Research On The Single-phase Unified Power Quality Controller

Power is regarded as the most convenient source, and promotes the progress of the modern technology and the quick development of social economy. Recently, as commodity, power is accepting the governmental guidance and the supervision of public opinion in market. The certified power quality has become a common goal of the power department and user, and is also hot-business that the power equipment manufacturer concerned. So, power quality is one of the goals of the robust smart grid that our country is currently building. Since 1980s, FACTS based on the power electronic technology has been widely researched, among which Customer Power (CUSPOW) facing the distribution systems is an efficiency method to resolve the power quality. UPQC is considered the most promising control equipment for the power quality, and has comprehensive adjustment ability among many CUSPOW equipments, which consists of the series and shunt converter. It not only improves the power quality of the grid-side, and get the high power factor, but also can improve power quality of loading-side and stabilize the load voltage. In this paper, five aspects of the research on the single-phase UPQC system are presented, by the method of the engineering design.This paper analyzes the work principle and the general control strategies. According to DC-side has no the large-capacity storage unit of the single-phase UPQC, the strategy of the double current source is put forward. It can make the series converter become the sine current-source, which stablizes the load voltage and isolates the harmonic interference; make the shunt converter become the non-sine current-source, which compensates the reactive power of the load and restraints the harmonic. The Paper carries through the theoretical analysis based on the system stability. On the assumption condition, it has proved the feasibility of the separate control of series and shunt converter from the mathematical point of view, and has deduced the analytic expression of the control method. It also discusse the active power flow and reactive power flow of the system are in the different condition. And it points out the difference between the theoretical hypothesis and the actual situation validated through the latter experiments. It discusses the influence of V-A capacity of the system because of the different factors, which provides the intuitive and quantitative guideline for the system design.According to the features of the strategy of the double current source, the paper discusses the principle of adaptive harmonic detection and the method of the control instruction extraction in detail. Through the simulation and the experiment, the disadvantage of the traditional variable step-size arithmetic has appeared when detecting the large-signals of the sudden-changing. So the paper presents the optimizing variable step-size arithmetic based on the estimation-error fixed-frequency filter. And then, the experiment of the optimizing variable step-size arithmetic can substantially improve the steady-state accuracy to remain the good dynamic response of the original method. This optimizing method expands the scope of application of the strategy of the double current source as to variable loads.Based on the hypothesis of the separate control, the series converter is functionally made equivalent to DVR. The converter can control the resistive load of the rated current by the way of controlling the sinusoidal current source, through the magnetometive restrictions of the series transformer, which means to indirectly control the rated load voltage. The control model is constructed with the Period Average Model (PAM) of the load current. The method of the Magnetizing Current Compensation (MCC) is put forward in accordance with the effect of the exciting current of the series transformer. Through the experiment, it shows that the load-current direct-control method can stabilize the load voltage and restraint the fluctuation of the grid voltage, that MCC can evidently improve the precision of the load voltage.Same way, the shunt converter is functionally made equivalent to APF, and the method of the traditional compensation for the non-sinusoidal current source is used in the control. Considering the establishment and stability of the DC-voltage is the priority of the normal operation of the UPQC system, the shunt converter is controlled as PWM rectifier in order to meet the demands of the DC voltage; the function of UPQC energy flow is achieved by controlling the stability of DC-voltage; the function of APF is achieved by adding the reactive and harmonic current instruction. Through the simulation and experiments, it finds that the proportional control can compensate the load reactive power but not restraint the harmonic. As for this, the multi-control strategy is induced combining the proportional control with the repetitive control which is introduced in detail. And the design procedure of the repetitive controller is summarized; a set of the practical engineering methods is concluded. It indicates that adding the repetitive control technology is to improve the effect of the current harmonic compensation and the function of APF.At last, this paper summarizes the above design parameters, and the single-phase UPQC (10kVA) experiment platform is set up. It discusses the design of the control system, and designs the START and STOP procedure of the system. Based on the double current source control strategy of UPQC, the comprehensive experiments on UPQC system are carried out under the various working condition. It verifies the validity of the control strategy, and analyzes the system performance of the UPQC in detail.