| Continuously increasing growth of renewable energy generation such as wind turbine(WT) and photovoltaic(PV) is posing new challenges to distribution network with increasing pressure on energy and environmental protection. The active distribution network(ADN) is an effective approach to solve the problems such as the high-penetration of intermittent renewable energy, interaction between grid and charge-discharge facilities, and also the analysis and operation of smart grid. However, the ADN is still in the development stage and there are many urgent theoretical and technical issues to be solved. A key issue of power electronic devices in distribution system is to develop the intelligent power devices in order to match the growing demand for different purposes, such as voltage regulation, reactive power compensation, harmonic suppression, energy conversion and the integration of renewable distributed generation(DG). In this dissertation, the key technologies of power quality and energy conversion in ADN are researched. The research subject is the control methods for pulse width modulation(PWM)converter with fast dynamic response and high quality of the current and voltage waveforms. The main contents include mathematical model and power analysis, voltage sag detection, control method, experimental platform development and digital signal processor(DSP) control system implementation. The process of theoretical analysis, simulation study, experimental verification and DSP code programming are proposed in order to provide appropriate assurance and technical support for development of intelligent power devices in AND system. The main contents of this dissertation are proposed as the following:1) The mathematical models, analysis and calculations of power for PWM converter are proposed. In abc stationary coordinate, the mathematical models of three-phase voltage-source PWM converter are presented using switching function description method and the calculation formulas of active power and reactive power are derived with the instantaneous power theory. Further, the power calculation equations under different coordinate systems such as ?? stationary frame and dq synchronous rotating frame are analyzed by Clarke transformation and Park transformation, respectively.2) A novel voltage sag detection method for single-phase voltage system is presented. With the sampling discrete data, a fictitious three-phase system is created from a reference single-phase voltage with30°phase angle shift according to phasor relationship phase voltage and line voltage. The delay time of proposed detection method is just1/12grid period and the theoretical delay time is1.67ms, which is faster than the instantaneous voltage dq conversion method with3.33ms delay and the ?? detection method with5.0ms delay, respectively. The sensor number and the design costs of three-phase system can be reduced using the proposed method. The implementation process and simulation results are presented.3) A novel quasi direct power control(DPC) method with fixed switching frequency is proposed. The principle of switching table modulation mechanism are discussed and the explanation of control effect to active and reactive power with different space vector from switching table is introduced in detail, respectively. The reasons for choosing different zero vectors are analyzed and the defects of power hysteresis control based on switching table are discussed. A novel quasi DPC method is proposed with the idea that PWM converter functions for rectifier and inverter, and power system control for instantaneous active and reactive power are considered simultaneously. The novel quasi DPC method with fixed switching frequency can not only control the instantaneous active and reactive power, but also give rapid regulation and protection for internal current loop. The design of controller parameters and simulation results are given and the results show the excellent performance of the proposed method for PWM converter control.4) Control methods for PWM converter based on abc coordinate, named natural coordinate in this dissertation, including direct current control(DCT), without line voltage sensors control and natural coordinate direct power control(NC-DPC), are presented. The unit vectors of active and reactive power in phase are derived using the three-phase voltages and a quadrature transformation. The total reference currents, which are equivalent to vector control, can be computed with the unit vectors. The sensorless control system is based on phase voltage estimation and virtual flux(VF) estimation. The VF are estimated using phase voltage of PWM converter with project integrator instead of traditional derivation. In NC-DPC, there are internal current loop and external power loop. Compared to the conventional control method, the natural coordinate control method has some advantages, such as no coordinate transformation, no trigonometric function and clear physical concept. The steady and transient simulation results are given and the results show the excellent performance of the proposed method for PWM converter control.5) A PWM converter integrated real-time control platform based on dSPACE is developed for experimental tests according to the V-cycle development process. The power circuit, voltage and current measurement circuit, PWM drive circuit, power supply circuit, fault diction and protection circuit are designed. The experimental tests for power quality and energy conversion are introduced including distribution static synchronous compensator(DSTATCOM), dynamic voltage restorer(DVR), unified power quality conditioner(UPQC), PWM rectifier/inverter and so on. The corresponding static and dynamic experimental results are given, and show the excellent performance of the proposed method for PWM converter control. The dynamic and static characteristics are improved compared to the method of DPC-SVM.6) A PWM converter control system is developed based on DSP. The development of50kvar DSTATCOM experimental prototype based on32-bit high-performance processor TMS320F2812is proposed. The implementation process, experimental tests and experimental results are introduced in detail.The simulation results and experimental results in this dissertation show that the proposed method of signal detection and control method for PWM converter has better detection performance and real-time control performance. The research can play a certain theory assurance and technical support for the study of power quality controller and power conversion systems and the system implementation can also provide a reference for the development of intelligent power equipments. |
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