Research On Single-stage Boost Inverters And Their Application Technologies

Traditional voltage-source inverter (VSI) is buck-type converter. On the one hand, of low or wideinput voltage, such as renewable power system, a boost converter should be added in front of theinverter bridge to step up the dc input voltage to a higher level to output a desired ac voltage. On theother hand, the conventional VSI should avoid the shoot-through issue in case of overcurrent damage.Therefore, dead-time is always used. While it will casuse output voltage distortion. Under thebackground, the thesis proposes novel single-stage boost inverters, and researches the circuitcharacteristics and their advantages and problems in applications. The contents are shown as follow:The thesis researches a novel coupled-inductor single-stage boost inverter (CL-SSBI). Byintroducing a unique impedance network with coupled inductor and previously forbiddenshoot-through zero states, this converter can output ac voltage much higher than the dc input. Thesteady-state performance and boost characteristics of CL-SSBI, the design procedures of the keycomponents, the influence of impedance network to dynamic performance and the losses of the circuitare analyzed in detail and verified. By introducing the concept of swithed coupled inductor to ZSI andquasi-ZSI, the paper proposes swithed-coupled-inductor ZSI (SCL-ZSI) and swithed-coupled-inductorquasi-ZSI (SCL-qZSI). The steady-state performance and boost characteristics, the design proceduresand stresses of the key components are analyzed and verified.Then CL-SSBI is applied to grid-connected phovoltanic power system to realize boost, inversion,fed to the gird with unity power factor and maximum power tracking in one conversion stage. Itscontroller is analyzed and designed. In order to further decrease the volumn, weight and cost of thesystem, and increase the conversion efficiency, the transformerless photovoltaic power system basedCL-SSBI is also analyzed. To eliminate the leakage current and keep the advantages of impedancenetwork, only a diode is added in the front of the topology compare to the original topology, to blockthe leakage current loop when in the active vector and open-zero vector. Meanwhile, the near-statePWM technique is applied with shoot-through zero vectors is used. By using this modulation method,the VDE0126-1-1standard can be satisfied.In order to improve the conversion effierency, decrease the current stress of coupled inductor andsimplify the circuit structure, single-stage boost inverters with tapped inductor networks are proposed,including tapped-inductor quasi-Z-source inverter (TL-qZSI), tapped-inductor single-stage boostinverter (TL-SSBI) and double-tapped-inductor single-stage boost inverter (DTL-SSBI). Compared to ZSI, TL-qZSI not only improves the boost ability, decreases the capacitances and their voltagestresses, but also has common ground between input source and dc-link and continuous input current,which is suitable for renewable power system. TheTL-SSBI is more concise and practical, and hashigher boost ability.To discuss the realization of electrolytic-less TL-qZSI, the paper presents all the possible steadystates of the TL-qZSI proposed. It is shown that, the abnormal states can be avoided by selectingsuitable value of the capacitors and inductors. The paper also presents guidelines to design theimpedance network accurately and predicts the critical values of inductance and capacitance. It is alsofind that smaller capacitance can be used to process power conversion, which means film capacitorwith high reliability and low capacitance can be used to maintain the nomal operation.The TL-qZSI without electrolytic capacitor is used to adjustable speed system with single-phaseac input. By introducing film capacitors, system reliability is improved and volumn and weight arereduced. Without large electrolytic capacitors, the dc-link would couple ripple related to input acsource. Then harmonic is injected into shoot-through dudy cycle and modulation index to suppressbus voltage ripple and improve input power factor, respectively. Experimental results are carried outto verify that the in the condition of adjustable speed system with large inertia load, the performancesof riding through input voltage sag, high input power factor and speed control can be realized.