What are the main components of an AC-DC-AC frequency converter?
The main circuit of an AC-DC-AC frequency converter consists of three parts: the rectifier main circuit, the intermediate circuit, and the inverter circuit.
1. Main Circuit: This is the power conversion section that provides voltage and frequency adjustable power to the asynchronous motor. The main circuit of a frequency converter can be broadly divided into two categories: voltage-source converters, which convert DC voltage to AC, and current-source converters, which convert DC current to AC, and current-source converters, and current-source converters, which convert DC current to AC, and current-source converters, and current-source converters, which use inductors for DC filtering.
2. Intermediate Circuit: The converter with rectifier diodes transforms the mains frequency power supply into DC power. Two sets of transistor converters can also be used to construct a reversible converter, which can operate in regenerative mode due to its reversible power direction.
3. Inverter: Unlike a rectifier, an inverter converts DC power into AC power at the required frequency. By switching six switching devices on and off at predetermined times, a three-phase AC output can be obtained. The switching time and voltage waveform are shown as an example using a voltage-source PWM inverter.
AC-DC-AC frequency converter performance characteristics
1. The main circuit rectifier transformer can be one of six double-winding rectifier transformers or two three-phase three-fracture structure transformers.
2. The motor and converter adopt a double Y-type connection structure to form a 12-pulse waveform, which greatly reduces harmonics. Through switching cabinet switching, each transformer and converter can operate independently at full load or half speed, greatly increasing applicability and flexibility.
3. The synchronous motor excitation adopts irreversible thyristor three-phase full-bridge control. In addition to a high-capacity varistor absorption circuit, the protection circuit is also equipped with a dedicated fast protection circuit for diode BOD detection and thyristor switching control.
