Leonardo Bruno Garcia Campanhol

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.

Single-phase grid-tied photovoltaic system with boost converter and active filtering

This paper deals with a single-phase grid-tied photovoltaic system, which can operate, simultaneously, as shunt active power filter and injecting active power into the grid. The photovoltaic system is composed of DC/DC step-up (boost) converter and full-bridge DC-AC converter, performing both reactive power compensation and harmonic current suppression generated by nonlinear loads. The photovoltaic system is implemented utilizing an equivalent electric model, and its maximum power point is tracked by means of P&O algorithm, which is used to control the DC-DC step-up converter. The algorithm adopted to obtain the current reference of the DC-AC converter is based on the synchronous reference frame (SRF) method. Furthermore, an anti-islanding technique is implemented, in order to guarantee the safe operation of photovoltaic system. Simulation results are present to validate the proposed control strategy, and to verify the system feasibility.

A grid-connected photovoltaic power system with active power injection, reactive power compensation and harmonic filtering

This paper presents a study of a single-phase photovoltaic system, which is connected to the utility grid by means of a full-bridge DC/AC converter. The grid-connected system has active power injection ability from photovoltaic panels. Simultaneously, it performs reactive power compensation and harmonic current suppression generated by nonlinear loads. The photovoltaic system is implemented utilizing an equivalent electric model proposed in the literature. The algorithm adopted to obtain the current reference of the DC/AC converter is based on the synchronous reference frame (SRF), which is implemented along with a maximum power tracking technique. Simulation results are present to validate the proposed control strategy, as well as to verify the system feasibility.

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.

A three-phase four-wire grid-connected photovoltaic system using a dual unified power quality conditioner

This paper proposes a photovoltaic (PV) power generation system, which is implemented by means of multilevel converters. The PV system is connected to utility grid and operates as a unified power quality conditioner (UPQC). Thus, the PV-UPQC system injects active power into the there-phase grid and, simultaneously, performs active power-line filtering, in order to improve the power quality. By using dual compensating strategy, the proposed PV-UPQC system is implemented by means of two back-to-back NPC converters sharing the same dc-bus, which is directly connected to the PV array. Both voltage and current controllers are implemented in the synchronous rotating reference frame (dq0-axis), such that they operate interconnected with the maximum power point tracking algorithm, as well as the dc-bus voltage controller. Simulation results are presented to verify the static and dynamic performances of the grid-tied PV-UPQC system.

A comparative analysis between the PI and fuzzy controllers for current conditioning using a shunt active power filter

This paper presents a comparative analysis between the PI and fuzzy controllers applied in the current control loop of a single-phase shunt active power filter. The active filter is used to compensate the reactive power and suppress the current harmonics components of nonlinear loads. The compensation reference current is obtained from the synchronous reference frame algorithm. The total harmonic distortion of the compensated source current, the utility power factor and the digital processing time are used as evaluation criteria to determine the performance of the PI and fuzzy current controllers. Simulation and experimental results are also presented in order to validate the theoretical development.

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.

Grid-Connection strategy with reduced current spikes for grid-tie module-integrated converter

Module-Integrated Converters (MICs) are becoming an interesting option for residential photovoltaic (PV) applications because the PV modules are enabled s to work as plug and play devices. Reducing the costs and increasing the lifetime of the MICs are the main challenges for large-scale adoption of MIC technology. Particularly, current spikes during the connection of the MICs with the grid cause unnecessary oversizing of power components and lifetime decreasing. In this way, this paper presents a novel grid-connection strategy with reduced current spikes in order to achieve these goals. The proposed strategy does not require any controller transitions between the connection control mode and the steady-state control mode. Furthermore, the connection relay could be turned on at any instant without zero-cross switching constraints. Experimental results of a real prototype are provided in order to demonstrate the effectiveness of the proposed strategy.

Single-phase frequency detector algorithm applied to grid-connected power conditioning systems

This paper proposes a single-phase algorithm used to estimate the frequency, as well as the phaseangle of the utility grid. The algorithm uses self-tuning filters (STFs) operating in conjunction with low-pass filters (LPFs). The STFs are used to extract the fundamental components of the orthogonal voltages that represent a fictitious two-phase stationary reference frame (αβ-axes), while the LPFs are employed for frequency detection purpose. Therefore, both the STFs and the LPFs must be properly adjusted to avoid the compromising of the algorithm transient response. The operation principle of the proposed algorithm is presented, which is based on the frequency response analyses of both the STFs and the LPFs involved. Furthermore, simulation and experimental results are presented in order to validate the theoretical development, as well as verify the performance of the proposed synchronization algorithm under utility grid disturbances, such as voltage harmonics, voltage sags and swells, phase jumps and frequency variations.