AU636533B2 - Circuit interruption system for an electric vehicle - Google Patents

Description

636533

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION NAME OF APPLICANT(S): Hitachi, Ltd.

ADDRESS FOR SERVICE: DAVIES COLLISON CAVE Patent Attorneys 1 Little Collins Street, Melbourne, 3000.

INVENTION TITLE: Circuit interruption system for an electric vehicle The following statement is a full description of this invention, including the best method of performing it known to me/us:la- BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a circuit interruption system for use in electric vehicles.

Description of the Related Art The article titled "Development and Practical Utilization of a Vacuum Circuit Breaker mounted on Electric Vehicles" ("RAILWAY, ELECTRIC ROLLING STOCKS" (Japanese title "DENKISHA NO KAGAKU"), March 1990, Vol. 43, No. 3, p.p. 33-38) discloses the following circuit interruption system for an electric vehicle in Fig. 5 on page 0e thereof.

Namely, between a pantograph of an electric vehicle and a load, such as an invertor for controlling voltage applied to driving motors of the electric vehicle, there is provided the circuit interruption system, which is formed by a series connection of two circuit disconnecting switches (also called unit switches) and a vacuum circuit breaker connected in series therewith. The vacuum circuit breaker is provided with a non-linear resistance element coupled in parallel therewith, which is available to absorb very high voltage appearing across contacts of the circuit 2 breaker, when it is opened.

In the prior art circuit interruption system, as mentioned above, load current is at first interrupted by opening the vacuum circuit breaker at a very high speed, and then the load is released from line voltage by opening the two unit switches.

Although the aforesaid article does not describe details, there is usually used, as such unit switches, a well known air circuit disconnecting switch of the type that arc appearing across contacts thereof upon opening is blown out by electromagnetic force. To this end, such a disconnecting switch has a blow-out coil, through which current to be interrupted flows.

When the switch is opened, arc appears across its contacts, and the blow-out coil generates magnetic field by current still flowing through the arc, so that electromagnetic force, which is created by interaction of e.

the arc current and the generated magnetic field, blows out the arc. If, therefore, current to be interrupted is smaller than a certain extent, the electromagnetic force created is not enough to blow out the arc, with the result that the arc continues for longer time.

Generally, as shown in Fig. 4, an arc continuing time in a switch of the type mentioned above abruptly increases, when current to be interrupted becomes smaller than 40-60 amperes. That time indicates a peak value at 7 or 8 amperes of the current, and the switch will almost lose the interruption ability, which is however recovered again, 3 when the current decreases down to about 1 ampere or less.

A current zone, in which the arc lasts for extremely long time, is usually called a weak zone of a switch.

Now, in the circuit interruption system of the aforesaid prior art, the non-linear resistance element provided in parallel with the vacuum circuit breaker is gradually deteriorated by very high voltage applied thereto repeatedly. The deterioration of the non-linear resistance element results in the increase of leakage current flowing therethrough. It can increase up to several amperes. The leakage current of this value will undoubtedly bring the interruption operation of the switch into the weak zone.

As a result, the arc comes to last for long time, whereby the surface of contacts of the switch is terribly injured. If the contact surface is heavily damaged, both the contacts may be melted to adhere to each other.

Further, in a conventional switch, arc is usually blown out toward the outside of the switch by electromagnetic force created by a blow-out coil, so that 9...9 devices mounted around the switch are subjected to various limitations in their installation. In addition, the switch ee ree must be provided with a big arc-shoot, in order to cool arc and extinguish it rapidly. These facts become the severe disadvantage in electric vehicles, because various devices are to be mounted in a very limited space.

SUMMARY OF THE INVENTION -4- According to the present invention there is provided a circuit interruption system for an electric vehicle, which is provided between a current collector and a power converter for controlling driving motors and includes a non-arcing type circuit breaker and two unit switches, all being coupled in series; characterized in that each of said two unit switches is a switch of the type that an arc source thereof is enveloped in a sealed chamber, whereby arc appearing across contacts upon opening of the unit switch is confined within the unit switch, there is provided an absorber so as to bridge a series connection of said circuit breaker and one of said unit switches, and said circuit interruption system is provided with a circuit interruption controller, which produces a trip signal to said circuit breaker and applies an open signal to said unit switches such that said one unit switch is open'd earlier than the other of said unit switches.

It is possible, using the principles of the invention, to construct circuit interruption systems of small size, whereby various devices may be efficiently mounted in a limited space in an electric vehicle.

By suitably arranging the circuit breaker and unit switches and the operating 25 sequence for these, the operation frequency of the circuit breaker may be reduced, so as to prolong the life of the circuit breaker.

o• o 930224,p:\opci\kat,14867.92,4 5 BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 schematically shows a circuit arrangement of an electric vehicle, which includes a circuit interruption system according to an embodiment of the present invention; Fig. la shows another example of a non-arcing type circuit breaker capable of being used in the circuit interruption system as shown in Fig. 1; Fig. 2 is a block diagram showing the configuration of a circuit interruption controller used in the system as shown in Fig. 1; Figs. 3a and 3b are graphs showing the relationship of an exciting current of an operating coil of a unit switch and a set value for detecting some disconnection; and Fig. 4 is a graph showing the relationship of an arc continuing time and current interrupted for the purpose of explaining a weak zone of a unit switch.

DETAILED DESCRIPTION OF THE INVENTION Referring at first to Fig. i, explanation will be made of the overall arrangement of a main circuit of an electric vehicle, which includes a circuit interruption system according to an embodiment of the present invention.

In the figure, reference numeral 1 denotes a trolley wire, with which pantograph 2 as a current collector for the electric vehicle is in contact. Reference numeral 3 denotes a fuse. Usually, there is provided arrester 25 in 6 parallel with the fuse 3. Reference numerals 7 and 8 denote a resistor and a capacitor, respectively, which forms a filter. To the filter is coupled invertor 9, which can convert DC electric power into poly-phase, usually three-phase, AC electric power and vice versa.

As is well known, the invertor 9, during the power running of the electric vehicle, supplies AC electric power of variable frequency and variable voltage to induction motors (IM) 10 for driving the electric vehicle, and during the regenerative braking, functions as a converter to convert AC electric power generated by the driving motors 10 functioning as generators into DC electric power. The converted AC electric power is fed back to the trolley wire 1.

The operation of the invertor 9 as mentioned above is carried out under the control of invertor controller 26.

To this purpose, the invertor controller 26 is supplied with a signal indicating current of the driving motors a signal from a master controller (not shown) manipulated 20 by an operator and so on, which are necessary to achieve the required control. However, details thereof are omitted in the figure, because those signals have no particular close connection with the present invention, and the structure and operation of the invertor 9 and its controller are well known. In the following description, they will be described as needed.

Between the fuse 3 and the filter resistor 7 is provided a circuit interruption system according to this 7 embodiment, which comprises the series connection of two vacuum unit switches 15a and 15b as well as vacuum circuit breaker 13 connected in series therewith. There is provided non-linear resistance element 16 so as to bridge the vacuum unit switch 15b and the vacuum circuit breaker 13. Further, reference numeral 27 denotes a current detector provided for detecting current flowing through the circuit interruption system.

The circuit breaker 13 used in this embodiment is a well known vacuum circuit breaker, which has a vacuum chamber enveloping contacts therein, so that arc appearing across the contacts upon their opening can be confined within the chamber and never leaks outside the circuit breaker.

In stead of the vacuum circuit breaker 13 as described above, a circuit breaker composed of two reverse-parallel e connected gate turn-rff (GTO) thyristors 11 and 12 as shown in Fig. la, for example, can also be used, because such a GTO thyristor circuit breaker originally never produces 20 arc, when it interrupts current flowing therethrough.

In the circuit breaker as shown in Fig. la, either one of the GTO thyristors 11 and 12 is tuned on in accordance with whether the electric vehicle is in the power running or in the regenerative braking. When the overcurrent is detected, a turn-off signal is applied to a gate of a GTO thyristor then being in conductive state.

A circuit breaker of such type that arc never leaks outside or is not generated is referred to as a non-arcing 8 type circuit breaker.

Further, as is well known, since the vacuum unit switches 15a and 15b have the operating mechanism different from the vacuum circuit breaker 13, the former can not operate as quickly as the latter. By way of example, the circuit breaker con open its contacts in about 0.6 msec in response to a trip signal, whereas the unit switch takes about 50 msec to open its contacts in response to an open signal, Similarly to the vacuum circuit breaker 13, however, a S: vacuum unit switch used as the unit switches 15a and also has a vacuum chamber enveloping its contacts therein, so that arc never leaks outside. With use of such a unit switch, the circuit interruption system of this embodiment can be constructed in the arc-less type, as a whole.

A control circuit for the main circuit of the electric vehicle as mentioned above is formed, as follows.

Reference numeral 18 denotes a trip coil of the circuit breaker 13. In Fig. 1, an electric source of the 20 coil 18 and other details are omitted for simplification of •the drawing. The circuit breaker 13 is closed, during the coil 18 is excited, however it is opened to interrupt current flowing therethrough very quickly, when the coil 18 is de-excited in response to a trip signal, as referred to later.

Further, reference numerals 17a and 17b denote operating coils of the unit switches 15a and respectively. The contacts of both the unit switches *c

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*5*S S. -9and 15b are kept closed, during the respective coils 17a and 17b are excited, and opened during no excitation of those coils 17a and 17b.

In this embodiment, the coils 17a and 17b are connected in series, and therefore the excitation of both can be stopped simultaneously. Since, however, the operating coil 17a of the unit switch 15a is provided with a time delay element formed by resistor 20 and capacitor 2i, the unit switch 15b is always opened earlier than the unit switch Reference numeral 22 denotes electric source for exciting the coils 17a and 17b. In an excitation circuit of the coils 17a and 17b, there are included two contacts 23 and 24 connected in series. These contacts are contacts 15 of relays, which operate in response to signals, as referred to latgr. Current detector 28 is further provided in the excitation circuit to detect excitation current of the coils 17a and 17b. Circuit interruption controller 19 takes therein outp'it signals of both the current detectors 27 and 28 and a notch-off signal from the invertor controller 26. In response to those signals, the controller 19 produces the trip signal for stopping the excitation of the coil 18 to trip the circuit breaker 13 and an open signal for opening the contact 23. Further, the contact 24 is opened by the notch-off signal from the invertor controller 26.

Fig. 2 is a block diagram showing the more detailed configuration of the circuit interruption controller 19.

10 As shown in the figure, the output signals of the current detectors 27 and 28 are coupled to overcurrent detecting part 190 and disconnection detecting part 191, respectively. As well as being used to open contact 192, an output of the detecting part 190 is coupled to one of two terminals of OR gate 194. An output of the detecting part 191 is coupled to the other terminal of the OR gate 194 through two contacts 192 and 193 connected in series.

The contac- 193 opens in response to the notch-off signal from the invertor controller 26.

Circuit breaker controlling part 195 is a kind of sequence circuit, which at first produces the signal to the trip coil 18 of the circuit breaker 13 and then the signal to the contact 23, when it receives an output of the OR gate 194.

In the controller 19 constructed as above, the overcurrent detecting part 190 compares the current detected by the current detector 27 with a predetermined reference and produces its output signal, when the ',.r.mer 20 exceeds the latter. Namely, the current detector 27 and the detecting part 190 functions as a well known overcurrent relay.

Further, the disconnection detecting part 191 is provided to detect the wire disconnection or some other troubles in the excitation circuit of the operating coils 17a and 17b. Also this detecting part 191 compares the current detected by the current detector 28 with a certain set value and produces its output signal, when the detected 11 current becomes smaller than the value.

The set value will be determined, as follows. For example, it can b° set at half a rated excitation current i of the coils 17a and 17b, as shown in Fig. 3a. In this case, if wire disconnection or some other troubles occur in the excitation circuit at time point to, the excitation current decreases, so that the wire disconnection is detected, when the excitation current becomes smaller than the set value.

If occurrence of intermittent disconnection is taken into consideration, the set value is preferable to be set at a smaller value, for example, at one third of the rated excitation current ic, as shown in Fig. 3b. With this, the reliable trouble detecting operation can be secured even in the case of the intermittent disconnection.

S. In the following, explanation will be made of the operation of the circuit interruption system, as mentioned above.

It is assumed at first that a fault, such as earthing, 20 occurs somewhere in the main circuit of the electric vehicle and current flowing through the main circuit increases extremely. Such current, fault current, is detected by the detector 27 and compared with the predetermined reference in the overcurrent detecting part 190. If the fault current exceeds the predetermined reference, the overcurrent detecting part 190 produces its output signal, which is given to the circuit breaker controlling part 195 through the OR gate 194.

12 When receiving the output signal, the circuit breaker controlling part 195 at first produces the trip signal to the coil 18 of the circuit breaker 13 and then the open signal to the contact 23. Accordingly, the circuit breaker 13 is at first opened to interrupt the fault current.

At this time, high voltage is induced across the circuit breaker 13 by inductance of the main circuit of the electric vehicle and the trolley wire 1. Since, however, the non-linear resistance element 16 is provided so as to 10 bridge the circuit breaker 13 and the unit switch which is not opened at this time, the non-linear resistance element 16 is electrically coupled in parallel with the circuit breaker 13 and therefore can serve as an absorber of the high voltage induced.

After that, since the excitation circuit of the unit switch operating coils 17a and 17b is opened by the contact S 59 S23, the coil 17b is de-excited to open the unit switch After some delay time determined by the resistor 20 and the capacitor 21, the coil 17a is de-excited to open the unit switch 15a. Thereby, the main circuit of the electric vehicle is perfectly released from the line voltage.

In the case where wire disconnection or some other troubles occur in the excitation circuit of the unit switch operating coils 17a and 17b, it is detected by the disconnection detecting part 191, which produces the output signal to the OR gate 194 through the contacts 192 and 193.

Thereafter, the same operation as mentioned above is caused. Also in this case, therefore, the circuit breaker 13 13 at first interrupts the current of the main circuit of the electric vehicle and then the unit switches 15a and open to release the main circuit from the line voltage. In this manner, the unit switches 15a and 15b never interrupt heavy current flowing through the main circuit, whereby the safe and reliable interruption takes place.

Next, let's consider the case where an operator manipulates a master controller (not shown) to issue a notch-off instruction.

10 In this case, this instruction is given to the invertor controller 26, which causes the invertor 9 to reduce the current flowing through the main circuit of the electric vehicle. At this time, the main circuit current is preferable to be reduced to a value smaller than a socalled chopping current of a vacuum switch used as the unit switch 15b. Then, the invertor controller 26 also produces the notch-off signal to the controller 19 and the contact 24.

In response to this notch-off signal, the contact 24 boo" b 20 is opened to de-excite both the coils 17a and 17b. As a result, the unit switch 15b is at first opened. At this time, since the current of the invertor 9 is reduced down to a small value, the unit switch 15b only interrupts small current.

Even if the current interrupted is small, high voltage can be induced across the unit switch 15b, because the trolley wire 1 has considerably large inductance. Since, however, the non-linear resistance element 16 is provided

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14 so as to bridge the circuit breaker 13, which is not opened at this time, and the unit switch 15b, the non-linear resistance element 16 is electrically coupled in parallel with the unit switch 15b and therefore can serve as an absorber of the high voltage induced.

After some delay time from opening of the unit switch the unit switch 15a is opened to release the main circuit of the electric vehicle from the line voltage. In this manner, the non-linear resistance element 16 is used 10 in common by the circuit breaker 13 and the unit switch In view of the main purpose only of the present eeoc invention, it is of course that there can be provided separate non-linear resistance elements in parallel with the circuit breaker 13 and the unit switch "respectively. However, the common usage of a single nonolinear resistance element, which is originally provided to the circuit breaker 13, as shown in Fig. 1, has the advantage of no increase of cost in manufacturing.

20 By the way, the notch-off signal is also applied to the controller 19 to open the contact 193 therein. Even if, therefore, the excitation current decreases by opening the contact 24 of the excitation circuit in response to this signal and the disconnection detecting part 191 produces the output, the circuit breaker controlling part 195 never produces the output signal to the coil 18 of the circuit breaker 13.

Namely, the circuit interruption system according to 15 the present embodiment is so designed that the circuit breaker 13 is never operated in response to the notch-off instruction issued by the operator, but is tripped, only when some fault occurs and fault current reaches the reference value predetermined for the overcurrent protection. As a result, the operation frequency of the circuit breaker 13 is reduced to the great extent, whereby the life thereof is much improved.

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Claims (9)

1. A circuit interruption system for an electric vehicle, which is provided between a current collector and a power converter for controlling driving motors and includes a non-arcing type circuit breaker and two unit switches, all being coupled in series; characterized in that each of said two unit switches is a switch of the type that an arc source thereof is enveloped in a sealed chamber, whereby arc appearing across contacts upon opening of the unit switch is confined within the unit switch, there is provided an absorber so as to bridge a series connection of said circuit breaker and one of said unit switches, and said circuit interruption system is provided with a circuit interruption controller, which produces a trip signal to said circuit breaker and applies an open signal to said unit switches such that said one unit switch is opened earlier than the other of said unit switches.

2. A circuit interruption system according to claim 1, wherein when overcurrent in said circuit interruption system is detected, said circuit interruption controller at first produces the trip signal to said circuit breaker and then the open signal to said unit 20 switches. 'I

3. A circuit interruption system according to claim 1, wherein when a notch-off signal occurs after said power converter reduces current flowing therethrough, said circuit interruption controller produces the open signal to said unit switches and prevents the trip 25 signal to said circuit breaker from being produced. S

4. A cicuit interruption system according to claim 1, wherein when the interruption of excitation of said unit switches is detected, said circuit interruption controller at first produces the trip signal to said circuit breaker and then the open signal to said unit switches.

A circuit interruption system according to claim 1, wherein said circuit 930224,p;\opcr\kat,14867.9216 17 interruption controller at first produces the trip signal to said circuit breaker and then the open signal to said unit switches upon detection of overcurrent in said circuit interruption system and produces the open signal, while preventing the trip signal from being produced, upon occurrence of a notch-off signal after said power converter reduces current flowing therethrough.

6. A circuit interruption system according to claim 1, wherein said circuit interruption controller at first produces the trip signal to said circuit breaker and then the open signal to said unit switches upon detection of interruption of excitation of said unit switches and produces the open signal, while preventing the trip signal from being produced, upon occurrence of a notch-off signal after said power converter reduces current flowing therethrough.

7. A circuit interruption system according to claim 1, wherein said circuit interruption controller at first produces the trip signal to said circuit breaker and then the open signal to said unit switches, when overcurrent in said circuit interruption system and/or the interruption of excitation of said unit switches are detected.

8. A circuit interruption system according to claim 1, wherein said interruption system controller at first produces the trip signal to said circuit breaker and then the open signal to said unit switches upon detection of overcurrent in said circuit interruption Ssystem and/or the interruption of excitation of said unit switches and produces the open signal, while preventing the trip signal from being produced, upon occurrence of a notch-off signal after said power converter reduces current flowing therethrough.

9. A circuit interruption system substantially as hereinbefore described with reference to the drawings. .DATED this 24th day of February, 1993 HITACHI, LTD. By its Patent Attorneys S DAVIES COLLISON CAVE 930224,p:\ope\k 14867.92,17