Shoot-through Zero State Research Articles

Two new impedance source network topologies for inverter applications

ABSTRACTIn the last decade, the impedance source networks have been vastly used in electrical power conversion such as in electric vehicles, industrial machines, medical systems and avionics, with considerable efficiency improvements. In this study, two new impedance source network topologies for inverter applications have been designed and tested. The first one is a one-cell switched inductor (SL), the second is a two-cell switched inductor (X-SL) combined with the classical Z-source inverter (ZSI). This novel combination allows the switched inductor to store the unused source energy in the interval when the source separates from the ZSI network during the shoot-through zero state. The design is generalised by adding multiple branches of series inductors and diodes which further improve the circuit performance. The National Instrument Multisim programme is used for the simulations of the new topologies. Both of the proposed topologies, SL combined with classical ZSI (SL&ZSI) and X-SL combined with classical ZSI (X-SL&ZSI), are tested with specific inductance and capacitance values. Major improvements are observed in the boost factor and the elimination of the start-up inrush current for both topologies, compared to the classical ZSI scheme. Furthermore, in both topologies, a significant reduction in the capacitor stress levels is obtained.

Research on a Time-Variant Shoot-Through Modulation Strategy for Quasi-Z-Source Inverter

This letter proposes a time-variant shoot-through pulsewidth modulation strategy for the traditional modulation techniques used in quasi-Z-source inverters. By introducing the proposed strategy into the traditional modulation techniques, like the simple boost modulation, the bus voltage amplitude can be reduced at the nonpeak areas, and the switching loss can be greatly saved to improve system efficiency. Because the output voltage gain can still be guaranteed, the waveform quality is not influenced. At the same time, for the traditional zero states in the proposed strategy are fully used as the shoot-through zero states, the switching times can be evidently reduced and the system efficiency can be further increased. Theoretical analysis and experimental results are presented to verify the real performance.

Stator Current Harmonic Reduction in a Novel Half Quasi-Z-Source Wind Power Generation System

The generator stator current gets distorted with unacceptable levels of total harmonic distortion (THD) because impedance-source wind power generation systems use three-phase diode rectifiers. The stator current harmonics will cause increasing losses and torque ripple, which reduce the efficiency and stability of the system. This paper proposes a novel half quasi-Z-source inverter (H-qZSI) for grid-connected wind power generation systems, which can reduce the generator stator current harmonics a great deal. When H-qZSI operates in the shoot-through zero state, the derivative of the generator stator current is only determined by the instantaneous value of the generator stator voltage, so the nonlinear relationship between generator stator current and stator voltage is improved compared with the traditional impedance-source inverter. Theoretically, it is indicated that the stator current harmonics can be reduced effectively by means of the proposed H-qZSI. Finally, simulation and experimental results are given to verify the theoretical analysis.

Comparative Analysis of PWM Controlling Techniques of Single Phase Z-Source Inverter

Background/Objectives: This paper analysis the various PWM controlling Techniques of Single Phase Z-Source Inverter (ZSI) and suggest the most suitable controlling technique for renewable power conversion applications. Methods/Statistical Analysis: This ZSI is the Buck-Boost Inverter. The boost in the output voltage can be controlled by Shoot-Through (ST) zero state. This ST zero state can be controlled by Simple Boost Control (SBC), Maximum Boost Control (MBC) and Constant Boost Control (CBC) methods. The performances of the controlling techniques are investigated against the simplicity in control technique, harmonic content and the peak value of output voltage. The controlling techniques are validated by simulation of the circuits in Simulink. Findings: The MBC method is the simplest one to implement but voltage stress across the switches is high. The CBC method gives a higher voltage gain but implementing the Shoot-Through envelope is difficult. In SBC method Voltage stress across the switches is less but voltage gain is less. The Photo Voltaic Energy conversion system requires high voltage gain with reduced harmonic content in the output. Therefore, the CBC method is suitable for the Solar PV system to provide higher voltage gain with less harmonic content in the output voltage. Application/Improvements: The CBC method gives higher voltage gain with less harmonic content in the output voltage, therefore it is most suitable for the standalone Solar PV system.

Modelling analysis and power loss of coupled‐inductor single‐stage boost inverter based grid‐connected photovoltaic power system

The coupled-inductor single-stage boost inverter (CI-SSBI) has been proposed and applied to photovoltaic (PV) power system. As previously presented, the CI-SSBI has the feature of stepping up input voltage to a higher voltage level by properly designing the turns ratio of coupled inductor and regulating the shoot-through duty cycle. The CI-SSBI based grid-connected PV system integrates some characteristics together in one stage, including boost inversion, feeding current into the grid with high power factor, and maximum power point tracking. Moreover, system reliability can be improved by using the shoot-through zero states as a normal operation mode. This study focuses on the power loss analysis of main elements, and control analysis of both bus voltage loop and inner current loop of the proposed PV system. Simulation and experimental results are presented to verify the analysis and show the real system performance.

High-efficient three-phase on-line UPS by using T-source inverter with third harmonic injected maximum constant boost PWM control

This paper presents the analysis of three-phase on-line uninterruptible power supply (UPS) by employing T-source inverter (TSI) with third harmonic injected maximum constant boost PWM control and the results are compared with traditional UPS. Traditional UPS consists of step-up transformer or DC–DC booster along with voltage source inverter which decreases the efficiency and increases energy conversion cost. The proposed three-phase UPS using TSI has high-voltage boost capability through shoot-through zero state which is not present in traditional voltage source inverter (VSI) and current source inverter. This proposed UPS with TSI increases the efficiency with fewer components, reduces the harmonics, increases the voltage gain, and reduces the voltage stress. The performance of three-phase on-line UPS based on TSI is analyzed and evaluated in MATLAB/SIMULINK software and the results are compared with Z-source inverter-fed UPS and VSI-fed UPS. Experimental results are presented for the validation of the simulation and theoretical analysis.

English

In many modern energy conversion systems, a dc voltage, which is provided from a sustainable energy source or energy storage device, must be boosted and converted to an Ac voltage with a fixed amplitude and frequency. The single-stage inverter circuit provides boost inversion ability which can eliminate the limitations of conventional voltage source inverter. By regulating the shoot-through zero state and the parameters of coupled inductor, the proposed inverter can boost the bus voltage and output desired output voltage even when input dc voltage is low. By controlling the shoot-through zero state when the coupled inductor is present, the fuel cell output voltage is controlled. When a very high boost gain is demanded, the duty cycle may come to its extreme and large duty cycles causes serious reverse-recovery problems. The single-stage operation of the converter may lead to improved reliability and higher efficiency .The results are obtained using MATLAB/SIMULINK software.

Coupled‐inductor single‐stage boost inverter for grid‐connected photovoltaic system

This study presents a coupled-inductor single-stage boost inverter for grid-connected photovoltaic (PV) system, which can realise boosting when the PV array voltage is lower than the grid voltage, converting dc voltage into ac voltage, feeding current to the grid with high-power factor and maximum power point tracking (MPPT) together. By introducing an impedance network including coupled inductor in front of the three-phase inverter bridge, and adjusting the previously forbidden shoot-through zero state, the converter can step up input voltage to a higher voltage level. System reliability is also improved by using shoot-through zero state as a normal operation mode. Cost can be reduced by single-stage operation and also by using economical MPPT method only via grid current. Theoretical analysis, simulation and experimental results are presented to verify its good performance.

Three Carrier PWM Control of Improved Z-Source Inverter

A kind of three carrier PWM control method is put forward for improved Z-source inverter. The switches are controlled by comparing three carrier and three reference waves. The shoot-through zero state are injected in the time when traditional zero vector worked. The voltage gain is determined by the dc offset voltage of carrier wave when the modulation index is constant. Boost factor is made independent of the modulation index. And the switching loss is reduced. The voltage stress on the capacitances and switches are analyzed in detail. Simulation results show that this method possesses better control performance.

Single-Stage Boost Inverter With Coupled Inductor

Renewable power systems as distributed generation units often experience big changes in the inverter input voltage due to fluctuations of energy resources. Often, a front-end boost converter is added to step up the dc voltage when the energy resources are at a weak point. However, when a very high boost gain is demanded, the duty cycle may come to its extreme, and large duty cycles causes serious reverse-recovery problems. This paper proposes a novel single-stage boost-type inverter with coupled inductor. By introducing impedance network, including coupled inductor, into the three-phase bridge inverter, and adjusting the previously forbidden shoot-through zero state, the converter can realize a high boost gain and output a stable ac voltage. The single-stage operation of the converter may lead to improved reliability and higher efficiency. Theoretical analysis, simulation, and experimental results are presented to verify good performance.

Low-Cost Semi-Z-source Inverter for Single-Phase Photovoltaic Systems

This paper presents several nonisolated semi-Z-source inverters for a single-phase photovoltaic (PV) system with low cost and doubly grounded features. These semi-Z-source inverters employ the Z-source/quasi-Z-source network and only two active switches to achieve the same output voltage as the traditional voltage-fed full-bridge inverter does. The two active switches of the semi-Z-source inverter are controlled complementarily. Different from the traditional single-phase Z-source/quasi-Z-source inverter, shoot-through zero state is not applicable to the semi-Z-source inverter. The input dc source and the output ac voltage of the semi-Z-source inverter share the same ground, thus leading to less leakage ground current advantages over other nondoubly grounded inverters, such as voltage-fed full-bridge inverter. This is a preferred feature for nonisolated grid-connected inverters, especially in PV application. A revised nonlinear sinusoid pulse width modulation method for a semi-Z-source inverter is also proposed. By using this method, desired duty cycle can be generated to output the sinusoidal voltage. Other dc-dc converters with similar voltage gain curve, which can also be used as a single-phase inverter, are also discussed and summarized. A single-phase semi-Z-source inverter prototype is built; experimental results are provided to verify and demonstrate the special features of the proposed circuit.

Switched Inductor Z-Source Inverter

On the basis of the classical Z-source inverter, this paper presents a developed impedance-type power inverter that is termed the switched inductor (SL) Z-source inverter. To enlarge voltage adjustability, the proposed inverter employs a unique SL impedance network to couple the main circuit and the power source. Compared with the classical Z-source inverter, the proposed inverter increases the voltage boost inversion ability significantly. Only a very short shoot-through zero state is required to obtain high voltage conversion ratios, which is beneficial for improving the output power quality of the main circuit. In addition, the voltage buck inversion ability is also provided in the proposed inverter for those applications that need low ac voltages. Similar to the classical Z-source inverter, the proposed concepts of SL Z-source inverter can be applied to various applications of dc-ac, ac-ac, dc-dc, and ac-dc power conversion. A detailed topology analysis and a generalized discussion are given. Both simulation and experimental results verify the analytical results.