JP6555635B2 - Power converter - Google Patents

Description

  The present invention relates to a high-frequency insulation type power conversion device capable of shortening start-up time and suppressing overcurrent at start-up.

  Conventionally, in a commercial insulation type power conversion device, for example, an auxiliary power supply device for a railway vehicle, DC power supplied from an overhead wire or a third rail is converted into AC power by an inverter, and an LC filter composed of a reactor and a capacitor After being insulated by an insulating transformer, it is converted into three-phase AC power or single-phase AC power of 50/60 [Hz] required for in-vehicle equipment (air conditioning equipment, display device, etc.).

FIG. 7 shows the prior art of this type of auxiliary power supply, which is roughly divided into a three-phase inverter 7, an LC filter 8, and a commercial insulation transformer 9 of 50/60 [Hz]. It is constituted by. In FIG. 7, 1a is a pantograph, 1b is an input switch, 1c is an initial charging resistor, 1d is a short-circuit switch, 1e is an input reactor, 1f is an input capacitor, 1g is a wheel (rail), and 1h is a diode.
In this prior art, since the insulating transformer 9 is excited by an AC voltage of 50/60 [Hz], the required cross-sectional area of the iron core becomes very large, and the mass and volume of the insulating transformer 9 increase. There is.

  In recent years, for the purpose of reducing the size and weight of an insulating transformer, high-frequency insulating transformers are also applied to relatively large-capacity power converters such as industrial power converters and auxiliary power supplies for railway vehicles. In a high-frequency insulation transformer, it is necessary to convert the input to high-frequency alternating current. Therefore, direct current is converted into high-frequency alternating current by an inverter and input to the high-frequency insulation transformer, and the alternating current output is rectified and smoothed by a rectifier circuit and a smoothing capacitor again. A DC-DC converter circuit for converting to DC is generally used.

Usually, a transformer has a feature that it can be reduced in size as the frequency is increased. Therefore, in order to further reduce the size and weight of the transformer, it is necessary to switch the semiconductor device used in the inverter at a frequency as high as possible. is there.
However, since the loss generated from the semiconductor device increases in proportion to the switching frequency, the upper limit value of the switching frequency is also restricted by the performance of the radiator of the apparatus.

  Under such circumstances, as a means for increasing the switching frequency while reducing the loss generated in the semiconductor device, the turn-on operation is performed after the voltage applied to the semiconductor device becomes zero, or the semiconductor device flows to the semiconductor device. A current resonance type DC-DC converter that performs a turn-off operation after the current becomes zero is known. If this current resonance type DC-DC converter is used, the loss generated in the semiconductor device can be suppressed while increasing the switching frequency, and the insulation transformer can be reduced in size and weight.

For example, as described in Patent Document 1 to be described later, control of the output voltage using a conventional current resonance type DC-DC converter is performed by controlling the switching frequency of the semiconductor switching element. For example, when the output voltage is lower than the target value, the switching frequency is controlled to be lower than the resonance frequency so that the output voltage follows the target value. Conversely, when the output voltage is higher than the target value, the switching frequency is substantially equal to the resonance frequency. It is possible to make the output voltage follow the target value by making it equal or higher than the resonance frequency.
Moreover, when starting from the state where the output voltage is 0 [V], the overcurrent accompanying charging of the output capacitor of the converter can be suppressed by gradually decreasing the switching frequency from a high frequency.

  Further, in Patent Document 2 to be described later, when the converter is switched at a high frequency when the residual voltage remains in the output capacitor of the resonant DC-DC converter, power cannot be transmitted to the output side. A current resonance type DC-DC converter that detects and determines an appropriate start-up frequency based on the characteristics of output voltage versus switching frequency and drives a low-breakdown-voltage switching element by soft start is disclosed.

  Non-Patent Document 1 below describes a circuit using a step-up chopper at the input of a resonant DC-DC converter. In the step-up chopper, the input voltage of the converter can be controlled to be constant even if the input voltage fluctuates, and the output voltage can be maintained at a constant value without changing the switching frequency of the converter.

JP 2006-204048 A (paragraphs [0026] to [0037], FIG. 1 etc.) JP 2012-29436 A (paragraphs [0051] to [0065], FIG. 1, FIG. 4, FIG. 5, etc.)

J Weber, et al., “Galvanic separated high frequency power c onverter for auxiliary railway supply”, EPE2003.

  In the control method of the current resonance type DC-DC converter shown in Patent Documents 1 and 2, when the input voltage becomes high, the output voltage is kept constant by controlling the switching frequency of the converter to a frequency higher than the resonance frequency. However, there is a problem that the switching loss increases as a result of the increase of the turn-off current of the switching element. Furthermore, in order to increase the switching frequency, an expensive control device having a high computing capacity is required, which increases the cost.

  The circuit disclosed in Non-Patent Document 1 includes a step-up chopper that stabilizes the voltage in the previous stage of the resonant DC-DC converter. Therefore, even if the switching frequency of the converter is constant regardless of the fluctuation of the input voltage, the circuit is disclosed. It is possible to control the output voltage according to the target value. However, according to this circuit, circuit elements such as a step-up chopper increase as compared with a commercial insulation type power converter as shown in FIG. 7, so that if no measures are taken, it is required on the load side. There was a problem that the start-up time until power was output was long.

  SUMMARY OF THE INVENTION Accordingly, a problem to be solved by the present invention is to provide a power converter that shortens the startup time of the entire device including the resonant DC-DC converter and that can suppress the inflow of overcurrent to the output capacitor during startup. It is in.

In order to solve the above-mentioned problem, the invention according to claim 1 includes a chopper that converts a DC voltage into a predetermined DC voltage;
Resonance type that converts the DC output voltage of the chopper into a high-frequency AC voltage through an inverter unit, a resonance circuit, and an insulation transformer, and converts the AC voltage into a predetermined DC voltage by rectification and smoothing by a rectifier circuit and an output capacitor. A DC-DC converter ,
A voltage detector for detecting output voltages of the chopper and the resonant DC-DC converter, respectively, and the chopper and the resonant DC- detected by the voltage detector when the resonant DC-DC converter is activated; based on the DC converter output voltage, the line power sale power converter soft-start while controlling the on / off time of the semiconductor switching elements constituting the inverter,
The semiconductor switching element constituting the inverter unit when the output voltage of the resonant DC-DC converter is larger than a first output voltage determined by the output voltage of the chopper and the switching frequency of the resonant DC-DC converter When the output voltage of the resonant DC-DC converter is smaller than the first output voltage, the on-time of the semiconductor switching element is changed from zero to the short-circuit prevention time. The maximum on-time except for is extended .

The invention according to claim 2 is the power converter according to claim 1, wherein the second power converter that converts the DC voltage of the output capacitor into a predetermined DC voltage or AC voltage is the resonant DC-DC. It starts after the converter starts up .

The invention according to claim 3 is a chopper for converting a DC voltage into a predetermined DC voltage;
Resonance type that converts the DC output voltage of the chopper into a high-frequency AC voltage through an inverter unit, a resonance circuit, and an insulation transformer, and converts the AC voltage into a predetermined DC voltage by rectification and smoothing by a rectifier circuit and an output capacitor. A DC-DC converter,
A voltage detector for detecting output voltages of the chopper and the resonant DC-DC converter, respectively, and the chopper and the resonant DC- detected by the voltage detector when the resonant DC-DC converter is activated; In the power conversion device that performs soft start based on the output voltage of the DC converter while controlling the on / off time of the semiconductor switching element constituting the inverter unit ,
The on-time of the semiconductor switching element constituting the inverter unit is increased from zero to the maximum on-time excluding the short-circuit prevention time, and the resonant DC-DC converter is started simultaneously with the chopper .

According to a fourth aspect of the present invention, in the power conversion device according to any one of the first to third aspects, the switching frequency of the inverter unit is controlled to a constant value equal to or lower than the resonant frequency of the resonant circuit. .

  According to the present invention, while controlling the on / off time of the switching element of the inverter unit constituting the converter based on the output voltage of the chopper and the resonant DC-DC converter constituting the high-frequency insulation type power converter. By starting up, it is possible to shorten the start-up time of the entire apparatus and suppress the inflow of overcurrent to the output capacitor.

It is a circuit diagram of the power converter device concerning the 1st example of the present invention. It is a circuit diagram of the power converter device which concerns on 2nd Example of this invention. It is a circuit diagram of the power converter device which concerns on 3rd Example of this invention. It is a circuit diagram of the power converter device which concerns on 4th Example of this invention. It is a circuit diagram of the power converter device which concerns on 5th Example of this invention. It is a circuit diagram of the power converter device which concerns on 6th Example of this invention. It is a circuit diagram which shows the auxiliary power supply apparatus of the conventional commercial insulation system. It is a wave form diagram showing operation of a resonance type DC-DC converter. It is a wave form diagram which shows operation | movement of a resonance type DC-DC converter. It is a wave form diagram which shows operation | movement of a resonance type DC-DC converter. 2 is a timing chart showing a conventional start-up method for the circuit of FIG. 1 and a start-up method in the present invention. It is a timing chart which shows the conventional starting system for the circuit of FIG. 2, and the starting system in this invention. It is a timing chart which shows operation | movement in the case of restarting in the state in which a residual voltage exists in an output capacitor. It is a timing chart which shows operation | movement in the case of restarting in the state in which a residual voltage exists in an output capacitor. It is a wave form diagram which shows the drive signal of the switching element which comprises a resonance type DC-DC converter, a resonance current, and the exciting current of an insulation transformer.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, the following description and the content of each figure show one Embodiment to the last, and do not limit the technical scope of this invention at all.

  First, FIG. 1 is a circuit diagram of a power converter according to a first embodiment of the present invention. In this power converter, a general step-up chopper is used as a chopper provided in the front stage of a resonant DC-DC converter. Used. In FIG. 1, the same parts as those in FIG. 7 are denoted by the same reference numerals, and the following description will focus on the parts different from those in FIG.

In FIG. 1, reference numeral 110 denotes a step-up chopper, which is a series circuit of a reactor 2a and a switching element 2b connected to both ends of an input capacitor 1f, and a series of a diode 2c and a smoothing capacitor 2d connected to both ends of the switching element 2b. And a circuit.
Reference numeral 200 denotes a resonant DC-DC converter (hereinafter also simply referred to as a resonant converter) connected to the output side of the boost chopper 110. The DC output voltage of the boost chopper 110 is converted to an AC voltage by high-frequency switching of the switching elements 3a to 3d. An inverter unit 3 for converting to a resonance circuit, a resonance capacitor 4a and a resonance reactor 4b that constitute a resonance circuit, an insulating transformer 4c, diodes 5a to 5d that constitute a rectifier circuit, and an output capacitor 6. Here, the resonant reactor 4b may be substituted by a leakage inductance component of the insulating transformer 4c.

  Both ends of the output capacitor 6 are connected to a three-phase inverter 7 and an LC filter 8 as a second power converter. The second power converter is not limited to the three-phase inverter 7 and may be a DC-DC converter that converts the DC output voltage of the resonant converter 200 into a predetermined DC voltage.

In FIG. 1, V _fc is the voltage of the input capacitor 1 f, V _ch is the output voltage of the boost chopper 110, V _io is the output voltage of the resonant converter 200 (rectifier circuit), and V _inv is the output voltage of the three-phase inverter 7. is there. Although not shown, this power converter is provided with a voltage detector for detecting each of the voltages V _fc , V _ch , V _io , and V _io .

Next, a conventional starting method and a starting method according to the present invention for the circuit of FIG. 1 will be described with reference to FIG.
11, in the conventional starting system, and receiving via the pantograph 1a from the overhead line at time t _0, by placing the input switch 1b, an input capacitor 1f is charged through the initial charging resistor 1c and the input reactor 1e At the same time, the smoothing capacitor 2d provided at the output of the step-up chopper 110 is also charged via the reactor 2a and the diode 2c. As a result, the voltages V _fc and V _ch rise almost in the same manner.

Initial charging is completed at time t ₁ in FIG. 11, the initial charging resistor 1c is shorted by the short-circuit switch 1d. Thereafter, the step-up chopper 110 soft start, outputs a voltage target value as by completing a soft start at time t _2.
Here, as is well known, soft start is a chopper that suppresses inrush current by reducing the duty ratio indicating the ON / OFF ratio of the switching element at the start of startup and controlling the duty ratio as time elapses. Or to start the converter.

Maximum resonance converter 200, the time t ₂ after, excluding switching elements 3a of the inverter unit 3, 3d pairs, and the switching element 3b, and the on-time of 3c pair the dead time from 0% alternately in the switching cycle on-time gradually increased until (see Figure 15), complete the soft-start at time t _3.
When the load is connected to the subsequent stage of the output capacitor 6, this completes the start-up, but when the three-phase inverter 7 is connected as shown in FIG. 1, the output voltage V _io of the resonant converter 200 is the time t ₃ from the three-phase inverter 7 having established by soft start, the output voltage of the time t ₄ to the three-phase inverter 7 is to complete the activation of the entire power conversion device is constant.

On the other hand, in the start-up method according to the present invention (the overhead line voltage, the input capacitor voltage V _fc , and the boost chopper output voltage V _ch are the same as those in the conventional start-up method), the boost chopper 110 starts a soft start in FIG. resonant converter 200 also performs a soft start at the same time at the time _{t 1,} to complete the soft-start at the time _{t 2.} This soft start operation of the resonant converter 200 detects the output voltage V _ch of the boost chopper 110 and the output voltage V _io of the resonant converter 200, and based on these detection values, the switching elements 3a, 3b, 3c of the inverter unit 3 are detected. , 3d is controlled by controlling on / off.

Thereby, in both cases where a load is connected to the subsequent stage of the output capacitor 6 and a second power conversion device such as a three-phase inverter 7 is connected, the resonant converter 200 is compared with the conventional startup method. The start-up time of the entire power conversion device is shortened by the amount that the start-up time is increased. Also, the resonant converter 200, the output voltage is low in the step-up chopper 110, the time _{t 1} after the switching elements 3a, 3d pair, and the switching element 3b, gradually extending the maximum on-time of 3c pairs Thus, the peak value of the charging current of the output capacitor 6 can be suppressed as compared with the conventional startup method.

FIG. 2 is a circuit diagram of a power conversion apparatus according to the second embodiment of the present invention. In this power converter, a step-down chopper is used as a chopper. 2, the same parts as those in FIG. 1 are denoted by the same reference numerals, and the following description will focus on parts different from those in FIG. 1.
The step-down chopper 120 of FIG. 2 includes a series circuit of a switching element 2b and a diode 2c connected to both ends of the input capacitor 1f, and a series circuit of a reactor 2a and a smoothing capacitor 2d connected to both ends of the diode 2c. It is configured.

Next, a conventional starting method and a starting method according to the present invention for the circuit of FIG. 2 will be described with reference to FIG. 12, the overhead line voltage, the input capacitor voltage V _fc , and the output voltage V _ch of the step-down chopper 120 are the same as those in the conventional starting method.

In the circuit of FIG. 2, the capacitor 2d on the output side of the step-down chopper 120 is charged by the switching element 2b when charging the input capacitor 1f via the initial charging resistor 1c, as compared with the circuit using the step-up chopper 110 of FIG. Since the route is interrupted, it is not charged. For this reason, the resonant converter 200 can soft-start simultaneously with the step-down chopper 120 from the state where the output voltage of the step-down chopper 120 is 0 [V] at time t ₁ , so that the peak value of the charging current of the output capacitor 6 is suppressed. It is effective.
In addition, according to FIG. 12, as in FIG. 11, the startup time of the entire power converter can be shortened by the amount that the startup time of the resonant converter 200 is earlier than in the conventional startup method.

  Here, the starting method shown in FIGS. 11 and 12 is a case where the initial voltage value (residual voltage) of the output capacitor 6 is 0 [V]. Accordingly, FIGS. 13 and 14 show operations when the output capacitor 6 is started up in a state where there is a residual voltage due to a temporary failure of the power converter or the like.

First, FIG. 13 shows a case where a second power converter such as a three-phase inverter 7 is connected to the subsequent stage of the output capacitor 6 of the resonant converter 200. In both the conventional method and the present invention, the three-phase inverter 7 in the subsequent stage is stopped until the time when the start of the resonant converter 200 is completed.
If the residual voltage of the output capacitor 6 of the resonant converter 200 is higher than the output voltage determined by the residual voltage of the smoothing capacitor 2d of the chopper 110 or 120 and the switching frequency of the inverter unit 3 of the resonant converter 200, before starting the chopper to the switching elements of the resonant converter 200 activates the maximum on-time except for the dead time, then the chopper is soft start at time t _1.

When the soft start of the chopper is completed at time t _{2 and} an output voltage according to the target value is applied to the resonant converter 200, the output voltage of the resonant converter 200 also becomes the target value, and then the three-phases in the subsequent stage of the output capacitor 6. The inverter 7 performs a soft start.
Even if the switching element of the inverter unit 3 of the resonant converter 200 is instantly activated with the maximum on-time, the secondary output voltage of the isolation transformer 4c is smaller than the residual voltage of the output capacitor 6, and therefore rectification composed of diodes 5a to 5d. The circuit is not conducted, and only the current corresponding to the exciting current flows on the primary side of the insulating transformer 4c. Further, subsequent three-phase inverter 7 of the output capacitor 6 by starting a soft start to time t _2, the the load is gradually increased, there is no possibility that current in the resonant converter 200 is vibrated.

FIG. 14 is a timing chart in the case where the output capacitor 6 is started in a state where there is a residual voltage, as in FIG. 13, but a load is directly connected to the output side of the resonant converter 200, and the residual of the output capacitor 6 The voltage is lower than the output voltage level determined by the residual voltage of the smoothing capacitor 2d of the chopper and the switching frequency of the inverter unit 3 of the resonant converter 200.
In this case, at the same time the resonant converter 200 and the soft start of the chopper performs a soft start at time t _2, the while suppressing the peak value of the charging current of the output capacitor 6, shorten the power converter activation of the entire time.
As apparent from FIGS. 13 and 14, according to the present invention, even when there is a residual voltage in the output capacitor 6, the start-up time can be shortened compared to the conventional case.

In the circuit shown in FIG. 1 or FIG. 2, the switching frequency of the inverter unit 3 of the resonant converter 200 is a constant value, and this switching frequency is equal to the resonant frequency of the resonant circuit (the resonant capacitor 4a and the resonant reactor 4b) Alternatively, a value lower than the resonance frequency is set.
Here, FIGS. 8 to 10 respectively show the resonance current, the exciting current of the insulating transformer, the switching elements 3a to 3d, and the diodes 5a to 5a when the switching frequency of the inverter unit 3 is lower than, equal to, or higher than the resonance frequency. It is a wave form diagram of the electric current which flows through 5d, and the gate signal of switching element 3a-3d.

When the switching frequency of the inverter unit 3 is lower than the resonance frequency or equal to the resonance frequency, the switching elements 3a to 3d are turned off by the weak excitation current of the insulating transformer 4c, whereas the switching frequency of the resonance converter 200 is When the resonance frequency is higher than the resonance frequency, the switching elements 3a to 3d are turned off in the middle of the resonance period, so that the turn-off current increases and consequently the switching loss increases.
In the present invention, as shown in FIG. 8 or FIG. 9, by making the switching frequency of the inverter unit 3 lower than or equal to the resonance frequency, the turn-off current becomes smaller than that in FIG. Reduction is possible.

3 to 6 are circuit diagrams of power converters according to third to sixth embodiments of the present invention.
FIG. 3 shows an embodiment in which a three-level boost chopper 130 is used as a chopper. 2b1 is a switching element, 2c1 is a diode, and 2d1 is a smoothing capacitor. FIG. 4 shows an embodiment using a three-level step-down chopper 140 as a chopper, and 1f1 is an input capacitor.
5 shows an embodiment in which a half-bridge type inverter unit 3A composed of smoothing capacitors 2d and 2d1 and switching elements 3a and 3c is used as an input unit of the resonant converter 210. FIG. In this embodiment, a half-bridge type inverter unit 3A is used for the unit, and a synchronous rectifier circuit including switching elements 5a1, 5b1, 5c1, and 5d1 is used for the output unit.

  In the circuits shown in FIGS. 3 to 6 as well, by applying the present invention, it is possible to shorten the start-up time of the entire device and suppress the peak value of the charging current of the output capacitor 6.

  INDUSTRIAL APPLICABILITY The present invention can be used for various high-frequency insulation type power converters in which a chopper and a resonant DC-DC converter are connected in series.

1a: Pantograph 1b: Input switch 1c: Initial charging resistor 1d: Short-circuit switch 1e: Input reactor 1f, 1f ₁ : Input capacitor 2a: Reactor 2b, 2b1: Switching element 2c, 2c1: Diode 2d, 2d1: Smoothing capacitor 3, 3A : Inverter units 3a, 3b, 3c, 3d: switching element 4a: resonant capacitor 4b: resonant reactor 4c: isolation transformers 5a, 5b, 5c, 5d: diodes 5a1, 5b1, 5c1, 5d1: switching element 6: output capacitor 7 : Three-phase inverter 8: LC filter 110: step-up chopper 120: step-down chopper 130: three-level step-up chopper 140: three-level step-down chopper 200, 210, 220: resonance type DC-DC converter (resonance type converter)

Claims (4)

A chopper for converting a DC voltage into a predetermined DC voltage;
Resonance type that converts the DC output voltage of the chopper into a high-frequency AC voltage through an inverter unit, a resonance circuit, and an insulation transformer, and converts the AC voltage into a predetermined DC voltage by rectification and smoothing by a rectifier circuit and an output capacitor. A DC-DC converter ,
A voltage detector for detecting output voltages of the chopper and the resonant DC-DC converter, respectively, and the chopper and the resonant DC- detected by the voltage detector when the resonant DC-DC converter is activated; based on the DC converter output voltage, the line power sale power converter soft-start while controlling the on / off time of the semiconductor switching elements constituting the inverter,
The semiconductor switching element constituting the inverter unit when the output voltage of the resonant DC-DC converter is larger than a first output voltage determined by the output voltage of the chopper and the switching frequency of the resonant DC-DC converter When the output voltage of the resonant DC-DC converter is smaller than the first output voltage, the on-time of the semiconductor switching element is changed from zero to the short-circuit prevention time. A power converter characterized by extending the maximum on time excluding . In the power converter device according to claim 1,
A power converter that starts a second power converter that converts a DC voltage of the output capacitor into a predetermined DC voltage or AC voltage after the startup of the resonant DC-DC converter . A chopper for converting a DC voltage into a predetermined DC voltage;
Resonance type that converts the DC output voltage of the chopper into a high-frequency AC voltage through an inverter unit, a resonance circuit, and an insulation transformer, and converts the AC voltage into a predetermined DC voltage by rectification and smoothing by a rectifier circuit and an output capacitor. A DC-DC converter,
A voltage detector for detecting output voltages of the chopper and the resonant DC-DC converter, respectively, and the chopper and the resonant DC- detected by the voltage detector when the resonant DC-DC converter is activated; In the power conversion device that performs soft start based on the output voltage of the DC converter while controlling the on / off time of the semiconductor switching element constituting the inverter unit ,
Longer on-time of the semiconductor switching elements constituting the inverter section until the maximum on-time except for the dead time from zero, and power, characterized in that activating the resonant DC-DC converter to the chopper and simultaneously Conversion device. In the power converter device given in any 1 paragraph of Claims 1-3,
The power converter according to claim 1, wherein the switching frequency of the inverter unit is controlled to a constant value equal to or lower than the resonance frequency of the resonance circuit .

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