Research On Power Quality Comprehensive Control Of Microgrid And Distribution Grid With Microgrid

Microgrid is a weak inertial system, which is different from the traditional large power grid. It is a highly nonlinear environment which contains many electronic converters, different power electronic converter control strategy between mutual coupling interference. In addition to the power quality problems in the traditional power network, the microgrid power quality problem has its unique characteristics. It is necessary to study the power quality control of the microgrid and the grid with microgrid. In view of the above question, this article separately from the micro source operation control strategy, microgrid and the grid with microgrid power quality active management method, microgrid and the grid with microgrid power quality passive management method, electric energy quality control devices in high precision control strategy. This article is from four angles to carry on the discussion and the research, specific work and innovations embodied in:For the drawbacks of traditional micro-source inverter control algorithms need switch between the micro-grid grid-tied and islanding operation, a novel hybrid control mode for micro-grid seamless control is proposed in this paper. The hybrid control strategy algorithm can work with grid-tied and islanding state, which eliminated the state switching instant impact when the software switches. In the stage of the micro-grid grid-tied the hybrid control mode make the micro-source inverter with active power filter functions, eliminating harmonic current created by the non-linear loads. A proportional resonant controller is utilized in voltage loop effectively eliminates the inverter output voltage static error in islanding state. When the power quality compensation equipment can not be installed at each improtent node in microgrid due to the conditions, the traditional local compensation stratage will no longer apply. The microgrid network topology model is established to guarantee the power quality of important nodes, get the output command current and reasonable installation location of the power quality compensation equipment. Mathematical programming model is established for a number of important nodes in this paper, configuration problem of power quality compensation equipment is decomposed into two parts:the primary problem and the secondary problem. The location of power quality compensation equipment is determined at the primary level, while the output command current is solved at the secondary level, the primary problem and the secondary problem iterative to obtain the optimal configuration.For low-voltage micro-grid lines generally mix resistive and inductive impedance, classic droop control equation is no longer applicable. An improved method which adds virtual impedance in the voltage-current dual loop controller is adopted, which reduces the sensitivity of inverter power sharing control for the output line impedance. In addition, the reactive power controller without integral element in the traditional power control loop makes output voltage have static error in the island situation, so an improved power controller is adopted to make the micro-source output voltage have no static error, at the same time the reactive power output is not associated with output line impedance. For the low accuracy power sharing and effects of nonlinear loads problems with the traditional droop controller in low-voltage micro-grid, the equivalent line output impedance is designed to be resistive near the power frequency to meet the line impedance characteristics of low-voltage micro-grid by designing the virtual impedance, while reducing the inverter output power sharing control of the sensitivity of the line impedance. The equivalent line output impedance is designed to be inductive, which effectively suppress high frequency harmonics caused by non-linear loads. At the same time, the improved power control loop to avoid voltage dropping caused by a larger equivalent output impedance of the resistive, auto-tracking phase angle controller ensure a smooth transition during the grid-tie operation.As large-capacity nonlinear load harmonic compensation, the paper presents multiple APFs parallel operation to improve the system compensation capacity. For parallel operation coordinated control scheme of multiple APFs, proportionate current limiting and truncating current limiting ensure the safe and reliable operation of the APFs. In the classical algorithm of active power filter, harmonic current detection part of the load current is just a feed-forward link. New direct and indirect current control methods for a fault-tolerant active power filter topology are presented in this paper. Since a three-phase four-switch topology has a phase bridge current which cannot be directly controlled, a hysteresis control method in the α-β plane which controls the three-phase current in the two-phase stationary coordinate system is proposed. The improved SVPWM algorithm is able to eliminate the operation of the trigonometric functions in the traditional algorithm by rotating the α-βcoordinates and alternating the sequence of the output vectors, which in turn simplifies the algorithm and reduces the switching frequency. The selection of the DC-side reference voltage and DC-side capacitor equalization strategy are also discussed.Thus, the load and output current detection unit can be eliminated by using the non-harmonic detection algorithm, which controls the DC voltage loop. In order to enhance its dynamic performance, a non-harmonic detection control method based on the adaptive prediction algorithm is proposed. The coefficient of adaptive filter under this method is rolling on-line iterative, the step is renewed in time, as well as the grid current is able to be predicted in the next state. Deadbeat control is widely used in active power filter control. However, deadbeat control without the prediction is actually a control method with one or two beats shortage. Therefore, in this paper, a novel method built-in a repetitive controller is put forward to make up periodic error in deadbeat algorithm and discrete control system. The design of the plug-in repetitive controller ensures stability margin and steady precision of the system. Accounting for the poor dynamic performance of repetitive controller, the paper uses hysteresis control strategy based on space vector combined with double hysteresis control thoughts. When the error current falls into the inner ring, the accurate switching state can be obtained by the optimal vector modulation. While the error current falls into the outer ring, the error current decreases to a new steady state through the fastest vector control.