The fundamental difference between the brush less motor and the brush motor is that the electronic commutator is used to replace the mechanical commutator of the brush motor, so the control methods are quite different and the complexity is obviously improved. In the BLDCM controller, six power MOSFETs are used to form the electronic commutator, whose structure is shown in Figure 2. In the figure, MOSFET tubes VT1 and vt4 constitute the bridge arm of phase a winding of BLDCM, VT3 and VT6 constitute the bridge arm of phase B winding of BLDCM, and vT5 and vt2 constitute the bridge arm of phase C winding of BLDCM. In any case, the upper and lower tubes of the same bridge arm cannot be connected at the same time, or the tubes will be burned.

When six power MOSFETs are turned on in sequence according to certain requirements, the three-phase windings of a, B and C of the BLDCM can be turned on in turn, and the commutation requirements can be completed, and the motor can operate normally. In the controller of electric vehicle's BLDCM, these six power tubes have the use of two-way and three-way power on modes. Two-way power on means that two power tubes are powered on at the same time in each instant, and three-way power on means that three power tubes are powered on at the same time in each instant. For the two-way power on mode, the power tube must follow the power on sequence of VT1, vt2; vt2, VT3; VT3, vt4; vt4, vT5; vT5, VT6; VT6, VT1; VT1, vt2, so that the motor can operate normally. For the three-way power on mode, the power tube must be powered on in the order of VT1, vt2, VT3; vt2, VT3, vt4; vT5, VT6; vT5, VT6, VT1; VT6, VT1, vt2; VT1, vt2, VT3, so that the motor can operate normally.

2. The driving circuit of the power transistor front stage is used to drive six MOSFETs of the electronic commutator. Because six MOSFETs constitute three identical bridge arms, the driving circuit of the three identical bridge arms is the same, so the driving circuit of the power transistor front stage is composed of three groups of circuits with the same structure. 3 shows a typical power transistor front stage Driving circuit, for a brushless controller, there are three such circuits, respectively driving three bridge arms.

3. MCU main control circuit

The main control circuit of single-chip microcomputer is the core part of the controller of BLDCM. The hall signal, turning signal, over-current detection signal and brake signal of the motor are all directly input to the single-chip microcomputer, which processes them and outputs the front drive signals of the three bridge arms of the electronic commutator to control the operation of the motor. Therefore, the main control circuit of the single-chip microcomputer is the BLDCM The heart part of the controller. Pic16f72 is the main control chip of the electric vehicle's BLDCM controller, which determines the pulse width of the output drive signal and the speed of the motor. At present, the output signal voltage of the handle of the electric vehicle on the market is generally 1 ~ 4.2V, which is composed of a linear Hall element and a magnet. When the handle is rotated and the magnet moves, the hall element senses the changing magnetic field and outputs the changing voltage.

4. Speed limit circuit

The speed limiting circuit is to reduce the maximum voltage signal sent to the single chip microcomputer through the partial voltage resistance, thus limiting the speed. When the split terminal is grounded, r67 and R68 form a voltage dividing circuit to reduce the voltage of the 5-pin input signal (spsig) to the single chip microcomputer, thus limiting the maximum speed of the electric vehicle.

5. Hall signal detection circuit

Resistance r31-r36 and capacitance c16-c18 form the input circuit of Hall signal detection. Resistance r34-r36 forms pull-up potential, while capacitance c16-c18 plays the role of filtering and suppressing interference signals. The 15, 16 and 17 pins of the single chip microcomputer respectively detect three channels of hall position signals from the motor to determine the commutation time.

6. Undervoltage detection circuit

Components r70, R71, R72 and C23 form a battery voltage detection circuit, and the detection value is sent to the three pins of the single-chip microcomputer. When the detection value of the pin is lower than a certain value, the controller of the BLDCM can be forced not to work, so as to protect the battery.

8. The power circuit in the BLDCM controller generally requires two sets of power supply, one is 14V power supply for MOSFET driving, the other is 5V power supply for the single chip microcomputer, motor Hall, handlebar hall and other circuits. 14V power supply is generally obtained from LM317 regulator, and 5V power supply is generally obtained from 78l05.

9. Current limiting / over-current protection circuit

The current limiting protection is to control the BLDCM controller to work under a certain maximum limiting current value. For 36V controller, the current limiting value is generally 14 ± 1a, for 48V controller, the current limiting value is generally 17 ± 1a. In fact, the current limiting protection is overload protection. When the slope and load are going up, the load will increase and the current will increase, but the limit of current increase is the current limiting value.