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LVVariable-frequency Drive

Variable-frequency Drive(VFD) is a power control equipment which applies variable frequency techology and microelectronic technology to control the AC motor by changing the working power frequency of the motor. The voltage and frequency of the output power supply are adjusted mainly by the breaking of the internal IGBT, and the required power supply voltage is provide acording to the actual needs of the motor, thereby achieving the purpose of energy saving and speed regulation.

Brief Introduction

Variable-frequency Drive(VFD) is a power control equipment which applies variable frequency techology and microelectronic technology to control the AC motor by changing the working power frequency of the motor. The Variable-frequency Drive is mainly composed of rectification (AC to DC), filtering, inverter (DC to AC), braking unit, drive unit, detection unit, and micro processing unit and others. The Variable-frequency Drive adjusts the voltage and frequency of the output power supply by the breaking of the internal IGBT, and supplies the required power supply voltage according to the actual needs of the motor, and then achieving the purpose of energy saving and speed regulation. In addition, Variable-frequency Drive has many protection functions, Such as overcurrent, overvoltage, overload protection and so on. With the continuous improvement of industrial automation, Variable-frequency Drive have also been very widely used.
      However, due to the influence of various factors on the power grid, voltage drop and short-term power supply interruption are inevitable, which causes the Variable-frequency Drive to have a new problem in use—low voltage protection trips of Variable-frequency Drive. Generally, Low voltage protection value of the Variable-frequency Drive will be set at 85%, some Variable-frequency Drives can achieve about 65% of low voltage protection value, as long as the bus voltage is lower than the setings, the Variable-frequency Drive will trip protectively, the motor stops working, production is Seriously affected, which has brought great economic losses to users.
      For example, when the busbar voltage of Variable-frequency Drive of the powder feederin thermal power plant is instantaneously lower than its low-voltage protection value, Variable-frequency Drive trips and the motor stops working, which causes the powder feeder to stop, and will simultaneously send powder feeder stop signal to the boiler safety monitoring system. which will cause the thermal power generator set to trip protectively, resulting in unplanned outage of the thermal power generating unit, affecting the safe and stable operation of the power grid, and also bringing great economic losses to the thermal power plant itself.

PRINCIPLE

Variable-frequency Drive is a device that converts a industrial frequency power supply (50 Hz or 60 Hz) into an AC power source of various frequencies to realize variable speed operation of the motor, among which the control circuit completes control of the main circuit, and the rectifier circuit converts the alternating current into direct current, and the DC intermediate circuit smoothly filter the output of the rectifier circuit, and the inverter circuit re-inverts the direct current into alternating current.
      The voltage detection components of the Variable-frequency Drive are all set on the DC bus side. As long as the control system of Variable-frequency Drive detected that the DC bus voltage is lower than a certain set value, the Variable-frequency Drive will trip protectively. Grid system failure, large motor of the same AC busstart, and short-time power interruption may cause that the DC busbar voltage of the Variable-frequency Drive is lower than a certain set value, leading to low voltage protection tripping of the Variable-frequency Drive. Therefore, as long as the DC bus voltage can be maintained no less the protection set value, low voltage ride through of the Variable-frequency Drive can be solved.
      Add a DC power supply to the DC bus of the Variable-frequency Drive. When the external disturbance causes short interruption of the common power supply or short-time voltage drop, the added DC power supply will immediately supply power to the DC bus of the Variable-frequency Drive, maintain the DC bus voltage not lower than the protective set value. ensure that the Variable-frequency Drive continues to work, does not affect the normal operation of the terminal motor; when the grid AC power supply resumes normal power supply again, the added DC power supply is quickly disconnected, and the Variable-frequency Drive is changed to the grid AC power supply.
      The added DC power supply can be a bypass DC power supply against voltage drop, a storage battery, a super capacitor or a security power supply for power plant according to the user's field conditions.
TECHNICAL CHARACTERSITICS
Fast voltage sag detection technology;
Sound switching control strategy;
Complete Reliability Guarantee Design of Power Supply 
Maintenance free design;
Modular design
Long service life;
Ultra-wide input voltage range.

DEVICE COMPOSITION

The Variable-frequency Drive is mainly composed of rectification (AC to DC), filtering, inverter (DC to AC), braking unit, drive unit, detection unit, and micro processing unit and others

TECHNICAL PARAMETER

Input voltage: AC 0-430V
Output voltage: DC 510±5% can be set
Rated power: 1kW~800kW
Power supply time: 1~10S
Full load operating efficiency: 98%
Switching time: ≤200μs
Cooling method: air cooling
Protection level: IP5
Noise: ≤55dB