If you are looking for a place to improve motor efficiency, one place to start is with Power Factor Correction (PFC). Power Factor Correction can be a critical opportunity to improve efficiency, particularly if that action can be accomplished at the motor controller.
In an alternating current system, the power factor is defined as the ratio of the real power (the capacity to perform work) to the apparent power, and is expressed as a number between 0 and 1. Low power factors are generally produced by inductive loads where the current is used to create a magnetic field, and the magnetic field produces the desired work. Inductive loads include transformers and electric motors. Low power-factor loads of this type increase losses and raise energy costs. For example, in some instances a non-linear load can even cause the apparent power to be greater than the real power.
According to the US Dept. of Energy, low power factors are expensive and inefficient. Indeed, many utility companies charge an additional fee if your power factor is less than 0.95. A low power factor also reduces your electrical system’s distribution capacity by increasing current flow and causing voltage drops.
PFC is a method by which the characteristics of an electrical load such as that produced by a motor are altered to bring the power factor closer to 1 by supplying reactive power of opposite sign. One of the keys to achieving PFC and improving efficiency is thus the motor controller. Today’s more capable controller chip technology can provide reliable and cost-effective PFC for line-driven motor control applications. Indeed, some digital signal controllers (DSCs) can now execute the PFC algorithm and motor control algorithms on a single chip. However, to perform this action successfully, it is important that the device be able to allow the PFC loop to operate much faster than the motor controller.
The key point is the central function of PFC is to make the input current drawn from the system sinusoidal and in-phase with the input voltage.
Some DSCs offer multiple time-base options to support PFC and motor control on the same device (PFC, as noted, is a faster loop). DSCs also can support more efficient designs with advanced motor control algorithms like field-oriented control (FOC). Using an FOC algorithm, it is possible to dynamically control motor torque and speed for the most efficient operation possible.
In short, combining PFC with FOC can provide great strides in efficiency. Motor control software solutions for PFC are also an element in delivering a solution – either out of the box or tailored to your specific requirements. In fact, on-chip active power factor correction using software can lower overall system costs by using the processing power on one DSC for both PFC and motor control applications.
Note: Some DSC vendors describe the PFC in their application notes and even provide free source code.
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