Abraham Marquez

Model Predictive Control: A Review of Its Applications in Power Electronics

Model-based predictive control (MPC) for power converters and drives is a control technique that has gained attention in the research community. The main reason for this is that although MPC presents high computational burden, it can easily handle multivariable case and system constraints and nonlinearities in a very intuitive way. Taking advantage of that, MPC has been successfully used for different applications such as an active front end (AFE), power converters connected to resistor inductor RL loads, uninterruptible power supplies, and high-performance drives for induction machines, among others. This article provides a review of the application of MPC in the power electronics area.

Extended State Observer-Based Sliding-Mode Control for Three-Phase Power Converters

This paper proposes an extended state observer (ESO) based second-order sliding-mode (SOSM) control for three-phase two-level grid-connected power converters. The proposed control technique forces the input currents to track the desired values, which can indirectly regulate the output voltage while achieving a user-defined power factor. The presented approach has two control loops. A current control loop based on an SOSM and a dc-link voltage regulation loop which consists of an ESO plus SOSM. In this work, the load connected to the dc-link capacitor is considered as an external disturbance. An ESO is used to asymptotically reject this external disturbance. Therefore, its design is considered in the control law derivation to achieve a high performance. Theoretical analysis is given to show the closed-loop behavior of the proposed controller and experimental results are presented to validate the control algorithm under a real power converter prototype.

Predictive Optimal Switching Sequence Direct Power Control for Grid-Connected Power Converters

Grid-connected power converters play a key role in several applications such as the integration of renewable energy sources and motor drives. For this reason, the development of high performance control strategies for this particular class of power converters has increasingly attracted the interest of both academic and industry researchers. This paper presents the predictive optimal switching sequence (OSS) direct power control (DPC) (OSS-DPC) algorithm for grid-connected converters. The OSS-DPC method belongs to the predictive-DPC family and provides the desired power references by calculating globally OSSs. To address computational and implementation issues, an efficient control algorithm, named reduced OSS-DPC, is introduced. The implementation of the proposed control strategy in a standard DSP is evaluated on a two-level power converter prototype working as a STATCOM. Experimental results show the algorithms potential to provide high performance during both transient and steady states.

Advanced control of a multilevel cascaded H-bridge converter for PV applications

The integration of renewable energy systems and specifically of solar photovoltaic (PV) systems into the grid has become an important issue in the last decade because of the huge expansion of new power plants. PV systems have experienced an important evolution in the overall efficiency and in the variety of locations from low power installations (PV roof systems in domestic and residential applications) to high-power power plants currently reaching up to 550 MW. This fact has led to the appearance of new PV converter topologies and, among them, multilevel converters are very attractive due to its good features such as high nominal power and high quality of output waveforms. In this paper, a multilevel cascaded H-bridge converter is used to directly integrate the PV arrays into the grid. The proposed controller implements independent MPPT algorithms for each H-bridge extracting all the possible power from the available irradiation. Simulation results are presented to demonstrate the good performance of the PV system. The proposed system is modular and can be easily scaled to reach higher power so it could be used in large PV plants just adding extra H-bridges to the converter.

Variable-Angle Phase-Shifted PWM for Multilevel Three-Cell Cascaded H-Bridge Converters

Multilevel cascaded H-bridge converters have become a mature technology for applications where high-power medium ac voltages are required. Normal operation of multilevel cascaded H-bridge converters assumes that all power cells have the same dc voltage, and each power cell generates the same voltage averaged over a sampling period using a conventional phase-shifted pulse width modulation (PWM) technique. However, this modulation method does not achieve good results under unbalanced operation per H-bridge in the power converter, which may happen in grid-connected applications such as photovoltaic or battery energy storage systems. In the paper, a simplified mathematical analysis of the phase-shifted PWM technique is presented. In addition, a modification of this conventional modulation method using variable shift angles between the power cells is introduced. This modification leads to the elimination of harmonic distortion of low-order harmonics due to the switching (triangular carrier frequency and its multiples) even under unbalanced operational conditions. The analysis is particularized for a three-cell cascaded H-bridge converter, and experimental results are presented to demonstrate the good performance of the proposed modulation method.

Predictive direct power control for grid connected power converters with dc-link voltage dynamic reference design

Development of control strategies for grid connected power converters is a fundamental aspect for applications such as integration of renewable energy sources, motor drives and energy storage systems. Hence, this topic has received significant attention from both academic and industry researchers. This paper presents the use of the Reduced Optimal Switching Sequence Direct Power Control (ROSS-DPC) together with a dynamic voltage reference design strategy for grid connected power converters. This predictive controller allows the converter to regulate the dc-link voltage reference and to track the instantaneous active and reactive power commands. Simulation results validates the proposed control strategy, which provides high performance during both transient and steady states.

Adaptive phase-shifted PWM for multilevel cascaded H-bridge converters for balanced or unbalanced operation

Among multilevel converters, the cascaded H-bridge topology is one of the most industrially accepted solution for multiple applications, mostly for motor drives and flexible AC transmissions systems. Besides, other applications are being considered taking advantage of its modularity. The conventional phase-shifted PWM is the common method to generate the power devices switching of the converter. However, the performance is poor when an unbalanced operation is present. In this paper, an adaptive modulation method is presented where the angle to be applied to the phase-shifted PWM modulator is not fixed, but it is variable and calculated in real time depending on the operational conditions. Some simulation results are presented in order to demonstrate the good performance of the system.

A Generalized Predictive control for T-type power inverters with output LC filter

In this paper a Model Predictive Control (MPC) strategy is proposed for a T-type power converter used for standalone applications. The proposal uses a Generalized Predictive control (GPC) strategy, a fast Space Vector Modulation (SVM) scheme and includes a dc-link capacitors voltage balancing approach. The GPC strategy proposed for the T-type converter involves developing a system of dynamic equations for the output LC filter and load. Then, they are transformed to a Controlled Auto-Regressive and Moving-Average (CARIMA) model in order to obtain a sequence of control signals, so that a cost function is optimized. A computationally efficient fast SVM is used to provide the reference output voltages. Additionally, a dc-link capacitor voltage balancing approach is included in order to ensure proper work of the T-Type power converter. The system performance is analyzed by means of simulation results.

FCS-MPC and observer design for a VSI with output LC filter and sinusoidal output currents

Voltage source inverter (VSI) with output LC filter can be used to generate sinusoidal output voltages with reduced low frequency harmonics content. This application is suitable for uninterruptible power supply (UPS) systems. Finite control set model predictive control (FCS-MPC) has proved to be a good candidate for controlling such kind of devices. FCS-MPC relies on accurate system model to achieve high performance. However, output load is not always known for UPS applications. Under this condition, the use of observers to estimate the output load currents is a good solution. In this paper, a FCS-MPC strategy using an unknown input observer (UIO) is assessed. To design the UIO, the nature of the output load has been considered. This paper is focused on output loads with sinusoidal output currents. Two different UIO are evaluated. The first one uses a conventional approach and the second one takes into account the sinusoidal nature of the output load currents. Experimental results in a VSI prototype show that the second approach can provide superior performance independently of the output load connected to the power inverter.

Adaptive phase-shifted PWM for multilevel cascaded H-bridge converters with large number of power cells

Cascaded H-bridge multilevel converters are usually applied for high-power systems with independent dc sources. It can be used as PV inverter or to operate independent battery stacks. In these cases, as each dc source can be working at different operational points, conventional modulators lead to high distorted output waveforms degrading the converter performance. In this paper, a modulation method as a modified version of conventional phase-shifted PWM is presented when the CHB converter has a large number of power cells. This method is an extension of a previous technique only suitable for CHB converters with three power cells per phase. Simulation results show the good performance of the proposal with higher number of cells.