It's happening again. Another energy crisis is hitting the country and consumers are left scrambling for solutions. In the past, it was the oil shortages with gas lines and escalating pump prices. This time, it's an electric power shortage on the West Coast with the threat of rolling blackouts in California. This crisis could be another opportunity for the power electronics industry to expand its market.
Traditionally, the field of power electronics has dealt with the control aspects of electrical energy, rather than the generation of the energy itself. But if we analyze and extend the concept of power electronics to its logical extreme, we could add the process of generation to this field in addition to control.
To do this, we need to define the concept of power electronics. The term “power” usually refers to a raw form of energy that is available to perform work. The term “electronics” generally refers to the microscopic management of electrical energy usually at the molecular level through the use of a variety of solid-state devices. Besides various types of solid-state devices, we also have capacitors, resistors, batteries, conductors and superconductors, magnetics, motors, generators, photovoltaics, and other components used to build power electronic systems. These are some of the basic ingredients we now have to accomplish the generation and distribution of electric power.
Generating and distributing electrical energy requires:
A source of raw energy. Sources of raw energy are available, but to a limited extent in oil, coal, natural gas, hydroelectric facilities, and nuclear materials. But fossil fuels are a limited quantity that won't last indefinitely, and hydroelectric and nuclear plants are expensive to build. However, we do have renewable and unlimited raw alternative energy sources such as solar and wind power. Future innovations include the possibility of controlled nuclear fusion.
A method of capturing the raw energy and storing it if necessary. This method is available, but to a limited extent. Present photovoltaic technologies in the form of solar panels are relatively low in efficiency, expensive to purchase, and sunshine is intermittently available.
Wind turbines generate electricity with two or three propeller-like blades attached to the rotor of a generator, followed by an inverter. You can use these turbines stand-alone or in wind farms connected to a utility power grid. Potential power quality problems include voltage flicker from gusty winds and inverter harmonics. Turbines must accommodate variation in wind speed using fixed pitch or adjustable pitch blades. Photo 1 shows a typical wind farm. Wind power generators are relatively efficient, fairly low in cost, but wind energy is also intermittent in availability. Although wind turbines and generators now have an acceptable efficiency, improving their efficiency is possible by broadening the RPM range of the turbine/generator.
It's necessary to increase conversion efficiency of photovoltaic devices and wind generators, and develop methods of storing energy generated from these intermittent sources. Batteries and ultra capacitors are candidate solutions for the storage problem.
A method of final conditioning the energy and distributing it to the consumer. This usually involves inversion of the power, i. e., converting it from dc to ac at the correct frequency and phase angle for transmission and distribution to the consumer. We also have this technology available from the power electronics industry and existing utility lines or building wiring.
Better yet, it's possible to capture, store, condition, and distribute the energy right at the consumer's own site in “personal energy systems.”
Photo 2 shows a DIP Intelligent Power Module (DIP IPM) consisting of a 3-phase IGBT bridge with the associated free wheel diodes along with a low-voltage ASIC for driving the lower IGBTs and a HVIC. It includes level shifting, to eliminate the need for external optocoupler isolation while driving the high-side IGBTs.
So what steps should the power electronics industry take to make alternative energy generation a technical and economic reality?
First, let's look at the problems requiring solutions. Solar and wind energy are only intermittently available because of the day-night cycle and weather conditions. Therefore, we must consume the energy in real time while it's available or store the unused portion for later consumption.
Presently, we can store the energy in batteries. However, batteries are expensive, deteriorate over a few years, and contain toxic materials that you must recycle or dispose.
The best solution will be ultra capacitors that can store a lot of energy for a long period of time. The electronic industry is now developing these ultra capacitors, however a much longer charge decay period (time constant) is necessary for alternative energy storage applications. A much higher energy storage capability (Joule Rating) is also necessary. Photo 3 shows a 1200-F ultra capacitor measuring 155 mm 61mm 33 mm that caches 3750 J at a nominal 2.5V.
The present photovoltaic panels are fairly inefficient only about 12% at best. Therefore, the goal of the photovoltaics industry will be to improve the management of photons and electrons at the molecular level for greater efficiency in terms of watts captured per unit area of solar panel products. The figure is a diagram of a photovoltaic (PV) system; it has a dc input and an ac output via an inverter or motor generator set.
Finally, we should vigorously pursue the development of room temperature superconductors to micromanage our power at the molecular level.
Electronic power conditioning is well suited for alternative energy applications. Power conditioning units can accept a variety of inputs from solar panels or wind generators. Let's look at some of the issues the industry can consider in planning a future strategy.
Compatibility Issues
Specifically, how will ordinary home appliances be affected when running off an inverter? Which type of inverter is best for personal energy systems the IGBT-based PWM type or the ferro-resonant type? The items of concern are the operation of appliance motors, microwave ovens, TVs, and compact fluorescent lamps. Most of the present IGBT inverters were designed for industrial motor applications. Problems with motor and transformer insulation damage from IGBT inverter spikes and EMI problem can arise especially if appliances aren't well grounded. Photo 4 shows an inverter delivering 1200VA from a battery bank or other dc source.
Safety will be a major issue with ultra capacitors, taking precautions to prevent a severe explosion if an ultra-cap is shorted. It's necessary to provide emergency disconnect switches and interlocks to protect the user and system service personnel from the amount of stored energy in ultra-caps. Underwriters Laboratories, CSA, etc. must inspect and test all components, and the entire system installation must be done in accordance with all applicable electrical codes.
Economic Opportunities
With the technical problems well addressed, what about the economic issues? With rapidly increasing electric rates, economic forces should kick in and provide an impetus to develop alternative energy systems.
In response to the electric cost hikes in the 1980s, the power electronics industry made a contribution to energy conservation by developing solid state drives for industrial motors. As an example, thousands of passenger elevators have been upgraded from rotating motor-generator sets to SCR drives for control of the cable hoisting machinery. Building owners quickly recovered their capital expenditure for the solid-state drives through a 30% reduction in power elevators consume.
Compact fluorescent lamps are another contribution the power electronics industry has made to energy savings, and economic forces will make these lamps more financially attractive.
If electric rates continue to rise with blackouts looming, consumers will once again be looking for solutions from the power electronics industry. Could personal energy systems with solar panels on the roof and converters in the closet be the wave of the future in new construction? Considering the excellent solutions that the power electronic industry has provided in response to past energy problems, it may be a reality. With California's electric crisis, the power electronics industry has a new frontier to explore. And with new ideas, the electric crisis is another opportunity to expand the scope of power electronics.
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The Energy Situation & PowerSystems World
The importance of the energy situation has prompted PCIM Power Electronic Systems to cover this subject in the keynote presentations for the PowerSystems World conference on September 11. Speakers will include
- Vlatko Vlatkovic, General Electric Corporate R&D, “Power Electronics in Power Systems: Technology and Business.”
- Alex Lidow, International Rectifier, “The Motor Drive Revolution in the Energy-Starved Generation.”
- Neil E. Rasmussen, American Power Conversion, “Data Center/Facility Infrastructure for the Next Millennium.”
- David Kreiss, Kreiss-Johnson Technologies, “Power Management Not an Option.”