A high gain grid connected single stage inverter system with reactive power control

A Reactive Power Compensation Strategy in Radial Distribution Network with High PV Penetration

Abstract: The introduction of photovoltaics (PV) based power generation has brought about the trend of residential rooftop PVs. Therefore the concept of energy market of buying and selling of power between the utility and consumers has been established. However, high penetration of PV causes congestion leading to voltage violation conditions, especially in case of grid fault that requires islanding of the PV systems. Furthermore, in case of radial distribution system (RDN), high PV penetration imposes over-voltage and under-voltage issues during peaking PV production and peak loading conditions respectively. Taking these into consideration, this paper proposes a voltage regulation methodology based on active-reactive power management through PV inverters. A PQ-V control curve is formulated for the PV inverters and corresponding tuning parameters are introduced for rapid voltage regulation using real-time measurements. The control strategy is evaluated on two scenarios of RDN based on different R/X ratios and nodes distances to validate its robustness.

Analysis and Design of a Transformerless Boost Inverter for Stand-Alone Photovoltaic Generation Systems

Abstract: A novel transformerless boost inverter for standalone photovoltaic generation systems is proposed in this paper. The proposed inverter combines the boost converter with the traditional bridge inverter. The switch S1 not only realizes the boost function but also participates in inverting process. The inverter has a higher voltage gain and good characteristics when the inductor L1 is operated in discontinuous mode (DCM) and the nonpolarized capacitor can be chosen as bus capacitor, which makes the volume smaller and the service life of the inverter is increased. The inverter consists of five switches in which only two switches are operated at high frequency state and a monopole sinusoidal pulse width modulation (SPWM) strategy is used. Therefore, the modulation strategy of switches is very simple and the switching loss is reduced. The principle of inverter is described in detail and mathematical models are built by small-signal analysis. Finally, the correctness of the theoretical analysis is verified by simulation and experiment.

A Transformerless Boost Inverter for Stand-alone Photovoltaic Generation Systems

Abstract: a novel transformerless boost inverter for standalone photovoltaic generation systems is proposed in this paper. The proposed inverter combines the boost converter with the traditional bridge inverter. The switch S1 can not only realize the boost function but also participate in inverting process. The inverter has a higher voltage gain and good characteristics when the inductor L 1 is operated in discontinuous mode (DCM) and the nonpolarized capacitor can be chosen as bus capacitor, which makes the volume smaller and the service life of the inverter is increased. The inverter consists of five switches in which only two switches are operated at high frequency state and a monopole SPWM strategy is used. Therefore, the modulation strategy of switches is very simple and the switching loss is reduced. The principle of inverter is described in detail and the correctness of the theoretical analysis is verified by simulation and experiment.

Active-Reactive Power Control of Grid-Tied Solar Energy Systems, Using Multi-Parameter Band Control for Grid Voltage Regulation

Abstract: One of the most studied and funded renewable energy sources is solar energy, all over the world. Solar panels are used to obtain electrical energy from the sun. They should be used effectively due to their expensive structure and challenging installation. However, as the sun light only reaches to the earth during daylight hours, solar systems cannot generate active power during the night, or in cases where daylight is not enough, the whole power capacity of the solar inverters have not been used. In this study; it was shown that in addition to the active power generation during the daytime hours, the solar systems were able to generate reactive power with the remaining capacity of the inverter. Thereby adjusting the grid voltage was provided by the solar system’s reactive power control. Designed solar system generates completely reactive power at nights. Thus, the efficiency of the solar systems has been increased by ensuring that the solar systems have used to keep the grid voltage within the values, which stated in the standards, by producing reactive power as well as active power. Matlab/Simulink was used to model the system when using hysteresis band method for system control.

A Strategy for Utilization of Reactive Power Capability of PV Inverters

Abstract: A high penetration of solar photovoltaics will result in the voltage violations in residential distribution networks. In addition, increased power demand during peak load conditions exacerbates the risk of extreme voltage violation. Enhanced voltage regulation and reactive power control is difficult to be achieved by a centralized control as they are limited by communication and computational burden. In contrast, local voltage regulation is based on measurements in real-time and will have a faster response to the PV power fluctuations and its associated stabilization of the system. This paper proposes a local voltage control strategy based on the reactive power capability of PV inverters. A Q-V based control curve is formulated for the PV inverters and further to ensure its faster response, tuning parameters based on active power and bus voltage measurements are introduced. Considering different value of R/X ratio, the proposed control strategy has been evaluated for urban and rural residential distribution network.

A boost DC-AC converter: analysis, design, and experimentation

Abstract: This paper proposes a new voltage source inverter (VSI) referred to as a boost inverter or boost DC-AC converter. The main attribute of the new inverter topology is the fact that it generates an AC output voltage larger than the DC input one, depending on the instantaneous duty cycle. This property is not found in the classical VSI, which produces an AC output instantaneous voltage always lower than the DC input one. For the purpose of optimizing the boost inverter dynamics, while ensuring correct operation in any working condition, a sliding mode controller is proposed. The main advantage of the sliding mode control over the classical control schemes is its robustness for plant parameter variations, which leads to invariant dynamics and steady-state response in the ideal case. Operation, analysis, control strategy, and experimental results are included in this paper. The new inverter is intended to be used in uninterruptible power supply (UPS) and AC driver systems design whenever an AC voltage larger than the DC link voltage is needed, with no need of a second power conversion stage.

A Single-Stage Grid Connected Inverter Topology for Solar PV Systems With Maximum Power Point Tracking

Abstract: This paper proposes a high performance, single-stage inverter topology for grid connected PV systems. The proposed configuration can not only boost the usually low photovoltaic (PV) array voltage, but can also convert the solar dc power into high quality ac power for feeding into the grid, while tracking the maximum power from the PV array. Total harmonic distortion of the current, fed into the grid, is restricted as per the IEEE-519 standard. The proposed topology has several desirable features such as better utilization of the PV array, higher efficiency, low cost and compact size. Further, due to the very nature of the proposed topology, the PV array appears as a floating source to the grid, thereby enhancing the overall safety of the system. A survey of the existing topologies, suitable for single-stage, grid connected PV applications, is carried out and a detailed comparison with the proposed topology is presented. A complete steady-state analysis, including the design procedure and expressions for peak device stresses, is included. Necessary condition on the modulation index "M" for sinusoidal pulsewidth modulated control of the proposed inverter topology has also been derived for discontinuous conduction mode operation. All the analytical, simulation and experimental results are presented.

Review and Comparison of Step-Up Transformerless Topologies for Photovoltaic AC-Module Application

Abstract: This paper presents a comprehensive review of step-up single-phase non-isolated inverters suitable for ac-module applications. In order to compare the most feasible solutions of the reviewed topologies, a benchmark is set. This benchmark is based on a typical ac-module application considering the requirements for the solar panels and the grid. The selected solutions are designed and simulated complying with the benchmark obtaining passive and semiconductor components ratings in order to perform a comparison in terms of size and cost. A discussion of the analyzed topologies regarding the obtained ratings as well as ground currents is presented. Recommendations for topological solutions complying with the application benchmark are provided.

A Single-Stage Three-Phase Grid-Connected Photovoltaic System With Modified MPPT Method and Reactive Power Compensation

Abstract: Single-stage grid-connected photovoltaic (PV) systems have advantages such as simple topology, high efficiency, etc. However, since all the control objectives such as the maximum power point tracking (MPPT), synchronization with the utility voltage, and harmonics reduction for output current need to be considered simultaneously, the complexity of the control scheme is much increased. This paper presents the implementation of a single-stage three-phase grid-connected PV system. In addition to realize the aforementioned control objectives, the proposed control can also remarkably improve the stability of the MPPT method with a modified incremental conductance MPPT method. The reactive power compensation for local load is also realized, so as to alleviate grid burden. A DSP is employed to implement the proposed MPPT controller and reactive power compensation unit. Simulation and experimental results show the high stability and high efficiency of this single-stage three-phase grid-connected PV system.

Microcomputer Control of a Residential Photovoltaic Power Conditioning System

Abstract: Microcomputer-based control of a residential photovoltaic power conditioning system is described. The microcomputer is responsible for array current feedback control, maximum power tracking control, array safe zone steering control, phase-locked reference wave synthesis, sequencing control, and some diagnostics. The control functions are implemented using Intel 8751 single-chip microcomputer-based hardware and software. The controller has been tested in the laboratory with the prototype power conditioner and shows excellent performance.