Classifications

• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
  • H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
  • H02J7/02—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries for charging batteries from AC mains by converters
  • H02J7/04—Regulation of charging current or voltage
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
  • H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
  • H02J7/007—Regulation of charging or discharging current or voltage
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
  • H02J2310/00—The network for supplying or distributing electric power characterised by its spatial reach or by the load
  • H02J2310/40—The network being an on-board power network, i.e. within a vehicle
  • H02J2310/44—The network being an on-board power network, i.e. within a vehicle for aircrafts

Definitions

• This invention relates to an AC to DC converter of an electrical power system.
• a conventional power system design includes a Transformer
• Rectifier Unit as a main DC power source, the output voltage of which varies with applied load. Due to the varying nature of its output voltage, the TRU has been considered unsuitable for charging batteries that are relied on for backup/auxiliary power supply. Specifically, the varying nature of the TRU output voltage does not enable a constant potential or constant current charging mode. To address this drawback, some systems use an ON/OFF device to connect and disconnect the battery from the TRU bus to improve charging performance. [0004] Another conventional approach utilizes a DC generator as a main power source to generate a constant output voltage.
• RTRU Transformer Rectifier Unit
• the RTRU can charge batteries at constant potential, but can neither limit the current flowing into the battery nor compensate for temperature variations. Also, by not controlling the amount of trickle charge, the RTRU causes the battery to lose electrolytes over time.
• additional equipment such as a separate battery charger, is commonly used in addition to the main DC power source. Since the charging voltage may be high at times, the battery must be disconnected from the main DC bus of the power system during charging. This requires special power bus arrangements and restricts the use of the battery as a bus presence, thereby affecting DC power system flexibility and quality.
• the present invention addresses these drawbacks of conventional power system designs by providing a multi-functional AC to DC converter that controls AC to DC conversion as a function of at least one characteristic of a battery connected to a DC power bus, such that the voltage output by the converter to the DC power bus is varied to efficiently charge the battery while providing power for the bus connected loads.
• a multi-functional AC to DC converter also adjusts the voltage output to the DC power bus based on a starting condition of an auxiliary power unit (“APU") so that the supplied voltage is suitable for starting the APU.
• APU auxiliary power unit
• the present invention is suitable for implementation in an aircraft power system to maintain the voltage output within the compliance range of the DC power bus (e.g., between 27.5 and 29.5 Vdc) while adjusting the output voltage to efficiently charge a battery connected to the bus and/or start an APU connected to the bus.
• the DC power bus e.g., between 27.5 and 29.5 Vdc
• a multifunctional AC to DC converter includes a power control unit that monitors the current level drawn by a recharging battery and controls the voltage output by the AC to DC conversion circuitry based on the charging state of the battery.
• the power control unit controls the output voltage to a relatively low level (within the compliance range of the power system) to prevent the battery from drawing an uncontrolled or excessive amount of current.
• the power control unit allows the output voltage to increase, thereby maintaining the current flowing to the battery at an adequate level for efficiently charging the battery.
• the power control unit When the output voltage reaches a threshold level, the power control unit initiates a second control stage to maintain the output voltage constant at the elevated level (e.g., near the upper compliance limit of the DC power bus) so that the battery continues to charge, albeit at continually decreasing current.
• the power control unit in one implementation of the present invention controls output voltage as a function of battery temperature so that the output voltage is lower for higher battery temperatures and higher for lower battery temperatures. This temperature compensation improves the efficiency of the battery charging process.
• the power control unit When the current drawn by the battery drops below a threshold level (e.g., indicating that the battery is about 80% percent recharged), the power control unit initiates a third power control stage to lower the output voltage to a nominal regulated level (e.g., 28 Vdc in an aircraft DC bus implementation) to trickle charge the battery (i.e., achieve constant potential trickle charge mode).
• a nominal regulated level e.g., 28 Vdc in an aircraft DC bus implementation
• This third power control stage prevents electrolyte loss during trickle charge.
• the present invention enables No-Break- Power-Transfers (NBPT) in the DC subsystem during AC power interrupts or other system failures and reduces DC system weight and cost as compared to a system requiring a separate battery charger.
• NBPT No-Break- Power-Transfers
• FIG. 1 is a block diagram illustrating an exemplary implementation of a multi-functional AC to DC converter and its integration into a typical aerospace DC Subsystem according to the present invention
• FIG. 2 is a block diagram of a multi-functional AC to DC converter according to an embodiment of the present invention
• FIG. 3 is a diagram illustrating the power control stages utilized by a multi-functional AC to DC converter to implement a battery charging control sequence according to an embodiment of the present invention.
• FIG. 4 is a block diagram of an exemplary DC/DC converter configuration, which is implemented as part of a multifunctional AC to DC converter in accordance with an embodiment of the present invention.
• FIG. 1 illustrates an exemplary implementation of a multifunctional AC to DC converter and its integration into a typical aerospace DC Subsystem according to the present invention.
• a multi-functional converter 100, a battery 200, and an auxiliary power unit 400 are connected to a DC power bus 300, which may be one of multiple DC power buses of an aircraft power subsystem. It should be readily apparent that various electrical loads and other elements may be connected to the DC power bus 300.
• the multi-functional converter 100 receives an AC input (e.g., 1 1 5 or 230 Vac) and outputs a voltage that is regulated in accordance with principles of the present invention discussed in detail below.
• a battery current sensor 1 0 is provided between the DC power bus 300 and the battery 200 to monitor current flow to the battery 200.
• an APU current sensor 20 is provided between the DC power bus 300 and the APU 400 to monitor current flow to the APU 400.
• the multi-functional converter 100 receives the output of the battery current sensor 1 0 and the APU current sensor 20, as well as the output of a temperature sensor 210, which monitors temperature of the battery 200.
• the multi-functional converter 100 also receives the point- of-regulation (“POR”) voltage as an indication of increasing/decreasing load levels on the DC power bus 300.
• POR point- of-regulation
• the multi-functional converter 100 controls output voltage to be within the compliance range of the corresponding DC power subsystem (e.g., within the range of 27.5 to 29 Vdc for aircraft implementation) while adjusting the output voltage to efficiently recharge and prevent electrolyte loss of the battery 200. Furthermore, the multi-functional converter 1 00 adjusts the output voltage during start-up of the APU 400 to limit the starting current of the APU 400 to a level needed for efficient start up.
• the AC to DC converter 1 00 may independently start the APU 400 or assist a battery in the starting process.
• FIG. 2 is a block diagram of a multi-functional AC to DC converter 1 00 configuration according to an embodiment of the present invention. As seen in FIG.
• the multi-functional converter 100 includes: (a) a first stage AC/DC converter 1 10; (b) a switching module 1 20; (c) a power control unit 1 30; (d) an output transformer 1 40; (e) and an output rectifier and filter unit 1 50.
• the first stage AC/DC converter receives 3-phase AC voltage (e.g., 1 1 5 or 230 Vac at 400 Hz or variable frequency of 360 to 800 Hz) and converts the 3-phase AC voltage to an intermediate DC voltage (e.g., 270 Vdc). This initial AC to DC conversion may be performed by a combination of phase-conversion and rectification circuitry.
• a 3-phase to 9- phase auto-transformer may convert the input 3-phase voltage to a 9-phase AC voltage connected to an 1 8-pulse rectifier (not shown) to convert the resulting 9-phase AC voltage to DC voltage.
• the switching module 1 20 converts the DC voltage output by the first stage AC/DC converter 1 1 0 to an AC voltage based on switch gating signals output by the power control unit 1 30.
• the switching module 1 20 may be implemented as a known "H-bridge” configuration of power devices, e.g., insulated gate bipolar transistors ("IGBTs") in which two IGBT pairs are alternatively activated to create an AC voltage across the primary winding of the output trans ormer 1 0.
• IGBTs insulated gate bipolar transistors
• the switching control module 120 generates an AC voltage having a root-mean-square (“RMS") level that is controlled by the power-control unit 1 30 based on one or more of the following: (1 ) output of the battery current sensor 1 0; (2) output of the battery temperature sensor 210; (3) output of the APU current sensor 20; and (4) POR voltage, which indicates load on the DC power bus 300.
• RMS root-mean-square
• This switching control is discussed in more detail below with reference to FIGS. 3 and 4.
• the AC voltage output by the switching module 1 20 is transformed to a lower AC voltage by the output transformer 140 (i.e., a step-down transformer).
• the lower AC voltage output by the output transformer 140 is rectified and filtered by the output rectifier and filter unit 1 50 to output a regulated voltage level to the DC power bus 300.
• the regulated voltage output by the output rectifier and filter unit 1 50 is also fed back to the power control unit 1 30 to assist regulating voltage to a desired level.
• Operation of the power control unit 1 30 for achieving efficient battery charging will next be described with reference to the diagram of FIG. 3, which illustrates output voltage (solid line) and battery input current (dashed line), as measured by the battery current sensor 1 0, over a charging cycle of the battery 200. As illustrated in FIG.
• the power control unit 1 30 operates to achieve three recharge stages of the battery 200 while maintaining the output voltage within the compliance range of the DC power bus 300 (e.g., between 27.5 and 29.5 Vdc).
• the power control unit 1 30 controls the output voltage to a relatively low level (within the compliance range of the power system) that maintains constant limited current flow into the battery 200.
• This power control stage prevents the battery 200 from drawing an uncontrolled or excessive amount of current which could damage the battery or overload the converter 100.
• the power control unit 1 30 allows the output voltage to increase, thereby maintaining the current flowing to the battery 200 at a constant level.
• the power control unit 1 30 initiates a second control stage to maintain the output voltage constant at or near the maximum converter output voltage so that the battery 200 continues to charge, albeit at continually decreasing current.
• the charging current into the battery 200 decreases continually due to the increase in the internal battery impedance.
• the power control unit 1 30 in one implementation of the present invention controls output voltage as a function of battery temperature to optimize the battery charging process, such that the output voltage is made lower for higher battery temperatures and higher for lower battery temperatures. This temperature compensation improves battery charging efficiency.
• the power control unit 1 30 initiates a third power control stage to lower the output voltage to a nominal regulated level (e.g., 28 Vdc in an aircraft DC bus implementation) to trickle charge the battery (i.e., achieve constant potential trickle charge mode).
• a threshold level e.g., indicating that the battery is about 80% percent recharged
• This voltage level is lower than the one employed during the second control stage in order to minimize the electrolyte loss.
• the charging current into the battery 200 is maintained at a very low level (e.g., 1 amp or less).
• the power control unit 1 30 can determine within certain limits the level of battery charge and output a signal indicating the estimated charge state of the battery. For example, the power control unit 1 30 may output a signal to the Flight Deck in an aircraft implementation to indicate readiness of the battery 200 for flight.
• the power control unit 1 30 While controlling the output voltage of the converter 1 00, the power control unit 1 30 ensures that the output voltage is maintained within a range that is compliant with the requirements of the power quality standard in use for the application. This voltage level enables the battery 200 to be continuously connected to the DC power bus 300. Thus, the battery 200 is readily available during AC power interrupt or other system failures.
• the above-described battery charging stages may be implemented in the power control unit 130 in the form of a dedicated integrated circuit (“IC") card and may be implemented with hardware, software, or a combination of hardware and software. In order to optimize the charging process, the voltage applied may be temperature compensated, e.g., lower for higher battery temperatures and higher when low battery temperatures are measured.
• the power control unit 1 30 includes a pulse width modulation ("PWM") unit 1 32 that receives a measure of POR voltage, current measurements for the battery 200 and APU 400, temperature of the battery 200, and a measure of output voltage of the converter 100.
• the PWM unit 132 generates a sequence of pulses, the width of which are varied depending on at least one characteristic of the battery 200 (e.g., depending on the battery charge state). The pulse width may further be adjusted to account for changes in load, reflected by the POR voltage, and to account for a start up condition of the APU 400.
• the PWM unit 132 outputs the generated PWM signal to the gate driver 134, which drives the switches of the switching module 1 20.
• the switching module 1 20 is a conventional H-bridge configuration of power devices, which are n-channel IGBTs in the exemplary implementation shown in FIG. 4.
• the switching module 1 20 shown in FIG. 4 includes first, second, third, and fourth IGBT modules 1 22, 1 24, 1 26, and 1 28, each formed of an IGBT and an anti-parallel diode, the anode of the anti-parallel diode being connected to the emitter of the corresponding IGBT and the cathode being connected to the collector of the corresponding IGBT.
• the gates of the first, second, third, and fourth IGBT modules 1 22, 1 24, 1 26, and 1 28 are connected to receive an output of the gate driver 134.
• the PWM switching signals output by the gate driver 1 34 to the IGBT module pairs are offset so that that IGBT module pairs alternately turn ON/OFF, thereby creating an AC voltage across the primary winding of the transformer 140, which is a center-tapped transformer in the exemplary configuration of FIG. 4. [0025] As shown in FIG. 4, the collector of the first IGBT module
• the emitter of the first IGBT module 1 22 is connected to the collector of the third IGBT module 1 26 and to a first side of the primary winding of the output transformer 140.
• the emitter of the fourth IGBT module 1 28 is connected to the collector of the second IGBT module 1 24 and to a second side of the primary winding of the output transformer 140.
• the emitter of the third IGBT module 1 26 and the emitter of the second IGBT module 1 24 are connected to the (-) output of the first stage AC/DC converter 1 10.
• the gate driver 134 By alternately activating two switching module pairs formed of the first and second IGBT modules 1 22, 124 and the third and fourth IGBT modules 1 26, 1 28 respectively, the gate driver 134 causes the switching module 1 20 to create an alternating voltage across the primary winding of the output transformer 1 40.
• the RMS value of this alternating voltage is affected by the pulse width of the gating signals output by the gate driver 1 34, which is altered as a function of at least one of: battery charge characteristics, battery temperature, APU start condition, and POR voltage according to principles of the present invention.
• the output rectifier and filter unit As further shown in FIG. 4, the output rectifier and filter unit
• the output rectifier and filter unit 1 50 includes a pair of diodes 1 52a, 152b, each connected to an end of the secondary winding of the output transformer 140 to convert the transformed AC voltage to DC.
• the output rectifier and filter unit 1 50 further includes an inductor 1 54 connected between the output of the pair of diodes 1 52a, 1 52b and the output of the output rectifier and filter unit 1 50 and a capacitor 1 56 connected between the output end of the inductor 1 54 and a negative terminal of the converter arrangement, which is shown as a grounded connection in the implementation of FIG. 4.
• This arrangement of the inductor 1 54 and the capacitor 1 56 filters the rectified DC voltage resulting from the pair of diodes 1 52a, 1 52b. It should be recognized that various alternative arrangements may be suitable for the output rectifier and filter unit 1 50.
• the power control unit 1 30 may also continuously monitor the current drawn by the APU 400 (as shown in FIG. 2.) When used in an APU start application, the power control unit 1 30 limits the starting current drawn by the APU 400 to a value which is suitable for the converter 1 10 to independently start the APU 400 or to start the APU 400 in conjunction with a battery. As further shown in FIG. 2, the power control unit 1 30 continuously monitors the POR voltage so as to regulate output voltage as a function of load. Increased load on the DC power bus 300 will cause higher losses to occur in the first stage AC to DC converter 1 1 0, which will result in lower RMS voltage applied to the output transformer 140.
• the power control unit 1 30 adjusts the pulse width for the switch gating signals output to the switching module 1 20 based on load levels to maintain the desired output voltage of the converter 1 00.
• the AC to DC converter 100 of the present invention improves reliability because additional Line Replaceable Units ("LRUs") and associated switching devices are not required to connect/disconnect the charging battery 200 to/from the DC power bus 300 and requires less control and power wiring.
• LRUs Line Replaceable Units
• NBPT No-Break-Power-Transfers

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• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Dc-Dc Converters (AREA)
• Charge And Discharge Circuits For Batteries Or The Like (AREA)
• Rectifiers (AREA)

Priority Applications (3)

Applications Claiming Priority (4)

Publications (2)

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• 2001
  • 2001-10-19 US US10/085,788 patent/US6577106B2/en not_active Expired - Fee Related
  • 2001-11-28 WO PCT/US2001/044558 patent/WO2002045248A2/en not_active Ceased
  • 2001-11-28 JP JP2002546276A patent/JP2004525590A/ja active Pending
  • 2001-11-28 DE DE60131188T patent/DE60131188T2/de not_active Expired - Fee Related
  • 2001-11-28 AT AT01999034T patent/ATE377279T1/de not_active IP Right Cessation
  • 2001-11-28 EP EP01999034A patent/EP1338075B9/en not_active Expired - Lifetime

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