Foreword
With energy shortages and increasing environmental pressures, energy-saving and environmentally friendly new energy vehicles will undoubtedly become the future direction of automobile development. The United States, Japan, and Europe have successively introduced encouraging policies to support the development of electric vehicles and the marketization of electric vehicles. Major auto companies both at home and abroad have shown great enthusiasm in this field and invested huge human and material resources to develop electric vehicles. Every day in the UK, 20,000 electric vehicles deliver fresh milk to households; France has 10,000 electric vehicles; and the electric buses operated by Santa Barbara City in the US, and electric vehicles in New York City Buses are popular with the public; in Japan, the combination of EV and ITS has become a new approach to commercialization and commercialization of electric vehicles.
China has a certain gap between the research and development of electric vehicles and developed countries. However, under the support of national policies, China's electric vehicle industry has made rapid progress. The “10 cities, 1,000 vehicles†demonstration and promotion of energy-saving and new energy vehicles pilot cities and other policies and measures All provide great support for electric cars. Since 2010, the country has listed the new energy automotive industry as one of seven strategic emerging industries, formulated its mid- to long-term development goals, and proposed to “breakthrough the key core technologies in the field of power batteries, drive motors and electronic control, and push forward. The promotion and application of electric hybrid vehicles and pure electric vehicles and industrialization."
The EV550 is a dedicated drive control vector-type inverter developed by China Metallurgical South (Wuhan) Automation Co., Ltd. for electric buses.
Requirements for Electric Drive Systems for Electric Vehicles
The ultimate goal of electric vehicles is to replace the mechanical propulsion system with an electric drive system, use the battery instead of gasoline as the vehicle's energy, and to meet or exceed the technical specifications of the fuel vehicle on the premise of achieving zero emissions or reducing emissions.
Like ordinary fuel vehicles, the operating conditions of electric vehicles are complex and changeable. They must be able to fly at high speeds, and must be capable of frequent braking, ups and downs, rapid overtaking, and emergency braking. As an on-the-ground running machine on the ground, electric vehicles must also be able to adapt to adverse weather conditions such as snow, rain, summer, and severe winter, withstand the bumpy vibration of roads, and ensure the comfort and safety of drivers and passengers. Therefore, the requirements for electric drive systems for electric vehicles are very different from those for general industrial applications and can be summarized as follows:
1, has a wide range of speed and torque output capabilities. In the area below the base speed (ie, rated speed), a constant high torque should be able to output to meet the requirements of quick start, acceleration, load ramping, frequent start-stop and other requirements. In areas above the base speed, it operates at high speed, low torque, and constant power to meet the requirements of highway speeding and overtaking.
2. Maximize the efficiency within the entire speed/torque range to maximize the mileage of the battery after a single charge. Developing new batteries with higher specific power is the most fundamental solution to this problem, but improving the efficiency of motors and their electric drive systems is also an important part.
3, the motor and its electric drive system should be sturdy, small size, maintenance-free or less maintenance, anti-jump vibration, with high safety.
4. The electric motor drive motor requires high work controllability, high steady-state accuracy, and good dynamic performance;
5, advanced energy management system.
6, operating performance in line with the driver's habits, smooth operation, comfortable ride, electrical system failure protection measures to improve.
7, unit power system equipment cost-effective. At present, the cost of electric vehicles is still much higher than that of ordinary cars, which also limits the marketization of electric vehicles.
Electric vehicle electric drive system
Fig.1 Schematic diagram of the vehicle control system of China Metallurgical Southern Automation Corporation
An electric vehicle is a motor that is driven wholly or partially by motors. At present, it mainly refers to three types of pure electric vehicles, hybrid electric vehicles, and fuel cell electric vehicles. It is a collection of machinery, energy, electronics, computers, information, and other technologies. The ultimate goal of a typical high-tech product is to achieve high efficiency, zero pollution, digitization, intelligence, and lightweight, which is also superior to traditional automobiles.
The key technologies for the research and development of electric vehicles include batteries, motors, motor drive systems, body and chassis design, and energy management technologies. Among them, the first three items constitute the electric drive system of electric vehicles and the development bottleneck of electric vehicles.
The battery system serves as the power source for the vehicle. Its main function is to provide energy for the drive control system and to supplement the power with periodic charging. Power battery packs are the key equipment for electric vehicles. Its quality and volume, as well as stored energy, play a decisive role in the performance of electric vehicles. The calculated battery system uses lithium-ion batteries.
The motor and its drive control system are the heart of the electric vehicle. Its task is to efficiently convert the energy of the battery into the kinetic energy of the wheels under the control of the driver and drive the car forward. The drive control system is mainly composed of a motor and a motor controller. The energy flow between the motor and the battery is regulated by the controller, and the motor and the wheel are connected together through a mechanical transmission. AC motors, permanent magnet synchronous motors, DC motors or switched reluctance motors can be used as drive motors.
The chassis includes transmission driving system, steering system, braking system, suspension and front axle, among which the driving system is mainly composed of transmission, transmission shaft, rear axle and wheels, etc. The system scheme is shown in Fig.1.
EV550 Vector Frequency Converter and Its Control Strategy in Electric Vehicles
Vector converter (motor controller) converts a DC power source into an AC output to drive a three-phase motor in an electric vehicle and converts the electrical energy into mechanical energy to drive the vehicle. 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 entire vehicle's power performance and passenger comfort.
The following figure shows the basic frame of the vector inverter.
Figure II Vector Frequency Converter Frame
The EV550 series vector inverter and control system is designed and developed by China Metallurgical South (Wuhan) Automation Co., Ltd. for electric vehicles. Its real-time control and safety performance requirements are high. It can not only complete complex vector control operations and pulse width modulation algorithms, It can also collect and process data, control the execution system of the external system, and complete the vehicle logic control strategy with the vehicle controller.
The core requirements for using the EV550 vector converter to build its control system are:
1. Safe and reliable power-up sequence control.
The power controller on the motor controller must be controlled according to certain timing, otherwise it will cause controller damage. When the driver presses the motor controller closing button, the motor controller closes the pre-charging contactor after receiving the closing command of the vehicle controller, so that the battery pack is charged to the capacitor group in the motor controller through the pre-charging resistor slowly, when the motor is controlled After detecting that the DC bus voltage reaches 90% of the rated input voltage, the motor controller contactor is closed, and the precharge contactor is cut off. At this time, the main motor controller is completely connected to the battery pack to complete the main power-on process.
2, high-performance control algorithms.
The vector control algorithm (field oriented control) is a leap in the AC speed regulation technology. It realizes the decoupling control in the AC motor through the orientation of the motor flux, and makes the amplitude and spatial position of the motor flux vector dynamic. Steady-state controllable, so that the steady-state, dynamic performance of AC motor speed control can be comparable with the DC motor speed control system, and in some cases even surpass the latter. As a result, this algorithm is applied to the field of electric vehicles to meet the electric motor's high torque at low speeds, ensuring that it has good acceleration performance and climbing ability; at the same time, it also satisfies its wider speed range to make electric The car has the ability to drive at high speeds on flat roads.
3, the optimal energy utilization.
The optimal utilization of energy is another basic requirement for electric vehicles, requiring their control systems to use energy as much as possible, including the use of overheating and regenerative braking energy, making full use of limited energy. Capability feedback can achieve this function. It includes two kinds of vehicle braking capability feedback and vehicle glide ability feedback. In the feedback state, the drive motor is operated by the generator and converts the kinetic energy of the vehicle into electric energy, which can play three roles: auxiliary braking; recovering the energy to charge the power battery, thereby prolonging the driving range of the vehicle; and providing heat in the vehicle. When needed, this part of electric energy can be directly used for heating and heating.
Figure: EV550 motor controller
The main advantages of EV550 inverter products for electric vehicles are:
1. Reliability: Triple overcurrent protection, triple overvoltage protection and triple drive protection ensure the 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 motor;
3, large-capacity output capability: The motor output does not need to be equipped with a gearbox or reducer, greatly reducing the noise of the fault point and mechanical transmission system, saving costs, simple control mode, higher reliability, good vehicle operation and stability;
4, excellent dynamic performance: good acceleration performance (0-50km/h within 15 seconds), and more good economic performance (0.9 degrees / km @ 40km / h);
5, fault diagnosis and processing: In order to improve the reliability of the vehicle, the motor control system must have a fault diagnosis function, and can save the fault for future analysis, in addition through the diagnostic port can be implemented online debug controller, record a variety of Running curve to facilitate the optimization of the entire control system;
6, efficient braking energy recovery: give full play to the structural advantages of pure electric vehicle power system, improve energy utilization, motor control system must have braking energy recovery.
7. Simplicity: The motor controller has reliable quality, light weight, easy layout, and easy maintenance of the wiring. The industrialization prospect is very good.
to sum up
The drive control technology of AC motors, driven by high-power semiconductor device technology, microprocessor technology and control theory, has made great strides today, and it is gradually replacing DC drive in the field of electric drive, and has become the mainstream development technology. The introduction of the EV550 vector inverter will also create a broader application in the field of electric vehicles with its superior control performance.
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