Leonardo R. Limongi

Enhanced Power Quality Control Strategy for Single-Phase Inverters in Distributed Generation Systems

Power electronic converters are commonly used for interfacing distributed generation systems to the electrical power network. This paper deals with a single-phase inverter for distributed generation systems requiring power quality features, such as harmonic and reactive power compensation for grid-connected operation. The idea is to integrate the DG unit functions with shunt active power filter capabilities. With the proposed approach, the inverter controls the active power flow from the renewable energy source to the grid and also performs the non-linear load current harmonic compensation keeping the grid current almost sinusoidal. The control scheme employs a current reference generator based on Sinusoidal Signal Integrator (SSI) and Instantaneous Reactive Power (IRP) theory together with a repetitive current controller. Experimental results obtained on a 4 kVA inverter prototype demonstrate the feasibility of the proposed solution.

Digital current-control schemes

The paper is about comparing the performance of digital signal processor-based current controllers for three-phase active power filters.

Analysis and Comparison of Phase Locked Loop Techniques for Grid Utility Applications

This paper presents an analysis and comparison of phase locked loop techniques used in grid utility applications to find the voltage vector angle generated from the supply voltages. The phase locked loop (PLL) has a wide range of applications as distributed generation (DG), flexible AC transmission systems (FACTS), static VAR compensators, cycloconverters, active power filters (APFs) and others systems connected to the utility. The performance of these systems in grid connected applications is strongly influenced by the adopted PLL strategy. For this reason, the goal of the proposed paper is to present a comparison of different PLL-based techniques for utility applications to indicate the appropriate solution dedicated to a specific application. The criteria to compare the phase locked loops techniques is the performance under distorted and unbalanced supply voltages.

New Stationary Frame Control Scheme for Three-Phase PWM Rectifiers Under Unbalanced Voltage Dips Conditions

A new stationary frame control scheme for three-phase pulsewidth-modulation (PWM) rectifiers operating under unbalanced voltage dips conditions is proposed in this paper. The proposed control scheme regulates the instantaneous active power at the converter poles to minimize the harmonics of the input currents and the output voltage ripple. This papers novelty is the development of a new current-reference generator implemented directly in stationary reference frame. This allows using proportional sinusoidal signal integrator (P-SSI) controllers for simultaneous compensation of both positive and negative current sequence components. No phase-locked loop (PLL) strategies and coordinate transformations are needed for the proposed current-reference generator. Experimental results are presented for a 20-kV A alternative current (ac)/direct current (dc) converter prototype to demonstrate the effectiveness of the proposed control scheme. A comparison with two other existing control techniques is also performed. Fast dynamic performance with small dc-link voltage ripple and input sinusoidal currents are obtained with this control scheme, even under severe voltage dips operating conditions.

FPGA Implementation of the Generalized Delayed Signal Cancelation—Phase Locked Loop Method for Detecting Harmonic Sequence Components in Three-Phase Signals

Fundamental-frequency and harmonic positive- and negative-sequence components detection is an important task for implementing power converters for renewable energy systems, uninterruptible power supplies, active power filters, dynamic voltage restorers, and also for power systems protection relays. Detection techniques of this kind are generally implemented in digital signal processor (DSP) with the execution time limited by the sampling period. The computational effort of the control algorithm can considerably increase the execution time, due to the sequential nature of processing in DSP. A promising technique for sequence components separation of three-phase signals is the so called the generalized delayed signal cancelation-phase locked loop (GDSC-PLL). Field programmable gate arrays (FPGAs) capacity of exploring the parallelism of operations present in the GDSC-PLL is demonstrated in this paper through the mapping of this technique directly in hardware, allowing for a much shorter execution time than in DSP. The proposed architecture is presented, and the efficient detection of the fundamental-frequency positive-sequence with FPGA is demonstrated, with the obtained results compared with a traditional DSP implementation. In particular, the advantages and possibilities of the use of FPGA are demonstrated in comparison with the DSP. For this comparison, a metric for evaluating the capacity of complexity increase in application algorithms is proposed.

New Stationary Frame Control Scheme for Three Phase PWM Rectifiers under Unbalanced Voltage Dips Conditions

A new stationary frame control scheme for three-phase pulse width modulation (PWM) rectifiers operating under unbalanced voltage dips conditions is proposed in this paper. The proposed control scheme regulates the instantaneous active power at the converter poles to minimize the harmonics of the input currents and the output voltage. The paper novelty is the development of a new current-reference calculation implemented directly in stationary reference frame. This allows using proportional - sinusoidal signal integrators (P-SSI) controllers for simultaneous compensation of both positive and negative current sequence components. No phase locked loop (PLL) strategies and coordinate transformations are needed. A comparison with two other existing control techniques is also performed. Experimental results are presented for a 20 kVA AC/DC converter prototype to demonstrate the effectiveness of the proposed control scheme. Fast dynamic performance with small DC-link voltage ripple and input sinusoidal currents are obtained with this control scheme even under severe voltage dips operating conditions.

Transformerless Hybrid Power Filter Based on a Six-Switch Two-Leg Inverter for Improved Harmonic Compensation Performance

One of the most important power quality issues is related to current harmonics generated by nonlinear loads such as diode and thyristor front-end rectifiers. Well-established solutions to overcome this problem, such as active power filters (APFs), have the required high power rating components as a major disadvantage. An alternative, called hybrid power filter (HPF), mixes low power rating active filters with passive filters. Unfortunately, many of these HPF topologies have, as a common disadvantage, a great number of passive components and/or transformers. Based on this fact, new concepts of HPFs, consisting of small-rated inverters and LC filters, have been introduced with wide acceptance. The advantage comes from the fact that these HPFs are connected to the grid without any matching transformer. Recently, some topologies based on dual-converter configurations have been shown to be very attractive, where the APF (or HPF) must deal with highly nonlinear loads with high values of di/dt and supplying the reactive power together with harmonic compensation. On the other hand, the drawback of dual converters is the high number of switch devices. Therefore, this paper proposes a transformerless HPF based on a new six-switch two-leg inverter with an enhanced harmonic compensation capability. Aside from presenting a reduced number of switches when compared with dual topologies, the proposed solution is capable of providing fully compensation even for loads with high harmonic content. Experimental results are presented for an HPF inverter prototype in order to demonstrate that the harmonic compensation performance meets the IEEE 519 standard.

Frequency-domain analysis of resonant current controllers for active power conditioners

This paper performs a frequency-domain analysis of three different resonant current controllers for active power conditioners. The analysis is focused on the closed loop frequency response and Nyquist plots for all current controllers of interest. The system stability when the active power conditioner attempts compensating high order harmonics is investigated. To perform this analysis, the time delay introduced by the inverter and the sampling is taken into account in the current controller closed loop transfer function. This procedure demonstrates the importance and effectiveness of the delay compensation to maintain the whole system stability. Experimental results obtained for a 25 kVA shunt active power conditioner prototype are presented to confirm the theoretical analysis.

New control scheme for single-phase active power filters

A new control scheme for a single phase shunt Active Power Filter (APF) is proposed in this paper. The goal is the introduction of a new reference generator along with a repetitive current control scheme. The proposed reference generator uses a filter based on a sinusoidal signal integrator and the instantaneous reactive power theory to compute the APF reference current. The proposed scheme can be easily adapted to work in a distributed generation system, injecting active power into the grid. The whole control algorithm has been implemented on the dSPACE DS1103 development system controlling a single phase APF prototype to demonstrate the feasibility of the proposed solution.

Single-phase inverter with power quality features for distributed generation systems

This paper is focused on control solutions for a single-phase inverter for distributed generation (DG) systems requiring power quality features as harmonic and reactive power compensation for grid-connected operation. Based on these characteristics, a new current reference generator based on sinusoidal signal integrator (SSI) and instantaneous reactive power (IRP) is proposed. Simulation and experimental results have been obtained from the proposed scheme implemented along with the repetitive current control.