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In this paper, a new approach is proposed to increase the flexibility of the reference current generation for active compensators. Although compensating all useless components of the current is ideal, it is sometimes desirable to target a subset of the possible components of the current due to power electronic converter power, switching speed limitations, etc. Furthermore, power quality objectives may vary over time. The proposed strategy utilizes a novel reference signal generator to provide online flexibility with respect to the compensation objectives. The reference signal generator utilizes a computationally efficient moving-window discrete Fourier transform along with an orthogonal decomposition of the current instead of the filters typically used to extract the desired components of the current. Each orthogonal component of the current can be adjusted independently in any percentage, thus providing the selective current compensation. The proposed reference signal generator also allows for easy extrapolation of the measured current, effectively canceling the delay inherent in the digital current control loop. Cancellation of the delay allows for the elimination of the spikes that typically occur due to poor tracking of fast slope transitions of the current reference. The advantages of the proposed control architecture have been verified by an experimental prototype. Index Terms--Active compensators, active power filter, harmonics, predictive control, recursive discrete Fourier transform (RDFT), selective current compensation.

Electric Power Research Institute's Control Center Application Programming Interface proposed the Common Information Model (CIM) as the common information exchange model, which provides an excellent platform for representing the components of a power system. This paper discusses using CIM for data modeling for ship power system analysis. Features include using the CIM to accommodate shipboard power systems. Detailed data models for a pulsed load and an active filter are presented and validated through simulation in Matlab. The general process to extend CIM for shipboard power system is briefly outlined. Further efforts are underway to develop a CIM-based shipboard baseline test case to standardize modeling terminology. Index Terms--Active filter, Common Information Model (CIM), data model, pulsed loads, shipboard power system.

Shunt active power filters (APF) are commonly used for the reduction of current harmonics and improvement of the power factor in power systems with nonlinear loads, such as diode rectifiers. A pulsewidth modulation (PWM) power converter constitutes the main component of the APF. The low-order harmonics of the line current are attenuated, but the switch-mode operation of the converter results in electromagnetic interference (EMI) spreading to the grid. Specifically, clusters of harmonics appear in the frequency spectra of voltages and currents of the converter at multiples of the switching frequency. In this paper, transferring the discrete spectral power of those harmonics to the continuous spectral power density is proposed as means for mitigation of the EMI. It is accomplished by randomization of the switching periods using a novel random PWM method (RPWM II). In contrast to the existing random PWM methods, in RPWM II the sampling frequency of the digital modulator is constant and equal to the average switching frequency. Computer simulations and experimental investigation of an APF designed for shipboard power systems are described, and the results are presented. They demonstrate significant reduction of the EMI, a feat achieved at practically no expense. Index Terms--Active power filters (APFs), electromagnetic interference (EMI) mitigation, random pulsewidth modulation (RPWM).

Resonant harmonic filters (RHFs) are effective devices for reducing supply current harmonics when only those load generated harmonics for which they are tuned are present. Other current harmonics as well as supply voltage harmonics may reduce the effectiveness of RHFs in harmonic suppression. To counter such reductions in effectiveness, an optimization based method for selection of filter branch parameters is developed for the conventional RHF. It takes into consideration the interaction of the filter with the distribution system and provides filter parameters that give the maximum effectiveness with respect to harmonic suppression. To accomplish this, a cost function is developed, its behavior examined, and appropriate constraint functions are developed. The results for optimized filters, applied in a test case, are given. Index Terms--Harmonic distortion, harmonic filter design, passive harmonic filters, shunt tuned harmonic filters.

Distribution voltage harmonics and load current harmonics other than harmonics to which a resonant harmonic filter (RHF) is tuned, deteriorate the filter efficiency in reducing harmonic distortion. The paper presents results of a study on dependence of this deterioration on the method of the filter design. The study was confined to four-branch RHFs of the 5th, 7th, 11th, and 13th order harmonics, installed on buses that predominantly supply six-pulse ac/dc converters or rectifiers. The filters under investigation were designed according to two different approaches: a traditional approach and an approach based on an optimization procedure. In the traditional approach, the reactive power allocated to particular branches of the filter and their tuning frequencies are selected at the designer's discretion, according to recommended practices. In the optimization based approach, the reactive power allocated to particular branches and tuning frequencies are resultants of an optimization procedure that minimizes the bus voltage and the supply current THD in the system with the filter under design. Index Terms--Harmonic distortion, harmonic filter design, non-sinusoidal systems, resonant harmonic filters.

The effectiveness of resonant harmonic filters (RHFs) in harmonic suppression is the resultant of two different types of resonance that affect the filters' effectiveness in an opposite manner. They are the resonance of the filter branches and the resonance of the entire filter with the distribution system inductance. Damping these resonances by reduction of the filter Q-factor affects the filter performance in a complex way. There are suggestions in the literature on RHFs that such a damping would improve the filter effectiveness. Unfortunately, no quantitative information to support such a suggestion is available. This paper presents the results from a study of the effect of the Q-factor on the filter effectiveness and on the loss of active power in the filter. Index Terms--Harmonics, resonant harmonic filters.

In this article, an approach is proposed for the online diagnostic analysis of power electronic converters utilizing real-time, probabilistic digital twinning. Under this approach, a digital twin (DT) of a power converter is defined as a real-time, probabilistic simulation model with stochastic (random) variables, developed using generalized polynomial chaos expansion. The DT models are partitioned in perspective of control layers for power converter subsystems in the approach, with emphasis on the application and converter control layers. Real-time executed solvers of these divided probabilistic DT models are embedded into power converter controllers running on field programmable gate array (FPGA) computing devices. Using a monitoring system, the real-time probabilistic DTs at each control layer and the corresponding physical twins of the power converter are compared by the controllers to determine if the power converter is operating within probable behavior. Knowing the large computational cost of probabilistic modeling, the resource usage and timing of real-time DT solvers on modern FPGAs is reported for common power electronic converter topologies, showing the approach is feasible and able to perform probabilistic real-time simulation of smaller power converters in perspective of application and converter control layers using ≤ 2 μs time steps, with as low as 70 ns steps; while staying embeddable within FPGA-based controllers. To highlight the capabilities of the proposed approach, a case study is presented using a probabilistic DT in the application layer controller of a pair of converters to comparatively monitor their behavior and corresponding controller action under hardware-in-the-loop testing. [ABSTRACT FROM AUTHOR]

The ability to manage energy within an autonomous microgrid, which enables system optimization, requires coordinated control of the connected power sources. This generally involves coordination of active and reactive power generation. To increase energy management capability, coordination of converter connected power sources can be extended to other tasks such as harmonic compensation and load balancing. However, some units in microgrids, such as wind and photovoltaic (PV) power sources, have local criteria such as maximum power point tracking that determines the reference value for active power generation. In this paper, a distributed control structure for independent sharing of tasks among sources is introduced where units with local active current reference can contribute to generation of only non-active current components in coordination with other units while their active current is generated autonomously. For task-sharing among units, an objective function based on current components is presented. In order to verify the proposed method, optimization of a microgrid with a PV unit is simulated. [ABSTRACT FROM AUTHOR]

This paper describes the implementation of a distributed coordinating control system for power electronic converters in a shipboard distribution system that ensures system optimization dynamically. Multiple agents take part in the process to determine optimal power sharing for the converters. A distributable optimization method suitable for real-time coordination of converters is developed for deployment in multi-agent system type frameworks. The presented optimal power-sharing method ensures minimum distribution losses and economic dispatch of sources while enforcing constraints such as source ramp rates and capacity limits. [ABSTRACT FROM PUBLISHER]

When the control functions of various types of power electronics systems are examined, a significant degree of common functionality emerges, irrespective of the target application. It is possible to define hierarchical control architectures for these systems using common interface definitions between control system divisions or layers. Such definitions enable the use of common designs for multiple applications and the use of commercially available electronics and communications modules allowing cost reduction in power electronics applications. This paper presents various partitioning strategies of a hierarchical control architecture for use in high power electronics control systems and defines various parameters/functions that need to be handled within each layer, and those that need to be communicated between the layers. Each layer has characteristic processing and communication speed requirements, irrespective of the final applications. [ABSTRACT FROM PUBLISHER]

A new high-impedance fault (HIF) detection method using time-frequency analysis for feature extraction is proposed. A pattern classifier is trained whose feature set consists of current waveform energy and normalized joint time–frequency moments. The proposed method shows high efficacy in all of the detection criteria defined in this paper. The method is verified using real-world data, acquired from HIF tests on three different materials (concrete, grass, and tree branch) and under two different conditions (wet and dry). Several nonfault events, which often confuse HIF detection systems, were simulated, such as capacitor switching, transformer inrush current, nonlinear loads, and power-electronics sources. A new set of criteria for fault detection is proposed. Using these criteria, the proposed method is evaluated and its performance is compared with the existing methods. These criteria are accuracy, dependability, security, safety, sensibility, cost, objectivity, completeness, and speed. The proposed method is compared with the existing methods, and it is shown to be more reliable and efficient than its existing counterparts. The effect of choice of the pattern classifier on method efficacy is also investigated. [ABSTRACT FROM AUTHOR]

When employed in systems with higher frequency variability and nonideal supply voltage, the synchronization method used in grid-connected power electronic converter control systems must be considered. A method is presented here that achieves synchronization implicitly through the use of a discrete Fourier transform in combination with the computation of an effective admittance. It is shown that the method is suitable for systems with high frequency variability as well as for systems with nonideal supply voltage including heavy voltage asymmetry. [ABSTRACT FROM PUBLISHER]

Electric Power Research Institute's Control Center Application Programming Interface proposed the Common Information Model (CIM) as the common information exchange model, which provides an excellent platform for representing the components of a power system. This paper discusses using CIM for data modeling for ship power system analysis. Features include using the CIM to accommodate shipboard power systems. Detailed data models for a pulsed load and an active filter are presented and validated through simulation in Matlab. The general process to extend CIM for shipboard power system is briefly outlined. Further efforts are underway to develop a CIM-based shipboard baseline test case to standardize modeling terminology. [ABSTRACT FROM AUTHOR]

In this paper we present an approach for real-time simulation and Hardware-in-the-Loop (HIL) testing of Modular Multilevel Converters (MMCs) that rely on switching models while supporting system level analysis. Using the Latency Based Linear Multistep Compound (LB-LMC) approach, we achieved a 50 ns simulation time step for systems composed of several MMC converters and for converters of various complexity. To facilitate system level testing, we introduce the use of a serial communication-based (Aurora) interface for HIL testing of MMC converters and we analyzed the effect that communication latency has on the accuracy of the HIL test. The simulation and HIL results are validated against an MMC laboratory prototype. [ABSTRACT FROM AUTHOR]