Kosuke Kurokawa

Analysis Results of Output Power Loss Due to the Grid Voltage Rise in Grid-Connected Photovoltaic Power Generation Systems

This paper describes the connected photovoltaic (PV) power generation systems 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 systems 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 PCSs 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.

A Novel Microcontroller for Grid-Connected Photovoltaic Systems

The purpose of this paper is to develop a novel microcontroller for grid-connected photovoltaic (PV) systems. As a prototype model, a 100-W-class module-integrated converter composed of the proposed controller and a flyback inverter has been built and tested. The prototype model is designed to satisfy the Japanese grid-connection guideline. Basic functions as those of a grid-connected PV inverter, such as the maximum-power-point tracking and the anti-islanding protection, have been confirmed in the experiments using a distribution network simulator located in a laboratory. This paper presents the description of the controller and the experimental results. A microcontroller has been developed with a 50-MHz-class microcomputer and simple interfaces. By revising the program, the proposed controller can be applied to various types of PV systems or grid-connected equipment

A Novel Maximum Power Point Tracking Method for PV Module Integrated Converter

Solar cell has the current-voltage (I-V) characteristic which is affected by the radiation and the temperature. To obtain the maximum electricity from the solar cells, the power converters for PV (photovoltaic) module have a function called MPPT (maximum power point tracking). The dc voltage and current are controlled to track the maximum power point (MPP) where the PV modules feed the maximum output power. AC module is composed of a PV module and a module integrated converter (MIC). The output port is connected with the ac wiring. Each module can operate with tracking the own MPP. In case of AC module, the basic characteristic of the PV module is well-known by the manufacturer. Therefore the domain of MPP is approximately predicted. In this paper, a novel MPPT method for the MIC is proposed. The proposed method takes full advantage of the known PV module characteristic. The I-V plane is divided into two domains by a linear function. One includes MPPs and the other one never includes MPPs under the normal temperature and radiation conditions. The operating point can be rapidly approached to the MPP using the linear function. Around the MPP, the algorithm is switched to the IncCond method. Circuit experiments have been carried out. The measured time taken for the approach to the MPP is reduced from 22 % to 48 % compared to the conventional algorithm. The proposed method is quite simple so that it can be easily applied to various MPPT algorithms

An evaluation method of PV systems

Data evaluation methods have wide adaptations, such as feedbacks to PV system operation management and design. The authors have already developed sophisticated verification method (SV method) of PV systems, which is a simple evaluation method to identify six kinds of system loss rates using basic information and simple four measurable data. This time, the authors introduced quality diagnosis to our previous model for compensating the measurement errors in field data, and improved the algorithm of the model. Consequently, validity of the evaluation result became better than the previous model.

Dynamic evaluation of maximum power point tracking operation with PV array simulator

Abstract This paper presents an innovative method to measure the dynamic control ability of maximum power point tracking for PV inverters under the condition of irradiance fluctuation. The PV array I–V curve simulator is a kind of indoor testing facility and easy to be adopted by industries. Basic functions are given by a specially designed PV array I–V curve simulator composed of the active power load. Most of the parameters are controllable by sophisticated software with capability of treating a lot of 1-s data for a very long period of time. In this paper, detailed structure of the equipment is described and test examples are also given by using a commercial PV inverter.

The Japanese experiences with national PV system programmes

Abstract The paper summarises Japanese activities concerning photovoltaic systems including those for residential use, which is one of the major targets for a domestic alternative energy supply. Fiscal year 1999 marked the 25th anniversary of the Sunshine Project that was initiated in July 1974. The Sunshine Project was subsequently reorganised into the New Sunshine Program to include renewable energy, energy conservation and environmental technology. The major target of the Photovoltaic Technology Development Project in the Programme, from an early stage of R&D, has been focused on utility-connected, residential applications mounted on roofs. Recently, it can be considered that technologies for the target have been fundamentally established and a series of new activities have been introduced to promote the commercialisation and diffusion of PV systems. To review those activities, several condensed tables are presented, i.e., R&D history of residential applications, recent trends in regulation and code improvements, and new institutional activities to disseminate PV systems. The authors also present performance results collected from a large number of PV systems by using a very effective evaluation method called the ‘SV method’. The paper finishes by introducing a good example of simple system monitoring with good verification that can establish a knowledge circle from a variety of PV fields, including to factories, engineers, owners and investors, and it seems to be quite cost-effective.

Measurements, analyses and evaluation of residential PV systems by Japanese monitoring program

Abstract This paper is about measurements, analyses and evaluation of residential PV systems in the Japanese Monitoring Program, on which JQA was subsidized by NEDO (New Energy Development and Industrial Technology Organization) that is currently proceeding [NSS R&D] from FY1997 to FY 2000. The aim of this investigation refers, through the data evaluation and analyses, to obtain knowledge required for optimizing design of PV systems, such as system performance, characteristics and regional dependency under practical operation and to develop the system evaluation technology on the design parameter method.

Evaluation of effective shading factor by fitting a clear-day pattern obtained from hourly maximum irradiance data

The authors have developed the sophisticated verification (SV) method, which can evaluate involving performance ratio, power conditioner efficiency, temperature factor, shading factor, load matching factor and other array parameter. So, we also have ensured adequacies of the evaluation of PV systems. However, the originally proposed method accepts PV installations facing the south only. In this paper, we have modified the SV method by taking into account the arbitrary orientation and inclination, because of improved the accuracy of evaluation. Therefore, the shading effect can be intelligible for each hour. The maximum value of shading losses reached 13.1%.

Improvement of performance in redox flow batteries for PV systems

Abstract A redox flow battery (RFB) is a new type battery. A new piping sytem to improve the performance of RFBs for PV systems is introduced. In this new system, the piping for the electrolytes also connects each stack in series just like the electric circuit. In this system, the leak current through the electrolytes in the piping between each stack is suppressed. This system is called multitank system because it has many minitanks between each stack. It is clarified from the experimental and simulation results of the multitank system that this system improves the performance of RFBs.

Conceptual considerations on PV systems composed of AC modules

AC module technology has become popular and a number of AC module types are commercially available. Although their specifications are clear, it seems that their technological meaning has not yet been well developed. Therefore, the authors tried to create the total concepts of PV systems composed of AC modules. They are abbreviated AC module-composed PV system or ACM-PV. In the paper, the possible structural configurations of simple AC modules and battery integrated ones are classified in principle. System categories are also classified to show their total concept. Necessary electrical terminals and interfaces, voltage matching method between inverter and PV part, and AC module testing methods are also discussed.