Optimization of a Single-Phase Induction
Motor Drive
Additional Information
Commercial
Case Studies/Projects
Geothermal Energy
Energy Resource Station
NBCIP
Lighting Research Center
Grant #: 96-02
Principal Investigator: Alvin L. Day
Organization: Iowa State University
Subgrantee Organization: Potter Solar
Services, Inc.
Technical Area: Energy Efficiency
Background and Significance:
The operating efficiency of a single-phase induction motor decreases dramatically as the load on the motor decreases when the voltage applied to the motor remains constant. Constant voltage is the operational mode for most of the installed base of single-phase induction motors in residential, commercial and industrial settings. As the cost of power-electronic devices has decreased, the possibility for economically justifiable applications of motor controllers has increased. Applications where the motor operates at light load levels for extended periods of time are the most likely to economically benefit from motor control.
In most installations of single-phase induction motors, the motor windings are directly connected to the voltage source without electronic control. Induction motors are designed to operate at their greatest efficiency when the mechanical load is near the full-load rating of the motor. When the mechanical load is reduced, the motor continues to operate, but at a lower efficiency level. The efficiency can be improved at the reduced load levels by decreasing the voltage applied to the motor windings.
Project Objectives:
With advances in power-electronic devices, new opportunities exist to improve the techniques used to control single-phase induction motors. This project focuses on the capacitor-run type of motor. The primary objective was to develop a controller design that would utilize the existing capacitor on a capacitor-run motor such that both high efficiency and high power factor would be automatically maintained at all mechanical load levels.
Summary of Work:
Allan Potter, a consultant working for Potter Solar Services, Inc. has investigated various designs of switch-mode controllers. Alvin Day, the principal investigator, has collaborated with Potter on evaluating these designs. Several designs have been constructed and tested in a laboratory. The most promising design is the AC Switching Regulator which could control the voltage applied to the Auxiliary Phase winding, or it could control the voltage to both the Auxiliary Phase winding and Main Phase winding.
The laboratory tests have revealed that the circuit induces high switching-transient currents into the power line, which tended to make the modulator circuit output unstable. Because of this instability, it wasn’t possible to do field testing of the circuit. Potter Solar Services plans to continue to develop the circuit by trying various filtering techniques to reduce the switching transients.
The discreet component costs for the circuit design shown in Figure 1 were estimated from large quantity catalog prices. If the design was further developed for large volume production, it is expected that the per unit cost would decrease significantly.
The economic pay back time for the circuit cost will be dependent on the operation of the motor. If the motor is operated at light loads for extended periods of time, the pay back time will be shorter.
Example calculation: ½ hp motor operated at light load 4 hours per day, 5 days per week
Estimated annual energy savings (based on lab tests): (100 W)(4 hr/day)(5 days/wk)(52 wks/yr.) = 104 kWh per year
Estimated annual cost savings: (104 kWh)(0.10 $/kWh) = $10.40
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