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Distributed generators are more expected with the capability to continue supporting power to local critical loads in both intended and unintended islanding conditions, in addition to its house‐keeping functions of grid‐connected condition. With this purpose, this paper proposes a control strategy of single‐phase grid‐connected inverter with both decoupled power control capability for grid‐connected mode and load voltage regulation capability for standalone mode. It also enables automatic voltage regulation on point of common coupling, which enables seamless transfer after islanding occurrence. An impedance model is disclosed to analyze the operation mechanism during transient state, with further investigations on both the effect of system parameters in different modes and the system operating features. Simulation and experimental results are provided to evaluate its effectiveness. [ABSTRACT FROM AUTHOR]

Summary: Battery energy stored single‐phase quasi‐Z‐source inverter photovoltaic (BES‐qZSI‐PV) power system shows many advantages in comparison with other tri‐port inverter‐based PV power systems. However, the existing BES‐qZSI‐PV power system does not work at night or cloudy day because of its circuit limitation. This paper proposes a 24‐h operational BES‐qZS‐PV system by the following approaches: (1) the main power circuit is proposed for the day and night operation; (2) the detailed circuit models including the DC model and the second‐harmonics ripple model are built by considering scenarios of day and night operations; (3) the design method of quasi‐Z‐source network parameters is proposed to meet the requirement of day and night operations; and (4) the control strategy is proposed to achieve the high‐performance system operation all the time and seamless transition between day and night operation. After theoretical modeling and analysis, the built models are verified by comparing their calculation results with the circuit‐based simulation and experimental results. The proposed single‐phase BES‐qZSI‐PV power system is tested; experimental and simulation results are captured when the system operates in day, night, and transition to validate the proposed 24‐h operational BES‐qZSI‐PV system. [ABSTRACT FROM AUTHOR]

A discrete-time average model-based predictive control (DTA-MPC) is proposed for a quasi-Z-source inverter (qZSI). As a single-stage inverter topology, the qZSI regulates the dc-link voltage and the ac output voltage through the shoot-through (ST) duty cycle and the modulation index. Several feedback strategies have been dedicated to produce these two control variables, among which the most popular are the proportional–integral (PI)-based control and the conventional model-predictive control (MPC). However, in the former, there are tradeoffs between fast response and stability; the latter is robust, but at the cost of high calculation burden and variable switching frequency. Moreover, they require an elaborated design or fine tuning of controller parameters. The proposed DTA-MPC predicts future behaviors of the ST duty cycle and modulation signals, based on the established discrete-time average model of the quasi-Z-source (qZS) inductor current, the qZS capacitor voltage, and load currents. The prediction actions are applied to the qZSI modulator in the next sampling instant, without the need of other controller parameters’ design. A constant switching frequency and significantly reduced computations are achieved with high performance. Transient responses and steady-state accuracy of the qZSI system under the proposed DTA-MPC are investigated and compared with the PI-based control and the conventional MPC. Simulation and experimental results verify the effectiveness of the proposed approach for the qZSI. [ABSTRACT FROM PUBLISHER]

Active ripple decoupling technique of the single-phase inverter is a popular topic to minimize the dc-link capacitance. However, the existing control methods are based on tracking sinusoidal or predetermined voltage waveforms of the compensation capacitor, assuming the inverter outputs are pure sinusoidal voltage and current. Therefore, the performance of existing methods degrades when the inverter output voltage and current are not purely sinusoidal. Furthermore, the limited dynamic performance threatens the safety of dc-link capacitor when the load changes. This happens, because the inrush ripple power is injected into dc link with small capacitance and the dc-link voltage will suddenly rise up when the ripple power is not buffered during transients. In this paper, a direct instantaneous power predictive control is proposed for the decoupling circuit to buffer ripple power of the single-phase inverter, which combines instantaneous ripple power control with model predictive control to overcome the issues above. The proposed method tracks the instantaneous ripple power rather than voltage or current waveforms. In this way, it can fully buffer all ripple powers in the system even for distorted output voltage and current of the inverter and enables the full utilization of storage capacitor. In addition, model predictive control makes the proposed method have fast dynamic and perfectly compensate ripple power during transients and steady states. The buck-type active ripple decoupling circuit is chosen to implement the proposed method after comparing with another typical decoupling topology. The proposed method is also compared with conventional method using proportional-integral-resonant regulator to track the predetermined capacitor voltage waveform. Experimental tests verify the theoretical analysis and the proposed control method. [ABSTRACT FROM AUTHOR]

A battery-energy-stored quasi-Z-source cascaded multilevel inverter (qZS-CMI)-based photovoltaic (PV) power generation system combines advantages of a qZS inverter, a CMI, and a battery energy storage system. However, unbalanced battery state of charge (SOC) between cascaded H-bridge inverter modules will degrade an entire system's performance and shorten battery lifespan. This paper proposes a control method to balance battery SOCs of all modules, no matter the intermittent states of each module's PV power. The method is on the basis of battery SOCs, SOC limits of each module, and the total power injected into the power grid. Simulation and experimental results verify the proposed control method that ensures identical SOCs for the battery-energy-stored qZS-CMI PV system. [ABSTRACT FROM PUBLISHER]

The second harmonic pulsating power flows through the dc side of a single-phase quasi-Z-source inverter (qZSI), which requires bulky capacitor banks and inductors to suppress low-frequency ripple of dc-link voltage and inductor currents in the passive ripple reduction way. However, the resultant huge qZS network seriously deteriorates the system reliability, efficiency, volume, weight, and cost. This paper proposes an active-filter-integrated single-phase qZSI to transfer low-frequency power ripple directly from ac load to active filter's ac capacitor, so that low-frequency power ripple does not present in dc side anymore and constant inductor currents and constant capacitor voltages are ensured. Thus, much small qZS impedance is employed to only smooth high-frequency ripple and active filter's capacitor supports ac voltage (large ripple allowed) with small capacitance. The operation principle, parameter design method, and modeling and control strategy of the proposed topology are investigated. Comparative evaluation, simulation, and experimental results verify the proposed new topology system. [ABSTRACT FROM PUBLISHER]

The second harmonic $(2\omega)$ power ripple of single-phase quasi-Z-source (qZS) photovoltaic (PV) inverter highly affects the whole system's design and performance. The topology's $2\omega$ ripple model is very important to analyze qZS PV inverter's $2\omega$ voltage and current ripple. The existing models did not consider the PV-panel dynamic and terminal capacitors, which causes the theoretical results apart from the truth. In this paper, a comprehensive modeling for single-phase qZS-PV inverter is proposed, where the $2\omega$ ripple model of the qZS-PV inverter system with a real PV source is established and discussed without and with a PV terminal capacitor. The influences from qZS inductance and capacitance, and PV-panel terminal capacitance to the $2\omega$ voltage and current ripple are investigated using the built model. The system parameter design method is proposed to mitigate this ripple. Simulation and experimental results validate the proposed $2\omega$ ripple model and parameter design method. [ABSTRACT FROM PUBLISHER]

The quasi-Z-source cascaded multilevel inverter (qZS-CMI) presented many advantages over conventional CMI when applied in photovoltaic (PV) power systems. For example, qZS-CMI provides the balanced dc-link voltage and voltage boost ability, saves one-third modules, etc. However, current research studies only disclosed control of single-phase qZS-CMI-based PV power systems, and there was no literature related to control of three-phase qZS-CMI-based PV power systems. In this paper, for the first time, three-phase qZS-CMI's control is proposed and demonstrated for application to PV power systems. The models of PV-panel-fed qZS H-bridge module and qZS-CMI-based PV power system are built to accurately design control algorithms for each module and the whole system. The proposed control method includes the distributed maximum power point tracking for each module, dc-link peak voltage balance control for all modules, and grid-tie control for the whole system; moreover, a new multilevel space vector modulation method is proposed for the three-phase qZS-CMI. Simulation and experimental results on a test bench with a three-phase seven-level qZS-CMI-based PV power system verify the proposed control and modulation methods. [ABSTRACT FROM PUBLISHER]

The quasi- $Z$ source (qZS) cascaded multilevel inverter (CMI) (qZS-CMI) presents attractive advantages in application to photovoltaic (PV) power system. Each PV panel connects to an H-bridge qZS inverter (qZSI) to form a power generation module. The distributed maximum power point tracking and all modules' dc-link peak voltage balance can be achieved. However, it is the same with the conventional CMI that the second-harmonic ( $2\omega$) voltage and current ripples exist in each qZSI module. It is crucial for a qZS-CMI to design the reasonable qZS network parameters to limit the ripples within a desired range. This paper proposes an analytic model to accurately calculate the $2\omega$ voltage and current ripples of each qZSI module. A qZS impedance design method based on the built model is proposed to limit the $2\omega$ ripples of dc-link voltage and inductor current. Simulated and experimental results through using the designed 1.5-kW prototype validate the proposed analytic model and the design method. Furthermore, this paper analyzes all of the operating states for a qZSI module and calculates the power loss. The measured efficiency from the prototype verifies the theoretical calculation, and the qZS-CMI-based grid-tie PV power system is tested in practical. [ABSTRACT FROM PUBLISHER]