From the inverter circuit components, the inverter can be divided into AC - AC inverter and AC - DC - AC inverter.
1. AC - AC drive
It is a fixed frequency AC power directly into the frequency of AC power continuously adjustable, the main advantage is that there is no intermediate links, high conversion efficiency. However, its continuously adjustable frequency range is narrow, the use of more devices, its application is greatly restricted.
2. AC - DC - AC inverter
First, a fixed frequency AC rectifier into DC, and then through the inverter circuit, the DC inverter into the frequency of continuous adjustable three-phase AC, the DC into the AC inverter is easier to control, so the frequency adjustment range and Frequency motor characteristics improved, etc., have obvious advantages, the most used inverter are all AC - DC - AC inverter.
(1) According to the DC link energy storage methods to points, AC - DC - AC inverter can be divided into two types of voltage and current.
① voltage type. If the rectifier after the capacitor to filter, this AC - DC - AC inverter called voltage-driven inverter, and now most of the voltage-driven inverter.
② current type. If the rectifier after the filter if the inductance, this AC - DC - AC inverter called current-mode inverter, this form of inverter is less common.
(2) According to different voltage regulation methods, AC-DC-AC inverter can be divided into pulse amplitude modulation (PAM) and pulse width modulation (PWM).
① pulse amplitude modulation (PAM). Inverter output voltage is the size of the DC voltage by changing (UD) to achieve this method is now rarely used.
② pulse width modulation (PWM). The size of the inverter output voltage is achieved by changing the duty cycle of the output pulse.
At present, the most widely used is the sine wave pulse width modulation whose duty cycle varies according to the sine law, that is, the SPWM mode.