Quasi Impedance Source Inverter Research Articles

Control of PV power plants with quasi-Z-source cascaded H-bridge multilevel inverters under failure

At the present time, quasi-Z-source cascaded H-bridge multilevel inverters (qZS-CHBMLI) have gained attention in photovoltaic (PV) applications, due to their advantages over traditional multilevel inverters. They allow single-stage power conversion of a PV power plant by independently adjusting the DC voltage in each module; thus, each PV array operates at the maximum power. This advantage permits dispensing with a DC/DC boost converter and reduces the number of modules required. This paper develops a novel control strategy for a qZS-CHBMLI connected to a single-phase system that guarantees proper operation when a fault occurs in a quasi-impedance source inverter (qZSI). The control strategy is employed in a grid-connected qZS-CHBMLI with three modules, each one with a quasi-impedance network, a 4.8 kW PV array and a voltage source inverter (VSI), with H-bridge topology. The purpose of the control system is to deliver a suitable DC voltage at the input of the VSI and ensure the grid power requirements after a fault in a module. The proposed control system is evaluated through a 40 s simulation in MATLAB/Simulink® in two cases: A) analysis of the system behaviour when there is a variation in the operation limit equation; and B) evaluation of the control strategy under dissimilar operating conditions. In addition, an experimental setup based on an OPAL RT-4510 unit and a dSPACE MicroLabBox prototyping unit is employed to validate the results. The results confirmed the correct response of the applied strategy with the failure of a single module.

Photovoltaic-Based q-ZSI STATCOM with MDNESOGI Control Scheme for Mitigation of Harmonics

Static compensators (STATCOMs) are often used in distribution systems to enhance power quality. There is a need to enhance the performance of STATCOM to optimize its utilization and facilitate the provision of additional ancillary services. This paper employs the multilayer discrete noise-eliminating second order generalized integrator (MDNESOGI) to regulate the quasi-impedance source inverter (qZSI)-STATCOM for power exchange with the grid. Compared to conventional second-order generalized integrator (SOGI), MDNESOGI exhibits a higher capability for rejecting DC offset. In instances of abnormal grid operation or system malfunction, the inclusion of DC rejection capability enhances the robustness and reliability of the system. The suggested control algorithm only requires two integrators, three mathematical operators, and a damping factor, making it far easier to implement than transformation-based methods. The distorted load current is broken down into its active and reactive components using this control mechanism. The reference currents are then calculated by multiplying these parts by their corresponding voltage standards. The DC offset is reduced and transient oscillations in the weight component are eliminated by adjusting the damping factor. The suggested algorithm effectively handles power quality tasks like (a) reducing harmonic distortion, (b) compensating for reactive power, (c) adjusting for power factor, and (d) balancing the load under different conditions in the distribution system. The experimental study results are used to examine the stability of the proposed control scheme in both static and dynamic scenarios. In addition, a comparison to traditional methods is provided to demonstrate the new method’s superiority. Experimentation results show that the suggested controller is superior to its contemporaries in all scenarios where power quality is a factor, meeting the IEEE standard requirements.

A Transformerless Enhanced-Boost Quasi-Z-Source Inverter with Low Input Current Ripple for Stand-Alone RES-Based Systems

The main drawback of DC-source-based renewable energy sources (RESs), such as photovoltaic (PV) panels or fuel cells (FCs), is that the voltage generated by a panel or cell is less than the required voltage for connection to a DC–AC inverter for grid applications. In this paper, a single-switched DC–DC boost converter equipped with a quasi-impedance source inverter (QZSI) with a modified switching model is proposed to increase the output voltage of these RESs and convert it to a fixed AC grid voltage for loads. By changing the position of the inductor in a classic step-up converter and using a switched-inductor block, the input current ripple is significantly decreased, and the reliability and long-life of the input sources are increased, which is the main contribution of this work. The quality of the generated AC voltage and the low amount of total harmonic distortion (THD) in the projected topology are significant, and no overshoot and undershoot have been reported for both output voltages and currents under different operating conditions with variable loads. Theoretical analysis, simulation results, and comparison with similar topologies are examined and a prototype with a power of 200 to 400 watts is presented. Experimental results confirm the theoretical studies.

Three-Level T-Type qZ Source Inverter as Grid-Following Unit for Distributed Energy Resources

Distributed energy resources (DERs), such as solar photovoltaics (PVs), are required to achieve a high performance and an efficient use of generated renewable power in grid-integrated applications, both in normal and fault operating conditions. In this article, a grid-following (GFL) multifunctional control strategy for a three-phase three-level T-type quasi-impedance source inverter (3L-T-type qZSI) is studied through simulation and experimental tests. The GFL functionality is achieved by a proportional–integral (PI)-based dq current controller for the active and the reactive power tracking. A PI-based dc controller is used for the dc-link voltage control by taking advantage of the quasi-impedance source (qZS) network ability for input voltage boosting. The dc–ac power conversion is accomplished through a space vector pulsewidth modulation (SVPWM) with inner capacitors voltages balancing capability and minimum common-mode voltage (CMV) generation. Besides, a low-voltage ride-through (LVRT) strategy was implemented to fulfill the fault requirements imposed by the Spanish standard. The simulation and experimental results demonstrate the abovementioned functionalities and validate the stability and good dynamic response of the grid-connected 3L-T-type qZSI. Thus, this work supposes a novel contribution due to the few works previously reported in the literature concerning the performance of this relatively recent inverter topology in grid-tied applications.

Optimal online battery power control of grid-connected energy-stored quasi-impedance source inverter with PV system

This study presents an optimal online control that implements a biogeography-based optimization (BBO) algorithm on a battery energy system (BES) integrated into an energy-stored quasi-impedance source inverter (qZSI) that connects a photovoltaic (PV) power plant to the grid. The BBO algorithm was used to tune the PI regulator in the BES current control loop by minimizing the integral time absolute error (ITAE). Two different options for the BBO are compared in this application:1) a PI controller with online self-tuning based on BBO, and 2) a PI controller with offline tuning using BBO. Moreover, the BBO-based PI controllers were compared with a third controller tuned online using the particle swarm optimization (PSO) algorithm. To evaluate and compare the controllers, a PV power plant with a battery energy-stored qZSI was simulated under different operating conditions, such as step changes in the BES current reference, different sun irradiance, and a grid voltage sag. The results demonstrate better control of the BES current with the online tuning techniques (BBO and PSO) than with the offline tuning procedure, and similar results between the two online tuning algorithms. Nevertheless, throughout the simulation, the time of use of the BBO algorithm was almost 2.5 times smaller than the PSO algorithm. Therefore, the online BBO-based PI controller is considered the most suitable option.

Experimental verification of STATCOM based on quasi impedance source inverter for power quality enhancement in the hybrid distributed generation system

PurposeThis paper aims to introduce the quasi impedance source inverter (qZSI)-based static compensator (STATCOM), which is incorporated into the hybrid distributed power generation system for enhancement of power quality. The distributed power generation system includes the photovoltaic (PV), wind energy conversion system (WECS) and battery energy storage system.Design/methodology/approachThe WECS is used by the self-excited induction generator (SEIG) and the flywheel energy storage system (FESS). To regulate its terminal voltage and frequency, the SEIG requires adjustable volt-ampere reactive (VAR). A combination of a STATCOM and a fixed condenser bank usually serves to satisfy the VAR demand. The maximum correntropy criterion-based adaptive filter technique (AFT) is proposed to control the qZSI-STATCOM and to guarantee that the voltage at the SEIG terminal is harmonic-free while providing non-linear three-phase and single-phase loads.FindingsThe coordinated operation of the suggested voltage control and flywheel control systems ensures that load voltage and frequency are retained in their respective values at very low harmonic distortions regardless of wind speed and load variation. The simulation and experimental studies are carried out under different load conditions to validate the efficiencies of the PV-assisted STATCOM.Originality/valueTo improve system stability and minimize total costs, extra load current sensors can also be avoided. This paper proposes to control the SEIG terminal voltage and harmonic elimination in the standalone WECS systems using maximum correntropy criterion-based AFT with a fuzzy logic controller.

Five-phase induction motor drive for electric vehicle with high gain switched-inductor quasi impedance source inverter

Switched-inductor quasi-impedance source inverter (SL-qZSI) with high gain fed five-phase induction motor drive for electric vehicle (EV) applications is proposed in this paper. Multi-phase electric machines have been predicted for application where the entire system should have better reliability and demanded power per phase is low especially for autonomous applications like EVs. To supply variable voltage and frequency to multi-phase machines, multi-phase inverters are required. SL-qZSI offers enhanced boost capability with respect to traditional impedance source converters by inserting three diodes and only one inductor to the basic quasi-impedance source inverter (qZSI). Also, SL-qZSI offers withstanding capability during voltage dip results line harmonics are diminished; enhances reliability of inverter; and extended output voltage range. The key idea of this paper is to design and develop a high performance and highly reliable SL-qZSI fed five-phase Induction Motor drive and validate the proposed system depends on results of Simulation with the help of MATLAB; these findings were comparable to the similar type of existing converters. We can notice from the performance analysis of the proposed system that it can provide enhanced voltage boosting capability and proved that it has significant potential for the suggested multi-phase variable speed drive (VSD) system.

Sinusoidal pulse width modulation for a photovoltaic-based single-stage inverter

The work proposed in this paper focuses on providing an effective solution to the shortage of power in rural areas with an effective technique implemented in an economically feasible way. The traditional inverters used for either residential or commercial purposes consume electrical energy from the grid to fulfill the charging and discharging of the battery, which may lead to overloading. The shortcomings of the traditional inverters such as the nonrenewable nature of power sources increased cost of manufacturing, and multistage conversion complexity is considered by the researchers for improvement. As a result, an attempt has been made to provide a cost-effective renewable energy system with a single-stage topology for ac power applications. Single-stage power conversion with an allowed shoot through the state is used here to avoid additional components and reduce the switching losses. Unlike the traditional inverters, the quasi-impedance source inverter (QZSI) that is brought forward can be utilized as a standalone system or a capable backup at the time of power outages. Sinusoidal pulse width modulation (SPWM) is applied to attain reduced harmonics which are measured by observing the harmonic pattern in the total harmonic distortion (THD) curve. The lab results obtained through MATLAB simulation confirm the noteworthy diminution of the THD level in the proposed system compared to the reported one. Usage of photovoltaic (PV) panels to tap energy with reduced stochastic fluctuations due to the high filtering capacity of the proposed circuit, eliminating the need for additional filters, is the uniqueness of this technique.

Comparative analysis of Si, SiC and GaN based quasi impedance source inverter

The impedance source inverter reduces the number of stages of energy conversion due to its ability to increase the output voltage. Silicon based semiconductor power devices are commonly used for inverters, but as the voltage and current rating of the inverter increases with demand for high efficiency, the Silicon Carbide and Gallium Nitride power devices are most preferred. These wide bandgap devices enable the switches to be operated at high switching frequencies and with the increase in switching frequency, the size of the impedance network elements present in the inverter can be reduced. Thus, obtaining a compact and highly efficient inverter module. This paper presents a comparative analysis of Silicon, Silicon – Carbide and Gallium Nitride based quasi – impedance source inverters through simulation study. The performance of the inverters is analysed based on its efficiency, voltage stress and current stress across the switches and the results are validated.

Three-Level T-Type Quasi-Z Source PV Grid-Tied Inverter With Active Power Filter Functionality Under Distorted Grid Voltage

Distributed energy resources (DER) such as solar photovoltaic (PV) interfaces with the utility grid by high-efficiency power electronic converters. This equipment is sometimes underutilized in terms of its power capacity; thus, the remaining capacity can be used to provide support to the distribution system. In this sense, this work assesses the performance of the three-level T-type quasi-impedance source inverter (3L-T-type qZSI) injecting not only active power to the grid, but also providing support to it by injecting reactive power and acting as an active power filter (APF) simultaneously. The global control strategy of the grid-connected inverter is derived from the instantaneous <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$i_{d}$ </tex-math></inline-formula> - <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$i_{q}$ </tex-math></inline-formula> power theory. The combination of an improved deadbeat current controller and a level-shifted carrier-based pulse-width-modulation (PWM) technique, using both the upper shoot-through (UST) and the lower shoot-through (LST) alternating states, allows a successful tracking of the current references. Both the dc-link voltage control and the neutral-point balancing are properly achieved by taking the advantage of the shoot-through (ST) states and the redundant states simultaneously. These control actions are implemented by simple proportional-integral (PI) controllers. The simulation and experimental results demonstrate the above-mentioned functionalities and verify the stability and good dynamic response of the grid-connected 3L-T-type qZSI.

Two-Stage Control for Small-Signal Modeling and Power Conditioning of Grid-Connected Quasi-Z-Source Inverter with LCL Filter for Photovoltaic Generation

Grid-connected inverter-based photovoltaic (PV) systems play an important role in Distributed Power Generation (DPG). For this application, quasi impedance source inverter is very suitable due to its ability to increase or decrease the output voltage of the inverter in a single-stage and high reliable condition. Conventionally, to remove the harmonics, which are yielded by switching the grid-connected inverter, LCL filters are utilized at the inverter output. These filters can cause some problems at the Point of Common Coupling (PCC). The aim of this paper is to improve the quality of the injected power of the photovoltaic array, which is connected to the low voltage grid by quasi-Z-source inverter (QZSI). For this purpose, a two-stage control procedure containing DC and AC stages is performed. In the DC stage, the dynamic characteristics of the quasi-Z-source network are investigated by small-signal analysis. Using the transfer functions obtained from the dynamic model, the capacitor voltage of the quasi-Z-source network is suitably controlled to generate the appropriate voltage to the grid interface inverter. In the AC stage, in order to inject high-quality current into the grid as well as eliminating the resonance peak caused by the LCL filter, a systematic procedure is used to design the PR controller parameters and active damping coefficient. Simulation of the overall system includes solar panels, maximum power point tracking algorithm, quasi-Z-source inverter, and LCL filter to model the grid-tied PV system with the possible details. Simulations are carried out in MATLAB/Simulink environment, and results depict suitable performance of the studied power conditioning system with designed parameters.

Novel Level-Shifted PWM Technique for Cascaded Multilevel Quasi-Impedance Source Inverter

In a multilevel quasi-impedance source inverter (qZSI), phase-shifted carrier pulsewidth modulation (PS-PWM) is the most popular modulation method as it offers advantages such as simple implementation and evenly powered distribution among all qZSI modules with optimum total harmonic distortion (THD). However, it results in higher switching losses. An approach to solving this problem would be development and implementation of a PWM method which results in lower switching losses. With this aim, a novel hybrid phase-opposition disposed, phase-shifted (PWM) (PODPS-PWM) technique is proposed in this article. With the proposed PWM method, reduced switching losses are achieved. Active state losses are reduced to 6% and switching losses are reduced to at least >39% in qZSI modules. A mathematical relationship between the PS-PWM and the proposed PODPS-PWM has been deduced. For experimental validation, a 1.5-kW seven-level qZSI setup is developed. Different performance aspects are presented, discussed, and analyzed, which help in validating the superior performance of the proposed solution. Moreover, an application for the solar photovoltaic (PV) multilevel inverter system has been discussed, for the partial shading condition. During this condition, the PS-PWM forces the extraction of lower power from the remaining healthy modules. This is due to the evenly powered distribution nature of the PS-PWM. Comparatively, the proposed PWM yields higher power. To validate higher power extraction, simulation results are presented and compared for both modulations under healthy and different partially shaded conditions. Under extreme partial shading conditions, the increase in power extraction is up to 29%.

A Simple Space Vector Modulation Method With DC-Link Voltage Balancing and Reduced Common-Mode Voltage Strategy for a Three-Level T-Type Quasi-Z Source Inverter

Single-stage converters based on an impedance source (IS) network merged with a multilevel inverter remain a trending research topic, from both the topological and control perspectives, because of their potential in applications involving renewable energy. This paper presents a new, simplified space vector pulse-width modulation (SVPWM) for a three-phase three-level T-type quasi-impedance source inverter (3L-T-type qZSI). The benefits of the proposed modulation strategy include functionalities, such as boosting the input voltage and controlling the neutral-point (NP) voltage using the redundant small vectors, to mitigate the inner capacitors voltages imbalance. The proposed SVPWM guarantees a minimum common-mode voltage while preserving a very simple implementation, thus reducing the complex computations and cascaded proportional-integral (PI) control loops of the conventional SVPWM methods. The proposed algorithm can be applied to different multilevel inverter configurations combined with an IS network. A comprehensive simulation study and experimental results demonstrated the good performance of the proposed control method for dynamic response and imbalance conditions.

Lyapunov-Function-Based Controller for Single-Phase NPC Quasi-Z-Source Inverter with 2ω Frequency Ripple Suppression

This paper proposes a high-performance control technique based on Lyapunov’s stability theory for a single-phase grid-connected neutral-point-clamped quasi-impedance source inverter with LCL filter. The Lyapunov function based control is employed to regulate the inverter output current, whereas the proportional resonant controller is used to produce the reference of the inverter output current that is needed in the Lyapunov function based control. Use of proportional resonant controller ensures the zero steady-state error in the grid current. An important feature of the proposed Lyapunov function based control is the achievement of resonance damping without using a dedicated damping method. Furthermore, the modified simple boost control technique is proposed to eliminate the double-line frequency ripples in the quasi-impedance source inductor currents and minimize the double-line frequency ripples in the quasi-impedance source capacitor voltages. The proposed control technique considerably reduces the inverter size, weight, and cost as well as increases overall system efficiency since the required inductances and capacitances sizes are lower. Experimental results obtained from a 2.5 kW neutral-point-clamped quasi-impedance source inverter prototype are presented to validate the performance of the Lyapunov function based control technique.

Design and Implementation of Cascaded Multilevel qZSI Powered Single-Phase Induction Motor for Isolated Grid Water Pump Application

This article presents the design and implementation of solar-powered V/f controlled single-phase capacitor-start induction motor. Multilevel quasi impedance source inverter controls the power flowing from the photovoltaic (PV) array to a single-phase induction motor. In solar powered drive systems, the main concern is stable intended operation of drive when subjected to variations in power generation of the PV array. For same environmental conditions, the PV power extraction is different at different torques for constant speed application. Due to this, the extraction of maximum power with an MPPT algorithm is not achieved with only motor load. To address this concern, concept of the battery storage system is introduced in the system that helps in achieving maximum power when the PV power generation capability exceeds rated motor input power. In addition to this, battery storage system can supply power to the load when the PV power generation is less than the rated motor input power. Conclusively, the design of control algorithm must address issues of the MPPT algorithm, control of battery storage system, and stable operation of V/f-controlled induction motor drive operation. MATLAB/Simulink model of the proposed system with 4 kW PV array rating is developed. The proposed control algorithm achieves satisfactory operation of single-phase motor drive in all the three operation modes (depending upon PV power generation). The variation of the solar irradiation and temperature are simultaneously considered for introducing perturbation in the PV power generation. Hardware results for this system are also presented, which validates the effectiveness of the control algorithm for the proposed system.

Fuzzy Logic Controlled PV Based Quasi Impedance Source Inverter for Charge Balancing

A photovoltaic power generation system based on battery-energy quasi impedance source cascaded multi-level inverter incorporates the advantages of a quasi-impedance source inverter, a CMI, and a battery-energy storage unit. Unbalanced battery charging between cascaded H-bridge inverter modules will degrade the efficiency of an entire system and reduce the lifetime of the battery. This paper proposed a control method for tracking the maximum power point and balancing the SOC of the battery under the large variation of solar input. A fuzzy based optimized linearizer for the battery charge and maximum power point tracking are proposed. The fuzzy controller is proposed to enhance the battery state of charge regulation takes as a individual modules as a loop to reduce over charge condition. The Proposed method validation is done by comparing it with base work control by PI and P&amp;O with the performance parameters. The base work and proposed work are designed and simulated in the Matlab Simulink software.

Quasi-Z-Source Inverter using Space Vector Modulation and Sine PWM Method

This paper presents the performance comparison of sine PWM and SVPWM based quasi impedance source inverter (QZSI).QZSI are used to boost the DC link voltage and convert DC voltage into AC voltage in a single stage with a concentrated number of semiconducting devices. Space vector pulse width modulation (SVPWM) method is used to control the inverter output voltage and reduce the current harmonic. MPPT technique is also integrated into the SVPWM technique to improve the maximum output power obtained from PV cells. Shoot through concepts is used to increase the DC link voltage and reduce the separate requirement of the boost stage. The projected QSZI inverter is simulated using MATLAB simu-link. SPWM and SVPWM method are used to determine the circuit performance. The circuit performance is compared with simulation results.

Robust controller for grid-connected quasi-admittance source inverter for photovoltaic system

This paper presents a robust control technique, such as an H∞ control technique, for a grid-connected quasi-admittance source inverter (QYSI). A QYSI inherits all the advantages of a quasi-impedance source inverter, such as high voltage conversion gain, and draws continuous current from the source and reliable grid operation. The QYSI has high boost capability, reducing the voltage stresses on devices and suppressing the start-up inrush current. A closed-loop controller system design is significant in a QYSI, as it influences the boosting of photovoltaic voltage (PV), maximum power point tracking (MPPT), and grid connection. In grid connection, variations in grid impedance may cause system instability when the grid current controllers are not robust. Hence, in this work, a robust controller is proposed to enhance the stability margin and reliability of the system. Along with this control, it is essential to extract the maximum power from the PV source and hence, a reinforcement learning-based MPPT algorithm is used to track a maximum power point from the PV. The proposed system is compared with a proportional resonant controller. The QYSI system is tested for variations in grid impedances, grid frequency, and voltage amplitude. The simulation results show the effectiveness of the proposed controllers in terms of power quality. The simulation results are validated with real-time experiments.

Fault tolerant single‐phase capacitor start capacitor run induction motor powered with cascaded multilevel quasi impedance source inverter

In this study, the performance of fault tolerant single-phase capacitor start capacitor run induction motor powered using seven-level quasi-impedance source inverter (qZSI) is analysed. The seven-level inverter consists of three units of qZSI connected in cascade. When one of the qZSI module fails (due to semiconductor failure), the resultant rms voltage applied to the motor will be reduced by one-third. This leads to reduction in both mechanical speed and electromagnetic torque of the motor. To restore the performance of the motor to pre-fault condition, the voltage deficit must be compensated. In conventional CHB inverter, it is not possible to achieve the pre-fault voltage. However, in qZSI, it is possible to achieve required voltage boost by application of shoot through duty cycle. Here, voltage of other two healthy operating modules can be boosted to reach pre-fault inverter output voltage during post-fault condition. The maximum voltage boost achievable is limited by the maximum shoot-through duty cycle which is related with modulation index. To verify the concept, simulation results of single-phase capacitor-start capacitor-run induction motor with or without proposed control algorithm are discussed. Experimental results for the proposed algorithm with RL load are discussed.

Optimized FPGA Implementation of PWAM-Based Control of Three—Phase Nine—Level Quasi Impedance Source Inverter

Inherent buck–boost capability, reduced component count, controlled power injection and multilevel operation are some of the advantages which makes cascaded qZSI popular for integrating the generated solar energy with the utility grid. Phase–Shifted Carrier PWM (PSCPWM) and Pulse Width Amplitude Modulation (PWAM) are the most popular techniques for achieving multilevel qZSI operation. Generally, closed loop control implementation of three – phase qZSI system consists of large number of slave controllers (placed locally for voltage control) and one centralized master controller (for grid integration or load current control). Since the aim is to control single system with this highly distributed control structure, issues of clock pulse and interrupt signal synchronization, hardware and software redundancy are common in these implementations. This limits the utilization factor and step size of these control boards. To address these issues, either more optimized solutions must be suggested, or distribution of control structure must be reduced. In this paper, closed loop control of nine – level three – phase qZSI system is implemented using single FPGA control board thereby eliminating above said problems. Since, PWAM control algorithm is more complex than PSCPWM, FPGA based implementation for PWAM control is discussed. Critical implementation processes consisting of DAC – ADC interfacing, FPGA code per unitization, PI Controller realization and different clock pulse utilization are presented. For highlighting and comparing the resource consumption, PWAM and PSCPWM modulation are compared in terms of device utilization. Transient analysis and control algorithm are presented and validated during both starting and load transient conditions by means of simulation results. Finally, hardware results of these modulation methods are discussed and analyzed.