Digital Control Strategy for Harmonic Compensation of Dynamic Voltage Restorer - Intelligent Computing for Sustainable Energy and Environment - page 10

Digital Control Strategy for Harmonic
Compensation of Dynamic Voltage Restorer
Jianwei Wang, Xiaoguang Hu, Guoqing Hu, and Yi Wang
School of Automation Science and Electrical Engineering, Beihang University,
100191, Beijing, China
[e-mail]
Abstract. To make dynamic voltage restorer (DVR) compensate the
low-order harmonic voltage, overcome the effects on system performance
of digital control, and improve the voltage compensation effect, a dual
closed-loop digital PR control strategy, consisting of voltage outer loop
fundamental proportional resonant (PR) control and current inner loop
low-order harmonic PR control is proposed. The discretization methods
of PR controller are analysed, a detailed analysis and parameter design
of the fundamental PR controller and the 3rd, 5th and 7th harmonic PR
controller in the discrete domain are carried out. The analysis shows that
the harmonic PR controller can effectively compensate for the 3rd, 5th
and 7th harmonic voltage, the fundamental PR controlled can achieve
zero steady-state error tracking and inhibit the effects on output voltage
of load current, and digital control system has good dynamic response
characteristics. Based on the theoretical analysis, 11KVA DVR prototype
is developed and tested. The effectiveness and feasibility of the proposed
control strategy are verified by experimental results.
Keywords: dynamic voltage restorer, harmonic compensation, digital
control, fundamental PR controller, harmonic PR controller.
1 Introduction
When the dynamic voltage restorer detects the system voltage, if the system
voltage drops, the invert unit will instantaneously produce dynamic offset voltage
to compensate the dropping voltage to a rate level. That will ensure normal
operation for the system sensitive load [1-3].
As the DVR is a new power quality series compensation device, the domes-
tic and foreign relevant researchers have made enormous study on its control
strategy. But few DVR control strategy considers the distortion of the voltage
waveform caused by low order harmonics which are produced by the dead time
of the inverter unit switching devices and the nonlinear load [8], and calculation
delay of digital control causing the adverse effects on the dynamic characteristics
of the DVR.
In order to improve the DVR inverter unit's ability to restrain the low or-
der harmonics, overcome digital control's effect on the system and have better