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Principle of BLDC Motor Controller for Electric Vehicle
Brushless DC motor controller of electric vehicle mainly consists of MCU main control circuit, power tube pre-stage drive circuit, electronic commutator, Hall signal detection circuit, switch signal circuit, undercurrent detection circuit, current limiting/overcurrent detection circuit, brake signal circuit, speed limiting circuit, power supply circuit and so on.
Electronic Commutator
The fundamental difference between brushless DC motor and brushed motor is that brushless DC motor uses electronic commutator instead of mechanical commutator, so the control methods are different and the complexity is obviously improved. In the brushless DC motor controller, an electronic commutator is composed of six power MOSFET transistors. Its structure is shown in Figure 1. In the figure, the bridge arm of phase A winding of brushless DC motor is composed of MOSFET tube VT1 and VT4, the bridge arm of phase B winding of motor is composed of VT3 and VT6, and the bridge arm of phase C winding of motor is composed of VT5 and VT2. In any case, the upper and lower tubes of the same bridge arm can not be connected at the same time, otherwise the tube will be burned out.
Fig.1 Electronic commutator drive circuit
Six power MOSFET transistors can turn on sequentially according to certain requirements, so as to realize the rotating current of three-phase windings A, B and C of brushless DC motor, complete the commutation requirements and make the motor run normally.
Power Tube Pre-stage Drive Circuit
The power tube pre-stage driving circuit is used to drive the six MOSFET tubes of the electronic commutator. Since the six MOSFET tubes form three identical bridge arms, the driving circuits for the three identical bridge arms are the same, and thus the power tube The pre-driver circuit is composed of three sets of circuits of the same structure. Figure 2 shows a typical power tube pre-stage drive circuit. For a brushless controller, there are three such circuits, respectively driving three bridge arms.
Fig.2 Power tube pre-stage driving circuit
MCU Main Control Circuit
The main control circuit of single chip computer is the core part of the brushless DC motor controller. The Hall signal, turn signal, overcurrent detection signal and brake signal of the motor are directly input to the single chip computer. The single chip computer processes them and outputs the front driving signals of three bridge arms of the electronic commutator by the single chip computer to control the operation of the motor. Therefore, the main control circuit of single chip computer is the controller of the brushless DC motor. The heart part. Figure 3 shows the typical application circuit of the brushless controller. It includes the main input and output signals of the brushless DV motor controller. The signal is sent to the fifth foot of the single chip computer through the network composed of resistance R69 and R68. According to the voltage signal of the foot, the single chip computer determines the pulse width of the output driving signal, thereby deciding the speed of the motor.
Fig.3 BLDC motor ontroller driving circuit
Speed Limiting Circuit
The speed-limiting circuit reduces the maximum voltage signal of the switch fed into the single-chip computer by dividing the voltage resistance, thus limiting the speed. If the SPLIMT terminal is grounded in Figure 3, R67 and R68 form a voltage dividing circuit, which reduces the voltage of the five legs of the SPSIG into the MCU, thus limiting the maximum speed of the electric vehicle.
Hall Signal Detection Circuit
In Figure 3, resistance R31 ~ R36 and capacitance C16 ~ C18 constitute Hall signal detection input circuit. Resistance R34 ~ R36 forms pull-up potential. Capacitance C16 ~ C18 acts as filter to suppress interference signal. The 15, 16 and 17 feet of the single chip computer detect the three Hall position signals from the motor respectively to determine the commutation time.
Undervoltage Detection Circuit
In Figure 3, the components R70, R71, R72 and C23 constitute the battery voltage detection circuit. The detection value is fed into the three legs of the single chip computer. When the detection value of the legs is lower than a certain value, the brushless motor controller can be forced to not work, thus protecting the battery.
Brake Signal Circuit
For electric bicycles, when the handlebar brakes, the single-chip computer gets the braking signal, the brushless motor controller stops output control signal, and the motor is cut off. This is called braking power. For some brushless controllers, when the single-chip computer gets the braking signal, the control signal is output, forcing the motor to hold, so that the motor can not rotate. This is called electric braking. At present, there are two kinds of braking signals for electric brakes on the market, high-level braking signal and low-level braking signal. Generally, only one of them can be recognized for single-chip microprocessors. If level conversion circuit is used, two kinds of braking signals can be identified. In Figure 4, when the BK signal terminal is low level, the 7th foot of MCU obtains the low level braking signal and informs the brushless controller to complete the braking process. When the HBK terminal is at high level, the level conversion is completed by resistors R66, R81, R88 and transistor VT20, the collector of transistor VT20 becomes low level, and the 7th foot of single chip computer is low. The brushless controller is notified to complete the braking action.
Power Circuit
In the controller of brushless DC motor, two sets of power supply are generally needed, one is 14V power supply for power MOSFET drive, the other is 5V power supply for MCU, motor Hall, switch Hall and other circuits. The 14V power supply is generally obtained by LM317 regulator, and the 5V power supply is generally obtained by 78L05. The circuit program is shown in Fig.4.
Fig.5 Power circuit
Current Limiting/Overcurrent Protection Circuit
Current limiting protection is to control the brushless motor controller to work under a certain maximum limit current value. For 36V controller, the current limiting value is generally 14 + 1A, and for 48V controller, the current limiting value is generally 17 + 1A. Current limiting protection is actually overload protection. When uphill, load will inevitably lead to load aggravation and current increase, but the limit of current increase is current limiting value. In Figure 3, the operation and resistance R73, R74, R75, R76 and RT of IC6B (LM358) constitute the current limiting signal detection circuit. RT is a resistance wire connected in series to the MOSFET tube, as shown in Figure 3.
Electronic Commutator
The fundamental difference between brushless DC motor and brushed motor is that brushless DC motor uses electronic commutator instead of mechanical commutator, so the control methods are different and the complexity is obviously improved. In the brushless DC motor controller, an electronic commutator is composed of six power MOSFET transistors. Its structure is shown in Figure 1. In the figure, the bridge arm of phase A winding of brushless DC motor is composed of MOSFET tube VT1 and VT4, the bridge arm of phase B winding of motor is composed of VT3 and VT6, and the bridge arm of phase C winding of motor is composed of VT5 and VT2. In any case, the upper and lower tubes of the same bridge arm can not be connected at the same time, otherwise the tube will be burned out.
Fig.1 Electronic commutator drive circuit
Power Tube Pre-stage Drive Circuit
The power tube pre-stage driving circuit is used to drive the six MOSFET tubes of the electronic commutator. Since the six MOSFET tubes form three identical bridge arms, the driving circuits for the three identical bridge arms are the same, and thus the power tube The pre-driver circuit is composed of three sets of circuits of the same structure. Figure 2 shows a typical power tube pre-stage drive circuit. For a brushless controller, there are three such circuits, respectively driving three bridge arms.
Fig.2 Power tube pre-stage driving circuit
The main control circuit of single chip computer is the core part of the brushless DC motor controller. The Hall signal, turn signal, overcurrent detection signal and brake signal of the motor are directly input to the single chip computer. The single chip computer processes them and outputs the front driving signals of three bridge arms of the electronic commutator by the single chip computer to control the operation of the motor. Therefore, the main control circuit of single chip computer is the controller of the brushless DC motor. The heart part. Figure 3 shows the typical application circuit of the brushless controller. It includes the main input and output signals of the brushless DV motor controller. The signal is sent to the fifth foot of the single chip computer through the network composed of resistance R69 and R68. According to the voltage signal of the foot, the single chip computer determines the pulse width of the output driving signal, thereby deciding the speed of the motor.
Fig.3 BLDC motor ontroller driving circuit
The speed-limiting circuit reduces the maximum voltage signal of the switch fed into the single-chip computer by dividing the voltage resistance, thus limiting the speed. If the SPLIMT terminal is grounded in Figure 3, R67 and R68 form a voltage dividing circuit, which reduces the voltage of the five legs of the SPSIG into the MCU, thus limiting the maximum speed of the electric vehicle.
Hall Signal Detection Circuit
In Figure 3, resistance R31 ~ R36 and capacitance C16 ~ C18 constitute Hall signal detection input circuit. Resistance R34 ~ R36 forms pull-up potential. Capacitance C16 ~ C18 acts as filter to suppress interference signal. The 15, 16 and 17 feet of the single chip computer detect the three Hall position signals from the motor respectively to determine the commutation time.
Undervoltage Detection Circuit
In Figure 3, the components R70, R71, R72 and C23 constitute the battery voltage detection circuit. The detection value is fed into the three legs of the single chip computer. When the detection value of the legs is lower than a certain value, the brushless motor controller can be forced to not work, thus protecting the battery.
Brake Signal Circuit
For electric bicycles, when the handlebar brakes, the single-chip computer gets the braking signal, the brushless motor controller stops output control signal, and the motor is cut off. This is called braking power. For some brushless controllers, when the single-chip computer gets the braking signal, the control signal is output, forcing the motor to hold, so that the motor can not rotate. This is called electric braking. At present, there are two kinds of braking signals for electric brakes on the market, high-level braking signal and low-level braking signal. Generally, only one of them can be recognized for single-chip microprocessors. If level conversion circuit is used, two kinds of braking signals can be identified. In Figure 4, when the BK signal terminal is low level, the 7th foot of MCU obtains the low level braking signal and informs the brushless controller to complete the braking process. When the HBK terminal is at high level, the level conversion is completed by resistors R66, R81, R88 and transistor VT20, the collector of transistor VT20 becomes low level, and the 7th foot of single chip computer is low. The brushless controller is notified to complete the braking action.
Power Circuit
In the controller of brushless DC motor, two sets of power supply are generally needed, one is 14V power supply for power MOSFET drive, the other is 5V power supply for MCU, motor Hall, switch Hall and other circuits. The 14V power supply is generally obtained by LM317 regulator, and the 5V power supply is generally obtained by 78L05. The circuit program is shown in Fig.4.
Fig.5 Power circuit
Current limiting protection is to control the brushless motor controller to work under a certain maximum limit current value. For 36V controller, the current limiting value is generally 14 + 1A, and for 48V controller, the current limiting value is generally 17 + 1A. Current limiting protection is actually overload protection. When uphill, load will inevitably lead to load aggravation and current increase, but the limit of current increase is current limiting value. In Figure 3, the operation and resistance R73, R74, R75, R76 and RT of IC6B (LM358) constitute the current limiting signal detection circuit. RT is a resistance wire connected in series to the MOSFET tube, as shown in Figure 3.
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