1. Field of the Invention
This invention generally relates to the field of electric power generation and electric power conversion, and in particular to a system for maintaining the voltage level of a power supply bus coupled to a load.
2. Description of the Related Art
The need for mobile commercial-grade alternating current (AC) power comes in many applications and cuts across many industries. There is an emerging need for a mobile power generation system that can satisfy the demands of power hungry machinery, like heavy construction tools, while still being capable of delivering well-regulated power to sensitive equipment, like computers. Moreover, not only should the mobile system have the capacity to generate such power while operating at a stationary site, it should also provide the same type of power while the system is in transit. For example, a mobile power generation system should be versatile enough to support the power requirements of emergency response vehicles rendering life-saving services while in transit, as well as satisfy the power demands of sensitive intelligence/news-gathering computer and telecommunications equipment in isolated regions of the world.
There is also a need to provide this same AC power during occasions when the running of the vehicle""s engine is not desirable. Late night work in residential areas, where engine noise is an issue, is an example of one such occasion. Generation of power without the need to run an engine is also desirable to reduce air pollution caused by engine exhaust.
One solution for this need is to derive the power from storage batteries, converting the energy from a direct current (DC) source to AC. A device that performs such a function is called an xe2x80x9cinverterxe2x80x9d. Inverters are in the prior art and are commercially available. The conventional inverters typically depend on either the charging system of the vehicle to restore charge to the batteries once they are drained, and/or by a plug-in battery charger. It is common for a vehicle with an inverter to be plugged into standard utility power overnight to xe2x80x9ctop offxe2x80x9d the batteries then depend on the vehicle""s alternator to replenish charge level during operation. It is also common for a vehicle to be outfitted with a high output alternator to provide additional charging capacity.
The conventional inverters suffer from various disadvantages. For example, in some of the conventional inverters, the power demands from the inverter exceed by a large margin the ability of an alternator to provide charge. In such a case, there comes a point when the batteries are completely drained, and because of the alternator""s inability to keep up alone, inverters shut down and work requiring AC power ceases.
Another disadvantage of the conventional inverter system is that a vehicle alternator produces its least amount of charging current at low engine RPM""s. When the batteries are drained, the typical response is to start the vehicle""s engine to recharge the batteries with the alternator. At idle RPM the alternator is limited in capacity and will tend to overheat, reducing alternator life and potentially creating a fire danger.
A further disadvantage of the conventional inverter system is that the inverter typically continues to pull power off of the batteries until the batteries are very deeply discharge. Deep discharging of batteries may greatly limit the life of the batteries.
Yet another disadvantage of the conventional inverter system is that the typical automotive alternator recharges based on voltage level only, not battery temperature, which in some cases limits the amount and rate of battery charging and reducing battery life.
Yet another disadvantage of the conventional inverter system is it typically lacks the capability of providing very high power, short duration demands, such as those that occur when starting certain AC electric motors.
According to one aspect of the invention, a power generation system is provided for supplying electrical power to a load from at least one of a generator and a battery. The power generation system includes a power bus coupled to the generator and a bi-directional conversion unit coupled between the power bus and the battery. The bi-directional conversion unit is capable of transitioning between a first direction wherein electrical power flows from the power bus to the battery and a second direction wherein electrical power flows from the battery to the power bus.
In one aspect of one embodiment, the present invention provides a way to continually supply AC power, even when the generator is no longer producing electrical power, by converting DC power from a battery source into AC power.
In another aspect of one embodiment, the present invention provides a system that transitions between a battery power operation to a generator power operation without AC power interruption.
In another aspect of one embodiment, the present invention provides a smooth transition from a mode where a battery source is supplying power to AC load to another mode where a generator source is supplying power to the AC load.
In another aspect of one embodiment, the present invention is capable of simultaneously supplying DC and AC power without interruption.
In yet another aspect of one embodiment, the present invention provides means for supplying power from both a generator source and a battery source during times of high power demand.
In yet another aspect of one embodiment, the present invention provides an alarm to an operator that the charge levels of the batteries are getting low, providing time for the operator to start the engine and begin recharging the batteries.
In yet another aspect of one embodiment, the present invention monitors battery temperature and adjusts the charging rate accordingly, enhancing battery life and maximizing the amount of useful charge stored in the battery.
In yet another aspect of one embodiment, when the electrical power generated by the generator exceeds the AC load demand, the excess power is used to recharge a battery source.