Young Gyu Jin

Determining the Optimal Reserve Capacity in a Microgrid With Islanded Operation

A microgrid can be a useful entity to support stable and efficient operation of power systems with large-scale penetration of distributed generators. Suppose that a microgrid should provide reserve operation in a decentralized environment; determining a suitable reserve capacity becomes an important problem for reliable and economic operation. To address this problem, in this paper we present a method of determining the optimal reserve capacity under the power exchange for frequency control (PXFC) market environment. After creating some penalty rules that take microgrid islanding into account, determining the optimal reserve capacity is formulated as an optimization problem. Microgrid islanding probability (MIP) is proposed as an index to describe the likelihood of microgrid islanding. The effectiveness of the method in terms of the operating cost is investigated using simulations, where our method and two further methods are applied to microgrids with different generation capabilities. The properties of MIP are also demonstrated by the simulations.

Decentralized Vehicle-to-Grid Design for Frequency Regulation within Price-based Operation

The utilization of electric vehicles has been suggested to support the frequency regulation of power system. Assuming that an intermediate aggregator exists, this study suggests a decentralized vehicle-to-grid operation scheme in which each vehicle-to-grid aggregator can behave independently of the power system operator. To implement this type of decentralized operation, this study adopts a price-based operation that has been proposed by many researches as an alternative operation scheme for the power system. In this environment, each vehicle-to-grid aggregator can determine its participation in vehicle-to-grid service in consideration of its residual energy of aggregated system and real-time market price. Consequently, the main purpose of this study is to verify whether or not the vehicle-to-grid power can effectively support the current frequency regulation function within the price-based operation scheme. Specifically, a frequency regulation method is proposed based on the real-time price signal, and a feedback controller for battery management is designed for decentralized vehicle-to-grid operation.

The Design of an Optimal Demand Response Controller Under Real Time Electricity Pricing

The use of a demand response controller is necessary for electric devices to effectively respond to time varying price signals and to achieve the benefits of cost reduction. This paper describes a new formulation with the form of constrained optimization for designing an optimal demand response controller. It is demonstrated that constrained optimization is a better approach for the demand response controller, in terms of the ambiguity of device operation and the practicality of implementation of the optimal control law. This paper also proposes a design scheme to construct a demand response controller that is useful when a system controller is already adapted or optimized for the system. The design separates the demand response function from the original system control function while leaving the system control law unchanged. The proposed formulation is simulated and compared to the system with simple dynamics. The effects of the constraints, the system characteristics and the electricity price are examined further.

A Priority Index Method for Efficient Charging of PEVs in a Charging Station with Constrained Power Consumption

The sizable electrical load of plug-in electric vehicles may cause a severe low-voltage problem in a distribution network. The voltage drop in a distribution network can be mitigated by limiting the power consumption of a charging station. Then, the charging station operator needs a method for appropriately distributing the restricted power to all plug-in electric vehicles. The existing approaches have practical limitation in terms of the availability of future information and the execution time. Therefore, this study suggests a heuristic method based on priority indexes for fairly distributing the constrained power to all plug-in electric vehicles. In the proposed method, PEVs are ranked using the priority index, which is determined in real time, such that a near-optimal solution can be obtained within a short computation time. Simulations demonstrate that the proposed method is effective in implementation, although its performance is slightly worse than that of the optimal case.

Methods for Adding Demand Response Capability to a Thermostatically Controlled Load with an Existing On-off Controller

A thermostatically controlled load (TCL) can be one of the most appropriate resources for demand response (DR) in a smart grid environment. DR capability can be effectively implemented in a TCL with various intelligent control methods. However, because traditional on-off control is still a commonly used method in a TCL, it is useful to develop a method for adding DR capability to the TCL with an existing on-off controller. As a specific realization of supervisory control for implementing DR capability in the TCL, two methods are proposed - a method involving the changing of a set point and a method involving the paralleling of an identified system without delay. The proposed methods are analyzed through the simulations with an electric heater for different power consumption levels in the on-state. Considerable cost benefit can be achieved with the proposed methods when compared with the case without DR. In addition, the observations suggest that a medium power consumption level, instead of the maximum power, in the on-state should be used for consistently obtaining the cost benefit without severe temperature deviation from the specified temperature range for DR.

Operation Planning of Reserve in Microgrid Considering Market Participation and Energy Storage System

Innumerable microgrids would be operated independently by individual operators in a future smart grid. This kind of decentralized power system requires entirely different operation scheme in the actual power system and electricity market operation. Especially, frequency regulation is very important for successive energy trade in this multi-microgrid circumstance. This paper presents an optimal energy and reserve market participation strategy and operation strategy of energy storage system (ESS) by a microgrid operator (MGO). For definite evaluation of the proposed strategy, we postulate that the MGO should participate in the Power Exchange for Frequency Control (PXFC) market, which was devised by Maria Ilic and her coworkers and is suitable to the decentralized operation circumstances. In particular, optimal reserve capacity of the frequency control market and optimal market participation ratio of ESS between frequency control market and energy market are derived theoretically and evaluated by simulations utilizing Nordic Pool Elspot price data.

Contractual Framework for the Devolution of System Balancing Responsibility from the Transmission System Operator to Distribution System Operators

The goal of this research is to trigger the devolution of the system balancing responsibility entirely belonging to the transmission system operator (TSO) to several local distribution system operators by fairly allocating system balancing cost based on a cost-causality principle. Within the devolved system balancing scheme, distribution system operators (DSOs) have appropriate motivation for reducing the variability and uncertainty caused by units in their own area. As the number of renewable electricity sources (RES) being connected to the local distribution system increases, it would be advantageous for the TSO to share the increasing burden of the system balancing responsibility with multiple DSOs. To achieve this, we suggest that, first DSOs be designated as the representatives of their own jurisdictions with primary economic responsibility for balancing payments that are originally charged to each energy market participant. Second, this research proves that a cost-causality based cost allocation scheme(CC-CAS) is superior to an energy-amount based cost allocation scheme (currently widely used) in terms of economic efficiency. Additionally, to avoid the side effect that a DSO with a large amount of RES may face a high and risky balancing payment under the CC-CAS, this research also proposes an optimal balancing payment insurance (BPI) contract which helps the DSO hedge the risks associated with uncertain balancing payments.

Framework for determining the compensation price for output curtailment of distributed generation within active distribution network management

Within active distribution network management, distributed generations, which are contracted by the non-firm connection method, can be directly controlled by the distribution network operator to adjust their power factor and the active power output level. This is called an output curtailment of distributed generation. Although the purpose of the output curtailment is to stably operate the distribution network, it inevitably limits the revenue of distributed generations. Therefore, the need for suitable compensation to the output curtailment is often discussed. As an extension to the discussion, this study proposes the method to determine the suitable bounds of the compensation price for output curtailment. In the proposed method, the suitable bounds of compensation price are obtained from the profit analysis of stakeholders in accordance with the level of the compensation price through optimal power flow technique.

A simple algorithm for determining of movement duration in task space without violating joint angle constraints

In usual robot applications, velocity and acceleration constraints are represented in joint angle space, while on the contrary, a goal is specified in task space such as the Cartesian coordinates. This fact means that a task trajectory planner itself cannot resolve the constraint problem without working together with an inverse kinematics solving method. In this paper, we present a simple method to generate a joint angle trajectory without violating the joint velocity and acceleration constraints. The key idea is to determine movement duration to solve the constraint problem. The proposed method has a strong merit in that it can use the existing task trajectory planning method and inverse kinematics solving method without re-formulating them for the constraints. The validity of the proposed method is shown by the simulation with a two-link serial manipulator executing a circle-drawing task.