3. In addition, since the energy discharge IGBT tube IG7 is turned on, the braking resistor R2, the IGBT tube, and the bus filter capacitor C1 form the second discharge loop, and the energy of the bus filter capacitor C1 can be released through the braking resistor R2. This mode is applicable when the generated power energy of the load motor is relatively large and the system discharge capacity requirement is relatively high. At this time, the energy of the bus filter capacitor C1 can be quickly discharged in parallel through the braking resistor R2 and the discharge resistor R3.

[0045] After the energy discharge circuit provided in this embodiment ends the partial working mode, the system can continue to operate after the double-contact switch SW2 is switched from the first contact 2 to the second contact 1 without the need for reset.

[0046] After the energy discharge circuit provided in this embodiment ends the full working mode, the double-contact switch SW2 must be reset, and the system should also be reset and the bus filter capacitor C1 should be pre-charged. The full working mode is to ensure the safety of the bus filter capacitor C1 to the greatest extent when the motor rotor stores a large amount of energy. The voltage of the bus filter capacitor C1 is clamped to a very small value by the braking resistor R2 and IG7, and the grid energy is not replenished, which is the reason why it should be reset and the bus filter capacitor C1 should be pre-charged again after full operation.

[0047] The double-contact switch SW2 can be a single-pole double-throw switch or a double-contact travel switch, and this embodiment does not make specific restrictions.

[0048] Compared with the inverter power circuit structure that only has a conventional braking circuit, the energy discharge circuit provided in this embodiment adds a loop for directly discharging energy from the motor phase line, thereby increasing the energy discharge capacity of the inverter system. And compared with the original structure, when the energy discharge requirement is relatively low, only the energy discharge branch provided by this solution can be used to reduce the consumption of the energy from the rectifier and transformer system from the grid provided at the DC bus. When the energy discharge requirement is relatively high, the conventional braking circuit and the energy discharge branch in this solution are used simultaneously to quickly release the redundant energy and improve the energy discharge capacity.

[0049] In a preferred embodiment, the motor rotor energy discharge circuit for the frequency converter includes multiple energy discharge branches arranged in parallel. By paralleling multiple energy discharge branches, the discharge capacity of the system is further improved, achieving the effect of increasing the maximum discharge capacity limit. Please refer to Figure 7 , when the physical space permits, the energy discharge branches can be infinitely paralleled, and an infinite number of such branches can be added to eliminate the power limit of the discharge resistors R3 (marked as R13 and R23 when paralleled) and the current limiting capacity limit of the motor rotor energy discharge diodes D1, D2, D3 (marked as D11, D21 and D12, D22 and D13, D23 when paralleled). The maximum energy that can be released by the branches can be infinitely increased until it is limited by the maximum current-carrying capacity of the system and the maximum current-carrying capacity of the double-contact switch SW2.

Claims

1. A motor rotor energy discharge circuit for a frequency converter, characterized in that, it includes a double-contact switch, a freewheeling diode and an energy discharge branch; the energy discharge branch includes a discharge resistor, an A-phase rotor energy discharge diode, a B-phase rotor energy discharge diode and a C-phase rotor energy discharge diode; the first contact end of the double-contact switch is connected to the output end of the rectifier in the frequency converter power supply circuit, the moving end is connected to the first end of the bus filter capacitor and the braking resistor in the frequency converter power supply circuit, and the second contact end is connected to the first end of the discharge resistor; the second end of the discharge resistor is respectively connected to the anodes of the A-phase rotor energy discharge diode, the B-phase rotor energy discharge diode and the C-phase rotor energy discharge diode, and the cathodes of the A-phase rotor energy discharge diode, the B-phase rotor energy discharge diode and the C-phase rotor energy discharge diode are correspondingly connected to the A, B, and C phase windings in the three-phase AC motor; the cathode of the freewheeling diode is connected to the second end of the braking resistor and the collector of the IGBT tube, and the anode is connected to the emitter of the IGBT tube and the second end of the bus filter capacitor; the motor rotor energy discharge circuit for the frequency converter has two working modes: Partial working mode: The IGBT tube is turned off, and the moving end of the double-contact switch is connected to the second contact, so that the freewheeling diode, the braking resistor, the discharge resistor, the A-phase, B-phase and C-phase rotor energy discharge diodes, and the A-phase, B-phase, and C-phase inverter power switch IGBT lower tubes form a first discharge loop, and the rotor energy of the three-phase AC motor is released through the series-connected braking resistor and discharge resistor; the energy of the bus filter capacitor is released through the discharge resistor; Full working mode: The moving end of the double-contact switch is connected to the second contact, so that the freewheeling diode, the braking resistor, the discharge resistor, the A-phase, B-phase and C-phase rotor energy discharge diodes, and the A-phase, B-phase, and C-phase inverter power switch IGBT lower tubes form a first discharge loop, and the rotor energy of the three-phase AC motor is released through the series-connected braking resistor and discharge resistor; the energy of the bus filter capacitor is released through the discharge resistor; and the IGBT tube is turned on, so that the braking resistor, the IGBT tube and the bus filter capacitor form a second discharge loop, and the energy of the bus filter capacitor is released through the braking resistor.

2. The motor rotor energy discharge circuit for a frequency converter according to claim 1, characterized in that, when not working, the moving end of the double-contact switch is connected to the first contact, and the frequency converter power supply circuit charges the bus filter capacitor and provides kinetic energy for the three-phase AC motor.

3. The motor rotor energy discharge circuit for a frequency converter according to claim 1 or 2, characterized in that, it includes multiple energy discharge branches arranged in parallel.

4. The motor rotor energy discharge circuit for a frequency converter according to claim 1 or 2, characterized in that, it further includes a soft charging resistor, and the soft charging resistor is arranged between the output end of the rectifier and the bus filter capacitor.

5. The motor rotor energy discharge circuit for a frequency converter according to claim 1 or 2, characterized in that, the frequency converter power supply circuit includes a three-phase AC bus of the power grid, a three-phase autotransformer regulator and a three-phase diode uncontrolled rectifier connected in sequence.

6. The motor rotor energy discharge circuit for a frequency converter as described in claim 1 or 2, characterized in that, the double-contact switch can be a single-pole double-throw switch or a double-contact travel switch.

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