WO2012032585A1

WO2012032585A1 - High response power system for vehicle

Info

Publication number: WO2012032585A1
Application number: PCT/JP2010/005552
Authority: WO
Inventors: Shouichi Tanaka
Original assignee: Three Eye Co., Ltd.
Priority date: 2010-09-10
Filing date: 2010-09-10
Publication date: 2012-03-15

Abstract

It is one object to provide a simple vehicle power system capable of changing a torque of a starter-generator or an alternator, in particular the torque of a wound field machine, rapidly. The power system has a battery, a capacitor and a series switch connected to one another in series. A parallel switch including a parallel diode is connected to the pair of the capacitor and the series switch in parallel. The pair of the capacitor and the battery is charged and discharged via the series switch. Furthermore, the battery can be charged and discharged to an inverter of the starter-generator. The freewheeling current can charge the pair of the capacitor and the battery with a high voltage, because the freewheeling current is produced by a residual magnetic energy of the field winding. Connection of two field windings can be changed between parallel connection and series connection by using a connection-changing circuit fixed on a rotor of the wound field machine. The connection is changed in response to a field voltage applied to the field winding.

Description

HIGH RESPONSE POWER SYSTEM FOR VEHICLE

Background of Invention

1. Field of the Invention
The present invention relates to improve response of power system driving an electric rotary machine for a vehicle, in particular, to improve a torque response of a wound field machine of an automobile.

2. Description of the Related Art

A starter-generator with less wear of brushes is preferable for an idle stop vehicle repeating to start an engine. A wound field machine with a field winding wound on a rotor core is preferable for the starter-generator, because it is easy to control current generation. However, the starter-generator employing the wound field starter-generator has problems.

The largest problem is that the field winding with many turns has a long time constant being more than a few hundred milli seconds. To decrease the turns increases a copper loss...

Another problem is on a power source. The power source must apply a high voltage, when the starter-generator supplies a large current for starting the engine. Because, the motor torque is proportional to the current being proportional to the voltage applied from the power source. However, some electric load requires a conventional low voltage, 14V.

After all, the idle stop start er-generator requires a dual voltage system capable of applying a high voltage and a low voltage, which is well-known as the dual voltage system or the 42V/14V system. However, the dual voltage system with two Pd-acid batteries increases a weight of the system. The dual battery system, for example Japan patent No. 3736300, has a heavy weight. The weight of the system is reduced by employing a pair of a battery and a capacitor instead of the two batteries. Because, the capacitor such like an EDLC has a very larger current/weight ratio than the battery. The current/weight ratio is further important for the idle stop than a storage energy/ weight ratio.

However, the dual voltage system with the battery and the capacitor needs a chopper type DC/DC converter, because the capacitor voltage is changed largely by the charging. The c hopping DC/DC converter having a reactor increases a weight and a cost. Furthermore, an inverter of the DC/DC converter switched with a high frequency increases a power loss.

After all, it is considerable that the power system having the battery and the capacitor is more preferable so as to repeat the driving of the starter-generator, if the power system does not require the DC/DC converter. However, the battery-capacitor system has another problem. One is a leakage current of the capacitor with a large capacitance. The large capacitor such like an electric double layer capacitor has a large leakage current, Accordingly, the EDLC should be separate by means of turning-off of the switch so as to avoid a SOC loss of the battery. However, a large plunge current flows from the battery to the capacitor, when the capacitor with a low voltage is connected to the battery with a high voltage in parallel. The large plunge current gives damage to a capacitor life. Consequently, the parallel connection of the battery and the capacitor connected to each other in parallel causes the battery charge loss problem or the plunge current problem. Accordingly, it is considered that the parallel-connected pair of the battery and the capacitor is not desirable for the idle stop system.

Prior power supply systems employing a pair of the battery and the capacitor without the DC/DC converter, called the converter-less battery-capacitor system, are explained referring to Figures 1-7.

Japan unexamined patent publication No. 2004/108226 shown in Figure 1 proposes one converter-less battery-capacitor system having a battery 101 and a capacitor 106. A pair of a battery switch 104 and the battery 101 connected to each other in series is connected to an inverter 102. A pair of a capacitor switch 105 and the capacitor 106 connected to each other in series is connected to the inverter 102. Capacitor 106 can be charged by a high generating voltage of the starter-generator via an inverter 102, when battery switch 104 is turned off. However, the capacitor 106 needs a large capacitance. Furthermore, the large plunge current flows into capacitor 106 through the turned-on switches 104-105, if the capacitor voltage is decreased by the leakage current of the capacitor 106.

Japan unexamined patent publication No. 2005/207243 shown in Figure 2 proposes another converter-less battery-capacitor system having a battery 101 and a capacitor 106. A pair of battery switch 104 and battery 101 is connected to a capacitor 106 in parallel. Capacitor 106 can be charged by a high generating voltage of the starter-generator via an inverter 102, when battery switch 104 is turned off. However, the capacitor 106 needs a large capacitance. Furthermore, battery 101 must supply the leakage current of the capacitor 106, until the starter-generator supplies a generation current.

Japan unexamined patent publication No. 2004/282800 shown in Figure 3 proposes another converter-less battery-capacitor system having a battery 101 and capacitors 106A and 106B. The capacitors 106A and 106B are connected to the inverter 102 via a circuit 106C changing the capacitor connection. However, the capacitor 106 needs a large capacitance. Furthermore, battery 101 must supply the leakage current of the capacitor 106A and 106B, until the starter-generator supplies a generation current.

Japan unexamined patent publication No. 2001/41135 proposes another converter-less battery-capacitor system having a battery and a capacitor for driving a starter motor. The system has three relays changing between parallel connection and series connection of the battery and the capacitor. However, the changing circuit having three relays is complicate. Furthermore, 135' publication does not disclose that the parallel connection can be abbreviated by employing the starter-generator, because the battery and the capacitor connected to each other in series can be charged by the starter-generator.

After all, the capacitors in the above converter-less battery-capacitor system are capable of connecting to the battery in parallel. However, the capacitor must be separated from the battery, because the capacitor has the leakage current. As the result, the large plunge current is supplied from the battery to the capacitor, just after the capacitor is connected to the battery in parallel. The large plunge current decreases the capacitor life. Furthermore, large short-cut current flows from the battery to the capacitor connected in parallel, when the capacitor is broken.

Japan unexamined patent publication No. 2010/035,331 shown in Figure 5 proposes another converter-less battery-capacitor system employed by a field current supply system of an alternator. A freewheeling current of a field winding 10 charges a capacitor 2 via a freewheeling diode 11 in a changing mode when a field current switch 12 is turned off as shown in Figure 6. A field current is supplied from the capacitor 2 to the field winding 10 via a series diode 6 in a discharging mode when a field current switch 12 is turned on. After discharging of the capacitor 2, a battery 1 supplies the field current to the field winding 10 via a parallel diode 50 as shown in Figure 7. The field windings increases and decreases rapidly, because the voltage applied to the field winding 10 becomes high.

But, a source electrode S of transistor 6 is connected to capacitor 2 and diode 11, and a drain electrode D of transistor 6 is connected to diode 50 and field winding 10 in the original wiring diagram described in the above publication No. 2010/035,331. However, a parasitic diode of the transistor 6 in the above connection can not stop the freewheeling current of the field winding 10. Therefore, the connection of the parasitic diode of transistor 6 is amended in Figure 5. The charging mode and the discharging mode are executed alternately by switching of both

switches

12 and 6. The time constant of the field winding 10 is shortened equivalently by applying the high voltage.

However, capacitor 2 can not charge a sufficient energy, because capacitor 2 discharges by next turning-on of

transistors

6 and 12 just after charging of the capacitor 2. Further, ripple of the field current becomes large, because the freewheeling current is decreased quickly by charging capacitor 2. Furthermore, capacitor 2 becomes large.

Japan patent No. 3736300 Japan unexamined patent publication No. 2004/108226 Japan unexamined patent publication No. 2005/207243 Japan unexamined patent publication No. 2004/282800 Japan unexamined patent publication No. 2001/41135 Japan unexamined patent publication No. 2010/035331

One object of the invention is to provide a simple power system improving torque response of the vehicle. Another object of the invention is to provide a simple and economical idle stop system with quick response. Another object of the invention is to provide a simple and economical alternator system with quick response.

The inventor understands that the starter-generator of the micro hybrid system must generate a large motor torque for very short engine-starting period, for example a half second. In almost period, the starter-generator charges a conventional low voltage (12V) battery. Accordingly, the starter-generator mostly designed as the conventional alternator with the low voltage is preferable, if it can produce a large torque for the engine start. It is preferable to apply the high voltage to the mostly conventional alternator for the very short engine-stating period.

According to a first aspect of the invention, the battery (1) is connected to the inverter (8) via a pair of a capacitor (2) and a series switch (6) connected to each other in series. The pair of the capacitor (2) and the series switch (6) is connected to a parallel switch (5) in parallel. The parallel switch (5) is capable of stopping a current supplied from the battery (1) to the inverter (8). The series switch (6) is capable of stopping a current supplied from the battery (1) and the capacitor (2) to the inverter (8). The pair of the battery (1) and the capacitor (2) is charged by the inverter via the series switch (6).

In the other words, the pair of the capacitor and the 12V battery connected to series applies the high voltage for the engine start. By only turning-off of the series switch, the starter-generator can play as the conventional alter nator. The pair of the discharged capacitor and the battery is charged by the inverter as a rectifier of the starter-generator, when the generation volt age of the inverter is increased. This high voltage generation of the inverter should be executed in a braking period when the vehicle speed is decreased.

The power system of the first aspect has advantages explained hereinafter. The power system does not require the expensive and heavy DC/DC converter. Next, the power system does not have the leakage problem and the plunge current problem of the large capacitor, because the capacitor is connected to the battery to series. Or, the capacitor is se parated from the battery. In the other words, the capacitor connected to the battery in series does not generate the plunge current. The capacitor can nave a small capacitance, because the capacitor can discharge until the capacitor voltage becomes an allowable lowest voltage. Furthermore, it is important that the battery does not have damage if the switch is broken.

According to a preferred embodiment, the parallel switch (5) consists of a pair of a transistor and a parallel-diode connected to each other in parallel. An anode electrode of the parallel-diode is connected to a positive terminal of the battery (1). The series switch (6) consists of a pair of a transistor and a series-diode connected to each other in parallel. A cathode electrode of the series-diode is connected to one terminal of the capacitor (2). As the result, structure of the power system becomes simple and small. Furthermore, the capacitor (2) is not discharged, even though either one of the parallel switch (5) or the series switch (6) is broken.

According to another preferred embodiment, the power system has a charging mode and a discharging mode and a keeping mode. The inverter with the high voltage operation is connected to the series-connected capacitor and battery via the series switch. The inverter with the low voltage operation is connected to only battery via the parallel switch. As the result, the operation of the power system becomes simple.

According to another preferred embodiment, the capacitor (2) and the battery (1) connected to each other in series are charged with a high generation voltage of a wound field starter-generator with a field winding. The inverter of the wound field starter-generator can produce the high voltage for charging the series-connected capacitor (2) and the battery (1) easily, because the generation voltage of the wound field starter-generator is easily increased by means of increasing the field current in accordance with a charging state of the capacitor. For example, the inverter can output 42V at 2400 rpm of the engine, if the inverter can output 14V at 800 rpm of the engine. Furthermore, the inverter can output larger DC voltage, if the rotor flux is increased by means of increasing the field current. Preferably, a differential value of a capacitor voltage being mostly proportional to the charging current is employed as the above charging state of the capacitor. It is preferable to control the charging current in a predetermined range. Because, the field current should be feedback-controlled in the range that the differential value of the capacitor voltage is in the predetermined range. As the result, the charging control of the capacitor becomes simple.

According to another preferred embodiment, the high voltage for charging the capacitor is generated by chopping the generation current of the starter-generator at a low engine rotation speed. In the other words, the high voltage is generated with the residual magnet ic energy accumulated in a stator inductance by means of turning-off of the parallel switch (5). The boost voltage is applied to the series-connected pair of the capacitor (2) and the battery (1) after turning-off of the parallel switch (5). As the result, the high voltage can be applied even though the generation voltage of the inverter is low at the low engine speed.

According to another preferred embodiment, the charging circuit consists of the inverter (8) of which either one group of upper arm switches (81-83) and lower arm switches (84-86) is switched in the charging mode at the low engine rotation speed. In the other words, the high voltage for charging the capacitor is produced by means of chopping of the upper arm switches or the lower arm switches of the inverter. The high voltage is generated with the residual magnetic energy accumulated in a stator winding. As the result, the high voltage charging can be possible even though the generation voltage of the inverter is low at a low engine speed.

According to a second aspect of the invention, the capacitor (2) is charged by a freewheeling current of the field winding of the wound field machine via a freewheeling diode (11) connecting a field winding (10) to a connecting point between the capacitor (2) and the series switch (6) in the charging mode. The series-connected pair of the capacitor (2) and the battery (1) applies the high voltage to the field winding in the discharging mode. As the result, this second aspect of the invention can have the same advantages as the first aspect of the invention described above. Furthermore, the field current can change rapidly by the above charging and discharging with the high voltage of the capacitor. It means that the response of the wound field machine is improved largely.

According to a preferred embodiment, the power system has a keeping mode, when the field current switch (12) is turned on, and the series switch (6) is turned off, and when the field current switch (12) is turned off, and the series switch (6) is turned on. In the keeping mode, the capacitor can keep the high voltage so as to execute the engine-start and et al. Furthermore, ripple of the field current is reduced in the keeping mode, because decreasing of the freewheeling current of the field winding is reduced in the keeping mode.

According to a third aspect of the invention, a field winding consists of two portions, which are an upper field winding (10A) and a lower field winding (10B). The two portions are can have either of the series connection and the parallel connection. The connection is c hanged by the connection-changing circuit (44). As the result, the field current can change rapidly, if the parallel connection is selected. The copper loss is reduced, if the series connection is selected.

According to a preferred embodiment, the series connection is selected, when the low voltage is applied to the upper field winding (10A) and the lower field winding (10B). The parallel connection is selected, when the high voltage is applied to the upper field winding (10A) and the lower field winding (10B). As the result, the changing of the connection is operated with a simple circuit. Furthermore, the field current can increase very rapidly, by the applied high voltage and the selected parallel connection.

According to another preferred embodiment, the connection-changing circuit has a comparator (44) cooperating the applied voltage and a predetermined reference value. As the result, the connection-changing circuit becomes simple.

According to another preferred embodiment, each of the lower switch (41) and the upper switch (43) has a freewheeling diode connected to each other in parallel. As the result, the freewheeling current of the field winding can be circulated simply.

Figure 1 is a circuit diagram showing a prior converter-less capacitor-battery circuit having two switches. Figure 2 is a circuit diagram showing another prior converter-less capacitor-battery circuit having only one switch. Figure 3 is a circuit diagram showing another prior converter-less capacitor-battery circuit having a connec tion changer circuit and two capacitors. Figure 4 is a circuit diagram showing another prior converter-less capacitor-battery circuit for applying a boost voltage to a field winding. Figure 5 is a circuit diagram showing another prior converter-less capacitor-battery circuit for applying a boost voltage to a field winding. Figure 6 is a schematic equivalent circuit diagram showing high-voltage-charging operation of the circuit shown in Figure 5. Figure 7 is a schematic equivalent circuit diagram showing high-voltage-discharging operation of the circuit shown in Figure 5. Figure 8 is a wiring diagram showing a power supply system of the first embodiment. Figure 9 is a wiring diagram showing a boost operation of the inverter shown in Figure 8. Figure 10 is a wiring diagram showing a boost operation of the inverter shown in Figure 8. Figure 11 is schematic equivalent diagram showing the discharging of two batteries connected to each other in series. Figure 12 is schematic equivalent diagram showing the discharging of one battery and one capacitor connected to each other in series. Figure 13 is a schematic equivalent circuit diagram showing four capacitors. Figure 14 is a schematic equivalent circuit diagram showing one capacitor and one battery. Figure 15 is a flow chart showing a charging mode of the power circuit shown in Figure 8. Figure 16 is a wiring diagram showing the changing series-parallel connection of the field winding shown in Figure 8. Figure 17 is a wiring diagram showing the power system supplying the field current to the field winding of the alternator of the second embodiment. Figure 18 is a timing chart showing waveforms of the field current in the field winding shown in Figure 17. Figure 19 is a schematic equivalent circuit diagram showing the charging mode of the alternator shown in Figure 17. Figure 20 is a schematic equivalent circuit diagram showing the discharging mode of the alternator shown in Figure 17. Figure 21 is a schematic equivalent circuit diagram showing the keeping mode of the alternator shown in Figure 17. Figure 22 is a schematic equivalent circuit diagram showing the keeping mode of the alternator shown in Figure 17. Figure 23 is a diagram showing a table explaining the operation modes shown in Figures 19-22. Figure 24 is a wiring diagram showing an arranged embodiment of the power system shown in Figures 17. Figure 25 is a flow chart showing a control operation of the power supply system shown in Figures 17.

Detailed Description of Preferred Embodiment

(First embodiment)
A first embodiment is explained referring to Figures 8-16. The first embodiment shows a power system with high response, which applies a boost voltage to a starter-generator rapidly. In Figure 8, a power supply circuit 3 is connected to a three-phase inverter 8 via

DC link lines

401 and 402. The inverter 8 consisting of three upper arm switches 81-83 and three lower arm switches 84-86 is connected to a three-phase winding 800 of a wound field starter-generator with a field winding 10. Further, the power supply circuit 3 is connected to a field current circuit 40 via

DC link lines

402 and 403. The field current circuit 40 controls a field current supplied to the field winding 10. The wound field starter-generator is connected mechanically to an internal combustion engine of a vehicle.

Power supply circuit 3 consists of a battery 1, capacitor 2, a parallel switch 5, a series switch 6 and a controller 7. The battery 1 is connected to the inverter 8 via a pair of the capacitor 2 and the series switch 6 connected to each other in series. The pair of capacitor 2 and series switch 6 is connected to the parallel switch 5 in parallel. Parallel switch 5 consists of a pair of a transistor and a parallel-diode connected to each other in parallel. An anode electrode of the parallel-diode is connected to a positive terminal of battery 1. Series switch 6 consists of a pair of a transistor and a series-diode connected to each other in parallel. A cathode electrode of the series-diode is connected to a one terminal of capacitor 2.

Parallel switch 5 is capable of stopping a current supplying a current from battery 1 to inverter 8. Series switch 6 is capable of stopping a current supplying a current from battery 1 and capacitor 2 to inverter 8. The pair of battery 1 and capacitor 2 is charged by inverter 8 via series switch 6.

Control operation of the controller 7 is explained referring to Figure 8. Inverter 8 applies a three-phase voltage to the wound rotor starter-generator producing a motor torque. Inverter 8 work s as the three-phase rectifier, when a generated three-phase voltage of a stator winding of the starter-generator is larger than the three-phase voltage applied to the stator winding by inverter 8. The generation voltage of the starter winding is controlled by a field current supplied to the field winding 10.

Firstly, a discharging mode for starting of the engine is explained. A capacitor voltage of capacitor 2 is kept in a predetermined range capable of starting of the engine. For example, battery has 14V, and capacitor 2 has 28V before the engine is started. Parallel switch 5 is turned off, and series switch 6 is turned on. The added voltage of 42V is applied to inverter 8 and field current circuit 40. Field current circuit 40 supplies the increasing field current to field winding 10. The starter generator gives an engine-start torque to the engine by driving inverter 8, after the field current becomes larger than a predetermined value. The discharging of capacitor 2 must be stopped before the capacitor voltage is smaller than a predetermined value. The discharging mode can be executed, when the vehicle speed is increased.

Next, a charging mode for regenerating of a kinetic energy of the car is explained. The charging mode can be executed, while a brake pedal is pushed down. A capacitor voltage of capacitor 2 is kept in another predetermined range capable of charging. For example, battery has 14V, and capacitor 2 has less than 10V before the charging mode. The generation voltage of the starter-generator is increased by in creasing the field current, after parallel switch 5 is turned off. Series switch 6 is turning off. The increased charging current flows through the diode of series switch 6, after a rectified generation voltage of the inverter 8 is larger than the sum of the capacitor voltage and the battery voltage. The transistor 6 can be turned on so as to decrease a diode power loss. The field current is decr eased, after the capacitor voltage is larger than a predetermined value. Preferably, the field current is controlled in the charging mode so as to keep a differential value of the capacitor voltage in a predetermined range. The differential value of the capacitor voltage is mostly proportional to the charging current. Accordingly, the charging current value is kept in the preferable current range.

Next, a keeping mode for keeping the capacitor voltage is explained. The keeping mode should be executed, when a differential value of the vehicle speed is smaller than a predetermined value. Parallel switch 5 is turned on, and series switch 6 is turned off. The rectified generation voltage of inverter 8 is mostly equal to an object value of battery 1, for example 14.5V by means of feedback-controlling of the field current.

Next, a first boost charging method of the charging mode is explained referring to Figure 8. For example, the generation voltage of the starter-generator is not large at a low vehicle speed even though the field current becomes the largest value. In this first boost charging method, parallel switch 5 is switched with a predetermined frequency. A DC link voltage of the DC link line 401 is increased by a residual magnetic energy of each inductance Lu, Lv ad Lw of stator winding 800. As the result, the boosted voltage of the DC link line 401 charges capacitor 2 and battery 1 through series switch 6.

Next, a second boost charging method of the charging mode is explained referring to Figures 9-10. For example, the generation voltage of the starter-generator is not large at a low vehicle speed even though the field current becomes the largest value. In this second boost charging method, the DC link voltage of the DC link 401 is increased by a residual magnetic energy of each inductance Lu, Lv ad Lw of stator winding 800. In Figure 9, low arm switches 84-86 of inverter 8 are turned on. As the result, the generation voltages of each phase winding increases each phase current by means of short-cutting of each phase winding. The residual magnetic energy in each phase winding is accumulated in each winding. Accord ingly, the freewheeling current of inverter 8 increases the DC link voltage of DC link line 401 through upper arm switches 81-83, when the low arm switches 84-86 are turned off as shown in Figure 10. The boosted DC link voltage charges capacitor 2 and battery 1 through series switch 6. The above-explained boost method can be used for rapid-charging of capacitor 2.

Next, one benefit of the series-connected capacitor/battery system is explained referring to Figures 11-12. Figure 11 shows a conventional dual battery system with 42V/14 V, shown in Japan patent No. 3736300. Figure 12 shows the series-connected capacitor/battery system with 42V/14 V. Figures 11-12 shows a discharging state just after the discharging is started. In Figure 11, series-connected three Pb-acid batteries discharge the engine-starting current. However, a voltage loss of 12V is generated, when a voltage loss of the 12V battery is 4V. As the result, the con ventional dual battery system as shown in Figure 11 outputs 30V just after turning-on. In Figure 12, the series-connected capacitor/battery discharges the engine-starting current. The voltage loss of almost 4.5V is generated, when the battery voltage loss is 4V, and the capacitor voltage loss is 0.5V. As the result, the series-connected capacitor/battery system shown in Figure 12 can output 37V just after turning-on. After all, the output voltage of the power system of the embodiment increases more than 25 %. By increasing of the output voltage, the discharging current can be decreased.

Next, another benefit of the series-connected capacitor/battery system is explained referring to Figures 13-14. In Figure 13, a capacitor network consisting of nine capacitors 20 connected in series and in parallel supplies the engine-starting current. The capacitor network has the capacitance C, if each capacitor 20 has a capacitance C. Figure 14 shows the series-connected capacitor/battery system of the embodiment. Four capacitors 20 connected in series and in parallel are connected to the battery 2 in series. The capacitor network consisting of four capacitors 20 has the capacitance C, if each capacitor 20 has the capacitance C. An output voltage of the power system as shown in Figure 13 changes from 42V to 14V by the discharging. An output voltage of the power system as shown in Figure 14 changes from 42V to 14V by the discharging. The above two power systems transmit equal energy to inverter 8. By comparing between the two power systems shown in Figures 13 and 14, it is considered that the series-connected capacitor/battery system shown in Figure 14 can have a small capacitor 2 with a half capacitance in comparison with the capacitor network shown in Figure 13. As the result, the production cost and weight of the power system is reduced largely.

Next, the charging mode is explained referring to the flow chart of Figure 15. Firstly, it is judged whether or not the capacitor voltage Vc is lower than a predetermined value at step S200. It is judged whether or not the vehicle is braking at step S202, if the capacitor voltage Vc is lower. At next step S204, it is judged whether or not the generation voltage Vg of inverter 8 is higher than a predetermined value. The field current is increased at step S208, if the generation volt age Vg is higher. The boost operation explained above is executed at step S208, if the generation voltage Vg is lower.

Next, the field current circuit 40 shown in Figure 8 is explained referring to Figure 16. Field winding 10 is divided to an upper field winding 10A and a lower field winding 10B. The field current circuit 40 has a field current switch 12, an upper field winding 10A, a lower field winding 10B, a lower switch 41, a connection diode 42, an upper switch 43 and a connection-changing circuit 44 and et al. Field current circuit 40 is fixed on a rotor of the wound field machine except the field current switch 12. The upper field winding 10A and the lower field winding 10B are connected to each other in series via the connection diode 42. The lower switch 41 is conn ected to a pair of the lower field winding 10B and the connection diode 42 in parallel. The upper switch 43 is connected to a pair of the upper field winding 10A and the connection diode 42 in parallel.

A high potential DC line 403 of the power supply circuit 3 is connected to a DC line 405 in the rotor via an ignition switch 49 and a slip ring 47. A low potential DC line 402 of the power supply circuit 3 is connected to a DC line 406 in the rotor via a field current switch 12, a slip ring 48. A resistor 45 and a zenner diode 46 connected to each other in series output a reference voltage Vref to the comparator 44. The resistor voltage-dividing circuit consisting of two resistors r1 and r2 connected to series outputs a divided voltage of the voltage Vf. Com parator 44 compares a divided voltage of the DC line 405 and the reference voltage Vref. An output voltage of comparator 44 is applied to lower switch 41. Further, the output voltage of comparator 44 is applied to upper switch 43 via a level shift circuit 71. A constant voltage circuit 70 outputs a power source voltage to the comparator 44.

Next, operation of field current circuit 40 is explained referring to Figure 16. Comparator 44 turns on lower switch 41 and upper switch 43, when the divided voltage is higher than the reference voltage Vref. As the result, the upper field winding 10A and the lower field winding 10B are connected in parallel. Comparator 44 turns off lower switch 41 and upper switch 43, when the divided voltage is lower than the reference voltage Vref. As the result, the upper field winding 10A and the lower field winding 10B are connected to series. After all, the field current increases very rapidly, when the power supply circuit 3 applies a high voltage to the field current circuit 40. Accordingly, the field current is increased very quickly at the engine-starting timing. The time constant of the

field windings

10A and 10B become long, when the power supply circuit 3 applies a low voltage to the field current circuit 40. Accordingly, the copper loss and current ripple of the field winding 10A and 10B are decreased in the keeping mode. The diodes of the lower switch 41 and upper switch 43 can play as the freewheeling di odes.

(Second embodiment)
A second embodiment is explained referring to Figures 17-25. The second embodiment shows a power system with high response, which applies a boost voltage to a field winding of an alternator rapidly. In Figure 17, a power supply circuit 3 is connected to a field current circuit 4 consisting of a field winding 10, a freewheeling diode 11 and a field current switch 12. A voltage of power supply circuit 3 having battery 1, capacitor 2, a parallel diode 50 and a series switch 6 is applied to a pair of field winding 10 and field current switch 12 connected to each other in series. A contacting point X between capacitor 2 and series switch 6 is connected to a cathode electrode of a freewheeling diode 11. A contacting point Y between field winding 10 and field current switch 12 is connected to an anode electrode of a freewheeling diode 11.

Operation of power supply circuit 3 shown in Figure 17 and 23 is explained. In the charging mode, series sw itch 6 and the field current switch 12 are turned off. Capacitor 2 and battery 1 are charged by the freewheeling current of field winding via freewheeling diode 11 as shown in Figure 19. The charging mode is employed, when the field current must be decreased rapidly.

In the discharging mode, series switch 6 and the field current switch 12 are turned on. Capacitor 2 and battery 1 are discharged to the field winding as shown in Figure 20. The field current is increased rapidly. The discharging mode is employed, when the field current must be increased rapidly.

In the keeping mode, series switch 6 is turned off, when the field current switch 12 is turned on as shown in Figure 22. Furthermore, series switch 6 is turned on, when the field current switch 12 is turned off as shown in Figure 21. Batt ery voltage is applied to field winding, and the freewheeling current circulates via the freewheeling diode 11 and series switch 6. Accordingly, the ripple of the field current becomes small. Furthermore, the power loss is decreased.

Benefits of power supply circuit 3 and field current circuit 4 are explained referring to Figures 18. Figure 18 shows field current waveforms. The line A is one field current waveform, when battery voltage Vb, 14V, is applied to field winding 10. The field current becomes an approximately largest value Ia at timing point t2, because an inductance of field winding 10 is large. The line B is another field current waveform, when the high voltage, 28V, is applied to field winding 10. The field current becomes the approximately largest value Ia at timing point t1. A time T1 is very shorter than a time T2. In the other words, the time when the field current reaches the value Ia is shortened less than 25%, when the voltage applied to the field winding becomes double.

Another arrangement of the power supply circuit 3 is explained referring to Figure 24. Figure 24 shows power supply circuit 3 and field current circuit 4, which are fundamentally equal to them shown in Figure 6 except the field current switch 12 is shifted at a high side.

Figure 25 is a flow chart showing one control example of the power supply circuit 3 shown in Figure 17. Firstly, it is judged whether or not the battery voltage Vc is lower than a predetermined value at step S100. Capacitor 2 is rapid-charged at step S102, if the battery voltage Vc is low. Next, it is judged whether or not the vehicle engine is started at step S104. Capacitor 2 is discharged rapidly, and the high voltage is applied to the field winding at step S106, if the engine should be started.

Next, it is judged whether or not the vehicle is braking at step S108. Capacitor 2 is discharged rapidly, and the high voltage is applied to the field winding and the inverter at step S110, Therefore, the inverter rectifies a high three-phase voltage if the vehicle is braking. Next, it is judged whether or not the vehicle is accelerated at step S112. Capacitor 2 is discharged rapidly, and the high voltage is applied to the field winding and the inverter at step S114, Therefore, the motor generates a large torque if the vehicle is accelerated.

Claims

A power system having a power supply circuit (3) connected to an inverter (8) of a starter-generator connected mechanically to a vehicle internal combustion engine:
Wherein the power supply circuit (3) has a battery (1), a capacitor (2), a parallel switch (5) and a series switch (6);
the battery (1) is connected to the inverter (8) via a pair of the capacitor (2) and the series switch (6) connected to each other in series;
the pair of the capacitor (2) and the series switch (6) is connected to a parallel switch (5) in parallel;
the parallel switch (5) is capable of stopping a current supplied from the battery (1) to the inverter (8);
the series switch (6) is capable of stopping a current supplied from the battery (1) and the capacitor (2) to the inverter (8); and
the pair of the battery (1) and the capacitor (2) is charged by the inverter via the series switch (6).
The power system according to claim 1, wherein the parallel switch (5) consists of a pair of a transistor and a parallel-diode connected to each other in parallel;
an anode electrode of the parallel-diode is connected to a positive terminal of the battery (1);
the series switch (6) consists of a pair of a transistor and a series-diode connected to each other in parallel; and
a cathode electrode of the series-diode is connected to one terminal of the capacitor (2).
The power system according to claim 1, wherein the power supply circuit (3) has a controller (7) controlling the parallel switch (5) and the series switch (6);
the controller (7) turns off the parallel switch (5) and turns on the series switch (6), in a charging mode and a discharging mode when the capacitor (2) is charged or disc harged; and
the controller (7) turns on the series switch (6) and turns off the series switch (6), in a keeping mode when the only battery is charged or discharged.
The power system according to claim 3, wherein the capacitor (2) and the battery (1) are charged with a generation voltage of the starter-generator consisting of a wound field machine with a field winding; and
the controller (7) controls the generation voltage of wound field machine in the charging mode by means of controlling a field current supplied to the field winding in accordance with a charging state of the capacitor.
The power system according to claim 3, wherein the pair of the capacitor (2) and the battery (1) is charged by the starter-generator in the charging mode.
The power system according to claim 5, wherein the controller (7) switches the parallel switch (5), when the inverter (8) works as a rectifier.
The power system according to claim 5, wherein the controller (7) switches either of upper arm switches (81-83) and lower arm switches (84-86) of the inverter (8).
A power system having a power supply circuit (3) connected to a field current circuit (4) of a wound field machine connected mechanically to a vehicle internal combustion engine:
wherein the power supply circuit (3) has a battery (1), a capacitor (2), a parallel diode (50) and a series switch (6):
the field winding circuit (3) has a pair of freewheeling diode (11) and a field current switch (12), which is connected to one end of a field winding (10) of the wound field machine;
the battery (1) is connected to the other end of the field winding (10) via a pair of a capacitor (2) and a series switch (6) connected to each other in series;
the pair of a capacitor (2) and a series switch (6) is connected to a parallel diode (50) in parallel;
the parallel diode (50) is capable of stopping a current supplying a current from the battery (1) to the field winding (10);
the series switch (6) is capable of stopping a current supplying a current from the battery (1) and the capacitor (2) to the field winding (10); and
the freewheeling diode (11) is connected to a connecting point (X) between the capacitor (2) and the series switch (6).
The power system according to claim 8, wherein the power supply circuit (3) has a controller (7) controlling the field current switch (12), the parallel diode (50) and the series switch (6);
the controller (7) turns off the field current switch (12) and the series switch (6) in a charging mode;
the controller (7) turns on the field current switch (12) and the series switch (6) in a discharging mode;
the controller (7) turns on the field current switch (12), and turns off the series switch (6) in a keeping mode; and
the controller (7) turns off the field current switch (12), and turns on the series switch (6) in the keeping mode.
A power system having a power supply circuit (3) connected to a field current circuit (40) of a wound field machine connected mechanically to a vehicle internal combustion engine:
wherein the wound field machine has a field current circuit (40) having an upper field winding (10A), a lower field winding (10B), a lower switch (41), a connection diode (42), an upper switch (43) and a connection-changing circuit (44), which are fixed on a rotor of the wound field machine;
the upper field winding (10A) and the lower field winding (10B) are connected to each other in series via the connection diode (42);
the lower switch (41) is connected to a pair of the lower field winding (10B) and the connection diode (42) in parallel;
the upper switch (43) is connected to a pair of the upper field winding (10A) and the connection diode (42) in parallel; and
the connection-changing circuit (44) switches the lower switch (41) and the upper switch (43) in response to a received signal.
The power system according to claim 10, wherein the connection-changing circuit (44) turns on the lower switch (41) and the upper switch (43), when a voltage applied to the field current circuit (40) is higher than a predetermined value; and
the connection-changing circuit (44) turns off the lower switch (41) and the upper switch (43), when a voltage applied to the field current circuit (40) is lower than the predetermined value.
The power system according to claim 10, wherein each of the lower switch (41) and the upper switch (43) has a freewheeling diode connected to each other in parallel.