Voltage-type Γ-Z-source inverters are proposed in this letter. They use a unique Γ-shaped impedance network for boosting their output voltage in addition to their usual voltage-buck behavior. Comparing them with other topologies, the proposed inverters use lesser components and a coupled transformer for producing the high-gain and modulation ratio simultaneously. The obtained gain can be tuned by varying the turns ratio $\gamma _{\Gamma Z} $ of the transformer within the narrow range of $1 . This leads to lesser winding turns at high gain, as compared to other related topologies. Experimental testing has already proven the validity of the proposed inverters.

Γ-Z-Source Inverters

This paper proposes a control scheme to control the microgrid side voltage-source converter (μG-VSC) using instantaneous symmetrical components theory. The μ G-VSC with proposed control can be utilized 1) as a bidirectional power sharing converter to control the power flow from the dc side to the ac side and vice versa, based on renewable power available at the dc link; 2) as a power quality compensator with the features of reactive power compensation, load balancing, and mitigation of current harmonics generated by nonlinear loads at the point of common coupling, thus enabling the grid to supply only sinusoidal current at unity power factor; and 3) to damp out the oscillations in the μG-VSC currents effectively using damping filter in the control algorithm. The mathematical models are derived and stability aspects are analyzed in detail through the frequency domain approach. The multifunctional features of the proposed control algorithm are demonstrated using extensive simulation studies and are also validated through experimental results.

Multifunctional VSC Controlled Microgrid Using Instantaneous Symmetrical Components Theory

Inverters with high-output voltage gain usually face the problem of high-input current flowing through their components. The problem might further be exaggerated if the inverters use high-frequency magnetic devices like transformers or coupled inductors. Leakage inductances of these devices must strictly be small to prevent overvoltages caused by switching of their winding currents. To avoid these related problems, cascaded trans-Z-source inverters are proposed. They use multiple magnetic cells in an alternately cascading pattern rather than a single magnetic cell with large turns ratio. Simulation and experimental results have shown that the multicell inverters can produce the same high-voltage gain, while keeping currents and voltages of the components low. The inverters can also step down their output voltages like a traditional voltage-source inverter without compromising waveform quality.

Cascaded Multicell Trans-Z-Source Inverters

Impedance-source networks are an increasingly popular solution in power converter applications, especially in single-stage buck–boost power conversion to avoid additional front-end dc–dc power converters. In the survey papers published, no analytical comparisons of different topologies have been described, which makes it difficult to choose the best option. Thus, the aim of this paper is to present a comprehensive analytical comparison of the impedance-source-based buck–boost inverters in terms of passive component count and semiconductor stress. Based on the waveform of the input current, i.e., with or without a transformer, and with or without inductor coupling, the impedance-source converters are classified. The main criterion in our comprehensive comparison is the energy stored in the passive elements, which is considered both under constant and predefined high frequency current ripple in the inductors and the voltage ripple across the capacitors. Two-level and multilevel solutions are described. The conclusions provide a “one-stop” information source and a selection guide of impedance-source-based buck–boost inverters for different applications.

Comparison of Impedance-Source Networks for Two and Multilevel Buck–Boost Inverter Applications

This paper presents a new three-phase inverter based on the Cuk converter. The main feature of the proposed topology is that the energy storage elements, such as inductors and capacitors, can be reduced in order to improve the reliability, and reduce size and total cost. The buck-boost inherent characteristic of the Cuk converter, depending on the time-varying duty ratio, provides flexibility for standalone and grid connected applications when the required output ac voltage is lower or greater than the dc side voltage. This property is not found in the conventional current source inverter when the dc input current is always greater than the ac output or in the conventional voltage source inverter as the output ac voltage is always lower than the dc input. The proposed system allows much smaller, more reliable nonelectrolytic capacitors to be used for energy source filtering. The new three-phase inverter is convenient for photovoltaic applications where continuous input currents are required for maximum power point tracking operation. Average large and small signal models are used to study the Cuk converter's nonlinear operation. The basic structure, control design, and MATLAB/SIMULINK results are presented. Practical results substantiate the design flexibility of the Cuk-based topology controlled by a TMSF280335 DSP.

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A Single-Stage Three-Phase Inverter Based on Cuk Converters for PV Applications

Three-phase pulsewidth-modulated (PWM) boost-buck rectifiers with power-regenerating capability are investigated. The converters under consideration are capable of: (1) both voltage step-up and step-down; (2) bidirectional power processing; and (3) almost unity-power-factor operation with nearly sinusoidal AC current. Expected advantages are: (1) applicability to lower voltage applications, e.g., direct retrofit to replace diode or thyristor rectifiers; (2) switching loss reduction in the inverter load; (3) low-order harmonic control in the inverter load output voltage; (4) blanking time effect mitigation in the inverter load; and (5) a modest level of voltage sag/swell compensation. In this paper, firstly, a step-by-step power stage derivation process is described. Then, taking the Cuk-Cuk realization as an example, its operating principle and modulation scheme are described. A steady-state model and dynamic model for controller design are also described. Representative results of circuit simulations and hardware experiments are presented. Through these procedures, the feasibility of the presented three-phase PWM boost-buck rectifier with power-regenerating capability is demonstrated.

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J. Kikuchi

Papers

Three-phase PWM boost-buck rectifiers with power-regenerating capability