Modulation techniques for AC/DC converters in ultrafast battery charger applications

A variety of different modulation techniques have been presented in literature about 2-levels and 3-levels converters control. The modulation technique largely defines the generated harmonic content of voltages and currents, making this aspect of the project of the converter a key point that must be studied in depth; thus, depending on the application, there will be a modulation technique more suitable than others. All modulation schemes applicable to 2-levels rectifiers can be applied to interleaved or multi-level converters since any sub-unit can generate their outputs independently.
A primal characterization concerns continuous and discontinuous modulation techniques. In continuous technique each phase modulation index mf, with f = {a, b, c} (or duties dA, dB, dC), varies with continuity instantaneously, while in discontinuous techniques, for a certain interval of time (or exactly, phase), one or more phase indexes result to be clamped to the to the upper and lower DC-link rails (both or singularly). In this way, discontinuous techniques avoid switching around the maxima [5] (because the clamping happens when the phase current results close to its maximum value) but they are not suited for iM control.
Consequently, discontinuous techniques are chosen if the purpose of control is oriented to switching loss reduction, while continuous one are preferred in terms of performance (ripple reduction), flexibility, and high frequency component attenuation.
In this paper, 4 different techniques will be presented:
• Space Vector PWM (SVPWM), where the common-mode voltage v0 is the one obtained by the standard space-vector approach (PWM compute as in 2-levels converter);
• Discontinuous PWM with 30° Upper/Lower Clamping (DPWM4) in which each phase is alternatively clamped to the upper and lower DC-link rails, each for 30°;
• Three Level SVPWM (TLSVPWM or simply CSVM, continuous space vector modulation), in which the duty calculation works in a continuous manner in all phases (PWM compute for 3-levels converters);
• Zero Mid-Point Current PWM (ZMPCPWM), in which the modulation strategies is wholly oriented to mid-point current magnitude minimization.
Next paragraphs will explain in a comprehensive way the main features of those techniques, considering phase voltages, common-mode voltage injection, duties waveform and grid current harmonic content. [...]