In this letter, to handle the over-generation issue of photovoltaic (PV) systems based on maximal power point tracking (MPPT) algorithms, and to provide the power reservation for power grids, an optimal point shifting design based on virtual impedance is proposed for PV systems with flexible power point tracking. With the introduction of the virtual impedance, the virtual PV power is provided to auto-shift optimal power points on PV power-voltage curves. With a MPPT algorithm applied to the virtual PV power, the actual PV power is auto-turned without the estimation of maximum available PV power. The proposed design is validated through simulation studies of a PV-battery charging system and experimental studies of a grid-tied PV system, where both the overcharging of the battery and the over PV power generation are effectively avoided by reducing actual PV power according to the increasing of the battery SOC or the grid RMS voltage, respectively.

In this paper, two open problems of the existing bounded UDE-based robust control method are investigated: the input constraint with multiple control inputs, and the performance degradation caused by the introduced additional time-varying control variable. A modified bounded UDE-based robust control method is developed for the MIMO system with the inputs constrained by a general positive defined matrix, which is a more general condition of the norm constraint for control inputs. A nonlinear designed is further proposed to modified the direct multiplication of the additional time-varying variable to mitigate the performance degradation of the existing bounded UDE-based robust control, and the guidance of the nonlinear design procedures is provided. The proposed design is applied to the vector control of a PMSM drive system, and the simulation studies are provided to validate the proposed design under voltage constraint of the vector control with both normal operation and voltage constraint triggered.

The high-speed maglev train based on the doubly-fed linear motor (DFLM) has the potential advantages to achieve suspension, traction, and contactless power transfer simultaneously, which improves the reliability of the maglev system and system cost. However, there is still a lack of relevant designs of the doubly-fed linear motor to meet critical requirements for practical high-speed maglev applications, e.g., the low fluctuations of the levitation and thrust forces. In this paper, based on the performance of the German TR08 maglev train, finite element analysis (FEA) technology is used to investigate the effects of different pole-slot combinations and multi-phase winding structures on the suspension force and thrust force of the doubly-fed linear motor. A doubly-fed linear motor topology based on 36-slot 12-pole three-phase stator and 20-slot 12-pole five-phase mover is proposed, which can greatly reduce the fluctuations of suspension and thrust forces, and its performance is close to the level of TR08 maglev train. Finally, the performance of the contactless power transfer for the DFLM is analyzed.

Compared to a long-stator linear synchronous motor (LLSM), a long-stator doubly-fed linear motor (DFLM) exhibits two distinct advantages for high-speed maglev application: 1) It has two additional degrees of freedom with both the frequency and the phase angle of the mover to improve its control accuracy and dynamic responses; 2) It can use the slip power to feed the mover contactlessly and directly. In order to achieve the propulsion, the levitation, and the contactless power transfer through the common air-gap magnetic field, the “quasi-synchronous operation (QSO)” principle of the DFLM is proposed for high-speed maglev train. Based on the DFLM modeling and distinctive constraints for maglev train, the operation point analysis of the performance evaluation is further investigated. To validate the feasibility of the DFLM application for high-speed maglev train, a unit DFLM prototype is designed and tested, and the corresponding simulation studies of the QSO control structure are investigated.

In this paper, a quasi-synchronization operation of a doubly-fed linear motor is proposed to achieve accurate regulation of both the traction and the contactless power transfer. A new control structure is proposed to achieve the loose coupling control between the stator side and the mover side, where the scalar control is used for the stator side controller (SSC), and the field-oriented control (FOC) is adopted for the mover side controller (MSC). The SSC and the MSC is with “frequency-coupling”, which enhances the reliability of the whole control system with less information exchange between the SSC and the MSC. The effectiveness of the proposed design is validated through both simulation and experimental studies.