This article presents a hierarchical finite-set model predictive control (MPC) scheme to enable autonomous operation and self-balancing cascaded multilevel inverter. The proposed approach is an alternative to MPC scheme based on a generic cost function, which in some applications is ill fit or challenging to design. The proposed controller has a hierarchical framework to eliminate the overall cost function optimization and associated weight factor design stage of the control objectives. The control formulation approach allows for multiobjective optimization with a cost-tolerance framework. The concept is well suited to simplify the control design stage of cascaded H-bridge inverters at the grid-edge with advanced functionality. The control scheme achieves active and reactive power control with switching event reduction while equalizing power draw from the independent voltage sources. The latter of these objectives is made possible by the proposed hierarchical approach to the control objective tracking. The control is modularized for each phase, making the system robust to unbalanced grid conditions. The concept is explained in depth in simulation, and then tested experimentally on hardware.

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Hierarchical Model Predictive Control of Grid-Connected Cascaded Multilevel Inverter

It is well-known that the presence of non-linear loads in the distribution system can impair the power quality. The problem becomes worse in microgrids and power electronic-based power systems as the increasing penetration of single-phase distributed generation may result in a more unbalanced grid voltage. Shunt active power filters (SAPFs) are used for improving the power quality and compensating for the unbalance grid voltage. This study presents a modification of the classical control structure based on the finite control set model predictive control (FCS-MPC). The proposed control structure can retain all the advantages of FCS-MPC, while improving the input current quality. Furthermore, a computationally efficient cost function based on only a single objective is introduced, and its effect on reducing the current ripple is demonstrated. The presented solution provides a fast response to the transients as well as compensates for the unbalanced grid voltage conditions. A straightforward single loop controller is compared to the conventional way of realising the active power filters, which is based on space vector pulse width modulation. The simulation results have been obtained from MATLAB/SIMULINK environment, while the obtained experimental results, utilising a 15 kVA power converter, highlight the effective performance of the proposed control scheme and verifies the introduced MPC-based method as a viable control solution for SAPFs.

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Harmonics mitigation and non-ideal voltage compensation utilising active power filter based on predictive current control

Finite-control-set model-based predictive current control (FCS-MPCC) technique is distinguished by a variable switching frequency which causes high harmonic distortion a low sampling frequency. This latter could be considered an undesired behavior for active power filter for grid-connected applications. To overcome this issue, this paper proposes a modulated FCS-MPCC applied to a three-phase four-wire active power filter based on H-bridge converter. Simulation results are developed to demonstrate the efficiency of the proposed modulated FCS-MPCC comparing with classic FCS-MPCC, thus concluding the advantages and limitations of each technique at transient and steady states.

Modulated Predictive Current Control Technique for a Three-Phase Four-Wire Active Power Filter based on H-bridge Two-Level Converter

recently, the finite control set model predictive control (FCS-MPC) has obtained a lot of attention for power converter control due to its advantages of high dynamic performance and multi-objective capability. However, it poses a challenge for the current processors directly applying this control to the multilevel inverter in real-time application. Especially for CHB-STATCOM multilevel inverter, there are a huge number of switching combinations and redundancies due to its topology structure. Real-time searching for the optimal switching state among the extremely large candidate pool through exhaustive search algorithm is almost impossible especially when the inverter output voltage levels increases. To end this problem, this paper has presented a new fast FCS-MPC formulation scheme based multilevel CHB-STATCOM. Instead of resorting to existing heuristic optimization algorithms, the FCS-MPC is reformulated mathematically to a matrix problem that can be easily solved on-line. The proposed single step FCS-MPC formulation is validated through simulation based on a seven levels CHB-STATCOM. It has been shown that the proposed single step MPC has the advantages of fast current tracking, minimum CMVphase-shiftedand good voltage balancing capability. Compared with the existing FCS-MPC schemes, the computational burden of the proposed MPC formulation is largely reduced which makes it more suitable for multilevel CHB-STATCOM. Moreover, the proposed FCS-MPC formulation can be easily developed and applied to other multilevel topologies with a large number of voltage levels and redundancy.

A New Fast Formulation of Model Predictive Control For CHB STATCOM

The optimal sizing of the unified power quality conditioner (UPQC) system has been investigated in this paper. The optimal VA ratings of the transformer and series/shunt converter of the UPQC system are designed by a two-level algorithm. The UPQC-P and UPQC-VAmin based systems are chosen as the benchmarks in this paper. Furthermore, the displacement angle control (DAC) is utilized to minimize the overall VA loading of the power converters for all operational points. Finally, the corresponding controllers are developed for the designed systems.

Two-Level Algorithm for UPQC Considering Power Electronic Converters and Transformers

Conventional model based predictive control for cascade H-bridge multilevel STATCOM produces a different switching pattern for different cells. As a consequence, stresses, DC-link imbalance and active power losses are generated among the cells. To solve the aforementioned issues, this paper proposes to include a switcher of redundant vectors on the conventional model based predictive method. Additionally, improve the performance in terms of total harmonic distortion and remain focus the reactive power compensation. Simulation results are analyzed to verify the effectiveness of this proposal.

Model based predictive control with switcher of redundant vectors for a cascade H-bridge multilevel STATCOM

Model predictive control techniques are characterized by a variable switching frequency which cause noise as well as large voltage and current ripple In this paper a predictive control strategy with a fixed switching frequency for a single-phase active power filter, namely modulated model predictive control, is proposed This technique produces modulated waveform at the output of the converter The feasibility of this strategy is evaluated using simulation results to demonstrate the advantages of predictive control, such as fast dynamic response and the easy inclusion of nonlinearities The constraints of the system are maintained but the performance of the system in terms of power quality is improved compared to the traditional model predictive control strategy

J. Pacher

Papers

Model based predictive control with switcher of redundant vectors for a cascade H-bridge multilevel STATCOM

Modulated model predictive current control for H-bridge two-level single phase active power filters STATCOM