General Electric introduction and the principle, composition and application purpose and use of the inverter

First, General Electric Introduction

The three-phase squirrel-cage AC motor is the most common type of induction motor, and its structure and characteristics are as follows:

Schematic diagram of induction motor

Schematic diagram of the motor

Motor characteristics

Second, the principle and composition of the inverter

The frequency converter is a control device that can easily and freely change the speed of the AC motor. The method of changing the speed of the AC motor is as follows.

The frequency converter achieves speed regulation by changing the frequency of the AC motor power supply:

The composition of the inverter is as follows:

1, converter (rectifier)

A large number of diode bridge rectifiers are used, as shown in Figure 1, which converts the commercial power supply to a DC power supply. Two sets of transistor converters can also be used to form the inverter, and the regenerative operation can be performed because the power direction is reversible.

2, flat wave circuit

The DC voltage rectified by the rectifier contains a ripple voltage of 6 times the frequency of the power supply, and the ripple current generated by the inverter also causes the DC voltage to fluctuate. In order to suppress voltage fluctuations, the ripple voltage (current) is absorbed by the inductor and the capacitor. When the device capacity is small, if the power supply and the main circuit constitute a device with a margin, the inductance can be omitted, and a simple smooth wave circuit is used.

3. Inverter

In contrast to the rectifier, the inverter converts the DC power to the AC power of the required frequency, and the 6 switching devices are turned on and off at the determined time to obtain the 3-phase AC output.

4, the brake circuit

When the asynchronous motor is used in the regenerative braking region (the slip rate is negative), the regenerative energy is stored in the smoothing circuit capacitor to increase the DC voltage. Generally speaking, the energy accumulated by the inertia of the mechanical system (including the motor) is larger than the energy that the capacitor can store. When fast braking is required, the inverter can be used to feed back the power supply or set the brake circuit (switch and resistor) to regenerate. The power is consumed to prevent the DC circuit voltage from rising.

Third, the application purpose and use of the inverter

The adjustable speed drive composed of the inverter and the AC motor is called the inverter drive, and its function is as follows. They may be related to each other and there is no clear classification. This table is for reference only.