DC-Link High-Frequency Current Ripple Elimination Strategy for MMCs Using Phase-Shifted Double-Group Multicarrier-Based Phase-Disposition PWM
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The active circulating current suppression may cause high-frequency current ripple in the dc link of modular multilevel converters (MMCs). In this article, a phase-shifted double-group multicarrier-based phase-disposition pulsewidth modulation strategy is proposed to eliminate the dc-link high-frequency current ripple of MMCs, where the fundamental frequency component and the second-order component of the arm reference are modulated, respectively, by two groups of carriers. By shifting the phase angles of double-group multicarrier in each carrier period, the high-frequency current ripple injected into the dc link of MMCs can be eliminated. The proposed strategy not only eliminates the dc-link current ripple, but also extends the active and reactive power region of MMCs in comparison with the existing method. Simulation and experimental studies are conducted, and their results verify the effectiveness of the proposed strategy.Keywords:
Modulation (music)
Input ripple analysis of five-phase pulse width modulated (PWM) inverters is presented. The analytical expressions for the rms value of the input current and voltage ripples as a function of the PWM reference signal are derived. Similar to three-phase PWM inverters, the input current ripple does not depend on the employed reference signal, so the ripple cannot be minimised by changing the shape of reference signal. On the other hand, different from three-phase PWM inverters, it is shown that a pure sinusoidal signal is the optimum reference signal that produces a minimum input voltage ripple in five-phase PWM inverters. Input voltage ripples under several modulation techniques are compared. Experimental results are included to verify the proposed analysis method.
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Modulation (music)
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Virtual space vector pulse-width modulation (VSV-PWM) is commonly used in neutral point clamped (NPC) three-level (3-L) inverters due to its intrinsic neutral point potential balancing feature. However, VSV-PWM brings higher switching loss than the traditional space-vector PWM (SV-PWM) under the same current harmonic content. To solve this problem, a variable switching frequency VSV-PWM (VSF-VSV-PWM) method based on the prediction of current ripple is proposed in this paper. Firstly, the current ripple of 3-L inverters under VSV-PWM is analyzed and a comparison of current ripple distribution under VSV-PWM and SV-PWM is presented. Based on the analytical results, a current ripple prediction method for 3-L inverters under VSV-PWM is proposed. In the proposed VSF-VSV-PWM, the current ripple is kept constant by varying the switching frequency dynamically according to the predicted current ripple. With this approach, the switching loss is reduced while the current ripple is controlled to track a given value. The distribution of current harmonics is dispersed and the electromagnetic interference (EMI) noise is mitigated using VSF-VSV-PWM. Experimental results are presented to validate the effectiveness of the proposed current ripple prediction and the VSF-VSV-PWM method.
Harmonic
Harmonic Analysis
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Effects of ripple width in rippled-spectrum signals on ripple density resolution was investigated. Two measurement paradigms were tested: (i) ripple density resolution for discrimination between two rippled signals and (ii) discrimination between a rippled test signal and non-rippled reference signal. The ripple widths varied from 9% to 64% of the ripple frequency spacing. For both paradigms, the ripple density resolution increased with deceasing the ripple width. For discrimination between two rippled signals, the resolution was 8.1 ripples/oct for a ripple width of 64% and increased to 15.1 ripples/oct at the ripple width of 9%. For discrimination between a rippled test and non-rippled reference signal, the resolution was 9.3 ripples/oct at a ripple width of 64% and increased to 85 ripples/oct at a ripple width of 9%. Discrimination between two rippled signals is hypothesized to depend on ripple depth in the excitation pattern; the depth increases with narrowing the ripple width. Discrimination between a rippled test and non-rippled reference signal is hypothesized to depend on temporal processing; the effect of the ripple width appears due to increasing the ratio of the autocorrelated to uncorrelated components of the input signal with narrowing the ripples.
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Uncorrelated
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It is critical for buried target detection via ripple scattering to know the ripple structure, e.g., the ripple height and spatial wavelength. In the present paper, backscattering data from a 300-kHz system show that ripple wavelength and height can potentially be estimated from backscattering images. Motivated by the backscatter data, we have developed a time-domain numerical model to simulate scattering of high-frequency sound by a ripple field. This model treats small-scale scatterers as Lambertian scatterers distributed randomly on the large-scale ripple field. We have found that this approach characterizes the field data well. Numerical simulations are conducted to investigate the possibility of remotely sensing bottom ripple heights and wavelength.
Backscatter (email)
Ripple marks
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This paper analyzes the mechanism of ripple generation,summarizes characteristics of the ripple and its effects on load,and puts forward a discussion of methods for measuring ripple of DC stabilized power supply.
Ripple marks
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Signals with rippled frequency spectra are used to investigate capabilities of hearing to analyze and discriminate complex sounds. Till now, rippled signals with the difference between discriminated signals equal across the frequency band were exploited. In the present study, signals of different ripple densities in which ripple differences varied across the signal band were used. Ripple-density difference (RDD) thresholds increased with increasing the standard ripple density. At a standard ripple density of 2 to 10 ripples/oct, RDD threshold dependence on ripple density was identical for signal frequencies of 1 to 4 kHz: thresholds were from 0.06 ripples/oct at a standard density of 2 ripples/oct to 5–7 ripples/oct at a standard ripple density of 10 ripples/oct; RDD thresholds were not measurable at standard ripple densities above 10 ripples/oct and frequencies of 1 and 2 kHz. However, at a frequency of 4 kHz, RDD thresholds were measurable at standard ripple densities of 15 ripples/oct and higher. Hypothetically, at ripple densities of up to 10 ripples/oct, the signals were discriminated by the excitation-pattern mechanism; at ripple densities above 10 ripples/oct and a signal center frequency of 4 kHz, the signals were discriminated by the temporal-processing mechanism. [Work supported by Russian Science Foundation, Grant 16-15-10046.]
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Hysteresis
Ripple marks
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When a solid object or wheel is repeatedly dragged on a dry sandy surface, ripple patterns are formed. Although the conditions to form ripple patterns have been studied well, methods to eliminate the developed ripple patterns have not been understood thus far. Therefore, history-dependent stability of the ripple patterns formed on a sandy surface is investigated in this study. First, the ripple patterns are formed by sweeping the flat sandy surface with a flexible plow at a constant speed. Then, the sweeping speed is reduced, and the variation of ripple patterns is measured. As a result, we find that the ripple patterns show hysteresis. Specifically, the increase in amplitude of ripples is observed when the reduced velocity is close to the initial velocity forming the ripple pattern. In addition, splitting of ripples is found when the reduced velocity is further decreased. From a simple analysis of the plow's motion, we discuss the physical mechanism of the ripple splitting.
Hysteresis
Ripple marks
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On the basis of establishing average model for pulse width modulation(PWM) rectifier of cascading H-bridge,the paper analyzes harmonic characteristics of single polarity and bipolar modulation algorithms.It proposes cascading modulation algorithm based on independent modulation of left and right bridge arms and analyzes mechanism of voltage imbalance at cascading DC side and modulation method;it presents balance control algorithm at DC side based on reconstitution of modulation ratio.Simulation by MATLAB/Simulink verifies effectiveness of modulation strategy and control strategy.
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Rectifier (neural networks)
Harmonic
H bridge
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This paper introduces an optical direct current sensor, that uses technical ripple current to determine the magnitude of direct current, under consideration of the influence of temperature. Therefor, the influence of temperature is compensated with help of a method, that uses two wavelengths in time multiplex and technical current ripple. A simulation model of the sensor is used to describe the main influences of temperature, where linear birefringence changes are identified as the most important reasons for errors in current measurements. Due to lower costs and easy installation, a magnetic field sensor is used to determine the magnitude of a direct current with technical ripple, witch is installed in a electric single phase configuration in a climatic chamber. The method is proven by presenting comparisons of the results of current amplitude measurements in a range of realistic ambient temperatures to a conventional clamp-on current probe, with significant reduced derivation.
Current sensor
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