J. M. Sosa

A Model-Based Controller for the Cascade H-Bridge Multilevel Converter Used as a Shunt Active Filter

This paper presents the modeling and control processes of the single-phase cascade H-bridge multilevel converter used as a shunt active filter. Based on the obtained model, a controller is proposed to compensate for harmonic distortion and reactive power caused by a nonlinear load. These issues are solved by guaranteeing tracking of the line current toward an appropriately defined current reference. In the proposed approach, the current reference has been selected to be a signal proportional to either the line voltage or to its fundamental component; however, the proposed method can also be extended to other reference definitions. The proposed controller also includes voltage loops to guarantee regulation and balance of the involved capacitor voltages toward constant references. Experimental results on a 2-kVA prototype are presented to assess the performance of the proposed controller.

Direct Power Control of a Three-Phase Rectifier Based on Positive Sequence Detection

This paper presents a model-based controller for the direct control of real and reactive powers in a three-phase three-wire rectifier. As the unbalanced operation is considered, it is convenient to express the grid voltage in terms of both positive and negative sequences, in order to obtain a more complete description of the system. In particular, the positive sequence of the grid voltage is used as the transformation basis to reconstruct the average, i.e., a particular subset, of the conventional power definition. Based on this transformation, the regulation of the average of both real and reactive powers is possible without deformation of the grid current. The proposed controller also incorporates an adaptation mechanism to cope with parameter uncertainties. For comparison purposes, a conventional controller based on the complete definition of the instantaneous powers is also presented. Experimental results are provided to assess the performance of the proposed positive-sequence-based solution and compared with those obtained using a conventional controller.

Model based controller for an LCL coupling filter for transformerless grid connected inverters in PV applications

Voltage source inverters (VSI) connected to the grid by means of LCL filters offer benefits in the injection of active power into the grid, since they provide low harmonic distortion and a small size of the output filter. However LCL grid connected VSI must be designed in order to provide damping at the filter resonance frequency. This paper presents the design and analysis of a model based controller for an LCL coupling filter to inject active power into the grid for single phase photovoltaic transformerless applications. The control objectives are to provide closed-loop stability and to assure that the current to be injected follows a reference which is proportional to the grid voltage. Therefore, these objectives guarantee the active power injection to the grid. The proposed output feedback controller is based on the error model of the LCL filter and makes use only of the measurements of the output current of the inverter and the grid voltage.

A modulation strategy for single-phase HB-CMI to reduce leakage ground current in transformer-less PV applications

Single-phase cascade multilevel inverters are able to synthesize a sinusoidal AC voltage by means of multiple voltage levels at the output. This feature makes them appealing for photovoltaic (PV) applications given their low harmonic distortion and therefore, the small size of the filter used. However, the cascade multilevel inverter (CMI) is not directly functional in grid-connected PV transformer-less systems since the variable voltage across the stray capacitances embodied between the PV panel and the ground, may generate large leakage ground currents. In order to address this problem, it is proposed a modulation strategy to control the HB-CMI. This modulation strategy allows to operate the converter with very low leakage ground currents. Among the advantages of this CMI topology is that the amplitude of the output voltage, compared with a single HB topology, is higher and makes possible the power injection into the grid without a voltage boost stage. Numerical results show that the proposed modulation strategy reduces the leakage current and make the topology suitable for transformer-less PV applications.

Transformerless single-phase multilevel inverter for grid tied photovoltaic systems

Single-phase transformerless photovoltaic (PV) inverters have become more widespread in the solar energy market. This is due to the higher efficiencies they achieve together with the very low ground currents, which are their main advantages. In this paper a multilevel transformerless single-phase topology, based on the H-bridge with an active clamping, is proposed. Multilevel output voltage is achieved by using a split DC link and an active bidirectional switch to clamp the first leg in the H-bridge circuit. Therefore, a good behavior is achieved regarding total harmonic distortion (THD). A sinusoidal based pulse width modulation (PWM) strategy is also proposed to control the power converter. Numerical results show that the proposed PV inverter complies with the transformerless norms and regulations, operating with high efficiency, and being suitable for the transformerless PV inverters market.

Comparative analysis of single-phase grid connected transformerless photovoltaic inverter topologies

Transformerless inverters have change the way to connect a photovoltaic (PV) system to the electrical grid, due to their excellent performance in the energy conversion process. Nowadays, there are many different topologies for this kind of systems, that most have three main characteristics; high efficiency, constant common mode voltage and small size. Moreover, the control implementation must be simple and the cost should be low. Due to the wide variety of topologies, in this paper, a comparative analysis of efficiency in the case of three main single-phase topologies for transformerless grid connection is performed. The analysis is focus in the common mode currents and in the efficiency. The efficiency analysis includes an analysis of power losses distribution in the semiconductors which provide information to perform a good thermal design of the converter.

A model-based controller for a DC-DC boost converter with an LCL input filter

This paper studies a modified DC-DC boost converter where the input inductance has been replaced by an LCL filter. The voltage conversion ratio of the proposed converter is equivalent to the conversion ratio of a conventional boost converter, and it has only one active switching device. A controller is proposed to regulate the output voltage to a given reference with guaranteed reduced input current ripple, i.e., high-frequency current components are minimized at the input current source. Low current ripple is required when dealing with sensitive electric power sources such as fuel cells, batteries and electrolytic capacitors used at DC-links in power electronics applications. The controller design follows a Lyapunov approach, and provides active damping to the input LCL filter. Numerical simulations are presented to evaluate the closed-loop performance.

Control of mechanical systems on Lie groups based on vertically transverse functions

The transverse function approach to control provides a unified setting to deal with practical stabilization and tracking of arbitrary trajectories for controllable driftless systems. Controllers derived from that approach offer advantages over those based on more classical techniques for control of nonholonomic systems. Nevertheless, its extension to more general classes, such as critical underactuated mechanical systems, is not immediate. The present paper explores a possible extension by developing a framework that allows one to cast point stabilization problems for (left-invariant) second-order systems on Lie groups, including simple mechanical systems. The approach is based on “vertical transversality,” a property exhibited by derivatives of transverse functions. In this paper, we lay out the theoretical foundations of our approach and present an example to illustrate some of its features.

Comparative evaluation of L and LCL filters in transformerless grid tied converters for active power injection

This paper presents a comparison between two different passive filters for power converters tied to the grid with the application of active power injection. It addresses the L (inductive) filter and the LCL (inductive-capacitive-inductive) filter in single-phase power converters for which are presented the parameter design and modeling. These filters provide coupling of the power converter to the electrical grid and mitigation of high frequency harmonics which are inherent to switching power converters. It is obtained the state-space model and the transfer function of both type of filters and some design considerations for active power injection are presented. An evaluation, by means of numerical simulations, is presented for a single-phase H-bridge inverter with unipolar pulse width modulation for active power injection.

Analysis of buck converter control for automobile LED headlights application

This paper presents an electronic ballast based high power LEDs for headlights automobile. The ballast is based on a buck converter to feed a load of high power LED. The load is divided into five high power LED (10W), in automobile lighting systems rapid changes of lighting is required (power changes), therefore the buck converter must deliver constant voltage levels to changes in power and further the current necessary to maintain a flow of light required. To solve this problem this paper proposes a control law for buck converter control, which maintains a fixed voltage level for the different power (10.9W, 21.8W, 32.7W, 43.6W, 54.5W) dynamic response to these changes is fast and constant levels of current and luminous flux at each change of load is maintained.