JP3211071B2 - Power converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power converter for converting between AC and DC used in an AC electric vehicle.

[0002]

2. Description of the Related Art As a power converter of an AC electric vehicle that drives an induction motor using AC as a power source, there are a PWM converter and an inverter electric vehicle shown in FIG. 1 is an AC power supply, 2
Is a transformer primary winding, 3 is a transformer secondary winding, 4 is a PWM converter, 5 is a smoothing capacitor, 6 is a PWM inverter, 7 is an induction motor, 8, 9 are AC contactors for turning on and off the circuit, 10 indicates a charging resistance. PWM converter 4 and P
The WM inverter 6 includes a self-extinguishing element such as GTO and IGBT and a diode connected in antiparallel to the self-extinguishing element. With this configuration, during power running of the electric vehicle, the PWM converter 4 converts the single-phase alternating current on the power supply side into direct current, and
The inverter 6 converts the direct current into a three-phase alternating current and supplies the three-phase alternating current to the induction motor 7, whereby the induction motor 7 is driven and the electric vehicle runs. At the time of regeneration, the induction motor 7 is used as a power source, and is converted into DC by the PWM inverter 6.
The regenerative brake is applied by converting the power into a single-phase AC by the PWM converter 4 and returning the power to the AC power supply 1. During power running and regeneration, the AC contactor 8 is closed and the AC contactor 9 is closed.
Keep open. In FIG. 6, when the electric vehicle is first started, or when shifting from the coasting state to the powering and regenerating states, and when the smoothing capacitor 5 is not charged, the AC power supply 1 during the powering and the induction during the regeneration. Using the electric motor 7 as a power source, a large rush current flows through the smoothing capacitor 5, and there is a risk of damaging equipment and elements. In addition, the smoothing capacitor 5 is overcharged and an overvoltage occurs. To prevent this, it is necessary to initially charge the smoothing capacitor 5 corresponding to a DC power supply before starting the PWM inverter 6. In this case, by opening the AC contactor 8 and closing the AC contactor 9, the smoothing capacitor 5 is charged from the AC power supply 1 through the transformer 3 through the charging resistor 10 and the diode of the PWM converter 4. When the charging is completed, the AC contactor 9 is opened, and the AC contactor 8 is closed, so that the state can be shifted to the power running or the regenerative state. By switching between the AC contactors 8 and 9 and charging through the charging resistor 10 in this manner, the smoothing capacitor 5 can be charged without flowing an inrush current. FIG. 7 shows a configuration of a power converter of another AC train. Those having the same functions as those in FIG. 6 are given the same numbers. In FIG. 7, 11 is a mixed bridge circuit using a diode and a thyristor having no self-extinguishing ability, and 12 is a smoothing reactor. Initial charging of the smoothing capacitor 5 by this circuit is performed by adjusting the firing angle of the thyristor of the mixed bridge circuit 11 and gradually generating a voltage. Thereby, charging can be performed without flowing an inrush current without using an initial charging circuit such as the AC contactor 9 and the charging resistor 10 in FIG. However, in this configuration, since the regenerative brake cannot be applied, other brake circuits such as a power generation brake circuit (FIG. 7)
Not shown. ) Is required. FIG. 8 shows a configuration of a power converter of another AC train. 13 is a uniform bridge circuit, 14 is a PB converter for switching the circuit by powering and regeneration, 15 is a tertiary winding of a transformer, and 16 is a mixed bridge circuit. This is a uniform bridge circuit in which all the mixed bridge circuits are thyristors in order to perform regeneration with the configuration shown in FIG. 7, and a PB converter 14 that switches the circuit between power running (P) and regeneration (B) is provided. It is. However, in this case, when the PB converter 14 is set to the regenerative (B) side, the smoothing capacitor 5 is connected to the uniform bridge circuit 13.
, The smoothing capacitor 5 cannot be initially charged. Therefore, a circuit for performing initial charging from the transformer tertiary winding 15 by the mixed bridge circuit 16 is added. In Japanese Patent Application Laid-Open No. 63-186568, a primary winding of a transformer is connected to an AC power supply via a contactor, and a large DC circuit is connected from a secondary winding of the transformer via an AC / DC converter. It describes that in a power converter that supplies power to a capacitor having a capacity, a separate power supply including a storage battery and an auxiliary inverter is provided, and the capacitor is initially charged from the separate power supply with the contactor opened.

[0003]

In the initial charging circuit having the configuration shown in FIG. 6, the AC contactor 9 and the charging resistor 10 are in a high voltage circuit (for example, the voltage of the secondary winding 3 of the transformer is 10 V).
00V. ), It is necessary to increase the insulation distance, and there is a problem that the device becomes large.
Further, the configuration using the thyristor converter shown in FIG. 7 does not require an initial charging circuit, but has a problem that regeneration cannot be performed. Further, in the uniform bridge circuit configuration including the thyristors shown in FIG. 8, there is a problem that the PB converter 14 and the mixing bridge circuit 16 need to be added in order to perform regeneration. Further, Japanese Patent Application Laid-Open No. 63-18656
In the power converter described in Japanese Patent Publication No. 8 (1994), since the contactor is connected between the AC power supply and the primary winding of the transformer, a power supply for initial charging cannot be secured from this transformer, Therefore, it is necessary to provide a separate power supply consisting of a storage battery and an auxiliary inverter, and there is a problem that a device as the separate power supply becomes large and an initial charging circuit becomes complicated. An object of the present invention is to provide a power converter suitable for simplifying the initial charging circuit, reducing the size of the device, and reducing the cost in a PWM converter and a PWM inverter electric vehicle.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a converter in which an AC side is connected to a secondary winding of a transformer having a primary winding connected to an AC power supply via a first contactor, and a DC smoothing device. The capacitor and the P connected to the AC motor driving the electric car
In a power converter for an AC electric vehicle including a WM inverter, the converter is a PWM converter that converts AC to DC or reversely converts DC to DC using a plurality of self-extinguishing elements in which diodes are connected in parallel with opposite polarities. A tertiary winding provided in the transformer and outputting a voltage lower than the secondary winding, and connected to the output of the tertiary winding via a second contactor to boost the tertiary winding output voltage And a rectifying circuit for rectifying the output of the boosting side of the boosting transformer and charging the DC smoothing capacitor. When the power running of the electric vehicle starts, the second contactor is closed and rectified by the diode of the PWM converter. Initially charge the DC smoothing capacitor to a predetermined value lower than the rectified voltage of the secondary winding, and then close the first contactor to precharge the DC smoothing capacitor to the rectified voltage of the secondary winding. By, it is achieved.

[0005]

The present invention relates to a transformer for forming a power supply of a main circuit.
A secondary winding is provided, and the voltage of the tertiary winding is converted to the voltage of the transformer secondary winding (for example, 1000 V) forming the power supply of the main circuit.
When the voltage is lowered to, for example, about 500 V, the transformer 3
An AC contactor with low withstand voltage and charging resistor can be used on the secondary winding side, and even if a diode bridge circuit is added, the size of the device as the initial charging circuit can be reduced in size and cost can be reduced. it can. When the smoothing capacitor is initially charged by the initial charging circuit on the transformer tertiary winding side, the initial charging voltage becomes 500 V
(Effective value), it becomes 707 V which is twice the route. Thereafter, by closing the AC contactor on the secondary winding side of the transformer and further precharging, the inrush current can be reduced as compared with the case where initial charging is not performed, and occurrence of overcharge can be prevented.

[0006]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes an AC power supply, for example, 25000 V in the case of a Shinkansen, 2 denotes a primary winding of a transformer, 3
Is the secondary winding of the transformer which drops to about 1000V, 4 is PW
M converter, 5 a smoothing capacitor, 6 a PWM inverter, 7 an induction motor, 8 an AC contactor, 15 a transformer tertiary winding that generates a lower voltage (for example, 500 V) than the transformer secondary winding 3 , 17 are an AC contactor, 18 is a charging resistor, and 19 is a diode bridge circuit. The tertiary transformer winding 15, the AC contactor 17, the charging resistor 18, and the diode bridge circuit 19 constitute an initial charging circuit. PW
The M converter 4 and the PWM inverter 6 are connected in series with two circuits each composed of a self-extinguishing element such as GTO and a diode connected in anti-parallel to the self-extinguishing element, and have one phase.

With this configuration, during power running of the electric vehicle, a single-phase AC of the AC power supply 1 is supplied to the PWM converter 4 through the AC primary contactor 2 and the secondary winding 3 through the AC contactor 8, The PWM converter 4 converts the single-phase AC on the power supply side to DC through a circuit composed of a diode,
In the M inverter 6, the self-extinguishing element such as GTO is controlled by ignition to convert DC to three-phase AC, supply the three-phase AC to the induction motor 7 to drive the induction motor 7, and the electric vehicle runs. . At the time of regeneration, the induction motor 7 is used as a power source, the three-phase alternating current is converted into a direct current by a PWM inverter 6 via a diode circuit, and the PWM
A self-extinguishing element such as TO is controlled by firing to convert it to single-phase AC, and the power is returned to the AC power supply 1 via the AC contactor 8 and the transformer primary winding 2 and secondary winding 3 to regenerate power. Apply the brake.
Here, during power running and regeneration, the AC contactor 8 is closed and the AC contactor 17 is open.

When the smoothing capacitor 5 is not charged, for example, at the time of starting the electric car or during regenerative braking, the AC contactor 8 is opened, the AC contactor 17 is closed, and the transformer tertiary winding 15 is opened.
, Through the charging resistor 18 and the diode bridge circuit 19, the initial charge is performed to a voltage twice the root of the transformer tertiary winding voltage. For example, if the tertiary winding voltage of the transformer is 500 V (effective value), the initial charging voltage of the smoothing capacitor 5 is 707 V which is twice the route. Then AC contactor 17
Is opened and the AC contactor 8 on the transformer secondary winding 3 side is closed. In this case, the transformer secondary winding voltage is 1000 V (effective value).
Then, the smoothing capacitor 5 is further charged via the diode bridge circuit of the PWM converter 4. At this time, since the smoothing capacitor 5 has already been initially charged,
The inrush current is small, and the smoothing capacitor 5 is charged without overcharging.

Here, after the initial charging by the initial charging circuit 19, the pre-charge voltage and the smoothing capacitor 5 when the AC contactor 8 is closed and the charging is further performed from the secondary winding 3 of the transformer are performed.
FIG. 9 shows the calculation result of the relationship between the inrush current flowing through the capacitor and the charging voltage of the smoothing capacitor. The calculation conditions here were a transformer secondary voltage of 1000 V (effective value), a smoothing capacitor capacity of 24 mF, and a circuit inductance of 1 mH. According to FIG. 9, when the pre-charge voltage becomes 500 V or more, the charge resistance 1
Even if the AC contactor 8 is closed directly without passing through the smoothing capacitor 8, the smoothing capacitor 5 will not be overcharged, and the charging voltage of the smoothing capacitor will be 1414 at twice the root of the secondary voltage 1000V of the transformer.
V. In addition, when the pre-charging is not performed, a rush current of 6000 A flows when the pre-charging is not performed. However, when the pre-charging voltage is set to, for example, 707 V, it can be suppressed to about 2500 A. As described above, in the present embodiment, when the smoothing capacitor 5 is not charged, such as at the time of starting the electric car or during regenerative braking, the inrush current and overcharge of the smoothing capacitor are suppressed, so that the initial charging circuit is a low-voltage device. Since the device can be configured and the current capacity of the diode bridge circuit 19 is small enough to allow the charging current to flow, the size of the device is smaller than that in the case where the initial charging circuit is provided on the transformer secondary winding side of the conventional main circuit. Therefore, the size can be reduced, the cost can be reduced, and the circuit can be simplified.

FIG. 2 shows another embodiment of the present invention. In this embodiment, a three-level PWM converter 22 and a three-level PWM inverter 23 are used instead of the PWM converter 4 and the PWM inverter 6 shown in FIG. At this time, the smoothing capacitor has two capacitors connected in series like 5a and 5b. In this case as well, an initial charging circuit may be connected to both ends of the smoothing capacitors 5a and 5b as in FIG. 1, and the operation of the initial charging circuit is the same as that in FIG.

FIG. 3 shows still another embodiment of the present invention. In this embodiment, the operation of the electric vehicle at the time of power running and at the time of regeneration is the same as that of FIG. 1, and the AC contactor 17 and the charging resistor 1 of FIG.
8. A mixed bridge circuit 16 is used as an initial charging circuit instead of the initial charging circuit including the diode bridge circuit 19. In this case, the initial charging is performed by adjusting the firing angle of the thyristor and gradually generating a voltage by using a circuit (not shown) for adjusting the firing angle of the thyristor of the mixed bridge circuit 16. In the present embodiment, the regenerative braking can be applied to the electric vehicle, and by using the mixed bridge circuit 16 as the initial charging circuit,
Since the AC contactor 17 and the charging resistor 18 can be omitted, the initial charging circuit can be simplified, and the device can be reduced in size and cost.

FIG. 4 shows still another embodiment of the present invention. Although the transformer tertiary winding 15 is used as a power source for the initial charging circuits in FIGS. 1 to 3, this embodiment uses a DC power source such as a battery. In this case, the smoothing capacitor 5 is charged from the battery 20 through the contactor 17 and the charging resistor 18 as shown in FIG. The operation of the electric vehicle during power running and during regeneration is the same as that in FIG. In the present embodiment, since the power supply is direct current, rectifier circuits such as the diode bridge circuit 19 shown in FIG. 1 and the mixed bridge circuit 16 shown in FIG. 3 are not required, and the initial charging circuit can be simplified and the device can be downsized.
The cost can be reduced. Also, regenerative braking can be applied to the electric vehicle.

FIG. 5 shows another embodiment in which the present invention is applied to an actual PWM converter and a PWM inverter electric vehicle. Those having the same functions as those in FIG. 1 are given the same numbers. Reference numeral 21 denotes a transformer. Here, the transformer secondary windings 3a and 3b, the AC contactors 8a and 8b, and the PWM converters 4a and 4b are formed by connecting the transformer secondary winding 3, the AC contactor 8, and the PWM converter 4 in FIG. Although the connection is made, this is due to the relationship of the current capacity of the self-extinguishing element of the PWM converter and does not affect the configuration of the initial charging circuit of the present invention. Although the number of the induction motor 7 is one in FIG. 5, a plurality of induction motors 7 may be connected in parallel. As for the initial charging circuit, the tertiary winding 15 used as a power source for the auxiliary equipment of the electric vehicle is used as a power source, so that the tertiary winding voltage is four.
It is about 00V. Therefore, the AC contactor 17 and the charging resistor 18 used in the initial charging circuit can also use low-voltage devices of about 400V. In the configuration of the initial charging circuit, the voltage is raised from 400 V to 800 V by the transformer 21 through the AC contactor 17 and the charging resistor 18, rectified by the diode bridge 19, and connected to the smoothing capacitor 5. The boosting of the transformer 21 is performed in order to reduce the inrush current when the AC contactor 8 is closed by setting the initial charging voltage of the smoothing capacitor 5 high. With this configuration, when performing initial charging, the AC contactors 8a and 8b are opened, the AC contactor 17 is closed, and the transformer tertiary winding voltage is boosted by the transformer 21 through the charging resistor 18, The current is rectified by the diode bridge 19 and the smoothing capacitor 5 is initially charged. At this time, the initial charging voltage becomes 1131 V by double the route of 800 V.
Thereafter, the AC contactor 17 is opened and the AC contactors 8a and 8b are opened.
Is closed, and the smoothing capacitor 5 is charged from the secondary windings 3a and 3b of the transformer. The inrush current at this time is 1000 A or less from FIG. 9, and there is no overcharging. In the present embodiment, there is no need to provide a separate large-sized power supply including a storage battery and an auxiliary inverter as a power supply for the initial charging circuit as in the related art, and an existing power supply transformer is used. When the battery charge is low, a transformer is provided in the initial charging circuit and the voltage is boosted, so that the initial charging circuit can be simplified, and the device can be downsized and reduced in cost. Charging can be suppressed. It is needless to say that the initial charging circuit shown in FIGS. 3 to 5 can be applied to the power converter including the three-level PWM converter 22 and the three-level PWM inverter 23 shown in FIG.

[0014]

According to the present invention, a tertiary winding is provided on a transformer forming a power supply of a main circuit, and a voltage of the tertiary winding is supplied to a secondary winding of a transformer forming a power supply of the main circuit. Since the voltage is lower than the voltage, the withstand voltage of devices such as an AC contactor and a charging resistor used on the tertiary winding side of the transformer constituting the initial charging circuit can be reduced, and the current capacity of the diode bridge circuit is also initially charged. Since only a small current-flowing device is required, the initial charging circuit can be simplified, and the device can be reduced in size and cost, as compared with the conventional initial charging circuit. In addition, it is not necessary to provide a separate large power supply as a conventional power supply for the initial charging circuit, and an existing power supply transformer is used.
Since the step-up transformer is provided in the initial charging circuit to boost the voltage, the initial charging circuit can be simplified, and the device can be reduced in size and cost, and the rush current and overcharge of the DC smoothing capacitor can be suppressed. .

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a circuit configuration diagram showing another embodiment of the present invention.

FIG. 3 is a circuit diagram showing another embodiment of the present invention.

FIG. 4 is a circuit diagram showing another embodiment of the present invention.

FIG. 5 is a circuit diagram showing another embodiment of the present invention.

FIG. 6 is a diagram showing a configuration of a power converter and an initial charging circuit of a conventional AC electric vehicle.

FIG. 7 is a diagram showing a configuration of a power converter and an initial charging circuit of another conventional AC electric vehicle.

FIG. 8 is a diagram showing a configuration of a power converter and an initial charging circuit of another conventional AC electric vehicle.

FIG. 9 is a diagram showing a relationship between a pre-charging voltage, an inrush current of a smoothing capacitor, and a charging voltage.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 AC power supply 2 Transformer primary winding 3 Transformer secondary winding 4 PWM converter 5 Smoothing capacitor 6 PWM inverter 7 Induction motor 8, 9, 17 AC contactor 10, 18 Charging resistor 11, 16 Mixed bridge circuit 12 Smoothing Reactor 13 Uniform bridge circuit 14 PB converter 15 Transformer tertiary winding 19 Diode bridge circuit 20 DC power supply 21 Transformer 22 3-level PWM converter 23 3-level PWM inverter

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02M 7/48 B60L 9/24

Claims (1)

(57) [Claims] 1. A converter having an AC side connected to a secondary winding of a transformer having a primary winding connected to an AC power supply via a first contactor, and a DC connected to a DC side of the converter. In a power converter for an AC electric vehicle, comprising: a smoothing capacitor; and a DC inverter connected to a DC side of the DC smoothing capacitor, and an AC side connected to an AC motor for driving the electric vehicle. What is claimed is: 1. A PWM converter for converting AC to DC or vice versa by using a plurality of self-extinguishing elements connected in parallel, wherein the PWM converter is provided in the transformer and outputs a lower voltage than the secondary winding. A booster transformer connected to the output of the tertiary winding via a second contactor for boosting the output voltage of the tertiary winding; Smoothing conde A rectifier circuit for charging the electric vehicle, wherein the second contactor is closed at the start of power running of the electric vehicle, and a predetermined value lower than a rectified voltage of the secondary winding rectified by the diode of the PWM converter. A power converter characterized in that the DC smoothing capacitor is initially charged to a voltage of not more than a predetermined voltage, and then the first contactor is closed to precharge the DC smoothing capacitor to a rectified voltage of the secondary winding. .