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The overmodulation strategy plays an important role in the field weakening control for high-speed permanent magnet synchronous motor (PMSM) drives. However, the voltage jumps between the output voltage vectors (OVVs) in high overmodulation regions result in the deterioration of both current performance and loading capability. In order to solve this problem, a novel overmodulation strategy based on the voltage vector space division is proposed. The overmodulation regions are divided by the amplitude and the phase of reference voltage vectors to guarantee the continuity of OVVs. When the overmodulation region changes, the voltage jump can be efficiently suppressed, which contributes to eliminating current ripples. In addition, the proposed parallel projection replaces the traditional center projection to increase the modulation index, which can also improve the fundamental voltage amplitude, and make a reduction of the field weakening current and its current overshoot. By improving the utilization of the dc bus voltage, the higher capability of the output torque can be achieved in the field weakening region. Finally, the effectiveness of the proposed strategy is verified on a high-speed surface-mounted PMSM platform by the experimental results. [ABSTRACT FROM AUTHOR]

Communication links, as a part of coordinated control in dc microgrids (MGs), play an essential role in achieving high operational performance. In this article, a bipolar topology based on series modular structure of dc MG is designed, and a complementary dual-window dc bus interacting (CDBI) method which combines droop control with antidroop control is proposed to improve the robustness of system and against communication failure. In the proposed CDBI method, distributed generations regard dc buses as common communication channels for information exchange, and the coordinated control within the dc MGs can be realized through predesigned sequences of voltage pulses without extra communication links. Finally, the proposed symmetrical bipolar structure and communication-free coordinated control scheme have been verified in various cases through rapid control prototype. The experimental results show that the bipolar-type dc MG controlled by the proposed CDBI method can supply high-quality power for a long time even in the case of communication failure. [ABSTRACT FROM AUTHOR]

This article proposes a coordinate impedance compression strategy for high frequency inverter systems. Based on a two parallel inverter structure, the strategy adopts two methodologies: 1) a passive LC network to adjust the current and voltage seen by each inverter module, and 2) an active modulation of the inverter input voltage and output voltage phase to adjust the load current distribution. For the proposed strategy, the resistance and reactance can be compressed coordinately, which can help the inverter to operate in high efficiency load range. The Half-Bridge Class D inverter is taken as an example to be analyzed. A 10-MHz prototype is built and the experimental results verify the correctness and feasibility of the proposed strategy. [ABSTRACT FROM AUTHOR]

The nonlinearity of the voltage source inverter (VSI) leads to the error between output voltage and reference voltage, and causes the phase current harmonics. It is necessary to compensate its influence in the fields such as parameter identification, sensorless control, and servo drives. In this article, an industrial solution for VSI nonlinear compensation method based on lookup table (LUT) is introduced. The characteristics of semiconductor devices, equivalent dead-time and influence of parasitic capacitance effects are calculated quantitatively though injecting increase and decrease current during self-commissioning process. The critical current value for parasitic capacitor and the variation of equivalent dead time are verified through different distorted voltage curves. Considering dc-link voltage variation is irresistible for industrial products, 3-D linear interpolation is adopted to compensate the variation of VSI nonlinearity under different voltage conditions. Proposed LUT method does not require VSI datasheet and complicated calculation formula during implementation. Experiments are carried out on a commercial permanent magnet synchronous motor drive system to verify the proposed LUT method. [ABSTRACT FROM AUTHOR]

Under weak grid condition, negative influence is brought in on system stability because the grid impedance and the grid-connected converter control system are coupled to each other. The key factor affecting the stability of the system is the perturbation of the voltage fluctuation at the point of common coupling (PCC) to the phase-locked loop (PLL) and the dc-link voltage loop. In this article, the impedance model of a three-phase grid-connected converter, including the current loop, PLL, and dc-link voltage loop in the dq frame, is adopted, because it includes coupling information of the converter and reflects the transferring relationship among grid-connected system variables. Based on the transferring relationship, this article analyzes the perturbation paths of PCC voltage and proposes the corresponding compensation methods, i.e., the PLL and dc-link voltage loop compensation terms, which are inserted into the q and d axes of the current loop controller, respectively. The impedance analysis results show that the proposed method can effectively improve the system stability. In addition, the experimental results verify the correctness of the theoretical analysis and the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Bipolar LVdc distribution is a promising solution for better integration of renewables and enhancement of system efficiency and reliability, but it also faces the challenge of pole voltage imbalance. By simple modifications of the bidirectional CLLC dc/dc converter, this article presents a dc/dc converter with integrated pole voltage balance capability. The converter presents less number of semiconductors, smaller overall footprint, and lower power loss compared to the employment of additional pole voltage balancers. Operating principle of this dc/dc converter and its inherent pole voltage balancing capability are explained, while further control scheme is also developed to compensate the small pole voltage difference caused by the dead time effect. Simulation results with 150 kW/±375 V bipolar output demonstrate the effectiveness of the converter, and the experimental results from a 500 W/±50 V downscaled prototype further prove the proposed concept. [ABSTRACT FROM AUTHOR]

In the transition process from the base-speed region to the field-weakening region of induction motor (IM), the voltage margin would suddenly disappear due to the limited inverter voltage. This insufficient voltage margin would deteriorate the current control of IM, causing severe voltage saturation and current ripple. To address this problem, a circular arc voltage trajectory method is proposed with the smooth transition-combined field-weakening controller. The voltage and current behavior are analyzed quantitatively during the transition process. The theoretical analysis shows that the studied circular arc trajectory can suppress the sudden decrease of the voltage increasing rate in the transition region, leading to the reduced voltage saturation and current ripple. The sufficient voltage margin and smooth current can be realized at the cost of < 10% voltage utilization ratio. The effectiveness of the studied method is verified by contrast experiments on an ARM-based 3.7-kW IM platform. [ABSTRACT FROM AUTHOR]