CN102437803A - Switched reluctance motor bootstrap drive circuit with low cost and high isolation characteristic - Google Patents

Abstract

The invention discloses a switched reluctance motor bootstrap drive circuit with low cost and high isolation characteristic, which comprises an upper switching tube drive circuit and a lower switching tube drive circuit; the upper switching tube driving circuit comprises a first switching circuit based on an optocoupler, a first charging circuit, a first discharging circuit, a bootstrap capacitor and a bootstrap diode; the lower switching tube driving circuit comprises a second switching circuit, a second charging circuit and a second discharging circuit. The invention adopts a single power supply working mode based on the bootstrap capacitor and adopts the photoelectric coupler as the switching element of the core switching circuit, thereby avoiding the influence of a low-voltage control signal by a high-voltage driving signal and improving the safety of circuit control; moreover, the on-off time of the driving circuit and the power converter is strictly consistent with the low-voltage control signal of the microprocessor, and the method is suitable for working occasions under a high-frequency PWM control mode.

Description

Bootstrap drive circuit for switched reluctance motor with low cost and high isolation

technical field

The invention relates to a switched reluctance motor, in particular to a drive circuit of the switched reluctance motor.

Background technique

Switched reluctance motors have some unique advantages, such as simple structure, firmness, maintenance-free, large torque and low current at start-up and low speed; wide range of high-speed constant power range, good performance, and excellent performance in a wide range of speed and power. High output and high efficiency; it can operate with phase loss and has strong fault tolerance; it can be flexibly controlled and can easily realize four-quadrant operation; it has strong regenerative braking ability, etc. This makes the switched reluctance motor system widely used in household appliances, general industry, servo and speed control systems, traction motors, high-speed motors, aerospace and other fields. A switched reluctance motor is an electromechanical energy conversion device. According to the reversible principle, the switched reluctance motor is the same as the traditional motor, it can convert electrical energy into mechanical energy - electric operation, and can also convert mechanical energy into electrical energy - power generation operation.

The switched reluctance motor control system can be roughly divided into two parts: the processing part and the switch main circuit part. The processing part includes the sampling circuit and the processing circuit, which are respectively responsible for signal sampling, analysis and processing and control signal output; the switch main circuit part includes the drive circuit. and the power converter, which are respectively responsible for weak current signal enhancement drive and power signal switch control.

The traditional drive circuit mainly uses a single-supply drive circuit composed of a bootstrap diode and a triode, or a single-supply drive circuit using a bootstrap capacitor and a triode, a metal-oxide-semiconductor (MOS) tube, and a dedicated integrated drive circuit. Chip single power supply drive circuit. The isolation characteristics of the first two technical solutions are poor. The reason is that there is a parasitic Miller capacitance between the base-collector inside the triode or between the gate-source inside the MOS transistor used in the core switching circuit. As a result, the high-voltage drive signal in the drive circuit may be coupled to the low-voltage control signal channel of the microprocessor through the parasitic Miller capacitance, which may cause the low-voltage control signal waveform to be distorted, or cause the low-voltage control signal to reverse, resulting in the drive circuit. In addition, the consequences of poor isolation characteristics will also affect the dynamic characteristics of the drive circuit and power converter under the high-frequency pulse width modulation (PWM) control mode, that is, the drive The turn-on and turn-off time of the circuit and power converter cannot be consistent with the low-voltage control signal, and the expected control effect cannot be achieved. In the third solution, a dedicated integrated driver chip is used. The chip is designed with a better isolation circuit, so its isolation and dynamic characteristics are better, but the cost is very high.

Contents of the invention

Purpose of the invention: In view of the problems and deficiencies in the prior art above, the purpose of the present invention is to provide a low-cost, high-isolation switched reluctance motor bootstrap drive circuit, which uses the principle of capacitor energy storage to continuously provide multiple The charge required for the first turn-on, so that the upper switch tube can be frequently turned on in a short period of time in PWM mode when the single drive power supply is supplied. In addition, the low-voltage control signal is prevented from being affected by the high-voltage drive signal, thereby improving the safety of circuit control.

Technical solution: In order to achieve the purpose of the above invention, the technical solution adopted in the present invention is a low-cost, high-isolation switched reluctance motor bootstrap drive circuit, including an upper switch tube drive circuit and a lower switch tube drive circuit; The input signal of the upper switching tube drive circuit includes the drive power supply and the upper tube drive signal, the output terminal is connected to and drives the grid of the upper switching tube, the drain of the upper switching tube and one end of the motor winding; the input of the lower switching tube driving circuit is The signal includes a drive power supply and a lower tube drive signal, and the output terminal is connected to and drives the grid of the lower switch tube; the drain of the upper switch tube and the source of the lower switch tube are connected in series with a motor winding; the drive circuit of the upper switch tube includes A first switch circuit, a first charging circuit, a first discharge circuit, a bootstrap capacitor, and a bootstrap diode; the lower switch tube drive circuit includes a second switch circuit, a second charge circuit and a second discharge circuit.

The first switch circuit may include a first resistor, a photocoupler (optocoupler), a second resistor and a fifth resistor; wherein the first resistor is connected in series between the upper tube drive signal and the input terminal of the internal light-emitting diode of the optocoupler; The output end of the internal LED of the coupler is connected to the ground wire; the emitter of the internal triode of the optocoupler is connected to the ground wire after being connected in series with the fifth resistor; the collector of the internal triode of the optocoupler is connected to one end of the second resistor and the first charging circuit. The connection points of the bases of the first transistors are connected.

The first charging circuit may include a first triode, a second diode and a third resistor; wherein the base and the emitter of the first triode are respectively connected to the two ends of the second resistor in the first switch circuit connected, and the emitter of the first triode is respectively connected with one end of the bootstrap capacitor and the negative end of the bootstrap diode; the collector of the first triode is connected in series with the second diode and one end of the third resistor in sequence, and Connect with the base of the second transistor in the first discharge circuit and one end of the fourth resistor; after the other end of the third resistor is connected with the emitter of the second transistor in the first discharge circuit, connect and drive The gate of the upper switch.

The first discharge circuit may include a second triode and a fourth resistor; wherein both ends of the fourth resistor are respectively connected to the base and the collector of the second triode; the collector of the second triode is connected to the upper switch tube connected to the drain terminal of the motor winding.

The second switch circuit may include a fourth triode, a sixth resistor, a seventh resistor and a ninth resistor; the base of the fourth triode is connected to the weak current power supply, and the emitter of the fourth triode is connected to the seventh resistor. The resistors are connected in series to the driving signal of the lower tube, and the collector of the fourth transistor is connected to one end of the sixth resistor and the base of the third transistor in the second charging circuit.

The second charging circuit may include a third triode and an eighth resistor; wherein the base and the emitter of the third triode are respectively connected to both ends of the sixth resistor in the second switch circuit, and the third triode The emitter of the tube is connected to the drive power supply, the base of the third triode is connected to the collector of the fourth triode in the second switch circuit; one end of the eighth resistor is connected to the collector of the third triode, and the other After one end is connected to the collector of the fifth triode in the second discharge circuit, it is connected to and drives the gate of the lower switching transistor.

The second discharge circuit may include a fifth triode; the base of the fifth triode is connected in series with the ninth resistor in the second switch circuit to the lower tube drive signal, and the emitter of the fifth triode is connected to to ground.

The key operating principles of the above-mentioned low-cost, high-isolation switched reluctance motor bootstrap drive circuit include:

(1) In the driving circuit of the upper switching tube (referred to as "upper tube"), the first switching circuit receives the driving signal of the upper switching tube from the microprocessor, and enables the first charging circuit. The first charging circuit is used to increase the gate voltage of the upper switch tube to the conduction voltage so as to make it conduct. The first discharge circuit is used to reduce the gate voltage of the upper switch tube to zero so as to turn it off.

(2) In the driving circuit of the lower switching tube (referred to as "lower tube"), the second switching circuit receives the driving signal of the lower tube from the microprocessor, and alternately enables the second charging circuit and the second discharging circuit, that is, the second switching circuit The charging circuit and the second discharging circuit can only be turned on in turn. The second charging circuit is used to increase the gate voltage of the lower switch tube to the conduction voltage to make it conduct. The second discharge circuit is used to reduce the gate voltage of the lower switch tube to zero so as to turn it off.

(3) The working principle of the low-cost, high-isolation switched reluctance motor bootstrap drive circuit is that first, the drive signal of the lower tube enables the second switch circuit in the lower tube drive circuit, thereby turning on the second switch circuit in the lower tube drive circuit. The second charging circuit makes the lower switching tube turn on, and at the same time, the driving signal of the upper tube keeps turning off the first switching circuit and the first charging circuit, so that the upper switching tube is turned off. At this time, the connection point b between the upper switching tube and the motor winding The voltage is 0, so the drive power can charge the bootstrap capacitor through the diode; then the upper tube drive signal enables the first switch circuit, turns on the first charging circuit to charge the gate of the upper switch tube, and turns on the upper switch tube , at the same time, the voltage at point b is raised to the power supply voltage, and the voltage at point a is also raised to the sum of the power supply voltage and the driving power supply voltage, the diode is reversed, and the charge on the bootstrap capacitor continues to maintain the conduction pass the required charge.

(4) The working principle of the PWM mode of the bootstrap drive circuit of the switched reluctance motor with low cost and high isolation characteristics is that after both the lower switching tube and the upper switching tube are turned on, then the driving signal of the upper switching tube is reversed, and the optocoupler gradually The stage reliably turns off the first switching circuit and the first charging circuit, and then the second charging circuit is turned on by itself, the gate charge of the upper switching tube can be discharged, the grid voltage of the upper switching tube drops to 0 and the upper switching tube is turned off. When the voltage at point b drops to 0, the voltage at point a drops back to the driving power supply voltage, the bootstrap diode is forward-conducting, and the bootstrap capacitor is charged to the same voltage as the driving power supply; then the upper tube drive signal is reversed again, through the light When the coupling is controlled step by step and finally turns on the upper switch tube, the steps (3) and (4) are repeated, so as to achieve the effect of normal operation in PWM mode.

(5) Since the voltage at point a will change frequently, the range of change will reach the sum of the driving power supply voltage and the power supply voltage, so the potential of the emitter and collector of the internal triode of the optocoupler will also change significantly. However, Due to the high isolation characteristics of the optocoupler, that is, the input and output terminals of the internal light-emitting diode and the emitter and collector of the internal triode can reach 4 or 5 kV without mutual interference. This characteristic makes the voltage and potential changes of the above points The internal light-emitting diode input terminal and output terminal of the optocoupler are not affected, thereby ensuring the stability of the upper tube drive signal from the microprocessor and improving the safety of the microprocessor.

Beneficial effects: the present invention utilizes firstly to charge the bootstrap capacitor to the driving power supply voltage when only the lower switch tube is turned on, and then turns on the optocoupler switch circuit (that is, the first switch circuit) so that the voltage on the bootstrap capacitor is quickly turned on to the upper switch tube , to avoid the problem that the upper switch tube fails to conduct due to the insufficient gate voltage of the upper switch tube due to the increase of the voltage of the terminal b when the motor phase winding is turned on, which leads to the abnormal operation of the motor, and the capacitor can be used The principle of energy storage realizes the function of switching the upper switching tube frequently in a short time in PWM mode. Moreover, by utilizing the high-voltage isolation characteristics of the optocoupler, the upper tube drive signal from the microprocessor in the circuit is not affected by the high-voltage circuit signal, and has good isolation and dynamic characteristics. The present invention utilizes a bootstrap drive circuit composed of optocoupler, bootstrap capacitor, diode and commonly used resistors, triodes and other components, and can follow the drive signal to drive the switch tube in real time. The circuit structure is simple, the cost is low, and the practicability is strong.

Description of drawings

Figure 1 is a low-cost, high-isolation characteristic switched reluctance motor bootstrap drive circuit diagram;

Fig. 2 is a comparison chart of the upper switching tube drive signal UP and the gate signal of the upper switching tube M1 of the reported adopting diode or MOS tube and the switched reluctance motor bootstrap drive circuit of the present application;

FIG. 3 is a low-cost, high-isolation switched reluctance motor bootstrap drive circuit operating in PWM mode, the upper switch tube drive signal UP and the signal diagram on the gate of the upper switch tube M1.

Detailed ways

Below in conjunction with accompanying drawing and specific embodiment, further illustrate the present invention, should be understood that these embodiments are only for illustrating the present invention and are not intended to limit the scope of the present invention, after having read the present invention, those skilled in the art will understand various aspects of the present invention Modifications in equivalent forms all fall within the scope defined by the appended claims of this application.

Figure 1 is a low-cost, high-isolation switched reluctance motor bootstrap drive circuit diagram:

(1) It includes an upper switch tube drive circuit and a lower switch tube drive circuit. The input signal of the upper switch tube drive circuit includes the drive power supply, the upper tube drive signal UP from the microprocessor, the output terminal is connected to and drives the gate of the upper switch tube M1, the drain of the upper switch tube M1 is connected to one end of the motor winding L The input signal of the driving circuit of the lower switch tube includes the drive power supply, the weak power supply, and the lower tube drive signal DOWN from the microprocessor, and the output terminal is connected to and drives the gate of the lower switch tube M2. A motor winding L is connected in series between the drain of the upper switch M1 and the source of the lower switch M2. The upper switch tube drive circuit includes a first charging circuit, a first discharge circuit, a first switch circuit, a bootstrap capacitor C2, and a bootstrap diode D1; the lower switch tube drive circuit includes a second charge circuit, a second discharge circuit , the second switching circuit.

(2) The first charging circuit is composed of a first triode Q1, a second diode D2 and a third resistor R3. The base and the emitter of the first triode Q1 are respectively connected to the two ends of the second resistor R2 in the first switch circuit, and the emitter of the first triode Q1 is respectively connected to one end of the bootstrap capacitor C2, the self- The negative end of the diode D1 is connected at point a; the collector of the first triode Q1 is connected in series with the second diode D2 and one end of the third resistor R3 in series, and connected with the second triode Q2 in the first discharge circuit The base of the fourth resistor R4 and one end of the fourth resistor R4 are connected at point c; the other end of the third resistor R3 is connected to the emitter of the second triode Q2 in the first discharge circuit, and then connected to and drives the gate of the upper switch M1 pole.

(3) The first discharge circuit is composed of a second transistor Q2 and a fourth resistor R4. Both ends of the fourth resistor R4 are respectively connected to the base and collector of the second triode Q2; the collector of the second triode Q2 is connected to the drain of the upper switch M1 and one end of the motor winding L at point b.

(4) The first switch circuit is composed of a first resistor R1, an optocoupler OPT1, a second resistor R2 and a fifth resistor R5. The first resistor R1 is connected in series between the upper tube drive signal UP and the internal light-emitting diode input terminal ① of the optocoupler OPT1; the internal light-emitting diode output terminal ② of the optocoupler OPT1 is connected to the ground wire GND; the internal triode emitter of the optocoupler OPT1 ③ The fifth resistor R5 is connected in series to the ground wire GND; the internal transistor collector ④ of the optocoupler OPT1 is connected to the connection point between one end of the second resistor R2 and the base of the first transistor Q1 in the first charging circuit.

(5) The second charging circuit is composed of a third transistor Q3 and an eighth resistor R8. The base and emitter of the third triode Q3 are respectively connected to both ends of the sixth resistor R6 in the second switch circuit, the emitter of the third triode Q3 is connected to the driving power supply +15V, and the base of Q3 Connected to the collector of the fourth transistor Q4 in the second switch circuit; one end of the eighth resistor R8 is connected to the collector of the third transistor Q3, and the other end is connected to the fifth transistor Q5 in the second discharge circuit After the collectors of the two are connected, they are connected and driven to the gate of the lower switching tube M2.

(6) The second discharge circuit is composed of a fifth triode Q5. The base of the fifth triode Q5 is connected in series with the ninth resistor R9 in the second switch circuit and then connected to the lower transistor driving signal DOWN from the microprocessor, and the emitter of Q5 is connected to the ground line GND.

(7) The second switch circuit is composed of a fourth transistor Q4, a sixth resistor R6, a seventh resistor R7, and a ninth resistor R9. The base of the fourth triode Q4 is connected to the weak power supply +3.3V, the emitter of Q4 is connected in series with the seventh resistor R7 and then connected to the down tube drive signal DOWN from the microprocessor, and the collector of Q4 is connected to the sixth resistor R6 One end of the charging circuit and the base of the third transistor Q3 in the second charging circuit are connected.

The present invention utilizes the isolation characteristic of the optocoupler, first controls the first switch circuit in the upper switch tube drive circuit through the optocoupler, so that the bootstrap capacitor is charged to the driving power supply voltage when the lower switch tube is turned on, and then utilizes the voltage on the bootstrap capacitor to conduct Turning on the switching tube avoids the problem that when the motor phase winding is turned on, the grid voltage of the upper switching tube is raised due to insufficient grid voltage, which leads to its conduction failure, which leads to the abnormal operation of the motor; secondly, it makes the upper switching tube The high-voltage signal transmitted by the first switch circuit in the switch tube drive circuit is completely isolated from the low-voltage signal from the microprocessor, which can improve the reliability of the microprocessor. The invention has good circuit isolation characteristics and dynamic response characteristics, simple structure and strong practicability. FIG. 2 is a comparison chart of the upper switching tube drive signal UP and the gate signal of the upper switching tube M1 between the reported diode or MOS tube and the switched reluctance motor bootstrap drive circuit of the present application. The feature of the present application is to eliminate the adverse effect on the drive signal UP of the upper switch tube M1 caused by the turn-on and turn-off of the upper switch tube M1.

In addition, the present invention is also applicable to applications requiring frequent switching of the upper switching tube in a short time in a pulse width modulation (PWM) mode.

A high-voltage 3-phase switched reluctance motor drive circuit adopts the technical solution of the present invention. The windings of each phase motor are driven by the optocoupler-based switched reluctance motor bootstrap drive circuit shown in Figure 1. The input signal of the upper switch tube drive circuit includes the drive power supply +15V, the upper tube drive signal UP from the microprocessor (its high and low levels are +3.3V and 0 respectively), the output terminal is connected to and drives the gate of the upper switch tube M1, M1 A high-voltage metal-oxide-semiconductor (MOS) tube is used, and point b is connected to the drain of the upper switching tube M1 and one end of the motor winding L. The input signal of the drive circuit of the lower switch tube includes drive power +15V, weak power supply +3.3V, and the drive signal DOWN of the lower tube from the microprocessor (its high and low levels are the same as the UP signal), and the output terminal is connected to and drives the gate of the lower switch tube M2 Pole, M2 uses the same type of MOS tube as M1. A motor winding L is connected in series between the drain of the upper switch M1 and the source of the lower switch M2. The power supply voltage is +120V.

The three phases of the switched reluctance motor work in turn, and one of the phases works in PWM mode as an example.

(1) First is the charging stage of the bootstrap capacitor. At this time, the lower switching tube driving the motor winding of this phase is turned on and the upper switching tube is turned off. The DOWN signal should be 0 first, enabling the second switch circuit in the down tube drive circuit, thereby turning on the second charging circuit in the down tube drive circuit, so that the down switch tube M2 is turned on; at the same time, the up tube drive signal UP is also 0, keep turning off the first switching circuit and the first charging circuit, so that the upper switching tube M1 is turned off. At this time, the voltage at the connection point b between the upper switching tube M1 and the motor winding L is 0, so the driving power can be supplied to the battery through the diode D1. The bootstrap capacitor C2 is charged.

(2) Then there is the winding excitation stage, at this time, both the upper and lower switch tubes driving the motor winding of this phase are turned on. The DOWN signal is maintained at 0, and the lower switching tube M2 is kept on; at the same time, the upper tube drive signal UP is +3.3V, enabling the first switching circuit, and turning on the first charging circuit to charge the gate of M1, so that the upper switch The tube M1 is turned on, and at the same time, the voltage at point b is raised to the power supply voltage +120V, and the voltage at point a is also raised to the sum of the power supply voltage and the driving power supply voltage, which is +135V, and the diode D1 reverses to cut off. The charge on the lifting capacitor C2 continues to maintain the charge required for the upper switch M1 to be turned on;

(3) Next, in the PWM mode, the upper tube drive signal UP alternately appears +3.3V and 0, the lower tube drive signal DOWN remains at 0, and the winding also enters the freewheeling phase and excitation phase alternately. The state of the lower switching tube is consistent with (1) the charging phase of the bootstrap capacitor.

(4) Finally enter the winding turn-off stage, at this time, the upper and lower switching tubes driving the motor winding of this phase are both turned off, the UP signal is 0, and the DOWN signal is +3.3V. At the same time, the other phase in the 3-phase winding starts to enter the above-mentioned working mode.

Figure 3 shows the drive signal UP of the upper switching tube and the gate of the upper switching tube M1 of the bootstrap drive circuit of the switched reluctance motor with low cost and high isolation characteristics described in steps (1)-(4) working in PWM mode The signal graph above.

Claims (7)

1. A low-cost, high-isolation switched reluctance motor bootstrap drive circuit is characterized in that: it comprises an upper switch tube drive circuit and a lower switch tube drive circuit; the input signal of the upper switch tube drive circuit includes a drive The power supply and the upper tube drive signal, the output terminal is connected to and drives the gate of the upper switch tube, the drain of the upper switch tube and one end of the motor winding; the input signal of the lower switch tube drive circuit includes the drive power supply, the weak current power supply and the lower tube Drive signal, the output terminal is connected to and drives the gate of the lower switching tube; the drain of the upper switching tube and the source of the lower switching tube are connected in series with motor windings; the driving circuit of the upper switching tube includes a first switching circuit, a first A charging circuit, a first discharging circuit, a bootstrap capacitor, and a bootstrap diode; the lower switching transistor drive circuit includes a second switching circuit, a second charging circuit and a second discharging circuit. 2. The low-cost, high-isolation switched reluctance motor bootstrap drive circuit according to claim 1, characterized in that: the first switch circuit includes a first resistor, a photocoupler, a second resistor and a fifth Resistor; wherein the first resistor is connected in series between the upper tube drive signal and the input terminal of the internal light-emitting diode of the photocoupler; the output terminal of the internal light-emitting diode of the photocoupler is connected to the ground wire; the emitter of the internal triode of the photocoupler The five resistors are then connected to the ground wire; the collector of the internal triode of the photocoupler is connected to the connection point between one end of the second resistor and the base of the first triode in the first charging circuit. 3. The switched reluctance motor bootstrap drive circuit with low cost and high isolation characteristics according to claim 1, characterized in that: the first charging circuit includes a first triode, a second diode and a third resistance; wherein the base and the emitter of the first triode are respectively connected to the two ends of the second resistor in the first switch circuit, and the emitter of the first triode is respectively connected to one end of the bootstrap capacitor and the bootstrap diode The negative terminal of the first triode is connected in series with the second diode and one end of the third resistor in series, and is connected with the base of the second triode in the first discharge circuit and one end of the fourth resistor ; After the other end of the third resistor is connected to the emitter of the second triode in the first discharge circuit, it is connected to and drives the gate of the upper switching tube. 4. The switched reluctance motor bootstrap drive circuit with low cost and high isolation characteristics according to claim 1, characterized in that: the first discharge circuit comprises a second triode and a fourth resistor; wherein the fourth resistor The two ends are respectively connected to the base and collector of the second triode; the collector of the second triode is connected to the drain of the upper switching tube and one end of the motor winding. 5. The low-cost, high-isolation switched reluctance motor bootstrap drive circuit according to claim 1, characterized in that: the second switch circuit includes a fourth triode, a sixth resistor, a seventh resistor and The ninth resistor; the base of the fourth triode is connected to the weak current power supply, the emitter of the fourth triode is connected in series with the seventh resistor and then connected to the drive signal of the lower tube, the collector of the fourth triode is connected to the sixth resistor One end of the charging circuit and the base of the third triode in the second charging circuit are connected. 6. The switched reluctance motor bootstrap drive circuit with low cost and high isolation characteristics according to claim 1, characterized in that: the second charging circuit includes a third triode and an eighth resistor; wherein the third three The base and the emitter of the transistor are respectively connected to the two ends of the sixth resistor in the second switch circuit, the emitter of the third transistor is connected to the drive power supply, and the base of the third transistor is connected to the second switch circuit connected to the collector of the fourth transistor in the circuit; one end of the eighth resistor is connected to the collector of the third transistor, and the other end is connected to the collector of the fifth transistor in the second discharge circuit, connected and driven The gate of the lower switch tube. 7. The switched reluctance motor bootstrap drive circuit with low cost and high isolation characteristics according to claim 1, characterized in that: the second discharge circuit includes a fifth triode; the base of the fifth triode It is connected in series with the ninth resistor in the second switch circuit and then connected to the driving signal of the lower tube, and the emitter of the fifth triode is connected to the ground wire.

Images