Design of a Three Phase Z-Source Inverter for Photovoltaic Systems

The main purpose of this study is to engage in research on a grid-connected photovoltaic (PV) power generation system smart inverter. The research content includes a smart maximum power point tracking (MPPT) controller and an inverter with power regulation. First, use the PSIM software package to establish the simulation environment of the grid-connected photovoltaic power generation system and use the Sanyo HIP-186BA19 photovoltaic module to form a 744 W system for simulation. In order to enable the photovoltaic module array (PVMA) to output the maximum power under different solar insolation and ambient temperature, the architecture is based on the extension theory-based smart MPPT method to improve the dynamic response and steady-state performance of photovoltaic power generation systems compared to perturb and observed (P&O) MPPT. When the sunshine is 1,000 W/m2, the photovoltaic power generation system adopts the extension theory-based maximum power tracking method. The time required to track the maximum power point is only 0.32 s, and the steady-state ripple is only 4.127 W. However, using the traditional P&O method requires 0.741 s to track the maximum power point, and the steady-state ripple reaches 18.131 W. Thus, the dynamic response speed of the maximum power tracking method proposed is 50% faster than that of the P&O method. The steady-state performance is also better compared to the P&O method. At the same time, a simple proportional-integral (PI) controller is used to regulate the DC-link voltage, output voltage, and current of the inverter to make the voltage of the grid-connected point stable at an effective value of 220 V. Then, the voltage-power control technology is added to the photovoltaic grid-connected inverter, and a simple proportional-integral controller is used to regulate the output of the smart inverter reactive power to improve the power quality of grid voltage. Finally, simulation and experimental results are used to verify the effectiveness of the regulation performance of the developed smart inverter.

When the power grid impedance mutates, the output power of the grid-connected photovoltaic power generation system controlled by drooping will become very unstable. To solve this problem, an improved droop control algorithm based on network impedance detection is proposed. Taking photovoltaic grid-connected power generation system as the research object, the influence of power grid impedance on traditional droop control is firstly expounded by introducing power grid impedance value into traditional droop control. Then the method of real-time network impedance extraction is introduced. Furthermore, according to the bandwidth and phase angle constraints of the equivalent output impedance phase frequency characteristics of the photovoltaic grid-connected inverter, the controller parameters are updated in real time to achieve the purpose of adaptive network impedance mutation. Finally, the proposed method is tested and verified by real-time simulation in the loop respectively. The results show that the proposed method is correct.

In a standalone photovoltaic (PV) power generation system, the author previously proposed a new type of MPPT (Maximum Power Point Tracking) control method in which the I-V characteristics are scanned with detection interval control at specified intervals and the maximum power point is monitored. The author obtained satisfactory results using this new MPPT control method. This paper investigates applying the new MPPT control method to power conditioning system (PCS) in an industrial grid-connected type PV power generation system. The experimental results clearly demonstrate that the developed PCS offers outstanding effectiveness in partially shaded environments.

The characteristics of grid-connected photovoltaic (PV) power generation system are subject to environmental factors, grid voltage, and control strategies, so it is much difficult to model the system. In this paper, a steady-state model of PV generation system based on the power electronic converter is proposed. The model is divided into DC part, inverter and AC part, which can completely describe the steady-state operation of the system. If the model integrates with control strategies, the effect of strategies on system performance can be analyzed. The analysis of model example shows that the model can exactly describe the system, and accurately track the changes of operating point when irradiance or grid voltage changes.

In this paper, a new control method for the paralleled quasi-Z-source inverters (qZSI) with a battery for application in grid-connected photovoltaic (PV) power generation systems is proposed. The use of paralleled inverters in distributed generation (DG) applications has several advantages, such as high degree of redundancy, ease of maintenance and high reliability. By introducing the shoot-through states in the permissible switching states of the inverter bridge, the qZSI can boost/buck the output voltage of PV panel in a wide range. Also, the energy storage system, which is assisted with quasi Z-source network, provides the full use possibility of PV power. The proposed control method can manage the battery power, extract the maximum power from the PV panel, control the inverters output power with desired power factor and maintain the balance of power injected by the paralleled inverters into the grid, simultaneously. Also, the controller system is able to suppress both types of circulating-current, including cross and zero-sequence circulating-currents through a modification of the conventional control schemes. The ability of the proposed PV system is investigated by simulation results carried out using MATLAB/Simulink.

The islanding detection technology is beneficial to the safe and stable operation of the grid-connected photovoltaic (PV) power generation system. However, in the traditional reactive power perturbation method, the perturbation deviation is probably counterbalanced by the load deviation, which affects the detection results significantly. Aiming at this problem, a new islanding detection method with delay trigger is proposed by taking the abrupt change of the total harmonic distortion (THD) as the trigger condition. The frequency variation curve is calculated and analyzed, and the setting value of delay time is given explicitly. The grid-connected PV power generation system simulation model was built based on MATLAB/Simulink platform, and the simulation results verified the effectiveness and feasibility of the proposed method.

An improved grid-connected photovoltaic (PV) power generation system is proposed to solve the problem that the total harmonic distortion (THD) of grid-connected current generally exceeds 5% under the condition of low output power of PV array in this paper. The system includes a larger capacity master inverter with an LCL filter and a smaller capacity slave inverter with an L filter. Two inverters are connected in parallel with the utility grid via an isolated line-frequency transformer. Two inverters can operate in one of three working modes according to output power of the PV array to reduce the grid-connected harmonic current in full power ranges. Moreover, an active harmonic compensation circuit and its control method are presented to eliminate the harmonic current generated by the inverter. Design process of the system is studied. Control strategies of the different working modes are discussed. Simulation results verify that the system and its control strategies are feasible.

A high density of grid-connected photovoltaic (PV) power generation systems is expected to occur in urban areas. The connection of distributed generation (DG) may cause serious problems in the distribution system such as voltage rise. Several voltage control strategies exist to avoid the over-voltage at the power grid. In particular, reactive power control methods have been proved to successfully bring DGs voltages within the admissible voltage range without reducing the production of active power. In addition, the possible use of communication infrastructure to link DGs opens up the development of new reactive power control methods where control actions at each DG may be decided using both local and global information. This paper presents a comparative study of existing and novel distributed reactive power control methods that have been designed exploiting the information exchange facility provided by a communication infrastructure.

Herein, the feasibility of a grid‐connected photovoltaic (PV) power generation system with five tracking models in Hefei is evaluated comprehensively. The comprehensive evaluation of grid‐connected PV power generation system mainly includes three aspects: technology, economy, and environment. The results show that the performance ratio of grid‐connected PV system with dual‐axis tracking device is the highest among the five kinds of PV systems with a value of 81.2%, while the performance ratio of grid‐connected PV system without tracking device is the lowest with a value of 77.3%. The grid‐connected PV system with dual‐axis tracking device is economically attractive, so users can be encouraged to purchase and install such systems to meet their electrical energy needs in Hefei. Furthermore, the grid‐connected PV system with dual‐axis tracking device is the most environmentally friendly and contributes to carbon emission reduction. Finally, it is concluded that the adoption of dual‐axis tracking grid‐connected PV power generation system in Hefei area is very attractive, and can provide a certain reference for the local promotion and use of such grid‐connected PV power generation system.

A remote supervision fault diagnosis meter for photovoltaic power generation systems

ABSTRACTA low-power grid-connected photovoltaic (PV) power generation system based on automatic solar tracking is designed in this paper. In order to increase the level of accuracy of automatic solar tracking, the part of automatic solar tracking adopts the method of hybrid tracking and uses pin-cushion two-dimensional position sensitive detector plus four silicon PV cells as the photosensitive element. An adaptive topological structure of the main circuit based on a cascaded Boost converter circuit and the H6-type inverter topology are designed for the system to obtain a better working condition. Then an MPPT algorithm combined modified constant voltage algorithm with modified variable step-size increment conductance algorithm is proposed in order to improve the efficiency of PV power generation. The experimental results showed the effectiveness of the control system. Finally, the hardware and software of the system are also designed. Moreover, a graphic interface made with the LabVIEW software allows the user to monitor and save the data in a file.

This paper describes the connected photovoltaic (PV) power generation system's grid overvoltage protection function and summarizes the occurrence of the output power loss due to the grid voltage rise. Power injection from the PV system will raise the voltage at the power distribution line. A power conditioning subsystem (PCS) needs to regulate its output if the voltage becomes higher than the upper limit in order to avoid the overvoltage at the power grid. Thus, a PV system cannot generate electricity under the high grid voltage. There are 553 residential PV systems installed in Ota, Japan, for the demonstration research project of clustered PV systems. Measurement data of these 2.1-MW grid-connected PV systems are used for the analysis. Only the limited number of PV systems experienced a significant amount of output energy loss due to the high grid voltage in a particular day, whereas the other system's outputs also raise the grid voltage. The causes of this maldistribution of the output energy loss are the difference of the line impedance, the difference of the starting voltage of the PCS's grid overvoltage protection function, and the imbalance of the load in single-phase three-wire power distribution systems. The present control of the PCS successfully avoids the overvoltage on the grid but cannot share the loss.

In recent years, the capacity of distributed generations has a rapid growth, high penetration of distributed generation technology is facing new problems compared to the traditional distribution network. Therefore, it is necessary to evaluate the grid-connection before the distributed power source is connected to the grid. In this paper, based on the actual distributed photovoltaic and energy storage power generation system, the power control capability and response speed of the hybrid energy storage system are tested, The grid-connection of hybrid energy storage system and photovoltaic power generation system under smooth fluctuation, tracking plan instruction and peak to valley power generation scenario is evaluated, Provide a reference for the follow-up of distributed generations collocation network evaluation technology.

In order to implement the national energy policy, the rail transit industry actively uses renewable energies such as solar energy to explore ways to cope with energy shortage, ease power shortage and guarantee sustainable development. In this paper, the feasibility, necessity and advantages of applying solar energy to urban rail transit are introduced. Based on the characteristics of urban rail transit, the principle and composition of solar photovoltaic power generation system are analyzed. The application of photovoltaic grid-connected power generation system to urban rail transit vehicle base is proposed Design principles, design of the program and the design of relevant protection measures. The successful cases of the pilot PV grid-connected power generation system in China are summarized. It provides a new idea for the utilization of new energy in the current rail transit design. At the same time, Base roof photovoltaic power generation has done a large-scale promotion and development of accumulated experience for the follow-up project to provide design reference scheme for photovoltaic grid-connected power generation project has an important pioneering significance.

In this paper, the performance of a new Z-source inverter (ZSI)-based single-stage power conditioning system (PCS) is analyzed for a standalone photovoltaic (PV) power generation system. The proposed ZSI-based PCS includes two main parts: one is the input from PV units and the other is the ZSI. In this work, a new topology, termed the switched inductor-assisted strong boost ZSI (SL-SBZSI), is introduced for improving the performance of the PCS. The proposed topology shows high boosting capability during the voltage sag in PV units due to variations in solar irradiation and temperature. Another key advantage is the reduced capacitor voltage stress and semiconductor switch voltage stress of the inverter bridge, which ultimately minimizes the size and cost of the single-stage PCS. The proposed ZSI topology falls under the doubly grounded category of inverter by sharing the common ground between the input and output. This is an additional feature that can minimize the leakage current of PV units at the ac output end. The operational principles, detailed mathematical modeling, and characteristics of the proposed SL-SBZSI for a standalone photovoltaic (PV) power generation system is presented in this paper for analyzing performance. The simulation results, which are performed in MATLAB/Simulink, demonstrate the improved performance of the proposed SL-SBZSI for the standalone PV system. The performance of the proposed topology is also evaluated through an experimental validation on a laboratory-based PV system.