Power system including redundant power supplies

This invention relates to power supplies and, more particularly, to a fault-tolerant dual AC source redundant power supply system.

Power supplies may more precisely be called power converters because they receive a power source and change the source according to the demands of a load. For example, the power source may be a 120-volt alternating current (AC) power from an electrical outlet in a home or business and the load may be a personal computer motherboard requiring 5 volts of direct current (DC) power. Coupled between the source and load, the power supply is expected to reliably convert 120 volts AC to 5 volts DC.

The power supply typically includes a transformer, a rectifier, a filter, and a regulator. The transformer steps the incoming AC voltage either up or down and the rectifier converts the transformed voltage Into a pulsating unipolar (DC) voltage. The filter then smoothes out the voltage to a continuous one, and the regulator assures that a voltage within a certain range is supplied to the load at all times.

In addition to personal computers, many other power-consuming devices depend on power supplies for reliable operation. Mainframe computers, banking and traffic control systems, hospital equipment, emergency infrastructure, and security systems are but a few examples of systems in which disruption in service can be catastrophic or even life-threatening.

In such environments, power systems comprising multiple redundant power supplies may be used to avoid power disruptions. Such power systems are designed to connect to multiple power sources, and include circuitry for ensuring that, where at least one source is available, power to the load system remains uninterrupted.

The cost of redundancy, however, is not cheap. In a typical computer system, for example, a single power supply occupies a significant amount of space and generates enough heat to usually require its own fan. It is easy to understand why few stand-alone computer systems have redundant power supplies. For servers, mainframes, and other large-scale processing systems, however, redundant power supplies may be cost-justified, although these systems are often space-constrained as well.

Further, many power systems comprising redundant power supplies cannot conveniently be powered down for maintenance. If a component within the power system needs replacing, typically, it can only be replaced by turning the system off, e.g., removing the AC power source. This is the exact condition the power system was installed to avoid.

Thus, there is a continuing need to provide a power system comprising redundant power supplies, wherein the power system supports dual AC sources, is not prohibitive in size, and includes components that may be replaced while the system is operational.

FIG. 1 is a block diagram of a power system according to one embodiment of the invention;

FIG. 2 is a block diagram of the power system of FIG. 1 in a first power state according to one embodiment of the invention;

FIG. 3 is a block diagram of the power system of FIG. 1 in a second power state according to one embodiment of the invention;

FIG. 4 is a block diagram of the power system of FIG. 1 in a third power state according to one embodiment of the invention;

FIG. 5 is a block diagram of the power system of FIG. 1 in a fourth power state according to one embodiment of the invention;

FIG. 6 is a block diagram of an alternate embodiment of the power system of FIG. 1; and

FIG. 7 is a flow diagram showing operation of the transfer switch control circuit in switching the power system between its various power states according to one embodiment of the invention.

In accordance with the embodiments described herein, a power system for receiving dual alternating current sources and supplying direct current to drive a load is disclosed. The power system comprises four power supplies and two transfer switch modules, any of which may be removed and replaced from the power system during operation. A transfer switch control circuit activates, by opening or energizing, various relays within the transfer switch modules, in response to a change in one or both of the AC sources. As long as one of the AC sources maintains a voltage within a predetermined voltage range, three of the power supplies operate to deliver the direct current to the load. When both AC lines maintain voltages within the predetermined voltage ranges, all four power supplies are active.

In FIG. 1, a power system 100 comprising redundant power supplies is depicted. In one embodiment, the power system supplies a reliable direct-current (DC) output 40 from dual alternating-current (AC) sources 30 A and 30 B (collectively, sources 30 ) to drive a load 90 , such as a processor-based system. The power system 100 includes four power modules or power supplies 10 A- 10 D (collectively, power supplies 10 ), a transfer switch control circuit 80 , and two transfer switch modules 20 A and 20 B, coupled, respectively, to the AC sources 30 A and 30 B.

Using the nomenclature of the industry, the power system 100 is known as a “redundant 3+1” system, in which, while the AC sources are functioning, all four of the power supplies are operational while one of them is available as a backup power supply. When only one AC source is functioning, three of the four power supplies are active. As will be shown, the voltage maintained at each AC source 30 A, 30 B determines which three power supplies are active at a given moment.

The transfer switch modules 20 are arranged between the AC sources 30 and the power supplies 10 . Nevertheless, the power supply 10 A is connected directly to the AC source 30 A (line 14 ) while the power supply 10 D is connected directly to the AC source 30 B (line 22 ). The input lines of the power supplies 10 B and 10 C are connected together (line 12 ). The output lines of the four power supplies are connected in parallel, delivering the DC output 40 to drive the load 90 . In other embodiments, multiple output power supplies may be used.

The power system 100 includes relays within the transfer switch modules to automatically switch the path of one or both AC sources when the AC source exceeds a predetermined voltage range, drops to a zero voltage, or is unplugged from the power system 100 . The dashed lines in FIG. 1 indicate that the transfer switch control circuit 80 is distinct and separate from the other components depicted. The transfer switch control circuit 80 monitors the AC sources 30 A and 30 B, then automatically activates or de-activates relays within one or both transfer switch modules 20 , as described below, to change the path of current flowing through the power system 100 .

The power system 100 assumes one of five possible states, as indicated in the following description. A first power state, also known as the default state, is depicted in FIG. 2 . Second, third, and fourth power states are likewise depicted in FIGS. 3, 4 , and 5 , respectively. Where both AC sources fail or maintain an insufficient voltage, the power system 100 is said to be in a fifth power state, in which the power system 100 is turned off or shut down. Based on the voltages maintained by the incoming AC sources, the power system 100 assumes one of these five power states.

In referring to the AC sources, reference is made to particular voltages or voltage ranges. It is to be understood that, as alternating current sources, the AC sources are maintaining a voltage at a particular RMS level and frequency. For example, in the United States, a standard household outlet delivers approximately 120 volts AC at 60 Hz while in parts of Europe, 220 volts AC at 50 Hz is typically delivered. While reference throughout this document is made to particular voltages or voltage ranges, it is understood that these voltages are supplied at a particular frequency, although neither the voltages nor the frequencies referred to herein are meant to limit the scope of the invention.

For convenience, the AC source voltages are given the designations “good,” “acceptable,” and “bad,” in reference to preferred voltages for operating the power supplies. The AC sources maintain a “good” voltage, in which the voltage is within a predetermined voltage range. As the actual voltage maintained may vary somewhat, a predetermined voltage range for a US-based system may be 90-120 volts AC, as one example.

Likewise, the AC sources maintain an “acceptable” voltage, in which some voltage is delivered, despite being outside the predetermined voltage range. The AC source voltage is characterized as a “bad” voltage when no voltage is maintained, or when the voltage is fast approaching a zero voltage, such as when the AC source has been disconnected from the power system 100 .

Table 1 illustrates the relationship between the AC sources 30 A and 30 B and the five power states of the power system 100 . Entries are included for each voltage range measured from each AC source. In one embodiment, the power system is not operational (i.e., shutdown) when neither the AC source 30 A nor the AC source 30 B operate in the “good” voltage range.

The terms “good,” “acceptable,” and “bad” are understood to be in reference to the power system's operation and are not to be construed more broadly than intended. Thus, for example, a non-zero voltage outside the predetermined voltage range is designated as “acceptable” because of its effect on operation of the power system 100 only, not because of its effect on other systems not discussed here. Further, the voltage ranges designated for each term may be adjusted according to the power supply requirements, the load requirements, and other considerations.

The power system 100 assumes the first power state (FIG. 2) when the voltages maintained by the two AC sources 30 A and 30 B are “good,” or when the voltage from the first AC source 30 A (hereinafter first AC source voltage 30 A) is “acceptable” while the voltage from the second AC source 30 B (hereinafter second AC source voltage 30 B) is “good.” The power system 100 assumes the second power state (FIG. 3) when the first AC source voltage 30 A is “bad” and the second AC source voltage 30 B is “good.” In the third power state (FIG. 4 ), the AC source voltage 30 A is “good” while the AC source voltage 30 B is “acceptable.” In the fourth power state, the AC source voltage 30 A is “good” while the AC source voltage 30 B is “bad” (FIG. 5 ). These four states are described in more detail below.

In one embodiment, when the AC source voltage 30 A is “good,” power supplies 10 A, 10 B, and 10 C are supplying or delivering the DC output 40 to drive the load 90 , while the state of power supply 10 D depends on the condition of the AC source 30 B. If the AC source 30 B is “good,” then power supply 10 D acts in parallel with the other three power supplies 10 A, 10 B, and 10 C, one of which may be considered redundant. If the AC source 30 B is “acceptable” or “bad,” then the power supply 10 D is disabled and only three power supplies deliver power to the load 90 .

Alternatively, when the AC source voltage 30 B is “good” (and the AC source voltage 30 A is not “good”), power supplies 10 B, 10 C, and 10 D deliver the DC output while power supply 10 A is disabled. Controlled by the transfer switch control circuit 80 , the two transfer switch modules 20 A and 20 B can change the path of current delivered to the power supplies from the AC sources.

The transfer switch control circuit 80 tests the AC sources 30 to determine the voltage ranges of each. The transfer switch control circuit 80 then automatically opens or closes relays within the transfer switch modules, which, in turn, changes the path of current passing through the power system 100 , possibly causing the power state to change.

First Power State (Default)

FIG. 2 illustrates the first power state (default) of the power system 100 of FIG. 1, including a depiction of the transfer switch modules. Transfer switch module 20 A includes dual safety relays 50 A and 50 B, transfer switch relay 60 A, and fuse 70 A. Transfer switch module 20 B includes dual safety relays 50 C and 50 B, transfer switch relay 60 B, and fuse 70 B. If the safety relay has an adequate gap between its contacts, then it is possible to configure the power system 100 with single safety relays rather than dual safety relays.

In the default power state of FIG. 2, the AC sources 30 A and 30 B are maintaining the “good” voltage. The safety relays 50 A, 50 B, 50 C, and 50 D are closed. The transfer switch relays 60 A and 60 B are positioned such that power supplies 10 B and 10 C are connected to AC source 30 B. (In FIG. 2, the transfer switch relays 60 A and 60 B are said to be in a “de-energized” state). Thus, the power supply 10 A receives current from the AC source 30 A while the power supplies 10 B, 10 C, and 10 D receive current from the AC source 30 B. All four power supplies may contribute to the DC output 40 .

Alternatively, the first (default) power state is sustained when the AC source voltage 30 A is outside the predetermined voltage range, yet maintains a non-zero voltage (i.e., is an “acceptable” voltage). When the AC source 30 A fails to maintain a voltage within the predetermined voltage range, the transfer switch relays 60 A and 60 B do not change state. Power supplies 10 B, 10 C and 10 D continue to receive current from the AC source 30 B. When such a condition on the AC source 30 A occurs, the power supply 10 A is not relied upon to contribute to the DC output 40 . Despite the change of the AC source 30 A from “good” to “acceptable,” the power system 100 remains in the first power state.

If, however, the AC source voltage 30 A drops to zero or is unplugged (i.e., goes “bad”), the safety relays 50 A and 50 B open. This provides a proper safety clearance to the user-accessible AC source 30 A connector. The dual relays 50 A and 50 B at the AC source 30 A satisfy standard safety requirements known to those of ordinary skill in the art, for preventing a current from the AC source 30 B to the AC source 30 A when the power cord of the AC source 30 A is unplugged and input contacts of transfer switch module 20 A are exposed.

The second power state of the power system 100 is depicted in FIG. 3 . Here, the AC source voltage 30 A is “bad” and AC source voltage 30 B is “good.” Safety relays 50 A and 50 B are opened to disconnect the AC source 30 A from the rest of the circuitry, thus, preventing leakage from source 30 B to 30 A. The transfer switch relays 60 A and 60 B remain in the de-energized state. With the AC source 30 B as the sole source of current, DC output 40 is supplied through power supplies 10 B, 10 C, and 10 D, while power supply 10 A is idle.

Third Power State

When the AC source voltage 30 B drops to “acceptable,” the transfer switch control circuitry 80 detects the condition and activates (i.e., energizes) the transfer switch relays 60 A and 60 B. The effect of energizing the transfer switch relays is to change the AC source (for power supplies 10 B and 10 C) from the AC source 30 B to the “good” AC source 30 A. This keeps power supplies 10 B and 10 C active, and ensures that full power is delivered from power supplies 10 A, 10 B, and 10 C.

In one embodiment, transfer switch relays 60 A and 60 B are energized simultaneously, and vice-versa. That is, if transfer switch relay 60 A is energized, transfer switch relay 60 B is energized at the same time; if transfer switch relay 60 B is de-energized, transfer switch relay 60 A is likewise de-energized concurrently. The transfer switch control circuit 80 simultaneously activates the relays, whether to energize or to de-energize them. Nevertheless, the fuses 70 A and 70 B are present in case simultaneous activation does not occur. The fuses are described in more detail, below.

The third power state, in which the AC source voltage 30 B drops to an “acceptable” voltage, is depicted in FIG. 4 . The transfer switch control circuit 80 detects the change in voltage and simultaneously energizes the two transfer switch relays 60 A and 60 B. This causes the power supplies 10 B and 10 C to be supplied from the “good” AC source 30 A. Thus, in the third power state, power is delivered to drive the load 90 through power supplies 10 A, 10 B, and 10 C. Although the AC source voltage 30 B has changed from “good” to “acceptable,” some low power may continue to be delivered to the power supply 10 D.

Fourth Power State

If the AC source voltage 30 B drops to zero or is unplugged, the safety relays 50 C and 50 D open to provide safety clearance from the AC source 30 B to the AC source 30 A connector for the purpose of safety. The safety relays are opened to provide safety clearance from the user-accessible AC source 30 B connector to the high voltage on the AC source 30 A connector.

The fourth power state is depicted in FIG. 5, according to one embodiment. Safety relays 50 C and 50 D are opened, as shown, cutting off the AC source 30 B from the power system 100 . As in the third power state, the transfer switch relays 60 A and 60 B are energized. Accordingly, current is supplied to the power modules 10 A, 10 B, and 10 C from the AC source 30 A while the power module 10 D is idle.

Once the AC source 30 B recovers and is within the “good” voltage range, the safety relays 50 C and 50 D close to reconnect the AC source 30 B to the power supply 10 D and the transfer switch relays 60 A and 60 B return to the de-energized (default) state. In the first (default) power state, DC current is delivered to drive the load 90 from all four power supplies 10 A- 10 D.

Safety Fuses

The fuses 70 A and 70 B, one in each transfer switch module 20 A and 20 B, respectively, protect against failures in the transfer switches 60 A and 60 B. If the transfer switch relay 60 A is energized when the transfer switch relay 60 B is stuck in the de-energized (default) state, the fuse 70 B will open and disconnect the AC source 30 B from the rest of the power system 100 . This protects against a short occurring between the AC source 30 A and the AC source 30 B. To make the transfer switch modules 20 A and 20 B interchangeable and standard, an additional two fuses may be used in series with the transfer switch relay 60 A, as in FIG. 6 . The power supplies 10 A, 10 B, and 10 C continue to receive current from the AC source 30 A. Likewise, if the transfer switch relay 60 B is energized when the transfer switch relay 60 A is stuck in the de-energized state, the fuse 70 A will open and disconnect the AC source 30 A from the rest of the power system 100 . This protects against a short occurring between the AC source 30 A and the AC source 30 B. The power supplies 10 B, 10 C, and 10 D continue to receive current from the AC source 30 B.

In one embodiment, the transfer switch modules 20 of the power system 100 are redundant. No single failure in either transfer switch module will cause the loss of full system power if all four power supplies are installed. Either of the transfer switch module 20 A or 20 B can be removed while the power system 100 is operating. In common parlance, the transfer switch modules are “hot-swappable.” This feature allows the transfer switch modules to be maintained in a runtime setting. Additionally, any one of the power supplies is hot-swappable as well, eliminating the need for downtime during maintenance of the power system 100 .

The arrangement of power supplies and transfer switch modules in the power system 100 reduces the cost and size relative to many prior art power systems. Rather than having three redundant power supplies to mirror three non-redundant power supplies, a single additional power supply provides the needed redundancy at a reduced cost, both in terms of money spent and space used. In one embodiment, the power system 100 achieves a noticeably higher power density, in terms of watts per cubic inch (W/in 3 ) by reducing the number of used modules by one third, relative to a 3+1 redundant system, which indudes six power supplies. Despite having fewer power supplies, the power system 100 nevertheless supports dual/redundant AC sources. The presence of fewer power supplies results in a smaller size for the load 90 and an increase in airflow within a power-consuming unit comprising both the power system 100 and the load 90 .

In FIG. 6, a flow diagram illustrates how the transfer switch control module 80 logically changes the state of the power system 100 . Recall that the transfer switch control circuitry 80 tests the AC sources 30 to determine whether they are maintaining a voltage within the predetermined voltage range and controls the relays within the transfer switch modules 20 when a change of state is appropriate.

In the flow diagram of FIG. 6, various steps are illustrated as occurring in a particular order. However, system designers of ordinary skill will recognize that the steps of the flow diagram may be arranged in a different order, or some steps may be performed simultaneously by different logic within the transfer switch control circuitry.

The transfer switch control circuit tests whether the AC source 30 A is maintaining a “good” voltage (diamond 302 ). If so, the same test is performed on the AC source 30 B (diamond 308 ). If the AC source voltage 30 B is also “good,” the power system 100 assumes the first (default) power state, as depicted in FIG. 2 (block 310 ).

If, instead, the AC source voltage 30 B is not “good” (the “no” prong of diamond 308 ), the transfer switch control circuit tests whether the AC source 30 B is “bad” (diamond 316 ). If so, the power system assumes the fourth power state, as in FIG. 5 (block 318 ). Otherwise, the AC source voltage 30 B is deemed “acceptable,” and the power system assumes the third power state, as in FIG. 4 (block 320 ).

When the AC source voltage 30 A is not “good” (the “no” prong of diamond 302 ), the transfer switch control circuit tests whether the AC source voltage 30 B is “good” (diamond 304 ). If not, then both AC sources are maintaining inadequate voltages and the power system is shut down (block 306 ). In one embodiment, the system shutdown occurs, as the power supplies internally shut down whenever the voltage source drops below a specified voltage.

If, instead, the AC source voltage 30 B is “good” (the “yes” prong of diamond 304 ), the transfer switch control circuit tests whether the AC source voltage 30 A is “bad” (diamond 312 ). If not, the power system assumes the default state (block 310 ) because the AC source voltage 30 A is “acceptable.” If the AC source voltage 30 A is “bad” (the “yes” prong of diamond 312 ), the power system assumes the second power state, as depicted in FIG. 3 (block 314 ).

Once the power system assumes one of the five possible states, the operations of FIG. 6 are performed again. Thus, the flow diagram of FIG. 6 is understood to describe an operation that is performed by the transfer switch control circuitry periodically or continuously, as long as the power system 100 is operating.

While the invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of the invention.