GB2537020A

GB2537020A - Railway vehicle drive system

Info

Publication number: GB2537020A
Application number: GB1602392.1A
Authority: GB
Inventors: Sugiura Tetsu; Nozaki Yuichiro; Tachihara Shuuichi; Ayata Masataka
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 2015-02-17
Filing date: 2016-02-10
Publication date: 2016-10-05
Anticipated expiration: 2036-02-10
Also published as: DE102016202419B4; JP6349269B2; CN105897023A; CN105897023B; JP2016152665A; GB2537020B; GB201602392D0; DE102016202419A1

Abstract

A railway vehicle drive system receiving power from an overhead line has control technology to suppress a beat phenomenon which occurs in a main converter of an alternating current electric vehicle. The system comprises: a first power converter 5 converting single-phase AC power from the overhead wire into DC power; a second power converter 9 converting the DC power into three-phase AC power supplied to a motor 11. A resonance filter 6 is parallel-connected to the first power conversion device and has a resonance point which is double the frequency of the first power supply. A pulsation suppression device 205 suppresses pulsation superposed on the three-phase AC power by controlling output from the second power conversion device depending on a voltage detected by a voltage detector 7. The drive system further includes first 22 and second 23 AC power supplies, with associated overhead lines 24, 25, having different frequencies. The pulsation suppression device may be activated or deactivated dependant on from which supply the vehicle is receiving power.

Description

TITLE OF THE INVENTION

RAILWAY VEHICLE DRIVE SYSTEM

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a drive system of a railway vehicle. The invention particularly relates to control technology to suppress a beat phenomenon which occurs in amain converter of an alternating current (AC) electric vehicle.

2. Description of the Related Art

A drive system of a railway vehicle that is supplied with input power from an AC overhead wire includes, a converter to convert single-phase AC power into direct current (DC) power, an inverter to convert the DC power that is output from the converter into three-phase AC power having a specified frequency, and amain electric motor driven by the AC power that is output from the inverter. A DC circuit conneccing the converter and the inverter is called a DC stage.

The voltage in the DC stage has the propecy that a frequency which is double the frequency of an AC overhead wire is superposed on the voltage in the DC stage, since the voltage in the DC stage is produced by full-wave rectifying a single-phase AC voltage supplied from the overhead wire. Meanwhile, when the inverter converts a DC voltage into an AC voltage, components of the sum of, and the difference between the fundamental frequency of the inverter and the oscillation frequency of the DC voltage appear in the output voltage of the inverter. In particular, in the case of the component of the difference between the above frequencies, as the fundamental frequency of the inverter and the oscillation frequency of the DC voltage are closer to each other, the frequency component of the difference becomes lower. Accordingly, the impedance of the main electric motor is reduced. As a result, the current of the main electric motor pulsates at the frequency of the difference. Such pulsation is known and is generally called a beat phenomenon.

As an example of a method for suppressing The beat phenomenon described above, there is a method in which a resonance filter having the resonance point at a frequency which is double the frequency of the AC overhead wire is provided. Another example is a method called beatless control. In the beatless control, the frequency component of the output voltage of the inverter, which causes the beat phenomenon, is suppressed, by adjusting the frequency of the output voltage of the inverter by switching control of the inverter. A beat phenomenon suppression method using a resonance filter is disclosed in EP-1288060-A. A configuration of the beatless control is disclosed in JP-H11-164565-A.

SUMMARY OF THE INVENTION

However, the technologies for suppressing The beat phenomenon described in EP-1288060-A and JP-H11-164565-A have the following problems.

In the case of using the resonance filter described in EP-1288060-A, an AC electric vehicle which runs on a rail line formed of multiple sections with different AC overhead wire frequencies, and is therefore supplied with AC power having multiple frequencies, needs to be equipped with resonance filters for each of the frequencies. This causes a problem, because the volume of an on-vehicle device (the resonance filter) increases undesirably.

In the case of using the heatless control described in SP-H11-164565-A, when the vehicle is supplied with power from a low frequency AC power supply, if the capacitance of a smoothing capacitor which is parallel-connected to the converter and inverter in the DC stage is not sufficiently large, pulsation of the output voltage of the inverter is not suppressed. For this reason, when the vehicle is supplied with power from a low frequency AC power supply, the smoothing capacitor in the DC stage needs to have a large capacitance so as to stabilize an AC voltage to be output from the inverter. This causes a problem, because the volume of an on-vehicle device (the smoothing capacitor) increases undesirably.

To solve the above problems, configurations described in the claims are adopted.

The above problems can be solved by providing a vehicle drive system for a vehicle which runs on both a rail line having a first overhead wire supplying first single-phase AC power, and a rail line having a second overhead wire supplying second single-phase AC power having a frequency higher than a frequency of the first single-phase AC power, the vehicle drive system including: a first power conversion device configured to convert single-phase AC power supplied from the first overhead wire or the second overhead wire into DC power, and to output the DC power to a DC power line; a second power conversion device configured to convert the DC power having been output to the DC power line into three-phase AC power; a motor for driving the vehicle, the motor being supplied with the three-phase AC power; a resonance filter connected to the DC power line in parallel to the first power conversion device, the resonance filter having a resonance point in a frequency band which is double the frequency of the first single-phase AC power; a voltage detector configured to detect a voltage of the DC power line; and a pulsation suppression device configured to control output from the second power conversion device, depending on a detection value obtainedbyThe voltage detector, to suppress pulsation superposed on the three-phase AC power.

The present invention reduces the size of an on-vehicle device of an AC electric vehicle which runs in multiple sections differing in frequency.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a diagram showing a configuration of the drive system in a first embodiment; Fig. 2 is a diagram showing a configuration of the drive system in a second embodiment; Fig. 3 is a diagram showing a configuration of the drive system in a third embodiment; and Fig. 4 is a diagram showing the relation between the power supply frequency, and the capacitance of the smoothing capacitor, in the first embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The embodiments of the present invention are described below, with reference to the drawings.

First embodiment The first embodiment of the present invention is described with reference to Fig. 1. Fig. 1 shows a configuration of the vehicle drive system in the present embodiment.

The drive system includes a current collector 1, a transformer 2, a converter 5, a resonance filter circuit 6, a smoothing capacitor 8, an inverter 9, a motor 11, and a wheel 21. The converter 5 includes a switching element thereof 5a-5d. The resonance filter circuit 6 includes a resonance reactor 6a, and a resonance capacitor 6b. The inverter 9 includes a switching element thereof 9a-9f.

The drive system also includes a voltage detector 3 to measure the secondary side voltage of the transformer 2, a current detector 4 to measure the secondary side current of the transformer 2, a voltage detector 7 to measure a voltage across the smoothing capacitor 8, and a current detector 10 to measure the current of the main electric motor 11.

The drive system further includes a first AC power supply 22, a second AC power supply 23 having a frequency different from that of the first AC power supply 22, a first overhead wire 24 to supply power from the first AC power supply 22 to the vehicle, a second overhead wire 25 to supply power from the second AC power supply 23 to the vehicle, a non-electrified section 26 to insulate the first overhead wire 24 and the second overhead wire 25 from each other, and a track 27 for the vehicle.

In the present embodiment, as an example, a two-level single-phase full-bridge power conversion device, and a two-level three-phase full-bridge power conversion device are used as the converter 5 and inverter 9, respectively. However, the converter and inverter may be a power conversion device having a configuration other than that described above. For example, a three-level circuit can be used to form the converter and the inverter.

The present drive system is an apparatus to accelerate and decelerate a vehicle. AC power is input to the vehicle through the current collector 1 and the wheel 21, via the overhead wire 24 and the track 27 in the case of AC power supplied from the first AC power supply 22, and via the overhead wire 25 and the track 27 in the case of AC power supplied from the second AC power supply 23. At the time of acceleration, the main transformer 2 steps down the AC power having been input, and then the converter 5 converts the AC power into DC power. The power having been converted into the DC power is smoothed by the smoothing capacitor 8. After that, the DC power is inversely converted into AC power by the inverter 9, and then supplied to the main electric motor 11, so that the vehicle is accelerated by variable speed drive.

At the time of deceleration, AC power generated by a regeneration brake of the main electric motor 11 is converted into DC power by the inverter 9. The power having been converted into the DC power is smoothed by the smoothing capacitor 8. After that, the DC power is inversely converted into AC power by the converter 5, and then boosted by the main transformer 2, to be subsequently returned to the overhead wire 24 or 25 through the current collector.

The voltage detector 3 detects a frequency of the voltage supplied to the vehicle, thereby determines from which of the overhead wires 24 and 25 differing in frequency the vehicle is supplied with power. Another option for determining the overhead wire is to use vehicle-position detection technology. As a position detection device, a detection device using a track circuit which is not shown, a detection device using travel distance information obtained by integrating speed information of the vehicle, and a detection device using a global positioning system (GPS) are applicable. Beat suppressing functions performed by a resonance filter and a beatless control part, which are described later, are switched between each other, depending on a power supply identified by the voltage detector and the position detection technology mentioned above. When the power supply frequency of the overhead wire 24 is lower than that of the overhead wire 25, and in addition, when it is determined that the vehicle is supplied with power from the overhead wire 25, the drive system activates the beatless control part, so that the pulsation can be suppressed by the beatless control. When it is determined that the vehicle is supplied with power from the overhead wire 24, the pulsation is suppressed by the resonance filter. When the resonance filter operates to suppress the pulsation, the beatless control is not necessary. However, the beatless control may either be deactivated, or may be kept enabled instead.

Further, Fig. 1 shows a converter control unit 100 which provides a control of power conversion in the converter 5. The converter control unit 100 has a power supply phase detector 101, a sine wave generator 102, a subtractor 103, 106, 108, a voltage regulator 104, a multiplier 105, a current regulator 107, and a pulse width modulation (PWM) controller 109.

In the converter control unit 100, the voltage detector 3 detects the secondary side voltage of the main transformer 2. The power supply phase detector 101 detects the electric angle of the voltage. The sine wave generator 102 produces a sine wave which is in phase with the power supply voltage, and the amplitude thereof is 1, based on information about the electric angle.

In parallel with the above, the voltage detector 7 detects the DC voltage Ed of the smoothing capacitor 8. The subtractor 103 subtracts the DC voltage Ed from a DC voltage command value Ed*. The voltage regulator 104 produces, based on the result of the subtraction, a secondary-current effective-value command Is* to adjust the DC voltage Ed to the command value Ed*. The multiplier 105 multiplies the command Is* by a sine wave generated by the sine wave generator 102, to produce a secondary current command is of the main transformer 2. The secondary current command is is in phase with the secondary voltage of the main transformer 2, thereby power that is input to the converter 5 is controlled so that the power factor of the converter 5 is 1.

Subsequently, the subtractor 106 subtracts a secondary current is detected by the current detector 4 from the secondary current command is*. The current regulator 107 produces an AC voltage command ec, based on the result of the subtraction. Subsequently, the subtractor 108 subtracts the AC voltage command ec from a secondary voltage es. The PWM controller 109 produces a converter pulse command Sc, based on the result of the subtraction.

The converter pulse command Sc is input into the converter 5. The switching element 5a-5d is switched on and off, based on the converter pulse command Sc, so that the DC voltage Ed is controlled to be constant.

Further, Fig. 1 shows an inverter control unit 200 which provides a control of power conversion in the inverter 9. The inverter control unit 200 has a coordinate transformer 201, a subtractor 202, 203, a current regulator 204, a beatless controller 205, an adder 206, and a PWM controller 207.

The inverter control unit 200 inputs a three-phase AC current iu, iv, iw detected by the current detector 10 into the coordinate transformer 201, to produce a d-axis current Id and a q-axis current Iq. The subtractor 202 subtracts the d-axis current Id from a d-axis current command Id*. The subtractor 203 subtracts the q-axis current Iq from a q-axis current command Iq*. The current regulator 204 calculates, based on the result of the subtraction obtained by each of the subtractors 202 and 203, a modulation rate Vc, an output frequency Fi, and an output argument 5, which are required for variable speed operation of the main electric motor 11. The beatless controller 205 outputs a correction value 4Fi of the output frequency, based on the DC voltage Ed of the smoothing capacitor 8, which is detected by the voltage detector 7. The adder 206 produces an output frequency command Fi*, by adding the output frequency Fi and the correction value AFi together. Next, the PWM controller 207 produces an inverter pulse command Si, based on the modulation rate Vc, the output frequency command Fi*, and the output argument 6. The PWM controller 207 then inputs the inverter pulse command Si into the inverter 9, to drive the main electric motor 11.

Meanwhile, when a vehicle is equipped with a plurality of resonance filters for different frequencies of AC power, the volume of an on-vehicle device (the resonance filters) increases undesirably. When the beatless control is used, the smoothing capacitor in the DC stage needs to have a large capacitance, to prepare fora low frequency AC power supply. This also causes an increase in the size of an on-vehicle device (the smoothing capacitor). In addition, as another problem which arises when the capacitance of the smoothing capacitor becomes larger, a large discharge current flows at the time of a short-circuit failure of the converter or the inverter, which increases a risk of a secondary failure.

In view of the above, the present embodiment is provided in a railway vehicle which runs on a rail line having two (2) or more levels of power supply frequency. The embodiment has both the resonance filter 6, and the beatless controller 205, so as to suppress a beat phenomenon which appears in a current passing through the main electric motor 11, due to pulsation of a frequency superposed on the DC voltage, the frequency being double the AC power supply voltage. For an overhead wire voltage having the lowest frequency, the drive system suppresses the pulsation of a frequency superposed on the DC voltage, the frequency being double the AC power supply voltage, using the resonance filter 6 having a resonance point at the frequency being double the AC power supply voltage. For an overhead wire voltage having a frequency other than the lowest frequency, the drive system suppresses the pulsation which occurs in a current passing through the main electric motor, by the beatless control, i.e., switching control of the inverter. The details of the present embodiment are discussed further below.

For example, the embodiment of the present invention is applied to a railway vehicle which runs on a rail line with two (2) types of AC power supplies each having a frequency of 16.7 Hz and 50 Hz. For the AC power supply having a low frequency of 16.7 Hz, the resonance filter, which is hardware, suppresses the pulsation of a frequency superposed on the DC voltage, the frequency being double the AC power supply voltage. For an overhead wire voltage having a high frequency of 50 Hz, the beatless control, which is software, suppresses the pulsation which occurs in a current passing through the main electric motor.

First, a description is given below of pulsation of the DC voltage Ed at the time when there is no resonance filter 6 in the DC stage.

The pulsation of the DC voltage Ed of an AC vehicle is caused by rectification in the converter 5, or by voltage conversion in the inverter 9.

The pulsation due to the rectification in the converter 5 is generated by the rectification of a single-phase AC. A main/principal frequency band of the pulsation, therefore, has a frequency which is double the frequency of the overhead wire voltage. Mathematical Formula (1) represents the relation in this case between the pulsation of the DC voltage Ed, and the capacitance of the smoothing capacitor 8, which is required for the beatless control. 1' 2 -e

Mathematical Formula (1) Where, the pulsation amplitude of the DC voltage is denoted by LEcf, the maximum power of the vehicle drive system is denoted by P, the angular frequency of the overhead wire voltage is denoted by cc, the capacitance of the smoothing capacitor 8 is denoted by Cf, and a DC component of the DC voltage is denoted by Ecf.

Mathematical Formula (1) shows that the pulsation amplitude of the DC voltage LEcf is inversely proportional to the AC frequency of the overhead wire voltage cc.

The pulsation due to the voltage conversion in the inverter 9 is generated by the conversion of a direct current to a three-phase AC current. A principal frequency band of the pulsation, therefore, has a frequency which is six (6) times the frequency of the output frequency of the inverter. Mathematical Formula (2) represents the relation in this case between the pulsation of the DC voltage, and the capacitance of the smoothing capacitor 8, which is required for the beatless control.

6 ' * Cy.Eqf Mathematical Formula (2) Where, the angular frequency of a point at which the output power of the inverter is maximum is denoted by col. In the system which does not have the resonance filter 6 in the DC stage, the heatless control of the inverter is used for the suppression of the pulsation of the AC output voltage of the inverter. It is thus necessary for the smoothing capacitor to have the capacitance Cf indicated in Mathematical Formulae (1) and (2). Accordingly, in a rail line having two (2) types of AC overhead wires, such as AC overhead wires each having a frequency of 16.7 Hz and 50 Hz, the pulsation of the AC output voltage of the inverter needs to be suppressed, using the heatless control, with respect to the following three (3) types of DC voltage pulsation: (a) the DC voltage pulsation due to the rectification in the converter 5, with the overhead wire frequency of 16.7 Hz; (b) the DC voltage pulsation due to the rectification in the converter 5, with the overhead wire frequency of 50 Hz; and (c) the DC voltage pulsation under the condition in which the DC voltage pulsation in the operation of the Inverter is maximum.

The condition in which the DC voltage pulsation in the operation of the inverter is maximum means the condition in which the output voltage of the inverter 9 is maximum. An inverter unit of a railway vehicle, in order to improve voltage-use efficiency, is saturated with an output voltage at an inverter frequency Fi which corresponds to approximately a half of the nominal speed of the railway vehicle. At a speed higher than the above speed, therefore, the inverter frequency Fi only is controlled. The speed at which the output voltage reaches saturation is called a V/ f terminal velocity. At a speed higher than the terminal velocity, the output power of the inverter is maximum, and accordingly, the pulsation amplitude of the DC voltage AEcf is also maximum.

The following is a description of the capacitance Cf of the smoothing capacitor 8, which is required for the beatless control at this time.

Mathematical Formula (3) represents the capacitance Cf of the smoothing capacitor 8, which is required for the beatless control at the time when the pulsation amplitude generated by the operation of the converter is desired to be equal to or less than the pulsation amplitude of the DC voltage AEcf. In Mathematical Formula (3), the rate of the pulsation superposed on the DC voltage Ed is denoted by k. \Fe

Mathematical Formula (3) Mathematical Formula (4) represents the capacitance Cf of the smoothing capacitor 8, which is required for the beatless control at the time when the pulsation amplitude generated by the operation of the inverter is desired to be equal to or less than the pulsation amplitude of the DC voltage AEcf. *.

Mathematical Formula (4) For example, for the vehicle drive system in which the resonance filter 6 is not connected to the DC stage, a condition which satisfies F) = 1630 kW, Ecf = 2400 V, and k < 0.04 is discussed below. The following is the capacitance Cf of the smoothing capacitor 8, which is required to suppress the pulsation of the AC output voltage of the inverter by using the heatless control, for the three (3) types of DC voltage pulsation (a) -(c) described previously.

(a) When the overhead wire frequency is 16.7 Hz, the overhead wire frequency cc in Mathematical Formula (3) is obtained as follows: cc = 2 x n x 16.7 rad/s. Accordingly, the capacitance Cf of the smoothing capacitor 8, which is required to suppress the pulsation of the AC output voltage of the inverter by using the beatless control, for the DC voltage pulsation due to the rectification in the converter 5 in the case of the overhead wire frequency of 16.7 Hz, is as follows: Cf > 28800 gF.

(b) When the overhead wire frequency is 50 Hz, the overhead wire frequency cc in Mathematical Formula (3) is obtained as follows: coc = 2 x n x 50 rad/s. Accordingly, the capacitance Cf of the smoothing capacitor 8, which is required to suppress the pulsation of the AC output voltage of the inverter by using the beatless control, for the DC voltage pulsation due to the rectification in the converter 5 in the case of the overhead wire frequency of 50 Hz, is as follows: Cf > 9600 up'.

(c) For the condition in which the DC voltage pulsation in the operation of the inverter is maximum, the DC voltage pulsation due to the operation of the inverter tEcf is maximum at the V/f terminal that is the point at which the output power is maximum. In Mathematical Formula (4), therefore, the inverter operation frequency Fi is 50 Hz, and each frequency is obtained as follows: col = 2 x n x 50 rad/s. Accordingly, the capacitance Cf of the smoothing capacitor 8, which is required to suppress the pulsation of the AC output voltage of the inverter by using the beatless control, for the DC voltage pulsation due to the operation of the inverter, is as follows: Cf > 3200 laF.

As described above, the capacitance Cf of the smoothing capacitor 8, which is required to suppress the pulsation of the AC output voltage of the inverter by using the beatless control is the largest, with respect to the DC voltage pulsation generated at the time when the converter converts the AC voltage having a low frequency of 16.7 Hz to a DC voltage. The capacitance Cf is the second largest, with respect to the DC voltage pulsation generated at the time when the converter converts the AC voltage having a frequency of 50 Hz to a DC voltage. The capacitance Cf is the smallest, with respect to the DC voltage pulsation under the condition in which the DC voltage pulsation generated by the operation of the inverter is maximum.

Fig. 4 shows the relation between a power supply frequency and the capacitance of the smoothing capacitor 8, which are required to suppress the pulsation of the AC output voltage of the inverter by using the beatless control, for the DC voltage pulsation. The abscissa represents the power supply frequency. The ordinate represents the capacitance of the smoothing capacitor 8. Fig. 4 shows a result of an estimation, based on Mathematical Formula (3), of the capacitance of the smoothing capacitor 8, which is required to suppress the pulsation of the AC output voltage of the inverter by using the beatless control, for a pulsation component superposed on the DC voltage. Values given in (a) and (b) described above are used as calculation conditions.

As shown in the result, the capacitance of the smoothing capacitor 8, which is required to suppress the pulsation generated by the operation of the inverter, by using the beatless control, is inversely proportional to the power supply frequency. Therefore, for a frequency which is double the low frequency of 16.7 Hz of the AC overhead wire (i.e., for a low frequency), the pulsation of the DC voltage is suppressed by adjusting the resonance characteristics of the resonance filter 6 to the frequency. On the other hand, for a frequency which is double the high frequency of 50 Hz of the AC overhead wire (i.e., for a high frequency), the pulsation of the DC voltage AEcf is prevented from propagating to the main electric motor ll on the inverter output side, by applying the beatless control. As a result of providing both the resonance filter 6 and the heatless control function, and adjusting the resonance characteristics of the resonance filter 6 to the DC voltage pulsation at the lowest frequency, as described above, the capacitance required for the smoothing capacitor 8 is reduced to approximately one-third (1/3) or less, as shown in Fig. 4. The capacitance required for the beatless control, can be provided from the capacitance of both the smoothing capacitor 8 and a resonance capacitor 6b of the resonance filter 6. The capacitance required for the resonance capacitor 6b is, therefore, calculated by the following Mathematical Formula (5) . 2.toc4K-P,c1-Mathematical Formula (5) Where, the capacitance of the resonance capacitor 6b is denoted by Clc.

Further, the relation between the inductance of the resonance reactor 6a and the capacitance of the resonance capacitor 6b is determined so that the resonance point of the resonance filter 6 can be set at the frequency which is double the overhead wire frequency of 16.7 Hz, or, in other words, so that Mathematical Formula (6) is satisfied.

MC-

Mathematical Formula (6) Where, the inductance of the resonance reactor 6a is denoted by Llc.

Accordingly, the inductance of the resonance reactor 6a in the present embodiment is determined by Mathematical Formula (7) which is obtained by expanding Mathematical Formula (6). 002(

Mathematical Formula (7) With the configuration described above, when the capacitance Cf of the smoothing capacitor 8 is determined, the capacitance Clc of the resonance capacitor 6b and the inductance Llc of the resonance reactor 6a are determined. As a result, the apparatus of the vehicle drive system having multiple frequencies of power supply is reduced in volume and weight, and is optimized.

As mentioned above, "Cf > 28800 bF" is the capacitance of the smoothing capacitor 8, which is required to suppress the pulsation of the AC output voltage of the inverter by using the heatless control, for the DC voltage pulsation due to the rectification in the converter 5 in the case of the overhead wire frequency of 16.7 Hz. The capacitance of Cf > 28800 HF is much larger than both the capacitance of the resonance capacitor 6b, which is required to suppress a pulsation component being double the overhead wire frequency of 16.7 Hz, and the capacitance of Cf > 9600 HF of the smoothing capacitor 8, which is required to suppress the pulsation of the AC output voltage of the inverter by using the beatless control, for a pulsation component being double the overhead wire frequency of 50 Hz. This means that the capacitance of the capacitors which is required for the system as a whole is reduced, when the system is separately provided with the capacitance of the resonance capacitor 6b, which is required to suppress a pulsation component being double the overhead wire frequency of 16.7 Hz, and the capacitance of Cf > 9600 HF of the smoothing capacitor 8, which is required to suppress the pulsation of the AC output voltage of the inverter by using the heatless control, for a pulsation component being double the overhead wire frequency of 50 Hz.

Meanwhile, when a short-circuit failure occurs in the converter 5 and the inverter 9, a charge having been stored in the smoothing capacitor 8 is discharged to a failure part, causing an undesirable current flowing through the failure part. With the above configuration of the embodiment, the capacitance of the smoothing capacitor is reduced such that the current is suppressed. As a result, a secondary damage of the apparatus is prevented.

Second embodiment A second embodiment of the present invention is described below, with reference to Fig. 2. Fig. 2 shows a configuration of the embodiment.

In Fig. 2, a component which is the same as that in Fig. 1 is denoted by the same reference sign as used in Fig. 1, and will not be defined repeatedly.

Aresonance filter 12 is shown in Fig. 2. The resonance filter 12 includes a resonance reactor 12a, a resonance capacitor 12b which is series-connected to the resonance reactor 12a, and a contactor 12c which is parallel-connected to the resonance reactor 12a.

A feature of the resonance filter circuit 12 is, different from the resonance filter circuit 6 of the first embodiment, that the reactor of the resonance filter is short-circuited by closing the contactor 12c in response to an externally-input open-and-close command.

The vehicle drive system of this embodiment is provided in a railway vehicle which runs on a rail line having two (2) or more levels of power supply frequency. The embodiment has both the resonance filter circuit 12, and the beatless controller 205, so as to suppress a beat phenomenon which appears in a current passing through the main electric motor 11 due to pulsation superposed on the DC voltage, the pulsation having a frequency which is double the power supply frequency. In this respect, the drive system of the present embodiment is the same as the drive system of the first embodiment, while the present embodiment is distinctive in that it has the contactor 12c, as a part of the resonance filter 12, in addition to the resonance reactor 12a and the resonance capacitor 12b.

In the present embodiment, the method for suppressing the pulsation of the DC stage voltage is changed, depending on the power supply frequency of the AC power supply. To suppress the pulsation, the resonance frequency of the resonance filter 12 is determined, as in the first embodiment, in such a manner that the resonance frequency of the resonance filter 12 (a series-connected body formed of the resonance reactor 12a and the resonance capacitor 12b) is adjusted to a frequency which is double the lowest frequency among the frequencies of a plurality of the AC power supplies. For a frequency of the AC power supply other than the lowest frequency, the pulsation is suppressed by the beatless controller 205.

The beatless controller 205 switches between pulsation suppression by the resonance filter 12 and pulsation suppression by the beatless control, depending on the frequency of the pulsation superposed on the voltage of the smoothing capacitor 8, which is measured by the voltage detector 7.

When the voltage detector 7 detects pulsation having a frequency which is the same as the resonance frequency of the resonance filter 12, with the contactor 12c closed, the beatless controller 205 outputs a command to open the contactor. The contactor 12c of the resonance filter 12 is then opened, so that the resonance filter 12 suppresses the pulsation of the DC stage. In this case, although the beatless control is not necessary, the heatless control may either be disabled, or be kept operable.

When the voltage detector 7 detects pulsation having a frequency other than the resonance frequency of the resonance filter 12, with the contactor 12c open, the beatless controller 205 outputs a command to close the contactor. The contactor 12c of the resonance filter 12 is then closed, so that the pulsation of the DC stage is suppressed by the heatless control. At this time, the resonance reactor 12a is short-circuited as a result of closing the contactor 12c, which causes the resonance capacitor 12b to serve as the smoothing capacitor of the DC stage.

In the present embodiment, the capacitance Cf of the smoothing capacitor 8, which is required to suppress the pulsation superposed on the DC voltage is different, compared to the first embodiment. In other words, with the configuration of this embodiment, the resonance capacitor 12b is utilized as part of the smoothing capacitor, reducing the capacitance Cf of the smoothing capacitor 8, which is required to suppress the pulsation of the DC voltage AEcf. This, as a result, miniaturizes the apparatus, and also reduces loss made in the resonance reactor 6a in the beatless control.

A configuration of the present embodiment has been described in which the heatless controller 205 controls the open and close of the contactor 12c, and the enabling and disabling the beatless control, based on the voltage of the smoothing capacitor. It is also possible for the beatless controller 205 to control the open and close of the contactor 12c, and the enabling and disabling the beatless control, based on the voltage detected by the voltage detector 3, and the power supply frequency determined by the position detection device, as in the first embodiment.

In this case, when it is determined that the vehicle is supplied with power from the AC power supply having a frequency which is the same as the resonance frequency of the resonance filter 12, a command to open the contactor is output, and the contactor 12c of the resonance filter 12 is opened, so that the pulsation of the DC stage is suppressed by the resonance filter 12. When it is determined that the vehicle is supplied with power from the AC power supply having a frequency which is different from the resonance frequency of the resonance filter 12, a command to close the contactor is output, and the contactor 12c of the resonance filter 12 is closed, so that the pulsation of the DC stage is suppressed by the beatless control.

In this embodiment, the converter control unit 100 may have a device for determining whether or not the voltage of the smoothing capacitor 8 is the same as the resonance frequency of the resonance filter 12, outputting a control command to open or close to the contactor 12c, based on the result of the above determination, and outputting a control command to enable or disable the beatless control to the beatless controller 205 located in the inverter control unit 200.

Third embodiment A third embodiment of the present invention is described below, with reference to Fig. 3. Fig. 3 shows a configuration of the embodiment.

In Fig. 3, a component which is the same as that in Fig. 1 is denoted by the same reference sign as used in Fig. 1, and will not be defined repeatedly, as such component has the same function as that in the first embodiment.

A resonance filter 13 shown in Fig. 3 includes a resonance reactor 13a, a resonance capacitor 13b which is series-connected to the resonance reactor 13a, and a contactor 13c which is further series-connected to the resonance reactor 13a. A converter control unit 100 includes a failure detector 110. An inverter control unit 200 includes an output regulator 208.

A feature of the resonance filter circuit 13 is, different from the resonance filter circuit 6 of the first embodiment, that the resonance filter circuit can control the open and close of the contactor 13c as desired, in response to an externally-input open-and-close command. When the resonance filter 13 is operating properly, the contactor 13c of the resonance filter circuit 13 is closed.

In the vehicle drive system of the present embodiment, when the resonance reactor 13a or the resonance capacitor 13b of the resonance filter circuit 13 has a failure, the failure detector 110 detects the failure. The failure detector 110 determines whether or not the failure has occurred by detecting the resonance frequency of the resonance filter circuit from the DC voltage Ed which has been detected by the voltage detector 7.

When the voltage detector 7 detects pulsation other than the resonance frequency of the resonance filter 13, or when it is determined by the function of identifying/determining the power supply frequency, which is described in the first embodiment, that the vehicle is supplied with power from the power supply having the lowest frequency, the beatless control is implemented. The beatless controller outputs a beatless control command SiA to the PWM controller 207, to suppress the beat phenomenon in the main electric motor 11, which arises from a DC voltage vibration.

On the other hand, when it is determined by the function of identifying the power supply frequency, which is described in the first embodiment, that the vehicle is supplied with power from the power supply having the lowest frequency, the beatless control is deactivated, and the pulsation superposed on the DC voltage is suppressed by the resonance filter 13. If the voltage detector 7 detects the resonance frequency of the resonance filter circuit, when the pulsation in the DC stage is suppressed by the resonance filter 13 while the beatless control is deactivated, the vehicle drive system determines that a failure has occurred in the resonance filter circuit 13. The failure detector 110 then outputs a command, to the contactor 13c of the resonance filter circuit 13, to open the contactor. As a result, the faulty resonance filter circuit 13 is disconnected from the other circuits, so that the other circuits are not affected by the failure. At the same time, the failure detector 110 outputs failure-detection information to the heatless controller 205 and the output regulator 208.

The beatless controller 205 is deactivated when the resonance filter 13 is operating properly. The beatless controller 205 starts operating, on receiving the failure-detection information, and outputs a beatless control command ASi, to the PWM controller 207, to suppress the beat phenomenon in the main electric motor 11, which arises from a DC voltage vibration.

In the vehicle drive system equipped with the resonance filter 13, when the resonance filter 13 has a failure, and is disconnected from the other circuits by the contactor 13c, there is not enough capacitance in the smoothing capacitor 8, making it difficult to suppress the vibration by the control at full load. Meanwhile, the vibration of the DC voltage Ed increases in proportion to the amount of current flowing through the smoothing capacitor 8. When, therefore, the running speed of the vehicle is decreased so as to reduce the load of the main electric motor 11, the current flowing through the smoothing capacitor 8 reduces in proportion to the motor load. This reduces the vibration of the DC voltage, making it possible to suppress the beat phenomenon in the main electric motor 11 by the control. Accordingly, when a failure is detected, the failure-detection information is input to the output regulator 208 to limit a current command, so that the current flowing through the main electric motor 11 decreases. This makes it possible to suppress the beat phenomenon by using the beatless control, and, as a result, enables the vehicle to operate continuously, even in the event of a resonance filter failure.

The configuration of this embodiment, as with the other embodiments, reduces the capacitance Cf of the smoothing capacitor 8, which is required to suppress the pulsation of the DC voltage LEcf. As a result, the apparatus is miniaturized. In addition, with this configuration, the faulty resonance filter circuit 13 is disconnected from the other circuits, so that the other circuits are not affected by the failure. Furthermore, in this configuration, the beatless control is implemented when a failure is detected in the resonance filter circuit 13. This enables the vehicle to operate continuously, even if a failure occurs in the resonance filter.

A configuration of the present embodiment has been described in which the failure detector 110 is placed in the converter control unit 100. It is also possible, however, to place the failure detector 110 in the inverter control unit 200.

Claims

What is claimed is: 1. A vehicle drive system for a vehicle which runs on both a rail line having a first overhead wire supplying first single-phase AC power, and a rail line having a second overhead wire supplying second single-phase AC power having a frequency higher than a frequency of the first single-phase AC power, the vehicle drive system comprising: a first power conversion device configured to convert single-phase AC power supplied from the first overhead wire or the second overhead wire into DC power, and to output the DC power to a DC power line; a second power conversion device configured to convert the DC power having been output to the DC power line into three-phase AC power; a motor for driving the vehicle, the motor being supplied with the three-phase AC power; a resonance filter connected to the DC power line in parallel to the first power conversion device, the resonance filter having a resonance point in a frequency band which is double the frequency of the first single-phase AC power; a voltage detector configured to detect a voltage of the DC power line; and a pulsation suppression device configured to control output from the second power conversion device, depending on a detection value obtained by The voltage detector, to suppress pulsation superposed on the three-phase AC power.
2. The vehicle drive system according to claim 1, wherein the resonance filter absorbs pulsation having a frequency component which is double the frequency of the first single-phase AC power, the pulsation being superposed on the DC power, and the pulsation suppression device controls output from the second power conversion device, so as to suppress pulsation having a frequency component which is double the frequency of the second single-phase AC power, the pulsation being superposed on the three-phase AC power.
3. The vehicle drive system according to claim 2, comprising a power supply determination device configured to determine from which of the first and second overhead wires the vehicle is supplied with power, wherein when the power supply determination device determines that the vehicle is supplied with power from the first overhead wire, the drive system deactivates the pulsation suppression device, and when the power supply determination device determines that the vehicle is supplied with power from the second overhead wire, the drive system activates the pulsation suppression device.
4. The vehicle drive system according to claim 1, further comprising a smoothing capacitor connected to the DC power line in parallel to the first power conversion device, the smoothing capacitor being configured to stabilize the DC power, wherein the resonance filter has a resonance reactor and a resonance capacitor connected in series to each other.
5. The vehicle drive system according to claim 4, wherein the resonance filter further includes a contactor connected in parallel to the resonance reactor, the contactor is opened, when the voltage detector detects pulsation having a frequency which is the same as the resonance frequency of the resonance filter, and the contactor is closed, when the voltage detector detects pulsation having a frequency which is different from the resonance frequency of the resonance filter.
6. The vehicle drive system according to claim 4, wherein the resonance filter further includes a contactor connected in series to the resonance reactor, the contactor is opened, and the beatless control is implemented, when the voltage detector detects pulsation of the resonance frequency of the resonance filter, and the contactor is closed, and the beatless control is disabled, when the voltage detector does not detect pulsation of the resonance frequency of the resonance filter.