ASHRAE AB-10-024-2010
可调速（变频）驱动器的热增益

Heat Gain from Adjustable Speed (Variable Frequency) Drives

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标准号

ASHRAE AB-10-024-2010

发布

2010年

发布单位

ASHRAE - American Society of Heating@ Refrigerating and Air-Conditioning Engineers@ Inc.

 

 

适用范围

INTRODUCTION The Adjustable Speed Drive (ASD) is also known as an Adjustable Frequency Drive (AFD) or Variable Frequency Drive (VFD). ASDs are used in industrial processes that need to control the shaft speed in rotation equipment such as fans@ pumps and assembly lines. ASDs can be mechanical where a transmission with belt or chain could be used@ hydraulic@ electrical where resistors and special motors could be used@ and electronic using solid state components. AC motors are used more frequently than DC motors because they can be connected directly to the utility power lines. For this reason@ VFDs have greater use than other ASDs. Electronic ASDs or VFDs are popular because they are easy to use and are energy efficient. Efficiency@ functionality@ and the economics of VFDs have motivated increased use of these devices. The VFD is one type of ASD used for AC motors. Hereafter@ VFD will be consistently used. VFDs are used in industrial processes that need to control the shaft speed of AC motors in assembly lines@ fans@ pumps and other mechanical equipments. The VFD can be diagrammatically represented by three blocks: an AC-DC rectifier@ a DC bus link and a DC-AC inverter as shown in Figure 1. The principle of the VFD is to transform the stable 50 or 60 Hz power line frequency into a variable frequency through two steps. First@ the sinusoidal input voltage of the rectifier is converted to a DC voltage. Following the rectification@ the DC voltage is chopped into an AC output voltage of the desired frequency according to the required AC motor speed. While the input frequency of the AC-DC rectifier is always constant@ the output frequency of the DC-AC inverter is variable causing modification of the AC motor speed. The efficiency of a VFD is related to its power loss. The VFD power losses consist of both constant and variable quantities. The constant losses are comprised of cooling fans and electric circuit excitation and these losses do not depend on the load. The variable losses consist of switching and lead losses in the power semiconductors and these losses do depend on the load as pointed out by Lidenborg (1998). VFD power losses at part-loads are needed by HVAC engineers and designers for correctly estimating the indoor environmental heat gain. Two analytical VFD power loss models will be presented and compared in later sections. These models consist of a linear model in which power losses vary linearly with the load and a quadratic model in which the power losses do not vary linearly with the VFD load.

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