Locked Antiphase PWM
A method in which the two legs of the H-bridge are driven from a single PWM signal so that each is the inverse of the other. A duty ratio of 50 percent corresponds to zero speed, 100 percent to full forward and 0 percent to full reverse; direction and speed are given with a single signal.
In this method the motor is never released; during one part of the period it sees voltage in one direction and during the rest in the opposite direction. The net average voltage is the difference between the two. At 50 percent the forward and reverse times are equal, so the average is zero and the motor stops.
Its advantage is control behaviour. Since current circulates continuously in the motor even around zero speed there is no dead band; the direction transition is uninterrupted and linear. This is valuable in applications requiring position control and precise motion at low speed.
The price is that current circulates even at standstill. Although the motor is stopped, a ripple current flows through the winding; this heats both the motor and the driver for nothing. To limit the loss, a high switching frequency and sufficient motor inductance are required.
In typical AXI applications such as automatic doors, barriers and actuators the motor is most of the time either stopped or running at a certain speed; in this scenario the sign-magnitude method is generally more efficient. Locked antiphase is preferred in precise position controls that constantly oscillate around zero.
The context in which this term is used: DC Motor Driver Selection Guide