By: Dr. Shiyoung Lee, Assistant Professor of Electrical Engineering
When I was in middle school, I was a devoted experimenter who liked to disassemble and assemble any electrical and/or electronic apparatus. One ambitious experiment that makes me smile, even today, was the control of light intensity of an incandescent light bulb with a potentiometer (instrument for volume or brightness control) from an old radio set. Despite the smoke emitted from the poor device, there was a short “wow” moment when the light bulb dimmed.
Since then, I have been fascinated with the safe and efficient control of electric power with electronic circuitry. During my college years, I applied my knowledge of power electronics, which was application-oriented and multidisciplinary in nature and encompassed several electronic courses, to create hand-made electronic dimmer-equipped desktop lamps as gifts for my friends. A dimmed incandescent lamp was multi-functional as an exotic mood light and as a regular light.
The dimmer module was a straight analog-type power controller that used a triode for alternating current (TRIAC). This makes the phase-control possible for both positive and negative cycles of ac voltage. Implementation of the phase-control was dominantly analog circuitry, but it was gradually replaced with digital circuitry after the advent of the microprocessor or microcontroller.
Digital power control relates directly to the controller as a part of the power electronic system consisting of input and output power, the power processor, and the controller.
Electric power is used almost everywhere as the major form of energy in modern human society. Digital power control is an electronic method to convert raw electrical energy to a usable form of electrical energy. In addition to the two types of electric form–ac and dc–various voltage levels and frequencies are involved in power control.
The power input is usually a form of raw electrical energy, such as single- or three-phase ac voltage or dc voltage from a battery, or solar cell panel or fuel cell. The power processor incorporates a matrix of power-switching devices and it performs the actual power conversion and processing of the energy from input to output.
The controller deals with steady-state and dynamic characteristics of a closed-loop system to control the amount of power transferred to the output effectively. In terms of the nature of the controller circuitry, there are analog and digital controllers.
Analog controllers use many components that result in a large footprint. Component values deteriorate with age, temperature, and other environmental conditions, adversely impacting system stability and response. Moreover, analog controllers are very difficult to duplicate the same performance precisely.
On the other hand, digital power control offers less complex, smaller, and lower power consumption designs.
The power output is the form of desired electrical or mechanical energy. The controller directs the power processor to take feedback signals that are measured at output and compared to the command signal. For the implementation of digital power control, a microcontroller, microprocessor, or digital signal processor (DSP) is required. Therefore, using digital power control requires lots of software programming with high level programming languages.
The Digital Power Conversion Research Laboratory at Penn State Berks was established in 2007. The lab focuses on the study of efficient power converter topologies and their control algorithms, which could apply to the various electric motor drives to improve overall system efficiency.
The Digital Power Conversion Research Laboratory is equipped with various TMS320 series DSP-based development platforms from Texas Instruments for long-term research on digital power control for both power converters and motor drives. Among them, the renewable energy development platform is a scaled down version of the digitally controlled dc-ac inverter. It is equipped with all the necessary current and voltage measurements to implement advanced algorithms, such as the maximum power point tracking for solar power generation. The dual motor control and power factor correction (PFC) development platform leverages the real-time control capabilities of the processor to bring high performance field-oriented motor control (FOC) and active PFC into performance and cost-sensitive applications.
Power conversion with a powerful and efficient digital controller will be the inevitable choice for not only today’s power-hungry applications but also for the future’s maximum conservation of electrical energy.