Electricity: battery or capacitor charging or discharging – Capacitor charging or discharging
Utility Patent
1999-04-05
2001-01-02
Wong, Peter S. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Capacitor charging or discharging
C320S167000
Utility Patent
active
06169389
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is directed toward the field of energy storage systems. In particular, the invention is directed to energy storage systems for use with remotely powered electronic or telecommunication devices.
Remotely powered devices are devices that are provided power from a power source located some distance away through the use of power transmission wires. When the remotely powered device's load demands are low or average, the power transmission wires are capable of delivering sufficient current and voltage. But, during peak load demand periods, the power transmission wires may not be capable of delivering sufficient power because of, among other things, power losses in the transmission wires and the power source's power supplying limits. To counteract these limitations, remotely powered devices are often provided with energy storage systems that store energy during low and average load demand periods and supply energy to the remotely powered devices during peak load periods.
A specific type of remotely powered electronic device is known as an optical network unit (“ONU”). An ONU is a device that is used as an interface between fiber optic telecommunication lines and traditional wires used to provide telecommunication services such as cable television and telephonic services to homes or other buildings. The ONU has a power supply that typically includes: (i) input protection and filter circuitry; (ii) energy storage circuitry, (iii) input voltage monitors and threshold circuitry, (iv) D.C. to D.C. power converters; (v) ringing generators; and (vi) alarm and digital interface circuitry.
Power is supplied to the ONU from a central location through thin telephone wires. As a result, the available peak power is extremely limited. At an ONU, the load current demand varies depending on the customers' telecommunication service usage. Peak loads occur, for example, when phone sets ring or when a coin-phone executes a coin-collection operation. The peak power requirement is substantially higher than the average requirement and typically exceeds the available power supplied over the power transmission wires. Thus, some form of local energy storage is needed that can supply energy to the ONU during peak load periods.
A few storage methods have been proposed to help meet the peak power requirement. In the past, batteries have been used for energy storage. Batteries, however, have limited service life and require periodic maintenance. They are not well accepted for use with modem remote telephone equipment.
Other methods include the use of a very large storage capacitor C to provide the energy storage, such as a 200V, 8000&mgr;F capacitor. When this method is used with an ONU, a capacitor is coupled across the input terminals of the ONU and is charged up, when the load conditions are low or average, to the input line voltage of typically 90V to 140V. During a peak load event, the input powering line will supply some of the power while the storage capacitor supplies a substantial portion of the load power by discharging its stored energy.
This method, however, is very inefficient. For example, the capacitor will only discharge enough energy to decrease the capacitor voltage from typically 90V, (V
1
), the voltage level at which the capacitor is initially charged, to typically 70V, (V
2
). In this example, the available energy is equal to ½*C[(V
1
)
2
−(V
2
)
2
]=12.8 Joules. The energy stored in the capacitor before the discharge, however, was ½*C(V
1
)
2
=32.4 Joules. Thus, only 40% of the stored energy in the capacitor was made available to supply peak loads. As a result, larger and more costly capacitors must be used to meet peak load demands.
Therefore, there remains a need in this art for a more efficient energy storage system that can make more efficient use of the stored energy to meet peak load power demands. There remains a more particular need for an efficient energy storage system that can utilize smaller storage elements resulting in a substantial reduction in cost and size.
SUMMARY OF THE INVENTION
The present invention overcomes the problems noted above and satisfies the needs in this field for an efficient energy storage system. The pumped storage system of the present invention interposes a bi-directional pump, or alternatively known as a switching power converter, between the input powering terminals of the remotely powered device and a storage device. Whenever the available input power exceeds the load power demands, the bi-directional pump will pump energy into the storage device, charging it close to its voltage limit, which is higher than the level the storage device would be charged to under presently known methods. When the available input power is less than the load power demand, the bi-directional pump will reverse direction and pump energy from the storage device into the input terminal, supplying power to the load. The bi-directional pump is capable of supercharging the storage device, i.e., storing more energy into the storage device than presently known methods, making this form of storage much more space efficient.
The present invention provides additional features not found in the presently known energy storage systems. Not all of these features are simultaneously required to practice the invention as claimed, and the following list is merely illustrative of the types of benefits that may be provided, alone or in combination, by the present invention. These advantages include: (1) a bi-directional current limiter for added protection against short circuits; (2) more efficient use of the storage elements resulting in cost savings, physical space savings and the capability of using fewer, smaller, and less costly capacitors; and (3) a safety discharge circuit for added safety in handling the storage elements.
In accordance with the present invention, an energy storage system is provided that includes input terminals for receiving input energy from a remote power source and an energy storage device coupled to the input terminals. The energy storage device is operative to store at least a portion of the input energy and to supply stored energy to the input terminals. A pump device is also coupled to the input terminal and to the storage device. The pump device is operative to cause the energy storage device to store at least a portion of the input energy when the available input power exceeds the load power demands, and to cause the energy storage device to supply energy to the input terminals when the available input power is less than the load power demand.
In one embodiment the pump device uses power threshold levels to determine whether the available input power exceeds the load power demands. The power threshold levels are voltage threshold levels in one embodiment. In another embodiment, the power threshold levels are current threshold levels.
In yet another embodiment, the pump device is operative to cause the energy storage device to store at least a portion of the input energy when the available input power exceeds a first power threshold level, and to cause the energy storage device to supply energy to the input terminals when the available input power is less than a second power threshold level. In this embodiment, the power threshold levels may not correspond to whether the available input power exceeds the load power demands.
The energy storage system is optionally provided with a current limiter for added protection against short circuits. In one embodiment, the current limiter is bi-direction; it protects against short circuits originating at both the power source and within the energy storage system. Also, the energy storage system is optionally provided with a safety discharge circuit that discharges the energy storage system upon its removal from the remotely powered device.
REFERENCES:
patent: 3911348 (1975-10-01), Takemura et al.
patent: 5563779 (1996-10-01), Cave et al.
patent: 5714863 (1998-02-01), Hwang et al.
Jones Day Reavis & Pogue
Luk Lawrence
Marconi Communications Inc.
Wong Peter S.
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