This paper proposes a new family of random modulation techniques for three-phase power converters which operate with a fixed switching frequency. The techniques are based on adjusting the duration of the zero-vectors or adjusting the three pulse positions in a switching period. Three methods are selected for experimental tests because they preserve the fixed switching frequency known from standard PWM techniques. The new methods are also compared with random switching frequency modulation and with fixed switching frequency modulation. Voltage, current and acoustic noise spectra are used for comparison and it is concluded that two of the techniques are especially useful at lower fundamental frequencies. The techniques can substitute classic random modulation techniques with variable switching frequency in some applications.

A novel method for accurate calculation of power spectra of the pulsewidth modulation (PWM) voltage-source inverter with randomized switching frequency is presented. The case of a limited pool of switching frequencies, convenient and adequate for technical purposes, is considered, and a mathematical background for this type of random PWM (RPWM) is provided. It is shown that the limited-pool RPWM gives rise to not only a continuous spectrum, but, also, under certain circumstances, pure power spectral components (harmonics), typical for the deterministic PWM. Criteria for the existence of harmonics are given, and formulae for both the power and the power spectral density are derived and verified experimentally.

Recent developments within the field of medium voltage wide-bandgap semiconductor devices are drawing attention from both researchers and industries due to the demanding requirements for more efficient high-power energy conversion. The rapid development has entailed an increased awareness of the negative impact of the increased rate of change in voltage, d v /d t , and its derived issues caused by the inevitable parasitic capacitive couplings. This article is dedicated to present an overview of the parasitic capacitive couplings in high-power medium voltage power electronic converter systems, using an example reference system enabled by medium voltage SiC mosfet s. The definitions of capacitive couplings are presented and the impacts raised by parasitic capacitive couplings are reviewed. In addition, the similarities of different capacitive couplings introduced by components in practical medium voltage systems are presented and summarized. Lastly, the challenges and future work with respect to parasitic capacitive couplings in medium voltage power electronics converter systems are shared from the authors' perspective.

Fast-switching seat valves suitable for digital hydraulic pumps and motors utilize direct electromagnetic actuators, which must exhibit superior transient performance to allow efficient operation of the fluid power pump/motor. A moving coil actuator resulting in a minimum valve switching time is designed for such valves using transient finite-element analysis of the electromagnetic circuit. The valve dynamics are coupled to the fluid restrictive forces, which significantly influence the effective actuator force. Fluid forces are modeled based on transient computational fluid dynamics models. The electromagnetic finite-element model is verified against experimental measurement, and used to design an optimum moving coil actuator for the application considering different voltage-current ratios of the power supply. Results show that the optimum design depends on the supply voltage-current ratio, however, the minimum switching time obtained is nearly independent on this voltage-current ratio. Selecting a suitable power supply based on thermal considerations yields a switching time just above one millisecond for a travel length of 3.5 mm while submerged in oil. The proposed valve has a pressure drop below 0.5 bar at 600 L/min flow rate, enabling efficient operation of digital hydraulic pumps and motors.

Results of an experimental investigation of the impact of random pulse width modulation (RPWM) on the electromagnetic interference generated in inverter-fed drive systems are presented. A novel voltage space-vector RPWM technique with a limited pool of switching frequencies was employed. Experiments with an induction motor supplied from a voltage-source inverter, performed in a certified shielded chamber, were focused on the electromagnetic noise conducted to mains. In comparison with the deterministic modulation case, significant reduction of the noise, especially with regard to the quasi-peak values, is shown, demonstrating an important advantage of random modulation.