Pablo Acuna

Improved Active Power Filter Performance for Renewable Power Generation Systems

An active power filter implemented with a four-leg voltage-source inverter using a predictive control scheme is presented. The use of a four-leg voltage-source inverter allows the compensation of current harmonic components, as well as unbalanced current generated by single-phase nonlinear loads. A detailed yet simple mathematical model of the active power filter, including the effect of the equivalent power system impedance, is derived and used to design the predictive control algorithm. The compensation performance of the proposed active power filter and the associated control scheme under steady state and transient operating conditions is demonstrated through simulations and experimental results.

Selective Harmonic Elimination Model Predictive Control for Multilevel Power Converters

In this study, a model predictive control (MPC) strategy that combines finite-control-set MPC with selective harmonic elimination (SHE) modulation pattern in its formulation is proposed to govern multilevel power converters. Based on a desired operating point for the system state (converter current reference), an associated predefined SHE voltage pattern is obtained as a required steady-state control input reference. Then, the cost function is formulated with the inclusion of both system state and control input references. According with the proposed reference and cost function formulation, the predictive controller prefers to track the converter output current reference in transients, while preserving the SHE voltage pattern in steady state. Hence, as evidenced by experimental results, a fast dynamic response is obtained throughout transients while a predefined voltage and current spectrum with low switching frequency is achieved in steady state.

Multi-Cell High-Current Rectifier

A multi-cell rectifier (MC) structure is presented. The topology is based on power cells implemented with IGCTs thus replacing the SCR standard industry solution for the past 35 years. This rectifier is a reliable, compact, efficient, non-polluting alternative and cost effective solution for electrolytic applications. It injects quasi-sinusoidal input currents and provides unity power factor without the use of passive or active filters. A complete evaluation based on IEEE standards 493-1997 and IEEE C57.18.10 for average down time, failures rates and efficiency is included. For comparison purposes results are shown against conventional systems known for their high efficiency and reliability

Model Predictive Control for Single-Phase NPC Converters Based on Optimal Switching Sequences

In this paper, a model predictive control (MPC) based on optimal switching sequences (OSSs) for a single-phase grid-connected full-bridge neutral-point-clampled (NPC) power converter is presented. The predictive control algorithm is formulated in terms of OSSs, which was originally proposed to govern three-phase power converters. In this paper, the OSS concept is extended to control single-phase power converters. The proposed MPC algorithm belongs to the continuous control set MPC and is able to provide fixed switching frequency while handling system constraints. The proposed algorithm has been experimentally tested in an NPC power converter prototype. Experimental results show the desired fixed switching behavior in the steady-state condition and the intrinsic fast dynamic provided by MPC during transients. Furthermore, the test outcomes demonstrate the robustness of the proposed controller under large system parameter deviations.

Model Predictive Switching Pattern Control for Current-Source Converters With Space-Vector-Based Selective Harmonic Elimination

This paper presents a model predictive switching pattern control (MPSPC) for a current-source converter (CSC), which achieves superb low-order harmonics elimination performance in steady state and improved transient responses. Based on a proposed space-vector-based selective harmonic elimination (SHE) method and prediction of load current at the next sampling instant, MPSPC prefers to following a precalculated SHE-pulse width modulation (PWM) pattern in steady state, and governing the CSC through a model predictive control (MPC) approach during transients. In comparison with existing schemes, the advantages of MPSPC are threefold: First, quantization error, introduced by a constant sampling frequency in MPC and degrading steady-state low-order harmonic elimination, is mitigated in the proposed scheme. Second, there is no weighting factor in the cost function, as used in existing schemes. Finally, MPSPC is totally realized based on one-step prediction, which simplifies the structure of the scheme. Both simulation and experimental results verify the steady state and dynamic performance of MPSPC with different SHE-PWM patterns.

Multistep Model Predictive Control for Cascaded H-Bridge Inverters: Formulation and Analysis

In this paper, a suitable long prediction horizon (multistep) model predictive control (MPC) formulation for cascaded H-bridge inverters is proposed. The MPC is formulated to include the full steady-state system information in terms of output current and output voltage references. Generally, basic single-step predictive controllers only track the current references. As a distinctive feature, the proposed MPC also tracks the control input references, which in this case is designed to minimize the common-mode voltage (CMV). This allows the controller to address both output current and CMV targets in a single optimization. To reduce the computational effort introduced by a long prediction horizon implementation, the proposed MPC formulation is transformed into an equivalent optimization problem that can be solved by a fast sphere decoding algorithm. Moreover, the benefits of including the control input references in the proposed formulation are analyzed based on this equivalent optimization problem. This analysis is key to understand how the proposed MPC formulation can handle both control targets. Experimental results show that the proposal provides an improved steady-state performance in terms of current distortion, inverter voltages symmetry, and CMV.

Predictive Control of Cascaded H-Bridge Converters Under Unbalanced Power Generation

This paper presents a predictive control strategy for grid-connected cascaded H-bridge (CHB) converters under unbalanced power generation among each converter phase. The proposed controller belongs to the finite-control-set model predictive control (FCS-MPC) family and is designed to extract unbalanced power from each CHB converter phase while providing balanced power to the grid. The key novelty of this strategy lies in the way the unbalanced power generation among the phases is explicitly considered into the optimal control problem. Power balance is achieved by enforcing the CHB converter to work with a suitable zero-sequence voltage component. The proposed predictive controller is directly formulated in the original abc-framework to account for the common-mode voltage. Simulation and experimental results are provided to verify the effectiveness of the proposed FCS-MPC strategy.

On Improving Phase-Shifted PWM for Flying Capacitor Multilevel Converters

This letter proposes a phase-shifted pulse-width modulation (PS-PWM) technique for the flying capacitor (FC) multilevel converter that improves the quality of the line-to-line voltages. In traditional PS-PWM, the line-to-line voltages include intervals that switch between nonadjacent voltage levels, which deteriorates the harmonic performance. The proposed PS-PWM constantly achieves line-to-line voltages with switching transitions between two adjacent levels. The proposed modulation technique is implemented using two sets of n evenly phase-shifted carriers that are alternatively applied depending on the instantaneous value of the reference signal of each phase-leg. Furthermore, it can be implemented in FC multilevel converters with any number of levels while maintaining natural capacitor voltage balance. Experimental results from a four-level FC converter prototype are presented.

Model predictive control of cascaded H-bridge inverters based on a fast-optimization algorithm

In this work, a Finite Control Set Model Predictive Control (FCS-MPC) strategy for Cascaded H-bridge (CHB) inverters is proposed. The key novelty of our proposal comes from the way the cost function is designed. Generally, in standard FCS-MPC formulations for power converters, the cost function only considers the current tracking error. In this proposal, the proposed cost function also takes into account the control input tracking error. This allows one to obtain a reduced common-mode voltage during the steady-state while achieving a fast dynamic response during transients, similarly to the one provided by standard FCS-MPC. To account for calculation time, a fast-optimization algorithm based on sphere decoding is also considered. To verify the performance of the proposed predictive strategy, simulation results for a three phase five-level CHB inverter governed by the proposed FCS-MPC are presented.

Improved active power filter performance for distribution systems with renewable generation

A predictive control algorithm specially developed for shunt active power filters aimed to compensate reactive power and current harmonics components is presented and analyzed. The proposed predictive control algorithm is implemented in a three-phase four-leg voltage-source inverter (4L-VSI). The use of a 4L-VSI allows the compensation of current harmonics, reactive power and neutral current harmonics generated by single-phase non-linear loads. A detailed mathematical model of the filter, including the effect of the power system equivalent impedance is derived and used to design the proposed predictive control algorithm. The proposed active power filter and associated control scheme performance and compensation effectiveness are demonstrated by simulation and with experimental results.