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This paper presents the operation under fault and protection of multi DC smart grids connected to the DC transmission line. The smart grid consists of wind turbine and photovoltaic generators, controllable loads, generator side and grid side inverters. The voltage stability of the DC bus voltage is attained by applying the power consumption control of controllable loads, the power control of grid connected converter and power control of renewable plants. On the other hand, the fault protection for short-circuit and low resistance ground fault at the DC transmission line was sighted. Simulation results based on PSIM are provided to demonstrate the effectiveness of the system. [ABSTRACT FROM AUTHOR]

A photovoltaic (PV) system’s output power fluctuates according to the weather conditions. Fluctuating PV power causes frequency deviations in the power utilities when the penetration is large. Usually, an energy storage system (ESS) is used to smooth the PV output power fluctuations and then the smoothed power is supplied to the utility. In this paper, a simple fuzzy-based frequency-control method is proposed for the PV generator in a PV–diesel hybrid system without the smoothing of PV output power fluctuations. By means of the proposed method, output power control of a PV generator considering the conditions of power utilities and the maximizing of energy capture are achieved. Here, fuzzy control is used to generate the PV output power command. This fuzzy control has average insolation, change of insolation, and frequency deviation as inputs. The proposed method is compared with a maximum power point tracking control-based method and with an ESS-based conventional control method. The numerical simulation results show that the proposed method is effective in providing frequency control and also delivers power near the maximum PV power level. [ABSTRACT FROM AUTHOR]

This article explains a battery-based control method to reduce the photovoltaic output power fluctuations, which, in turn, will reduce the frequency deviations of the power system. The battery control method introduced here will maintain the state of charge near 50%. Therefore, it will increase the lifetime of the battery, as well as decreasing the maintenance cost. A local search algorithm is provided with this battery control method to search the optimal capacity of the battery required for smoothing the photovoltaic output power fluctuations. Then, a cost comparison is provided to realize the performance of the search algorithm. To verify the effectiveness of the proposed method, simulation results are presented using the actual insolation and load data. [ABSTRACT FROM AUTHOR]

A Photovoltaic (PV) system's power output is not constant and fluctuates depending on weather conditions. Fluctuating power causes frequency deviations and reduction in reliability of the isolated power utility or microgrid when large output power from several PV systems is penetrated in the utility. In this paper, to overcome these problems, a simple coordinated control method for leveling the fluctuations of combined power output from multiple PV systems is proposed. The conflicting objective of output power leveling and acquisition power increase is achieved by means of the proposed method. Here, output power command is generated in two steps: central and local. Fuzzy reasoning is used to generate the central leveling output power command considering insolation, variance of insolation, and absolute average of frequency deviation. In local step, a simple coordination is maintained between central power command and local power commands by producing a common tuning factor. Power converters are used to achieve the same output power as local command power employing P1 control law for each of the PV generation systems. The proposed method is compared with the method where a modified maximum power point tracking control is used for smoothing the short-term change in each of the PV system's output. Simulation results show that the proposed method is effective for leveling output power fluctuations and feasible to reduce the frequency deviations of the isolated power utility to maintain reliability. [ABSTRACT FROM AUTHOR]

In recent years, distributed generation, as clean natural energy generation and cogeneration system of high thermal efficiency, has increased due to the problems of global warming and exhaustion of fossil fuels. Many of the distributed generations are set up in the vicinity of the customer, with the advantage that this decreases transmission losses. However, output power generated from natural energy, such as wind power, photovoltaics, etc., which is distributed generation, is influenced by meteorological conditions. Therefore, when the distributed generation increases by conventional control techniques, it is expected that the voltage change of each node becomes a problem. Proposed in this paper is the optimal control of distribution voltage with coordination of distributed installations, such as the load ratio control transformer, step voltage regulator (SVR), shunt capacitor, shunt reactor, and static var compensator. In this research, SVR is assumed to be a model with tap changing where the signal is received from a central control unit. Moreover, the communication infrastructure in the supply of a distribution system is assumed to be widespread. The genetic algorithm is used to determine the operation of this control. In order to confirm the validity of the proposed method, simulations are carried out for a distribution network model with distributed generation (photovoltaic generation). [ABSTRACT FROM AUTHOR]

Photovoltaic power generation and wind power generation have an advantage that energy is clean and infinite, but they have a disadvantage in that electrical output energy is unstable, and initial and maintenance costs are expensive. This paper presents an optimal configuration for renewable generating systems in residence using a genetic algorithm (GA). We define that the objective function is the total cost, where the total cost is the sum of initial cost, an operation cost, and a maintenance cost. We determine an optimal configuration of renewable generating systems, where total cost is more reasonable using GA. The simulation using this technique is shown. [ABSTRACT FROM AUTHOR]

Abstract: Due to the depletion of energy resources and global warming, renewable energies such as the solar collector (SC) and photovoltaic generation (PV), are gaining more widespread use in residential areas. In Japan, incentive to install these units for consumers is provided by governmental support with the introduction of feed-in tariffs (FIT) and governmental subsidies. Thus, it is possible to reduce electricity cost in houses using time-of-use (TOU) price and to get benefit from selling power generated by PV. Furthermore, investment costs of PV and battery systems are decreasing year by year; on however, the price of purchased power for consumers is increasing and the selling price by FIT is decreasing annually. Hence, it is important to reveal which year, at what capacity, and which system and appliances are best choices for the consumer. In this paper, an expansion planning model of PV and battery systems for the smart house is presented. The expansion planning period is 20 years and ranges from 2015 to 2035. The proposed method clarifies the optimal installation year, capacity and appliances during the twenty year period considering variable characteristics such as investment cost, selling price and purchasing price which change year by year. [Copyright &y& Elsevier]

Abstract: Recently, renewable energy technologies such as wind turbine generators and photovoltaic systems have been introduced as distributed generation. The connection of large number of distributed generators causes voltage deviation beyond the statutory range in a distribution system. In this paper, a methodology for voltage control in proposed by using the tap changing transformers and the inverters interfaced with the distributed generators. In the proposed method, information of the voltage and power is collected via a communication network. Based on these information, the optimal reference values are calculated at the control center, and sent to the transformers and the inverters. The proposed method accomplishes a coordinated operation among the control equipments and reduces the voltage deviation. Effectiveness of the proposed method is verified by the numerical simulation results. [Copyright &y& Elsevier]

Abstract: In recent years, distributed generations based on natural energy or co-generation systems are increasing due to global warming and reduction of fossil fuels. Many of the distributed generations are set up in the vicinity of customers, with the advantage that this decreases transmission losses and transmission capacity. However, output power generated from renewable energy such as wind power and photovoltaics, is influenced by weather conditions. Therefore if the distributed generation increases with conventional control schemes, the voltage variation in a distribution system becomes a serious problem. In this paper, an optimal control method of distribution voltage with coordination of distributed installations, such as On Load Tap Changer (OLTC), Step Voltage Regulator (SVR), Shunt Capacitor (SC), Shunt Reactor (ShR), and Static Var Compensator (SVC), is proposed. In this research, the communication infrastructure is assumed to be widespread in the distribution network. The proposed technique combines genetic algorithm (GA) and Tabu search (TS) to determine the control operation. In order to confirm the validity of the proposed method, simulation results are presented for a distribution network model with distributed (photovoltaic) generation. [Copyright &y& Elsevier]

Abstract: As a new measure for smoothing PV output power fluctuations and for reducing frequency deviations of isolated power utility, firstly, this paper discusses a control method based on fuzzy reasoning for single PV system. The fuzzy reasoning produces output power command for smoothing PV system’s power fluctuations considering insolation and power utility conditions. Secondly, an energy storage based method is proposed. Here, PV output power fluctuations are leveled through battery charge/discharge action and the optimal size of the battery is calculated to minimize the system cost. Thirdly, a simple coordinated control method is proposed for multiple PV systems clustered in different locations. The coordinated method produces central leveling output power command by fuzzy reasoning. Local output power command is generated by multiplying individual maximum power command with tuning factor. All of the proposed methods are compared with the MPPT control and found effective in smoothing PV output power fluctuations. [Copyright &y& Elsevier]