While there's been a lot of discussion about electric vehicle batteries, the motors and electronic controls are equally important. What is the current state of domestic technology in this area? Most discussions about key components of electric vehicles focus on the power battery, with very little attention paid to the motor and electronic control systems. This is partly because new technologies and hot topics constantly emerge in the field of power battery technology, easily attracting media and reader attention.
In the field of motors and electronic controls, there are very few new technologies and hot topics; secondly, in the field of motors and electronic controls, especially in the field of electronic controls, domestic suppliers are still in a relatively early stage, and the products they develop cannot reach the international leading level. This also greatly limits the attention of consumers to motor and electronic control technology.
Motor Technology Analysis
An electric motor, as the name suggests, is an electrical device that converts electrical energy into mechanical energy and vice versa. When electrical energy is converted into mechanical energy, the motor exhibits the operating characteristics of an electric motor; when electrical energy is converted into mechanical energy, the motor exhibits the operating characteristics of a generator. In most electric vehicles, during braking, mechanical energy is converted into electrical energy, which is then used by the generator to recharge the battery.
An electric motor mainly consists of a rotor, stator windings, a speed sensor, and components such as a housing and cooling system. In the field of new energy vehicles, permanent magnet synchronous motors are widely used. "Permanent magnet" refers to the addition of permanent magnets during the manufacturing of the motor rotor, which further enhances the motor's performance. "Synchronous" means that the rotor's speed and the current frequency of the stator windings are always kept consistent. Therefore, by controlling the input current frequency of the motor's stator windings, the speed of the electric vehicle can ultimately be controlled. How to adjust the current frequency is a problem that the electronic control unit must solve.
Compared to other types of motors, the biggest advantage of permanent magnet synchronous motors (PMSMs) is their high power density and torque density. Simply put, compared to other types of motors, PMSMs can provide the greatest power output and acceleration for new energy vehicles with the same mass and volume. This is the main reason why PMSMs are the preferred choice for many automakers in the new energy vehicle industry, where space and weight are extremely critical.
Besides permanent magnet synchronous motors, asynchronous motors have also gained widespread attention due to their use by Tesla. Compared to synchronous motors, the rotor speed of an asynchronous motor is always less than the speed of the rotating magnetic field (generated by the current in the stator windings). Therefore, the rotor appears to have a "mismatch" frequency with the current in the stator windings, which is why it is called an asynchronous motor.
Compared to permanent magnet synchronous motors, asynchronous motors have the advantages of lower cost and simpler manufacturing process; however, their disadvantages are that their power density and torque density are lower than those of permanent magnet synchronous motors. The main reason Tesla chose an asynchronous motor for the Model S instead of a permanent magnet synchronous motor, besides cost control, is that the larger Model S body provides sufficient space to accommodate a relatively larger asynchronous motor.
Besides synchronous and asynchronous motors, in-wheel motors are another popular application in new energy vehicle motors. The biggest feature of in-wheel motors is that they integrate the vehicle's power unit, transmission, and braking system all within the wheel hub. Compared to traditional power units, the advantages of in-wheel motors are obvious: they eliminate many transmission components, resulting in a simpler vehicle structure. However, in-wheel motors still face many challenges in areas such as synchronous control and water sealing.
Analysis of electronic control technology
The electronic control unit (ECU) is equivalent to the ECU in a traditional car and is the main execution unit in an electric vehicle that controls high-voltage components. In addition to motor control, the ECU also controls related components such as the on-board charger and the DC-DC unit.
The core of the electronic control unit (ECU) is the control of the drive motor. The power unit's provider—the power battery—provides direct current (DC), while the drive motor requires three-phase alternating current (AC). Therefore, the ECU performs a process known in power electronics as inversion, converting the DC power from the power battery into AC power at the motor's input.
Common control strategies for modern motors include SVPWM (Space Vector Pulse Width Modulation), DTC (Direct Torque Control), sensorless control, and various novel intelligent control technologies. Numerous experts and scholars are also dedicated to improving motor control, enhancing motor stability, and strengthening motor anti-interference capabilities.
To achieve the inverter process, the electronic control unit (ECU) requires components such as a DC bus capacitor and IGBTs to work together. After the current is output from the power battery, it first passes through the DC bus capacitor to eliminate harmonic components. Then, through controlling the switching of the IGBTs and cooperating with other control units, the DC power is finally inverted into AC power, which ultimately serves as the input current for the motor. As mentioned earlier, by controlling the frequency of the three-phase input current of the motor and cooperating with the feedback values from the speed and temperature sensors on the motor, the ECU ultimately controls the motor.
Besides controlling the motor, the electronic control unit (ECU) is also the main control mechanism for components such as the on-board charger and the DC-DC converter. Charging is the opposite of motor control; it requires converting the AC power supplied by the grid into DC power from the battery, a process known as rectification in power electronics. The DC-DC converter, on the other hand, enables the charging of the 12V battery from the mains battery. The ECU needs to convert the high voltage from the mains battery to the low voltage of the 12V battery to ultimately charge the new energy vehicle.
In conclusion, electric vehicles, as an important area of future new energy applications, still represent a promising new direction for future development, despite many immature technologies. Motor control will also be a key factor hindering revolutionary innovation in electric vehicles.
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