Abstract
The brushless doubly fed machine (BDFM) drive system based on a fractional unidirectional converter is a promising low-cost variable-speed drive system, which shows great potential in applications of driving fans and pumps. However, the harmonic current generated by a diode rectifier can flow into the machine and the grid under a weak grid, which will cause a 6th-order frequency torque ripple and lead to voltage distortion. A steady equivalent circuit considering the uncontrolled rectifier and the grid impedance is built firstly to study the harmonic distribution characteristics. To eliminate the influence of harmonic currents, the harmonic equivalent impedance of the machine system should be regulated to change the harmonic distribution characteristics. This paper improves the conventional control method through adding a harmonic control loop to prevent harmonic currents from being injected into the machine or the grid, which is then applied in the fundamental synchronous frame. Two indirect parameters are selected to realize the two control targets. Afterwards, the influence of the control system on the harmonic equivalent impedance of the machine system under the conventional method and the proposed method are compared. Finally, experimental results obtained from a 30 kW BDFM prototype verify the proposed method.
Highlights
The continued development of brushless doubly fed machines (BDFMs) has led to increasingly mature design and control methods [1], [2]
The harmonic current contents in the machine and the grid are determined by the grid harmonic impedance and the harmonic equivalent impedance of the machine system
The BDFM variable speed drive system based on a fractional unidirectional converter has wide application prospects for loads that require only limited range speed regulation
Summary
The continued development of brushless doubly fed machines (BDFMs) has led to increasingly mature design and control methods [1], [2]. The harmonic distortion of the grid voltage is not constant Both the uncontrolled rectifier and the BDFM are the loads of the power grid. This paper proposes a harmonic current control method to eliminate harmonic influence on the machine or the grid for this BDFM driving system. Main contributions of this paper are: 1) Proposing a complete circuit model of the BDFM drive system by including unidirectional converter and grid impedance to analyze harmonic distribution characteristics; 2) Improving the control method to regulate the system harmonic distribution characteristic through changing the machine harmonic equivalent impedance by selecting the PW current and voltage as the effective control parameters. The harmonic current distribution characteristics of the BDFM drive system under a weak grid and different load conditions can be obtained.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
