University of Texas at Austin



Subject Senior Electrical Design Project: Industrial Power Supply

Date Aug 20, 2004

PROJECT REQUIREMENTS

This senior electrical design project is to design a 50V DC power supply for use in an industrial high temperature environment. The purpose of the industrial power supply is to convert a nominal AC voltage to a DC voltage used to power the electronic controls and electrical motors/actuators in the system.

The basic requirements of the proposed power supply are as follows.

The AC input voltage to the DC power supply is variable providing a maximum voltage and current of 1000VAC at 5A RMS, respectively. The proposed industrial power supply DC voltage is required to regulate its DC output to 50 Volts DC with a maximum current rating of 20 Amps. The load current varies and depends on the number of motors and actuators running at one time. The industrial power supply is required to regulate its DC output under these varying load conditions.

Note that the separation of distance between the AC power source and the industrial power supply can vary (maximum 4000ft) and this distribution distance should be taken into consideration in the power supply design.

CONVENTIONAL POWER SUPPLY DESIGN

A classical power supply scheme used in industrial systems is shown in Figure 1 (Upper). This classical scheme is recognized as the conventional full-wave rectified power supply that provides unregulated DC voltage.

The AC power is transformed, rectified and filtered, and delivered to the various loads (L). The DC output voltage is therefore a function of the AC input voltage, the cable loss, the transformer step-down ratio, the load impedance (L) and other environmental factors such as temperature etc. This DC output voltage is monitored and communicated to a computer located at the AC power source, which attempts to maintain a constant 50VDC at the output by varying the AC input voltage on the primary winding of the transformer.

This system works well under steady state conditions. However, changes in load, due to motors switching on/off or valves etc opening or closing can have a dramatic impact on the output voltage, and the latency in the control system results in unstable voltage regulation under transient load conditions.

For example, in Figure 2, the 50V output is shown for a load change from 0-5 Amps. It can be seen that the output drops to 35V and takes about 10 seconds to return to within 10% of the specified 50V rating.

PROPOSED POWER SUPPLY DESIGN

A new power supply scheme is proposed as an alternative to the conventional full-wave rectified power supply design. In the new power supply design, the diodes in the rectifier bridge are replaced with an active switching device, and a synchronous rectification control system, which can regulate the DC voltage using a pulsed width modulation scheme. A schematic for such a system is shown in Figure 1 (lower).

INDUSTRY SPONSOR ASSISTANCE

The sponsor company can provide assistance with components, test systems and supervision in order to help the teams reproduce the existing system in their labs and build working prototypes of the proposed solutions.

For further information about this project, the following people may be contacted:

|Name |Title |Phone |

|E. Harrigan |Manager |281-285-4174 |

|E. Quam |Electrical Engineer |281-285-7527 |

|W. Chow |Electrical Engineer |281-285-4199 |

Figures

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Figure 1: Existing (Upper) and Proposed (Lower) MRPC power supply systems

Figure 2: 50V regulation stability during a load change

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