Allan F. Cupertino

A novel adaptive current harmonic control strategy applied in multifunctional single-phase solar inverters

The inverter multifunctional operation is based on the harmonic current compensation, generated by nonlinear loads. The traditional harmonic detection methods tracks all harmonic contents of the load current and the control tuning tends to be complex with low flexibility. In many works, the proportional resonant (PR) controllers are used to control the inverter current reference. However, one PR controller needs to be designed for each harmonic frequency and this fact increases the control algorithm complexity. Therefore, this work proposes a novel adaptive current harmonic control strategy applied in multifunctional single-phase solar inverters. The strategy is based on a novel detection method of the harmonic load current. The harmonic current detection method is frequency adaptive and able to detect the load harmonic current with higher amplitude. This method consists in a cascade association of two phase-locked loop based on second order generalized integrator (SOGI-PLL). The detected frequency is used as feedback by the proportional resonant controller. Therefore, only two PR controller are required: one to track the fundamental component and another to track the harmonic component with higher magnitude. Simulation and experimental results show the performance of the proposed control strategy, improving significantly the grid current quality.

Adaptive saturation for a multifunctional three-phase photovoltaic inverter

This paper presents an inverter control scheme, based on proportional-resonant controllers, where the inverter works in multifunctional operation. In this case, the reactive power and harmonic compensation of the load are ancillary services. A resonant control is implemented in stationary reference frame (αβ), where is not necessary the use of a phase-locked loop (PLL). The instantaneous power theory (IPT) is used to detect the harmonic current and reactive power of the load. These components are used as references in the inverter control strategy. Most important fact and less related in literature is the inverter current limitation strategy. Thus, this work introduces a dynamic saturation scheme for a multifunctional three-phase inverter. This strategy possibilities partial or total reactive power and harmonic current compensation without injection of low order harmonics, ensuring that the inverter current does not exceeds the rated current.

Single-phase multifunctional inverter with dynamic saturation scheme for partial compensation of reactive power and harmonics

Single and three-phase photovoltaic inverters are essential components of the photovoltaic (PV) systems to extracting the PV power and injecting it into the grid. Thus, in order to extract the maximum power of the solar array for various solar irradiation tracks, it is used a maximum power point tracker (MPPT) algorithm. Due to variations in solar irradiance, inverters have a current margin, which is not explored during the day. Thereby, many works have proposed the multifunctional operation. This concept consists in aggregate to the inverter control strategy other functions, such as harmonics and reactive power compensation. However, most important fact and less related in literature is the necessity of techniques to compensate partially reactive power and harmonics of the load, ensuring that the inverter works below the rated current. Hence, the present work proposes a current dynamic saturation scheme in order to compensate partially reactive power and harmonics of the load during the multifunctional operation. Simulations show that the dynamic saturation prevents the inverter to inject low-order harmonics, while ensuring the operation below the system rated current. Furthermore, control performance is evaluated for five grid-connected PV system in parallel association, in order to show the effectiveness of proposed control strategy for various dispersed PV systems in the grid. To ensure that the proposed method is applied with the maximum efficiency of the PV system, this work compares, during inverter multifunctional operation, the instantaneous and dynamic efficiency between three MPPT algorithms proposed in literature: perturb and observe; dP - perturb and observe; modified perturb and observe.

Operation of a high gain bidirectional DC-DC converter for photovoltaic on-grid systems

The aim of this paper is to present a dc-dc converter with high-stepping ratio for photovoltaic (PV) systems operating in parallel arrangement. The converter utilizes a resonant LC circuit to continue provide an increasing voltage at the output terminals by rotating the polarity of the capacitor using a thyristor based H-bridge. Compared with the existing converters, the proposed circuit reach higher voltage gains with low switching frequency using simple circuitry. It works efficiently with minimal switching loss even dealing with high currents. The prototype has shown the usefulness of the converter for low input voltage applications, mainly when a string of photovoltaic panels is connected in parallel, with the possibility to power in a commercial inverter.

Comparison of MPPT strategies in battery charging of photovoltaic systems

In photovoltaic standalone systems it is crucial to absorb most of the available energy. Thus, in order to extract the maximum power of a solar panel for a given set of climatic conditions, it is used maximum power point tracker (MPPT). The MPPT consists in a power converter which controls the solar panel voltage. In this context, this work compares the instantaneous and dynamic efficiency of three MPPT algorithms proposed in literature: perturb and observe, dP - perturb and observe and modified perturb and observe used in a photovoltaic standalone systems. The system analyzed is composted by a 48 W solar panel, a battery of 60 Ah and a charger based on a buck converter. During solar irradiance variations the algorithms presented different instantaneous efficiencies, what can produce reduction in energy absorbed during cloudy days.

Lifetime evaluation of a multifunctional PV single-phase inverter during harmonic current compensation

Abstract The multifunctional operation of photovoltaic (PV) inverters consists in providing ancillary services to the power grid, such as reactive power injection, harmonic current compensation and frequency regulation. However, it is necessary to quantify the effect of those extra activities on the PV inverter life consumption. This work analyzes the life consumption of a single phase multifunctional inverter during harmonic current load compensation. The mission profile of harmonic current, irradiance and temperature are considered by the lifetime model to obtain a more realistic estimation. Therefore, the power losses and thermal stress were evaluated on the semiconductors devices. In addition, rainflow method, Bayerers model and Palmgrem-Miners rules are used in the methodology. The results show that life consumption is correlated to the harmonic order, phase angle and harmonic amplitude. In addition, when the harmonic phase angle is equal to 180°, the life consumption can be lower than a conventional inverter in 9.5%. On the other hand, when the phase angle is 0°, the converter life consumption can increase in 15.2%.

Life consumption of a MMC-STATCOM supporting wind power plants: Impact of the modulation strategies

Abstract The increasing penetration of Wind Power Plants (WPPs) has several impacts on the power system operation, such as voltage instability. Under such conditions, the literature suggests the use of static synchronous compensators (STATCOMs). Additionally, the Modular Multilevel Converter (MMC) is featured as a very suitable topology for STATCOM application. Therefore, this paper contributes to the knowledge in the field by analyzing the effect of the modulation strategies in losses and lifetime of a 17 MVA MMC-STATCOM. These analyses use two well-know modulation strategies: Phase-Shifted Pulse-Width Modulation (PS-PWM) and Nearest-Level Control (NLC). The results indicate that both strategies have similar conduction losses, although PS-PWM has almost twice more switching losses. As a result, the PS-PWM has annual energy consumption 31.4% higher than NLC. Regarding the lifetime evaluation, the results show superior performance for the NLC, for cell-level and system-level, with lifetime 25.6 and 10.6 times longer than PS-PWM, respectively.

An improved solar array simulator topology based on LCL filter

Photovoltaic energy has gained prominence in the current context of energy generation. The fundamental element of a photovoltaic system connected to the electric grid is the electronic converter. In order to be marketed, electronic converters must be tested and certified in accordance with current standards. In the certification process, an equipment known as a solar array simulator (SAS) is used. This work presents the modeling and the control structure of a 10 kW SAS for tests of electronic converters for photovoltaic systems. The novelty introduced in this work is the insertion of a passive filter at the SAS output. The purpose of this filter is to reduce the output current ripple, which is directly influenced by the input capacitance of the inverter under test (uncertain variable). It is considered a structure with 2 stages that allows a greater flexibility in relation to the arrangements to be emulated. The results showed that with the use of a passive filter the topology presented operational advantages being able to represent the characteristics of the photovoltaic arrangement and a considerable reduction in the output current ripple of the simulator.

Power losses in photovoltaic inverter components due to reactive power injection

The grid power stability is significantly affected as a result of the net impact of many small photovoltaic (PV) generators, since there is an increase of PV systems connected to distribution systems. There are many ways to improve the system stability, regarding voltage regulation. Some work proposes to use the PV inverter idle capacity to support reactive power to the grid. The main drawback of this solution is the increase of losses in the converter during this additional functionality. Therefore, this paper analyzes the power losses in the PV inverter components (IGBTs, diodes, a dc-link capacitor and damping resistance) during both active and reactive power injection. Simulations considering a 5kW three-phase PV inverter are performed with focus in conduction and switching losses, besides, the temperature in the semiconductor devices.