J.A. Sanchez

A Model-Based Direct Power Control for Three-Phase Power Converters

The direct power control (DPC) technique has been widely used as a control strategy for three-phase power rectifiers due to its simplicity and good performance. DPC uses the instantaneous active and reactive power to control the power converter. The controller design has been proposed as a direct control with a lookup table and, in recent works, as an indirect control with an inner control loop with proportional-plus-integral controllers for the instantaneous active and reactive power errors. In this paper, a model-based DPC for three-phase power converters is designed, obtaining expressions for the input control signal, which allow the design of an adaptive control law that minimizes the errors introduced by parameter uncertainties as the smoothing inductor value or the grid frequency. A controller design process, a stability study of the system, and experimental results for a synchronous three-phase power rectifier prototype are presented to validate the proposed controller.

Analysis of the Power Balance in the Cells of a Multilevel Cascaded H-Bridge Converter

Multilevel cascaded H-bridge (CHB) converters have been presented as a good solution for high-power applications. In this way, several control and modulation techniques have been proposed for this power converter topology. In this paper, the steady-state power balance in the cells of a single-phase two-cell CHB is studied. The capability to be supplied with active power from the grid or to deliver active power to the grid in each cell is analyzed according to the dc-link voltages and the desired ac output voltage value. The limits of the maximum and minimum input active powers for a stable operation of the CHB are addressed. Simulation results are shown to validate the presented analysis.

Conventional Space-Vector Modulation Techniques Versus the Single-Phase Modulator for Multilevel Converters

Space-vector modulation (SVM) is a well-suited technique to be applied to multilevel converters and is an important research focus in the last 25 years. Recently, a single-phase multilevel modulator has been introduced, showing its conceptual simplicity and its very low computational cost. In this paper, some of the most conventional multilevel SVM techniques have been chosen to compare their results with those obtained with single-phase multilevel modulators. The obtained results demonstrate that the single-phase multilevel modulators applied to each phase are equivalent with the chosen well-known multilevel SVM techniques. In this way, single-phase multilevel modulators can be applied to a converter with any number of levels and phases, avoiding the use of conceptually and mathematically complex SVM strategies. Analytical calculations and experimental results are shown, validating the proposed concepts.

Adaptive Vectorial Filter for Grid Synchronization of Power Converters Under Unbalanced and/or Distorted Grid Conditions

This paper presents a new synchronization scheme for detecting multiple positive-/negative-sequence frequency harmonics in three-phase systems for grid-connected power converters. The proposed technique is called MAVF-FLL because it is based on the use of multiple adaptive vectorial filters (AVFs) working together inside a harmonic decoupling network, resting on a frequency-locked loop (FLL) which makes the system frequency adaptive. The method uses the vectorial properties of the three-phase input signal in the αβ reference frame in order to obtain the different harmonic components. The MAVF-FLL is fully designed and analyzed, addressing the tuning procedure in order to obtain the desired and predefined performance. The proposed algorithm is evaluated by both simulation and experimental results, demonstrating its ability to perform as required for detecting different harmonic components under a highly unbalanced and distorted input grid voltage.

Improving transition between power optimization and power limitation of variable speed, variable pitch wind turbines using fuzzy control techniques

This paper presents an application of fuzzy controllers for improving wind energy capture for variable speed wind turbines. In recent works, it has been shown that variable speed wind turbines with torque and blade-pitch linear control provide an excellent performance of the closed loop system. However, this performance can be enhanced by using fuzzy control. In the present work, a computational fuzzy model is presented for a variable speed, variable pitch wind turbine. Simulation results show an excellent performance improving transition between power optimization and power limitation of the wind turbine, specially in the rated wind speed working conditions.

Controller design for a single-phase two-cell multilevel cascade H-bridge converter

In this paper is studied the single-phase two-cell multilevel cascade H-bridge power converter connected to the grid, acting as a synchronous rectifier. The power exchange process between the cells of the converter and the grid is analyzed. Based on this analysis and on the power converter model the stages of the controller design process are shown. A new controller for the cascade power converter is proposed, achieving the regulation of each DC-Link capacitor voltage towards its reference. The proposed controller includes a repetitive scheme in the current tracking loop, providing low current harmonic content and almost unity power factor. Simulation results have been carried out in a 10 kVA single-phase two-cell multilevel cascade H-bridge power converter model to illustrate the good performance of the proposed controller.

A 800 kW wind-diesel test bench based on the MADE AE-52 variable speed wind turbine

A field work have been made about the practical installation of a wind-diesel autonomous power system. A remarkable innovation on the control of the latter wind-diesel system is the ability of taking advantage of the kinetic energy available from the wind turbine. With such an extra energy, a power quality improvement can be achieved in the presence of load commutations. Besides of that, a convenient power sharing out can be obtained, allowing a high renewable energy penetration and fuel savings. Several results show the behaviour of the whole system, apart of the power quality improvement.

A new fuzzy logic controller to improve the captured wind energy in a real 800 kW variable speed-variable pitch wind turbine

This paper presents an application of fuzzy controllers for improving the captured wind energy and the performance of variable speed wind turbines using fuzzy controllers. The simulated fuzzy model has been satisfactorily implemented using a programmable logic controller as the designed fuzzy controller. Transition between power optimization and power limitation of the wind turbine is greatly improved especially in the rated wind speed working conditions. Fuzzy controller also permits to increase captured wind energy in low and high wind speed.

Digital Implementation Issues for a Three-Phase Power Converter Development Using a Repetitive Control Scheme

In this paper the digital implementation of the repetitive control scheme for the three-phase two-level power converter is investigated. The proposed controller has an outer control loop to regulate the output capacitor voltage and an inner control loop for the current tracking process, which is composed of a damping term plus a repetitive control scheme, with the aim to achieve unity power factor and low THD content at the input currents. The repetitive control scheme consists on a negative feedback array of a single delay line plus a feedforward path. The implementation in a digital signal processor of the repetitive term has some issues that are pointed out in this paper. An adaptation rule to the delay parameter of the repetitive controller is proposed in order to improve the system behavior. The experimental results have been carried out in a 30 kVA three- phase power converter prototype to illustrate the good performance of the digital implementation of the controller, including a comparative study of the system behavior under the repetitive controller with the theoretical and the modified delay parameter.

Optimized Direct Power Control Strategy using Output Regulation Subspaces and Pulse Width Modulation

In this paper, a direct power control (DPC) using output regulation subspaces (ORS) for a three-phase two-level converter is presented. An optimal controller design and the use of optimized modulation techniques permit to improve the system performance minimizing the necessary grid-connection inductance. ORS plus proportional controllers are proposed for the generation of the reference vector to decrease active and reactive power errors and to achieve unity power factor. The generation of the reference vector is carried out thanks to simple pulse width modulation techniques. The computational cost of the proposed control is really low and all the calculations can be done online allowing its implementation in low cost microprocessors. Simulation and experimental results are shown in order to illustrate the good performance of the proposed control strategy