Dynamic model of A DC-DC quasi-Z-source converter (q-ZSC)

Two quasi-Z-source DC-DC converters (q-ZSCs) with buck-boost converter gain were recently proposed. The converters have advantages of continuous gain curve, higher gain magnitude and buck-boost operation at efficient duty ratio range when compared with existing q-ZSCs. Accurate dynamic models of these converters are needed for global and detailed overview by understanding their operation limits and effects of components sizes. A dynamic model of one of these converters is proposed here by first deriving the gain equation, state equations and state space model. A generalized small signal model was also derived before localizing it to this topology. The transfer functions (TF) were all derived, the poles and zeros analyzed with the boundaries for stable operations presented and discussed. Some of the findings include existence of right-hand plane (RHP) zero in the duty ratio to output capacitor voltage TF. This is common to the Z-source and quasi-Z-source topologies and implies control limitations. Parasitic resistances of the capacitors and inductors affect the nature and positions of the poles and zeros. It was also found and verified that rather than symmetric components, use of carefully selected smaller asymmetric components L1 and C1 produces less parasitic voltage drop, higher output voltage and current under the same conditions, thus better efficiency and performance at reduced cost, size and weight

Design of module level converters in photovoltaic power systems

The application of distributed maximum power point tracking (DMPPT) technology in solar photovoltaic (PV) systems is a hot topic in industry and academia. In the PV industry, grid integrated power systems are mainstream. The main objective for PV system design is to increase energy conversion efficiency and decrease the levelized cost of electricity of PV generators. This thesis firstly presents an extensive review of state-of-the-art PV technologies. With focus on grid integrated PV systems research, various aspects covered include PV materials, conventional full power processing DMPPT architectures, main MPPT techniques, and traditional partial power processing DMPPT architectures. The main restrictions to applying traditional DMPPT architectures in large power systems are discussed. A parallel connected partial power processing DMPPT architecture is proposed aiming to overcome existing restrictions. With flexible ‘plug-and-play’ functionality, the proposed architecture can be readily expanded to supply a downstream inverter stage or dc network. By adopting smaller module integrated converters, the proposed approach provides a possible efficiency improvement and cost reduction. The requirements for possible converter candidates and control strategies are analysed. One representative circuit scheme is presented as an example to verify the feasibility of the design. An electromagnetic transient model is built for different power scale PV systems to verify the DMPPT feasibility of the evaluated architecture in a large-scale PV power system. Voltage boosting ability is widely needed for converters in DMPPT applications. Impedance source converters (ISCs) are the main converter types with step-up ability. However, these converters have a general problem of low order distortion when applied in dc-ac applications. To solve this problem, a generic plug-in repetitive control strategy for a four-switch three-phase ISC type inverter configuration is developed. Simulation and experimental results confirm that this control strategy is suitable for many ISC converters.The application of distributed maximum power point tracking (DMPPT) technology in solar photovoltaic (PV) systems is a hot topic in industry and academia. In the PV industry, grid integrated power systems are mainstream. The main objective for PV system design is to increase energy conversion efficiency and decrease the levelized cost of electricity of PV generators. This thesis firstly presents an extensive review of state-of-the-art PV technologies. With focus on grid integrated PV systems research, various aspects covered include PV materials, conventional full power processing DMPPT architectures, main MPPT techniques, and traditional partial power processing DMPPT architectures. The main restrictions to applying traditional DMPPT architectures in large power systems are discussed. A parallel connected partial power processing DMPPT architecture is proposed aiming to overcome existing restrictions. With flexible ‘plug-and-play’ functionality, the proposed architecture can be readily expanded to supply a downstream inverter stage or dc network. By adopting smaller module integrated converters, the proposed approach provides a possible efficiency improvement and cost reduction. The requirements for possible converter candidates and control strategies are analysed. One representative circuit scheme is presented as an example to verify the feasibility of the design. An electromagnetic transient model is built for different power scale PV systems to verify the DMPPT feasibility of the evaluated architecture in a large-scale PV power system. Voltage boosting ability is widely needed for converters in DMPPT applications. Impedance source converters (ISCs) are the main converter types with step-up ability. However, these converters have a general problem of low order distortion when applied in dc-ac applications. To solve this problem, a generic plug-in repetitive control strategy for a four-switch three-phase ISC type inverter configuration is developed. Simulation and experimental results confirm that this control strategy is suitable for many ISC converters

Advances in Control of Power Electronic Converters

This book proposes a list of contributions in the field of control of power electronics converters for different topologies: DC-DC, DC-AC and AC-DC. It particularly focuses on the use of different advanced control techniques with the aim of improving the performances, flexibility and efficiency in the context of several operation conditions. Sliding mode control, fuzzy logic based control, dead time compensation and optimal linear control are among the techniques developed in the special issue. Simulation and experimental results are provided by the authors to validate the proposed control strategies

Power Converters in Power Electronics

In recent years, power converters have played an important role in power electronics technology for different applications, such as renewable energy systems, electric vehicles, pulsed power generation, and biomedical sciences. Power converters, in the realm of power electronics, are becoming essential for generating electrical power energy in various ways. This Special Issue focuses on the development of novel power converter topologies in power electronics. The topics of interest include, but are not limited to: Z-source converters; multilevel power converter topologies; switched-capacitor-based power converters; power converters for battery management systems; power converters in wireless power transfer techniques; the reliability of power conversion systems; and modulation techniques for advanced power converters

Enhanced Performance Bidirectional Quasi-Z-Source Inverter Controller

A novel direct control of high performance bidirectional quasi-Z-source inverter (HPB-QZSI), with optimized controllable shoot-through insertion, to improve the voltage gain, efficiency and to reduce total harmonic distortion is investigated. The main drawback of the conventional control techniques for direct current to alternating current (DC-AC) conversion is drawn from the multistage energy conversion structure, which implies complicated control, protection algorithms and reduced reliability due to the increased number of switching devices. Theoretically, the original Z-source, Quasi-Z-source, and embedded Z-source all have unlimited voltage gain. Practically, however, a high voltage gain (>2 or 3), will result in a high voltage stress imposed on the switches. Every additional shoot-through state increases the commutation time of the semiconductor switches, thereby increasing the switching losses in the system. Hence, minimization of the commutation time by optimal placing of the shoot-through state in the switching time period is necessary to reduce the switching loss. To overcome this problem, a combination of high performance bidirectional quasi-Z-source inverter with a sawtooth carrier based sinusoidal pulse width modulation (SPWM) in simple operation condition for maximum boost control with 3rd harmonic injection is proposed. This is achieved by voltage-fed quasi-Z-source inverter with continuous input current, implemented at the converter input side which can boost the input voltage by utilizing the extra switching state with the help of shoot-through state insertion technique. This thesis presents novel control concepts for such a structure, focusing mainly on the control of a shoot-through insertion. The work considers the derivation and application of direct controllers for this application and scrutinizes the technical advantages and potential application issues of these methodologies. Based on the circuit analysis, a small signal model of the HPB-QZSI is derived, which indicates that the circuit is prone to oscillate when there is disturbance on the direct current (DC) input voltage. Therefore, a closed-loop control of shoot-through duty cycle is designed to obtain the desired DC bus voltage. The DC-link boost control and alternating current (AC) side output control are presented to reduce the impacts of disturbances on loads. The proposed strategy gives a significantly high voltage gain compared to the conventional pulse width modulation (PWM) techniques, since all the zero states are converted into shoot-through states. The simulated results verify the validity and superiority of the proposed control strategies

Model Predictive Control Technique of Multilevel Inverter for PV Applications

Renewable energy sources, such as solar, wind, hydro, and biofuels, continue to gain popularity as alternatives to the conventional generation system. The main unit in the renewable energy system is the power conditioning system (PCS). It is highly desirable to obtain higher efficiency, lower component cost, and high reliability for the PCS to decrease the levelized cost of energy. This suggests a need for new inverter configurations and controls optimization, which can achieve the aforementioned needs. To achieve these goals, this dissertation presents a modified multilevel inverter topology for grid-tied photovoltaic (PV) system to achieve a lower cost and higher efficiency comparing with the existing system. In addition, this dissertation will also focus on model predictive control (MPC) which controls the modified multilevel topology to regulate the injected power to the grid. A major requirement for the PCS is harvesting the maximum power from the PV. By incorporating MPC, the performance of the maximum power point tracking (MPPT) algorithm to accurately extract the maximum power is improved for multilevel DC-DC converter. Finally, this control technique is developed for the quasi-z-source inverter (qZSI) to accurately control the DC link voltage, input current, and produce a high quality grid injected current waveform compared with the conventional techniques. This dissertation presents a modified symmetrical and asymmetrical multilevel DC-link inverter (MLDCLI) topology with less power switches and gate drivers. In addition, the MPC technique is used to drive the modified and grid connected MLDCLI. The performance of the proposed topology with finite control set model predictive control (FCS-MPC) is verified by simulation and experimentally. Moreover, this dissertation introduces predictive control to achieve maximum power point for grid-tied PV system to quicken the response by predicting the error before the switching signal is applied to the converter. Using the modified technique ensures the iii system operates at maximum power point which is more economical. Thus, the proposed MPPT technique can extract more energy compared to the conventional MPPT techniques from the same amount of installed solar panel. In further detail, this dissertation proposes the FCS-MPC technique for the qZSI in PV system. In order to further improve the performance of the system, FCS-MPC with one step horizon prediction has been implemented and compared with the classical PI controller. The presented work shows the proposed control techniques outperform the ones of the conventional linear controllers for the same application. Finally, a new method of the parallel processing is presented to reduce the time processing for the MPC

Isolated Single-stage Power Electronic Building Blocks Using Medium Voltage Series-stacked Wide-bandgap Switches

The demand for efficient power conversion systems that can process the energy at high power and voltage levels is increasing every day. These systems are to be used in microgrid applications. Wide-bandgap semiconductor devices (i.e. Silicon Carbide (SiC) and Gallium Nitride (GaN) devices) are very promising candidates due to their lower conduction and switching losses compared to the state-of-the-art Silicon (Si) devices. The main challenge for these devices is that their breakdown voltages are relatively lower compared to their Si counterpart. In addition, the high frequency operation of the wide-bandgap devices are impeded in many cases by the magnetic core losses of the magnetic coupling components (i.e. coupled inductors and/or high frequency transformers) utilized in the power converter circuit. Six new dc-dc converter topologies are propose. The converters have reduced voltage stresses on the switches. Three of them are unidirectional step-up converters with universal input voltage which make them excellent candidates for photovoltaic and fuel cell applications. The other three converters are bidirectional dc-dc converters with wide voltage conversion ratios. These converters are very good candidates for the applications that require bidirectional power flow capability. In addition, the wide voltage conversion ratios of these converters can be utilized for applications such as energy storage systems with wide voltage swings

Emerging Power Electronics Technologies for Sustainable Energy Conversion

This Special Issue summarizes, in a single reference, timely emerging topics related to power electronics for sustainable energy conversion. Furthermore, at the same time, it provides the reader with valuable information related to open research opportunity niches

Emerging Power Electronics Technologies for Sustainable Energy Conversion

This Special Issue summarizes, in a single reference, timely emerging topics related to power electronics for sustainable energy conversion. Furthermore, at the same time, it provides the reader with valuable information related to open research opportunity niches