Model Predictive Control for Power Converters and Drives: Advances and Trends

Model predictive control (MPC) is a very attractive solution for controlling power electronic converters. The aim of this paper is to present and discuss the latest developments in MPC for power converters and drives, describing the current state of this control strategy and analyzing the new trends and challenges it presents when applied to power electronic systems. The paper revisits the operating principle of MPC and identifies three key elements in the MPC strategies, namely the prediction model, the cost function, and the optimization algorithm. This paper summarizes the most recent research concerning these elements, providing details about the different solutions proposed by the academic and industrial communitiesMinisterio de Economia y Competitividad TEC2016-78430-RConsejeria de Innovacion, Ciencia y Empresa (Junta de Andalucia) P11-TIC-707

Direct Torque Control for Silicon Carbide Motor Drives

Direct torque control (DTC) is an extensively used control method for motor drives due to its unique advantages, e.g., the fast dynamic response and the robustness against motor parameters variations, uncertainties, and external disturbances. Using higher switching frequency is generally required by DTC to reduce the torque ripples and decrease stator current total harmonic distortion (THD), which however can lower the drive efficiency. Through the use of the emerging silicon carbide (SiC) devices, which have lower switching losses compared to their silicon counterparts, it is feasible to achieve high efficiency and low torque ripple simultaneously for DTC drives. To overcome the above challenges, a SiC T-type neutral point clamped (NPC) inverter is studied in this work to significantly reduce the torque and flux ripples which also effectively reduce the stator current ripples, while retaining the fast-dynamic response as the conventional DTC. The unbalanced DC-link is an intrinsic issue of the T-type inverter, which may also lead to higher torque ripple. To address this issue, a novel DTC algorithm, which only utilizes the real voltage space vectors and the virtual space vectors (VSVs) that do not contribute to the neutral point current, is proposed to achieve inherent dc-link capacitor voltage balancing without using any DC-link voltage controls or additional DC-link capacitor voltages and/or neutral point current sensors. Both dynamic performance and efficiency are critical for the interior permanent-magnet (IPM) motor drives for transportation applications. It is critical to determine the optimal reference stator flux linkage to improve the efficiency further of DTC drives and maintain the stability of the drive system, which usually obtained by tuning offline and storing in a look-up table or calculated online using machine models and parameters. In this work, the relationship between the stator flux linkage and the magnitude of stator current is analyzed mathematically. Then, based on this relationship, a perturb and observe (P&O) method is proposed to determine the optimal flux for the motor which does not need any prior knowledge of the machine parameters and offline tuning. However, due to the fixed amplitude of the injected signal the P&O algorithm suffers from large oscillations at the steady state conditions. To mitigate the drawback of the P&O method, an adaptive high frequency signal injection based extremum seeking control (ESC) algorithm is proposed to determine the optimal reference flux in real-time, leading to a maximum torque per ampere (MTPA) like approach for DTC drives. The stability analysis and key parameters selection for the proposed ESC algorithm are studied. The proposed method can effectively reduce the motor copper loss and at the same time eliminate the time consuming offline tuning effort. Furthermore, since the ESC is a model-free approach, it is robust against motor parameters variations, which is desirable for IPM motors

A High-Power Medium-Voltage Open-Loop Induction Motor Drive for Industry Applications: Stability Analysis and Implementation

Due to their several advantages, induction motors are widely used for industrial applications today. The present study focuses on developing a robust high-power induction motor variable frequency drive. In order to test the algorithms of the motor control on an actual induction motor, it is important to first carry out simulation tests to verify and troubleshoot the control strategy. One of the most common software used for such a need is MATLAB/Simulink. To run such experiments requires a significant simulation time and at the same time must satisfy a certain level of accuracy. Therefore, one of the objectives of the thesis is to carry out a study on some of the ODE solvers of MATLAB/Simulink to choose the most efficient solver for the simulation tests of the motor control strategy. The fixed step solvers ode1, ode2 and ode4 and the variable step solvers ode45, ode113 and ode23 are studied in terms of the actual time taken to complete the simulations and the relative tolerance of each solver. Comparing the performance of the fixed step and variable step solvers it is evident that the variable step solvers outperformed the fixed step solvers in terms of both speed and accuracy. One of the most famous speed control strategies is the open loop V/Hz control. In this control method two modulation techniques were studied. This was the asynchronous modulation technique and the synchronous modulation technique. With the use of the asynchronous modulation technique subharmonics are introduced. To avoid the introduction of such harmful subharmonics the synchronous modulation technique is proposed. The synchronous modulation technique is implemented with the open loop V/Hz control strategy and simulation tests were carried out to verify the problem of subharmonics being removed. Another problem encountered with the open loop V/Hz control strategy is the presence of large current and torque oscillations of the motor at low to medium frequencies. This is due to the nonlinear interactions between the electrical and mechanical subsystems. To mitigate these unwanted oscillations a stability analysis of the open loop V/Hz control is carried out and a region of instability is determined. Two mitigation techniques are proposed in this thesis namely varying slope V/Hz control strategy and the active damping control strategy. The proposed techniques are verified and validated through simulation tests on a 7 MW medium voltage (MV) induction motor in MATLAB/Simulink and on a low voltage (LV) induction motor in laboratory without a mechanical load. Moreover, in this thesis it has been examined that with the consideration of the magnetic saturation of the motor, more stable operations are achieved. This is firstly verified in simulation where considering the magnetic saturation allowed the use of higher flux values providing more stable machine operations while at the same time allowing for a larger torque. With the experimental test on a 10-kW induction motor it was proved that the results obtained through simulations where more stable operations were seen as the value of the flux were increased were correct. In the power applications such as the ac-dc conversion for the above mentioned 7 MW medium voltage induction motor, a high total harmonic distortion (THD) can be seen in the primary currents with the use of the conventional diode-based ac-dc conversion. In addition, such a conversion does not permit the control of the dc link voltage and has not power factor correction. To overcome these shortcomings the Active Front End rectifier which uses IGBTs that can be electronically controlled is used. In the AFE, the waveform of the input current is monitored and is shaped to be sinusoidal as a result decreasing the THD. Another significant advantage of the AFE rectifier is its capability to handle regenerative power. In this thesis, two configurations of the AFE rectifier are studied. These two configurations include firstly the development of the AFE rectifier using a two-level three-phase inverter and secondly the development of the AFE rectifier with single phase H-bridge cells. From the comparison of the performance of the two configurations of the AFE it is seen that the AFE realised with the H Bridge cells and phase shifted secondary was the best in terms of the THD and the dc link voltage ripple. From these results the AFE realised with H Bridge circuits and phase shifted secondary is chosen for the operation of a real high-power induction motor controlled with the open loop V/Hz control strategy and equipped with the active damping technique for mitigating the current and torque oscillations

Power Converter of Electric Machines, Renewable Energy Systems, and Transportation

Power converters and electric machines represent essential components in all fields of electrical engineering. In fact, we are heading towards a future where energy will be more and more electrical: electrical vehicles, electrical motors, renewables, storage systems are now widespread. The ongoing energy transition poses new challenges for interfacing and integrating different power systems. The constraints of space, weight, reliability, performance, and autonomy for the electric system have increased the attention of scientific research in order to find more and more appropriate technological solutions. In this context, power converters and electric machines assume a key role in enabling higher performance of electrical power conversion. Consequently, the design and control of power converters and electric machines shall be developed accordingly to the requirements of the specific application, thus leading to more specialized solutions, with the aim of enhancing the reliability, fault tolerance, and flexibility of the next generation power systems

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

Evolutionary Gaps Stator Current Control of Multi-phase Drives Balancing Harmonic Content

Multiphase machines are increasingly used in research and industry applications due to their inherent advantages. Stator current control is a common strategy for this type of systems. The most important issue it must face is regulation of currents in the torque producing plane and the harmonic plane. For this task, finite control set model predictive control (FCS-MPC) constitutes an interesting alternative to methods using modulation. However, the implementation of FCS-MPC is characterized by a high computational demand, limiting the sampling frequency. This work proposes a predictive algorithm that needs less computation time. As a result, the sampling period can be reduced while producing predictive control. This brings about several benefits resulting from improved current tracking. The proposed method avoids the combinatorial optimization phase of standard FCS-MPC, which is the most time-consuming part. The algorithm is based on physical insights obtained from the application of FCS-MPC to multiphase drives leading to the concept of evolutionary gaps regions. The experimental results for a five-phase motor demonstrate improved performance. Moreover, the method is flexible enough to balance the tradeoff appearing between the torque producing plane and the harmonic plane.Ministerio de Ciencia e Innovación TED2021-129558B-C22 PID2021-125189OBI0