Through-Zero PWM With Period-Average-Zero Waveform Generation
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Solution Overview
Problem
Pulse-width modulation waveforms with fixed amplitude often introduce a non-sinusoidal additive term due to varying pulse width, causing issues in applications like motor control and communication systems, leading to problems such as saturation of magnetic components and undesired modulation products.
Innovation Solution
Generating a pulse waveform with a zero d.c. term in each period by using a pulse width control signal that varies linearly, comparing it with a reference signal, and subtracting a function of the control signal from the pulse waveform to produce an output with a zero average value, employing either analog or digital circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional pulse-width modulation is used with fixed amplitude, then the modulation process is simple, but a non-sinusoidal additive term is introduced causing saturation of magnetic components and undesired modulation products
Solution Approach 1:
The patent extracts and removes the problematic non-sinusoidal additive term from the pulse-width modulation waveform by using a symmetric bipolar pulse train centered at zero voltage. This eliminates the DC component and harmful additive terms while preserving the essential PWM modulation function.
Solution Approach 2:
The patent transitions from unipolar PWM (asymmetric, always positive) to bipolar PWM (symmetric, alternating positive and negative). This asymmetry principle is applied in reverse - by introducing symmetry through bipolar waveforms, the harmful asymmetric additive terms are eliminated, resolving the contradiction between simplicity and harmful effects.
2Adaptability or versatility
If pulse width is varied in conventional PWM, then control flexibility is improved, but the additive term varies causing problematic effects in applications
Solution Approach 1:
The varying additive term is extracted and removed by using bipolar symmetric waveforms. The control flexibility is maintained through varying the duty cycle of the bipolar pulses, while the harmful varying additive term is eliminated by the symmetric structure that centers the waveform at zero.
Solution Approach 2:
The patent changes the fundamental parameter of the PWM waveform from unipolar to bipolar, and from asymmetric to symmetric. This parameter change allows the duty cycle to be varied for control flexibility while the symmetric bipolar structure ensures the additive term remains zero or cancels out, resolving the contradiction between adaptability and harmful effects.
3Object-generated harmful factors
If a zero d.c. term pulse waveform is generated through comparison and subtraction, then saturation and modulation product issues are reduced, but the circuit complexity increases
Solution Approach 1:
Instead of adding complex filtering or correction circuits to remove the additive term, the patent inverts the approach by generating the bipolar symmetric waveform directly from the start. The comparison and subtraction operations are performed in the time domain during waveform generation, simplifying the overall circuit architecture while achieving the zero DC term objective.
Data Source
AI summary
New methods for generating through-zero pulse-width modulation are disclosed. In one approach, a periodic reference signal varies over time over at least one portion of the period. A pulse-width control signal varies linearly with time over at least one portion of the reference signal. The reference signal is compared with the pulse-width control value to produce a first pulse waveform. The value of a function of the control value is subtracted from the first pulse waveform to produce through-zero pulse-width modulation. In another approach, the difference in value between two ramp or sawtooth periodic waveforms is computed to produce a pulse waveform with a time-varying DC offset that varies linearly in time. The time-varying offset-term is retained with the pulse waveform, producing through-zero pulse-width modulation.