Distributed Energy Communications & Control (DECC) Laboratory

A new laboratory, called the “Distributed Energy Communications & Control” Laboratory has taken shape at building 3114 on the North end of the ORNL complex (see the photos in Figs. 1 & 2). The primary focus of the laboratory thus far as been on controls development to demonstrate the use of distributed energy (DE) such as microturbines, reciprocating engines and fuel cells to produce reactive power to boost local voltage dynamically; something that can’t currently be done with conventional power equipment. Reactive power is a necessary power ingredient for running inductive and capacitive loads such as motors and fluorescent lights; more on this later. We have chosen to focus on the controls for the conversion interface between the DE and distribution system, inverter for DC sources and generators for AC sources, for our development and testing. The laboratory achieved a key milestone in September with the simultaneous operation of a 125kVar programmable inverter and 300kVar Synchronous Condenser (SC)¹. A kVar, which stands for 1000 volt-amperes-reactive, is a unit measure of reactive power production. In comparison conventional capacitor banks used on distribution circuits range in size from 300 to 1200 kVar. Both the inverter and SC were controlled by a real-time control system using our control logic, which emulates the logic in firmware for the DE controller, to regulate local voltage. Each DE device regulated their local voltage since they are connected at different electrical locations in the ORNL distribution system (see Fig.3). The real-time controller used control logic that ORNL designed in the Matlab/Simulink environment on our laboratory PC.

Fig. 1. SC Test Area of the DECC Lab is shown with Shawn Henry2 of Florida State University.		Fig. 2. Inverter Test Area of DECC Lab is shown with Patricia Hoffman of DOE3 and Tom Rizy.

The successful parallel operation of the two reactive power producing DE devices in our testing is an important first step towards using multiple DE devices to provide dynamic voltage regulation; it is vital for its use on distribution circuits of the future. One of our industry partners, Southern California Edison, plans to implement our controls on a new distribution feeder in the not to distant future. These future circuits will depend on DE devices to provide most if not all of the reactive power needs of a circuit, such as 50 to 80% of the reactive load. Also, DE must operate so that they don’t interfere with each other or with the current protection practices and hardware of the distribution system. Our testing is also laying the groundwork for “Rules of Thumb” for this new DE paradigm which gives another added value to DE.

What is Reactive Power?

Electric power consists of two components, active and reactive power. Only active power does actual work while reactive power flows in and out in a cyclic manner to provide energy fields of various loads. Reactive power, which is measured in volt-amperes reactive (vars), is produced when electrical current is out of phase with the electrical voltage due to inductive or capacitive loads. Inductive loads produce current that lags voltage⁴ and results in lagging power factor⁵, and capacitive loads produce current that leads voltage and results in a leading power factor. Only active power is produced when there are purely resistive loads which produce current that is in phase with the voltage (unity power factor). Reactive power consumption results in lagging power factor and can cause increased losses and excessive voltage sags. Also, reactive power does not “travel well” – meaning it is much more effective if applied locally where it is needed as opposed to trying to send it over long electrical distances, such as from central generators over long transmission lines. Inadequate reactive power reserves can contribute to voltage instability and collapse and wide-scale power outages at the worst, so it is necessary to effectively manage reactive power levels.

Fig. 3. Electrical configuration for the Reactive Power Laboratory showing the two testing areas and how they interface to the ORNL Distribution System.

For further information, please contact:

John Kueck (kueckjd@ornl.gov, 574-5178)
Tom Rizy (rizydt@ornl.gov, 574-5203)
Leon Tolbert (tolbertlm@ornl.gov, 946-1332)
http://www.ornl.gov/sci/decc

Footnotes:

¹It is a large synchronous motor operating unloaded and overexcited. A synchronous condenser can only produce reactive power while a synchronous generator can produce both active and reactive power. The inverter was operated at around 10% of its rating.
²Shawn Henry was a HERE Student during the summer and the summer before last and is working towards his Phd in electrical engineering at Florida State University in Tallahassee.
³Patricia Hoffman of DOE’s Office of Electricity Delivery & Energy Reliability.
⁴The crest or peak of the current waveform in time occurs after that of the voltage waveform.
⁵Power factor is the cosine of the angle (phase difference) between voltage and current and represents the ratio of the average power delivered to the product of voltage and current.

Submitted by: Tom Rizy, Cooling, Heating and Power Group

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