U. Shajith Ali

A novel space vector PWM for Z-source inverter

This paper presents a novel space vector pulse width modulation (SVPWM) technique for three phase Z-source inverter. The proposed modified SVPWM has an additional shoot-through state for boosting the dc link voltage of the inverter beside active and zero states. The shoot-through states are evenly assigned to each phase within zero state. So zero voltage period is diminished for generating a shoot-through time, and active states are unchanged. Simulation and experimental results are presented to demonstrate the new features.

A novel carrier based pulse width modulation technique for quasi-z-source inverter with improved voltage gain

This paper proposes a new carrier based pulse width modulation (PWM) strategy for the quasi-z-source inverter (QZSI). The conventional triangular wave carrier used in simple boost control technique is replaced by sine wave, which improves the shoot-through duty ratio for a given modulation index. The technique is to employ sine wave as both carrier and reference signal, with which the simple boost control for the shoot-through states is integrated to obtain an output voltage boost. The proposed strategy gives a significantly high voltage gain compared to the traditional PWM techniques. Detailed analysis of output voltage gain, individual harmonic contributions and THD for various modulation indices is simulated and the results are presented.

Z-source inverter with improved performance for photovoltaic applications

A Z-source inverter with a modified carrier based pulse width modulation technique is proposed for photovoltaic systems. In this new technique, two carrier waves and three reference waves are used to produce the switching pulses. This paper demonstrates that the Z-source inverter can boost DC voltage when needed, perform maximum tracking and minimum output distortion, and interface with photovoltaic system. The control method is analyzed to exhibit the novelty of features. The control algorithm is corroborated by simulation and experimental results. A comparison in harmonic distortion between the new and traditional pulse width modulation techniques is performed.

Bipolar multicarrier PWM techniques for cascaded quasi-Z-source multilevel inverter

Quasi-Z-source inverters are educed with additional advantages of continuous current from source, lower switch stress and smaller component ratings in addition to buck/boost capability, inversion and single stage conversion of the basic topology of Z-source inverters. This work proposes a novel topology of cascaded quasi-Z-source multilevel inverter. The working and switching states of the proposed topology are explained. Modified multi-carrier bipolar PWM techniques are explicated for the proposed inverter. A five level quasi-Z-source inverter is designed, modeled and the simulation results are obtained. The total harmonic distortion and individual harmonic contribution in each pulse width modulation techniques are performed.

A modified space vector PWM for Bi-directional Z-source inverter

In this paper a novel modified space vector pulse width modulation (SVPWM) technique for bidirectional Z-source inverter is presented. The approach of PWM method is different here because of the additional switch present in the input side as compared to the basic version of Z-source inverter. In the proposed modified SVPWM the shoot-through states are evenly assigned to each phase within zero state. So zero voltage period is diminished for generating a shoot-through time, and active states are unchanged. Simulation and experimental results are presented to demonstrate the new features.

Stateflow based incremental conductance MPPT of a photovoltaic system using Z - source DC - DC converter

A new stateflow based maximum power point tracking technique is proposed for photovoltaic systems with Z-source DC-DC converter as the conditioning converter. The mathematical modeling of photovoltaic systems is presented. The new method of incremental conductance based MPPT technique is simulated with an interfacing Z-source dc to dc converter. This converter operates in bidirectional power flow mode, performs buck and boost functions and improves reliability as compared to other existing dc - dc converters. This paper studies the performance of photovoltaic systems under rapidly changing irradiance levels. The incremental conductance algorithm is selected to track the maximum power point. The simulations are presented and analyzed to prove that the proposed system receive the maximum power under varying irradiance levels.

Quasi Z-source inverter with improved incremental conductance MPPT for rapidly varying solar irradiation

The photovoltaic (PV) energy and its conversion into electrical energy has a raising importance in the renewable energy marketplace. It is essential to harvest the maximum power from the PV arrays since they have very low conversion efficiency. This process requires the power electronic converter as the power conditioning device. The quasi Z-source inverter is chosen as power conditioning device because of its capability of boosting and DC to AC conversion in single stage. An improved incremental conductance maximum power point tracking algorithm is developed with the aim to prevent the bewilderedness during rapidly changing solar irradiation. This algorithm controls the shoot-through duty cycle of the inverter to attain the maximum power point of the PV array. A novel modified space vector pulse width modulation technique with four shoot-through states is proposed for the inverter to control the inverter. Simulation and experimental results are provided to establish the performance of the proposed system. The comparison with the conventional algorithm is also presented.

Bi-Directional Z-Source Inverter for Superconducting Magnetic Energy Storage Systems

Superconducting magnetic energy storage (SMES) is basically a DC current energy storage technology which stores energy in the form of magnetic field. The DC current flowing through a superconducting coil in a large magnet creates the magnetic field. Because of its fast response during charging and discharging, ability of injecting/absorbing real or reactive power, high storage efficiency, reliability and availability, the SMES technologies are used in power system transmission control and stabilization, and power quality improvement. Generally, an SMES consists of the superconducting coil, the cryogenic system, and the power conversion system. The power conversion system normally uses a power electronic converter as an interface between the coil and AC output. This converter is needed to act as the boost converter during DC side to AC side power flow since the storage suffered from lower input voltage magnitude. On the other hand, the converter is required to work as buck converter during reverse power flow. So the converter must be having bidirectional power flow capability because the need to charge and discharge the coil. The bi-directional Z-source inverter is a new topology, which provides the circuit with bi-directional power flow capacity. This inverter can overcome the limitations of the basic Z-source inverter and be used as an interface between energy storage and utility. A novel modified space vector pulse width modulation (SVPWM) algorithm for bi-directional Z-source inverter is developed in this work, which improves the voltage gain during the boost mode. In the proposed modified SVPWM, four shoot-through states are assigned to each phase within zero state. So zero voltage time period is diminished for generating a shoot-through time, and active states are unchanged. Using MATLAB, the models of the bi-directional Z-source inverter based SMES is established, and the simulation tests are performed to evaluate the system performance.

A Modified Maximum Power Point Tracking Control for Bi-Directional Z-Source DC-DC Converter Based Solar Electric Vehicle

A solar electric vehicle is powered by photovoltaic arrays which allow for direct conversion of solar energy into electrical energy. Since space and weight are very limited with any vehicle, it is desired that the maximum possible amount of energy be obtained from the employed photovoltaic arrays. Every photovoltaic array has an optimum operating point, called the maximum power point (MPP), which varies depending on cell temperature and solar insolation level. This paper is focussed to find the mechanism best suited for employment in a moving vehicle to optimally track this point of maximum efficiency under rapid variation of solar insolation and adjust the operating point of the photovoltaic array accordingly. An integral part of any modern day electric vehicle is power electronic circuits comprising DC-DC converters for conversion and conditioning of electrical power. Recently, Z-source DC-DC converters show promising outcomes when integrated with photovoltaic array compared to conventional DC-DC converters. They provide larger range of output dc voltage, improve reliability and can reduce in-rush and harmonic current. A bi-directional Z-source DC-DC converter with a maximum power point tracking (MPPT) technique suitable for electric vehicle applications is developed to incur high electric power from photovoltaic array. The photovoltaic array output voltage is controlled and the maximum power point tracking is attained by controlling the duty cycle. The well known incremental conductance MPPT algorithm is modified by measuring the power in the middle of the sampling interval to prevent the bewilderedness during rapidly changing insolation condition. Computer simulation and experimental results are provided to establish the performance of the proposed system.