Kiyoshi Takigawa

Statistical evaluation of optimum islanding preventing method for utility interactive small scale dispersed PV systems

The optimum islanding preventing method for the small scale dispersed PV system were evaluated, based on a simulation analysis concerning the occurrence probability of islanding phenomenon in actual operation. As a result, it is sufficient to adopt only one developed measure when the PV penetration ratio to distribution line capacity is less than 20% to 30%. It is necessary to adopt a combination method consisting of 2 or more developed measures when the penetration ratio is more than 40%. The harmonic monitoring method is effective in the case of using it in a combination method.

Advanced grid connected PV system with functions to suppress disturbance by PV output variation and customer load change

The PV array has unstable output patterns dependent on weather conditions. Therefore, assuming high-density grid connection in the future, these unstable output patterns can be one of the main reasons to cause power disturbances such as the voltage variation, the frequency variation and the harmonic voltage generation into utility. And also it should be considered that a sudden customer load change is one of those reasons. Therefore, this study suggested a PV system with suppression functions against such disturbances in the side of amicable relationship with utility and verified the validity of the proposed system by EMTP and ACSL-based analysis.

Development and performance test of smart power conditioner for value-added PV application

Abstract It is a disadvantage that PV power generation is only useful for clear daytime. However, a new 24 hours of application in an extended area can be added by active utilization of potential ability of PV power conditioner. For this purpose, a new multi-functional power conditioner was developed, which has a smoothing function to reduce PV output variation and load fluctuation, and also has additional function to compensate harmonics current and reactive power caused by customers load. As a result of indoor testing, a reduction rate of around 1 20 for harmonics current and reactive power were achieved. In addition, the reduction rate around 1 10 for smoothing of PV output variation and load fluctuation were verified. The work was promoted by NEDO as part of the New Sunshine Project in Japan.

A development of compact and reliable protective control unit for grid connected small residential PV systems

In the future, serious problems may arise with the maintenance of power quality, stability and safety of electric utility grids interconnected with low quality private PV power systems, without adequate protection measures being taken. The safety problem is the most important factor for electric utilities in Japan and therefore the reliability of islanding protection of such power systems must be checked because the phenomenon will directly affect the safety of personnel and utility facilities. In order to solve this problem, a reliable and compact protective control unit for residential PV power system application was developed by CRIEPI. It is confirmed that the unit shows excellent reliability for interconnected power system islanding protection.

A voltage regulation method for dispersed grid-connected PV systems under high-density connection

This paper describes a voltage regulation method for dispersed grid-connected PV systems under high-density connection. In the near future, many PV systems will be connected to distribution systems. The reverse power flow of the grid-connected PV systems will raise line voltage to the upper limit of the legal voltage range. In the first part of this paper we examine the voltage characteristics of a distribution system under high-density connection, while the second part of the paper describes a voltage regulation method for high-density PV connections, using reactive power proportional to global irradiance. The results of tests clearly demonstrate a restraining effect on voltage during the daytime and a smoothing effect on voltage fluctuation.

Advanced concept for dispersed power supply system using AC modules

A method of for estimating the reliability of new conceptual stand-alone dispersed power supply systems using AC modules with self-contained logic was proposed and system reliability estimated using a yearly scale simulation. The AC module is able to supply AC power on each module and has the flexibility to enable construction of a grid-connected system. Power storage devices were required when applying AC modules to the stand-alone power supply system. For these power storage devices, we used a battery with a built-in DC/AC micro bi-directional inverter known as AC battery. To maintain the flexibility of the system extension, the AC modules and AC batteries were controlled by self-contained logic. This logic performs parallel operations for the voltage control inverter and keeps supply and demand in balance.

A new protective method for grid connected dispersed PV systems to detect short circuit fault in distribution line

Abstract A new protective meausre installed in the grid connected dispersed PV system for detecting short circuit fault with high-resistance in a high-voltage distribution line was designed. Relationship between voltage absolute value change and voltage phase change of the distribution line is monitored in the measure for achieving not only enhancement of detective performance but also prevention of misdetection in normal operation of the grid. It was clear from simulation results that the number of PV systems detecting the fault increased about 2 times as much as the existing method and the reduction of fault current at utility substation, which causes dangerous inability of utilitys protection, could be prevented effectively.

Islanding prevention performance test of Japanese manufacturers inverters

Popularization of PV systems is accelerating by the powerful policies of government and effect of cost reduction in Japan. As a result, it is feared that PV systems will be connected with high density in some local areas. In this situation, most important issues are the safety and stability of PV systems, especially because dangerous islanding phenomenon could easily occur. To clear the problems, performance tests of islanding prevention, as the safety and durability to daily fluctuation of voltage phase on utility grid or frequency swing in power system accident depends on the stability, were conducted with six types of inverters from the market in Japan at the Akagi testing center of CRIEPI. As a result of the islanding test, it was confirmed that there is no problem in the combination of passive and active islanding prevention method. On the other hand, stability test showed that most inverters are over sensitive as a power source of utility grid. The work has been promoted by NEDO as a part of New Sunshine Project in Japan.

Simulation of isolated operation in fault condition by loop power flow controller

6.6 kV overhead distribution systems are currently constructed in Japan as radial networks. The load imbalance of each feeder therefore has a negative impact on voltage stability. On the other hand, disconnecting distributed generators with faults causes line overload or under-voltage. Therefore, controlling line voltage and line power flow on the distribution system is critical for the open access of indefinite numbers of distributed generators. We are investigating a new loop or mesh structure distribution system to maximise network capacity. This paper describes a control method for a loop power flow controller (LPC) focusing on 1 line-to-ground (LG) fault states.

Simulation of Isolated Operation in Fault Condition by Loop Power Flow Controller

6.6 kV overhead distribution systems are currently constructed in Japan as radial networks. The load imbalance of each feeder therefore has a negative impact on voltage stability. On the other hand, disconnecting distributed generators with faults causes line overload or under-voltage. Therefore, controlling line voltage and line power flow on the distribution system is critical for the open access of indefinite numbers of distributed generators. We are investigating a new loop or mesh structure distribution system to maximise network capacity. This paper describes a control method for a loop power flow controller (LPC) focusing on 1 line-to-ground (LG) fault states.