TY - GEN

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

AU - Wang, Gang

AU - Kiamehr, Koosha

N1 - Publisher Copyright:
© 2016 ASHRAE.
Copyright:
Copyright 2020 Elsevier B.V., All rights reserved.

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.

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M3 - Conference contribution

AN - SCOPUS:85008367680

T3 - ASHRAE Transactions

SP - 149

EP - 159

BT - ASHRAE Transactions

PB - American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE)

T2 - 2016 ASHRAE Annual Conference

Y2 - 25 June 2016 through 29 June 2016

ER -