High Voltage Converter VFD Electronic Control Principle 1

The HV incoming power supply is applied to the primary side of the phase-shifting transformer through the incoming contactor. The secondary vice-side winding of the phase-shifting transformer is connected with the input end of the power unit, and three groups of vice-side windings with the same label respectively supply power to three power units in the same stage. One output of each power unit in the first stage is connected together to form a star connection point, and the other output is connected with the output of power unit from next stage. 

In this way, all power units in the same phase are connected in series to form a star-connected three-phase HV power supply, and the output directly drives the HV motor. The control system detects and controls the system.

According to the actual needs of the site, the HV bypass cabinet can be selected, which is mainly used to realize the switching of power frequency and frequency conversion. If the frequency conversion system fails, it can be switched manually or automatically through the selection of devices. The function of one converter for multi-motors can be realized by applying an output switch in the bypass cabinet on the spot.

The Fig.A below shows the manual switching bypass, after the frequency conversion fails. Manually disconnect the input and output isolation knives QS1 and QS2; and then close the bypass isolation knife QS3. The system can run with power frequency.

The Fig.B shows below shows the automatic switching bypass, after the frequency conversion fails. The system automatically turns off the input and output switches, and closes the bypass switch. At the same time, the bypass cabinet can also be manually switched.

The Bypass system in Fig.C is a soft-starting device, which is suitable for the site with small power grid capacity or high power. After the frequency conversion fails, the motor is driven by HV soft-starting device.