Application of DHVECTOL type VFD (Variable-frequency Drive) in the air induction system of 660MW ultra-supercritical thermal power generation unit

1DHVECTOL-HI04750/06 type VFD (Variable-frequency Drive) introduction

DHVECTOL-HI04750/06 high-voltage VFD (Variable-frequency Drive) adopts unit series multi-level technology, with direct 6kV input and 6kV output. It consists of main control system, transformer, inverter module and bypass system. The system consists of 24 power modules. Each 8 power modules are connected in series to form one phase. The three phases are Y-connected and directly output 6kV to the motor.

1.1 Main control system

The DHVECTOL-HI04750/06 VFD (Variable-frequency Drive) control system uses robust speed sensorless vector control to perform precise and intelligent control of 24 high-power modules, allowing the VFD (Variable-frequency Drive) to provide accurate and stable voltage and Frequency output also enables timely alarm and protection of faults. Since the control system uses a dedicated intelligent frequency conversion control chip, it has extremely high reliability and safety, as well as good anti-interference and high-precision control performance.

1.2 Input side transformer

The phase-shifting transformer converts the high voltage on the grid side into multiple sets of low voltage on the secondary side. Each secondary winding adopts the Yanbian delta connection method when winding, and there is a certain phase difference between them.

The secondary winding of the transformer is divided into 8 levels per phase, each level has a voltage of 460V, and the phases are shifted by 15° to form a 48-pulse rectification mode. This multi-stage phase-shifted superposition rectification method eliminates most of the harmonic currents caused by independent power modules and can improve the current waveform on the grid side. The grid-side power factor under load reaches above 0.95, effectively preventing the flow of electricity to the grid. Side grid pollution.

1.3 Inverter module

The inverter module is the basic unit for the entire VFD (Variable-frequency Drive) to realize voltage transformation and frequency conversion output. The voltage transformation and frequency conversion functions of the entire VFD (Variable-frequency Drive) are realized through a single power module. Each power module They are equivalent to an AC-DC-AC voltage single-phase low-voltage VFD (Variable-frequency Drive). The rectifier input side of the power module uses a diode three-phase full-bridge uncontrolled rectification, and an electrolytic capacitor is used in the middle for energy storage and filtering. The inverter output side is an H-bridge composed of 4 IGBTs. The U and V output terminals of each unit are connected in series to form a star connection to power the motor. By superimposing the PWM waveforms of each unit, a stepped sinusoidal PWM waveform can be obtained. This waveform has good sinusoidality, small dv/dt, and no damage to the insulation of the cable and motor. It can extend the length of the output cable without an output filter and can be directly used in ordinary motors.

1.4 Bypass system

Each set of induced draft fan VFD (Variable-frequency Drive) is equipped with a manual bypass cabinet. Through the switching operation of the bypass cabinet, the switching between the industrial frequency and variable frequency operating modes of the induced draft fan is realized. The isolating switches on the power frequency and frequency conversion sides adopt a combination of electrical interlocking and mechanical interlocking, which is easy to operate, safe and reliable.

2Application example description

The planned and designed capacity of Huaneng Jinggangshan Power Plant is 1.92 million kilowatts. The first phase of the project is 2×300MW coal-fired generating units, and the second phase of the project is 2×660MW coal-fired generating units; on December 25, 2009, as the #4 unit of the second phase of the project successfully passed the 168-hour trial operation, it was successfully realized# 3. Unit #4 has the goal of "double operation within the year", and the total installed capacity of the power plant reaches 1920MW. Since the 2×660MW ultra-supercritical coal-fired generating unit of the second phase project was put into operation, the unit has operated stably and achieved "first, safe operation, and second, energy conservation and emission reduction." In order to further improve economic benefits, save energy, reduce consumption, and reduce long-term wear and tear on equipment, it was decided to carry out frequency conversion technology transformation on a total of four boiler induced draft fans in #3 and #4 units respectively. The VFD (Variable-frequency Drive) was selected from Oriental Hitachi ( DHVECTOL-HI04750/06 high-power high-voltage VFD (Variable-frequency Drive) produced by Chengdu) Electronic Control Equipment Co., Ltd.

3Application effect analysis