Function and principle of motor drive system

The drive motor and the drive motor controller are the core components of the new energy vehicle driving system, which determines the main performance indicators of the vehicle and has an important impact on the dynamic, economic and control stability of the whole new energy vehicle.

The motor controller obtains the torque demand of the whole vehicle from the vehicle controller and the electrical energy from the power battery pack. Through the modulation of its own inverter, it obtains the current and voltage required to control the motor and provides it to the motor, so that the speed and torque of the motor can meet the driving needs of the whole vehicle.

1. Drive motor

(1) Composition and function of the drive motor

Permanent magnet synchronous motors are divided into sine wave permanent magnet synchronous motors and square wave-driven permanent magnet synchronous motors, which mainly provide driving force for vehicle driving and are power devices for electric vehicles.

Permanent magnet synchronous motor is mainly composed of stator and rotor, end cover, bearing, rotary transformer and other components.

(2) Working principle of permanent magnet synchronous motor

Permanent magnet in permanent magnet synchronous motor means that the rotor of the motor is a permanent magnet (permanent magnet), synchronization means that the rotor frequency is the same as the stator frequency, and the motor refers to the device that converts electrical energy into mechanical energy.

The permanent magnet synchronous motor rotates the outer magnetic field through electric magnetization. When the stator's outer magnetic field rotates, it can make the inner rotor permanent magnet follow the rotation through the principle of heterosexual attraction and same-sex repulsion of the magnetic field.

2. Motor controller

(1) Drive motor controller structure

The motor controller contains an inverter (DC/AC) and a DC converter (DC/DC); the inverter consists of IGBT, DC bus capacitor, drive and control circuit board to realize the transformation between DC (variable voltage, current) and AC (variable voltage, current, frequency). The DC converter is composed of high and low voltage power device transformers, inductors, drives and control circuit boards, etc., to realize the energy transfer from DC high voltage to DC low voltage. The motor controller also includes a cooler (through coolant) to dissipate heat to the electronic power device.

(2) Drive motor controller function

The motor controller is installed in the front cabin and adopts CAN communication control to control the transmission of energy between the power battery pack and the motor. At the same time, it collects the motor position signal and the three-phase current detection signal to control the operation of the drive motor.

The motor controller is a device that can not only convert direct current in the power battery into alternating current to drive the motor, but also has the device that converts the kinetic energy of wheel rotation into electric energy (AC to direct current) to charge the power battery.

Its main principle is: the motor is connected to the power supply, generating current and building a magnetic field. The alternating current generates an alternating magnetic field. When the winding is arranged at a certain angle in physical space, a circular rotating magnetic field will be generated. The motion is relative, which means that the magnetic field is cut by the conductor in its space range, so the induced electromotive force is established at both ends of the conductor. Through the conductor itself and the connecting parts, a loop is formed, generating a current and forming a current-carrying conductor. The current-carrying conductor will be affected by a force in the rotating magnetic field, which becomes the force in the output torque of the motor.

When the electric vehicle decelerates and brakes, that is, when the power supply is removed, the motor of the electric vehicle rotates inertially. At this time, it switches through the circuit.

The excitation power supply with relatively small power is provided to the rotor to generate a magnetic field. The magnetic field cuts the winding of the stator through the physical rotation of the rotor, so the stator senses the electromotive force and becomes a reverse electromotive force. At this time, the motor is equivalent to the function of the generator. The generated current generated is connected to the battery through the power changer, which is an energy feedback. At this point, the braking energy recovery process is completed.

(3) Working characteristics

VCU calculates the motor torque command request signal based on the acceleration pedal position, braking and gear, and torque limit signal received from each system.

Drive

UNDER DRIVING READY (OK), VCU CONTROLS THE MCU TO DRIVE THE VEHICLE THROUGH THE TARGET TORQUE.

Brake first

When VCU detects the acceleration pedal APS and brake pedal BPS input signals at the same time, the braking function is preferred, and VCU only responds to braking requests.

Charging and stopping

When any fast charging or slow charging connection signal is detected to be effective, and the motor speed is less than the set value, the VCU controls that the torque output of the motor controller is always 0, and the MCU enabling energy is 0.

Torque control of motor system

After the high-voltage power is completed, the VCU sends an enabling signal to the MCU, and the vehicle enters the driving state.

VCU calculates the driver's requested torque according to the acceleration pedal opening signal, brake pedal, gear signal, speed signal (motor speed signal), battery state and motor state.

VCU sends motor forward and back signals and torque command signals to MCU through CAN information, which controls the motor to drive the vehicle.