How is the counterpotential generated in a permanent magnet synchronous motor? Why is it called counterpotential?

1. How is the counterpotential generated?
In fact, the generation of reverse potential is very good to understand, memory a little better students should know that as early as in junior high school and high school have been in contact with, just then called the induced electromotive force, the principle is that the conductor cuts the magnetic susceptibility, as long as the two have a relative motion on the line, it can be that the magnetic field does not move, the conductor cut; it can also be that the conductor does not move, so that the magnetic field to move. For permanent magnet synchronous motor, its coil is fixed on the stator (conductor), the permanent magnet is fixed on the rotor (magnetic field), when the rotor rotates, the magnetic field generated by the permanent magnet on the rotor will rotate, and will be cut by the coil on the stator, and generate a counter electromotive force in the coil. Why is it called a counterpotential? As the name suggests, because the direction of the counterpotential E is opposite to the direction of the terminal voltage U (as shown in Figure 1).

2. What is the relationship between counterpotential and terminal voltage? From Fig. 1, the equation for the relationship between counterpotential and terminal voltage under load is:

For the test of the reverse potential, generally in the no-load state, no current, speed of 1000rpm test conditions. General definition of the value of 1000rpm, the reverse potential coefficient = average value of the reverse potential / speed, the reverse potential coefficient is a more important parameter of the motor, it is important to note that the reverse potential under load before the speed is not stabilized is constantly changing. Through the (1) formula can be seen under the load counterpotential is less than the terminal voltage, if the counterpotential is greater than the terminal voltage becomes a generator, the external output voltage. The value of the counterpotential is approximately equal to the terminal voltage and is limited by the rating of the terminal voltage because the resistance and current are small in practice.
3. Physical significance of the counterpotential
Imagine what would happen if the counterpotential did not exist. From equation (1), it can be seen that without the counterpotential, the entire motor is equivalent to a pure resistance, becoming a particularly serious device for heat generation, which is contrary to the conversion of electrical energy into mechanical energy by the motor.
In the electrical energy conversion relationship equation

UIt is the input electrical energy, such as to the battery, motor or transformer in the input electrical energy; I2Rt is the heat loss energy in each circuit, this part of the energy is a heat loss energy, the smaller the better; the input electrical energy and the difference between the heat loss of electrical energy, that is, with the counter-electromotive force corresponding to the part of the useful energy.

In other words, the reverse electromotive force is used to generate useful energy, which is inversely correlated with the heat loss; the greater the heat loss energy, the smaller the useful energy that can be realized.
Objectively speaking, the reverse electromotive force consumes the electrical energy in the circuit, but it is not a “loss”, and the part of electrical energy corresponding to the reverse electromotive force, will be converted into useful energy of the power-using equipment, for example, the mechanical energy of the motor, the chemical energy of the battery, and so on.
It can be seen, the size of the reverse electromotive force, means that the power equipment to the input of the total energy to the useful energy into the conversion of the strength of the ability to reflect the transformation of electrical appliances to the level of the ability.
4. What is the magnitude of the counterpotential related to? Give the formula for the counterpotential first:

E is the coil electromotive force, ψ is the magnetic chain, f is the frequency, N is the number of turns, and Φ is the magnetic flux.
According to the above formula, I believe you can probably say a few factors affecting the size of the counter electromotive force, here quote an article to summarize:
(1) The counterpotential is equal to the rate of change of the magnetic chain, the higher the rotational speed, the greater the rate of change, the greater the counterpotential;
(2) The magnetic chain itself is equal to the number of turns multiplied by a single-turn chain, so the higher the number of turns the larger the chain, the larger the antipotential;
(3) The number of turns and the winding program, star angle connection, the number of turns per slot, the number of phases, the number of teeth, the number of parallel branches, the whole pitch or short pitch program;
(4) Single-turn magnetic chain is equal to the magnetic potential divided by the reluctance, so the larger the magnetic potential, the smaller the reluctance in the direction of the chain, the larger the counterpotential;
(5) The magnetoresistance is related to the air gap and the pole-slot coordination, the larger the breath, the larger the magnetoresistance, the smaller the counterpotential. Pole slot with more complex to be specifically analyzed;
(6) Magnetic potential and magnet steel remanent magnetization and the effective area of the magnet steel, the larger the remanent magnetization, the higher the counter electromotive force. Effective area and magnet magnetization direction, size and placement are related to the position, need to be specifically analyzed;
(7) The remanent magnetization is also related to the temperature, the higher the temperature, the smaller the repulsive force.
To sum up, the factors affecting the electromotive force include rotational speed, number of turns per slot, number of phases, number of parallel branches, short pitch, magnetic circuit of the motor, length of the air gap, pole-slot coordination, residual magnetism of the magnets, magnet placement and size of the magnets, magnet magnetizing direction, and temperature.
5. How to choose the size of counterpotential in motor design?
In motor design, the inverse potential E is very important, I think the inverse potential design is good (the size is chosen appropriately, the waveform distortion rate is low), this motor is good. There are several main effects of the counterpotential on the motor:
1, the size of the counterpotential determines the weak magnetic point of the motor, and the weak magnetic point determines the distribution of the motor efficiency MAP map.
2, the reverse potential waveform distortion rate affects the motor ripple torque, which affects the smoothness of the torque output when the motor is running.
3, the size of the counterpotential directly determines the torque coefficient of the motor, the counterpotential coefficient and the torque coefficient are directly proportional to each other. This leads to the following points of conflict in motor design:
a. If the counterpotential is made large, the motor can keep high torque under the limit current of the controller in the low-speed operation area, but it can not output torque at high speed, and even can not reach the expected speed;
b. If the counterpotential is made small, the motor still has output capability in the high-speed region, but the torque cannot be reached under the same controller current at low speed.
Therefore, the design of the size of the counterpotential depends on the actual needs of the motor, for example, in the design of small motors, if the requirements of the low-speed can still output enough torque, then the counterpotential must be designed on the larger side.