Shunsuke Kawachi

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.

Energy capacity reduction of energy storage system in microgrid by use of heat pump: Characteristic study by use of actual machine

The installation of renewable energy sources based generators such as photovoltaic cells and wind turbines require energy storage systems(ESSs) to control power fluctuation. ESSs, however, are quite expensive. In order to reduce the necessary capacity of ESSs for microgrid applications, the control of heat pumps is researched. In this research, basic characteristic of a heat pumps power consumption is measured experimentally by use of heat pump chiller unit used in real building. Using the measured characteristic, a method to reduce the energy capacity of ESS is proposed and studied. The capacity reduction of ESS that can be achieved by use of heat pump control and the effect of control on temperature were calculated using simulations.

Feasibility Study on Short Period Power Fluctuation Compensation Using Heat Pump Air Conditioning System

In order to compensate power fluctuations caused by loads and renewable energy sources, the concept of controllable load has been proposed. In this paper, the use of heat pump air conditioning system as a controllable load is focused. To analyze the feasibility of using the heat pump for power fluctuation compensation, basic characteristics of heat pump concerning its power consumption and processed heat are measured by experiments and reported in this paper. The COP characteristics show that the efficiency of the heat pump is not affected so much by power consumption as long as it is operated above a certain level of power consumption. The Bode diagram of sinusoidal reference signal test shows that the heat pump can compensate power fluctuation which is in a certain region in the frequency domain without giving a large effect on processed heat.

Experimental Verification of Tie Line Power Flow Control of Microgrid by Use of Heat Pump Air Conditioning System and Energy Storage System

AbstractIn order to compensate power fluctuations caused by loads and renewable energy sources, the concept of controllable load has been proposed. In this paper, the use of heat pump air conditioning system (HPAC) as a controllable load is focused. To verify the advantage produced by control of HPACs power consumption as a controllable load, experiments are conducted using model microgrid system with real machines. The results of the experiments showed that the control of HPACs power consumption can contribute to power fluctuation compensation control in the microgrid. The energy capacity of energy storage system that is necessary to suppress the power fluctuation was analyzed and it has been clarified that the necessary energy capacity can be reduced by control of HPAC.

Proposal of Recurrence Formula Model Expressing Frequency Shift by Reactive-Power-Injection Frequency Shift Islanding Detection Method

AbstractWhen many power conditioning systems (PCS) of distributed generation are connected to the distribution line, the problem of islanding operation may arise. A grid-connected PCS should detect islanding operation for personnel and equipment safety. However, the islanding detection function might interfere with each other. To cope with this problem, the reactive-power-injection frequency shift islanding detection method (RPIFS-IDM) was developed. Japanese grid-interconnection code claims that RPIFS has enough capability for the detection with less interference. However, the suppression of interference between PCSs using this method has not been explained theoretically. In this paper, the frequency shift by RPIFS is modelled by a recurrence formula, using the amount of active and reactive power imbalance between loads and PCSs as parameters. This model enables to predict the frequency shift of the islanding system. Therefore, it gives the basis of discussions on the interference under the situation whe...

Basic study on interaction between synchronous machine and islanding detection method of power conditioning system

The interaction between synchronous generator and islanding detection of power conditioning system (PCS) for distributed generation, especially bases on positive frequency feedback by reactive power injection, is focused in this paper. When PCS using frequency-feedback islanding detection system are installed to power system intensively, PCSs are afraid to deteriorate the frequency stability. This research focuses on small islanding system such as microgrid, including a synchronous generator and a PCS. In a microgrid which is operated in islanding mode, its frequency stability may be sensitive to islanding detection system compared with a large scale grid. From the simulations using different automatic voltage regulator (AVR) and governor of the synchronous generator, it is found that there is a possibility of continuous frequency fluctuation caused by the interaction between AVR and islanding detection system. In addition, maximum tolerable capacity of PCS in the system used in this research is presented.

Experimental verification of power fluctuation compensation in microgrid by use of heat pump air conditioning system

To reduce the necessary capacity of energy storage systems (ESSs) for power fluctuation compensation, the concept of load control has been proposed. In this paper, heat pump air conditioning unit is treated as controllable load. Verification experiment of heat pump power consumption control has been conducted using model microgrid with gas engine(GE) and Nickel Metal Hydride (NiMH) battery. The fastest part of the power fluctuation is compensated by NiMH battery, and the slowest part of the power fluctuation is compensated by GE. The heat pump is used for compensation of mid-range power fluctuation. The control system was designed to keep the tie line power flow of the microgrid to a constant value. In the experiment, the fluctuation of the tie line power flow was small compared to that of load demand in microgrid. The result of the experiment suggests that heat pump has enough response speed and control of heat pumps power consumption as controllable load is effective for power fluctuation compensation.

Thermal comfort analysis during power fluctuation compensation by use of air-conditioning system

The power consumption control of hat pump air-conditioning system (HPACS) is expected to be an effective method to reduce energy capacity of energy storage systems (ESSs) that is necessary to compensate power fluctuation caused by renewable energy sources. In this research, experiments to control HPACSs power consumption directly has been conducted using real machine. The input signal of the HPACS has been calculated by microgrid control simulation. The heat output of the HPACS has been measured and thermal comfort of the room that is air-conditioned by the HPACS has been analyzed using room temperature calculation model. The results of the experiments and analysis show that by implementing appropriate temperature control loop, the HPACS can compensate power fluctuation in frequency range between 0.005Hz and 0.01Hz without affecting thermal comfort of the users.