The role of frequency converters in electric vehicles
The vector inverter (motor controller) in an electric vehicle converts the direct bai flow power source into an AC output to drive a three-phase motor and then converts electrical energy into mechanical energy to drive the car.
It is the core part of the entire electric drive system, so its control performance is directly related to the reliable and efficient operation of the drive motor, which will affect the dynamic performance of the entire vehicle and the comfort of passengers.
The core requirements for the inverter to construct its control system are:
1. Safe and reliable power-on sequence control.
The power and electricity on the motor controller must be controlled in a certain time sequence, otherwise the controller will be damaged. When the driver presses the motor controller closing button, the motor controller closes the pre-charge contactor after receiving the vehicle controller closing command, so that the battery pack slowly charges the capacitor bank in the motor controller through the pre-charging resistor.
After detecting that the DC bus voltage reaches 90% of the rated input voltage, the controller closes the contactor of the motor controller and cuts off the pre-charge contactor at the same time. At this time, the main power of the motor controller is completely connected to the battery pack to complete the main power-on process.
2. High-performance control algorithm.
The vector control algorithm (field-oriented control) is a leap forward in AC speed regulation technology. It realizes the decoupling control in the AC motor through the orientation of the motor flux, so that the amplitude and spatial position of the motor flux vector are in a dynamic and It can be controlled in steady state, so that the steady state and dynamic performance of AC motor speed control can be comparable to that of DC motor speed control system, and even surpass the latter in some cases.
In this way, this algorithm is applied to the field of electric vehicles, which satisfies the large torque of electric vehicles at low speeds, and ensures that they have good acceleration performance and climbing ability; at the same time, it also satisfies its wide speed range to make electric vehicles The car has the performance of high-speed driving on flat roads.
3. Optimal energy utilization.
The optimal utilization of energy is another basic requirement for electric vehicles, requiring its control system to use energy as much as possible, including the use of overheating and regenerative braking energy, so that limited energy can be fully utilized. Ability feedback can achieve this function.
It includes two types: vehicle braking capability feedback and vehicle gliding capability feedback. In the feedback state, the drive motor operates as a generator and converts the kinetic energy of the vehicle into electrical energy.
It can play three functions: assisting braking; reclaiming energy to charge the power battery, thereby extending the driving range of the vehicle; When required, this part of the electric energy can be directly used for heating.
The main advantages of inverter products used in electric vehicles are:
1. Reliability: triple overcurrent protection, triple overvoltage protection, triple drive protection to ensure reliable and stable operation of the motor controller.
2. Superior control strategy: The motor controller adopts vector control technology, which has superior performance and high reliability, and is suitable for AC asynchronous or permanent magnet synchronous motors;
3. Large-capacity output capability: The motor output end does not need to be equipped with a gearbox or reducer, which greatly reduces the point of failure and the noise of the mechanical transmission system, saves costs, simple control mode, higher reliability, and good vehicle running stability;
4. Excellent power performance: good acceleration performance (0～50km/h in 15 seconds), and good economic performance (0.9 degrees/km @40km/h);
5. Fault diagnosis and treatment: In order to improve the reliability of the whole vehicle, the motor control system must have fault diagnosis function and be able to save the fault for future analysis. In addition, the motor controller can be debugged online and recorded through the diagnosis port. Running curve, convenient to optimize the entire control system;
6. Efficient braking energy recovery: Give full play to the structural advantages of the power system of pure electric vehicles, improve energy utilization, and the motor control system must have the braking energy recovery function.
7. Simplicity: The motor controller has reliable quality, light weight, easy layout, and convenient wiring maintenance. The industrialization prospect is very good.