Real-time Digital Power System Simulator Research Articles

Robust, Accurate, and Fast Decentralized Power Sharing Mechanism for Isolated DC Microgrid Using Droop-Based Sliding-Mode Control

In this paper, a droop-based sliding mode controller (DBSMC) is designed for power sharing in an isolated DC microgrid (DC MG), with improved nonlinear droop model, in the presence of bounded structured uncertainties and external disturbances. The proposed DBSMC strategy does not require any communication link. The design process of the proposed controller is such that the trade-off between the two factors proportional power sharing and precise voltage regulation reaches the minimum possible. The creative design of the controller greatly reduced the control action stress, in such a way that, the occurrence of various uncertainties in the nonlinear droop model is compensated by applying small intelligent changes in the control parameters, using a fuzzy approximator. To evaluate the efficiency of the designed DBSMC controller, simulations are performed on an isolated DC MG with DC-DC buck configuration in MATLAB software. Finally, the real-time digital simulation results utilizing real-time digital power system simulator (RTDS) corroborate the performance of the proposed DBSMC controller. The simulation results obtained from MATLAB and the RTDS verify the robust, accurate and fast function of the proposed droop-based controller in power sharing of the isolated DC MG in the presence of variable operating conditions, parametric uncertainties and external disturbances.

Energy-Efficient Speed Control of Electric Vehicles: Linear Matrix Inequality Approach

In this paper, a stable fuzzy controller in the form of linear matrix inequalities (LMIs) is designed for an electric vehicle (EV). The proposed controller evaluates the stabilization of the EV speed with robust disturbance rejection approach throughout both transient and steady states and in the presence of external disturbances and parametric uncertainties. In order to achieve an efficient control, EV's battery voltage, as control input, and EV speed, as system output, are constrained. The proposed control strategy is based on Takagi–Sugeno (T-S) fuzzy model and the parallel distributed compensation (PDC) fuzzy controller. Proposed controller can be practically implemented due to low computational load of control input that is owing to the offline process of obtaining the feedback gains, very small amplitude of control input and low power consumption. To evaluate the performance of the designed controller, simulations in five steps are conducted on an EV equipped with a brushed direct current (BDC) motor as a case study in MATLAB simulation environment. Ultimately, the real-time digital simulation results using real-time digital power system simulator (RTDS) confirm the efficiency of the proposed input-output constrained robust disturbance rejection stable fuzzy controller (IOCRDRSFC) in stabilizing the EV speed. The simulation results obtained from MATLAB and the RTDS confirm the energy-efficient and robust performance of the proposed controller in quick stabilization of the EV speed in the presence of all structured and unstructured uncertainties.

Modified Re-Iterated Kalman Filter for Handling Delayed and Lost Measurements in Power System State Estimation

State estimator (SE) is a critical tool in the power system control center (CC) and is used by the system operators for real-time control and monitoring. Traditional SE techniques (static and dynamic) work under the assumption that there is no delay in communicating the sensor measurements to the CC. But in actual scenario, measurements are often randomly delayed and are not immediately available for processing. When the observations arrive with a delay, the current estimate of the system state may not be evaluated correctly, since the missing measurement may be carrying relevant information for estimating the states. With the increased deployment of phasor measurement units (PMUs) as sensors in the grid, time-stamped synchronized measurements are readily available. Time-stamped measurements enable the delay to be exactly known at the estimator. In this paper, a modified re-iterated Kalman filter that can handle both lost and delayed measurements without having any knowledge of the delay statistics, is proposed. The proposed algorithm is tested and validated in real-time using Real Time Digital Power System Simulator (RTDS).

Distributed Control With Virtual Capacitance for the Voltage Restorations, State of Charge Balancing, and Load Allocations of Heterogeneous Energy Storages in a DC Datacenter Microgrid

This paper proposes a distributed coordination control strategy for load sharing and energy balancing between heterogeneous energy storages. These control objectives are satisfied through a two-level control structure. At the primary level, the decentralized virtual impedance control, without the requirement of communication links, allocates the low frequency component of the loads to batteries, while the high frequency component is allocated to ultracapacitors. Distributed control strategy, introduced at the secondary level over a sparse communication network, achieves battery state of charge balancing and regulation of the local bus voltages. Two sets of data are exchanged via the communication links, the local bus voltages, and state of charges of batteries. The distributed controller for the restoration of local bus voltages implements an average consensus protocol, while the controller for energy balancing uses a cooperative protocol. In addition, the ultracapacitor voltages are locally restored at a slower time-scale. The proposed control strategy is resilient to communication link failures and features plug-and-play capability. Presented results demonstrate performance of the proposed control strategy for an islanded 380 VDC datacenter with variable loads. Different operating conditions are verified through the RTDS Technologies real-time digital power system simulator using switching converter models and nonlinear battery models.

Inertia-Free Stand-Alone Microgrid—Part I: Analysis on Synchronized GPS Time-Based Control and Operation

The inertia-free stand-alone (IFSA) microgrid is the new small power grid without synchronous generators equipped in conventional power systems. In other words, this system has the only converter-based generators (CBGs) based on energy storage devices and renewable energies. Therefore, it requires a new CBG control to provide strong voltage reference for the CBGs connected to the point of common coupling (PCC). This is because the IFSA microgrid is subject to a weak system such that it cannot maintain its rated frequency and/or bus voltage with the conventional real and reactive power controllers, which usually get their references from the PCC. This paper proposes the innovative conceptual approach for distributed coordination in the IFSA microgrid by applying the synchronized global positioning system time to the CBGs. Moreover, it is verified that the proposed physical structure of the IFSA microgrid makes it possible for all CBGs to share the real and reactive powers effectively. As the result, the proposed CBG control can provide the robustness, which is strongly required in the IFSA microgrid, based on timely outage management and restoration process. Several case studies are carried out with the microgrid of 36 MW to verify the effectiveness of the proposed CBG controller. The simulation and hardware-in-the loop tests are carried out using the power system computer-aided design/electromagnetic transient design and control (PSCAD/EMTDC) and the real-time digital power system simulator (RTDS), respectively.

Implementation of the frequency dependent line model in a real-time power system simulator

In this paper is described the implementation of the frequency-dependent line model (FD-Line) in a real-time digital power system simulator. The main goal with such development is to describe a general procedure to incorporate new realistic models of power system components in modern real-time simulators based on the Electromagnetic Transients Program (EMTP). In this procedure are described, firstly, the steps to obtain the time domain solution of the differential equations that models the electromagnetic behavior in multi-phase transmission lines with frequency dependent parameters. After, the algorithmic solution of the FD-Line model is implemented in Simulink environment, through an S-function programmed in C language, for running off-line simulations of electromagnetic transients. This implementation allows the free assembling of the FD Line model with any element of the Power System Blockset library and also, it can be used to build any network topology. The main advantage of having a power network built in Simulink is that can be executed in real-time by means of the commercial eMEGAsim simulator. Finally, several simulation cases are presented to validate the accuracy and the real-time performance of the FD-Line model.

A novel Bad Data Processing algorithm for analog data in substation automation systems

In this paper, a Bad Data Processing (BDP) algorithm for analog data in a substation is suggested. Considering that every substation has a standardized hierarchy and the electric power flows in a fixed direction, rules for detection and correction of bad data are derived through logical analysis of error–symptoms relations. Conservative reasoning combined with modular approach is utilized, in this paper, to enhance the efficiency and reliability of data correction. The rule base used in this paper is constructed through logical analysis of possible errors and their symptoms that may occur. The suggested algorithm is proved to be useful in both convenience and accuracy by excessive application to a substation emulator realized in real-time digital power system simulator.

96/05025 Closed-loop testing with the real-time digital power system simulator

96/05025 Closed-loop testing with the real-time digital power system simulator

Closed-loop testing with the real-time digital power system simulator

Most protection and control equipment is usually tested in the open-loop mode. However, closed-loop testing is often the only cost-effective approach. This paper highlights the areas where closed-loop testing of protective relays and control equipment is preferable. Test setups with a real-time digital simulator for closed-loop testing of protective relays, power system stabilizers, and controllers for controlled closing of individual poles of a shunt capacitor breaker are described.