GB2533678A

GB2533678A - Drive unit of railway vehicle

Info

Publication number: GB2533678A
Application number: GB1517974.0A
Authority: GB
Inventors: Nozaki Yuichiro; Tachihara Shuuichi; Ayata Masataka; Miyake Wataru
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 2014-10-24
Filing date: 2015-10-12
Publication date: 2016-06-29
Anticipated expiration: 2035-10-12
Also published as: JP2016086488A; GB2533678B; DE102015220736A1; GB201517974D0

Abstract

A drive unit of a railway vehicle is controlled to travel at a constant speed, wherein harmonic currents generated by a converter device are reduced, and harmonic losses of a transformer is reduced. When the railway vehicle is controlled to travel at a constant reference speed, or stopped, a carrier frequency of the converter device is raised from a first reference frequency to a second reference frequency, and when the vehicle is controlled by acceleration and deceleration commands, the carrier frequency is reduced from the second reference frequency to the first reference frequency. The drive unit comprises transformer 3 for stepping down the overhead wire 1 voltage and supplying single-phase AC power to a converter 5. The converter rectifies the single-phase AC power to DC power. A DC-side of the converter device is connected, via a capacitor 6 for stabilizing the voltage, to inverter device 7. The inverter device converts the DC power to three-phase AC power for driving at least one AC motor 8.

Description

DRIVE UNIT OF RAILWAY VEHICLE

Background of the Invention

Field of the Invention

The present invention relates to a drive unit of a railway vehicle for driving a railway vehicle by having power supplied from a single-phase AC overhead wire.

Description of the Related Art

In a railway vehicle traveling in an alternating-current feeding section, a system is used widely where AC power is supplied from a single-phase AC overhead wire through a transformer, and then the AC power is converted to DC power via a converter device before the AC power is converted to three-phase AC power via an inverter device to drive the AC motor.

The converter device and the inverter device performs control to turn multiple semiconductor switching elements on and off based on Pulse Width Modulation (PWM) and control the output voltage to a desired value.

The switching elements constituting the converter device are required to have a withstand pressure corresponding to the DC-side voltage of the converter device. In the case of a railway vehicle, especially in high speed railways and locomotives where high output is required, the DC-side voltage of the converter is set to 3000 V or higher, depending on the specification of the overhead wire or the vehicle, and the switching elements are required to have higher withstand voltage if the DC-side voltage is higher.

The switching elements with high withstand voltage must have semiconductor chips arranged therein with increased thicknesses in order to satisfy the withstand voltage, and as a result, the loss accompanying the switching operation is increased compared to switching elements with low withstand voltage. Therefore, in a converter device using switching elements with high withstand voltage, the loss accompanying the switching operation must be suppressed to avoid the increase in size of a cooling apparatus of the switching elements, so that the carrier frequency must be set low.

Normally, in a converter device, a secondary current of a transformer flowing in the AC-side is required to have the same level of quality as the power system supplying power to the overhead wire, so that the current must be formed into sine wave shape to reduce the harmonic current flowing in the overhead wire. Therefore, the carrier frequency must be set high within the range permissible by the cooling performance of the converter device. However, when using switching elements having a high withstand voltage as described above, it is desirable to lower the carrier frequency in order to suppress the loss accompanying the switching operation.

When the carrier frequency is lowered, the harmonic component of the secondary current is increased, by which the distortion of currents flowing in the overhead wire is increased, and the loss caused by a skin effect in a transformer winding is increased, leading to the deterioration of efficiency of the traction system.

The above-described harmonic component appears as a ripple in the AC-side current of the converter device, and this current ripple is determined uniquely by the carrier frequency and the constant of the transformer set in the converter device, the overhead wire voltage and the DC-voltage on the output side of the converter device, and does not depend on the input/output power of the converter device. That is, when the converter is operated via a constant carrier frequency, the amount of harmonic current components will not be changed regardless of the state of input/output power of the converter device, and a constant amount of harmonic loss continues to be generated from the transformer.

Citation List Non Patent Literature [NPL 1] Main Circuit Power Conversion System -Inverter / Converter, pp. 189 -203, Supervised by Japan Railway Rolling Stock & Machinery Association

Summary of the Invention

The loss caused by the harmonic current of the transformer winding can be reduced by raising the carrier frequency of the converter device, but when elements with a high withstand voltage are used as described earlier, it is not preferable to raise the carrier frequency from the viewpoint of restriction regarding the loss caused by the switching operation.

Generally, high speed railways or other vehicles that travel long distances are often driven at a constant speed for a long period of time. At that time, the power corresponding to the change in speed caused by travel resistance such as air resistance of the vehicle and gradients should be input or output through the converter device. The power corresponding to the change in speed caused by the travel resistance and gradients is relatively small, so that the fundamental wave component of the current of the transformer is small, but since the ripple current component does not depend on the input and output of the converter device by the reason described above, the harmonic loss of the transformer is not changed.

By driving the vehicle in that state for a long period of time, a state where the harmonic loss of the transformer is relatively high continues even though the input-output current of the converter device is small, and the efficiency of the device as traction system is deteriorated.

On the other hand, the loss accompanying the switching operation of the converter device depends on the carrier frequency and the input-output current, so that when driving a vehicle at constant speed or driving the vehicle with a small output torque from the AC motor, as described above, the input-output current of the converter device is small, so that the loss caused by the switching operation of the converter device is in a small state. Therefore, when considering a particular case where the vehicle speed is controlled to constant speed or where the output torque from the AC motor is small, it becomes possible to increase the carrier frequency of the converter device, reduce the harmonic loss caused by the skin effect in the transformer winding, and thereby cut down the power consumption. At this time, the switching operation of the converter device is increased and the loss caused by the switching is also increased, but since the converter loss depends on the basic wave current component of the input-output current of the converter device, the increase of loss caused by the switching operation of the converter device is very small.

In order to solve the problems, the present invention provides a drive unit of a railway vehicle, wherein when controlling a speed of the railway vehicle to a speed close to a target speed, a carrier frequency of a converter device is raised from a first reference frequency to a second reference frequency having a higher frequency than the first reference frequency, and when the speed of the railway vehicle is not controlled to a speed close to the target speed, the carrier frequency is reduced from the second reference frequency to the first reference frequency.

In another example of the present invention, the drive unit further comprises an auxiliary power supply connected to a DC-side of the converter device and supplying power for lighting or air-conditioning the railway vehicle, wherein when the railway vehicle is in a stopped state, the control unit raises a carrier frequency of the converter device from a first reference frequency to a second reference frequency having a higher frequency than the first reference frequency, and when the railway vehicle is transited from the stopped state to a traveling state, the carrier frequency of the converter device is reduced from the second reference frequency to the first reference frequency.

According to the present invention, it becomes possible to enhance the overall efficiency of the drive unit of the vehicle by considering the harmonic loss caused by the skin effect of the transformer winding and the switching operation of the converter device.

Specifically, the effect of the present invention appears significantly in rapid-transit railways and long-distance trains where acceleration and deceleration is less frequent and driving within a given speed range is continued for a long period of time.

Brief Description of the Drawings

Fig. 1 is a view showing a configuration example of a drive unit of a railway vehicle Fig. 2 is a view showing a relationship between travel position of the vehicle, carrier frequency of a converter device and vehicle speed.

Fig. 3 is a view showing a relationship between travel time of the vehicle, the carrier frequency of the converter device, the vehicle speed, and a secondary current of the transformer.

Fig. 4 is a view showing a relationship between speed of the vehicle, tractive effort of the vehicle, travel resistance received by the train, and the secondary current of the transformer.

Fig. 5 is a view showing a relationship between the travel position of the vehicle, the carrier frequency of the converter device, and the vehicle speed.

Fig. 6 is a view showing a relationship between the speed of the vehicle, the tractive effort of the vehicle, the travel resistance received by the train, and the secondary current of the transformer.

Fig. 7 is a view showing a relationship between the travel position of the vehicle, the carrier frequency of the converter device, and the vehicle speed.

Description of Preferred Embodiments

Now, the preferred embodiments of the present invention will be described.

Embodiment 1 A first embodiment of a drive unit of a railway vehicle according to the present invention will be described with reference to Figs. 1 and 2.

Fig. 1 illustrates a configuration example of a drive unit of a railway vehicle. A transformer 3 is connected via a pantograph 2 to an AC overhead wire 1 for stepping-down the overhead wire voltage and supplying single-phase AC power to a converter device 5. One end of the transformer 3 is connected via wheels 4 to a rail. The converter device 5 converts the single-phase AC power obtained from the transformer 3 to DC power. A DC-side of the converter device 5 is connected via a capacitor 6 for stabilizing the voltage to an inverter device 7. The inverter device 7 converts the DC power output from the converter device 5 to three-phase AC power, and drives an AC motor 8.

A first voltage detection means 9 detects the voltage applied from the AC overhead wire 1 to the transformer 3, converts the voltage based on a winding ratio of the transformer 3 to an AC-side voltage (secondary voltage) of the converter device 5 es, and outputs the same. The first voltage detection means 9 can also detect the AC-side secondary voltage es of the converter device 5 directly. A first current detection means 10 detects and outputs a secondary current is flowing at the AC-side of the converter device 5.

A second voltage detection means 11 detects and outputs a DC stage voltage Ecf, which is the voltage at both ends of the capacitor 6. A second current detection means 12 detects and outputs three-phase AC currents iu, iv and iw flowing to the AC motor 8. A speed detection means 13 detects and outputs a rotational frequency Fr of the AC motor 8.

A control unit 14 operates the converter device 5 so that the DC-side voltage of the converter device 5 is set to a given value, and at the same time, operates the inverter device 7 so that an output torque of the AC motor 8 is set to a given value satisfying the control command, and based on the secondary voltage es, the secondary current is, the DC stage voltage Ecf, the currents iu, iv and iw flowing into the AC motor 8, and the rotational frequency Fr, the control unit outputs gate commands Gc and Gi for operating switching elements constituting the converter device 5 and the inverter device 7.

Fig. 2 is a view showing a relationship between travel distance and carrier frequency of a converter device, and a relationship between travel distance and vehicle speed. The view showing the relationship between travel distance and vehicle speed illustrated on the lower side of Fig. 2 illustrates an operation curve where after the vehicle accelerates from a stop point and reaches a first reference speed Vi, constant speed control operation is started, and then when the vehicle approximates a next stop point, the vehicle decelerates to stop at a given position. The term stop point used here refers to a station, a signal station, and so on. The term constant speed control operation used here does not necessarily refer to an operation to maintain a constant speed, but can include an operation where the vehicle speed is maintained within a given range.

In the present invention, as shown in Fig. 2, at a point of time X1 where the speed of the vehicle is started to be controlled to a constant speed at the first reference speed Vi, a carrier frequency of the converter device is raised from a first carrier frequency Fc1 to a second carrier frequency Fc2 having a higher frequency than the first carrier frequency Fc-I. At this time, generally in a railway vehicle, the carrier frequency of the converter device 5 is set to an odd multiple of the frequency of the overhead wire voltage, so that the Fcl and Fc2 are also respectively set as odd multiples of the frequency of the overhead wire voltage.

Incidentally, if the second carrier frequency Fc2 is set high, the current approximates a sine wave with no distortion, so that harmonic components in the current flowing between the transformer 3 and the converter device 5 becomes small, and in order to reduce harmonic loss that occurs by a skin effect in a transformer wining caused by the harmonic components in the current, the frequency Fc2 should be as high as possible. On the other hand, if the carrier frequency is set high, the switching frequency of the converter device 5 is increased, so that the switching loss of the semiconductor constituting the converter device 5 is increased. Therefore, the amount of reduction caused by the harmonic loss in the transformer winding that is determined uniquely by the carrier frequency, the constant of the transformer, the overhead wire voltage, and the DC voltage at the output side of the converter device is compared in advance with the amount of increase by the switching loss in the converter device 5, and the carrier frequency Fc2 is set in advance so that the amount of increase by the relevant switching loss becomes smaller than the amount of reduction by the harmonic loss. Further, the carrier frequency Fc2 is set so that the overall loss generated by the converter device 5 when constant speed control is performed at the first reference speed V1 does not exceed a cooling performance of the converter device 5.

Further, if the auxiliary power supply that supplies power for lighting or air-conditioning the vehicle is connected to a DC-side of the converter device 5, it is preferable to set the second carrier frequency Fc2 by also considering the loss generated by the converter device 5 depending on the amount of power consumed by the auxiliary power supply.

At this time, for example, a method for performing constant speed control of the vehicle speed to the first reference speed V1 can be realized, for example, by a method in which a constant speed control command is entered from a driver's cab to the control unit 14, and the speed of the vehicle and the amount of change thereof is calculated based on a rotation frequency Fr of the AC motor 8 obtained from the speed detection means 13, based on which torque required to travel at the first reference speed V1 is calculated, and a torque command based on the calculated value is sent to the inverter device 7. Further, the state of the constant speed control can be determined by whether a constant speed control command has been entered from the drivers cab to the control unit 14 or not. Further, whether a time change rate of speed of the vehicle is within a given range based on the rotational frequency Fr can be set as the condition.

As another example of performing constant speed control, the constant speed control can also be executed by having acceleration and deceleration signals required to maintain a constant speed entered by a driver of the train from the drivers cab as a manual control command to the control unit 14. In that case, the state in which constant speed control is performed can be determined based on the condition that the acceleration and deceleration signals entered to the control unit 14 from the driver's cab is equal to or smaller than a given acceleration and deceleration.

Thereafter, at a point X2 in which the vehicle decelerates toward the stop point, that is, when the vehicle speed is in a state where it is not controlled to the first reference speed Vi, the carrier frequency of the converter device 5 is lowered from the second carrier frequency Fc2 to the first carrier frequency Fc1.

As described, by raising the carrier frequency of the converter device 5 when the vehicle is traveling at a speed controlled to a constant value, the ratio of harmonic components with respect to fundamental wave components of the current flowing in the transformer can be reduced. As a result, the switching loss of the converter device 5 is increased, but the harmonic loss that occurs in the winding wire of the transformer occupying a large rate of the loss can be suppressed, and the power consumption of the whole drive unit can be reduced.

Further, the present invention has an effect to improve the power factor and reduce reactive power in a state where the speed of the traveling vehicle is controlled to a constant value, so that loss reduction and downsizing of the transformer 3 is enabled.

Embodiment 2 A second embodiment of a drive unit of a railway vehicle according to the present invention will be described with reference to Figs. 3 and 4. The present embodiment differs from Embodiment 1 in the point that amount of a secondary current of the transformer is used in addition to the speed of the vehicle as the condition for changing the carrier frequency of the converter device.

Fig. 3 shows, from the top, the relationship between travel distance and carrier frequency of converter device, the relationship between the travel distance and the vehicle speed, and the relationship between the travel distance and secondary current of transformer 5. In Fig. 3, the operation curve shows an example where after the vehicle accelerates from the stop point and reaches the first reference speed V1, constant speed control operation is started. Thereafter, when the next stop point is approximated, the vehicle is decelerated to stop at a given position. The term stop point can refer to a station, a signal station and so on. The term constant speed control operation does not necessarily refer to an operation to maintain a constant speed, but can include an operation where the vehicle speed is maintained within a given range.

Fig. 4 illustrates a relationship between the speed of the vehicle and tractive effort, the relationship between the speed of the vehicle and travel distance, and the relationship between the speed of the vehicle and the secondary current of the transformer 3. In Fig. 4, among the tractive effort, tractive effort A shows a relationship between the tractive effort and the speed corresponding to a maximum output of the vehicle, and the secondary current of the transformer 3 at that time is illustrated as secondary current A. Similarly, tractive effort B illustrates an example of a tractive effort characteristic of a case where output of the vehicle has been reduced, and the secondary current of the transformer 3 at that time is illustrated as secondary current B. Further, Fig. 4 illustrates a travel resistance 1 and a travel resistance 2 as the two types of travel resistances while the train is travelling. Generally, a travel resistance refers to a sum of an air resistance received by the vehicle, a curve resistance while the vehicle passes a curve, and a gradient, for example. In the present description, an example is illustrated where the travel resistance at a flat section other than in a tunnel is referred to as travel resistance 1, and the travel resistance at a flat section in a tunnel is referred to as travel resistance 2. In this example, a travel resistance of travel resistance 1 at reference speed V1 is referred to as R1, and the size of the secondary current of the transformer 3 for having the vehicle travel at a constant reference speed is referred to as It1. Similarly, a travel resistance of travel resistance 2 at reference speed V1 is referred to as R2, and the size of the secondary current of the transformer is referred to as 1t2.

In the present invention, as shown in Fig. 3, at a point of time X1 when the speed of the vehicle is started to be constantly controlled to the first reference speed V1, the carrier frequency of the converter device 5 is raised from the first carrier frequency Fc1 to the second carrier frequency Fc2. However, when the vehicle subjected to speed control and traveling at a constant reference speed Vi enters a tunnel section, the travel resistance is increased from Ri to R2, so that in order to travel while maintaining reference speed Vi, the secondary current of the transformer 3 must be increased from It1 to 1t2. Actually, since the cars of a train formation enter the tunnel sequentially from the front car, the relevant current value changes successively from IM to 1t2.

When the secondary current of the transformer 3 is increased from 10 to 1t2, if the carrier frequency of the converter device 5 is set to Fc2, the loss caused by the switching operation of the converter device 5 is increased, and may exceed the cooling performance of the converter device 5. Therefore, when the current value is changed from 10 to 1t2, at point X2 exceeding the reference current value 11, the carrier frequency of the converter device 5 is lowered from the second carrier frequency Fc2 to the first carrier frequency Fc1.

Thereafter, when the train passes a tunnel section, the travel resistance is reduced from R2 to R1 and the train maintains reference speed V1 while traveling, so that the required secondary current of the transformer 3 is changed from 1t2 to Iti, and the loss accompanying the switching operation of the converter device 5 is also reduced. Therefore, at a point X3 where the current value changed from 10 to Iti drops to below a reference current value 12, the carrier frequency of the converter device 5 is raised again from the first carrier frequency Fc1 to the second carrier frequency Fc2, by which the harmonic loss of the transformer 3 is reduced.

The carrier frequency Fc2 is set in advance so that the amount of increase of switching loss of the converter device 5 that occurs when constant speed control is performed at the first reference speed Vi becomes smaller than the amount of reduction caused by the harmonic loss in the transformer winding. Further, when constant speed control is performed at the first reference speed V1, the carrier frequency Fc2 is set so that the overall loss occurring at the converter device 5 does not exceed the cooling performance of the converter device 5, and when setting the reference current value 11 and 12, they should similarly be set according to the loss of the converter device 5. If an auxiliary power supply supplying power for lighting and air conditioning the vehicle is connected to the DC-side of the converter device 5, it is preferable to set the second carrier frequency Fc2 and the reference current values 11 and 12 considering the loss that occurs at the converter device 5 corresponding to the amount of power consumed by the auxiliary power supply.

As described, by judging the rising of carrier frequency based on the speed and the secondary current of the vehicle, it becomes possible to prevent the secondary current of speed Vi to become greater than assumed according to the difference in travel resistance due to the track conditions, and having the amount of increase in switching loss of the converter device when the carrier frequency is raised to Fc2 exceed the amount of reduction of harmonic loss in the transformer winding, and also prevent the overall loss of the converter device 5 from exceeding the tolerance of cooling performance of the converter device 5, while achieving the effect of the present invention.

Embodiment 2 describes a case where the vehicle travels through only one tunnel section, but the number of the tunnel sections through which the vehicle travels is not limited to one. The tunnel section was illustrated as the cause of change of the travel resistance from travel resistance 1 to travel resistance 2, but other causes such as inclining or downhill grade, curve resistance when passing a curve, air resistance, and so on can also be the cause of change of travel resistance.

Further, Embodiment 2 describes a case where the travel resistance is changed to an increasing direction from travel resistance 1 to travel resistance 2, and the size of the secondary current of the transformer 3 increases, but the present embodiment is not restricted to the example where the travel resistance is increased. For example, in a downhill grade, the travel resistance is reduced and drops to a negative value, so that when the vehicle is decelerated using regenerative brake to raise the vehicle speed, the secondary current of the transformer 3 still flows. The amount of the current will be changed in response to the downhill grade.

Embodiment 3 A third embodiment of a drive unit of a railway vehicle according to the present invention will be described with reference to Figs. 5 and 6. Embodiment 3 differs from Embodiment 1 in that a case is added where the carrier frequency of the converter device is not changed according to the constantly controlled speed.

Fig. 5 is a view showing the relationship between the travel distance and carrier frequency of the converter device, and the relationship between the travel distance and vehicle speed. Fig. 5 illustrates an operation curve where after the vehicle is accelerated from the stop point to the first reference speed VIA, constant speed operation is performed at speed VIA within a constant speed control section A. Thereafter, the vehicle is accelerated to the next first reference speed Vi B, and constant speed operation is performed at speed VI B within a constant speed control section B. Thereafter, when the vehicle approximates the next stop point, the vehicle is decelerated to stop at the given position. The stop point described here can be a station, a signal station, and so on.

Fig. 6 is a view showing the relationship between speed and tractive effort of the vehicle, the relationship between speed and travel resistance of the vehicle, and the relationship between speed of the vehicle and a secondary current of the transformer 3. In Fig. 4, among the tractive effort, tractive effort A shows the relationship between the maximum output tractive effort and the speed of the vehicle, wherein the current of the transformer 3 at this time is referred to as secondary current A. Similarly, tractive effort B illustrates an example of tractive effort characteristic of the case where the output of the vehicle has been reduced, wherein the secondary current of the transformer 3 at this time is referred to as secondary current B. Generally, a travel resistance of a vehicle refers to a sum of an air resistance received by the vehicle, a curve resistance while the vehicle passes a curve, and gradient, for example. As shown in Fig. 6, when the vehicle is travelling on a track whose travel resistance is shown by a speed characteristic of travel resistance 1, the travel resistance of the first reference speed \MA is referred to as R1A, and the travel resistance of the subsequent first reference speed V1B is referred to as R1 B. Furthermore, an amount of the secondary current of the transformer 3 for constantly travelling at reference speed V1A is referred to as ItA, and similarly, an amount of the secondary current of the transformer for constantly travelling at reference speed V1B is referred to as ItB.

In the present invention, as shown in Fig. 5, from a point of time X1 where the speed of the vehicle is started to be controlled constantly to the initial first reference speed VIA, the carrier frequency of the converter device 5 is raised from the first carrier frequency Fc1 to the second carrier frequency Fc2. At a point X2 which is the end of the constant speed control section A controlled constantly to reference speed VIA, the vehicle is further accelerated. At this time, the speed of the vehicle is not controlled to a constant value, so that the carrier frequency of the converter device 5 is set from the second carrier frequency Fc2 to the first carrier frequency Fc1.

Thereafter, at point X3, the vehicle reaches speed Vi B, and the vehicle travels at this speed within the constant speed control section B. However, compared to the travel resistance R1A where the vehicle is controlled constantly to reference speed VIA, the speed is increased to reference speed Vi B, and depending thereon, the travel resistance is also increased to travel resistance RI B. Accordingly, when the vehicle travels through the constant speed control section B while maintaining the reference speed Vi B, the secondary current of the transformer 3 must also be increased from current ItA to ItB. When the secondary current of the transformer 3 is increased from ItA to ItB, if the carrier frequency of the converter device 5 is set to Fc2, the loss of the switching element of the converter device 5 is increased, and may exceed the cooling performance of the converter device 5. Therefore, in the constant speed control section B, the vehicle travels with the carrier frequency of the converter device 5 still set to the first carrier frequency Fc1.

Therefore, in a case where a second reference speed where the vehicle is enabled to travel via a constant speed control after the carrier frequency of the converter device 5 has been raised to the second carrier frequency Fc2 is set to V2, and the speed controlled constantly is set to a reference speed V2B, the vehicle should travel without changing the carrier frequency of the converter device 5 in a state where the reference speed V2B is equal to or greater than the second reference speed V2, and the vehicle should travel with the carrier frequency raised to the second carrier frequency Fc2 in a state where the speed V2B is smaller than the reference speed V2.

The carrier frequency Fc2 is set in advance so that when the speed is constantly controlled to second reference speed V2, the increase of switching loss of the converter device 5 becomes smaller than the amount of reduction of harmonic loss in the transformer winding. Further, the loss generated by the converter device 5 operating in the carrier frequency Fc2 should be set to be equivalent to the cooling performance of the converter device 5. Furthermore, if the auxiliary power supply supplying power for lighting or air conditioning the vehicle is connected to the DC-side of the converter device 5, the second carrier frequency Fc2 should be set by taking into consideration the loss generated by the converter device 5 corresponding to the amount of power consumed by the auxiliary power supply.

As described, by judging the increase of carrier frequency based on the speed of the vehicle, it becomes possible to prevent the secondary current during reference speed V1B from being greater than assumed due to the change in the travel resistance by the constantly controlled speed and exceeding the amount of increase of switching loss of the converter device 5 when the carrier frequency is raised to Fc2, that is, exceeding the amount of reduction of harmonic loss in the transformer winding, and further prevent the overall loss of the converter device 5 from exceeding the tolerance of the cooling performance of the converter device 5, while achieving the effect of the present invention.

In Embodiment 3, the first reference speed has been described as being composed of two kinds of velocities, speed VIA and speed VI B, but the number of first reference velocities being controlled as constant velocities is not restricted thereto.

Embodiment 4 A fourth embodiment of a drive unit of a railway vehicle according to the present invention will be described with reference to Fig. 7. The difference between Embodiment 4 and Embodiment 1 is that a reference speed displacement from a constantly controlled speed of a vehicle is also used as the condition for changing the carrier frequency of the converter device.

Fig. 7 is a view showing the relationship between travel distance and carrier frequency of the converter device, and the relationship between travel distance and vehicle speed. Fig. 7 illustrates an operation curve where after the vehicle accelerates from the stop point and reaches the first reference speed V1, a constant speed control is started within the constant speed control section. When the next stop point is approximated, the vehicle decelerates to stop at a given position. The term stop point can refer to a station, a signal station, and so on.

Normally, the travel resistance when the vehicle is travelling changes constantly depending on speed and track conditions. Especially in a track having many gradients and tunnels which are causes of significant changes in the travel resistance, even when the control unit 14 sends commands to the inverter device 7 to realize a constant reference speed V1 as the target speed depending on those resistances, the speed of the vehicle may be varied due to the delay in following commands and the like. In Fig. 7, the vehicle is controlled with a constant reference speed V-1 set as target, and the speed of the vehicle is controlled substantially at reference speed VI ± AV as reference speed displacement AV in the constant speed control section.

According to the present invention, as shown in Fig. 7, from the point X1 where the speed of the vehicle has been started to be controlled constantly to the first reference speed Vi, the carrier frequency of the converter device 5 is raised from the first carrier frequency Fc-I to the second carrier frequency Fc2.

Incidentally, when the vehicle is travelling from point X-1 to point X2, the speed is only displaced within the range of reference speed displacement ± AV from the reference speed Vi. However, in the section from point X2 to point X3, the speed displacement exceeds the speed V-1 +AV of the vehicle. On the other hand, the speed of the vehicle of the subsequent section from point X3 to point X4 is within the range of Vi ± AV, but as for the next section from point X4 to point X5, the speed drops below vehicle speed V-1 -V. Similarly, in the next section from point X5 to point X6, the speed of the vehicle is controlled to be within the range of Vi ± AV.

If the speed fluctuation of the vehicle is significant even though the vehicle is constantly controlled at reference speed, one possible cause is considered to be the travel resistance being changed significantly. In that case, if the travel resistance is high, similar to the case of the previous Embodiments 2 and 3, the secondary current of the transformer 3 is increased, so that if the carrier frequency of the converter device 5 is set to Fc2, the loss of the switching element of the converter device 5 increases, and may exceed the cooling performance of the converter device 5.

Therefore, according to the present invention, in the constant speed control section from point X1 to point X5 where the speed of the vehicle is controlled to be constant, the carrier frequency of the converter device 5 is set to a second reference frequency Fc2, but if a difference equal to or greater than the reference displacement ± AV from the first reference speed Vi occurs, for example, from point X2 to point X3, and from point X4 to point X5, the setting of the carrier frequency is set from the second reference frequency Fc2 to the first reference frequency Fcl.

The carrier frequency Fc2 is set in advance so that the amount of increase of the switching loss in the converter device 5 becomes smaller than the amount of reduction of harmonic loss in the transformer winding, even in a case where the speed is changed to V-1 ± AV with respect to the first reference speed V-1 being the control target. Further, the loss occurring in the converter device 5 should be set so as not to exceed the cooling performance of the converter device 5. Moreover, if the auxiliary power supply supplying power for lighting or air conditioning the vehicle is connected to the DC-side of the converter device, the carrier frequency Fc2 should be set considering the loss generated in the converter device 5 by the amount of power consumed by the auxiliary power supply.

As described, by determining the rising of carrier frequency based also on the fluctuation of the vehicle speed, it becomes possible to prevent the secondary current of the transformer 3 from being greater than assumed due to the difference in travel resistances by track conditions and exceeding the switching loss of the converter device when the carrier frequency is raised to Fc2, and exceeding the amount of reduction of harmonic loss of the transformer winding, and further prevent the overall loss of the converter device 5 from exceeding the tolerance of cooling performance of the converter device 5, while achieving the effect of the present invention.

In Embodiment 4, as the speed displacement excessive section within the constant speed control section, one section from point X1 to point X2 has been described as the representation of the section where the speed of the vehicle exceeds V1 + AV, and one section from point X4 to point X5 has been described as the representation of the section where the speed of the vehicle drops below V1 -AV, but this does not restrict the number of speed displacement excessive sections included in the constant speed control section.

In the technical field of railway vehicles, studies are progressing not only for saving energy of the respective devices, such as by adopting a high frequency motor or a low loss IGBT module, but also on an effective control method for enhancing the overall efficiency of all devices constituting the main circuit. The present invention relates to a means for cutting down power consumption that can be applied to AC vehicles regardless of the frequency of the overhead wire, which is a useful technique for further enhancing the saving of energy of the railway vehicle.

Embodiment 5 A fifth embodiment of the drive unit of a railway vehicle according to the present invention will now be described. The difference between Embodiment 5 and Embodiment 1 is that whether the vehicle is in a stop state or not is used as the condition for changing the carrier frequency of the converter device. The other configurations are the same as Embodiment 1.

In the present embodiment, an auxiliary power supply supplying power for lighting or air conditioning the vehicle is connected to the DC-side of the converter device 5 in the drive unit of a railway vehicle shown in Fig. 1. In such drive unit, when the railway vehicle is stopping at a station and the like, power is not supplied to the AC motor, but power to be supplied for lighting and air conditioning is supplied from the converter device to the auxiliary power supply.

The power supplied from the converter device to the auxiliary power supply is relatively small compared to the power supplied from the converter device to the inverter device for driving the railway vehicle. Therefore, this small power is used to determine the stop state of the railway vehicle supplied from the converter device, and the carrier frequency of the converter device is raised from carrier frequencyFcl to carrier frequency Fc2. Further, in the state where the railway vehicle is transiting from the stop state to the travel state, the carrier frequency of the converter device is reduced from carrier frequency Fc2 to carrier frequency Fcl. By such switching of carrier frequency, the ratio of the harmonic component to the fundamental wave component of the current flowing to the transformer can be reduced. As a result, the switching loss of the converter device 5 is increased, but the harmonic loss generated in the winding wire of the transformer that occupies a large ratio of the loss can be suppressed, and the power consumption of the drive unit of the vehicle can be reduced.

Here, the stop state of the railway vehicle can be determined when the speed of the vehicle is nearly zero based on the rotation speed Fr of the AC motor 8, or the stop state can be determined when the command for setting the door to an open state from the drivers cab is output.

The carrier frequency Fc2 is set in advance so that the amount of increase of switching loss of the converter device 5 becomes smaller than the amount of reduction of harmonic loss in the transformer winding when the vehicle is controlled to constant speed at the first reference speed Vi. Further, the carrier frequency Fc2 is set so that the when the railway vehicle is at a stop state, the overall loss generated by the converter device 5 does not exceed the cooling performance of the converter device 5.

As described, by determining the increase of carrier frequency based on whether the railway vehicle is in a stop state or not, the amount of increase of the switching loss of the converter device when the carrier frequency is increased to Fc2 can be prevented from exceeding the amount of reduction of harmonic loss in the transformer winding, and the overall loss of the converter device 5 can be prevented from exceeding the tolerance of the cooling performance of the converter device 5, while achieving the effect of the present invention.

Claims

CLAIMS1. A drive unit of a railway vehicle comprising: a transformer for stepping down an AC power obtained from a single-phase AC overhead wire and outputting the power to a secondary side; a converter device connected to a secondary side of the transformer and converting the AC power obtained via the transformer to a DC power; an inverter device connected to a DC-side of the converter device via a filter capacitor, and converting the DC power converted via the converter device to a three-phase AC power; a control unit providing a gate command to the converter device and the inverter device; and one or more AC motors driven by a three-phase AC power converted via the inverter device; wherein when a speed of the railway vehicle is controlled to a speed close to a target speed, the control unit raises a carrier frequency of the converter device from a first reference frequency to a second reference frequency having a higher frequency than the first reference frequency, and when the speed of the railway vehicle is not controlled to a speed close to the target speed, the carrier frequency is reduced from the second reference frequency to the first reference frequency.
2. The drive unit of a railway vehicle according to Claim 1, wherein when the speed of the railway vehicle is controlled to a speed close to the target speed, if the target speed is smaller than a reference frequency, the control unit raises a carrier frequency of the converter device from the first reference frequency to the second reference frequency; if the target speed is equal to or greater than the reference speed, the control unit sets a carrier frequency of the converter device to a first reference frequency; and in a state where the carrier frequency of the converter device is set to the second reference frequency, if the speed of the railway vehicle is not controlled to a speed close to the target speed, the control unit reduces the carrier frequency from the second reference frequency to the first reference frequency.
3. The drive unit of a railway vehicle according to Claim 1 or Claim 2, wherein in a state where a carrier frequency is set and operated in the second reference frequency, the converter device reduces the carrier frequency of the converter device from the second reference frequency to the first reference frequency when a size of an AC-side current or a DC-side current of the converter device becomes equal to or greater than a first reference current value; and when a size of the AC-side current or a DC-side current of the converter device becomes equal to or smaller than a second reference current value that is smaller than the first reference current value, the converter device raises the carrier frequency of the converter device from the first reference frequency to the second reference frequency.
4. The drive unit of a railway vehicle according to Claim 1 or Claim 2, wherein in a state where a carrier frequency is set and operated in the second reference frequency, the converter device sets the carrier frequency of the converter device to a second reference frequency when the speed of the railway vehicle is within a given speed displacement from the target speed; and when the speed of the railway vehicle exceeds the given speed displacement, the converter device reduces the carrier frequency from the second reference frequency to the first reference frequency.
5. A drive unit of a railway vehicle comprising: a transformer for stepping down an AC power obtained from a single-phase AC overhead wire and outputting the power to a secondary side; a converter device connected to a secondary side of the transformer and converting the AC power obtained via the transformer to a DC power; an inverter device connected to a DC-side of the converter device via a filter capacitor, and converting the DC power converted via the converter device to a three-phase AC power; a control unit providing a gate command to the converter device and the inverter device; and one or more AC motors driven by a three-phase AC power converted via the inverter device; wherein the drive unit further comprises an auxiliary power supply connected to a DC-side of the converter device and supplying power for lighting or air-conditioning the railway vehicle; and when the railway vehicle is in a stopped state, the control unit raises a carrier frequency of the converter device from a first reference frequency to a second reference frequency having a higher frequency than the first reference frequency, and when the railway vehicle is transited from the stopped state to a traveling state, the control unit reduces the carrier frequency of the converter device from the second reference frequency to the first reference frequency.
6. The drive unit of a railway vehicle according to any one of Claims 1 through 5, wherein the second reference frequency is set so that an amount of increase of switching loss of the converter device when the carrier frequency is switched from the first reference frequency to the second reference frequency becomes smaller than an amount of decrease of harmonic loss in the transformer.
7. The drive unit of a railway vehicle according to any one of Claims 1 through 6, wherein the first reference frequency and the second reference frequency is an odd multiple frequency with respect to a fundamental wave voltage frequency of the single-phase AC overhead wire.