Controller Hardware-in-the-loop Research Articles

Double integral action based sliding mode controller design for the back-to-back converters in grid-connected hybrid wind-PV system

In this paper, a double integral sliding mode based nonlinear controller (DISMC) is developed for the grid-connected hybrid wind-PV system. The proposed control approach provides better steady state response and robustness as compared to the existing control methods. The topology considered in this study for the wind and PV based hybrid distributed generator system is efficient. Wind and PV generator are connected to the utility grid via boost converter at the machine side followed by inverter at the grid side. Thus, the realized scheme has reduced number of DC-DC conversion stages as compared to the previous schemes. So far, no study investigates the design of nonlinear controller for this scheme. Proposed DISMC offers the maximum power point tracking (MPPT) for both wind and PV generator, DC bus voltage regulation, and smooth transfer of active power to the utility grid. Firstly, the detailed small-signal mathematical models for the proposed hybrid system and DC bus dynamics are developed. After that, three control laws based on DISMC are designed to ensure the stable operation under varying weather conditions and system uncertainties. Then, the stability of the hybrid system is proved using Lyapunov theory. Finally, the performance of the proposed framework has been verified using model-based MATLAB time-domain simulations, and controller hardware-in-the-loop (C-HIL) experiments. The superiority of the proposed control technique was approved by comparing the result with other control methods.

Cyber-Resilient Cooperative Control of Bidirectional Interlinking Converters in Networked AC/DC Microgrids

Bidirectional interlinking converters (BICs) are building blocks of the networked ac/dc microgrids (ac/dc NMGs). Such BICs are controlled using the communication assisted cooperative control thus forming tightly coupled cyber-physical systems (CPSs). One of lethal problems in such CPS is its vulnerability to cyber-attacks. In this article, a cyber-resilient cooperative control for BICs in ac/dc NMGs is proposed to enhance the system resilience under false signal injection attacks. The proposed control can maintain the frequency/voltage regulation and real/reactive power sharing among multiple BICs under both single and multiple node attacks. The suitability of the proposed method is supported by the stability analysis using Lyapunov methods. Efficacy of the proposed method is demonstrated by the controller hardware-in-the-loop (CHIL) experiment. An ac/dc NMG with four BICs is developed in the OPAL-RT-based real-time simulator. The cyber-resilient controllers are implemented on four commercial programmable logic controllers by B&R automation. The CHIL-based experimental results support the effectiveness of the proposed controller under various attack scenarios.

Controller hardware in the loop testing of microgrid secondary frequency control schemes

This paper describes a controller hardware-in-the loop (C-HIL) approach for testing centralized and distributed secondary frequency control schemes of AC microgrids operating in islanded mode. We describe the formulation of the secondary frequency control problem and the theory behind the centralized and distributed implementations of the control schemes. Then, we describe the testbed utilized for C-HIL testing activities. Finally, we provide the testing results that compare the performance (in terms of the system response time), and resilience (in terms of withstanding the failure of a control device), of both schemes.

Frequency- adaptive control of a three-phase single-stage grid-connected photovoltaic system under grid voltage sags

The low-voltage ride-through service is carried out in this paper according to the voltage profile described by the IEC 61400-21 European normative when short-duration voltage sags happen, and some instantaneous reactive power is delivered to the grid in accordance with the Spanish grid code; the mandatory limitation of the amplitude of the three-phase inverter currents to its nominal value is carried out with a novel control strategy, in which a certain amount of instantaneous constant active power can also be delivered to the grid when small or moderate voltage sags happen. A Multiple second order generalized integrator frequency-locked loop synchronization algorithm is employed in order to estimate the system frequency without harmonic distortions, as well as to output the positive- and the negative- sequence of the αβ quantities of the three-phase grid voltages when balanced and unbalanced voltage sags happen in a frequency- adaptive scheme. The current control is carried out in the stationary reference frame, which guarantees the cancellation of the harmonic distortions in the utility grid currents using a Harmonic compensation structure, and the implementation of a constant active power control in order to protect the DC link capacitor from thermal stresses avoiding the appearance of large harmonic distortions at twice the fundamental frequency in the DC link voltage. A case study of a three-phase single-stage grid-connected PV system with a maximum apparent power about 500 kVA is tested with several simulations using MATLAB/SIMULINK firstly, and secondly, with some experiments using the Controller hardware-in-the-loop (CHIL) simulation technique for several types of voltage sags in order to do the final validation of the control algorithms.

A Hardware-in-the-Loop Platform for DC Protection

Real-time (RT) simulation of power and energy conversion systems allows engineers to interface both simulation- and hardware-based controls using controller hardware-in-the-loop (CHiL) simulation of networks of power electronic converters (PECs) to de-risk highly developmental systems, such as next generation electrified transportation systems and dc microgrids. CHiL exploration and performance verification moves a design from technology readiness level (TRL) 3 to TRL 4 without incurring significant cost investments in developmental hardware platforms, which otherwise discourages such endeavors. An RT CHiL simulation platform suitable for explorations of protective equipment, protection schemes, and networked PEC dc and mixed dc-ac power distribution architectures must be capable of simulating common-mode behavior, various grounding schemes, and fault transients at sufficiently high resolution. This article demonstrates this capability using a latency-based linear multistep compound (LB-LMC) simulation method implemented in a commercially sustainable, adaptable, and expandable FPGA-based test and instrumentation platform. The proposed CHiL platform achieves RT power system simulations, including detailed switching commutations of networked PECs, with 50-ns resolution, and faithfully produces resonant and transient behaviors associated with line-to-ground (LG) and line-to-line (LL) faults and fault recovery in ungrounded PEC-based dc systems. This resolution in RT cannot be achieved with today's commercial off-the-shelf CHiL platforms. This article demonstrates the need for high-resolution RT simulation of LG and LL faults within dc systems, and demonstrates a CHiL approach that enables dc protection design explorations and protective control hardware testing while taking into account the realistic aspects that affect fault characteristics in PEC-based dc systems, such as cable current rating and length, cable and PEC parasitic LG capacitance, and PEC internal response to fault scenarios.

Remote Laboratory Testing Demonstration

The complexity of a smart grid with a high share of renewable energy resources introduces several issues in testing power equipment and controls. In this context, real-time simulation and Hardware in the Loop (HIL) techniques can tackle these problems that are typical for power system testing. However, implementing a convoluted HIL setup in a single infrastructure can be physically impossible or can increase the time required to test a smart grid application in detail. This paper introduces the Joint Test Facility for Smart Energy Networks with Distributed Energy Resources (JaNDER) that allows users to exchange data in real-time between two or more infrastructures. This tool enables the integration of infrastructures, exploiting the synergies between them, and creating a virtual infrastructure that can perform more experiments using a combination of the resources installed in each infrastructure. In particular, JaNDER can extend a HIL setup. In order to validate this new testing concept, a coordinated voltage controller has been tested in a Controller HIL setup where JaNDER was used to interact with an actual On Load Tap Changer (OLTC) controller located in a remote infrastructure. The results show that the latency introduced by JaNDER is not critical; hence, under certain circumstances, it can be used to expand the real-time testing without affecting the stability of the experiment.

Hardware-in-the-Loop and Field Validation of a Rotor-Side Subsynchronous Damping Controller for a Series Compensated DFIG System

In the past decade, several subsynchronous control interaction (SSCI) incidents have been reported in various large-scale grid-interfaced doubly-fed induction generator (DFIG) based wind farms. The subsynchronous oscillation caused by the SSCI endangers the safe and reliable operation of wind power systems. The DFIG's converter controls play a crucial role in such interactions; therefore, several SSCI mitigation schemes have been reported, which modify the DFIG's converter controls to stabilize the subsynchronous oscillation caused by the SSCI. However, the effectiveness of such converter control modifications has not been verified through laboratory or field experiments. This paper considers a practical rotor-side subsynchronous damping controller (RSDC) and fills the gap by first validating the RSDC's performance through controller hardware-in-the-loop (CHIL) simulations, and then implementing it in a real-world DFIG connected to a series compensated line. The RSDC fundamentally reshapes the effective impedance of the DFIG to stabilize the subsynchronous oscillation. The CHIL simulations, as well as the field tests, successfully validated the RSDC's ability to suppress the SSCI. The results enhanced the practical confidence of the SSCI mitigation strategy based on RSC's converter control modification.

On Stability of PV Clusters With Distributed Power Reserve Capability

This article presents a stability analysis of photovoltaic (PV) clusters forming a dc microgrid with a distributed power reserve capability. The PV clusters feature flexible PV power generation under fluctuating ambient conditions via the distributed power reserve control. The PV set-points are adjusted based on grid operator command that is accomplished in a decentralized manner. Stability analysis of the PV clusters has been carried out to determine the safe operation regions of the PV units with respect to operation set-point adjustments. The proposed stability analysis approach considers all the characteristics of the PV subsystems. The stability analysis demonstrates that the PV cluster architecture is stable as far as the dc bus stray resistance has a finite value. Also, the grid-interfacing converter must operate in input current control mode (CCM) instead of input voltage control mode (VCM) for better stability margin. Several case studies are emulated on an IEEE 5-Bus system using real-time controller hardware in the loop (C-HIL) to verify the stability and the theoretical expectations of the proposed system.

Leveraging National Laboratory Assets to Address Stability Challenges due to Declining Grid Inertia Using Geographically Distributed Electrical–Thermal Co-Emulation

Abstract Due to increased penetration of low-inertia resources into the electric grid, challenges are increasing for maintaining wide-area system stability. Grid stability assessment requires a faithful representation of the multiple-physics interaction at the system level, and timescales of interaction varying in orders of magnitude, from microseconds to seconds to several minutes. Along with the simulation-based techniques, hardware-in-the-loop (HIL), controller HIL, and power HIL techniques have been developed to better understand the emergent behavior of the system with emerging technologies. US National Laboratories have played a vital role in research and development to understand the behavior of individual technologies and devices integrated to the electric grid. Each national laboratory forwards a technological and strategic initiative tied core and enabling capabilities. Due to strategic, efficiency, and economic reasons, not all the labs have assets to conduct research on all technologies concomitantly, so it becomes crucial to integrate the labs across geographies to understand the interplay of different technologies together at the system level. This approach avoids duplication of the assets at different lab facilities and helps understand the integrated system behavior of various technologies representative of actual grid conditions by connecting multiple national labs. This paper talks about techniques of connecting three national laboratories to enable co-emulation of electrical–mechanical–thermal characteristics of devices and systems. Such an approach can be used to understand the dynamic and transient interaction of multi-physics in a system level, at-scale emulation using real-time simulation tools and techniques.

Model-Based Virtual Components in Event-Based Controls: Linking the FMI and IEC 61499

Various development and validation methods for cyber-physical systems such as Controller-Hardware-in-the-Loop (C-HIL) testing strongly benefit from a seamless integration of (hardware) prototypes and simulation models. It has been often demonstrated that linking discrete event-based control systems and hybrid plant models can advance the quality of control implementations. Nevertheless, high manual coupling efforts and sometimes spurious simulation artifacts such as glitches and deviations are observed frequently. This work specifically addresses these two issues by presenting a generic, standard-based infrastructure referred to as virtual component, which enables the efficient coupling of simulation models and automation systems. A novel soft real-time coupling algorithm featuring event-accurate synchronization by extrapolating future model states is outlined. Based on considered standards for model exchange (FMI) and controls (IEC 61499), important properties such as real-time capabilities are derived and experimentally validated. Evaluation demonstrates that virtual components support engineers in efficiently creating C-HIL setups and that the novel algorithm can feature accurate synchronization when conventional approaches fail.

Converter-Based Power System Protection Against DC in Transmission and Distribution Networks

The dc in a power system may be caused by geomagnetic disturbances that are the result of solar storms and high-altitude nuclear detonations. Increased inverter-based generation is also contributing to small dc injection into the power systems. The resultant dc could have serious consequences for the power systems as it may drive power transformers into saturation, cause transformer internal heating, cause large draw of reactive power, and misoperation of protective relays. This letter proposes a novel power electronics-based dc mitigation approach that involves a transformerless series active filter integrated between the neutral point and ground of power transformers serving multiple purposes. The first objective is to surpass the effect of dc injection, the second goal is voltage regulation, and the third is to provide harmonic isolation or impedance balancing. The proposed device is currently being developed on a 7.2-kV/240-V single-phase transformer; however, the solution is also relevant for 24-500-kV networks. The system circuitry, operation, and control are implemented and verified for this letter in a controller hardware-in-the-loop (C-HIL) test setup using a Typhoon HIL-402 simulator. Results indicate that our approach is a promising alternative to traditional neutral capacitor-blocking strategies.

Sampling-Based Model Predictive Control of PV-Integrated Energy Storage System Considering Power Generation Forecast and Real-Time Price

This paper proposes a novel control solution designed to solve the local and grid-connected distributed energy resources (DERs) management problem by developing a generalizable framework capable of controlling DERs based on forecasted values and real-time energy prices. The proposed model uses sampling-based model predictive control (SBMPC), together with the real-time price of energy and forecasts of PV and load power, to allocate the dispatch of the available distributed energy resources (DERs) while minimizing the overall cost. The strategy developed aims to find the ideal combination of solar, grid, and energy storage (ES) power with the objective of minimizing the total cost of energy of the entire system. Both offline and controller hardware-in-the-loop (CHIL) results are presented for a 7-day test case scenario and compared with two manual base test cases and four baseline optimization algorithms (Genetic Algorithm (GA), Particle Swarm Optimization (PSO), Quadratic Programming interior-point method (QP-IP), and Sequential Quadratic Programming (SQP)) designed to solve the optimization problem considering the current status of the system and also its future states. The proposed model uses a 24-hour prediction horizon with a 15-minute control horizon. The results demonstrate substantial cost and execution time savings when compared to the other baseline control algorithms.

Controller Hardware-in-the-Loop Validation of a Graph Search Based Energy Management Strategy for Grid-Connected Distributed Energy Resources

This article presents a controller hardware-in-the-loop (CHIL) validation of a novel energy storage management (ESM) solution designed to optimize the use of grid-connected distributed energy resources (DERs) based on the forecasting of generation, load, and real-time energy prices. The proposed control strategy aims to control the operations of the energy storage (ES) using the A* searching algorithm so that the total cost of energy used to serve the local electrical load is minimized. The proposed solution uses the energy storage states and available forecast data to generate a graph that is explored using the A* search algorithm with the objective of finding the optimum cost of energy. The proposed ESM is tested offline against genetic algorithm and sequential quadratic programming based solutions and shows cost improvement of 5% to 8.9%. A CHIL validation testbed was also implemented to evaluate the performance of the algorithm. A Florida based distribution grid was simulated using real field data in a DTRS, and the IEEE 1815 DNP3 communication protocol was used to establish the communication between the controller and the simulation. The graph search-based ESM was implemented in python in an external computer which served as the controller. Offline and real-time simulations are presented showing comparable results.

Device‐level modelling and FPGA‐based real‐time simulation of the power electronic system in fuel cell electric vehicle

Power electronic converters are essential components in the fuel cell electric vehicle (FCEV) powertrain, which precisely control the power output of the fuel cell stack, the charging and discharging process of the battery, and the operation of the traction motor. The hardware-in-the-loop (HIL) simulation plays an important role in the rapid validation of power converters in their early development stages. In this study, a device-level model of the power converters in FCEV powertrain is developed for the FPGA-based real-time simulation. By fulfilling the circuit topology partitioning and the switch model partitioning, the FCEV power electronic system can be simulated with sub-microsecond time-step while producing the detailed switching waveforms with 5 ns resolution. Therefore, the device electrical stress, and the switching power losses can be evaluated in real time. Furthermore, the electro-thermal converter model is developed accordingly, which makes it possible to evaluate the IGBT/Diode thermal behaviour in the HIL simulation. In this study, the FPGA hardware is designed with the NI LABVIEW FPGA module and implemented on the NI-7975R FLEXRIO FPGA board. The accuracy of the FPGA-based simulation results is evaluated by the results from offline simulation tools. The effectiveness of the proposed model is then validated by the controller HIL experiments.

A Model Predictive Power Control Method for PV and Energy Storage Systems With Voltage Support Capability

The cascaded control method with an outer voltage loop and an inner current loop has been traditionally employed for the voltage and power control of photovoltaic (PV) inverters. This method, however, has very limited power regulation capability. With the fast increasing penetration of PV power generation systems in the distribution network, the voltage rise/drop has become a serious problem impacting negatively on the power quality and grid stability. Therefore, flexible power regulation is highly desired for PV inverters to provide ancillary services. This paper proposes a novel model predictive power control (MPPC) scheme to control and coordinate the dc–dc converter and inverter for grid-connected PV systems with energy storage systems (ESS). By regulating the dc-bus voltage and controlling the active and reactive power flows, MPPC can support the power grid to maintain stable voltage and frequency and improve the power factor. Numerical simulation and controller hardware-in-the-loop (CHIL) testing have been conducted on a PV-ESS system to verify the capability and effectiveness of the proposed control strategy.

FACTS Providing Grid Services: Applications and Testing

The role of flexible alternating current transmission systems (FACTSs) in the provision of grid services is becoming increasingly important, due to the massive integration of intermittent renewable energy sources, energy storage systems, and the decommissioning of thermal plants. A comprehensive literature review of grid services offered by FACTS is performed, focusing on the different grid services that they can provide, such as power flow control, reactive power control, voltage control, power quality improvement, harmonic mitigation, improvement of transient stability, and damping of inter-area and intra-area oscillations. These grid services need to be realistically and economically validated in suitable testing environments. A review of relevant standards, guides, and the literature is performed, which covers the entire range from functional specification and factory testing up to the field testing of FACTS. Advanced industry practices, such as controller hardware in the loop (CHIL) testing of FACTS controllers by the manufacturer, and recent trends, such as CHIL testing of replica controllers by the owner, are underlined. Limitations of conventional testing and CHIL testing are explained and the use of power hardware in the loop (PHIL) simulation for FACTS testing is discussed. CHIL and scaled-down PHIL tests on a transmission static synchronous compensator (STATCOM) are performed and a comparison of the results is presented.

A Benchmark System for Hardware-in-the-Loop Testing of Distributed Energy Resources

In order to overcome challenges associated with the integration of distributed energy resources (DER) into state-of-the-art and future power grids, a common basis for testing using appropriate benchmark systems is required. Real-time hardware-in-the-loop (HIL) simulation has proven to be an advanced and efficient tool for the analysis and validation of electric power systems and DER components. However, a common methodology for HIL testing of DER along with the required set of reference systems has not yet been developed. This task-force paper proposes a benchmark system for HIL testing incorporating DER into the real-time simulation environment. A low-voltage benchmark system with detailed HIL setup is proposed for the testing of DER performance. The modeling of DER for real-time applications is discussed, and the detailed laboratory procedures and setups for both controller HIL (CHIL) and power HIL (PHIL) are provided. Results from CHIL simulation related to the centralized controls and experimental results of PHIL simulation related to local control on the benchmark system substantiate the suitability of the proposed real-time simulation approach.

Coordinated secondary control for autonomous hybrid three-port AC/DC/DS microgrid

This paper presents a coordinated secondary control (CSC) strategy for distributed power management for an autonomous hybrid three-port AC/DC/DS microgrid. The proposed CSC is on top of a generalized primary control (GPC), which consists of local power sharing (LPS) control within an individual AC or DC subgrid, global power sharing (GPS) control throughout the AC/DC subgrids, and storage power sharing (SPS) control in a distributed storage (DS) network. The CSC along with the GPC uses the local frequency/voltage deviations and offers decentralized power management with enhanced overall reliability. To eliminate the inherent frequency/voltage deviations in GPC and restore to their nominal values, a secondary control is normally applied to all distributed generators (DGs), which would degrade the performance of decentralized power management. To overcome this concern, a CSC strategy is proposed to concurrently restore frequency/voltage and re-establish a distributed power management by means of limited information exchange through the low-bandwidth communication links. The proposed control scheme has been verified by both simulations and controller hardware-in-the-loop (CHIL) experiments in an OPAL-RT digital simulator system.

Design and Evaluation of SunSpec-Compliant Smart Grid Controller with an Automated Hardware-in-the-Loop Testbed

With increasing penetrations of inverter-based, renewable energy resources on electrical grids around the world, new distributed energy resource (DER) interconnection and interoperability requirements have been introduced to address emerging power system operator needs. The inverter-based power conversion systems are capable of communicating with grid operators, providing voltage and frequency support, and supporting the grid during faults. However, DER vendors are under pressure to quickly and reliably update the interoperability and electrical capabilities of their equipment for different jurisdictions with the rapidly changing landscape of disparate codes and standards. The necessary power hardware required for testing power systems under the wide variety of operational conditions may be untenable for many organizations. Therefore, we introduce an approach for the concurrent development of controls and application software through a controller hardware-in-the-loop (CHIL) testbed integrated with an automated testing platform that allows for the cost-effective, flexible evaluation of advanced grid support functions without the need for large and expensive power hardware. We show this CHIL capability through the demonstration and automation of interconnection tests with a 34.5 kW Austrian Institute of Technology (AIT) smart grid converter (SGC) connected to a Typhoon HIL system. We have demonstrated the CHIL system with regards to connect/disconnect, active power curtailment, fixed power factor, reactive power control, volt-var, and frequency-watt advanced grid functionality tests. For all tests, the automated CHIL testing protocols for advanced functions were sufficient to demonstrate and evaluate the grid support behavior of the equipment under test.

Hardware in the loop simulation test platform of fuel cell backup system

Based on an analysis of voltage mechanistic model, a real-time simulation model of the proton exchange membrane (PEM) fuel cell backup system is developed, and verified by the measurable experiment data. The method of online parameters identification for the model is also improved. Based on the software LabVIEW/VeriStand real-time environment and the PXI Express hardware system, the PEM fuel cell system controller hardware in the loop (HIL) simulation plat-form is established. Controller simulation test results showed the accuracy of HIL simulation platform.