ABSTRACT
Let's turn now to the third and last amplifier type, the SCR. Both the smooth and PWM amplifier types require for their operation de power supplies. That is, we usually use the ac power line as our ultimate power source, so if a device needs de, we have to "make it" from ac. In fact, these de supplies represent a large fraction of the cost, size, and weight of smooth and PWM amplifiers. The SCR amplifier does not need or use such de supplies; it works directly from the ac power line. Its efficiency is even better than that of PWM types: 85 to 95%. It can be used in low or moderate power systems but it becomes the method of choice when the power level gets much above 30 hp, where its cost becomes signficantly less than the PWM. It can be used up to thousands of kilowatts, for both motion control and other applications such as electric heating. Its main drawback is a slower response speed, but this is often acceptable since the high-power rotating machines will tend to themselves be slow.
