Electric power conversion systems – Current conversion – Having plural converters for single conversion
Reexamination Certificate
2002-12-20
2004-08-17
Vu, Bao Q. (Department: 2838)
Electric power conversion systems
Current conversion
Having plural converters for single conversion
C363S070000
Reexamination Certificate
active
06778414
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
none.
STATEMENT REGRADING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
none.
BACKGROUND OF INVENTION
This invention generally pertains to implementation of innovative electrical power regulation, conditioning and distribution on an aircraft and more specifically, to a system and method for regulating, conditioning and distributing both constant and variable frequency electrical power in a more efficient and distributed manner to a plurality of different types of loads on an aircraft.
The primary electrical power systems on current commercial aircraft are provided by a 400 Hz constant frequency (CF) 3-phase 115V AC power source. As shown in
FIG. 1
, an engine produces mechanical power that is input to a device called an integrated drive generator (IDG). The IDG is used to convert the mechanical power at variable speed rotation of each aircraft engine into constant rotational speed as required so that the alternator can produce CF electrical power. The IDG consists of mechanical and hydraulic mechanisms to regulate the rotational speed of the generator. First, the variable speed input is converted by the IDG to a well-regulated constant speed. Then, an alternator coupled on the shaft of the IDG generates the CF electrical power. Conventionally, all AC loads, such as induction motors, are run directly from the 400 Hz AC power bus, while transformer rectifier units transform the AC power into DC for loads that require DC power.
Although most in-service aircraft employ the IDG-based, mechanically regulated CF power system, the IDG is a complex device made up numerous mechanical and hydraulic parts that are subject to extensive wear and tear. As a result, they are maintenance-intensive. Moreover, it takes only one faulty part to render the entire IDG inoperable, thereby limiting their reliability. In fact, their low reliability is a significant cause of flight schedule disruptions for commercial aircraft, not to mention a safety concern.
Given the complexity of IDGs, they are necessarily very expensive devices, especially when one takes into account the additional costs associated with their maintenance. Typical IDGs can cost anywhere in the range of $50,000-$100,000 per device, depending on the particular power requirements. Their size and weight are also fairly significant in order to accommodate all of the components that make up these devices. Given that an aircraft requires one IDG per engine, and most commercial aircraft have at least two to four engines, their weight and size has a substantial and negative impact on an aircraft's fuel consumption.
On the other hand, many of the electrical AC loads on an aircraft, such as galley and turbo-fan loads, are not frequency sensitive and can operate satisfactorily with a variable frequency (VF) power source directly. However, as shown in
FIG. 1
, conventional power systems employing IDGs distribute expensive CF power to all loads regardless of whether or not they need it. In addition, increasing the number of stages of power conversion required increases power losses and associated heat dissipation. Therefore, more power is required to operate the aircraft, thereby decreasing the aircraft's overall energy conversion efficiency. Moreover, IDGs themselves have a fairly low efficiency rate of approximately seventy percent (70%). Such inefficiencies in turn negatively affect power distribution and fuel efficiency, which in turn further increase the costs associated with operating the aircraft.
While many existing on-board AC loads operate satisfactorily with a variable-frequency power source, some electrical motors powering the on-board turbo-fan systems cannot. With a wide uncontrolled variable excitation frequency, the motor's output torque and speed largely deviates from the desired operating characteristics. The motor's torque also naturally decreases with increasing input power frequency above its base frequency, creating the potential of shifting the operating point to an unstable operating range. This problem can be partially addressed by using larger motors. However, the use of larger motors results in unacceptable increased heat rejection, weight, size and cost.
This problem can also be addressed by using power converters. Existing conventional cycle converters, however, are not fully optimized for aircraft applications. They generate harmonic pollution on the power bus, which can potentially cause malfunction or damage to other avionics equipment connected to the bus. This is especially true in the case of medium and large aircraft that contain large numbers of motor loads. For example, a Boeing 777 may contain ten such motors, and an even larger aircraft may contain up to 20 such motors. Due to the excessive harmonics, the output frequency of such converters is significantly limited. For example, the output frequency of a conventional cycle-converter is limited to less than ⅓ of the input frequency. Another type of existing conventional power converters are designed to have transformer-rectifier front-end feeding an IGBT based inverter bridge. However, they are application specific and are not capable of bi-directional power control. As a result, existing electrical power systems on aircraft cannot efficiently handle power conversion losses and typically incorporate a complex architecture to facilitate any required reconfiguration.
As a result, there is a need for an improved system and method for regulation, conditioning and distribution of electric power on an aircraft.
BRIEF SUMMARY OF THE INVENTION
An improved and novel system for regulating, conditioning and distributing electrical power on an aircraft is disclosed. The system comprises an alternator adapted to directly connect to an engine on the aircraft and generate variable frequency AC power, a variable frequency AC bus coupled directly to the alternator, and at least one of variable frequency AC load, coupled to the variable frequency AC bus. A bi-directional power converter is coupled directly to the variable frequency AC bus and adapted to convert the variable frequency AC power generated by the alternator into constant frequency AC power. At least one bi-directional, power converter may also be coupled directly to the variable frequency AC bus and adapted to convert the variable frequency AC raw power to a fully regulated adjustable-frequency and adjustable-voltage power to control AC motors or other high performance AC loads. At least one constant frequency AC load is coupled to a constant frequency AC bus that is in turn coupled between the constant frequency AC load and the bi-directional power converter. A first power bus controller is coupled between the power converter and the constant frequency AC bus and adapted to selectively and automatically reconfigure the direction of the flow of power there through. In a preferred embodiment, the power converter is bi-directional and adapted to convert constant frequency AC power to variable frequency AC power.
The-system may further include at least one high-voltage DC load, a DC bus coupled to the at least one DC load, and an AC/DC power converter coupled between the constant frequency AC bus and the DC bus and adapted to convert the constant frequency AC power to DC power. In a preferred embodiment, the AC/DC power converter is bi-directional and adapted to convert DC power to constant frequency AC power. The system further preferably includes a second bi-directional power bus controller coupled between the AC/DC converter and the DC bus and adapted to selectively and automatically reconfigure the direction of the flow of power there through. The first and second bi-directional controllers provide for the selective and automatic reconfiguration of the flow of power through the system.
The system may further include at least one low-voltage DC load, and a DC/DC power converter coupled between the DC bus and the low voltage DC load and adapted to convert DC power to low voltage DC power, as well as a first power conditioner coupled to the constant
Chang Jie
LeMond Charles H.
Wang Anhua
The Boeing Company
Thompson & Coburn LLP
Vu Bao Q.
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