Facilitating the transition to an inverter dominated power system : experimental evaluation of a non-intrusive add-on predictive controller

The transition to an inverter-dominated power system is expected with the large-scale integration of distributed energy resources (DER). To improve the dynamic response of DERs already installed within such a system, a non-intrusive add-on controller referred to as SPAACE (set point automatic adjustment with correction enabled), has been proposed in the literature. Extensive simulation-based analysis and supporting mathematical foundations have helped establish its theoretical prevalence. This paper establishes the practical real-world relevance of SPAACE via a rigorous performance evaluation utilizing a high fidelity hardware-in-the-loop systems test bed. A comprehensive methodological approach to the evaluation with several practical measures has been undertaken and the performance of SPAACE subject to representative scenarios assessed. With the evaluation undertaken, the fundamental hypothesis of SPAACE for real-world applications has been proven, i.e., improvements in dynamic performance can be achieved without access to the internal controller. Furthermore, based on the quantitative analysis, observations, and recommendations are reported. These provide guidance for future potential users of the approach in their efforts to accelerate the transition to an inverter-dominated power system

Initialization and synchronization of power hardware-in-the-loop simulations : a Great Britain network case study

The hardware under test (HUT) in a power hardware in the loop (PHIL) implementation can have a significant effect on overall system stability. In some cases, the system under investigation will actually be unstable unless the HUT is already connected and operating. Accordingly, initialization of the real-time simulation can be difficult, and may lead to abnormal parameters of frequency and voltage. Therefore, a method for initializing the simulation appropriately without the HUT is proposed in this contribution. Once the initialization is accomplished a synchronization process is also proposed. The synchronization process depends on the selected method for initialization and therefore both methods need to be compatible. In this contribution, a recommended practice for the initialization of PHIL simulations for synchronous power systems is presented. Experimental validation of the proposed method of establishing a PHIL simulation for a Great Britain network case study demonstrates the effectiveness of the approach in achieving stable operation

Tuningless Load Frequency Control Through Active Engagement of Distributed Resources

The increasing share of volatile and inverter-based energy sources render electric power grids increasingly susceptible to disturbances. Established Load Frequency Controls (LFCs) schemes are rigid and require careful tuning, making them unsuitable for dynamically changing environments. In this paper, we present a fast and tuningless frequency control approach that tackles these shortcomings by means of modern grid monitoring and communications infrastructures in a two-fold concurrent process. First, direct observation of supply and demand enables fast power balancing decoupled from the total system dynamics. Second, primary resources are actively involved in frequency restoration by systematic adjustment of their frequency reference setpoints. In contrast to the commonly used Automatic Generation Control (AGC), the proposed Direct Load Frequency Control (DLFC) does not require an integrator for frequency control in the closed loop even under partial grid observability. The approach is Lyapunov-stable for a wide range of system parameters, including ramping limits of controlled resources. A performance study against AGC has been conducted on a three area power system in simulations as well as in a real laboratory grid with an installed generation capacity of 110kW

Synchronous reference frame interface for geographically distributed real-time simulations

The increasing complexity of power systems has warranted the development of geographically distributed real-time simulations (GD-RTS). However, the wide scale adoption of GD-RTS remains a challenge owing to the (i) limitations of state-ofthe- A rt interfaces in reproducing faster dynamics and transients, (ii) lack of an approach to ensure a successful implementation within geographically separated research infrastructures (RIs) and (iii) lack of established evidence of its appropriateness for smart grid applications. To address the limitations in reproduction of faster dynamics and transients, this study presents a synchronous reference frame interface for GD-RTS. By means of a comprehensive performance characterisation, the superior performance of the proposed interface in terms of accuracy (reduced error on average by 60% and faster settling times) and computational complexity has been established. This study further derives the transfer function models for GD-RTS with interface characteristics for analytical stability analysis that ensure stable implementations avoiding the risks associated with multiple RI implementations. Finally, to establish confidence in the proposed interface and to investigate GD-RTS applicability for real-world applications, a GD-RTS implementation between two RIs at the University of Strathclyde is realised to demonstrate inertial support within transmission network model of the Great Britain power system

Aggregated energy storage for power system frequency control : a finite-time consensus approach

In future power systems, widespread small-scale energy storage systems (ESSs) can be aggregated to provide ancillary services. In this context, this paper aims to integrate energy storage aggregators (ESAs) into the load frequency control (LFC) framework for power system frequency control. Firstly, a system disturbance observer is designed to supplement the secondary frequency control, where the ESA can respond to the estimated disturbance and accelerate the system frequency recovery. Then, within the ESA, a finite-time leader-follower consensus algorithm is proposed to control the small-scale ESSs via sparse communication network. This algorithm ensures that the ESAs can track the frequency control signals and the state-of-charge balancing among each ESS in finite-time. The external characteristics of the ESA will resemble to that of one large-scale ESS. Numerical examples demonstrate the convergence of the ESA under different communication graphs. The effectiveness of the entire framework for power system frequency control is validated under a variety of scenarios

IEC-61850-based communication for integrated EV management in power systems with renewable penetration

As the number of EVs increases, their impact on electrical systems will be substantial. Novel management schemes are needed to manage the electrical load they require when charging. Literature is rich with different techniques to manage and control this effect on the grid by controlling and optimizing power flow. Although these solutions heavily rely on communication lines, they mostly treat communication as a black box. It is important to develop communication solutions that can integrate EVs, charging stations (CSs), and the rest of the grid in an interoperable way. A standard approach would be indispensable as there are different EV models manufactured by different companies. The IEC 61850 standard is a strong tool used for developing communication models for different smart grid components. However, it does not have the necessary models for implementing smart EV management schemes that coordinate between EVs and CSs. In this paper, these missing links are addressed through the development of corresponding models and message mapping. A hardware-in-the-loop test is performed to validate the communication models and cross-platform operation. Then, a co-simulation environment is used to perform a combined study of communication and the power system components. The developed communication model helps integrate the EVs to a centralized, coordinated voltage control scheme. These models can be used to run extensive impact studies where different domains of smart grids need to be considered simultaneously. The main contribution of this paper is the development of smartgrid communication solutions for enabling successful information exchanges

Assessment and development of stability enhancing methods for dynamically changing power hardware-in-the-loop simulations

In this paper, to extend the range of Power hardware-in-the-loop (PHIL) simulations into dynamically changing systems, i.e., setups where during the test scenario the ratio of impedance of the simulation and hardware under test changes, an adaptive Ideal Transformer Method (ITM) interface algorithm is proposed. The method incorporates voltage and current sources at both sides of the interface (simulation and hardware), a switch and an online stability assessment monitoring for the operation of the switch. Two different study cases have been developed for the assessment of the performance of the proposed adaptive ITM interface algorithm in a simulation environment. First, a simple test case with a variable resistive hardware under test has been carried out, followed by a case with a series resistive and inductive load. From the results obtained from the assessment of the proposed interface algorithm, a guideline for performing stability assessments of PHIL simulations in dynamically changing scenarios in a more accurate manner is also provided

On Modeling Depths of Power Electronic Circuits for Real-Time Simulation – A Comparative Analysis for Power Systems

Investigations of the dynamic behaviour of power electronic components integrated into electric networks require suitable and established simulation methodologies. Real-time simulation represents a frequently applied methodology for analyzing the steady-state and transient behavior of electric power systems. This work introduces a guideline on how to model power electronics converters in digital real time simulators, taking into account the trade-off between model accuracy and the required computation time. Based on this concept, possible execution approaches with respect to the usage of central processing unit and field-programmable gate array components are highlighted. Simulation test scenario, such as primary frequency regulation and low voltage ride through, have been performed and accuracy indices are discussed for each implemented real-time model and each test scenario, respectively. Finally, a run-time analysis of presented real-time setups is given and real-time simulation results are compared. This manuscript demonstrates important differences in real-time simulation modelling, providing useful guidelines for the decision making of power engineers

On Modeling Depths of Power Electronic Circuits for Real-Time Simulation – A Comparative Analysis for Power Systems

Investigations of the dynamic behaviour of power electronic components integrated into electric networks require suitable and established simulation methodologies. Real-time simulation represents a frequently applied methodology for analyzing the steady-state and transient behavior of electric power systems. This work introduces a guideline on how to model power electronics converters in digital real time simulators, taking into account the trade-off between model accuracy and the required computation time. Based on this concept, possible execution approaches with respect to the usage of central processing unit and field-programmable gate array components are highlighted. Simulation test scenario, such as primary frequency regulation and low voltage ride through, have been performed and accuracy indices are discussed for each implemented real-time model and each test scenario, respectively. Finally, a run-time analysis of presented real-time setups is given and real-time simulation results are compared. This manuscript demonstrates important differences in real-time simulation modelling, providing useful guidelines for the decision making of power engineers

Inverter-based voltage control of distribution networks : a three-level coordinated method and power hardware-in-the-loop validation

The reactive power of the photovoltaic (PV) inverters has great potential for voltage regulation of distribution networks. In this paper, a new three-level coordinated control method for PV inverters is proposed to address network voltage fluctuation and violation issues. In Level I, a ramp-rate control is designed to smooth the network voltage fluctuations, while in Level II, a droop control is designed to alleviate the network voltage deviations. If the local compensation provided by Level I and II is not enough to regulate the network voltages within the required limits, the Level III control based on dynamic average consensus can respond and share the reactive power requirement among other inverters in a distributed way. The proposed control method can smooth the voltage profiles, restrain the voltage rise/drop problem, and coordinate all PV inverters in real-time when there is no feasible local solution. The stability analysis of the proposed three-level coordinated control for network voltage regulation is provided. The power hardware-in-the-loop (PHIL) experiment has been conducted for validating the proposed control method under various scenarios