page_title: Switching control techniques
section_title: Deterministic Modulation
hierarchical_section_title: Switching control techniques / Mitigation of Electromagnetic Interference / Deterministic Modulation
caption_attribution_description: English: The figure shows two figures for EMI output:one spectrum and one spectrogram.
context_page_description: Switching Control Techniques address electromagnetic interference mitigation on power electronics. The design of power electronics involves overcoming three key challenges:
  power losses
  EMI
  harmonics
  Also, the use of PE introduces crucial drawbacks into the electrical grid regarding the EMI, that must be considered during its design and operation, especially when is desirable to meet the EMC constraints. Dealing with static converters designed with PE, for example, can causes signal disturbances in the electromagnetic environment, e.g. with respect to radio receivers, vehicle navigation systems, avionics, etc.
  Those disturbances are caused mainly by the high frequency interference from the semiconductor switching components inside PE. It is challenging to handle this aspect with filtering and shielding techniques as the demands for cost and size for its implementation increase, along with greater efficiency. Therefore, switching mode power supplies are used instead in order to obtain a higher efficiency.
context_section_description: PWM is considered the most common deterministic technique. Considering the example of a DC-DC converter, a controlled switch is designed to “cut-off” the DC waveform into a pulse-shaped waveform. Therefore, the voltage of this signal alternates at the switching frequency between a maximum value and zero. The converter also controls the duty cycle (𝐷), that is, the time frame in which the switch device is turned off in each cycle. Generally, the waveform of the power electronics interface (PEI) is a steady-state periodic time function.
  By the middle of 1990s, some researchers started to evaluate which frequency modulation techniques to apply to reduce EMI emissions, focusing on communications and microprocessor systems. The main concern with these latter approaches is that EMI is equally spread along the whole frequency spectrum, and these approaches do not provide any control over the bands where EMI energy is spread. This feature is crucial for telecommunications, telematics, and automation systems applications, where EMI at specific selective frequencies must be avoided. Investigations of such techniques applied to EMI reduction of digital systems is a subject of significant concern, included the introduction of a new area of research with modulation techniques to power electronics converters with randomized modulation.
  As an exemplification, Fig. 2.A at shows the spectrum and Fig. 2.B shows the spectrogram of EMI shaped-noise voltage output for a programmable PWM with switching frequency in a buck converter with 𝐷 = 0.50, in accordance with CISPR A standard.
  According to Fig. 2.A, the programmable switching frequency creates a significative impact by the EMI noise shape as well as the high sideband. Fig. 2.B shows the high peaks amplitude of EMI noise, at the switching frequency and their multiple harmonics.
caption: Fig. 2. EMI noise of output voltage for programmed switching frequency (PWM): a) Spectrum and b) Spectrogram.
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