They provide the necessary mechanical-to-electrical or electrical-to-mechanical conversion. In the United States, more than 50% of the electric power is consumed by electric motors.
The motors perform many different functions, from small applications like cooling fans in your personal computer that consume only a few watts of power all the way to huge pumps that consume megawatts.
The majority of motors used today, approximately 80%, are three-phase induction motors. Motors themselves have limited capabilities. In more complicated and technical applications, the motor itself does not perform the necessary tasks.
Today, a complete electric drive system is needed to control and manipulate the motor to fit specific applications. An electric drive system involves the control of electric motors in steady-state and dynamic operations. The system should take into account the type of mechanical load.
There are many different types of mechanical loads. When defining a load, torque versus speed characteristics are explored. The relationship is then used to design the type of electric drive system. In the past, electric drive systems required large and expensive equipment. These systems were inefficient and limited to the specific applications they where designed for.
Today, with advancements in power electronics, control electronics, microprocessors, microcontrollers, and digital signal processors (DSPs), electric drive systems have improved drastically. Power electronic drives are more reliable, more efficient, and less expensive.
In fact, a power electronic drive on average consumes 25% less energy than a classic motor drive system. The advancements in solid-state technologies are making it possible to build the necessary power electronic converters for electric drive systems.
The power electronic devices allow motors to be used in more precise applications. Such systems may include highly precise speed or position control. Systems that used to be controlled pneumatically and hydrolically can now be controlled electrically as well.