Sebastian Rosado

Open modular power electronics building blocks for utility power system controller applications

This paper explores using modular power electronics building blocks (PEBBs) in building power electronics based controllers for utility systems applications. The analysis of the existing and proposed controller functions identifies three basic PEBB converter functions for power system controllers: bidirectional AC switch, bidirectional AC/DC voltage source converter, and DC/DC converter. An open system hierarchical architecture is proposed to standardize the analysis, characterization and construction of applications based on PEBBs. Case study results on PEBB based STATCOM are presented. This work will allow us to focus on optimizing only limited number of standard PEBB converters to reduce the system cost and improve reliability.

Model-Based Digital Generator Control Unit for a Variable Frequency Synchronous Generator With Brushless Exciter

This paper presents the design and implementation of a digital signal processor (DSP)-based generator control unit (GCU) for a variable frequency synchronous generator with brush-less exciter. A novel model-based control algorithm is proposed to better account for the wide operating frequency range and various load conditions. In addition to the model-based inner-loop exciter field current regulator and outer-loop generator voltage regulator, the control algorithm also adopts a generator-model-based d-axis current feed-forward loop to compensate for the load disturbance. Simulation and test results show a considerable performance improvement for the new controller when compared to the existing controllers, including better dynamics, better damping stability margin, and more uniform response over the operating range.

Design of PEBB based power electronics systems

The standardization of power electronics that come with the power electronics building blocks (PEBB) is expected to expand the use of power electronics through reduced costs and higher reliability. Part of the cost reduction comes from the simplification in the design process that is obtained by using standard modules. This paper analyzes the PEBB based design process and discusses some ideas about the design of power converters based on power modules and appropriate tools for the design

Large- and Small-Signal Evaluation of Average Models for Multi-Pulse Diode Rectifiers

This paper analyses different average models of multi-pulse diode rectifiers. In the analysis a full-order and a simplified average model are compared to a detailed switching model. The main goal is to establish the validity of the simplified model. First the different models are discussed. Then the small and large signal evaluations of the models are presented. The input impedance frequency response of the models is used as basis for the small-signal evaluation. This parameter is important in the small-signal stability of the system. The large-signal evaluation is done by means of time domain simulations carried on with the different models. The results obtained indicate that the simplified average model can provide a good tool for the analysis of circuits using multi-pulse rectifiers

Control interface characterization of power electronics building blocks (PEBB) in utility power system applications

This paper focuses on developing methodology of characterizing the control interface for PEBB (power electronics building block) based power converters in power system applications. Using a multilevel hierarchical controller function partitioning, different applications (STATCOM, DVR, SSTS) are shown to share common control architecture and interface characteristics with different PEBB modules and control functions. Detailed analysis of the control signals involved allows quantifying the capacity requirements of the control interfaces, and helps construction of power converter applications using the PEBB concept.

Study of abnormal electrical phenomena effects on GSU transformers

Three generator step-up (GSU) transformers successively failed in recent years in a large pumped storage plant, resulting in a considerable economic loss for the utility. A comprehensive investigation was done to find out the possible failure causes. Several aspects are considered in this study, including switching transients resulting from routine switching operations, lightning overvoltages, and harmonics and spikes due to static frequency converter (SFC) operation. The study showed that circuit breaker and disconnector restriking may affect transformer insulation due to their frequent occurrence, gas insulated switching gear (GIS) side surge arresters provide inadequate lightning protection to GSU transformers, and SFC operation has little effect on transformer insulation. This paper presents the simulation results. Methods to lower the lightning transients at the transformer terminals were provided and implemented.

Model-based Digital Controller for a Variable Frequency Synchronous Generator with Brushless Exciter

This work describes the design and implementation of a DSP-based control regulating the output voltage of an electric generator for aircraft applications. Voltage regulation in an aircraft system is a challenging task due to a wide range of operating conditions. Control schemes based on the model of synchronous generators have been proposed because they naturally account for changes in the operation conditions. This paper proposes a multi-loop controller algorithm with model-based characteristics. That control algorithm was developed in simulations and tested experimentally in a DSP implementation. Simulation and test results show considerable improvement in the performance when compared to current practices. The controller has excitation and armature current loops whose characteristics are derived from the parameters of the machine and do not require additional tuning. Moreover, the model based characteristics produce a more uniform response in all the different operation conditions. In this way, the proposed controller algorithm overcomes some major issues currently existing for the type of applications under study

Large-Signal Stability Analysis in Power Systems with a Synchronous Generator Connected to a Large Motor Drive

This paper studies the large-signal stability of a synchronous generator connected to a motor drive of a similar power. The generator-motor drive set, with additional auxiliary lower power loads represents a simplified version of an all electric ship power system. The use of Lyapunov linearization method allows identifying the region of stable operation. This description is valid only locally. However, the boundaries of this region where the equilibrium points change their stability condition represent bifurcations of the nonlinear system. In addition, nonlinear behavior is likely to appear close to those boundaries. The paper also describes observed nonlinear behavior created by the action of hard limits in the system.

A full frequency range average model for Vienna-type rectifiers

This paper presents a new mathematical model for three-level non-regenerative Vienna-type rectifiers exploiting the equivalence of this topology with three-level neutral-point-clamped (NPC) converters. Specifically, it models the rectifier operation using a positive- and one negative-rail switching function-the standard approach for NPC converters. This equivalent modeling renders the state space model of Vienna-type rectifiers structurally time invariant, enabling its conversion into the synchronous d-q frame, and its averaging over a switching cycle basis. The resultant model is consequently valid up to half of the switching frequency. An in-depth small-signal analysis is then presented showing that only the d-d channel and dc port of the rectifier present truly time-invariant dynamics, given the intrinsically pulsating power transfer between its ac and dc terminals; quasi-stationary small-signal analysis is thus mandatory for this type of topology. Simulation and experimental results with a 20 kW motor drive and 2 kW experimental prototype are used for validation purposes.

Large-Signal Stability Assessment of AC/DC Systems with Multi-Pulse Rectification and DC-Fed PWM Motor Drives

This paper analyzes the large signal stability in an AC/DC system with a controlled AC generator and a regulated load of constant power characteristic. The method used in the analysis is based on Lyapunov direct method. The required Lyapunov function is constructed by means of solving a set of linear matrix inequalities derived from the system. Therefore, the models of the system components become relevant in the formulation and are also analyzed. In the Lyapunov based study it is desired that these models are simple, but represent the nonlinear and energy-flow behavior of the original equipment. Computer simulations are used along the paper to illustrate the discussion and support the validity of the proposed approach.