Efficient multiple-reference-frame controller for harmonic suppression in custom power devices

• Efficient implementation of controllers in multiple reference frames.
• Voltage sags, harmonics and unbalances in the supply voltage are tackled.
• The controller deals with slow grid frequency variations.
• Experimental results are presented.

Tracking harmonic currents and voltages in electric power systems with custom power devices exceeds the capabilities of conventional Proportional+Integral controllers and more sophisticated algorithms are required, especially under grid-frequency variations. This paper presents a control method based on multiple reference frames for harmonic control in the context of a series active power filter. The proposed scheme allows recursive calculation when referring signals to reference frames rotating synchronously with harmonic equivalent space vectors whilst a minimum of trigonometric-function evaluations are required. Furthermore, the control of each harmonic can be dealt with using simple integral controllers applied to the transformed signals. The paper presents the closed-loop-stability analysis and experimental results of a series active power filter. A scenario with grid-frequency variations is considered to show the intrinsic adaptation capability of the proposed controller.