Showing papers by "Luiz A. C. Lopes published in 2007"

Operation of Single-phase Grid-Connected Inverters with Large DC Bus Voltage Ripple

Abstract: Large electrolytic capacitors are usually employed in single-phase grid-connected voltage source inverters (VSI) of distributed energy resources (DER) They are bulky and have a relatively short life time what motivates their replacement by smaller film type capacitors Resulting issues such as the increased dc bus voltage ripple and smaller inertia to active power variations are discussed in this paper The former tends to increase the low order harmonics of the injected current, what becomes an even more challenging matter when the bandwidth of the voltage loop is increased to compensate for the latter A solution based on a voltage ripple estimator is presented and is verified by means of simulation results

Voltage and Frequency Regulation of a Stand-Alone Self-Excited Induction Generator

Abstract: This paper discusses the regulation of the voltage and frequency of a stand-alone self-excited squirrel-cage induction generator (SEIG) connected to an unregulated prime mover by means of a single voltage source inverter (VSI) connected in shunt with the stator of the generator A battery bank is used at the dc side of the VSI so that it can deal active and reactive power and affect the frequency and magnitude of the generated voltage The focus of this paper is on the experimental results obtained for a 4-pole 2 HP SEIG with an unregulated prime- mover with a linear torque versus speed characteristic typical of impulse type hydro turbines It shows that active and reactive power control yields a better voltage and frequency regulation to load variations than reactive power alone

Analysis of a Hybrid Current Source Converter with Bi-directional Power Flow Capability

Abstract: Current source converters (CSCs) present the desirable characteristics of inherent load and converter short- circuit protection Silicon controlled rectifiers (SCR) based CSCs are rugged and affordable but they create low order harmonics and do not allow active and reactive power to be controlled independently These drawbacks can be overcome with topologies based on more costly force-commutated switches This paper proposes a hybrid three-phase CSC that employs three SCRs and four IGBTs and presents features comparable to the fully controllable CSC The inherent commutation constraints of the SCRs are taken into consideration in the selection of a suitable space vector (SV) modulation technique Comparisons with the fully controllable CSC are provided for a fair assessment of the potential of the proposed hybrid CSC The theoretical analysis is verified by means of simulations

Design and Compliance of Frequency Drifting Islanding Detection Methods with the IEEE Standard 1547.1

Abstract: Islanding is one important concern for grid connected distributed resources due to personnel and equipment safety. Preliminary design and performance assessment of inverter-resident frequency drifting islanding detection methods (IDMs) can be done by means of non-detection zones (NDZs) in a load parameter space. However, this tool only reflects the steady-state condition, that is, if the frequency of the islanded system will end up within a normal frequency range, where islanding occurs. It does not provide any information regarding the transient period, which is an important factor for the definition of the load testing points for the IEEE Std. 1547.1. Time domain simulations are used to identify critical load testing points that yield the longest run times. Then, the impact of these load values on the effectiveness of the design of frequency drifting IDMs using NDZ is discussed. As a result, an additional criterion for IEEE Std. 1547 compliance is presented.