Junpei Baba

Effect of autonomous distributed vehicle-to-grid (V2G) on power system frequency control

Penetrating large amount of renewable energy sources into power system, battery energy storage performs an important role for smoothing their natural intermittency, ensuring grid-wide frequency stability, and suppressing voltage rise caused by reverse power flow. The ubiquitous power grid is one of the concepts as a smart grid in Japanese context, where the total battery capacity can be optimized by coordinating renewable energy sources, controllable distributed generators, and controllable loads on demand side, for example, heat pump based water heater with heat storage, and plug-in hybrid vehicle or electric vehicle with onboard battery, and so on. These controllable devices behave as an autonomous distributed smart storage by charging or discharging against the power system frequency measurement as paying attention to user convenience. In this paper, effects of the autonomous distributed smart storage on bulk power systems are investigated thorough a load frequency control simulation.

State of charge control for energy storage by use of cascade control system for microgrid

The hybrid control system, which is a combination of cascade control and local control, is proposed as a method to compensate power fluctuations caused by load and renewable energy sources in a microgrid using distributed power generation systems(DGs). When energy storage system(ESS) such as EDLC is used in the microgrid to compensate power fluctuations, its state of charge(SoC) should be controlled. In this paper, a new method to control ESSs SoC which would enable power compensation with less energy capacity and with less effect to the compensation result is proposed. This method uses the feature of the cascade control that faster DGs reference is dependent on slower DGs output. The new method is implemented on EDLC in the model microgrid and its effectivity is verified by a simulation and a experiment. The result of the simulation and experiment is also reported in the paper.

Power System Characteristics of the SCFCL in Parallel With a Resistor in Series With a ZnO Device

Superconducting fault current limiters (SCFCLs) are expected to improve the reliability and stability of power systems. The 3-phase FCL system, which consists of 3 superconducting fault current limiters of transformer type in parallel with a resistor in series with a ZnO device, was proposed and its small model was designed and made. In a power system the FCL system is expected to limit the peak of the fault current inductively and also to consume the acceleration energy of the generators by means resistive component. The power system characteristics of the proposed FCL system was experimentally investigated by use of the model FCL and a laboratory scale power system simulator. The FCL system switches its impedance from inductive type (L-type) to inductive+resistive type (L + R-type) in a cycle due to the ZnO device. The peak of the fault current was limited in the L-type time interval and the energy was consumed in L + R-type interval. The proposed FCL system limited the fault current at the simulated fault and successfully recovered the stand-by mode in the model power system. At the same time, the energy consumption in the resistor reduced the accelerating energy of the generator and then improves the power system transient stability.

Current Limiting Characteristics of Inductive Type SCFCL With ZnO Device and Resistor in Parallel

A new FCL system which consists of a L-type SCFCL in parallel with a resistor and a ZnO device is proposed. The proposed system limits the fault current inductively and also consumes excessive energy like R-type ones. A model system was made and studied experimentally. The ZnO device is off-state in stand-by mode. When a fault occurs, the SCFCL turns into current limiting mode and has high impedance. The voltage across the SCFCL exceeds a threshold voltage of the ZnO device. During one cycle of the voltage, the ZnO device is on-state around the peak of the voltage, and the current flows through both the SCFCL and the resistor. A certain amount of excessive energy is dissipated in the resistor. The ZnO device is off-state around the peak of the current which is suppressed only by the L-type SCFCL. Finally the proposed FCL system switches L-type and L+R-type in a cycle. Relations among the threshold voltage, the current limiting impedance and the resistance of the resistor were discussed. It was confirmed the proposed FCL system represents desirable current limiting characteristics

Voltage control using coordinated control of Heat Pump Water Heaters with large penetration of photovoltaic systems

It is expected that large amount of photovoltaic (PV) systems will be installed in future power systems. However, introduction of large PV systems create significant problems specially in the distribution system. One of main problems is voltage rise at the end of distribution line due to reverse power flow by the presence of PV systems. In order to mitigate this problem, we propose load control at the customer end. Heat Pump Water Heater (HPWH) has been selected as customer controllable load due its large thermal energy consumption and flexibility in operating time. In this paper, coordinated control of HPWHs is attained based on the node voltages and customer hot water demands. When one of nodes voltage goes closer to maximum allowable voltage or hot water in the tank becomes its minimum level, HPWH is operated in order to avoid voltage rise or hot water shortage. In the voltage control method, primary control priority for operating HPWH is set to maintain reasonable hot water and then set to avoid the voltage rise with intention to keep the participating customers convenience. It is found that proposed voltage control method not only avoids voltage rise but also maintain customer convenience.

A model experiment of current limiting characteristics of superconducting fault current limiter in the demand side with distributed generator

Superconducting Fault Current Limiters (SCFCLs) are expected to improve both reliability and stability of power systems. Specifications of SCFCLs, such as trigger current level, recovery characteristic and impedance must be considered precisely in introducing SCFCLs to a power system. In this paper, current limiting characteristics of SCFCL in the demand side, (that is, a customer who has distributed generators and loads), is studied and demonstrated experimentally by use of a small 18kVA synchronous test generator with a test three-phase SCFCL unit of a transformer type and an artificial transmission line. In general, a current limiting reactor of normal conductor is installed in order to reduce the large fault current from the generator, however, it also decreases the maximum output power of the generator to the grid. The current limiting tests were carried out by replacing the reactor with the SCFCL. It was experimentally confirmed that SCFCLs can suppress the fault current considerably and can improve the transient stability at a certain fault without reducing the steady state stability margin.

Determination of dynamic line drop compensation parameters of voltage regulators for voltage rise mitigation

Dynamic operation of voltage regulator (VR) has been proposed for voltage regulation in a distribution system with large integration of distributed generators (DGs). In conventional voltage control, VRs tap operation is adjusted based on the local bus voltage or voltage at load center. When considerable DGs are interconnected, voltage profile and power flow are not same as that of with conventional distribution system, at some instant reverse power flow may exist at the end of the distribution line or at VR. Thus there are possibilities of having voltage violation due to improper tap operation of VRs. This paper proposes a new method to determine line drop compensation (LDC) parameters based on the estimated current at VR. Voltage regulating point is shifted along the distribution line so that proper tap operation of VR is carried out to retain voltage regulation. It is found from the analysis that voltage violation is significantly reduced by the proposed method in comparison with conventional method.

Dynamic voltage regulator operation with demand side management for voltage control

Widespread interconnection of Photovoltaic (PV) systems in the distribution system may create voltage rise problem. In this paper, a decentralized voltage control method by use of voltage regulators (VRs) and demand side management using consumer controllable load has been proposed for voltage rise compensation. The proposed method includes a novel determination method to find dynamic line drop compensation (LDC) parameters for a VR that has reverse power flow using the measured line current through VR and an optimal method that determines a dead band for a VR in order to lessens the number of tap operations while minimizing voltage deviation and violation. The obtained results show that voltage violation is extensively mitigated by the proposed method and no significant increment in tap operations of VR is encountered.

Feasibility study on power consumption control of desalination plant with mechanical restrictions

It is proposed that the seawater desalination system as a controllable load for compensating the power fluctuation caused by renewable energy in small island power system. For controlling the power consumption of the system, the system modeling is needed. In this paper, the high pressure pump and the RO membrane are modeled, and the accuracy of that model is discussed. In addition, it is necessary to make it clear the boundary condition of the upper and lower limitation of the power consumption of the system. The boundary condition derived from the mechanical restriction of using RO membranes is discussed through modeling and experiment.

Positron annihilation study of high impact polystyrene

Abstract Positron lifetime spectra for general purpose polystyrene (GPPS), polybutadiene rubber (PBR), and their copolymers, styrenebutadiene rubber (SBR) and high impact polystyrene (HIPS) have been measured. It has been found that the free volumes in the copolymers are smaller than the average over the individual polymers, due to the interfacial interaction between the styrene and rubber phases. A long-lived component with a mean lifetime of about 123 ns was observed in the spectrum for deformed HIPS, showing the existence of ortho -positronium ( o -Ps) in the deformation induced crazes.