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In this paper, in order to reduce the dominant harmonic clusters in the output current's spectrum, a new switching method for PWM inverters is proposed. When an inverter with a constant switching frequency is used, it would result in narrow-band harmonics. These harmonic clusters can make acoustic noises and Electromagnetic Interference (EMI). In o...

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## Citations

... Reference [102] proposes an improved RPPPWM, which is easy to implement and integrate into motor drive systems. Then an improved RPWM that combines RCFPWM and RPPPWM is proposed, making the sampling frequency constant and harmonic cluster distribution more uniform [104]. RPWM has good performance in EMI suppression. ...

With the global attention given to energy issues, the electrification of aviation and the development of more electric aircraft (MEA) have become important trends in the modern aviation industry. The electric actuator plays multiple roles in aircraft such as flight control, making it a crucial technology for MEA. Given the limited space available inside an aircraft, the power density of electric actuators has become a critical design factor. However, the pursuit of high power density results in the need for larger rated power and higher switching frequency, which can lead to severe electromagnetic interference (EMI) issues. This, in turn, poses significant challenges to the overall reliability of the electric actuator. This paper provides a comprehensive review of EMI in high power density motor drive systems for electric actuator systems. Firstly, the state of the art of electric actuator systems are surveyed, pointing out the contradictory relationship between high power density and EMI. Subsequently, various EMI modeling approaches of motor control systems are reviewed. Additionally, the main EMI suppression methods are summarized. Active EMI mitigation methods are emphasized in this paper due to their advantages of higher power density compared with passive EMI filters. Finally, the paper concludes by summarizing the EMI research in motor drive systems and offering the prospects of electric actuators.

... This way of creating randomness is called random lead lag, RLL. [12], [14], [15]. RLL is of the RPPM type, randomly changing the position of the pulse in two arrangements. ...

... A non-constant cycle produces an unpredictable effect. The problem was raised in 1998 [21] and is studied in [15], [22], [23], and [24]. ...

It has been shown that the converters that integrate random PWM produce a spread spectrum in their harmonic emission, shortening the emission peaks. On the converter’s input side, the reduction minimizes electromagnetic interference EMI. On the output side of the converter, the reduction manages to smooth the voltage and current ripple in the load. We have built a flexible test bench (FTB) developed with FPGA to generate most of the proposed random PWM modes for converters. The conducted harmonic voltage emission of these modes, both on the input side of the converter and on the load side, has been measured and compared in a DC-DC Buck converter. FTB also has the ability to create new random PWM modes. Of the random modes, the ones that produce the greatest peak reductions are those with variable switching frequency. However, variable frequency modes lead to load feedback problems. A new random PWM method has been developed that significantly reduces the amplitude of the emission peaks but keeps the switching frequency constant.

The discrete tonal bands introduced in an AC machine’s stator current spectrum by constant switching frequency pulse width modulation schemes, have adverse impacts on the vibration, the acoustic noise, and the electromagnetic interference. Spreading the harmonic spectrum and reducing the magnitude of dominant harmonics is one solution to this problem. Ripples in the electromagnetic torque developed is another major concern in AC drives. Inspired by these factors, this study proposes two novel variable switching frequency schemes for a vector-controlled PMSM drive to disperse the frequency spectrum with a significant reduction in torque ripple. The modulation techniques use linear and trapezoidal variation of sub-cycle sampling period;
T<sub>s</sub>
during their implementation. Further, these methods would be able to eliminate the difficulty in compensator design, which is a major problem with other variable switching frequency schemes. The presented strategies achieve a maximum of 27 % reduction in torque ripple, 51.8 % reduction in dominant harmonics, and a dispersion index of 1.63, demonstrating their competency as promising variable switching frequency schemes. The suggested techniques also show excellent torque ripple reduction capability in comparison with latest spread-spectrum techniques in literature. The proposed techniques are implemented in simulation using MATLAB/Simulink and are experimentally validated using WAVECT-FPGA controller on a 1.07 kW, surface-mounted PMSM drive.

Aiming at suppressing the switching frequen-cy harmonics, a novel discrete hybrid dual random control (DHDRC) technique is proposed in this article. Based on the space vector pulsewidth modulation (SVPWM) strategy, the DHDRC-SVPWM technique is applied to randomize the switching period and pulse position by selecting dual discrete random factors from predefined discrete sequences. Accordingly, the original switching narrowband harmonic energy of SVPWM is extended to a wide range of frequencies. To analyze the harmonic dispersion degree quantitatively, the power spectrum is deduced to assess the performance of the discrete random SVPWM. Then, the connection between the discrete sequence and the harmonic energy distribution is obtained under random variables following a discrete uniform distribution. The obtained results demonstrate that the proposed technique significantly expands harmonic clusters in the frequency domain, thereby reducing the harmonic intensity. The present study provides a reference to investigate random SVPWM and improve electromagnetic interference and noise in power converters.

Random Pulse Width Modulation (RPWM) has been successfully applied in power electronics for nearly 30 years. The effects of the various possible RPWM strategies on the Power Spectral Density have been thoroughly studied. Despite the effectiveness of RPWM in spreading harmonic content, an appeal is consistently made to maintain the textbook Pulse Width Modulation scheme 'on average'. Random Switching (RS) does away with this notion and probabilistically operates the switch. In addition to fulfilling several optimality conditions, including being the only viable switching strategy at the theoretical limit of performance and having lower switching losses than any other RPWM; RS allows for design of the DC behaviour separately from that of the PSD. The pulse amplitude probability affects the DC and total PSD. The first and second moment of the pulse length probability distribution affects the shape of the envelope of the noise of the PSD. The minimum pulse length acts like a selective harmonic filter. The PSD can therefore be shaped without external filtering by changing these probabilities. Gaussian and Huffman pulse length probabilities are shown to be good choices depending on whether real-time PSD control or spectrum usage are the design goal. In addition, it is shown that C\'uk's state space averaging model applies to RS, with $D \to p$, hence no new tools are needed to understand the low frequency behavior or control performance. A benefit of closed loop random switching is that no filtering of the controlled variable is required. Randomly responding in a biased manner dependent on the error is hence shown to be useful. There are several good reasons to consider RS for high performance applications.

Pulse-width modulation (PWM) of a motor drive at a fixed switching frequency leads to harmonic currents in narrow bands around integral multiples of the switching frequency resulting in tonal frequency acoustic noise components, which are irritating to the human ear. Random variation of carrier frequency to spread the spectrum poses challenges in device loss calculation, thermal design, and closed-loop controller design. Random pulse positioning is not quite effective at high speeds of the drive, where the problem of acoustic noise is most pronounced. This paper proposes a simple variable-frequency PWM and evaluates the performance of the same experimentally on a 6-kW induction motor drive. The experimental results show that the acoustic noise is spread uniformly over a range of frequencies without introducing low-frequency current harmonics. Compared with fixed-frequency PWM, the dominant acoustic noise is reduced significantly over a wide range of speeds. The variable-frequency PWM is further shown to reduce line current total harmonic distortion at high speeds of the drive. The computational effort required by the variable-frequency PWM is only marginally higher than that required by fixed-frequency PWM.

Acoustic noise is one of the undesirable consequences of the harmonic currents fed into an induction motor by a voltage source inverter. If the inverter is modulated at a fixed switching frequency, the resulting current harmonic components are located in narrow bands around integral multiples of the switching frequency. This causes discrete tonal noise which is unpleasant to human ear. This paper experimentally evaluates a variable switching frequency PWM method on an 8-hp motor drive both from acoustic noise and total harmonic distortion (THD) perspectives. Experimental results show that the acoustic noise is spread uniformly over a range of frequencies without introducing low-frequency current harmonics. The variable frequency PWM is further shown to reduce the line current THD at high speeds of the drive, compared to fixed frequency PWM.