Operating principle of four-quadrant frequency inverter

For the motor, the four quadrants means that its running mechanical characteristic curve can run in four quadrants on the mathematical axis. The first quadrant is the forward motor state, the second quadrant is the feedback braking state, the third quadrant is the reverse motor state and the fourth quadrant is the reverse braking state. The frequency inverter can make the motor work in four quadrants which is called  four-quadrant frequency inverter.

Frequency inverter speed regulation has great advantages in speed regulation range, speed regulation accuracy, flexible control, work efficiency and ease of use.

Ordinary two-quadrant frequency inverters use diode rectifier bridges to convert AC power into DC power, and then use IGBT inverter technology to convert DC power into AC power with adjustable voltage and frequency to control AC motors. This type of frequency inverter can only work in the electric state, so it is called a two-quadrant frequency inverter. Since the two-quadrant frequency converter uses a diode rectifier bridge, it cannot realize the bidirectional flow of energy, so there is no way to send the energy of the motor feedback system back to the power grid.

The four-quadrant inverter uses IGBT as the rectifier bridge. The IGBT power module cooperates with the high-speed and high-computation DSP to realize the bidirectional flow of energy and generate PWM control pulses. On the one hand, it can adjust the input power factor and eliminate the harmonic pollution to the power grid, making the inverter a real "green product". On the other hand, it can send the electric energy generated by the motor feedback back to the power grid to achieve a thorough energy-saving effect.

The four-quadrant inverter is used in places with potential load characteristics in coal mines, such as under the large-angle coal mining face. When the coal mining machine goes down, the inverter side generates excitation current, and the gravity traction motor generates electricity. The motor is in the power generation state. The potential energy is converted into electrical energy and fed back to the power grid through the rectifier side. At this time, the bus voltage remains stable, effectively preventing the coal mining machine from slipping. At the same time, the four-quadrant inverter can reduce the harmonic pollution to the power grid.

Use an X-axis to represent the direction of the motor's running speed, the positive direction of the axis represents the positive speed, and the reverse direction represents the reverse speed;

Use a Y-axis to represent the direction of the motor's electromagnetic torque, the positive direction of the axis represents the positive electromagnetic torque, and the reverse direction represents the negative electromagnetic torque;

Constitute a plane coordinate system XOY, then the normal electric state of the motor is in the first quadrant (forward, electric), and the power generation (braking) regeneration operation is in the second quadrant (forward, power generation).

The coal mining machine traction motor is constantly reversed in the normal state, and can be powered or generated in both the upper and lower directions. In the four-quadrant operation state, the energy conversion direction of each state is different.