This article surveys background and consideration in California State of the United States as one example of oversea's Smart Inverter approaches. In addition, the outline of demonstration (Development of smart inverter & DERMS) that TEPCO is participating in is introduced.
The introduction of electric vehicles (EVs) has been increasing as well as photovoltaic generation (PV) systems. These introductions cause the voltage drop and rise on high-voltage distribution lines, so that voltage deviation will be out of the specified voltage range. As a countermeasure against this problem, the voltage control method with static Var compensators (SVCs) is implemented. However, SVCs are expensive and power losses on the distribution line increase. This paper proposes a novel voltage control method in which power conditioning systems (PCSs) output leading and lagging reactive power aiming to solve the above-mentioned problems. It is clarified that the proposed method is more effective in solution of these problems than compared with the voltage control method using SVCs.
This paper proposes differential evolutionary particle swarm optimization (DEEPSO) for load adjustment distribution state estimation (DSE) using correntropy. Practical equipment in distribution systems causes nonlinear characteristics in an objective function and evolutionary computation methods have been applied to DSE so far. This paper applies DEEPSO in order to improve estimation equality. Minimization of sum of square errors by the least squares method has a problem when outliers exit in measured values. Quality of estimated results is largely affected by the outliers using the least squares method, while correntropy has a possibility not to be affected by the outliers. The proposed method applied to a typical distribution system. The results indicate that the proposed DEEPSO based method can improve estimation results compared with conventional PSO and hybrid PSO based method and the correntropy based proposed method can estimate distribution system conditions more accurately than the conventional least squares method.
This paper proposes a real-time generation regulation system named as “On-demand Generation Regulation Control (OGRC)” system, which is suitable for small independent power grids with unstable renewable energy generators. It has been developed as a part of “Robust demand and supply control manager” and plays an important role of flexible frequency control that includes V2G (Vehicle to Grid) and generation restriction when necessary. The main feature of the system is the integrated framework to effectively deal with hard-to-predict control options in a flexible way by observing the unstable generator outputs and all generators/batteries status including electric vehicles (EV). In addition, a feedback system is also proposed to flexibly adjust the regulation capacity in case unexpected disturbances occur. The performance of the proposed system is verified through numerical simulations based on an actual test site with successful results.
In the field of power electronics and power systems, electrical signals, such as voltage and current, are expressed by trigonometric functions. Some functions are sinusoidal functions with periodically changing amplitude, which are expressed by the product of two sinusoidal functions with different frequencies. In this paper, we describe the effective value of the functions. The error of the effective value becomes large when the frequency of the functions is close to each other. However, the effective value is equal to the product of the effective values of the two functions when the frequency of the functions is far from each other. The method is simple and straightforward, and can be applied to the calculation of an effective value of ripple current and voltage flicker in power electronics equipment.
Photovoltaic and wind power generations are renewable and domestic energy, so increasing rapidly in recent power system of Japan. Power of PV and wind generating electricity is variable and unstable according to weather condition such as sunshine and wind velocity. Comparing costs of PV and wind generating electricity with other stable power generations such as thermal or nuclear power generation, it is necessary to arrange their conditions of stable supplying to demand. This paper analyzes costs of PV and wind generating electricity in two cases of using with storage battery or thermal power generation. As a result, stable supplying unit costs of PV and wind generations is several times of usually used generating unit costs that is only generating costs divided by unstable generating energy. In future, introduction of much PV and wind power generations is necessary to be increased gradually in the extent of stable operation of power system, in other words stable supply of electric power to demand, considering economical and technological situations.
This paper presents a solar radiation estimation method in winter using the meteorological satellite data and cloud and snow classification method. The method is planned to be introduced into the photovoltaic (PV) estimation system developed by the authors in order to reduce the solar radiation estimation error. This paper proposes the cloud and snow detecting method, which uses NDSI (Normalized Difference Snow Index) and BTD (Brightness Temperature Difference) derived from near infrared and infrared wavelength data observed by himawari-8. The proposed method can reduce the solar radiation estimation error by about 36 to 37%.
Although FRT capability is claimed in Japanese grid code for RE, DVS capability is not. In some European countries, not only FRT but also DVS is claimed. Whether this choice of our grid code is pragmatically adequate or not? To answer the question, it is necessary to evaluate FRT and DVS capabilities. But the past studies only evaluated qualitative merit of FRT and DVS, or evaluated quantitative merit on fictional system models. Since the authors intend to evaluate FRT and DVS capabilities in existing power system of Japan, some method for the evaluation must be invented.
For the evaluation, values of FRT and DVS capabilities are evaluated by reduction amount of stabilizing equipment (i.e. SVC in the paper). The evaluation based on strict optimal SVC disposition is quite difficult, because existing power system must be adequately modeled, because number of SVCs is large and because every power flow conditions must be considered. However, semi-optimal SVC disposition can be calculated as shown in the paper.
As the result, value of FRT is quite larger than value of DVS. And then, our grid code is proved as pragmatically adequate, except some flaw in claimed FRT design that is introduced in the paper.
For electromagnetic transient (EMT) analysis programs, faster simulations are always desired, since circuits to be simulated are becoming larger and larger. This paper proposes a non-zero element combination recording algorithm for fast search for non-zero elements in the LU decomposition of a large sparse matrix obtained from circuit equations. It should be noted that the solution process of the circuit equations occupies a large portion of the total simulation time. A sparse matrix routine with the proposed algorithm has been developed. In a simulation case with a synchronous generator model which requires frequent LU decompositions, the developed routine is faster by 1.5 times than the conventional one.
Recently, the penetration of wind farm (WF) has been increasing because of the global warming and the lack of the fossil energy resource. However, WF output fluctuate due to the weather and the seasonality. Specially, the long-term fluctuation is called “Ramp event”. It's difficult for WF output to dispatch to the power grid without controlling the ramp events. This paper proposes the method of scheduled operation to mitigate the ramp events and reduce the imbalance energy with the stochastic programming. In this method, it's necessary to use the WF output scenarios. However, there has never been studied the method of generating scenarios with the temporal correlation so far. Therefore, we propose the production method of generating scenarios considering the temporal correlation with copula. Finally, this paper shows the validity and the effectiveness of these methods through computational simulations using the integrated WF data of Tohoku area.
In this paper, an efficient Discrete CoFFWA method is proposed to deal with distribution network reconfigurations. It is useful for minimizing the active power network losses by switching on/off sectionalizing switches and shunt capacitors. The mathematical formulation may be expressed as one of combinatorial optimization problems. This paper presents a discrete version of CoFFWA (Cooperative Framework for Fireworks Algorithm) of advanced metaheuristics to solve distribution network reconfigurations efficiently. It is one of the efficient Fireworks Algorithms that imitate the behavior of firework explosion. To improve the solution accuracy, CoFFWA makes use of new strategies such as the independent selection method and the crowdness-avoiding cooperative strategy. The proposed method transforms CoFFWA into discrete one with multi-point mutation. The proposed method is successfully applied to the IEEE 69-node and 119-node distribution networks.
This paper discusses the effectiveness of frequency control and peak shift by Electric Energy Storage System (EESS) that consists of Lithium ion Capacitor (LiC) and Valve-Regulated Lead Acid (VRLA) battery in Izu-oshima. We demonstrate that EESS suppresses frequency fluctuation while maintaining the suitable State of Charge of LiC that has small capacity. We also demonstrate to reduce the peak load by scheduled discharge from VRLA, so it is shown that the possibility of reducing operating time of diesel generators that contributes to extend examination period.
In recent years, with the increase of wind turbines on the coast of the Sea of Japan, damages caused by winter lightning are often reported. The authors have carried out measurement of the current waveform on winter in 2013 to 2015 at Nikaho wind farms. In this paper, we discuss the relation between the meteorology and the charge transfer observed at Nikaho wind farm in winter.
In order to produce electric power with the highest efficiency from PV modules, it is necessary to operate at a Maximum Power Point (MPP). However, the MPP changes and is affected by external factors such as the of temperature and solar irradiance. In solving the problem, PV modules are in need of Maximum Power Point Tracking (MPPT) such as the perturb and observe method and the I-V characteristics scanning type of MPPT. The latter technique is accurate but it requires a certain time to mesure I-V characteristics and it causes power generation loss. But, the response speed is limited by the measurement system rather algorithm. In this paper, we propose a new MPPT method to solve these problems. This is based on estimating the I-V characteristic by using an equivalent circuit model of PV module. This method is capable of high-speed response and does not equire scanning of I-V characteristics. By experiments, we have demonstrated that the scan-less MPPT at 260ms intervals and that its Useful Utilization Factor (UUF) is 99.9 These performances are equivalent to those of the MPPT method measuring the I-V characteristics directly.
Recently, a large number of renewable energy (RE) sources such as wind farms (WFs), photovoltaic generations (PVs) have been introduced to power systems as a solution for the worldwide environmental issue. On the other hand, with the deregulation of the electric power industry such as the full liberalization of retail sector, power producer and suppliers who own RE sources have traded the generated electricity in the electric market. However, power outputs of RE sources fluctuate every moment and it is impossible to predict the power output perfectly. Thus, to operate RE sources according to the generation schedule notified in the market while suppressing their power output fluctuation, cooperation of energy storage systems with RE sources are required. This paper proposes a method for determining the scheduled generation of WFs by cooperating the predicted WF power output and heat pumps (HP)/biogas engine generator (BG) heat supply system (HP/BG heat supply system) which is a new energy storage technology developed by the authors. The proposed methods consist of two steps. In the first step, optimal operations of HP and BG are determined by utilizing the predicted WF generation so that the flexibility of HP/BG system can be ensured. In the second step, the operations of HP and BG are modified based on actual WF outputs including predicted errors. The validity and effectiveness of the proposed method are investigated through some computational simulations using MATLAB.
Calculations of short line fault (SLF) interruption performance for high voltage gas circuit breakers have been made by using arc models. Cassie and Mayr arc model are well known as an arc model. By combining the one Cassie and two Mayr models, the SLF interruption performance for SF6 gas circuit breaker and CO2 gas circuit breaker is able to be evaluated. Recently, power distribution systems have been changing due to the spread of renewable energy sources. Molded Case Circuit Breaker (MCCB) will interrupt direct current. In this paper, arc model of the air arc was constructed to evaluate the D.C. interruption performance of the MCCB. In the MCCB arc model, the arc parameters which are arc time constant, arc voltage for the Cassie model, arc time constant, arc power loss for the Mayr model were obtained by arc voltage measurements. It is able to set the arc time constants for Cassie and Mayr models are the constant value same as the SF6 gas circuit breaker and CO2 gas circuit breaker. The relation between arc power loss for Mayr model and peak value of interrupting current was derived from measurements. It is shown that the D.C. interruption performance for MCCB can be evaluated by using serially connected three arc models same as SF6 gas circuit breaker and CO2 gas circuit breaker.
Recently, demand for DC circuit breaker is increasing and in particular DCCB with VCB attracts much attention. In this paper, DC current interruption test by injection of high frequency current is performed in order to evaluate current interruption characteristics. In addition, we adopted the model where the A value, the product of the residual plasma and the slope of current at current zero point, determines whether the interruption will succeed or not. From the probability processing, it turned out that the interruption performance was good in order of Cu:Cr =8:2 electrode, pure copper electrode, and Cu:Cr =5:5 electrode.