Model predictive current control of grid-connected neutral-point-clamped converters to meet low-voltage ride-through requirements

The low-voltage ride through (LVRT) requirement demands the wind power plants to remain connected to the grid in the presence of grid voltage dips, actively helping the network overall control to keep network voltage and frequency stable. Wind power technology points to increase power ratings. Hence, multilevel converters, as for example, neutral-point-clamped (NPC) converters, are well suited for this application. Predictive current control presents similar dynamic response and reference tracking than other well-established control methods, but working at lower switching frequencies. In this paper, the predictive current control is applied to the grid-side NPC converter as part of a wind energy conversion system, in order to fulfill the LVRT requirements. DC-link neutral-point balance is also achieved by means of the predictive control algorithm, which considers the redundant switching states of the NPC converter. Simulation and experimental results confirm the validity of the proposed control approach.Postprint (author’s final draft

Model Predictive Controlled Active NPC Inverter for Voltage Stress Balancing among the Semiconductor Power Switches

© Published under licence by IOP Publishing Ltd. This paper presents a model predictive controlled three-level three-phase active neutral-point-clamped (ANPC) inverter for distributing the voltage stress among the semiconductor power switches as well as balancing the neutral-point voltage. The model predictive control (MPC) concept uses the discrete variables and effectively operates the ANPC inverter by avoiding any linear controller or modulation techniques. A 4.0 kW three-level three-phase ANPC inverter is developed in the MATLAB/Simulink environment to verify the effectiveness of the proposed MPC scheme. The results confirm that the proposed model predictive controlled ANPC inverter equally distributes the voltage across all the semiconductor power switches and provides lowest THD (0.99%) compared with the traditional NPC inverter. Moreover, the neutral-point voltage balancing is accurately maintained by the proposed MPC algorithm. Furthermore, this MPC concept shows the robustness capability against the parameter uncertainties of the system which is also analyzed by MATLAB/Simulink

Model predictive current control of grid-connected neutral-point-clamped converters to meet low-voltage ride-through requirements

The low-voltage ride through (LVRT) requirement demands the wind power plants to remain connected to the grid in the presence of grid voltage dips, actively helping the network overall control to keep network voltage and frequency stable. Wind power technology points to increase power ratings. Hence, multilevel converters, as for example, neutral-point-clamped (NPC) converters, are well suited for this application. Predictive current control presents similar dynamic response and reference tracking than other well-established control methods, but working at lower switching frequencies. In this paper, the predictive current control is applied to the grid-side NPC converter as part of a wind energy conversion system, in order to fulfill the LVRT requirements. DC-link neutral-point balance is also achieved by means of the predictive control algorithm, which considers the redundant switching states of the NPC converter. Simulation and experimental results confirm the validity of the proposed control approach

Predictive control of a back-to-back NPC converter-based wind power system

© 2016 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other worksAs wind power technology points to increase power ratings, the implementation based on a permanent-magnet synchronous generator (PMSG) with a full-power converter is expanding its market share. Multilevel converters, as for example, neutral-point clamped (NPC) converters, are therefore well suited for this application. Predictive current control presents similar dynamic response and reference tracking than other well-established control methods, but working at lower switching frequencies, and providing extensive flexibility to apply either online or offline different control laws to the same plant. In this work, the predictive current control is applied to both sides of the back-to-back NPC converter connecting a permanent-magnet synchronous wind power generator to the grid. DC-link neutral-point balance is achieved by means of the predictive control algorithm, which considers the redundant switching states of the back-to-back NPC converter. Reduced number of commutations, current spectrum control, and compliance with the low-voltage ride-through (LVRT) requirement are carried out with the predictive control. The obtained experimental results confirm the suitability of the proposed control approach.Peer ReviewedPostprint (author's final draft

Investigation of Variable Switching Frequency in Finite Control Set Model Predictive Control on Grid-Connected Inverters

Finite control set model predictive control (FCS-MPC) has been widely studied and applied to the power converters and motor drives. It provides the power electronics system with fast dynamic response, nonlinear system formulation, and flexible objectives and constraints integration. However, its variable switching frequency feature also induces severe concerns on the power loss, the thermal profile, and the filter design. Stemming from these concerns, this article investigates the variable switching frequency characteristics of FCS-MPC on the grid-connected inverters. An intuitive relationship between the switching frequency and the magnitude of the converter output voltage is proposed through the geometry analysis, where the switching frequency is maximized when the converter output voltage is around one-third of the DC bus voltage and decreasing when the output voltage moves away from this value. The impacts of this variable switching frequency property on the power loss and current harmonics are also analyzed. Simulation and experimental results both verify the proposed property. With this intrinsic property, FCS-MPC can autonomously achieve a less-varying temperature profile of power modules and an improved reliability compared with the conventional control strategy

Articles publicats per investigadors de l'ETSEIB. Producció científica a Futur 2015

Postprint (author's final draft

Articles publicats per investigadors de l'ETSEIB. Producció científica a Futur 2015

Postprint (author's final draft

A Virtual Space Vectors based Model Predictive Control for Three-Level Converters

Three-phase three-level (3-L) voltage source converters (VSC), e.g., neutral-point clamped (NPC) converters, T-type converters, etc., have been deemed to be suitable for a wide range of medium- to high-power applications in microgrids (MGs) and bulk power systems. Compared to their two-level (2-L) counterparts, adopting 3-L VSCs in the MG applications not only reduces the voltage stress across the power semiconductor devices, which allows achieving higher voltage levels, but also improves the quality of the converter output waveforms, which further leads to considerably smaller output ac passive filters. Various control strategies have been proposed and implemented for 3-L VSCs. Among all the existing control methods, finite-control-set model predictive control (FCS-MPC) has been extensively investigated and applied due to its simple and intuitive design, fast-dynamic response and robustness against parameter uncertainties. However, to implement an FCS-MPC on a 3-L VSC, a multi-objective cost function, which consists of a term dedicated specifically to control the dc-link capacitor voltages such that the neutral-point voltage (NP-V) oscillations are minimized, must be designed. Nevertheless, selecting proper weighting factors for the multiple control objectives is difficult and time consuming. Additionally, adding the dc-link capacitor voltages balancing term to the cost function distributes the controller effort among different control targets, which severely impacts the primary goal of the FCS-MPC. Furthermore, to control the dc-link capacitor voltages, additional sensing circuitries are usually necessary to measure the dc-link capacitor voltages and currents, which consequently increases the system cost, volume and wiring complexity as well as reduces overall reliability. To address all the aforementioned challenges, in this dissertation research, a novel FCS-MPC method using virtual space vectors (VSVs), which do not affect the dc-link capacitor voltages of the 3-L VSCs, was proposed, implemented and validated. The proposed FCS-MPC strategy has the capability to achieve inherent balanced dc-link capacitor voltages. Additionally, the demonstrated control technique not only simplifies the controller design by allowing the use of a simplified cost function, but also improves the quality of the 3-L VSC output waveforms. Furthermore, the execution time of the proposed control algorithm was significantly reduced compared to that of the existing one. Lastly, the proposed FCS-MPC using the VSVs reduces the hardware cost and complexity as the additional dc-link capacitor voltages and current sensors are not required, which further enhances the overall system reliability