### Abstract

Variable-frequency drives (VFDs) are widely applied on induction motors that drive fans, pumps, and compressors. Under partial loads, VFDs not only adjust frequency to reduce motor speed and mechanical output power (load) but also adjust voltage to reduce motor electrical input power. Traditionally, VFD manufacturers recommend controlling the voltage so that it is proportional to the square of the frequency for variable torque motor loads on fans and pumps and proportional to the frequency for constant torque motor loads on compressors. The purpose of this paper is to investigate energy-efficient voltage frequency ratios of VFDs using the motor equivalent circuit method. First, the motor load and speed correlation are derived for different applications. Then, VFD voltage is optimized for a given VFD frequency to maximize motor efficiency. Finally, the motor efficiency is simulated and compared under the optimal voltage and different preset voltages. The simulation results show that the motor efficiency with the ratio of voltage to frequency to the power of 1.5 is mostly close to the optimal efficiency for variable torque motor loads, and the motor efficiency with the ratio of voltage to frequency to the power of O. 5 is mostly close to the optimal efficiency for constant torque motor loads with efficiency improvement by up to 3% over traditional ratios.

Original language | English (US) |
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Title of host publication | ASHRAE Transactions - 2016 ASHRAE Annual Conference |

Publisher | Amer. Soc. Heating, Ref. Air-Conditoning Eng. Inc. |

Pages | 149-159 |

Number of pages | 11 |

Volume | 122 |

ISBN (Electronic) | 9781939200464 |

State | Published - 2016 |

Event | 2016 ASHRAE Annual Conference - St. Louis, United States Duration: Jun 25 2016 → Jun 29 2016 |

### Other

Other | 2016 ASHRAE Annual Conference |
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Country | United States |

City | St. Louis |

Period | 6/25/16 → 6/29/16 |

### Fingerprint

### ASJC Scopus subject areas

- Building and Construction
- Mechanical Engineering

### Cite this

*ASHRAE Transactions - 2016 ASHRAE Annual Conference*(Vol. 122, pp. 149-159). Amer. Soc. Heating, Ref. Air-Conditoning Eng. Inc..

**Simulated energy-efficient voltage frequency ratios of Variable-frequency drives on induction motors.** / Wang, Gang; Kiamehr, Koosha.

Research output: Chapter in Book/Report/Conference proceeding › Conference contribution

*ASHRAE Transactions - 2016 ASHRAE Annual Conference.*vol. 122, Amer. Soc. Heating, Ref. Air-Conditoning Eng. Inc., pp. 149-159, 2016 ASHRAE Annual Conference, St. Louis, United States, 6/25/16.

}

TY - GEN

T1 - Simulated energy-efficient voltage frequency ratios of Variable-frequency drives on induction motors

AU - Wang, Gang

AU - Kiamehr, Koosha

PY - 2016

Y1 - 2016

N2 - Variable-frequency drives (VFDs) are widely applied on induction motors that drive fans, pumps, and compressors. Under partial loads, VFDs not only adjust frequency to reduce motor speed and mechanical output power (load) but also adjust voltage to reduce motor electrical input power. Traditionally, VFD manufacturers recommend controlling the voltage so that it is proportional to the square of the frequency for variable torque motor loads on fans and pumps and proportional to the frequency for constant torque motor loads on compressors. The purpose of this paper is to investigate energy-efficient voltage frequency ratios of VFDs using the motor equivalent circuit method. First, the motor load and speed correlation are derived for different applications. Then, VFD voltage is optimized for a given VFD frequency to maximize motor efficiency. Finally, the motor efficiency is simulated and compared under the optimal voltage and different preset voltages. The simulation results show that the motor efficiency with the ratio of voltage to frequency to the power of 1.5 is mostly close to the optimal efficiency for variable torque motor loads, and the motor efficiency with the ratio of voltage to frequency to the power of O. 5 is mostly close to the optimal efficiency for constant torque motor loads with efficiency improvement by up to 3% over traditional ratios.

AB - Variable-frequency drives (VFDs) are widely applied on induction motors that drive fans, pumps, and compressors. Under partial loads, VFDs not only adjust frequency to reduce motor speed and mechanical output power (load) but also adjust voltage to reduce motor electrical input power. Traditionally, VFD manufacturers recommend controlling the voltage so that it is proportional to the square of the frequency for variable torque motor loads on fans and pumps and proportional to the frequency for constant torque motor loads on compressors. The purpose of this paper is to investigate energy-efficient voltage frequency ratios of VFDs using the motor equivalent circuit method. First, the motor load and speed correlation are derived for different applications. Then, VFD voltage is optimized for a given VFD frequency to maximize motor efficiency. Finally, the motor efficiency is simulated and compared under the optimal voltage and different preset voltages. The simulation results show that the motor efficiency with the ratio of voltage to frequency to the power of 1.5 is mostly close to the optimal efficiency for variable torque motor loads, and the motor efficiency with the ratio of voltage to frequency to the power of O. 5 is mostly close to the optimal efficiency for constant torque motor loads with efficiency improvement by up to 3% over traditional ratios.

UR - http://www.scopus.com/inward/record.url?scp=85008367680&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=85008367680&partnerID=8YFLogxK

M3 - Conference contribution

AN - SCOPUS:85008367680

VL - 122

SP - 149

EP - 159

BT - ASHRAE Transactions - 2016 ASHRAE Annual Conference

PB - Amer. Soc. Heating, Ref. Air-Conditoning Eng. Inc.

ER -