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

© 1982-2012 IEEE. 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 algorithm's potential to provide high performance during both transient and steady states

Robust Deadbeat Predictive Power Control with a Discrete-Time Disturbance Observer for PWM Rectifiers under Unbalanced Grid Conditions

© 2012 IEEE. This paper presents a robust deadbeat predictive power control (DPPC) for pulsewidth modulation (PWM) rectifiers with the consideration of parameter mismatches under unbalanced grid conditions. First, conventional DPPC is modified to extend its application to both ideal and unbalanced grid conditions. Second, a tracking error of the modified DPPC with inaccurate grid-side impedance is analyzed. Third, a discrete-time power disturbance observer (DPDO) is designed to achieve accurate power control with mismatched parameters. The designed DPDO can predict complex power at the next sampling instant and estimate system disturbance simultaneously. Therefore, the DPDO can contribute to eliminate the steady-state tracking error resulting from disturbances caused by inaccurate parameters and compensate one-step delay in digital implementation. Although satisfactory steady-state performance can be obtained with modified DPPC and DPDO, transient performance still deteriorates significantly with an inaccurate value of the grid-side inductance. Thus, an online adaptive method to estimate mismatched inductance is finally developed based on the proposed DPDO. Both DPPC and DPDO are implemented in the stationary reference frame without coordinate transformation. Theoretical analysis confirms that the proposed DPDO can track disturbance without phase lag or magnitude error. Experimental tests and comparative studies with a prior DPPC on a two-level PWM rectifier validate the effectiveness of the proposed scheme

三相電圧形インバータ用モデル予測制御のFPGAによる実装手法の開発： モデルベース設計手法，HILシミュレーション，FPGAリソース最適化

Model predictive control (MPC), a modern switching control method, has gained considerable interest in performing control objectives of power converters. One of the categories in a wide family of MPC is finite control set-MPC (FCS-MPC) that utilizes the discrete-time model of a power converter having a limited number of switching states for solving the optimization problem online. In FCS-MPC, a discrete-time model of the power converter is used to predict future values of control parameters and an optimization function (cost function) is used to select the optimized switching state of the converter. High computational requirements of the FCS-MPC is a concern for the system implementation. Field-programmable gate array (FPGA) is an effective alternative to handle the computational burden of the control algorithm because of its parallel processing nature. In general, the MPC algorithm is performed through a programming approach either for DSP or FPGA. However, digital resource utilization is another concern for the development and real-time system implementation. Digital resource optimization requires a high value of in-depth knowledge to write the hardware descriptive code. Moreover, debugging is also a tedious and time-consuming task that is not appropriate for the development and analysis of the controller as well as prototyping. In this work, the implementation of FCS-MPC is performed by adopting the modelling approach in a digital simulator that provides a virtual FPGA environment for system development. In addition, hardware-in-the-loop (HIL) technique is used for testing of controller performance before experimental validation. The current prediction is a core part of the FCS-MPC and a coefficient used for the current prediction that is computed using the system parameters affects the controller performance. In this work, a novel approach is presented to update the predictive model, called an adaptive predictive model, corresponding to a change in the load resistance while keeping a fixed value of load inductance. The fixed, approximated and adaptive values of a coefficient are adopted for current prediction to investigate the behaviour of the controller. The performance of the FCS-MPC depends on the sampling frequency used for the discretization of the converter model that governs the switching frequency of the converter. The performance can be improved with higher sampling frequency, however, resulting in higher switching frequency that ultimately increases the switching losses in the power devices. Apart from that, a non-zero steady-state error is one of the concerns of the FCS-MPC implementation. In general, dedicated constraints for the reduction in average switching frequency and SSE are incorporated inside a cost function in conventional FCS-MPC. Nevertheless, that ultimately increases the computational burden. A modified cost function based on a novel constraint is proposed for the improvement in SSE as well as a reduction in the switching frequency using the modified FCS-MPC approach. To validate the performance of the proposed constraint, a comparative analysis is presented with the constraint of a change in switching state considering indices SSE as well as average switching frequency. Moreover, the different load currents and sampling time are considered to evaluate SSE considering similar load current ripples. To evaluate the robustness of the FCS-MPC algorithms, a step-change in reference current is considered for the demonstration of dynamic performance. Moreover, an analytical approach based implementation strategies is proposed for FPGA resource optimization of the FCS-MPC development in a digital simulator for the FPGA-based system implementation. The implementation of FCS-MPC in stationary αβ and rotating dq frames is adopted for in-depth system analysis. The implementation strategies are compared based on FPGA resource requirements for the FCS-MPC in both frames corresponding to the fixed, approximated and adaptive coefficient values of the predictive model. The optimum design based controller model is used for the FPGA-based experimental system implementation. Xilinx system generator (XSG) as a digital simulator that is an integrated platform with MATLAB/Simulink is used for the development of the controller. The FCS-MPC is implemented for the load-side current control of a three-phase voltage source inverter (VSI) system. A Xilinx FPGA board (Zedboard Zynq Evaluation and Development Kit) is used for the HIL simulation as well as the real-time system implementation.九州工業大学博士学位論文 学位記番号：生工博甲第367号 学位授与年月日：令和2年3月25日1: INTRODUCTION| 2: FINITE CONTROL SET - MODEL PREDICTIVE CONTROL| 3: MODEL-BASED DESIGN AND HIL SIMULATION| 4: ADVANCED FCS?MPC: ADAPTIVE PREDICTIVE MODEL AND MODIFIED COST FUNCTION| 5: FPGA RESOURCE OPTIMIZATION| 6: CONCLUSIONS AND FUTURE WORK九州工業大学令和元年

Low-complexity dual-vector-based predictive control of three-phase PWM rectifiers without duty-cycle optimization

© 2013 IEEE. The conventional model-predictive-based direct power control (MPDPC) of the three-phase full-bridge AC/DC converters chooses the best single voltage vector for the following control period, which results in variable switching frequency and power distortion, and thus a relatively higher sampling frequency is needed to achieve acceptable results. This paper proposes a simplified dual-vector-based predictive direct duty-cycle-control (SPDDC) with an additional zero vector implemented in contrast to the MPDPC. With the same best vector selection method, the proposed strategy has retained the control simplicity with just one more step added and much better control performance as well as a fixed switching frequency in comparison to the MPDPC. On the other hand, the duty-cycle optimization procedure is eliminated while the negative duration issue is essentially resolved compared with the conventional dual-vector-based model predictive duty-cycle-control (MPDCC). Comprehensive comparisons of various control methods by numerical simulation and experimental testing show that the SPDDC can achieve better steady state and dynamic performance than the MPDPC and simpler algorithms than the MPDCC

Power Electronics Applications in Renewable Energy Systems

The renewable generation system is currently experiencing rapid growth in various power grids. The stability and dynamic response issues of power grids are receiving attention due to the increase in power electronics-based renewable energy. The main focus of this Special Issue is to provide solutions for power system planning and operation. Power electronics-based devices can offer new ancillary services to several industrial sectors. In order to fully include the capability of power conversion systems in the network integration of renewable generators, several studies should be carried out, including detailed studies of switching circuits, and comprehensive operating strategies for numerous devices, consisting of large-scale renewable generation clusters

Prädiktive Regelung und Finite-Set-Beobachter für Windgeneratoren mit variabler Drehgeschwindigkeit

This dissertation presents several model predictive control (MPC) techniques and finite-position-set observers (FPSOs) for permanent-magnet synchronous generators and doubly-fed induction generators in variable-speed wind turbines. The proposed FPSOs are novel ones and based on the concept of finite-control-set MPC. Then, the problems of the MPC techniques like sensitivity to variations of the model parameters and others are investigated and solved in this work.Die vorliegende Dissertation stellt mehrere unterschiedliche Verfahren der modellprädiktiven Regelung (MPC) und so genannte Finite-Position-Set-Beobachter (FPSO) sowohl für Synchrongeneratoren mit Permanentmagneterregung als auch für doppelt gespeiste Asynchrongeneratoren in Windkraftanlagen mit variabler Drehzahl vor und untersucht diese. Für die Beobachter (FPSO) wird ein neuartiger Ansatz vorgestellt, der auf dem Konzept der Finite-Control-Set-MPC basiert. Außerdem werden typische Eigenschaften der MPC wie beispielsweise die Anfälligkeit gegenüber Parameterschwankungen untersucht und kompensiert

Real-time grid parameter estimation methods using model based predictive control for grid-connected converters

In recent years, renewable and distributed generation (DG) systems have contributed towards an efficient and an economic way of transporting electricity to end-users as the generation sources are in general located nearer the loads. DG and renewable energy systems are modifying the old concept of distribution network by instigating a bi-directional power flow into the grid, facilitated through the use of power electronic grid-connected converters. A challenge associated with grid-connected converters arises when they are interacted with a grid that is not stiff, like weak micro grids. Small grid parameter variations in these systems can considerably affect the performance of the converter control and lead to higher values in current total harmonic distortion (THD) and loss of control and synchronization. Thus, the control of grid-connected power converters needs to be regularly updated with latest variation in grid parameters. Model Predictive Direct Power Control (MP-DPC) has been chosen as the control strategy for the work presented in this thesis due to its advantages over traditional control techniques such as multivariable control, no need of phase-locked loops (PLLs) for grid synchronization and avoidance of cascaded control loops. Two novel methods for estimating the grid impedance variation, and hence the grid voltage, are presented in this thesis along with a detailed literature review on control of grid-connected converters with special emphasis on impedance estimation techniques. The first proposed estimation method is based on the difference in grid voltage magnitudes at two consecutive sampling instants while the second method is based on a model-fitting algorithm similar to the concept of cost-function optimization in model predictive control. The proposed estimation methods in this thesis are integrated within the MP-DPC, therefore updating the MP-DPC in real-time with the latest variation in grid impedance. The proposed algorithms provide benefits such as: quick response to transient variations, operation under low values of short-circuit-ratio (SCR), robust MP-DPC control, good reference tracking to grid parameter variations and operation under unbalanced grid voltages. The thesis also presents the advantages and drawbacks of the proposed methods and areas where further improvement can be researched. The work presented has been tested on a three phase two-level grid-connected converter prototype, which is connected to a low voltage substation highly dominated by inductive component of grid impedance. It can be adapted and modified to be used for general grid impedance estimation, medium or high voltage applications, in case of multilevel grid-connected converter topologies or photo-voltaic (PV) grid-connected applications

A New DeadBeat-Based Direct Power Control of Shunt Active Power Filter with Digital Implementation Delay Compensation

Active Power Filter (APF) can significantly compensate the current harmonics produced by nonlinear loads. To do this feature, harmonic detection reference current generation play vital role. Direct Power Controller (DPC) has great harmony with instantaneous power compensation (PQ) algorithm as well as the ability to eliminate internal current loops. In addition, DeadBeat Controller (DBC) has high compatibility for digital implementation, superior control performance and fast dynamic response. However, DBC suffers from time delay linked to control action calculation and digital implementation. In this paper, a new deadbeat-based DPC method is proposed firstly to generate reference current and control of APF. Secondly, a simple and robust compensation method is proposed to eliminate aforementioned deadbeat delay thanks to the online/offline predictions. Several simulations are conducted in MATLAB/SIMULINK verified by experimental tests obtained from a DSP-based active power filter to illustrate the effectiveness and superior performance of the proposed control method. By employing the proposed control method, the Total Harmonic Distortion (THD) of grid current is decreased from 22% to 3% under steady state condition. While the dynamic response with proposed delay compensation validates significant transient response improvement.publishedVersionPeer reviewe