Permanent-magnet synchronous motors have attracted much attention due to their high efficiency and high-torque density. For higher control performance, finite control set model predictive control (FCS-MPC) and continuous control set MPC (CCS-MPC) have been developed. However, the former requires high computing power, whereas inverter voltage saturation is not considered in the latter. Therefore, this study proposes an optimal current control law taking into consideration the inverter output voltage. The effectiveness of the proposed method is verified by comparison with the FCS-MPC and the standard CCS-MPC through experiments. Nomenclature i a , i b , i c stator phase current in the a-c frame i d , i q stator phase current in the d-q frame i d ref , i q ref stator reference phase current in the d-q frame v a , v b , v c stator phase voltage in the a-c frame v a ref , v b ref , v c ref stator reference phase voltage in the a-c frame v d , v q stator phase voltage in the d-q frame v d ref , v q ref stator reference phase voltage in the d-q frame R stator winding resistance L d , L q stator winding d-q axes inductances Φ f electromotive force constant ω re electric angular velocity of rotor θ re electric angle of rotor E dc DC-link voltage
Filters are inevitable for grid-connected inverters to attenuate the current harmonics caused by the pulse width modulation which is usually used in power conversion systems. High-order filters have attracted much attention because they attenuate the current harmonics effectively. Nevertheless, the high-order filters have some resonances which cause instability of the system. In addition, the resonance frequencies shift to high as the inductors and capacitors are smaller. It implies that the resonance frequencies may be beyond the Nyquist frequency in downsizing the filter. This complicates the stability and performance analyses of the system. This paper investigates rigorous input-output stability and analyses a robust performance based on the sampled-data control theory regardless of whether the resonance frequencies are beyond the Nyquist frequency or not. Our analysis contributes to downsizing the filter synthesis while the stability and the robustness are guaranteed even if the resonance frequencies are beyond the Nyquist frequency. The effectiveness of the proposed method is verified through simulations and experiments.
Networked control systems have received increasing attention from many researchers because of their vast potential. The insertion of communication networks in a controlled system brings network-induced defects, which are mainly caused by limited network resources. This paper proposes a codesign of periodic communication scheduling and a controller using sparsity for efficient use of the network while improving initial control performance. The effectiveness of the proposed method is verified through two numerical simulations. K E Y W O R D S control system synthesis, linear matrix inequalities | INTRODUCTIONRecently, networked control systems (NCSs) have received increasing attention from many researchers because of their vast potential [1][2][3]. NCSs have communication networks between a plant and a controller. The communication networks reduce wiring, implementation, and maintenance costs. In addition, NCSs can be applied for many applications, such as teleoperated medical field, robotics, unmanned aerial/guided vehicles, electronic control in vehicle engines, and many other industries [4][5][6][7][8][9][10][11][12].The insertion of communication networks in a controlled system brings network-induced defects such as packet dropouts, time-varying delays, and packet disorders, which are mainly caused by limited network resources. These defects can be reduced by the efficient use of communication resources.To address these issues, numerous studies have been dedicated to the improvement of control performance through the efficient usage of communication resources, which is achieved through non-uniform sampling of the control system. This form of research can be roughly classified into three types: event-triggered, self-triggered, and time-triggered approaches.The event-triggered control schemes [13][14][15] decide the type of communication based on event occurrences. Typically, such an event occurs when a considered variable in a system exceeds a certain threshold. This kind of approach requires intelligent sensors that can detect event occurrences and additional power for them. Moreover, event occurrence conditions tend to be complicated when it comes to improving control performance. As a result, the codesign of event occurrence conditions and a controller requires numerous parameters to be tuned.Self-triggered control schemes [13,16,17] decide the timing of when the next control input is updated. Generally, this kind of approach assumes that the measurement is synchronised with the updated timing of the corresponding input. Therefore, the self-triggered method can be fully implemented on the controller side. However, these prerequisites, such as synchronisation, restrict the application to the asynchronous communication of multiple sensors. In the event and the self-triggered control approaches, a maximum communication rate is guaranteed, whereas in the worst-case scenario, it will tend to be a long-term communication with the maximum rate. Hence, it is important to guarantee the average communication rate rathe...
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