Chi Su

Optimal Operation of Plug-In Electric Vehicles in Power Systems With High Wind Power Penetrations

The Danish power system has a large penetration of wind power. The wind fluctuation causes a high variation in the power generation, which must be balanced by other sources. The battery storage-based Plug-In Electric Vehicles (PEVs) may be a possible solution to balance the wind power variations in the power systems with high wind power penetrations. In this paper, the integration of plug-in electric vehicles in the power systems with high wind power penetrations is proposed and discussed. Optimal operation strategies of PEV in the spot market are proposed in order to decrease the energy cost for PEV owners. Furthermore, the application of battery storage based aggregated PEV is analyzed as a regulation services provider in the power system with high wind power penetrations. The western Danish power system where the total share of annual wind power production is more than 27% of the electrical energy demand is chosen as the studied case. The results show that an optimal operation of PEV in both spot market and regulation market can not only decrease the energy costs for PEV owners, but also significantly decrease the power deviations between West Denmark and Union for the Coordination of Electricity Transmission (UCTE) control areas.

Reactive power capability of the wind turbine with Doubly Fed Induction Generator

With the increasing integration into power grids, wind power plants play an important role in the power system. Many requirements for the wind power plants have been proposed in the grid codes. According to these grid codes, wind power plants should have the ability to perform voltage control and reactive power compensation at the point of common coupling (PCC). Besides the shunt flexible alternating current transmission system (FACTS) devices such as the static var compensator (SVC) and the static synchronous compensator (STATCOM), the wind turbine itself can also provide a certain amount of reactive power compensation, depending on the wind speed and the active power control strategy. This paper analyzes the reactive power capability of Doubly Fed Induction Generator (DFIG) based wind turbine, considering the rated stator current limit, the rated rotor current limit, the rated rotor voltage limit, and the reactive power capability of the grid side convertor (GSC). The boundaries of reactive power capability of DFIG based wind turbine are derived. The result was obtained using the software MATLAB.

Optimal Placement of Phasor Measurement Units with New Considerations

Conventional phasor measurement unit (PMU) placement methods normally use the number of PMU installations as the objective function which is to be minimized. However, the cost of one installation of PMU is not always the same in different locations. It depends on a number of factors. One of these factors is taken into account in the proposed PMU placement method in this paper, which is the number of adjacent branches to the PMU located buses. The concept of full topological observability is adopted and a version of binary particle swarm optimization (PSO) algorithm is utilized. Results from the test on a 17-bus system are demonstrated.

Active power dispatch method for a wind farm central controller considering wake effect

With the increasing integration of the wind power into the power system, wind farm are required to be controlled as a single unit and have all the same control tasks as conventional power plants. The wind farm central controller receives control orders from Transmission System Operator (TSO), then dispatch the wind power reference to each wind turbine. One of the most commonly used dispatch methods is to dispatch the wind power reference to each wind turbine proportional to each wind turbines available wind power without the consideration of the wake effect. The wake which depends on the thrust efficient of upstream wind turbines in the wind farm influences the downstream wind speed which determines the available wind power of the downstream wind turbine. Optimize the wind power production of each wind turbine in the wind farm by the optimization of the pitch angle and tip-speed-ratio of each turbine can increase the total available wind power of the wind farm. This paper proposed a new dispatch method which dispatches the wind power reference to each wind turbine proportional to each wind turbines optimal wind power to increase the available wind power of the whole wind farm. Particle Swarm Optimization (PSO) is used to obtain the optimal wind power for each wind turbine. A case study is carried out. The available wind power of the wind farm was compared between the traditional dispatch method and the proposed dispatch method with the consideration of the wake effect.

Influence of wind plant ancillary frequency control on system small signal stability

Since large-scale wind farms are increasingly connected to modern power grids, the transmission system operators put more requirements as part of the grid codes on the integration of wind farms. System frequency control which is normally provided by conventional synchronous generators becomes a common requirement to wind farms. This ancillary frequency control provided by wind farms could have some influence on the system small signal stability. This paper implements an ancillary frequency control strategy on a direct-drive-full-convertor-based wind farm and studies its influence on the damping ratio values of the dominant oscillation modes within the connected power system. All the calculations and simulations are conducted in DIgSILENT PowerFactory 14.0.

Impact of wind shear and tower shadow effects on power system with large scale wind power penetration

Grid connected wind turbines are fluctuating power sources due to wind speed variations, the wind shear and the tower shadow effects. The fluctuating power may be able to excite the power system oscillation at a frequency close to the natural oscillation frequency of a power system. This paper presents a simulation model of a variable speed wind farm with permanent magnet synchronous generators (PMSGs) and full-scale back-to-back converters in the simulation tool of DIgSILENT/PowerFactory. In this paper, the impacts of wind shear and tower shadow effects on the small signal stability of power systems with large scale wind power penetrations are investigated during continuous operation based on the wind turbine model and the power system model.

Power System Structural Vulnerability Assessment Based on an Improved Maximum Flow Approach

With the increasing complexity of the power grid and the concerns on major blackouts, there is an urgent need for an efficient and effective tool to assess the power system structural vulnerability. To tackle this challenge, this paper proposes a maximum flow-based complex network approach to identify the critical lines in a system. The proposed method consists of two major steps. First, the power network is modeled as a graph with edges (transmission lines, transformers, etc.) and nodes (buses, substations, etc.). The critical scenarios are identified by using the principal component analysis and convex hull. Then the second step is to use an improved maximum flow-based complex network approach for topology analysis. Weighted vertices in the network are considered, enabling taking the selected operating conditions into consideration when identifying the vulnerable lines. The proposed method is validated using the western Danish power system. The vulnerable lines in the network are ranked. Simulation results demonstrate the effectiveness of the method by intentional attacks and comparison with the planning strategy from the system operator.

A Multiagent System-Based Protection and Control Scheme for Distribution System With Distributed-Generation Integration

In this paper, a multiagent system-based protection and control scheme is proposed to deal with diverse operation conditions in distribution system due to distributed-generation (DG) integration. Based on cooperation between DG controller and relays, an adaptive protection and control algorithm is designed on converter-based wind turbine DG to limit the influence of infeed fault current. With the consideration of DG control modes, an adaptive relay setting strategy is developed to help protective relays adapt suitable settings to different operation conditions caused by the variations of system topology and DG status. The proposed scheme is tested and validated on a test distribution system in a hardware-in-the-loop real-time testing platform.

Comparison study of power system small signal stability improvement using SSSC and STATCOM

A static synchronous series compensator (SSSC) has the ability to emulate a reactance in series with the connected transmission line. A static synchronous compensator (STATCOM) is able to provide the reactive power to an electricity network. When fed with some supplementary signals from the connected power system, both SSSC and STATCOM are able to participate in the power system inter-area oscillation damping by changing the compensated reactance or the provided reactive power. This paper analyses the influence of SSSC and STATCOM on power system small signal stability. The damping controller schemes for SSSC and STATCOM are presented and discussed. The IEEE 39-bus New England system model as the test system is built in DIgSIELNT PowerFactory, in which the damping control strategies for both SSSC and STATCOM are validated by time domain simulations and modal analysis. Furthermore, comparison studies show that the SSSC is a better solution in term of equipment capabilities and costs.

Reactive Power Dispatch Method in Wind Farms to Improve the Lifetime of Power Converter Considering Wake Effect

In wind farms (WF), the most popular and commonly implemented active power control method is the maximum power point tracking (MPPT). Due to the wake effect, the upstream wind turbine (WT) in WFs has more active power generation than the downstream WT at the wind directions and wind speeds that the WF has wake loss. In the case that WTs support the voltage control by reactive power, the upstream WTs power converter may have shorter lifetime even below the industrial standard. In this paper, based on the analysis of the wake effect, the reactive power capability of the doubly fed induction generator (DFIG) WT, and the lifetime of the DFIG WTs power converter, a reactive power dispatch method is proposed in the WF with DFIG WTs to improve the lifetime of the upstream WTs power converter. The proposed reactive power dispatch method is analyzed and demonstrated by the simulation on a WF with 80 DFIG WTs. It can be concluded that, compared with the traditional reactive power dispatch method, the proposed method can increase the lifetime of the upstream WTs power converter.