A high-voltage frequency converter is a series-connected high-voltage frequency converter, which uses multiple single-phase three-level inverters connected in series to output high-voltage AC power with variable frequency and voltage.
I. Operating Principle of High Voltage Frequency Converter
The high-voltage frequency converter consists of eighteen identical unit modules, with six modules forming a group, each corresponding to one of the three phases of the high-voltage circuit. The unit is powered by a phase-shifting transformer. Each power unit is equivalent to a three-level two-phase output low-voltage frequency converter. By superimposing, they become high-voltage three-phase AC power. The neutral point of the frequency converter is not connected to the neutral point of the motor. The output of the frequency converter is actually a line voltage. The UAB output line voltage generated by the A-phase and B-phase output voltages can reach 6000V, which is a 25-step wave.
II. Performance Characteristics of High Voltage Frequency Converters
1. Application Scope: Wide speed regulation range, allowing smooth adjustment from zero speed to mains frequency speed. It enables soft starting with low current on large motors, with starting time and method adjustable according to site conditions. Frequency adjustment is based on the motor's voltage-to-frequency ratio at low frequencies, resulting in lower heat generation and lower input voltage, which slows down the aging of motor insulation.
2. Innovative Technology: The application of series multiplexing superposition technology achieves true high-to-high voltage power conversion, eliminating the need for step-down and step-up conversion, reducing device losses, improving reliability, and solving the difficulties of high-voltage power conversion. The application of series multiplexing superposition technology also opens up new avenues for achieving pure sine waves and eliminating grid harmonic pollution.
