CN101714845B - Drive circuit of brushless DC motor - Google Patents

Abstract

The invention relates to a driving circuit of a brushless DC motor which can effectively reduce the switching loss of a switch tube and has a long service life, which comprises: a single chip microcomputer and three groups of two motor coils respectively used for connecting with the three groups of motor coils in the brushless DC motor The power supply circuit connected to the end; the single-chip microcomputer controls the PWM signal output of the PWM signal generation circuit in each power supply circuit according to the DC sampling signal and the voltage division sampling signal measured by the DC sampling and voltage division sampling loop in each power supply circuit. Duty ratio to adjust the current and voltage in the secondary loop of the transformer in each power supply circuit; at the same time, the single-chip microcomputer controls the three AND gate control output terminals to output corresponding voltages according to the Hall signals from the Hall sensors. level, so as to respectively control the oscillation state of the LC resonant circuits in each power supply circuit, so that the three sets of power supply circuits can generate three-phase power suitable for driving a three-phase brushless DC motor.

Description

Drive circuit for brushless DC motor

technical field

The invention relates to a driving circuit of a brushless direct current motor.

Background technique

The driver of the three-phase brushless DC motor includes a power supply part and a control part. The power supply part provides three-phase power to the motor, and the control part converts the input power frequency according to the demand.

The DC voltage of the power supply is converted into 3-phase voltage by the inverter to drive the motor. The inverter is generally divided into upper arm (Q1, Q3, Q5)/lower arm (Q2, Q4, Q6) by 6 power transistors (Q1~Q6) connected to the motor as a switch to control the flow through the motor coil. The control part provides PWM (pulse width modulation) to determine the switching frequency of the power transistor and the timing of the commutation of the inverter. During the use of the brushless DC motor, the speed can be stabilized at the set value when the load changes. The Hall sensor that can sense the magnetic field is installed inside the motor, which is used as a closed-loop control of the speed and also as a basis for phase sequence control. .

When the motor rotor rotates to the position where the Hall sensor senses another set of signals, the control part turns on the next set of power transistors, so that the cycle motor can continue to rotate in the same direction, until the control part decides to stop the motor rotor, it turns off The power transistor (or only turn on the lower arm power transistor); if the motor rotor is to be reversed, the power transistor is turned on in the opposite order. When the motor starts to rotate, the control part will compare the speed control command set by the driver with the speed of the signal change of the Hall sensor (or calculate by software) to determine the conduction of the next group of switches and the conduction time. If the speed is not enough, it will be long, and if the speed is too high, it will be shortened. This part of the work is done by PWM.

The disadvantage of the above-mentioned prior art is that: the on-off of the power transistor, that is, the VMOS switch tube, is directly controlled by the PWM rectangular wave output by the controller, so that the turn-on voltage or the turn-off voltage of the VMOS switch tube when it is turned on or off is often relatively low. High, resulting in switching loss and severe heating of the switch tube, which not only wastes electric energy, but also affects its switching characteristics and service life, which in turn affects the service life of the entire drive circuit.

Contents of the invention

The technical problem to be solved by the present invention is to provide a driving circuit of a brushless DC motor which can effectively reduce the switching loss of the switching tube and has a long service life.

In order to solve the problems of the technologies described above, the drive circuit of the brushless DC motor of the present invention includes: a single-chip microcomputer IC4 and three groups of power circuits that are respectively connected to the two ends of the three groups of motor coils in the brushless DC motor; each power circuit includes: A pulse transformation circuit 2 composed of a DC power supply 1, a switching tube VMOS and a transformer T, and an LC resonant circuit composed of a primary coil of the transformer T and a resonant capacitor C3 connected in parallel with it, are used to control the resonant circuit of the LC resonant circuit. A synchronous control circuit 5 for switching the switching tube VMOS on and off at the same frequency, a rectification circuit, a DC sampling and a voltage division sampling circuit 3 located at the secondary side of the transformer T, and a waveform rectification filter circuit 4 located at the secondary side of the transformer T; The output end of described rectification circuit is the output end that is used to connect motor coil of power supply circuit; Synchronous control circuit 5 comprises: PWM signal generating circuit and AND gate circuit IC5; Described single-chip microcomputer IC4 has: for three respectively and no The Hall signal input terminals connected to the three Hall sensors in the brushed DC motor, and the three sampling voltage detection terminals A connected to the sampling voltage output terminals of the DC sampling and voltage-dividing sampling circuits 3 in the three groups of power circuits respectively / D0, A/D1 and A/D2, and three PWM pulse width control output terminals D/A0, D/ A1 and D/A2; the PWM signal output terminal of the PWM signal generating circuit is connected with the first input terminal of the AND gate circuit IC5, and the single-chip microcomputer IC4 also has the second gate circuit IC5 respectively connected with the three groups of power supply circuits. The three AND gates connected to the input terminals control the output terminals P1.0, P1.1 and P1.2, and the output terminal of the AND gate circuit IC5 is connected to the gate of the switching tube VMOS; the PWM signal generating circuit is connected in parallel with the LC resonance circuit , to generate the same PWM signal as the oscillating frequency of the LC resonant tank; the PWM signal controls the switching tube VMOS to repeatedly turn on at the zero voltage moment of the positive half-wave rising edge of the sine wave in the oscillating waveform of the LC resonant tank, and at The zero voltage moment of the falling edge of the positive half-wave is turned off.

Single-chip microcomputer IC4 controls the duty ratio of the PWM signal output by the PWM signal generating circuit in each power supply circuit according to the DC sampling signal and the voltage division sampling signal measured by the DC sampling and voltage division sampling loop 3 in each power supply circuit , to adjust the current and voltage in the secondary circuits of the transformers T1, T2 and T3 in each power supply circuit; meanwhile, the single-chip microcomputer IC4 controls the three AND gate control output terminals respectively according to the Hall signals from the Hall sensors P1.0, P1.1, and P1.2 output corresponding levels to respectively control the oscillation state of the LC resonant circuit in each power supply circuit, so that the three sets of power supply circuits generate of three-phase power.

Further, the levels of the two input ends of the first comparator IC1 change with the frequency of the oscillation of the LC resonance circuit, and constantly switch the switching tube VMOS (the switching frequency is the same as the oscillation frequency of the LC resonance circuit), so as to Make the secondary circuit of the adjustment transformer T generate a normal driving voltage.

The present invention has positive effects: (1) the synchronous control circuit of the present invention takes out the positive half wave of the resonant voltage waveform of the LC resonant circuit, to open and close the switching tube at the zero voltage moment of the positive half wave rising edge and falling edge respectively , so that the switching tube works in a close to zero voltage on or off state, greatly reducing the switching loss and heating of the switching tube, saving electric energy, and ensuring its switching characteristics and service life; (2) PWM signal generating circuit of the present invention Including a sawtooth wave generation circuit, compared with the analog output of the PWM pulse width control terminal D/A, the PWM waveform is generated, and the waveform drives the VMOS switch tube to provide energy to the LC resonant circuit through an AND gate circuit; (3) DC sampling of the present invention The divided voltage value of the sampling circuit and the divided voltage sampling circuit is sampled by the microcontroller as the basis for programming the PWM pulse width control terminal to output the analog quantity and changing the duty cycle of the second comparator output PWM; at the same time, the DC sampling and the divided voltage sampling circuit pass through the first resistor The magnitude of the sampling current is amplified by the operational amplifier and then collected by the analog-to-digital conversion port of the single-chip microcomputer to program the output analog quantity of the PWM pulse width control terminal, and the current magnitude is changed by changing the duty cycle of the PWM signal output by the second comparator.

Description of drawings

Fig. 1 is the block diagram of the drive circuit of the brushless DC motor in the embodiment;

Fig. 2 is the schematic diagram of the circuit structure of a single-chip microcomputer and a group of power supply circuits in the drive circuit of the brushless DC motor in the embodiment;

Fig. 3 is the schematic diagram of the partial circuit structure of the drive circuit of the brushless DC motor in the embodiment;

Fig. 4 is the structural representation of three groups of motor coils of the brushless DC motor in the embodiment;

Fig. 5 is the program block diagram when the single-chip microcomputer in the embodiment works;

Fig. 6 is the relationship diagram of the voltage waveform output by the AND gate control output terminal P1.0 of the single-chip microcomputer in the embodiment, the voltage waveform of the PWM signal output by the PWM signal generating circuit in the corresponding power supply circuit, and the voltage waveform of the switching tube grid;

FIG. 7 is a relationship diagram between the voltage waveform of the gate of the switching tube and the voltage waveform of the drain of the switching tube in the same power supply circuit in the embodiment.

Detailed ways

See Fig. 1-7, the driving circuit of the brushless DC motor of the present invention comprises: single-chip microcomputer IC4 and three groups are used for respectively with three groups of motor coils in the brushless DC motor (comprising: the first group of motor coils X1-X2, the second group of motor coils The two sets of motor coils X3-X4, the third set of motor coils X5-X6, see the power circuit connected to both ends of Fig. 4).

Each power supply circuit includes: a pulse transformation circuit 2 composed of a DC power supply 1, a switching tube VMOS and a transformer T, and an LC resonant circuit composed of the primary coil of the transformer T and a resonant capacitor C3 connected in parallel with it, which is used in the LC resonant circuit. The synchronous control circuit 5 that controls the switching tube VMOS to switch on and off at the same frequency during resonance, the rectification circuit, DC sampling and voltage dividing sampling circuit 3 located at the secondary side of the transformer T, and the waveform located at the secondary side of the transformer T Rectification and filtering circuit 4; the output end of the rectification circuit is the output end of the power circuit for connecting the motor coil. The rectification circuit is a half-wave rectification circuit composed of diode D1, and a full-wave rectification circuit may also be used.

The synchronous control circuit 5 includes: a PWM signal generation circuit and an AND gate circuit IC5.

The single-chip microcomputer IC4 has: three Hall signal input terminals connected respectively with three Hall sensors in the brushless DC motor, three respectively connected with the DC sampling and voltage-dividing sampling circuits in the three groups of power circuits The sampling voltage detection terminals A/D0, A/D1 and A/D2 connected to the sampling voltage output terminal of 3 are used to obtain the direct current of the direct current sampling signal measured by the direct current sampling and voltage division sampling loop 3 in each power supply circuit Sampling signal input terminals D/A3, D/A4 and D/A5, and three PWM pulse width control output terminals D connected to the PWM pulse width control input terminals of the PWM signal generating circuits in the three groups of power circuits respectively /A0, D/A1, and D/A2.

The PWM signal output end of the PWM signal generating circuit is connected with the first input end of the said AND gate circuit IC5, and the single-chip microcomputer IC4 also has three links to each other with the second input end of the described AND gate circuit IC5 in the three groups of power supply circuits respectively. The AND gate controls the output terminals P1.0, P1.1 and P1.2, and the output terminal of the AND gate circuit IC5 is connected to the gate of the switching tube VMOS.

The PWM signal generating circuit is connected in parallel with the LC resonant tank to generate a PWM signal with the same oscillation frequency as the LC resonant tank; the PWM signal controls the switching tube VMOS to repeat the positive half of the sine wave in the oscillating waveform of the LC resonant tank It is turned on at the zero voltage moment of the rising edge of the wave and turned off at the zero voltage moment of the falling edge of the positive half wave.

Single-chip microcomputer IC4 controls the duty ratio of the PWM signal output by the PWM signal generating circuit in each power supply circuit according to the DC sampling signal and the voltage division sampling signal measured by the DC sampling and voltage division sampling loop 3 in each power supply circuit , to adjust the current and voltage in the secondary circuits of the transformers T1, T2 and T3 in each power supply circuit; meanwhile, the single-chip microcomputer IC4 controls the three AND gate control output terminals respectively according to the Hall signals from the Hall sensors P1.0, P1.1, and P1.2 output corresponding levels to respectively control the oscillation state of the LC resonant circuit in each power supply circuit, so that the three sets of power supply circuits generate of three-phase power.

The PWM signal generation circuit includes: a sawtooth wave generation circuit composed of a second capacitor C2, a second diode D2, a ninth resistor R9, and a first comparator IC1, and a first connection between the output terminal and the AND gate circuit IC5. The second comparator IC2 connected to one input terminal; the two input terminals of the first comparator IC1 are respectively connected in parallel to both ends of the resonant capacitor C3 through the first voltage divider circuit and the second voltage divider circuit, and the cathode of the second diode D2 It is connected to the DC power supply VCC, the anode of the second diode D2 is connected to the inverting input terminal of the second comparator IC2, the output terminal of the first comparator IC1 is connected in series with the second capacitor C2 and then connected to the inverting terminal of the second comparator IC2 The input terminal, the ninth resistor R9 is connected in parallel with the second diode D2, and the same direction input terminal of the second comparator IC2 is connected with the PWM pulse width control terminal D/A of the single-chip microcomputer IC4; the output terminal of the second comparator IC2 It is the PWM signal output terminal of the PWM signal generating circuit.

Each power supply circuit also includes a fourteenth resistor R14 connected to an AND gate control output terminal (taking port P1.0 as an example) of the single-chip microcomputer IC4, and the other end of the fourteenth resistor R14 is connected to the third diode D3. The cathode, the anode of the third diode D3 is connected with the second input terminal of the AND gate circuit IC5, and the second input terminal of the AND gate circuit IC5 is connected with the DC power supply VCC; the cathode of the third diode D3 It is connected to the inverting input terminal of the first comparator IC1 through the sixth capacitor C6.

As shown in Figure 2, when the first group of power circuits is powered on, the AND gate control output terminal P1.0 of the single-chip microcomputer IC4 connected to the group of power circuits generates a pulse from low to high, and passes through the fourteenth resistor After R14 and the sixth capacitor C6, a high-level pulse is generated, so that the potential of the inverting input terminal of the first comparator IC1 is raised, thereby reducing the potential of the inverting input terminal of the second comparator IC2, and is lower than that of the microcontroller The potential of the PWM pulse width control terminal D/A0 connected to the group of power supply circuits of IC4 makes the second comparator IC2 output a high level. At this time, the AND gate control output terminal P1.0 is high level, so that all The AND gate circuit IC5 drives the switching tube VMOS to turn on, so that the LC resonant circuit starts to oscillate.

The level of the two input terminals of the first comparator IC1 changes with the frequency of the oscillation of the LC resonant circuit, and keeps switching the switching tube VMOS, so that the secondary circuit of the adjustment transformer T generates a normal driving voltage.

In other implementation manners, the switch tube may use components such as IGBTs.

Claims (3)

1. A drive circuit for a brushless DC motor, characterized in that it comprises: a single-chip microcomputer (IC4) and three groups of power circuits that are used to be connected to the two ends of the three groups of motor coils in the brushless DC motor respectively; Each power supply circuit includes: a pulse transformation circuit (2) composed of a DC power supply (1), a switching tube (VMOS) and a transformer (T), which is composed of the primary coil of the transformer (T) and the resonant capacitor (C3) connected in parallel with it The LC resonant circuit is used to control the synchronous control circuit (5) of the switching tube (VMOS) switching on and off at the same frequency when the LC resonant circuit resonates, and the rectifier circuit and DC sampling set on the secondary side of the transformer (T) and a voltage dividing sampling circuit (3), and a waveform rectification and filtering circuit (4) arranged on the secondary side of the transformer (T); the output end of the rectification circuit is the output end of the power circuit for connecting the motor coil; The synchronous control circuit (5) includes: a PWM signal generating circuit and an AND gate circuit (IC5); The single-chip microcomputer (IC4) has: three Hall signal input terminals respectively connected to the three Hall sensors in the brushless DC motor, three respectively connected to the DC sampling and voltage dividing in the three groups of power circuits The sampling voltage detection terminals (A/D0, A/D1 and A/D2) connected to the sampling voltage output terminals of the sampling circuit (3), and three PWM pulses respectively connected to the PWM signal generating circuits in the three groups of power supply circuits PWM pulse width control output terminals (D/A0, D/A1 and D/A2) connected to the wide control input terminals; The PWM signal output terminal of the PWM signal generating circuit is connected to the first input terminal of the AND gate circuit (IC5), and the single-chip microcomputer (IC4) also has a second terminal connected to the AND gate circuit (IC5) in the three groups of power supply circuits respectively. The three AND gate control output terminals (P1.0, P1.1 and P1.2) connected to the input terminals, and the output terminal of the AND gate circuit (IC5) are connected to the gate of the switching tube (VMOS); The PWM signal generating circuit is connected in parallel with the LC resonant tank to generate a PWM signal with the same oscillation frequency as the LC resonant tank; the PWM signal controls the switching tube (VMOS) to repeat the sine wave in the oscillating waveform of the LC resonant tank Turn on at the zero voltage moment of the rising edge of the positive half wave, and turn off at the zero voltage moment of the falling edge of the positive half wave; The single-chip microcomputer (IC4) controls the PWM signal output by the PWM signal generation circuit in each power supply circuit according to the DC sampling signal and voltage division sampling signal measured by the DC sampling and voltage division sampling circuit (3) in each power supply circuit to adjust the current and voltage in the secondary loop of the transformers (T1, T2 and T3) in each power supply circuit; At the same time, the single-chip microcomputer (IC4) respectively controls the three AND gate control output terminals (P1.0, P1.1 and P1.2) to output corresponding levels in sequence according to the Hall signals from the Hall sensors. To respectively control the oscillating states of the LC resonant circuits in each power supply circuit, so that the three sets of power supply circuits generate a three-phase power supply suitable for driving a three-phase brushless DC motor; The PWM signal generating circuit includes: a sawtooth wave generating circuit composed of a second capacitor (C2), a second diode (D2), a ninth resistor (R9) and a first comparator (IC1), and an output terminal and The second comparator (IC2) connected to the first input terminal of the AND gate circuit (IC5); the two input terminals of the first comparator (IC1) are connected in parallel through the first voltage divider circuit and the second voltage divider circuit respectively Both ends of the resonant capacitor (C3), the cathode of the second diode (D2) is connected to the DC power supply (VCC), the anode of the second diode (D2) is connected to the inverting input terminal of the second comparator (IC2), The output terminal of the first comparator (IC1) is connected in series with the second capacitor (C2) and then connected to the inverting input terminal of the second comparator (IC2), and the ninth resistor (R9) is connected in parallel with the second diode (D2), The non-inverting input terminal of the second comparator (IC2) is connected to the PWM pulse width control terminal (D/A) of the microcontroller (IC4); the output terminal of the second comparator (IC2) is the PWM signal output; Each power supply circuit also includes a fourteenth resistor (R14) connected to an AND gate control output terminal (P1.0) of the microcontroller (IC4), and the other end of the fourteenth resistor (R14) is connected to the third diode (D3) cathode, the anode of the third diode (D3) is connected to the second input terminal of the AND gate circuit (IC5), and the second input terminal of the AND gate circuit (IC5) is connected to the DC power supply ( VCC) is connected; the cathode of the third diode (D3) is connected with the inverting input terminal of the first comparator (IC1) through the sixth capacitor (C6). 2. The driving circuit of brushless DC motor according to claim 1, characterized in that: when a group of power circuits is powered on, the AND gate control output terminal ( P1.0) generates a pulse from low to high, and generates a high-level pulse after passing through the fourteenth resistor (R14) and the sixth capacitor (C6), making the reverse input of the first comparator (IC1) The potential of the terminal increases, so that the potential of the inverting input terminal of the second comparator (IC2) decreases, and is lower than that of the PWM pulse width control terminal (D/A0) of the microcontroller (IC4) connected to the power supply circuit of the group. Potential, so that the second comparator (IC2) outputs a high level, at this time the AND gate control output terminal (P1.0) is at a high level, so that the AND gate circuit (IC5) drives the switching tube (VMOS) to open , so that the LC resonant tank starts to oscillate. 3. The brushless DC motor drive circuit according to claim 1 or 2, characterized in that: the levels of the two input terminals of the first comparator (IC1) change with the same frequency as the oscillation of the LC resonant circuit, and The switching tube (VMOS) is constantly switched on and off, so that the secondary circuit of the adjustment transformer (T) can generate a normal driving voltage.

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