Avista Microgrid Automatic Generator Controller

To ensure power system stability for Avista's future microgrid for the Spokane area, an Automated Generator Controller (AGC) will be implemented to maintain system frequency and regulate bus voltage.

Project Definition
System load variation has a direct impact on the system frequency. The frequencies of each hydro-generator are designated by their share of the system load and the amount of system load. An increase in system load will decrease the system frequency and vice versa. This also applies to the generator level; an increase in a generator’s load will decrease the operation frequency of the generator. The steady state speed characteristics of each generator will need to be examined in order to develop a control scheme for generator frequency. Once developed, the control scheme will distribute loads to the two generators to maintain the set frequency of each generator and thus maintain frequency stability for the entire system.

The Avista Microgrid Automatic Generator Controller is a project based around designing a controller to regulate and control two hydro-generator units on the Spokane River in a micro-grid operation. The problem occurs when attempting to operate both generators in a safe manner in response to changes in system load. It was the goal of this project team to design, simulate, and validate a model of the entire hydro system to later be the subject of an automatic generator controller.

Governor
The main function of the turbine governing system is to regulate the turbine-generator speed and hence the frequency and the active power in response to load variation. The speed control mechanism includes equipment such as relays, servomotors, pressure or power amplifying devices, levers and linkages between the speed governor and governor-controlled gates. The speed governor normally actuates the governor controlled gates that regulate the water input to the turbine through the speed control mechanism.

Turbine
Hydraulic turbines derive the potential energy of the fluid into kinetic energy and a conversion of kinetic energy, into useful work. Hydraulic turbines derive power from the force exerted by water as it falls from an upper to a lower reservoir. Turbine dynamics are characterized by the variations in flow, and output mechanical torque with respect to turbine speed, gate opening, runner blade movement and the difference in pressure between the turbine inlet and outlet. Hydraulic turbines are divided according to their hydraulic action into two main classes: impulse turbines and reaction turbines.

Impluse Turbines
An impulse turbine has a runner with numerous spoon-shaped “buckets” attached to its periphery which are driven by one or more jets of water issuing from fixed or adjustable nozzles. The kinetic energy is in the form of a high speed jet that strikes the buckets, mounted on the periphery of the runner. Impulse or action type turbines are represented by the Pelton water wheel and are typically used in high head configurations of 300 meters or more.

Reaction Turbines
In reaction turbines, the entire flow from the headwater to tail water takes place in a closed conduit system. Reaction turbines extract power from the kinetic energy of water because of the difference in pressure between the front and the back of each runner blade as the water flows through the turbine. Water pressure applies a force on the face of the runner blades. Reaction turbines are represented by radial flow Francis turbines and axial flow Kaplan turbines. Francis turbines are typically configured with heads of 40 to 600 meters and Kaplan turbines operate at heads of 10 to 100 meters.

Exciter
The rotor or the field coils in a generator produce the magnetic flux that is essential to the production of the electric power. The rotor is a rotating electromagnet that requires a DC electric power source to excite the magnetic field. This power comes from an exciter.

In many generators the exciters are considered static. The DC power for the electromagnet is from the main generator output itself. A number of high power thyristors recitify the AC current to produce a DC current which feeds to the rotor through slip rings. This eliminates the operation and maintenance problems associated with having another rotating machine. Static exciters offer a better control of the output than an electromechanical control. During start up, when there is no output from the generator, a large battery bank provides the necessary power for excitation.

System Specifications
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System Models
Before being able to design an AGC, the two generator units, Monroe Street and Upper Falls, need to be modeled. Below is the block diagrams for the hydro power units.

Validation
In verifying the models, we will compare the outputs of our system to an ATP (Alternative Transients Program) and Powerworld file that were created by previous master's students for the master thesis.

Team Meeting Minutes

 * [[File:SF2016 Meeting Minutes.pdf]]

Expo Poster

 * [[File:SF2016_ExpoPoster.pdf]]
 * [[File:SF2016 Final Expo Poster.pdf]]

Project Schedule

 * [[File:SF2016 Project Schedule.pdf]]