This article introduces a power compensator using Lithium-ion batteries for DC train system and a basic technology of a lifetime estimation of the battery during its operation. The technologies developed for the compensator are applicable to a large-scale storage for distribution system. The battery model used for the lifetime estimation is also applicable to a State of Charge (SOC) measurement. Because the model of the internal impedance is able to represent its frequency characteristic having close relation to its life, the model expresses transient response and lifetime of the battery. No extra charging/discharging circuit and no removal of the battery from equipment are required because the modelling method using voltage and current waveforms during its operation. The accuracy of the proposed modelling method is confirmed by a laboratory test and a running test of an electric bike.
In this paper, earthing system models for wind turbines are developed under variable frequency and transient conditions. Under high frequency and high resistivity, a fall in the earth potential rise occurs which suggests a strong capacitive effect at these frequencies. For on-shore windfarms, it was found that earthing interconnection of adjacent wind turbine structures is beneficial in reducing transient earth potential rise (TEPR) under impulse conditions. For the on-shore scenario, the benefits of interconnection extend to at least three turbines either side of the struck turbine. However, in an off-shore environment, the benefits of interconnection are less significant due to the low resistivity of the water which limits the effective length to less than that of a typical inter-turbine spacing. It was established that, for high frequency and transient conditions, the magnitude of the potential rise, seen from the point of injection, is significantly higher when the above-ground structure is taken into account. More importantly, the transient earth potential rise at the turbine base is also higher when the model includes the above-ground structure. Enhancements to the wind turbine earthing system are introduced using an insulated conductor in parallel with bare horizontal earth.
Because of global warming, the attention to the photovoltaic generation has increased, and a lot of photovoltaic generations will be installed in the power system. In Japan, most photovoltaic generations will be connected to the distribution system. This will make the power flow in the power system changed. That is to say that the forward power flow (flow from higher voltage system to lower voltage system) reduces, or, moreover, that the reverse power flow occurs. Because of the change in power flow, the voltage characteristics will be also changed. Consequently, it is expected that the penetration of photovoltaic generation has some impacts on voltage stability. In previous study, the voltage characteristics in simple power system model which consists of one infinite bus, one load, and one photovoltaic generation is made clear. It is indicated from the results that there is not only forward power flow limit but also reverse power flow limit (left nose in PV curve), and that, when the output power from photovoltaic generation is very large, left nose sometimes has some impacts on voltage stability. In this paper, the voltage stability in the simple power system model considering the dynamics of an induction motor is discussed.
In recent years, there has been a rise in the penetration of renewable energy. However, the proliferation of renewable energy has resulted in several problems faced by the power systems such as surplus power and system frequency fluctuation. In this research, a battery in an electric vehicle is considered as a control device to suppress the system fluctuation and a new EV smart charging is proposed with four charging sequences. The total controllable capacity of the EVs is estimated based on the lumped EV model for frequency fluctuation problem. The results show the effectiveness of the proposed control by smart charging on EV which can suppress the frequency fluctuation. In addition, the customer's convenience is taken into consideration by using the satisfaction index defined as the ratio of charged energy to the required energy. Lastly, a sensitivity analysis has been performed to investigate the sensitivity of parameters of both the control system and customers' data.
This paper presents applying multi-objective optimization methods to network expansion planning. The distribution network expansion planning minimizes system cost and distribution loss while satisfying the constraints. Problem formulation results in combinatorial optimization problems that are difficult to solve due to complexity. This research applies a genetic algorithm, which is a meta-heuristics method. The present study proposes a new method of multi-objective optimization methods; NSGA-II, SPEA2 and Controlled NSGA-II are assumed to be the best method now. The proposed method introduces the concept of a linkage identification genetic algorithm, enabling more efficient searching than methods hitherto known. In the past, most research that's network expansion planning didn't include load curve. This research demonstrated that the research has to include load curve. Also it proposed new method that's how to search including load curve for the research.
Renewable energy such as solar energy has collected the attention as alternative sources of fossil fuel. The output power in photovoltaic generation systems changes steeply. The change of the output power has influence on the electric power quality of the power system. For that reason, the system which can smooth the fluctuation of the output power is required. In this paper, the methods of moving average, modified moving average, single exponential smoothing and double exponential smoothing are applied to electric power smoothing control schemes for the distributed generation system with photovoltaic generation. The reduction rate of the power fluctuation and the maximum stored energy of electric double layer capacitors are adopted as evaluation methods of the system. To confirm the effectiveness of the power smoothing control methods, the distributed generation power system with photovoltaic generation systems is simulated by the power electronics circuit simulation software PSIM. Then, the methods are compared by evaluating the reduction in the capacity of electric double layer capacitors without loss in the power smoothing effect.
When a fault arc occurs in electric power equipment including insulation oil, it may cause damage to the equipment resulting from a rapid pressure rise, and lead to leakage and blowout of the oil and the generation of a high-temperature flammable gas. Therefore, we have examined these phenomena for an underwater arc from an experimental aspect, as a preliminary step toward clarifying the mechanism of pressure rise due to an arc in the oil. In this study, we have established a numerical simulation model for the pressure rise due to the underwater arc based on gas-liquid two-phase flow dynamics, and verified the validity of the model by comparing the experimental and simulation results.
MHD power generation experiments have been conducted by using a single-pulsed shock-tunnel facility, where the high temperature inert gas (pure argon) at a fixed total temperature of 9000K is introduced into a linear shaped Faraday type generator without any seeding. The fluctuations in the output power and the light emission from the plasma are found to be small, and the pure inert gas plasma seems to be rather stable free from the ionization instability. The output power is improved with increasing the magnetic flux density in almost quadric way and the enthalpy extraction ratio does not depend on the inlet total pressure (11.2%-12.9% for 0.063MPa-0.105MPa). The generator performance obtained here is surely competitive or superior to that of conventional seed plasma MHD generators in the past.
High temperature inert gas (argon) plasma MHD electrical power generation using a linear shaped channel with Hall and diagonal connections has been conducted. It is revealed from the observation by using a high-speed camera that the MHD power-generating plasma is almost stable regardless of the connection type. Enthalpy extraction ratios of 5.6% for the Hall connection, 6.7% for the diagonal connection (diagonal angle 53∼66 degree), and 10.1% for the diagonal connection (diagonal angle 36∼48 degree) have been achieved under the operating conditions of an inlet total temperature of 9000K, an inlet total pressure of 0.105MPa, and a magnetic flux density of 4.0T. The output power can suffer from a low electric field in the upstream region in a Hall connection, and is improved for no Hall current condition in a diagonal connection.
Recently, burning failure of MOV has increased in the market. However existing life test is not condition which can guarantee long-term reliability for 20 years. The objective of this letter is to present a method that can be used to evaluate electrical deterioration of MOV in order to assure the reliability.