The modeling, modulation and control of the three-phase four-switch (TPFS) PWM rectifier are investigated in this paper. Three space vector pulse width modulation methods using different equivalent zero vectors are developed, where sector identification and the trigonometric function are not required. Then, the high frequency model for the current ripple analysis is proposed, and the effects of three SVM approaches on the AC current ripple are investigated. According to the analytical results, the method introducing the smallest current ripple is selected. With the optimized SVM approach, a control-oriented model, considering the capacitor voltage oscillation and deviation, is built in the d-q synchronous frame to facilitate the controller design. Furthermore, a control strategy implementing the proportional controller is developed to eliminate the capacitor voltage deviation.
Meanwhile, the dual-loop control of the TPFS is not affected by the proposed strategy as the capacitor voltage deviation is eliminated. Finally, a novel linear modulation index function is defined to reject the low frequency harmonic current introduced by the overmodulation. Experimental results demonstrate that excellent current performance is achieved with comprehensive considerations of the modeling, modulation and control strategy.Index Terms-AC-DC power rectifiers, space vector modulation (SVM), three-phase four-switch (TPFS), current ripple root mean square (RMS), linear modulation.
0885-8993 (c)
This paper presents a novel transcranial magnetic stimulation (TMS) pulse generator with a wide range of pulse shape, amplitude, and width. Approach. The novel MM-TMS device is the first to use a modular multi-level circuit topology at full TMS energy levels. It consists of ten cascaded H-bridge modules, each implemented with insulated-gate bipolar transistors, enabling both novel high-amplitude ultrabrief pulses as well as pulses with conventional amplitude and duration. The MM-TMS device has 21 available output voltage levels within each pulse, allowing flexible synthesis of various pulse waveforms and sequences. The circuit further allows charging the energy storage capacitor on each of the ten cascaded modules with a conventional TMS power supply. Main results. The MM-TMS device can output peak coil voltages and currents of 11 kV and 10 kA, respectively, enabling ultrabrief suprathreshold pulses (> 8.25 μs active electric field phase). Further, the MM-TMS device can generate a wide range of near-rectangular monophasic and biphasic pulses, as well as more complex sinusoidal, polyphasic, and amplitude-modulated pulses. At matched estimated stimulation strength, briefer pulses emit less sound, which could enable quieter TMS. Finally, the MM-TMS device can instantaneously increase or decrease the amplitude from one pulse to the next by adding or removing modules in series, which enables rapid pulse sequences and paired-pulse protocols with various pulse shapes. Significance. The MM-TMS device allows unprecedented control of the pulse characteristics which could enable novel protocols and quieter operation.
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