Abstract:
A prospective low-cost variable-speed drive system with a lot of promise for driving fans and pumps is the brushless doubly fed machine (BDFM) drive system, which is based on a fractional unidirectional converter.
However, if the grid is weak, the harmonic current produced by a diode rectifier may enter the machine and cause a torque ripple at the sixth order of frequency, resulting in voltage distortion. First, a steady equivalent circuit with the grid impedance and uncontrolled rectifier is constructed in order to examine the properties of the harmonic dispersion.
The machine system’s harmonic equivalent impedance should be adjusted to alter the harmonic distribution characteristics and reduce the impact of harmonic currents. By incorporating a harmonic control loop to stop harmonic currents from entering the machine or the grid and then applying them in the basic synchronous frame, this article enhances the traditional control technique.
In order to achieve the two control aims, two indirect parameters are chosen. The impact of the control system on the machine system’s harmonic equivalent impedance under the suggested approach and the standard way are then contrasted. Ultimately, the proposed method is validated by experimental findings derived from a 30 kW BDFM prototype.
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