Pulse-width modulation
Along with maximum power point tracking (MPPT), it is one of the primary methods of controlling the output of solar panels to that which can be utilized by a battery.
[2] PWM is particularly suited for running inertial loads such as motors, which are not as easily affected by this discrete switching.
PWM also works well with digital controls, which, because of their on/off nature, can easily set the needed duty cycle.
These are commonly used for direct current (DC) motor control in robotics, switched-mode power supply regulation, and other applications.
The Philips, N. V. company designed an optical scanning system (published in 1946) for variable area film soundtrack which produced the PWM.
[4] Of note, for about a century, some variable-speed electric motors have had decent efficiency, but they were somewhat more complex than constant-speed motors, and sometimes required bulky external electrical apparatus, such as a bank of variable power resistors or rotating converters such as the Ward Leonard drive.
The intersective method is a simple way to generate a PWM output signal (magenta in above figure) with fixed period and varying duty cycle is by using a comparator to switch the PWM output state when the input waveform (red) intersects with a sawtooth or a triangle waveform (blue).
The incremented and periodically reset counter is the discrete version of the intersecting method's sawtooth.
In consequence, a digital PWM suffers from aliasing distortion that significantly reduce its applicability for modern communication systems.
Delta modulation produces a PWM signal (magenta in above figure) which changes state whenever its integral (blue) hits the limits (green) surrounding the input (red).
When the integral of the error exceeds the limits (the upper and lower grey lines in middle plot), the PWM output changes state.
In telecommunications, PWM is a form of signal modulation where the widths of the pulses correspond to specific data values encoded at one end and decoded at the other.
However, the load may be inductive, and with a sufficiently high frequency and when necessary using additional passive electronic filters, the pulse train can be smoothed and average analog waveform recovered.
(In the case of an electrical circuit, a capacitor to absorb energy stored in (often parasitic) supply side inductance.)
High frequency PWM power control systems are easily realisable with semiconductor switches.
Modern semiconductor switches such as MOSFETs or insulated-gate bipolar transistors (IGBTs) are well suited components for high-efficiency controllers.
Variable-speed computer fan controllers usually use PWM, as it is far more efficient when compared to a potentiometer or rheostat.
Home-use light dimmers typically include electronic circuitry that suppresses current flow during defined portions of each cycle of the AC line voltage.
These rather simple types of dimmers can be effectively used with inert (or relatively slow reacting) light sources such as incandescent lamps, for example, for which the additional modulation in supplied electrical energy which is caused by the dimmer causes only negligible additional fluctuations in the emitted light.
Some other types of light sources such as light-emitting diodes (LEDs), however, turn on and off extremely rapidly and would perceivably flicker if supplied with low-frequency drive voltages.
Perceivable flicker effects from such rapid response light sources can be reduced by increasing the PWM frequency.
In electric cookers, continuously variable power is applied to the heating elements such as the hob or the grill using a device known as a simmerstat.
The thermal time constant of the heating elements is several minutes so that the temperature fluctuations are too small to matter in practice.
Varying the duty cycle of a pulse waveform in a synthesis instrument creates useful timbral variations.
The term PWM as used in sound (music) synthesis refers to the ratio between the high and low level being secondarily modulated with a low-frequency oscillator.
Field-gradient coils in MRI machines are driven by relatively high-power PWM amplifiers.
Historically, a crude form of PWM has been used to play back PCM digital sound on the PC speaker, which is driven by only two voltage levels, typically 0 V and 5 V. By carefully timing the duration of the pulses, and by relying on the speaker's physical filtering properties (limited frequency response, self-inductance, etc.)
it was possible to obtain an approximate playback of mono PCM samples, although at a very low quality, and with greatly varying results between implementations.
In more recent times, the Direct Stream Digital sound encoding method was introduced, which uses a generalized form of pulse-width modulation called pulse-density modulation, at a high enough sampling rate (typically in the order of MHz) to cover the whole acoustic frequencies range with sufficient fidelity.
SPWM (sine–triangle pulse-width modulation) signals are used in micro-inverter design (used in solar and wind power applications).
