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Power Controller to Support Economic Growth
Stand-alone wind or hydro power often can provide the necessary energy for continued rural development. With a proper control system, local stand-alone installations can provide the same quality of electricity supply as good, grid-based systems.

By Steen Carlsen, M.Sc., Denmark
Migration from Rural Areas
A common, severe threat to most third-world countries is the common migration from rural areas to cities. This leads to growing slums, unemployment, and environmental strain in cities. The obvious remedy for the migration is to give people in rural areas better income opportunities and improved standard of living. A part of such improvement involves providing electricity to the villages.
Electrification of Rural Areas
The use of electrical power in villages can be divided into:
*Power used in private homes.
*Power used for public community facilities; e.g., water supply, public showers, street lighting.
*Power used for workshops, crafts, and small industry; e.g., lathes, welding machines.
In private homes, and home businesses the main benefits from electrification can be obtained by one-phase loads such as:
*Electrical light to replace kerosene (kerosene fumes often lead to lung diseases) and batteries.
*Refrigerator to store food and medicine.
*Radio, TV, and computers.
A larger economic advantage of electrification is, however, the possibility of setting up workshops, crafts, and small industry, which demand larger machines that need 3 phases.
Replacing Petrol & Diesel
Today, increasing numbers of villagers in many developing countries buy small 1-5 kW portable generators. Along with the generators come regular outlays for fossil fuels, that drain the economy and contribute to CO2 emissions.
Many of these villages have local wind- and/or micro hydro power potentials, which can replace or supplement petrol- and diesel-driven generators. The prospective lifetime for small hydro sites is typically on the order of +50 years, and, in the third world, costs are generally around 2000 $/kW.
Over Voltage Kills Bulbs
Small stand-alone renewable energy installations have been known for decades, but many of them have severe problems with voltage variations. Often the voltage variations range from below 180 V to over 250 V. If a standard incandescent bulb is exposed to a voltage just 5% above its rated voltage, its lifetime drops from the nominal 1200 hours to just 670 hours. If voltage rises to 10% above the nominal, the bulb’s lifetime drops from 1200 hours to a mere 385 hours. Costs of bulbs have been a severe expense for many users of stand-alone power systems. Voltage variations not only have killed bulbs, but have also reduced the use of radios, telefax, computers, and other types of machinery, all of which are important to a competitive infrastructure.
Control the Power
Many of the problems of voltage variations can be avoided by using a power controller. Its main task is to control and to maintain stable voltage, independent of variations in consumption and in wind / water-flow.
A power controller can be designed to monitor the voltages of all 3 phases. If the voltage of one of the phases raises, an electronic load-controller increases the amount of power transferred to other load(s). The controller adjusts the power dissipated in the other load(s), until the voltages match the preset level. In this way, the power controller maintains all 3 phase-voltages within, e.g., 2% (over a power consumption range from 0-100%).
The surplus power dissipated in the other load(s), can be utilized for:
1. Heating (e.g., of houses, hot water, greenhouses);
2. Cooling (e.g., of cold-stores, freezers, and/or refrigerators);
3. Water pumping (with buffer tanks or for irrigation).
Increasing Distance from Generator to User
One factor that can contribute to problems with varying voltages in small stand-alone systems is long distances between the power source (e.g., the hydro power turbine) and the consumers. Long distances increase the resistance of the wires, which leads to bigger voltage variations with load variations. If a power controller is equipped with a remote sense circuit, the controller can be installed far from the site, at which the voltages must be controlled. This increases the maximum allowable distance between turbine and consumers, hence raises the number of potential wind- and micro hydro power sites that are economically exploitable.
Motor as Generator
Traditional stand-alone systems are equipped with synchronous generators. A standard asynchronous electromotor can operate as a generator, when it is connected to a public grid (i.e., the utilities). Some power controllers are designed so they appear as a public grid to an asynchronous motor. This allows the motor to operate as a generator. Standard electromotors are cheap and robust, don’t require much maintenance, and are usually available locally.
Stand-alone or Stand-together
A power controller can be configured to allow a stand-alone system to be synchronized to other 3-phase supply systems. This enables a group of villages, to join their “stand-alone” installations, and form a “stand-together” group or cooperative, allowing exchange of electrical power between the villages.
The ability to synchronize the installation to another 3-phase system(s) allows a remote “stand-alone” installation to become grid-connected and to sell its surplus electricity production to the utilities, if/when the public grid later is extended to include the site.
Steen Carlsen, more information
Steen Carlsen is an electronic engineer and has developed a power controller for stand-alone systems up to 100 kW. In 1998, the power controller received The Danish Environmental Award for Joint Ventures for Adapted Environmental Technology.

Photo text::
The first 6-kW prototype of the power controller developed by Steen Carlsen.
The power house was built by the villagers of Quico 4,000 m high in the Andes in Peru.

Figure text 1:
The power controller used in stand-alone micro hydropower system. Fixed voltage is supplied to the house(s).Surplus power is supplied to a heating cartridge.

Figure text 2:
System blocks for a stand-alone micro system using a power controller to maintain fixed 3-phase voltage - and to control water intake.

More information:
Steen Carlsen, Carlsen Power Electronics,
Science Park, Gustav Wieds vej 10,
8000 Aarhus C, Denmark.
Ph: +45 86190319,
fax: +45 86201222,
e-mail: Carlsen@power-electronics.dk.
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ISSUE #30 (683KB) 18 pages (2000-08-11)
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