Muhamad Reza

Grid integration aspects of large solar PV installations: LVRT capability and reactive power/voltage support requirements

The current work focuses on two specific issues concerning grid-connected solar PV units, i.e. the fault ride-through capability, also called low voltage ride-through capability, and the voltage support function through reactive power injection during faults. With the first one the PV unit can actually provide some limited grid support, whereas with a defined reactive power characteristic it can give a complete dynamic grid support. These two requirements, already known for wind power generation but new for the PV, have been recently introduced in the German technical guidelines for connection to the MV grid. Scope of the paper is to implement these requirements in a large solar PV plant, modeled in DIgSILENT PowerFactory, in order to understand its operation, and to evaluate its behavior and impact on the grid, in terms of stability and voltage support during grid fault.

Dynamic Stability of Power Systems with Power Electronic Interfaced DG

In this paper, the transient stability of power systems with a high penetration level of power electronic interfaced (converter connected) distributed generation is explored by means of computer simulations. Small 2 and 3 bus test systems are used. The converter is modeled as a three-phase full-bridge IGBT voltage source converter (VSC). The control setting is such that during the actual disturbance the converter connected DG stays connected to the system but with a current limiter. The simulations are performed by using MATLAB SimPowerSystems

Impacts of distributed generation penetration levels on power systems transient stability

Concerns on environmental and economical issues drive the increasing developments that support small scale generators to be connected close to distribution networks, i.e. distributed generation (DG). When connected in small amounts, the impact of DG on the power system transient stability will be negligible, however, when the penetration of DG increases, its impact is no longer restricted to the distribution network but starts to influence the whole system, including the transmission system transient stability. In this paper, the transmission system transient stability is investigated when a fault is applied in all possible branches (regarding the N-1 security analysis). In this studie the penetration level of DG implementation is raised in two ways: (1) a load increase is covered by DG implementation (with a constant centralized generation) or increased CG output, and (2) a reduction of centralized generation is covered by DG (with a constant load).

Investigating impacts of distributed generation on transmission system stability

Driven by the increasing environmental concerns and the increasing amount of new generation technologies, it is expected that many new generation technologies, including renewable generation, will be connected to the electrical power system. A lot of these new technologies will be connected at the distribution level. When the penetration of this distributed/dispersed generation (DG) is low, the impacts of the DC on the transmission system transient stability may be neglected. However, when the penetration of DG strongly increases, its impact is no longer restricted to the distribution network but begins to influence the whole system. In this paper the impact of DG on the transmission system transient stability is investigated by considering different types of DG technologies and various penetration levels. It is observed that both the types of DG technologies and the penetration levels of DG in the power system have a strong influence on the transmission system transient stability.

Impacts of Stochastic Residential Plug-In Electric Vehicle Charging on Distribution Grid

In this paper, the impacts of residential Plug-In Electric Vehicles (PEVs) charging on a distribution grid are investigated. A stochastic charging model is developed and used to study the impacts on distribution transformer loading, hotspot temperature variation and Accelerated Aging Factor (AAF) of the transformer. Different penetration levels of PEVs are considered in a typical distribution system. Furthermore, distribution of State of Charge (SOC) is discussed which can be used to optimize battery capacity and required charging infrastructure. Distribution of parking time interval is also discussed which can be used to evaluate availability of PEVs for overnight charging. The merit of stochastic approach compared with deterministic approach is also illustrated. The main contribution of this paper is the stochastic approach to evaluate the impact of residential PEV charging on the distribution grid.

Transients in Wind Power Plants—Part II: Case Studies

This is the second part of a two-paper series. The first paper presented the transient modeling methodology for various components of wind power plants (WPPs). This paper presents a general methodology for transient analysis of WPPs and discusses case studies which investigate some of the most important high-frequency interactions between different components of the WPP. The focus has been on switching transients, and lighting transients have been excluded. Transient case studies conducted on a typical WPP are presented which discuss the impact of fast system surges on the performance of the circuit breaker and impact of fast surges caused by the circuit breaker on the adjacent power components. These case studies investigate the opening and closing of the collector grid vacuum circuit breaker for loaded and unloaded conditions. Simulation results provide a close match with the field measurements conducted on a laboratory prototype of a typical WPP. Differences caused by modeling assumptions or insufficient accuracy of measurement devices are highlighted. To understand the most onerous overvoltages that can be experienced in the test system, a couple of additional simulation case studies are reported. These case studies discuss the interruption of inrush current with an unloaded transformer and interruption of a small inductive current following the transformer energization.

Investigating the impact of wake effect on wind farm aggregation

Aggregation methodologies for creating equivalent wind farm models are needed for power system transient stability studies involving large wind farms. One strong argument in the literature suggests single machine equivalent representation of wind farm with the assumption that all wind turbines receive the same incoming wind speed and thus operate at the same loading condition. In this paper, we examine how the validity of such single machine equivalent is affected under different wind speeds across a feeder in a wind farm with many WTGs. In particular, we compare the total active power output from the WTGs which indicates significant difference between single machine equivalent and full wind farm model under certain wind speed ranges and distances between the WTGs. We then conclude the need to use multi-machine equivalent representation for large wind farm in order to achieve adequate accuracy under the full range of wind conditions.

The impact of synchronous distributed generation on voltage dip and overcurrent protection coordination

This paper investigates the impact of synchronous distributed generation (DG) in MV network on coordination between overcurrent protection in MV feeder and voltage dip sensed by customer at LV side. DG is expected to support keeping the remaining voltage of a feeder high during voltage dip. DG location affects the level of support that DG can provide. Depending on the location, DG can either increase or decrease short circuit current. Both increasing and decreasing the short circuit current needs readjustment of overcurrent protection, either to ensure the coordination with downstream overcurrent protection, or to maximize DG support during the dip. A voltage dip immunity of a sensitive equipment (SE), which is shown in a voltage-time characteristic, is used to investigate the behaviour equipment during the dip

Stochastic modelling and analysis of horizontally-operated power systems with a high wind energy penetration

A methodology for the modelling and analysis of horizontally-operated power systems, i.e. systems with a high penetration of stochastic renewable generation, is presented. The objective is to obtain insight in the steady-state of the transmission system when a high penetration level of stochastic distributed generation (in this study case wind power), is present in the underlying distribution systems. The results can be used for the adequacy assessment and risk management of the system. For the system stochastic modelling, the methodology proposes the decoupling of the individual (marginal) behavior of the input random variables from the dependence structure between them. The stochastic dependence is shown to be a major factor for the assessment of the aggregated effect of the distributed stochastic generation on the system. In particular, the stress in the system increases in cases of positive dependence between the inputs and the maximum stress, i.e. the worst-case scenario for the system, occurs when extreme positive dependencies are present between the inputs. Based on this modelling principle, the system operational planning and design can be performed by modelling the extreme dependencies in the system. This powerful computational method can be easily applied to large systems with a high number of stochastic generators.

Transients in Wind Power Plants - part II: Case studies

This is the second part of a two-paper series. The first paper presented the transient modeling methodology for various components of wind power plants (WPPs). This paper presents a general methodology for transient analysis of WPPs and discusses case studies which investigate some of the most important high-frequency interactions between different components of the WPP. The focus has been on switching transients, and lighting transients have been excluded. Transient case studies conducted on a typical WPP are presented which discuss the impact of fast system surges on the performance of the circuit breaker and impact of fast surges caused by the circuit breaker on the adjacent power components. These case studies investigate the opening and closing of the collector grid vacuum circuit breaker for loaded and unloaded conditions. Simulation results provide a close match with the field measurements conducted on a laboratory prototype of a typical WPP. Differences caused by modeling assumptions or insufficient accuracy of measurement devices are highlighted. To understand the most onerous overvoltages that can be experienced in the test system, a couple of additional simulation case studies are reported. These case studies discuss the interruption of inrush current with an unloaded transformer and interruption of a small inductive current following the transformer energization.