VARIABLE FREQUENCY SPEED CONTROL SYSTEM AND METHOD OF THE SAME

摘要

A variable frequency speed control system having a low voltage ride through function that includes a variable frequency drive having a rectifier, a DC bus and an inverter is provided. The variable frequency speed control system includes a voltage drop detecting module, a frequency control module, an operation mode selecting module and an inverter control module. The voltage drop detecting module generates a voltage drop coefficient according to a grid voltage and a rated grid voltage and generates an operation mode switching signal. The operation mode selecting module receives a target frequency signal and a frequency decreasing amount and generates an output frequency signal according to the operation mode switching signal. The inverter control module generates a three phase modulating signal according to the output frequency signal, which is used to control the operation of the inverter.

主权项

1. A variable frequency speed control system having a Low Voltage Ride Through (LVRT) function which comprises a variable frequency drive (VFD) having a rectifier, a DC bus and an inverter, wherein the rectifier converts a grid voltage to a DC bus voltage, the inverter converts the DC bus voltage to a three phase AC signal by the DC bus, the variable frequency speed control system further comprising:
a voltage drop detecting module electrically coupled to a grid, for sampling the grid voltage, generating a voltage drop coefficient according to the sampled grid voltage and a rated grid voltage, and generating a corresponding operation mode switching signal according to the voltage drop coefficient; a frequency control module for generating a target frequency signal according to a given frequency control signal; an operation mode selecting module for receiving the target frequency signal and a frequency decreasing amount, and generating an output frequency signal according to the operation mode switching signal; and an inverter control module for generating a three phase modulating signal according to the output frequency signal, which is used to control the operation of inverter.