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

1 Introduction of Sunwoele-HFV1000 VFD (Variable-frequency Drive)

Sunwoele-HFV1000 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 is composed of 24 power modules, and every 8 power modules are connected in series to form a phase, three-phase Y connection, and directly output 6kV to the motor.

1.1 Main control system

Sunwoele-HFV1000 VFD (Variable-frequency Drive) control system adopts robust speed sensorless vector control to perform precise and intelligent control on 24 high-power modules, so that VFD (Variable-frequency Drive) can provide accurate and stable voltage and frequency output , but also realize the timely alarm and protection of faults. Since the control system adopts a special intelligent frequency conversion control chip, it has extremely high reliability and safety, and has good anti-interference and high-precision control performance.

1.2 Input side transformer

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

The secondary windings of the transformer are divided into 8 stages for each phase, and the voltage of each stage is 460V, and the phases are shifted 15° between each other, forming a 48-pulse rectification method. This multi-stage phase-shifting superimposed rectification method eliminates most of the harmonic currents caused by independent power modules, and can improve the current waveform on the grid side. The power factor of the grid side under load can reach above 0.95, effectively preventing the side grid pollution.

1.3 inverter module

The inverter module is the basic unit for the entire VFD (Variable-frequency Drive) to achieve variable voltage and frequency output. The voltage and frequency conversion functions of the entire VFD (Variable-frequency Drive) are realized through a single power module. Each power module Both are equivalent to an AC-DC-AC voltage type single-phase low-voltage VFD (Variable-frequency Drive). The rectification input side of the power module uses a diode three-phase full-bridge uncontrolled rectification, and an electrolytic capacitor is used for energy storage and filtering in the middle. 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 supply power to the motor. By superimposing the PWM waveforms of each unit, a stepped sine PWM waveform can be obtained. This kind of waveform has good sine degree, small dv/dt, no damage to the insulation of the cable and the motor, no output filter is needed, the length of the output cable can be extended, and it can be directly used in ordinary motors.

1.4 Bypass system

Each set of VFD (Variable-frequency Drive) of the induced draft fan is equipped with a set of manual bypass cabinet, and the switch between the power frequency and the variable frequency operation mode of the induced draft fan is realized through the switching operation of the bypass cabinet. The combination of electrical interlock and mechanical interlock is adopted between the power frequency and frequency conversion side isolating switches, which is easy to operate, safe and reliable.

2 Description of application examples

The planning and design capacity of Huaneng Jinggangshan Power Plant is 1.92 million kilowatts. The first phase project is 2×300MW coal-fired generating units, and the second phase project is 2×660MW coal-fired generating units; on December 25, 2009, with the second phase project #4 unit successfully passed the 168-hour trial operation, the # 3. Unit #4 has the goal of "double investment within the year", and the total installed capacity of the power plant will reach 1920MW. Since the 2×660MW ultra-supercritical coal-fired power generation unit of the second phase project was put into operation, the unit has been operating stably, achieving "one is safe operation, and the other is energy saving and emission reduction". In order to further improve economic benefits, save energy and reduce consumption, and reduce long-term wear and tear on equipment, it was decided to carry out frequency conversion technology transformation for a total of 4 boiler induced draft fans of #3 and #4 units. The VFD (Variable-frequency Drive) selected Chengdu Sunwoele Co. .,ltd. produced Sunwoele-HFV1000 high-power high-voltage VFD (Variable-frequency Drive).

3 Application effect analysis