System control by use of phase rotation signaling

A load distribution and management system (LDMS) has a source of multi-phase power and multiple power lines. A separate power line is associated with each phase of power. These power lines connect the power source to a plurality of outlets. A threshold compare circuit is effective to compare power drawn through the plurality of outlets to a preset power limit and signal a phase rotation control if the power drawn exceeds the threshold power. The phase rotation control effective to interchange the power line associated with two of said multi-phases in response to said signal and a rotation detector disables those outlets not in use in response to the interchange of power and power lines. Conversely, when the power drawn is less than the preset threshold power, the phase rotation control returns the power phase to its associated power line signaling the rotation detector to enable disabled outlets. The LDMS is particularly useful where there is a limited supply of power, for example to provide power to passenger laptop computers and personal entertainment devices on a commercial aircraft.

CROSS REFERENCE TO RELATED APPLICATION(S)

U.S. GOVERNMENT RIGHTS

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a system to manage a limited amount of power. More particularly, the availability of power is indicted by a phase sequence of a multiphase power source.

2. Description of the Related Art

There are environments where a limited amount of power is available and the demand for power at time exceeds that available requiring a Load Distribution and Management System (LDMS). For example, the power available to passengers on a commercial aircraft for personal entertainment devices is limited. One LDMS is disclosed in U.S. Pat. No. 5,754,445, titled “Load Distribution and Management System,” by Jouper et al. The U.S. Pat. No. 5,754,445 patent is incorporated by reference herein in its entirety.

The U.S. Pat. No. 5,754,445 patent discloses a LDMS where a signal is used to convey whether power is available or power is restricted. When power is available, the signal is in a TRUE state as conveyed from unit to unit by a signal wire with a transmitter at one end of the wire and a receiver at the other end. The wire between the transmitter and receiver is typically of 20 AWG or larger in order to withstand the vibration and environmental stress of the aircraft environment. Because of the length of this conductor and the number of units installed in a system, this single conductor presents a significant weight impact to the overall system.

There remains a need for an LDMS having a reduced weight penalty capable of using existing power and power conductors.

BRIEF SUMMARY OF THE INVENTION

A load distribution and management system (LDMS) has a source of multi-phase power and multiple power lines. A separate power line is associated with each phase of power. These power lines connect the power source to a plurality of outlets. A threshold compare circuit is effective to compare power drawn through the plurality of outlets to a preset power limit and signal a phase rotation control if the power drawn exceeds the threshold power. The phase rotation control is effective to interchange the power line associated with two of the multi-phases in response to the signal and a rotation detector disables those outlets not in use in response to the interchange of power phases and power lines. Conversely, when the power drawn is less than the preset threshold power, the phase rotation control returns the power phase to its associated power line signaling the rotation detector to enable disabled outlets.

The LDMS is particularly useful where there is a limited supply of power, for example to provide power to passenger laptop computers and personal entertainment devices on a commercial aircraft.

Like reference numbers and designations in the various drawings indicated like elements.

DETAILED DESCRIPTION

A method to signal a limited set of data utilizes changing phase rotation. This method is used to reduce the number of conductors needed in a system requiring multiphase power and signaling. The method is particularly useful with a three phase system having a phase rotation of 120 degree separation. Normal rotation, Phase A, Phase B, Phase C, signals additional power is available. Abnormal rotation Phase A, Phase C, Phase B, signals power is in a restricted mode. When compared to a conventional LDMS as described above, a reduced number, or even no, signaling conductors are required to convey control of the system. As a result, this method can significantly reduce system weight while maintaining power management control and is particularly useful in environments having both power and weight limitations, such as on a commercial or military aircraft.

During normal operation, with power available, phase rotation of A-B-C with 120 degree separation from phase to phase is provided to the system. A phase detector in a load unit monitors for phase rotation with phase A as the reference, and phases B and C monitored based on zero cross timing of each phase. When the power demand reaches a prespecified maximum and power usage needs to be restricted, phase rotation is reversed between phases B and C. The phase detector detects this change in rotation and signals that the system has reached its power limit.

Phase rotation occurs in the head end controller. Head end power on an aircraft is generated by the head end controller which, in one embodiment, takes in 115 VAC 400 Hz power and converts it to 60 Hz three-phase output power. This may be accomplished by a microcontroller or digital signal processor to control output voltage, wave shape, frequency and phase rotation. The phase rotation will be in the enabled state when the power from the system reaches the pre-established threshold and the threshold compare circuit in the head end controller sends a signal to the rotation control in the microcontroller or processor controlling power output. In embodiments where the input power is 60 Hz, rotation control may be accomplished by solid state switching or relay switching by switching the B phase to the C output and the C phase to the B output.

When a load or user connects to the system, outputs from the system are activated only if the phase rotation is in A-B-C. Once the threshold power is reached, activation of the phase rotation will preclude the addition of loads or users while permitting loads and users currently connected to retain power.

FIG. 1depicts a schematic of a head end controller10and outlets11to a LDMS. The outlets11may be built into the seat back or arm rest of a passenger seat on a commercial aircraft to enable the passenger to power a personal computer or personal entertainment device. The head end controller10includes a power generator12which takes in power, such as from a generator driven by an aircraft engine, and creates a multi-phased output. Output from the power generator12passes through a power sense circuit14which measures the power drawn by measuring the current of the power lines22,24,26and communicates this to a threshold compare circuit16. The threshold compare circuit16has been preset with a threshold power limit18and compares a power drawn signal20from the power sense circuit14to the threshold power limit18. If the power drawn equals or exceeds the threshold power limit, the threshold compare circuit16generates a signal to activate rotation control28.

The rotation control28takes in the Phase B power from the power generator12and the Phase C power from the power generator. It does not take in Phase A power which remains at all times on power line22. When the threshold compare circuit16sends an activation signal29to rotate power, the rotation control28switches the Phase B power to the Phase C power line26and the Phase C power to the Phase B power line24. This contrasts with operation when additional power is available and the Phase B power is on the Phase B power line24and the Phase C power is on the Phase C power line26.

Power from the Phase A power line22, Phase B power line24and Phase C power line26goes to each of a plurality of power units30. A power unit30may be located under a passenger seat and provide power to outlets associated with the seats in the same row, same side of the aisle as the power unit. Inside the power unit30is a power monitor32which monitors the power coming in and the power drawn through outlets11serviced by the power unit30. If an outlet11is not currently drawing power, the rotation detector34detects whether the power has been rotated between Phases B and C and, if so, opens the respective output switch36disabling a flow of power to that outlet11.

FIG. 2depicts the implementation of the rotation control28and its signal to the rotation detectors34in the power units. Phase rotation is accomplished by four switches42,44,46, and48. Exemplary switches are solid state bi-lateral switches. The outputs of the switches are fed via power lines22,24,26to voltage comparators50,52, and54, which feed into the phase rotation detector34. The phase rotation detector34includes sequentially triggered flip-flops62,64, and66and an “AND” gate68. Exemplary flip-flops are D-type flip-flops. When the power is in A-B-C rotation, flip-flops62,64and66trigger in sequence placing a high signal at the Q output of each flip-flop and in turn a high signal is placed on the phase rotation detector output70enabling the output switches and allowing power to be available at the outlet. Rotation detection is accomplished by the phase rotation of successive phases. Comparators50,52and54create a pulse the width of the positive half cycle of the respective input phase. The basic waveform is a logic high from the point the phase voltage is greater than the reference voltage56. The output of the comparator is fed to the clock on one flip-flop and the D input on the next. Each half cycle is displaced by 120 degrees allowing for a successive clock edge to determine if the proper phase rotation is detected. An example of this is during a positive half cycle of Phase A comparator50output rising edge clocks flip-flop62and also sets the D input of flip-flop64high. Phase B comparator rising edge clocks the D input of flip-flop64to the Q output of flip-flop64. In turn, the Phase B comparator52output sets the D input of flip-flop66high. Phase C comparator rising edge clocks the D input of flip-flop66to the Q output of flip-flop66. In turn, the Phase C comparator54sets the D input of flip-flop62high and the next rising edge of Phase A comparator sets the Q output of flip-flop62high. When rotation control is activated, switches42and46are on and switches44and48are off, the phase displacement between the three phases is now reversed and the comparator timing to the phase rotation detector is reversed and the Q outputs of the flip-flops62,64,66are set low as well as the AND gate68.

Outlets in use are not disabled when the phase rotation is detected. When use of an outlet is terminated, that outlet is then disabled until phase rotation control is removed. When the power demand drops below the present power threshold, the phase rotation is reversed and B phase power is returned to power line24and C phase power is returned to power line26.

FIG. 3depicts the power signal before and after phase rotation. The horizontal axis is time, in milliseconds, and the vertical axis is voltage, in volts. A phase rotation occurs at time “T”. As illustrated in3A, output power is uninterrupted by the phase rotation for loads connected to the system. The signal of the Phase A output3B does not change. The signal of the Phase B output3C shifts120degrees as C power is applied to the Phase B output. The signal of the Phase C output3D shifts240degrees as Phase B power is applied to the Phase C output. The rotation detector senses the phase shift3E and outputs not connected to the system are disabled.