[Introduction] The motor technology is not as simple as we imagine. The domestic manufacturers of permanent magnet synchronous motors for vehicles lag behind in foreign countries for about five years. The future trend of motor products is higher output density, wider speed range, and lower manufacturing cost. , easier to integrate (currently the most significant integration is the motor, transmission and controller together)
The motor technology is not as simple as we imagine. The domestic manufacturers of permanent magnet synchronous motors for vehicles lag behind China by about five years. The difference lies in the design concept, raw materials and equipment, and the need to avoid foreign patents. ). In addition, there are gaps in the control of material loss, process, and key parameters, and the speed of product renewal is also slow. Future trends in motor products are higher output density, wider speed range, lower manufacturing costs, and easier integration (the most significant integration at the moment is the integration of motors, transmissions, and controllers). Companies that can make breakthroughs in technology and customer response in the future are expected to win.
First, the motor magnetic field and working principle
Electromagnetic force principle: Electromagnetic force refers to the energized wire in the magnetic field by the role of electromagnetic force, the electromagnetic force is the opposite sex attract, same-sex repulsion. The opposite sex attracts here certainly is right, but the homosexuality repulses here the same sex refers to not the same polarity, but refers to the electromagnetic magnetic field nature is the same. The current generation of motors is mainly due to suction.
The principle of power generation: The conductor is induced in the magnetic field that generates the voltage, so that the circuit forms a loop to generate the current.
The working principle of the permanent magnet synchronous motor: The stator generates a rotating magnetic field after alternating current. The rotating magnetic field attracts the magnetic field of the rotor, which is the rotation of the rotor following the stator magnetic field.
It should be noted here that most of the motors used in the vehicle are permanent magnet synchronous motors, and most of them are built-in synchronous motors. The main reason is that inline synchronous motors make good use of reluctance torque. The effect of the reluctance torque on the motor system is:
In the same motor anti-potential system, achieving the same torque can reduce the release of the current, which helps to improve the efficiency of the motor under low speed and high torque conditions, and also creates conditions for reducing the cost of the main components of the controller.
Under the same controller hardware conditions, a high reluctance torque motor has a higher idle speed than a low reluctance torque motor, which helps to improve the motor's high-speed and low-torque work efficiency, improve electromagnetic noise, and improve the speed of the motor system. range.
Second, the main performance parameters of the vehicle drive motor and interpretation
Measuring the main performance of the drive motor for vehicles mainly depends on the following data:
1. Minimum operating voltage at full power output: (Rated voltage is not important) It should be noted here that the motor used in the vehicle is AC, but the data generally given by the manufacturer is DC. The data needs to be converted into AC. DC is converted into AC. When passing through the controller, this step consumes a portion of the voltage.
2. The maximum working phase current: Can not use the data provided by the host plant, to combine the IGBT capability of the controller.
3. Peak torque: It is possible for a commercial vehicle customer to have a locked-rotor torque value.
4. Peak power: What should be the peak power at speed.
5. Rated power/torque: The operating point allowed to run for a long time is called rated power, but the reasonable rated power should be continuous torque and power for the entire vehicle manufacturer. For example, the motor running power at high speed can be used as the rated power. Consider the rated power at the sewing speed.
6. Maximum working speed: The maximum working speed includes the power at the highest working speed, the back electromotive force at the highest speed, and the mechanical stress at the highest speed (is it stable operation at high speed).
7. NVH: Low Cogging Torque and Negative Back-EMF Spectral Waves.
8. Efficiency: The data that needs attention here is the most commonly used efficiency of the motor. At the same time, we must also pay attention to the efficient matching of the needs of the customer's needs.
Third, the development trend
1. Higher output density - (big as big output 200kw)
Is there any material, low cost and high efficiency?
2. More wide speed range (0-18000 rpm, even 0-20000 rpm)
Is there any new principle that can reduce costs?
3. Lower manufacturing costs
New process (for example, there is no good insulation material can increase the temperature resistance)
4. easier to integrate
New application (currently the most significant integration is motor, transmission and controller together)
Fourth, IPMSM magnetic circuit structure
1 commonly used magnetic circuit structure
How do motor companies grasp the development trend of the automotive market to win the technical go-ahead?
2. Development trend of magnetic circuit structure of permanent magnet synchronous motor for vehicle
The trend is mainly summarized as: high power density, low material loss, high-speed rotation, and flexible control. Specifically:
Adapt to high reluctance torque performance and low magnet consumption
Meet the needs of integration of motors and gearboxes, and pursue rotor size and thin design
Development of New Magnetic Steel Process or High Performance Silicon Steel Sheet Material
Catering to innovative control strategies to transform the special requirements of motor magnetic circuit parameters
V. Permanent magnet synchronous motor related design parameters and values
1.I,P,Z,n values ​​(the most relevant parameters for motor design)
a) pole pair p
The more pole pairs, the more conducive to improving the motor torque density and power density
Without considering the rotor flux leakage, the more pole pairs of the motor, the weaker the armature reacts to the armature of the rotor.
Considering the actual process capability and the mechanical strength of the rotor, excessive pole pairs can lead to excessive drain coefficients, and the armature slot area of ​​the shrink-match is too small, which is not conducive to the improvement of power density.
The pole pair number determines the operating frequency of the motor at a certain speed. Therefore, the maximum number of pole pairs allowed by the motor can be obtained according to the ability of the motor lock to match the switching components of the controller and the maximum speed of the motor lock.
Priority recommendation: Meet motor controllability - meet motor manufacturability - take as many poles as possible.
b) Index Z (Generally, p must be decided before Z)
(Concept: Each group of slots per phase Q = Z / (3 * 2 * P), Q is an integer when the integer slot winding is called, otherwise it is called fractional slot winding)
If a high-power motor used in a vehicle has a concentrated winding, then the motor's Q = 0.5, then the number of slots Z = 3 * P, there are a small number of small-power motor 8 9 slot or 10 12 slots.
The larger the Q value, the smaller the back-EMF spectral wave of the motor, the smaller the cogging torque and torque ripple of the motor, but according to the experience Q>3, the improvement of the spectral wave can be ignored.
Since the power of the drive motor is large, and the number of motor single-phase series turns is small, many times the number of appropriate slots Z needs to be selected to ensure a reasonable number of motor turns.
The commonly used Q value of the motor is recommended as follows: Q=0.5; Q=1.5; Q=2; Q=2.5; Q=3 (The flat copper wire winding process is often used when the vehicle drive motor Q takes a large value.
C) Number of turns N
As the number of turns increases, the back EMF of the motor increases and the torque at the same current increases.
The increase in the number of turns means that the cross-sectional area of ​​the conductor is reduced, which may lead to excessive heat load on the armature.
Changing the volume of the motor changes the flux area of ​​the motor. Changing the structure of the magnetic circuit can change the air gap magnetostrictive polar arc coefficient and create conditions for adjusting the number of motor turns.
2. The main size is determined
1) Armature outer diameter value
Under normal circumstances, according to the size requirements of the vehicle, the thickness of the outer shell is removed to obtain the outer diameter of the stator core, and the thickness of the motor casing varies with the size of the motor and the shell process. In recent years, more and more widely used integrated Water-cooled enclosure, the thickness of its enclosure is recommended to be between 18 and 30mm
2) Armature inner diameter value
Definition: After determining the outer diameter of the stator, the inner diameter dimension of the armature can be determined. That is, the key is to design the motor's inner and outer diameter ratio kd.
Influence: The greater the Kd value is, the smaller the influence of the armature magnetic potential of the motor is. However, the magnetic flux of the rotor increases, the magnetic potential of the rotor increases, and it is easy to increase the power capability of the motor. However, the copper loss of the motor needs to be increased. Otherwise, the motor will be reduced. Power capability, but it can create conditions for improving motor efficiency. The Kd value also affects the size and shape of the armature slot. The smaller the Kd value, the deeper the slot, the smaller the armature slot and the increased slot leakage resistance.
3) Selection of motor stator and rotor air gap
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