Javier Morales

Sliding-Mode Control for a Three-Phase Unity Power Factor Rectifier Operating at Fixed Switching Frequency

This paper presents an improved variable hysteresis-band current-control in natural frame for a three-phase unity power rectifier. The proposed control algorithm is based on three decoupled sliding-mode controllers combined with three independent Kalman filters. The use of Kalman filters instead of a nonadaptive state observer improves the quality of the estimated signals in presence of noise, increasing the immunity of the control loop in noisy environments. To reduce drastically the computational load in the Kalman algorithm, a reduced bilinear model is derived which allows to use a Kalman filter algorithm instead of an extended Kalman filter. A fast output-voltage control is also presented which avoids output-voltage variations when a sudden change in the load or a voltage sag appears. Moreover, a fixed switching frequency algorithm is proposed which uses a variable hysteresis-band in combination with a switching decision algorithm, ensuring a switching spectrum concentrated around the desired switching frequency. The overall control proposal has been fully integrated into a digital signal processor. Selected experimental results are introduced to validate the theoretical contributions of this paper.

Model-Based Active Damping Control for Three-Phase Voltage Source Inverters With LCL Filter

This paper presents a robust model-based active damping control in natural frame for a three-phase voltage source inverter with LCL filter. The presence of the LCL filter complicates the design of the control scheme, particularly when system parameters deviation is considered. The proposed control method is addressed to overcome such difficulties and uses a modified converter model in a state observer. In this proposal, the converter model is modified by introducing a virtual damping resistor. Then, a Kalman filter makes use of this model to estimate the system state-space variables. Although the state estimates do not obviously match the real world system variables, they permit designing three-current sliding-mode controllers that provide the following features to the closed loop system: 1) robust and active damping capability like in the case of using a physical damping resistor; 2) robustness because the control specifications are met independently of variation in the system parameters; 3) noise immunity due to the application of the Kalman filter; and 4) power loss minimization because the system losses caused by the physical damping resistor are avoided. An interesting side effect of the proposed control scheme is that the sliding surfaces for each controller are independent. This decoupling property for the three controllers allows using a fixed switching frequency algorithm that ensures perfect current control. To complete the control scheme, a theoretical stability analysis is developed. Finally, selected experimental results validate the proposed control strategy and permit illustrating all its appealing features.

Model-Based Control for a Three-Phase Shunt Active Power Filter

This paper presents a robust model-based control in natural frame for a three-phase shunt active power filter. For the proposed control method, a linear converter model is deduced. Then, this model is used in a Kalman filter (KF) to estimate the system state-space variables. Even though the states estimation do not match the variables of the real system, it has allowed to design three sliding-mode controllers providing the following features to the closed-loop system: 1) robustness due to the fact that control specifications are met independently of any variation in the system parameters; 2) noise immunity, since a KF is applied; 3) a lower total harmonic distortion (THD) of the current delivered by the grid compared with the standard solution using measured variables; 4) the fundamental component of the voltage at the point of common coupling is estimated even in the case of a distorted grid; and 5) a reduction in the number of sensors. Thanks to this solution, the sliding surfaces for each controller are independent. This decoupling property of the three controllers allows using a fixed switching-frequency algorithm that ensures a perfect current control. Finally, experimental results validate the proposed control strategy and illustrate all its interesting features.

Sliding-mode control for a three-phase shunt active power filter in natural frame

This paper presents an improved variable hysteresis-band current-control in natural frame for a three-phase shunt active power filter. The proposed control algorithm is based on three decoupled sliding-mode controllers combined with three independent Kalman filters. The use of Kalman filters instead of a non-adaptive state observer improves the quality of the estimated signals in presence of noise, increasing the immunity of the control loop in noisy environments and also reducing the THD of the current delivered to the grid. The overall control proposal has been fully integrated into a digital signal processor. Selected experimental results are introduced to validate the theoretical contributions of this paper.

Active damping based on Ackermann's formula for a three-phase voltage source inverter with LCL filter

This paper presents an active damping method in natural frame for a three-phase voltage source inverter with LCL filter. The proposed method is based on the pole placement technique via Ackermanns formula. This approach is used to obtain the proper sliding surface vector coefficients to emulate a virtual resistor in series with the capacitor filter. Besides a well-known method in the literature have been used to obtain three decoupled controllers in natural frame. The stability is theoretically studied and experimental results shows the validity of this proposal.

Multi-objective optimized daily schedule for an efficient solar-based industrial microgrid

In this paper, an optimal daily management for a solar-based industrial microgrid is proposed by analyzing two different load profiles. For each profile, the first step is to find the optimum size of the battery bank in order to identify the best daily configuration. The second step is to solve a multi-objective optimization problem, which takes into account economic evaluation indices (such as the initial investment, replacement, maintenance cost and the cost related to selling or purchasing energy to or from the grid) as well as the loss of power-supply probability index for evaluating system reliability. To solve the multi-objective optimization problem, first the weighted-sum method is used to convert it into a single objective optimization problem. Second, the new formulation is solved using an enhanced version of the bacterial foraging algorithm.

Architecture and design of an inductive contactless energy transfer system with two mobile loads for residential applications

Inductive contactless energy transfer systems with multiple mobile loads are very complex systems. Main challenges of these systems are to propose a suitable architecture and to design their power components. These challenges are particularly more noticeable in residential areas where various types of consumers (loads) are expected. This paper introduces a new architecture and design guidelines for a high-frequency resonant transformer operating with frequency modulation. The design process includes the effects of 1) the resonant frequency, 2) the magnetizing inductance, and 3) the characteristic impedance. The excellent performance of the designed system is validated by simulation results.

Dynamic model of a grid-connected three-phase inverter with slope voltage control

Three-phase inverters are the mostly used converters for connecting distributed generation sources to the main grid. Conventionally, these renewable sources must inject only its generated active power. Recently, reactive power injection has been included in some national grid codes. In voltage regulation, the conventional PI control can not be used. The whole system tends to instability when PI controllers work distributively for voltage regulation in different connection points along the grid. The slope voltage controller seems to be the best option to avoid these instabilities. The parameters design of the slope voltage controller is normally carried out by trial and error methodology due to lack of a small-signal model of the complete system. With this widely used methodology, the dynamic behavior can not be determined by the designer. This work develops a closed-loop small signal model of a grid-connected distributed generation source with voltage regulation capabilities. The derived mathematical model predicts accurately the system behavior in the frequency range of interest. This model can be used in future research for tuning the controller parameters with the aim of achieve predefined design objectives. The model has been validated through simulation results.

Sliding mode control for three-phase unity power factor rectifier with vector operation

This paper present a sliding mode control operating at fixed switching frequency for a three-phase unity power factor rectifier using the vector operation technique. The proposed method allows to find a large-signal converter dynamic model in order to transform a tree-phase system into two decoupled subsystems. With this technique only two sliding-mode controllers are needed and the neutral point voltage influence is removed from the controllers dynamics. A fast output-voltage control is used which avoids output-voltage variations when a sudden change in the load appears. Besides a variable hysteresis band control is used in order to fix the switching frequency of the sliding-mode controllers. Experimental results are provided using a fully-digital control system in order to validate the theoretical predictions.

Modeling and sliding mode control for three-phase voltage source inverters with vector operation

This paper presents a detailed analysis of a voltage source inverter with vector operation technique allowing to derive a transformation from natural-frame to a new frame called from heron γθ-frame. This transformation leads to obtain a dynamic model for the voltage source inverter in γθ-frame in order to apply an sliding mode control to the system. Due to the behavior of the vector operation, the switching losses of the system can be reduced. Also, the sliding mode control provides to the system a fast transient response against command reference changes and a good current tracking capability working at quasi-fixed switching frequency. Experimental results are provided using a fully-digital control system in order to validate the performance of the proposed system.