WO2010114513A1

WO2010114513A1 - Three phase power supply fault protection

Info

Publication number: WO2010114513A1
Application number: PCT/US2009/038750
Authority: WO
Inventors: Prasad R. Atluri; Mark A. Lawrence
Original assignee: Hewlett-Packard Development Company, L.P.
Priority date: 2009-03-30
Filing date: 2009-03-30
Publication date: 2010-10-07

Abstract

A fault protection circuit for use in a three phase power supply system that has a three phase ac input, and three phases, with each phase having a power supply, includes a sensor in each phase that senses a phase drop out condition in its associated phase of the three phase power supply system, a relay in each phase coupled to the 5 sensor, with the relay de-energizing upon sensing the phase drop out condition, and a relay contact coupled to the relay. The relay contact opens upon de-energizing the relay, thereby removing ac power input to one or more of the power supplies.

Description

THREE PHASE POWER SUPPLY FAULT PROTECTION

Background

Three phase power supplies are used for many applications including in certain computer systems. The three phase ac input source is subject to various faults, including an open circuit in one of the three phases. Depending on the type of three phase power supply, such a fault can cause an abnormal interaction between the remaining two phases, and can lead to large input current pulses and EMI noise.

Description of the Drawings

The Detailed Description will refer to the following drawings in which like numerals refer to like items, and in which:

Figure 1 illustrates a typical delta-connected three phase power supply;

Figure 2 illustrates ac voltage traces for the power supply of Figure 1 with a fault in one of the phases;

Figure 3 illustrates the interaction of two phase of the power supply of Figure 1 with a fault in the third phase;

Figure 4 illustrates an exemplary three phase power supply fault protection circuit; Figure 5 illustrates an alternate, exemplary three phase power supply fault protection circuit;

Figure 6 illustrates an alternative exemplary three phase power supply fault protection circuit;

Figure 7 illustrates rectified ac input voltage waveforms in a three phase power supply with a fault in one of the three phases;

Figure 8 illustrates power factor corrected ac voltage waveforms in a three phase power supply with a fault in one of the phases; and

Figure 9 illustrates an exemplary three phase power supply fault protection circuit based on the waveforms of Figure 8. Detailed Description

Three phase ac-fed power supplies are used in many applications, including computer systems such as medium to high-end servers. In general, single phase ac- fed supplies are designed to operate from about 100 volts ac (VAC) πns to about 264 VAC rms. In North America, medium to high end servers are fed from the three phase ac input source and the single phase ac-fed power supplies are connected in a delta fashion. The discussion that follows will describe various embodiments of a fault protection circuit that may be implemented on a three phase power supply system. However, one skilled in the art will understand that variations of the same fault protection circuit may be implemented in other polyphase ac power supply systems. For example, a common practice for rectifier installations and in HVDC converters is to provide six phases, with 60 degree phase spacing, to reduce harmonic generation in the AC supply system and to provide smoother direct current. Experimental high-phase-order transmission lines have been built with up to 12 phases. These configurations allow application of Extra High Voltage (EHV) design rules at lower voltages, and would permit increased power transfer in the same transmission line corridor width.

Figure 1 illustrates such a three phase power supply system 10 that includes three phase ac input source 20 with phases A, B, and C, and delta-connected power supply 30, including individual power supplies PSl, PS2, and PS3, one for each of the phases A - C. In the configuration shown in Figure 1, PSl is fed from the ac input phases A and B, PS2 is fed from the ac input phases B and C, and PS3 is fed from the ac input phases C and A. The power supply system 10 also includes power analyzer 40, which measures ac voltage between each of the respective phases and ground.

Figure 2 illustrates ac voltage waveforms for the power supply of Figure 1 with a fault (open or phase drop out) in phase A at point X. With the A phase open at point X as shown, the power supply PS2 will be fed from phases B and C and will see no input voltage change (curve B-C). However, the power supplies PSl and PS3 will experience an abnormal input voltage that oscillates between zero volts and nominal voltage, mainly due to the delta connection of the power supplies PSl - PS3. Figure 3 illustrates the interaction of phases B and C of the power supply system 10 with a fault in phase A. Each power supply PSl - PS3 includes a diode rectifier circuit and a power factor correction circuit. As shown, front-end diode rectifier and power factor correction circuits 52 and 54 of power supplies PSl and PS3, respectively, are connected in series across the B and C phases. Under these conditions, power supplies PSl and PS3 will behave abnormally. Such abnormal behavior may include LEDs flashing between amber and green, inrush current relay contacts closing and opening at a low frequency (and making a clicking or chattering sound), and a pulsing output. An operator observing this abnormal behavior might not be able to determine if one of the power supplies PSl and PS3 is damaged or not. Furthermore, if the operator is not available to observe this abnormal behavior, then the power supplies PSl and PS3 may continue to operate in this abnormal fashion for an extended time, and the entire power supply system 10 might eventually fail.

To provide phase drop out fault protection, a three phase power supply fault protection circuit, an exemplary version of which is shown in Figure 4, may be added to a three phase power supply system 100, which includes Y-connected ac input circuit 110 with nominal 208 VAC supplies, three hot lines (phases A - C) and neutral N. The input circuit 110 provides three phase ac power to delta-connected power supplies PSl - PS3. Interspersed between the power supplies PSl - PS3 and the input circuit 110 is fault protection circuit 140 (which is applicable to a Y-connected (3- phase, 4 wire (three hot and one neutral)) power supply). As part of the fault protection circuit 140, each phase of the three phase power supply system 100 includes a normally open relay or bidirectional semiconductor switch (ka, kb, kc), which is operated by a corresponding relay coil (KA, KB, KC). As shown in Figure 4, the relay coils KA, KB, KC are connected at the input of their respective normally open (NO) relay contact (ka, kb, kc) and the neutral N. Under normal operating conditions, as soon as the ac input is present in the input circuit 110, the relay coils KA, KB, and KC are energized. Energizing the relay coils KA, KB, and KC causes the respective relay contacts ka, kb, and kc to shut and the ac input power is delivered to the power supplies PS 1 - PS3.

If one of the phases A - C drops out, or becomes open (such as at point X - phase A), then the associated relay coil (in this case, KA) is de-energized and the contact ka opens. Consequently, the PS 1 and PS3 input voltage is cut off (by the open contact ka), and the power supplies PSl and PS3 will turn off. However, if phase A opens at point Y (due to a fault), then the power supplies PS2 and PS3 will operate as normal power supplies, and only the power supply PSl will turn off.

When the input ac source is delta connected, there is no neutral wire, and the input voltage to each of the individual power supplies is line to line voltage. Such an input circuit 210 is shown in Figure 5, which also illustrates an alternate, exemplary three phase power supply fault protection circuit 240 applicable to a delta connected ac source. In Figure 5, relay coil KAB is connected between phases A and B, relay coil KBC is connected between phases B and C, and relay coil KAC is connected between phases A and C. Each of these relay coils is connected at the input of relay normally open contacts (respectively, kab, kbc, and kac). If phase A opens at X, then relays KAB and KAC de-energize, and the contacts kab and kac open, removing input power from the power supplies PSl and PS2. However, if phase A opens at Y, the power supplies PS2 and PS 3 operate as normal and only power supply PSl is de- energized.

The fault protection circuits 140 and 240 described above may be implemented outside of, or external to, the power supplies PSl - PS3. In another exemplary embodiment of a fault protection circuit, the circuit elements are included within the power supplies themselves (i.e., as part of the internal components of PSl - PS3). In these embodiments, the configuration (Y or delta) of the input ac source is immaterial. Figure 6 illustrates an exemplary fault protection circuit 340 incorporated following a rectified output section 330 of computer power supply 300, which is used to provide dc power to a computer system (not shown). In addition, the output of the power supply return (+ 12 VRTN) also is connected to the chassis ground. A rectified average output voltage 331 is fed to a PFC control IC (VRMS pin on the PFC control IC) and can protect the power supply 300 by turning off the PFC control IC 350 under loss of ac line/phase condition. However, if the power supply 300 is configured to operate from 90 VAC to 264 VAC input, and the power supply 300 is operating in the high range (above about 180 VAC), then the voltage at the VRMS pin of the PFC control IC 350 is not low enough (due to being configured to operate at 90 VAC input) to turn off the PFC control IC 350 during a loss of ac input phase/line condition. Under normal steady state conditions, the power supply 300 is configured as one of three power supplies in much the same manner as the power supplies PSl - PS3 of Figure 1. With the PFC control IC 350 operating, the sinusoidal input voltage waveform, as shown in Figure 2, is the voltage between two of the phases (e.g., phases B and C). Under loss of input ac phase (point X - phase A) the waveform shown in Figure 2 across the power supplies PSl and PS3 becomes distorted. Using PFC enable pin 352 of the PFC control IC 350, and the rectified ac input voltage (see Figure 7), the loss of ac phase/line input can be recognized and lead to shut down of the PFC control IC 350. Shutdown of the PFC control IC 350 de-energizes an inrush current limiting relay coil (not shown) of the power supply 300, causing the power supply 300 to shutdown with a zero voltage output.

The fault protection circuit 340 senses the rectified output voltage from rectifier section 330 to determine when a phase drop out condition has occurred.

Such a condition is shown in Figure 7, which illustrates rectified ac input voltage waveforms in a three phase power supply with a fault (drop out) in one of the three phases.

The fault protection circuit 340 includes resistors R4 and R5, diode D40, and detection circuit 360, coupled to the PFC enable pin 352 of the PFC control IC 350. Under a loss of phase condition, the voltage sensed at the output of the rectifier section 330 has a waveform as shown in Figure 7. This abnormal waveform is detected in the circuit 360 and causes the PFC control IC 350 to shutdown. Shutdown of the PFC control IC 350 causes an inrush current limiting relay coil to de-energize, removing input ac power from the power supply 300. The power supply 300 then is shutdown safely. When a phase dropout condition occurs, the voltage output of the power factor correction circuit in a power supply changes from its normal waveform to the abnormal waveform shown in Figure 8. As with an abnormal rectifier output section voltage, an abnormal power factor output voltage waveform may be used to detect the phase dropout condition and to initiate actions to shutdown the affected power supply. Figure 9 illustrates an exemplary three phase power supply fault protection circuit 440 based on the waveforms of Figure 8. As shown in Figure 9, the circuit 440 includes resistors R4 and R5, diode D40, and detection circuit 460, which again is coupled to the PFC control IC 350 by PFC enable pin 352. The abnormal voltage is detected by the circuit 440, which causes the PFC control IC 350 to de-energize. De- energizing the PFC control IC 350 causes a corresponding control relay coil to de- energize, which in turn opens an associated relay contact, thereby removing input ac power to the power supply 400, and causing the power supply 400 to produce a zero volts output.

The terms and descriptions used herein are set forth by way of illustration only and are not meant as limitations. Those skilled in the art will recognize that many variations are possible within the spirit and scope of the invention as defined in the following claims, and their equivalents, in which all terms are to be understood in their broadest possible sense unless otherwise indicated.

Claims

We claim:

1. A fault protection circuit for use in a three phase power supply system, the system comprising a three phase ac input, and three phases, each phase including a power supply, the circuit, comprising: a sensor in each phase that senses a phase drop out condition in its associated phase of the three phase power supply system; a relay in each phase coupled to the sensor, wherein the relay de-energizes upon sensing the phase drop out condition; and a relay contact coupled to the relay, wherein Ae relay contact opens upon de- energizing the relay, whereby ac power input to one or more of the power supplies is removed.

2. The circuit of claim 1, wherein the ac input is Y-connected and wherein the relay is coupled between ac input line and neutral.

3. The circuit of claim 2, wherein the phase drop out condition occurs between the relay and the ac input line, and wherein each relay de-energizes thereby removing ac input power to all of the power supplies.

4. The circuit of claim 2, wherein the phase dropout condition occurs between the relay and the power supply, and wherein when the relay in the phase experiencing the phase drop out condition de-energizes, ac input power to the power supply in the phase experiencing the phase drop out is removed.

5. The circuit of claim 1, wherein the ac input is delta connected and wherein the relay is connected line-to line in the ac input.

6. The circuit of claim 5, wherein the phase drop out condition occurs between the relay and the ac input line, and wherein each relay de-energizes thereby removing ac input power to all of the power supplies.

7. The circuit of claim 5, wherein the phase dropout condition occurs between the relay and the power supply, and wherein when the relay in the phase experiencing the phase drop out condition de-energizes, ac input power to the power supply in the phase experiencing the phase drop out is removed.

8. The circuit of claim 1, wherein the sensor is incorporated in to the power supply in its associated phase, wherein the sensor operates to de-energize a power factor control circuit within the power supply, whereby the relay is de-energized.

9. A fault protection system for use in a polyphase ac system including an input ac source and an output DC load, the fault protection system, comprising: means for determining that a fault condition exists within a specific phase in the ac system; and means for isolating all phases of the polyphase system affected by the fault condition.

10. The fault protection system of claim 9, wherein the polyphase ac system is a three phase system, the three phase system including an individual power supply for each phase of the three phase system, wherein the means for isolating comprises means for de-energizing each individual power supply.

11. The fault protection of claim 10, wherein the means for determining is external to the power supplies.

12. The fault protection system of claim 10, wherein the means for determining is internal to each individual power supply.

13. The fault protection system of claim 10, wherein when the fault condition is detected between the input ac source and the means for isolating, the means for isolating de-energizes each individual power supply.

14. The fault protection system of claim 10, wherein the fault condition is detected between the means for isolating and one of the individual power supplies, and wherein the means for isolating comprises means for de-energizing the individual power supply in the phase having the fault condition.

15. A method for protecting a polyphase computer server power supply system for a phase drop out condition, the power supply system including an input ac source, a plurality of phases, and at least one power supply for each phase of the power supply system, the method, comprising: determining that the phase drop out condition exists; determining a phase and a location within the phase having the phase drop out condition; and isolating one or more phases whereby abnormal interaction between normally operating phases is prevented.