A current sampling device and method for a frequency converter

Abstract

The invention relates to a current sampling device and method of a frequency converter. The device comprises a frequency calculating module, a phase shift compensation module, a first modulation module, a sampling module and a second modulation module; the frequency calculating module modulates and calculates first and second input switching frequencies to obtain first and second period values; the phase shift compensation module sets first and second phase compensation values according to the first and second period values respectively; the first modulation module sets a first period phase value according to the first period value and the first phase compensation value; the second modulation module sets a second period phase value according to the second period value and the second phase compensation value; and the sampling module carries out sampling according to the first and second period phase values. Thus, current sampling conflicts can be avoided.

Description

technical field [0001] The invention relates to a frequency converter, in particular to a current sampling device of the frequency converter and a method thereof. Background technique [0002] Inverter (Variable-frequency Drive, VFD) is a power control device that uses frequency conversion technology and microelectronics technology to control AC motors by changing the frequency of the motor's operating power supply. The inverter adjusts the voltage and frequency of the output power supply by switching off the internal IGBT, and provides the required power supply voltage according to the actual needs of the motor, thereby achieving the purpose of energy saving and speed regulation. With the continuous improvement of industrial automation, it is widely used in metallurgy, petroleum, chemical, textile, electric power and other industries. In order to improve its own power factor and avoid unnecessary harmonic interference to the power grid, the inverter should not only control...

AI Technical Summary

Problems solved by technology

[0005] (1) Reduce the control frequency of PFC, widen the sampling time of AC current, and limit the minimum pulse width of PWM at the same time, so that even if the sampling window of AC current is occupied by the sampling of motor phase current, there is enough sampling time before the current is turned off ; But reducing the control frequency of PFC will directly affect the performance of PFC, so it is necessary to use a larger and more expensive inductor to make up for it; and limiting the minimum pulse width of PWM will cause distortion of AC current;

[0006] (2) PFC owns one ADC and does not share it with other samples; this method needs to choose a single-chip microcomputer with two independent ADCs, which will undoubtedly increase the cost;

[0007] (3) Chinese patent application CN201610151650.5 discloses the idea of ​​sampling the bus current and performing sampling processing to avoid the problem of inaccurate AC current sampling, but this method will increase the complexity of control, and the sampling processing is cumbersome, and it is not suitable for Applications of Interleaved PFC

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