30 Basic Knowledge of Frequency Converter (I)

1. What is a frequency converter rectifier (converter)?

The rectifier (converter) is one of the three main parts in the main power supply of the inverter. The input AC power passes through the converter part and is rectified into DC voltage. The converter part consists of diodes, thyristor rectifiers or insulated gate bipolar transistors connected to a full-wave bridge.

2. What is the inverter DC bus?

The DC bus is the second major section in the main power supply of the frequency converter and consists mainly of capacitors used to smooth and store the current rectified by the converter. The DC bus may also contain pre-charge circuits and link chokes.

3. What is a frequency converter inverter?

The inverter is the third and final section in the main power supply of a variable frequency drive. The inverter section consists of IGBTs, which use either a pulsed DC bus voltage or pulse width modulation to produce a sinusoidal output current. The variable frequency drive itself is sometimes called an inverter, as the presence of the inverter section is the main difference between a VFD and a DC drive.

4. What is IGBT in inverter?

An insulated gate bipolar transistor (IGBT) is an electronically driven very fast semiconductor switch. By applying a small positive voltage between the gate and emitter of the IGBT, current is allowed to flow from the collector point to the emitter point. The switching rate of the IGBT in the inverter ranges from 2 to 15 kHz.

5.What is inverter PWM?

Pulse Width Modulation (PWM) is an inverter control scheme where a set of six power switches (usually IGBTs) are used to recreate a pseudo AC voltage waveform using a constant DC voltage. Varying the width of the fixed amplitude pulses controls the effective voltage. This PWM scheme works because the motor is a large inductor that does not allow current to pulse like voltage. When sequenced correctly, PWM outputs the motor current as a nearly perfect sinusoidal waveform.

6.What is the inverter carrier frequency?

Carrier Frequency In a PWM-based inverter, the rate at which the output transistors are gated or turned on, typically 2 to 15 kHz. Higher values ​​produce better current waveforms but incur more losses.

7.What are the common buses in frequency converters?

Common Bus - A method of connecting the DC bus sections of independent drives, or operating multiple independent drive sections from a common DC source. The advantage of this method is that motor operation sequencing can be used to balance motor drive and regeneration, so little or no dynamic braking is necessary.

8.What is inverter dynamic braking?

In a frequency converter, this refers to connecting a resistor to the DC bus via a transistor. The transistor closes and shunts power to the resistor only when the DC bus voltage exceeds a predetermined level, which usually occurs when the load is decelerating rapidly.

9.What is inverter grounding?

Ground, also known as ground, is the reference point for incoming AC power. If a power conductor is accidentally connected to ground, the AC power protection circuit will immediately electrically isolate the AC power from the point of contact. To create a ground point, a rod is usually driven into the ground, and all ground circuits are connected to the ground point. When the drive chassis is connected back to ground, a safe conduction path is created to prevent accidental shorting of conductors to metal parts of the enclosure.

10. What is kVA in frequency converter?

kVA is the effective power of the inverter based on the output voltage and current.