Vijay K. Sood

Developing a communication infrastructure for the Smart Grid

The Smart Grid of the future, while expected to affect all areas of the Electric Power System, from Generation, to Transmission, to Distribution, cannot function without an extensive data communication system. Smart Grid has the potential to support high levels of Distributed Generation (DG); however the current standards governing the interconnection of DG do not allow the implementation of several applications which may be beneficial to the grid. This paper discusses some of the Smart Grid applications, and estimates the communication requirements of a medium data intensive Smart Grid device. Two issues that will become very important with the spread of DG are DG Islanding and DG Availability. For each issue, we propose data communication enabled solutions and enhancements.

Dynamic Averaged and Simplified Models for MMC-Based HVDC Transmission Systems

Voltage-source converter (VSC) technologies are rapidly evolving and increasing the range of applications in a variety of fields within the power industry. Existing two- and three-level VSC technologies are being superseded by the new modular multilevel converter (MMC) technology for HVDC applications. The computational burden caused by detailed modeling of MMC-HVDC systems in electromagnetic transient-type (EMT-type) programs complicates the simulation of transients when such systems are integrated into large networks. This paper develops and compares different types of models for efficient and accurate representation of MMC-HVDC systems. The results show that the use of a specific type of model will depend on the conducted analysis and required accuracy.

Dynamic Average Modeling of Front-End Diode Rectifier Loads Considering Discontinuous Conduction Mode and Unbalanced Operation

Electric power distribution systems of many commercial and industrial sites often employ variable frequency drives and other loads that internally utilize dc. Such loads are often based on front-end line-commutated rectifiers. The detailed switch-level models of such rectifier systems can be readily implemented using a number of widely available digital programs and transient simulation tools, including the Electromagnetic Transient (EMT)-based programs and Matlab/Simulink. To improve the simulation efficiency for the system-level transient studies with a large number of such subsystems, the so-called dynamic average models have been utilized. This paper presents the average-value modeling methodologies for the conventional three-phase (six-pulse) front-end rectifier loads. We demonstrate the system operation and the dynamic performance of the developed average models in discontinuous and continuous modes, as well as under balanced and unbalanced operation.

Input Power Factor Compensation for High-Power CSC Fed PMSM Drive Using d -Axis Stator Current Control

In this paper, an input power factor compensation method is proposed for a high-power pulse-width-modulated current-source-converter (CSC)-fed permanent magnet synchronous motor (PMSM) drive system. The proposed method is based on controlling the d-axis stator current component in the field-oriented control (FOC) scheme of the drive system. The CSC-fed PMSM drive system and its FOC scheme are first introduced. Then, the relationships between the machine side, dc-link, and the line side are investigated. Based on the analysis, a new d-axis stator current control scheme that can ensure unity input power factor for the operating speed range is proposed. The main feature of the proposed scheme is to compensate the line-side power factor without the need for modulation index control in either the rectifier or the inverter. Therefore, offline Selective Harmonic Elimination (SHE) modulation schemes can be implemented on both line- and machine-side converters to minimize the total harmonic distortion. This results in reduced switching frequency and reduced switching losses. Simulation results for a 2.44 MW medium-voltage system and experimental results from a low-voltage 6.5 kW IPM motor drive are provided to verify the effectiveness of the proposed compensation method.

Sensorless Control of CSC-Fed IPM Machine for Zero- and Low-Speed Operations Using Pulsating HFI Method

In this paper, a sensorless method for low- and zero-speed operations is proposed for a high-power medium-voltage pulsewidth-modulated current-source-converter-fed interior-permanent-magnet motor drive system. The proposed method is based on the injection of a high frequency (HF) pulsating sinusoidal signal in the estimated synchronous reference frame of the drives field-oriented control (FOC) scheme. The conventional FOC control scheme, low switching frequency, dc-link inductor, and the inverter output three-phase filter capacitor of the medium-voltage high-power current-source drive present some challenges in the generation and design of the HF-injection signal. To overcome these challenges, the FOC scheme is modified by introducing a modulation index control with suitable dc-link current compensation to enhance the dynamic response of the injected signal and prevent any clamp in the injected signal. In addition, a multisampling-space-vector-modulation method is proposed to prevent the distortion in the HF signal due to a low switching frequency to injected signal ratio. A detailed study and analysis regarding the influence of low switching frequency, output filter capacitor, and magnetic saturation in the injection method is carried out to determine the visible HF range of the injected signal. It is found that, by using the proposed FOC scheme and multisampling modulation scheme and by the proper design of the HF signal, an accurate rotor flux angle can be estimated for sensorless zero-/low-speed operations. Experimental results are provided to verify the proposed control method.

Modeling of LCC-HVDC Systems Using Dynamic Phasors

This paper presents an average-value model of a line commutated converter-based HVDC system using dynamic phasors. The model represents the low-frequency dynamics of the converter and its ac and dc systems, and has lower computational requirements than a conventional electromagnetic transient (EMT) switching model. The developed dynamic-phasor model is verified against an EMT model of the CIGRE HVDC Benchmark. Simulation results confirm the validity and accuracy of the average-value model in predicting the low-frequency dynamics of both the ac and dc side quantities. Merits and applicability limitations of the average model are highlighted.

Dynamic Average-Value Modeling of Hybrid-Electric Vehicular Power Systems

This paper extends the concept of dynamic average-value modeling to power-electronic-intensive hybrid-electric vehicular power trains. Hybrid vehicles with plug-in capability are becoming increasingly important in the study of emerging smart power grids, and their simulation using digital programs has gained widespread attention. This paper demonstrates the usefulness of averaging in preserving the dynamic characteristics of the vehicular system while reducing the computational intensity of its simulation on an Electromagnetic Transients Program-type simulator. This paper presents an example of averaging for modeling, simulation, and system-level studies of a power-split gear hybrid drive-train.

A hybrid HVDC transmission system supplying a passive load

The operational characteristics of a Voltage Source Converter (VSC)-HVDC transmission system make it a versatile asset in modern power systems. The advantages of the new technology are somewhat offset by some drawbacks, such as the high power losses, equipment insulation stresses, and relatively high cost. A hybrid Line Commutated Converter (LCC)-VSC HVDC transmission system combines the benefits of both conventional LCC and new VSC technologies. In this paper, a hybrid HVDC system is used to supply a passive AC network. The control systems for rectifier and inverter are discussed, along with additional control schemes for starting, load shedding, and potential AC network fault situations. The operational characteristics of the hybrid system under selected control modes are validated by EMTP-RV simulation under both steady state and transient conditions such as load shedding and AC faults. Finally, a brief performance analysis of transmission efficiency and harmonic distortion is presented.

Steady-State and Dynamic Performance of Front-End Diode Rectifier Loads as Predicted by Dynamic Average-Value Models

Summary form only given. The detailed switch-level models of front-end diode rectifier loads can be readily implemented using a number of transient simulation programs, such as PSCAD/EMTDC, and the toolboxes in Matlab/Simulink. To improve the simulation efficiency for the system-level studies, the so-called dynamic average models have been widely used by researchers and engineers. Recently, several average-value modeling methodologies for the conventional three-phase (six-pulse) front-end rectifier loads have been discussed, and the dynamic performance of several developed models has been demonstrated in discontinuous and continuous modes. In this paper, the effects of topological variations of the ac-side filters on the system performance are investigated. Also, the steady-state and dynamic impedances predicted by the average models under balanced and unbalanced operation are compared. The studies and analyses presented here extend and complement those set forth in the preceding companion publication.

Dynamic Average-Value Modeling of CIGRE HVDC Benchmark System

High-voltage direct-current (HVDC) systems play an important role in modern energy grids, whereas efficient and accurate models are often needed for system-level studies. Due to the inherent switching in HVDC converters, the detailed switch-level models are computationally expensive for the simulation of large-signal transients and hard to linearize for small-signal frequency-domain characterization. In this paper, a dynamic average-value model (AVM) of the first CIGRE HVDC benchmark system is developed in a state-variable-based simulator, such as Matlab/Simulink, and nodal-analysis-based electromagnetic transient program (EMTP), such as PSCAD/EMTDC. The 12-pulse converters in the HVDC system are modeled with a set of nonlinear algebraic functions that are extracted numerically. The results from the average-value models are compared with the results of the detailed simulation to verify the accuracy of the AVMs in predicting the large-signal time-domain transients. The developed dynamic average models are shown to have computational advantages.