First, let me introduce what an electric vehicle motor controller is.
(I) Introduction to Motor Controllers
In simple terms, a motor controller consists of peripheral components and a main chip (or microcontroller). Peripheral components are functional devices such as actuators and samplers; these include resistors, sensors, bridge switching circuits, and devices that assist the microcontroller or dedicated integrated circuits in completing the control process. The microcontroller, also known as a microprocessor, is a computer chip that integrates memory, a decoder for changing signal language, a sawtooth wave generator, pulse width modulation circuitry, a drive circuit that controls the power transistors in the switching circuit to turn them on or off, controls the on-time of the power transistors using square waves to control the motor speed, and input/output ports, all on a single integrated chip. This is the intelligent controller for electric vehicles.
The design quality and characteristics of the controller, the functionality of the microprocessor used, the power switching device circuitry, and the layout of peripheral components directly affect the performance and operating status of the entire vehicle, as well as the performance and efficiency of the controller itself. Controllers of different qualities, used in the same vehicle and equipped with the same set of batteries with the same charge/discharge state, can sometimes show significant differences in driving range.
Since we've mentioned the driving range of electric vehicles, let me explain what driving range is:
Driving range refers to the distance an electric vehicle travels from the moment its battery is fully charged until the end of the standard-specified test.
Methods to extend driving range:
1. Select batteries with high specific energy.
2. Reduce energy loss in various aspects of EV (electric vehicle) operation.
3. Reduce the energy consumption of EV auxiliary systems by automatically controlling functions such as air conditioning and power steering.
4. When designing a new EV, the vehicle weight and drag should be reduced as much as possible in terms of styling, structure, materials and accessories.
(ii) Protection functions of the motor controller
The protection function refers to the protective measures taken by the circuit based on feedback signals when faults occur, such as over-discharge of the commutation power transistor in the controller, over-discharge of the power supply, and potential damage to the motor due to certain faults or misoperations during operation. The basic protection functions and extended functions of an electric vehicle are as follows:
1. Brake power off
During braking, the internal switch is either closed or opened, changing its original switching state. This change generates a signal that is transmitted to the control circuit. The circuit, according to a preset program, issues a command to immediately cut off the base drive current, thus stopping the power supply. Therefore, this protects both the power transistor and the motor, and also prevents power waste.
2. Undervoltage protection
This refers to the power supply voltage. During the final stage of discharge, under load, the power supply voltage approaches the "discharge termination voltage," and the controller panel (or instrument panel) displays a low battery warning, alerting the driver to plan their trip. When the power supply voltage reaches the discharge termination voltage, the voltage sampling resistor feeds shunt information to the comparator, and the protection circuit issues a command according to a pre-set program to cut off the current to protect the electronic components and the power supply.
3. Overcurrent protection
Excessive current can damage or even burn out a range of components in the motor and circuitry, which should absolutely be avoided. Control circuits must have overcurrent protection to cut off the current after a certain delay when an overcurrent occurs.
4. Overload protection
Overload protection and overcurrent protection are the same; exceeding the load limit will inevitably cause the current to exceed the limit.
5. Underspeed protection
It still falls under the category of overcurrent protection and is designed for brushless control systems that do not have a 0-speed start function.
This is a controller we saw at the China International Industry Fair. The text in the picture might not be very clear, but this controller has the following features:
1. The main controller adopts an advanced horizontal-to-vertical installation method, which provides natural vertical convection air for the controller's heat dissipation, resulting in a more significant heat dissipation effect.
2. The IP54 (dustproof and waterproof) protection rating eliminates installation restrictions for the controller.
3. A unique four-point damping structure eliminates resonant frequencies, protecting the controller from reliability issues caused by long-term vibration.
4. The internal DC bus section adopts a fully laminated structure, controlling the total stray inductance of the busbar (a busbar in a power supply system refers to the copper or aluminum busbar connecting the main switch and the switches in each branch circuit in the electrical cabinet. Its surface is insulated and its main function is to act as a conductor) to around a few nH. This not only improves EMI characteristics but also further enhances power supply utilization. Note: EMI is a type of filter, typically a low-pass filter circuit composed of series reactors and parallel capacitors. Its function is to allow normally operating frequency signals to enter the equipment while significantly impeding high-frequency interference signals.
5. The control signal interface, motor sensor signal interface, and communication and debugging interface are independently led out, which facilitates the layout of the vehicle wiring harness and further reduces interference.
6. Comprehensive I/O interface, configurable for different applications, supporting both CAN bus control and wire harness control.
Note:
a. Any device that can be connected to other devices on the machine belongs to the I/O interface.
b. CAN bus is a communication method and cannot directly control electrical appliances. For example, when reversing, the reverse light turns on. The reverse switch is the control terminal, and the reverse light is the electrical appliance. The traditional connection is directly from the reverse switch to the reverse light. If it is necessary to control through the CAN bus, two controllers (A and B) must be added. Controller A is used to collect the signal from the reverse switch and send the reverse signal through the CAN bus. Controller B is used to receive the CAN bus signal and extract the reverse signal from the received data to realize the function of the reverse light turning on when reversing.
(In existing vehicle models that use CAN bus communication, A may be TCU, i.e., automatic transmission controller, and B may be BCM, i.e., body control module.)
