JP3455797B2 - Power converter - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power converter for converting an alternating current into a direct current by using an alternating current as a power supply, and more particularly to a technology for dealing with a ground fault of the device. 2. Description of the Related Art As a conventional power converter for converting an alternating current into a direct current using an alternating current as a power supply, for example, Japanese Patent Application Laid-Open No. 63-1865 / 1988
There is No. 05 publication. The power converter disclosed in the publication is specified for an AC railway electric vehicle, and has the following configuration shown in FIG. [0003] A pantograph 1 for taking in AC power from an overhead line and a primary winding 4 of a transformer 3 are connected with an AC circuit breaker 2 interposed therebetween, and the other of the primary winding 4 of the transformer 3 is a rail (ground). Is connected via a ground brush 13 to a wheel 15 in contact with the vehicle. One end of the secondary winding 5 of the transformer 3 is connected to the AC input terminal (u phase) of the single-phase converter 51 via the contactor 7, and the other end of the secondary winding 5 is connected to the AC input terminal (v Phase). A series body of the charging resistor 6 and the auxiliary contactor 8 is connected to both ends of the contactor 7. A DC output terminal of the single-phase converter 51 is connected to a filter capacitor 11 and a DC side of a three-phase inverter 52, and an AC motor 12 is connected to an AC side of the inverter. [0005] Here, the single-phase converter 51 has, in the u-phase, an upper arm formed of a parallel body in which a semiconductor switching element (hereinafter abbreviated as an element) 20u and a freewheel diode 24u are connected in parallel with opposite polarities. The arm is also composed of an element 21u and a freewheel diode 25u, and the in-phase arm is composed of a series body of upper and lower arms. Also, in the v-phase, the device 20
v, 21v and freewheeling diodes 24v, 2
5v. On the other hand, the three-phase inverter 52 has an arm configuration similar to that of the above-described converter, and includes elements 30u, 31u, 30v, 31v, 30w, 31w for three phases u to u and freewheel diodes 34u, 35u, 34v, 35
v, 34w, and 35w. [0007] One end of the single-phase converter 51 on the DC side (the negative side of the filter capacitor in the figure) is connected (grounded) to the grounding brush 13 by a grounding line 14, and a ground fault current is detected on the grounding line. A grounding relay 53 is provided. Reference numeral 60 denotes a control box for housing equipment in a so-called control device, which is a single-phase converter 51, a three-phase inverter 52, a filter capacitor 1
1, a contactor 7, a charging resistor 6, and an auxiliary contactor 8
Is stored in. The housing 60 is electrically connected to the ground brush 13.
(Ground). Here, the functions of the contactor 7, the charging resistor 6, and the auxiliary contactor 8 are as follows. When the contactor 7 is turned on from a state where the filter capacitor 11 is not charged, an excessive charging current flows from the transformer 3 to the single-phase. The purpose is to prevent the flow into the converter 51. Therefore, when charging the filter capacitor 11, first, the auxiliary contactor 8 is turned on and the filter capacitor 1 is charged with the charging current limited by the charging resistor 6.
1 and a certain amount of charge is charged before contactor 7
Input. The function of the grounding relay 53 provided on the connection line 14 connecting the negative side of the filter capacitor 11 and the grounding brush 53 is as follows: the positive side of the filter capacitor 11 or the single-phase converter 51 or a three-phase inverter. When the ground fault occurs and the ground brush 13 is electrically connected to the same potential, the ground fault current is detected and the AC circuit breaker 2 is opened to prevent the ground fault current from continuing to flow. . A case where a ground fault occurs in the power converter shown in FIG. 2 will be considered. As described above, the plus side of the filter capacitor 11 or the single-phase converter 5
When the one or three-phase inverter 52 is grounded, the grounding relay 53 detects the ground fault current, and opens the AC circuit breaker 2 and simultaneously opens the contactor 7 and the auxiliary AC contactor 8. After that, the AC circuit breaker 2 is turned on to restart the operation.
At this time, if the ground fault has not yet been removed, and particularly if the ground fault has occurred between the secondary winding 5 and the contactor 7, the contactor 7 and the auxiliary contactor 8 will be removed. Even when the AC circuit breaker 2 is open, a ground fault occurs again along the path (housing 60-ground line 14-freewheel diode 23v-secondary winding 5) indicated by the arrow in FIG. At this time, a large exciting inrush current flows through the primary winding of the transformer 3 depending on the timing between the current due to the ground fault on the secondary winding side and the power supply phase when the AC circuit breaker 2 is turned on. As a result, a large electromagnetic force exceeding the mechanical strength acts on the coil of the transformer, and there is a problem that the transformer is damaged. Generally, when the power is supplied to the transformer, an inrush current flows through the primary winding, and the maximum inrush current is reduced with time when the power is supplied. The magnitude of the excitation inrush current depends on the power supply voltage, the power supply phase, the remanence of the iron core, and the like. If the power supply voltage is the same, the magnitude is the largest when the power supply phase is 0 degree and the remanence is maximum. 20k
When the primary voltage is 23 kV, the maximum inrush current of 550 A flows through the primary winding of the transformer for railcars of V, 80 A, secondary winding rated 900 V, 750 A × 2. Therefore, when a current in which the ground fault current and the rush current overlap when the AC circuit breaker 2 is turned on flows into the transformer, the current far exceeds the rated current. It is necessary to design so as to have the electrical and mechanical withstand capability, and particularly in an electric vehicle, there is a problem that the weight increases accordingly. Therefore, an object of the present invention is to reliably cut off the current caused by a ground fault even if a ground fault occurs in any place of the power converter, and to open the AC circuit breaker due to the ground fault. Even if the AC circuit breaker is turned on again without removing the grounding portion later, it is an object of the present invention to prevent an excessive current flowing through the transformer by overlapping the inrush current and the ground fault current. Means for Solving the Problems A semiconductor switching element has two sets of serial bodies in which a plurality of parallel bodies in which freewheel diodes are connected in parallel with opposite polarities are connected in series. A phase converter and a transformer in which a single-phase AC power supply is connected to a primary winding via an AC circuit breaker ,
Both ends of the secondary winding of the transformer and the AC side of the converter
First and second contactors for connecting both ends, a filter capacitor connected between the DC-side terminals of the single-phase converter,
A housing in which at least the first and second contactors, the single-phase converter and the filter capacitor are housed, a means for grounding the DC-side end of the single-phase converter and the housing with a ground wire, and a parallel connection to the second contactor a resistor that is provided with a ground relay which detects a current from one end of the DC side of the single-phase converter to ground, [0017] charging from the AC power supply of single phase capacitor exchange
Flow breaker, first contactor, second contactor in order
When the earthing relay is operating, it should be turned on.
After the AC circuit breaker is shut off in response to the output, the first and second contacts
It is characterized in that an interrupting sequence for interrupting the touch device almost simultaneously is adopted . Thus, even if a ground fault occurs between the secondary winding 5 and the contactor 7 in the same manner as in the above-described ground fault, at least the first contactor is opened by a signal from the ground relay. Therefore, the ground fault current flowing through the path shown in FIG. 2 can be cut off. Further, even when the AC circuit breaker 2 is turned on again without removing the grounding point, the secondary winding 5 of the transformer 3 is opened by the first and second contactors, so that the transformer is connected to the transformer. Only the inrush current flows. Then the first
When the contactor is turned on, a ground fault current flows and the secondary winding is short-circuited. At this time, however, the exciting rush current and the short-circuit current flow simultaneously because the exciting rush current is attenuated and disappears. Can be prevented. Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment applied to a power converter of a railway electric vehicle according to the present invention. Note that the basic configuration of FIG. 1 is the same as that of FIG. 2 and is denoted by the same reference numerals, and detailed description thereof is omitted since it has been described above. The configuration differs from that of FIG. 2 in that a switch is provided on the connection between the secondary winding 5 of the transformer 3 and the single-phase converter 51 and on the ground line 14. Both ends of the secondary winding 5 of the transformer 3 and both terminals on the AC side of the single-phase converter 51 are connected via a first contactor 9 and a second contactor 7, respectively. The charging resistor 6 is connected in parallel to both ends of the second contactor 7. The negative side of the filter capacitor 11 and the ground brush 13 are connected by a connection line 14 via a switch 54. This switch 54 is provided for an insulation test of the power converter, and is opened at the time of the test.
It is turned on during normal operation. Next, the switching operation function between the AC circuit breaker 2, the first contactor, and the second contactor for achieving the object of the present invention in the configuration of the power converter will be described. <Initial Charging Mode> In order to supply the motor 12 with alternating current of variable frequency and variable voltage from the three-phase inverter 52 to generate a predetermined torque and start the motor, the DC voltage of the filter capacitor 11 usually reaches a predetermined value. Wait until. Therefore, the following sequence is performed when the filter capacitor 11 is initially charged. First, the AC circuit breaker 2 is turned on.
Of the contactor 9 is supplied. Then, the filter capacitor 11
, The voltage of the secondary winding 5 is applied through the charging resistor 6, the freewheeling diodes 24u and 23v, and the charging current flows. After charging is completed, the second contactor 7 is turned on. <Ground fault, operation restart mode> It is assumed that a ground fault occurs between the secondary winding 5 and the second contactor 7, which cannot be dealt with by the prior art, as a ground fault assumption. In the ground fault path in this case, a ground fault current flows through the housing 60, the ground wire 14, the freewheel diode 23v, the first contactor 9 and the secondary winding 5. At this time, the grounding relay 53 detects the ground fault current, and in response to this detection, opens the AC circuit breaker 2 and simultaneously opens the first and second contactors 9 and 7 (meaning that the ground fault current is cut off). Then, it is not always necessary to open the second contactor at this time.) As a result, the ground fault current in this path is cut off. Thereafter, the operation may be restarted in a state where the ground fault location has not been removed yet with the ground fault cause unknown. At that time, the AC circuit breaker 2 is first turned on. At this time, the secondary winding 5 of the transformer 3 has not yet been turned on by the first and second contactors, and is kept open. As a result, only an inrush current flows through the primary winding of the transformer. Thereafter (after a predetermined time), the first contactor 9 is turned on. At this point, the ground fault current flows again along the same path, and the secondary winding is short-circuited. At this time, however, the exciting rush current and the short-circuit current cannot flow simultaneously because the exciting rush current is attenuated and disappears. Absent. As a result, even if a ground fault occurs at the worst place under the above-mentioned conditions, and even if the operation is restarted ignoring this, an excessive current is prevented from being generated in the transformer due to the ground fault. be able to. The ground fault is caused by the single-phase converter 51 or 3
When the voltage is generated on the phase inverter 52 side, the voltage applied to the corresponding portion at the time when the first contactor 9 is turned on is the voltage of the secondary winding of the transformer via the charging resistor 6. The ground fault current under the ground fault condition is small. Therefore, when the restart operation is performed without removing the grounding portion, the grounding portion can be distinguished from the grounding relay by the magnitude of the ground fault current. The sequence when the AC circuit breaker 2 and the first and second contactors 9 and 7 are turned on and off according to the present invention is summarized as follows. Order of application: AC circuit breaker 2-first contactor 9
A second contactor 7 (delayed by a predetermined time from 9) . Blocking sequence (ground fault): AC breaker 2 operates in first and second contactor 9,7 together substantially simultaneously. Next, a second embodiment of the present invention will be described with reference to FIG. The difference from FIG. 1 is that the single-phase converter 51 is a three-level converter. This single-phase converter 51
Is composed of elements 20u to 23u, freewheel diodes 24u to 27u, and clamp diodes 28u and 29u as u-phase components.
v to 23v, freewheel diode 24v to 27
v and clamp diodes 28v and 29v. Clamp diode 28 connected in series
The connection point between u and 29u and the connection point between 28v and 29v are respectively connected to the connection point between the filter capacitors 11p and 11n connected in series to form a neutral point. The three-level converter selects three potentials on the plus side of the filter capacitor 11p, the neutral point, and the minus side of the filter capacitor 11n according to the switching manner of the four series-connected elements of each phase. Output. As the grounding structure, the neutral point is set to the grounding brush 1
3 potential. In this example, when a ground fault occurs between the secondary winding 5 and the first contactor 7, a ground fault current flows through the filter capacitor 11n.
When the AC circuit breaker 2 is turned on again after a ground fault, which is a problem in the conventional example, the filter capacitor 11
n has been discharged, and the first wave of the ground fault current at the time of the occurrence of the ground fault again flows the same current as that obtained by short-circuiting the secondary winding. In addition, it is possible to prevent the ground fault currents from overlapping. Although the neutral point is normally grounded as the grounding structure in the embodiment of the figure, the negative side of the filter capacitor may be grounded in some cases.
However, the effect of the present invention does not change even if the grounding structure changes. According to the present invention, even after the AC circuit breaker is opened due to the occurrence of a ground fault and the AC contactor is turned on again without removing the grounding point, the transformer can be excited. The inrush current and the short-circuit current of the transformer overlap and flow, and it is possible to prevent the transformer from being damaged by an excessive electromagnetic force acting on the coil of the transformer.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a configuration diagram of a power conversion device for an AC railway vehicle according to a first embodiment of the present invention. FIG. 2 is a configuration diagram of a conventional power conversion device for an AC railway vehicle. FIG. 3 is a configuration diagram of a power conversion device for an AC railway vehicle according to a second embodiment of the present invention. [Description of Signs] 1 ... Pantograph, 2 ... AC circuit breaker, 3 ... Transformer, 4 ...
Primary winding, 5 Secondary winding, 6 Charge resistor, 7 Second contactor, 9 First contactor, 11 Filter capacitor, 12 Motor, 13 Ground brush, 14 Ground wire,
Reference numeral 15: wheels, 20u, 20v, 21u, 21v: switching elements, 24u, 25u, 22v, 23v: freewheel diodes, 51: single-phase converter, 52: three-phase inverter, 53: ground relay, 54: switch.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-186505 (JP, A) JP-A-62-230356 (JP, A) JP-A-5-223906 (JP, A) JP-A-3-3 218270 (JP, A) JP-A-9-37593 (JP, A) JP-A-5-22985 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H02M 7/06 B60L 9 / 16 H02H 3/16

Claims (1)

(57) Claims 1. A semiconductor switching element has two sets of parallel bodies in which a plurality of parallel bodies in which freewheel diodes are connected in parallel with opposite polarities are connected in series, and AC is converted to DC. A single-phase converter and a single-phase AC power supply
A transformer connected to the secondary winding, the secondary of the transformer
Connect both ends of the winding to both ends of the AC side of the converter
A first and a second contactor, a filter capacitor connected between the DC side terminals of the converter, a housing containing at least the first and second contactors, the converter and the filter capacitor, Means for grounding one end on the DC side of the converter and the housing with a ground line, a resistor connected in parallel to the second contactor, and a grounding relay for detecting a current from one end on the DC side of the converter to ground Charging the capacitor from the AC power supply
The AC circuit breaker, the first contactor, and the second contactor
The sequence is to be applied in the order of
During operation, the AC circuit breaker is shut off in response to the output of the relay.
After the disconnection, the first and second contactors are shut off almost simultaneously.
A power conversion device having a cutoff sequence .