Vinicius Dario Bacon

Single-Stage Three-Phase Grid-Tied PV System With Universal Filtering Capability Applied to DG Systems and AC Microgrids

This paper proposes a single-stage three-phase four-wire grid-connected photovoltaic (PV) system operating with a dual compensating strategy and feedforward control loop (FFCL). Besides injection of active power into the grid, the PV system operates as a unified power quality conditioner (UPQC), suppressing load harmonic currents and compensating reactive power. Furthermore, regulated, balanced, and harmonic-free output voltages are provided to the load. Since the PV-UPQC is based on a dual compensation strategy, the series converter operates as a sinusoidal current source, whereas the parallel converter operates as a sinusoidal voltage source. Thus, seamless transition can be achieved from the interconnected to the islanding operation modes, and vice versa, without load voltage transients. Moreover, to overcome problems associated with sudden solar irradiation changes, fast power balance involving the PV array and the grid is obtained, since the FFCL acts on the generation of the series inverter current references. As a result, the dynamic responses of both inverter currents and dc-bus voltage are improved. Detailed analysis involving the active power flow through the inverters is performed allowing proper understanding of the PV-UPQC operation. Experimental results are presented to evaluate both dynamic and static performances of the PV-UPQC tied to the electrical distribution system.

Dynamic Performance Improvement of a Grid-Tied PV System Using a Feed-Forward Control Loop Acting on the NPC Inverter Currents

This paper presents a three-phase grid-connected photovoltaic (PV) system, which is implemented using the neutral-point-clamped (NPC) inverter. A current feed-forward control loop (FFCL) is proposed to improve the PV system dynamic behavior, due to the PV array being constantly subjected to sudden solar irradiance change, which causes voltage oscillations in the dc bus and, hence, interferes in proper PV system operation. As the current FFCL acts to speed up the calculation of the inverter current references, the dynamic response of the currents injected into the grid is improved. As a consequence, the dynamic behavior of the dc-bus voltage is also enhanced, reducing both settling time and overshoot. Besides the injection of active power into the grid, the PV system is also controlled to perform active power-line conditioning, so that load harmonic currents are suppressed, as well as load reactive power is compensated. However, the NPC inverter must be properly designed to guarantee that its power rating will not be exceeded, since both fundamental and nonfundamental current components flow through the grid-tied inverter. Extensive experimental results based on a digital signal processor are presented in order to evaluate the effectiveness, as well as the static and dynamic performance of the PV system.

A Versatile Unified Power Quality Conditioner Applied to Three-Phase Four-Wire Distribution Systems Using a Dual Control Strategy

This paper presents the study, analysis, and practical implementation of a versatile unified power quality conditioner (UPQC), which can be connected in both three-phase three-wire (3P3W) or three-phase four-wire distribution systems for performing the series-parallel power-line conditioning. Thus, even when only a 3P3W power system is available at a plant site, the UPQC is able to carry out power-line compensation for installed loads that require a neutral conductor to operate. Different from the control strategies used in the most of UPQC applications in which the controlled quantities are nonsinusoidal, this UPQC employs a dual compensation strategy such that the controlled quantities are always sinusoidal. Thereby, the series converter is controlled to act as a sinusoidal current source, whereas the parallel converter operates as a sinusoidal voltage source. Thus, because the controlled quantities are sinusoidal, it is possible to reduce the complexity of the algorithms used to calculate the compensation references. Therefore, since the voltage and current controllers are implemented into the synchronous reference frame, their control references are continuous, decreasing the steady-state errors when traditional proportional-integral controllers are employed. Static and dynamic performances, as well as the effectiveness, of the dual UPQC are evaluated by means of experimental results.

Three-phase grid-connected PV system operating with feed-forward control loop and active power-line conditioning using NPC inverter

This paper presents a single-stage three-phase grid-connected photovoltaic (PV) system, which is implemented using the three-level neutral-point-clamped inverter. The PV system operates with an additional feed-forward control loop (FFCL), in order to improve the dynamic behavior of both dc-bus voltage and inverter currents, when the PV array is subjected to abrupt insolation changes. In other words, sudden solar radiation changes can cause large voltage oscillations on the inverter dc-bus, interfering in an adequate PV system operation, due to the generation of the inverter current references are computed taking into account the dc-bus voltage control loop. Thus, the use of the FFCL reduces the settling time and overshoot/undershoot of the dc-bus voltage. Moreover, the dynamic response of the currents injected into the grid are also improved. Simultaneously, the PV system is able to perform the active power-line conditioning by suppressing load harmonic currents and performing reactive power compensation. Although the FFCL can be used in conjunction with any maximum power point tracking technique, perturb and observe technique is adopted to generate the dc-bus voltage reference. Simulation results are presented in order the evaluate the performance, as well the effectiveness of the PV system operating with the proposed FFCL.

Tuning of a PI-MR Controller Based on Differential Evolution Metaheuristic Applied to the Current Control Loop of a Shunt-APF

This paper aims to present an alternative methodology to improve the tuning of proportional-integral multiresonant (PI-MR) controller applied to the current control loop of a shunt active power filter (SAPF) by using a differential evolution (DE) metaheuristic method. For computing the PI-MR controller gains, the methodology based on Naslin polynomial (NP) can be employed, although its performance is limited. On the other hand, tuning procedures accomplished by trial-and-error methods have been largely used. In order to fill the lack of methodological procedures to determine the PI-MR controller gains, the use of DE metaheuristic optimization algorithm is proposed to perform an optimal adjustment. The DE algorithm operates minimizing an appropriate cost function, taking into account the total harmonic distortion of the source current, the error of the compensation current control loop, and the saturation limit of the control action. The effectiveness of the proposed methodology is compared to the NP-based method, applied to a single-phase SAPF. The proposed methodology is validated by means of both simulation and experimental results. The evaluation of the static and dynamic performances is obtained from experimental tests performed based on a digital signal processor.

An adaptive phase-locked loop algorithm for single-phase utility connected system

This paper proposes a novel algorithm employed to detect both the phase-angle and the frequency of the single-phase utility grid voltage. The proposed algorithm uses an adaptive notch filter (ANF) operating in conjunction with a Phase-Locked Loop (PLL) system, yielding an algorithm called ANF-αβ-pPLL. The αβ-pPLL structure is based on the instantaneous active power theory for three-phase power systems. Thus, for single-phase systems, the proposed PLL algorithm can be analyzed into a fictitious two-phase stationary reference frame (αβ-coordinates), in which a normalized fictitious quadrature voltage (νβ) is obtained from the estimated PLL phase-angle. On the other hand, an adaptive filter is used to extract the fundamental component of the utility voltage, allowing the rejection of voltage harmonic disturbance. In order to validate the theoretical development, the performance of the single-phase ANF-αβ-pPLL algorithm is evaluated by means of both simulation and experimental tests under utility grid disturbances, such as voltage harmonics, voltage sags/swells, phase-angle jumps and frequency variations.

Unified control design approach applied to four-wire shunt active power filter topologies

This paper presents a unified control design approach involving four topologies of shunt active power filters (SAPF), which can be applied to three-phase four-wire distribution systems. The SAPF structures are deployed by means of the following inverter topologies: full-bridge composed of three modules, four-legs, split-capacitor and neutral point clamped. The SAPFs are compared to each other through detailed theoretical studies, resulting in mathematical models that can properly represent each topology. After that, a generalized mathematical model that is able to represent each SAPF schemes is proposed. As a result, through of a unified control design specification, all the controller gains employed in the current and voltage control loops can be properly obtained. In order to evaluate and validate the theoretical development, simulation results are presented taking into account the SAPFs performing reactive power compensation, harmonic current suppression, as well as load unbalance compensation.

Selective harmonic currents suppressing applied to a three-phase shunt active power filter based on adaptive filters

This paper proposes a selective strategy used to generate the harmonic current references, which are employed in the control loops of a three-phase active power filter (APF). By applying the aforementioned selective strategy, the selection of the harmonic components that will be suppressed by means of the filter is allowed. The proposed strategy comprises of an algorithm based on the synchronous reference frame. In addition, it uses adaptive filters in order to carry out the harmonic components selection. The APF topology is implemented by using a four-leg inverter, which is mathematically modelled in two-phase stationary reference frame (αβ0-axes). Due to the inherent decoupling in the αβ0-axes, proportional and integrative controllers are used in each one of the referred coordinates, allowing the individual control of the compensation currents. The SRF-based algorithm is mathematically analyzed, as well as experimental results are presented in order to validate the theoretical development.

An adaptive phase-locked loop structure for three-phase utility grid-connected systems

This paper proposes a phase-locked loop (PLL) structure, which is composed of non-autonomous adaptive filters (AFs) and a positive sequence detector (PSD), both operating in conjunction with the PLL based on synchronous reference frame (SRF-PLL). The AFs are used to extract the fundamental components of the utility voltages, whereas the PSD extracts the positive sequence components at fundamental utility frequency. The main purpose of the AF-based PLL is to overcome the drawbacks presented in the well-known SRF-PLL scheme, mainly in occurrence of non-ideal utility conditions, such as voltage harmonics and/or unbalances. Usually, such problems can be minimized reducing the bandwidth of the SRF-PLL system, at cost of compromising its dynamic response. Both static and dynamic performances of the AF-based SRF-PLL are compared to the conventional SRF-PLL by means of experimental tests, taking into account the following power quality problems: voltage harmonics and unbalances, voltage sags, phase-angle jumps and frequency variations.

A three-phase adaptive phase-locked loop scheme for utility grid-connected systems

This paper deals with a phase-locked loop (PLL) algorithm for both phase-angle and frequency detections in three-phase utility grid connected systems. The proposed algorithm uses non-autonomous adaptive filters (AFs) for extracting the fundamental components of the utility voltages, while a positive sequence detector (PSD) is employed for obtaining the positive sequence components at fundamental utility frequency. Both the AFs and the PSD operate in conjunction with a three-phase power-based PLL (3pPLL) yielding the scheme called AF-PSD-3pPLL. Therefore, power quality problems that interfere on the PLL performance are mitigated, such as voltage harmonics and unbalances. The performance of the proposed AF-PSD-3pPLL algorithm is evaluated by means of experimental tests considering utility disturbances, such as voltage harmonics, voltage unbalances, and voltage sags.