JP2018131022A - Power conversion device and power conversion method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an overcurrent and enable continuous operation without causing a failure when a series resonant circuit consisting of a capacitor and a transformer is used.SOLUTION: A power conversion device of one embodiment comprises a first power supply circuit, a second power supply circuit, and a control section. The first power supply circuit has an insulation circuit insulating first and second switching circuits and connecting them. The first power supply circuit drives the first switching circuit or the second switching circuit according to variations of a voltage of a DC power transmission path and generates a first voltage. The second power supply circuit adds a second voltage for addition to the first voltage. The control section stops driving of first to third switching circuits when the voltage of the DC power transmission path is greater than a sum of maximum output voltages of the first voltage and the second voltage.SELECTED DRAWING: Figure 1

Description

  Embodiments described herein relate generally to a power conversion device and a power conversion method.

  As one of systems for supplying electric power to overhead wires (feeding wires) of a DC electric railway, there is a DC feeding system. The overhead line (feeding wire) has an increase / decrease in the travel amount of the train and the regenerative energy returned from the train (regenerative vehicle) to the AC power supply system. The load fluctuation is severe, and the voltage of the feeder line also fluctuates greatly.

  In addition, in a DC feeding system, it is common to create a direct current using a diode rectifier. Therefore, in order to return the regenerative energy to the AC power supply system, it is necessary to install a regenerative inverter, and the regenerative current of the regenerative vehicle is reduced. If there is not enough load to absorb around the regenerative vehicle, the regenerative vehicle will fall into regenerative invalidation.

  Therefore, in order to cope with these voltage fluctuations and regenerative expiration, a power storage device such as a storage battery is installed. A power converter is used to control power between the storage battery and the overhead wire.

  As a conventional technique for mutually supplying power between two DC power supply circuits, it is known to connect a power converter such as a DCDC converter between the DC power supply circuits (see, for example, Patent Document 1). ).

  However, since the conventional DC / DC converter is used for a relatively small voltage fluctuation such as a hybrid electric vehicle, for example, it is not applicable to a DC power feeding system having a large voltage fluctuation.

  For overhead wires (wires) with large voltage fluctuations, for example, a power circuit using a series resonance circuit consisting of a capacitor and a transformer is provided in the power converter and insulated from the overhead wires (wires). It is conceivable that the voltage generated by the power supply circuit is added to the voltage of the storage battery, and the added voltage is changed by an inverter connected in series with the storage battery to charge and discharge the storage battery to perform power distribution with the overhead line (wire). .

JP 2012-44801 A

  However, feeders have large voltage fluctuations, and some storage batteries also have large internal resistance.When the feeder voltage rises beyond the amount of change in the addition voltage, the capacitor and transformer that are the power supply for series addition It is conceivable that an overcurrent flows through the resonance circuit of FIG. 5 and the circuit including the inverter at the subsequent stage fails (breaks).

  The problem to be solved by the present invention is that, when a series resonance circuit composed of a capacitor and a transformer is used as a power supply circuit for voltage addition, an overcurrent can be prevented and low loss and low operation that can be continued without failure. It is an object of the present invention to provide a capacity (small) power conversion device and a power conversion method.

  The power conversion device of the embodiment includes a first power supply circuit, a second power supply circuit, and a control unit. The first power supply circuit includes a first switching circuit, a second switching circuit, and an insulating circuit that insulates and connects the first switching circuit and the second switching circuit. The first power supply circuit generates the first voltage by driving the first switching circuit or the second switching circuit according to the fluctuation of the voltage of the DC power transmission line. The second power supply circuit includes a third switching circuit, and adds a second voltage generated by driving the third switching circuit to the first voltage. The control unit controls the first to third switching circuits based on the voltage of the DC transmission line and the first voltage, and adjusts the second voltage to adjust the current between the DC transmission line and the first and second power supply circuits. Control the flow. The control unit stops driving the first to third switching circuits when the voltage of the DC transmission line becomes larger than the sum of the first voltage and the maximum output voltage of the second voltage.

It is a figure which shows the circuit structure of the power converter device of one embodiment. It is a figure which shows a mode that an overcurrent flows into the circuit of a power converter device.

Hereinafter, embodiments will be described in detail with reference to the drawings.
(Embodiment)
FIG. 1 is a diagram illustrating a circuit configuration of a power conversion device 10 according to one embodiment.

  As shown in FIG. 1, a power conversion apparatus 10 according to an embodiment is one of DC feeding systems that mutually supply power to overhead lines of a DC electric railway (hereinafter referred to as “DC feeder 1”). A storage battery 2 as a first storage element, a capacitor 3 as a second storage element connected in parallel with the storage battery 2, a capacitor 7 as a third storage element, and a plurality of power supply circuits 5, 6 and a control unit 9 for controlling the operation of these circuits.

  The capacitor 7 is provided with a voltage detector 7a (for example, PT). The voltage detector 7a detects the voltage of the capacitor 7 and notifies the controller 9 of the voltage. Discharge resistors 11 are connected to both ends of the capacitor 7. The resistor 11 is for consuming the electric power charged in the capacitor 7.

  In addition to the storage battery 2, for example, an energy storage element such as a battery or a capacitor is used as the first storage element.

  A capacitor 4 is connected to the terminals 1a and 1b of the DC feeder 1, and a DC voltage generated between the feeder and the rail is applied in a DC electric railway. The capacitor 4 is provided with a voltage detector 4a (for example, PT). The voltage detector 4a detects the voltage of the capacitor 4 and notifies the controller 9 of the voltage. PT is an abbreviation for “Potential Transformer”.

  The DC feeder 1 is connected to a diode rectifier that outputs DC power obtained from an AC power supply system (not shown) by diode rectification and a regenerative vehicle (regenerative vehicle). A regenerative vehicle is also called a vehicle load.

  The power supply circuit 5 includes two full bridge circuits (a first switching circuit 51 and a second switching circuit 54), and a resonant insulation circuit in which a transformer 52 and a capacitor 53 as a capacitive element are connected in series.

  The two full bridge circuits (the first switching circuit 51 and the second switching circuit 54) are single-phase full bridge circuits, and for example, IGBT elements are used. The elements constituting the bridge circuit are not limited to IGBT elements, and may be MOSFETs, for example.

  The first switching circuit 51 is a circuit that generates power for charging the storage battery 2. The second switching circuit 54 is a circuit that generates power for charging the capacitor 3. The capacitor 3 is connected to the storage battery 2 in parallel. The capacitor 3 is provided with a voltage detector 3a (for example, PT). The voltage detector 3a detects the voltage of the capacitor 3 (storage battery 2) and notifies the controller 9 of the voltage.

  The resonant insulation circuit is a single insulation circuit (insulation coupling circuit) that insulates and connects the first switching circuit 51 and the second switching circuit 54.

  The power supply circuit 5 drives the first switching circuit 51 or the second switching circuit 54 according to the voltage fluctuation of the DC power transmission path 1 to supply power between the storage battery 2 (and the capacitor 3) and the DC power transmission path 1. It is the 1st power supply circuit which generates the 1st voltage for making it circulate.

  In this power supply circuit 5, when the second voltage of the capacitor 7 becomes higher than the first voltage of the capacitor 3, the controller 9 causes the first switching circuit 51 connected to the capacitor 7 to perform switching. 51 is controlled to lower the second voltage.

  On the other hand, when the second voltage of the capacitor 7 becomes lower than the first voltage of the capacitor 3, the controller 9 causes the second switching circuit 54 to switch so that the second switching circuit 54 connected to the capacitor 3 performs switching. 54 is controlled, and power is sent from the storage battery 2 to the capacitor 7 to increase the second voltage.

  The power supply circuit 6 has a function of adding the second voltage applied to the capacitor 7 to the voltage of the storage battery 2. Specifically, the power supply circuit 6 includes a third switching circuit 61 that generates a second voltage to be applied to the capacitor 7. The power supply circuit 6 is a second power supply circuit (series inverter circuit) that adds the second voltage generated by driving the third switching circuit 61 to the voltage of the storage battery 2.

  The control unit 9 controls the first to third switching circuits 51, 54, 61 based on the voltages notified from the voltage detectors 3 a, 4 a, 7 a of each circuit, and adjusts the second voltage to adjust the DC transmission line 1 to control the flow of current between the power supply circuits 5 and 6. The control unit 9 controls the voltage of the capacitor 4 by controlling the current flowing through the reactor 8.

  Specifically, the control unit 9 detects the voltage on the feeder side, the voltage of the storage battery 2 (capacitor 3), and the voltage of the capacitor 7, and drives and controls each switching element based on the detected voltages. That is, each switching element is turned ON / OFF depending on whether or not a gate signal which is an ON control signal of the switching element is output.

  For example, the control unit 9 determines that the voltage of the DC feeder 1 (the detection voltage of the voltage detector 4 a) is the first voltage of the storage battery 2 (capacitor 3) (the detection voltage of the voltage detector 3 a) and the second voltage of the capacitor 7. When it becomes larger than the sum of the maximum output voltage (calculated voltage), the driving of the first to third switching circuits 51, 54, 61 is stopped. The first to third switching circuits 51, 54, 61 may not be completely stopped, but the switching operation may be suppressed.

  When the voltage of the DC feeder 1 becomes smaller than the sum of the first voltage and the maximum output voltage of the second voltage, the controller 9 drives the first to third switching circuits 51, 54, 61. To resume. When the operation of the first to third switching circuits 51, 54, 61 is suppressed, the normal operation is restored.

  In addition, the power converter 10 includes a capacitor 4 and a reactor 8 connected in parallel to the DC feeder 1.

  The reactor 8 is for providing a filter function between the storage battery 2 and the capacitor 3, and has a function of suppressing harmonics flowing through the storage battery 2. This filter function may be constituted by a circuit in addition to a single element such as the reactor 8.

  In addition, for example, a reactor may be inserted between the DC feeder 1 and the capacitor 4 in order to suppress an accident current caused by a short circuit that may occur on the DC feeder 1 side and to have a filter effect.

Hereinafter, operation | movement of the power converter device 10 of this embodiment is demonstrated.
For example, consider a case where the voltage of the DC feeder 1 rises due to the influence of load fluctuation and the like, and the storage battery 2 is charged with the voltage from the DC feeder 1.
In this case, the control unit 9 causes power to flow through the series power supply circuit 5 in accordance with the ratio between the voltage of the difference between the voltage of the storage battery 2 and the voltage of the DC feeder 1 and the voltage of the storage battery 2.

  For example, if the voltage of the storage battery 2 is 500 V and the voltage of the DC feeder 1 is 1000 V, the difference is 500 V. For the power supply circuit 5, 1/2 of the power flowing from the DC feeder 1 is the power supply circuit 5. It flows to the storage battery 2 through a path through the (resonant circuit).

  Here, it is assumed that the output voltage of the power supply circuit 5 is the same in both the upper bridge circuit and the lower bridge circuit.

  In other words. When the voltage of the capacitor 3 is 500V, the output of the upper bridge circuit of the series power supply circuit 5 is the device specification in which 500V is output to the capacitor 7, that is, the transformer ratio in the series power supply circuit 5 is 1: This is the case of 1.

  At this time, the voltage that can be output by the power conversion device can output a voltage of 1000 V, assuming that ideal control without dead time of the inverter circuit of the power supply circuit 6 can be realized.

  However, when the voltage on the DC feeder 1 side exceeds 1000 V, the current control for the reactor 8 cannot be performed.

  At this time, an overcurrent flows through the series power supply circuit 5 in accordance with the voltage ratio between the capacitors 7 and 3 as in the operation described above.

  Normally, the inverter circuit of the power supply circuit 6 has dead time, and assuming that the output voltage is limited to about 98%, the voltage of the storage battery 2 is 500V + the output voltage of the series inverter circuit 6 is 500V × 0.98 = 990V. Only output.

  The output voltage (500 V × 0.98) of the power supply circuit 6 (series inverter circuit) here is the maximum voltage that can be added to the voltage of the storage battery 2.

  When the voltage on the DC feeder 1 side becomes larger than the sum of the voltage on the storage battery 2 side and the maximum voltage that can be added to this voltage (the output voltage of the power supply circuit 6), the current for the reactor 8 cannot be controlled. As a converter, an uncontrolled current flows to the power supply circuit 5, an overcurrent occurs, and an overcurrent flows in the route of A → B → C as shown in FIG. There is a possibility that the semiconductor element (switching element) of the circuit may break down (damage).

  Therefore, in the power conversion device 10 of the present embodiment, the control unit 9 determines a certain condition (described below (the following (the following (the following voltage)) from the relationship between the voltage on the DC feeder 1 side and the voltage (first voltage, second voltage) on the storage battery 2 side. When the condition (1) is satisfied, the first to third switching circuits 51, 54, 61 are gate-blocked.

  Specifically, the control unit 9 detects the voltage of the capacitor 4 detected by the voltage detector 4a, that is, the voltage of the DC feeder 1, and the voltage of the capacitor 3 detected by the voltage detector 3a, that is, the voltage of the storage battery 2. Based on the voltage of the capacitor 7 detected by the voltage detector 7a, the maximum voltage value that can be output by the power converter is determined.

  This value is, for example, ideal when there is no dead time as described above, for example, 1000V, or when the maximum voltage is determined due to the influence of dead time, as described above, if the voltage utilization rate is 98%, 990V, etc. It is such a value.

  Actually, the accuracy of the voltage detectors 3a, 4a, and 7a also becomes a problem. Therefore, considering this, a lower voltage may be set as the maximum voltage value that can be output.

  For example, if the measurement error of the voltage detectors 3a, 4a, and 7a is about 1%, it can be said that 990V × 0.99 = 980.1V is the maximum voltage that can be output.

Further, although the voltage of the capacitor 7 is directly measured by the voltage detector 7a, the voltage of the capacitor 7 may be estimated based on the transformation ratio in the power supply circuit 5 using the resonance circuit.
The following condition (Equation 1) is set in the control unit 9.

Voltage of DC feeder 1> Maximum voltage that can be output by power converter (Equation 1)
When the condition of (Equation 1) is satisfied, the control unit 9 controls the power supply circuits 5 and 6 by the gate signal to stop the switching operation of the power supply circuits 5 and 6.

  Thereby, the overcurrent with respect to the power supply circuit 5 accompanying a voltage rise can be prevented.

  Further, when the condition of (Expression 1) is not satisfied, the control unit 9 restarts the switching of the switching circuit, so that the operation can be continued.

  Such a phenomenon can be assumed in a feeding system for DC railway. Specifically, the DC feeder 1 is a train line, and the voltage of the train line increases with the regeneration of the train. If the voltage rises in the normal range, the condition of (Equation 1) is not satisfied, and the regenerative power can be charged in the storage battery 2.

  However, it can be assumed that an overvoltage is generated on the train line due to some abnormality, such as when there is a trouble in the regeneration control system of the train. At this time, it is conceivable that the overcurrent flows into the power supply circuit 5 as described above.

  Although there is a concept that the maximum voltage that can be output as a device should be designed high, in this case, it is necessary to increase the breakdown voltage of the elements of the switching circuits of the power supply circuits 5 and 6 as the voltage of the capacitor 7 increases. There is also an increase in switching loss. An increase in switching loss is not good because it directly leads to an increase in the volume of the cooler and an increase in the volume of the power converter.

  However, in this embodiment, it is possible to configure a power converter using low-voltage switching elements, and it is possible to configure a power converter with low loss, low capacity, and low cost.

  Thus, according to this embodiment, when the voltage of the DC feeder 1 becomes larger than the sum of the first voltage and the maximum output voltage of the second voltage, the control unit 9 performs the first to third switching operations. Since the driving of the circuits 51, 54, 61 is stopped and the driving is resumed when the circuit becomes smaller, the power supply circuit 5 includes the capacitor 53 and the power supply circuit 5 in mutual power supply between the DC feeder 1 and the storage battery 2. When using a series resonant circuit composed of a transformer 52, it prevents overcurrent generated in the power supply circuit 5 due to excessive voltage rise on the DC feeder 1 side, and can be operated continuously without failure, low loss and low capacity The (small) and low-cost power conversion device 10 can be provided.

  Although the embodiment of the present invention has been described, this embodiment is presented as an example and is not intended to limit the scope of the invention. The novel embodiment can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. This embodiment and its modifications are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  The components of the control unit 9 shown in the above embodiment may be realized by a program installed in a storage such as a hard disk device of a computer, and the program is stored in a computer-readable electronic medium: electronic media. The function of the present invention may be realized by the computer by causing the computer to read the program from the electronic medium. Examples of the electronic medium include a recording medium such as a CD-ROM, flash memory, and removable media. Furthermore, the present invention may be realized by distributing and storing components in different computers connected via a network and communicating between computers in which the components are functioning.

  DESCRIPTION OF SYMBOLS 1 ... DC power transmission path, 1a, 1b ... terminal, 2 ... Storage battery, 3, 4, 7 ... Capacitor, 3a, 4a, 7a ... Voltage detector, 5, 6 ... Power supply circuit, 8 ... Reactor, 9 ... Control part, DESCRIPTION OF SYMBOLS 10 ... Power converter, 11 ... Resistor, 51 ... 1st switching circuit, 52 ... Transformer, 53 ... Capacitor, 54 ... 2nd switching circuit, 61 ... 3rd switching circuit.

Claims (5)

A first switching circuit; a second switching circuit; and an insulating circuit that insulates and connects the first switching circuit and the second switching circuit. A first power supply circuit for driving the switching circuit or the second switching circuit to generate a first voltage;
A second power supply circuit having a third switching circuit and adding a second voltage generated by driving the third switching circuit to the first voltage;
Based on the voltage of the DC power transmission line and the first voltage, the first to third switching circuits are controlled to adjust the second voltage, and between the DC power transmission path and the first and second power supply circuits. And a control unit for controlling the current flow of
The controller is
A power converter that stops a switching operation of the first to third switching circuits when a voltage of the DC transmission line becomes larger than a sum of a maximum output voltage of the first voltage and the second voltage. A first switching circuit that generates power to charge the first power storage element; a second switching circuit that generates power to charge a second power storage element connected in parallel to the first power storage element; and the first switching circuit. And an insulating circuit that insulates and connects the second switching circuit and a third power storage element, and drives the first switching circuit or the second switching circuit in accordance with fluctuations in the voltage of the DC power transmission path. A first power supply circuit for generating a first voltage for distributing power between the first power storage element, the second power storage element, and the DC power transmission path;
A third switching circuit for generating a second voltage to be applied to the third power storage element; and adding the second voltage generated by driving the third switching circuit to the voltage of the first power storage element 2 Two power supply circuits;
Based on the voltage of the DC power transmission line and the first voltage, the first to third switching circuits are controlled to adjust the second voltage, and between the DC power transmission path and the first and second power supply circuits. And a control unit for controlling the current flow of
The controller is
A power converter that stops a switching operation of the first to third switching circuits when a voltage of the DC transmission line becomes larger than a sum of a maximum output voltage of the first voltage and the second voltage. The controller is
2. The power converter according to claim 1, wherein a second voltage that can be added to the first power supply circuit is obtained from a voltage of the DC transmission line, a transformation ratio, and a dead time when the third switching circuit performs a switching operation. The controller is
The first voltage of the first power supply circuit becomes larger than the sum of the voltage of the second power supply circuit and the maximum voltage that can be added thereto, and after the switching of the power converter is stopped, the first voltage and the first voltage are 3. The switching operation of the first to third switching circuits is resumed when a voltage summed with the maximum output voltage of the second voltage that can be added becomes larger than the first voltage. Or a power conversion device. A first switching circuit; a second switching circuit; and an insulating circuit that insulates and connects the first switching circuit and the second switching circuit. A first power supply circuit that generates a first voltage by driving the switching circuit or the second switching circuit; and a third switching circuit, wherein the second voltage generated by driving the third switching circuit is the first voltage. A second power supply circuit for adding to the voltage; a voltage of the DC transmission line; and controlling the first to third switching circuits based on the first voltage to adjust the second voltage to adjust the DC transmission line and the In the power conversion method in the power conversion device including a control unit that controls the flow of current between the first and second power supply circuits,
The controller is
A power conversion method for stopping a switching operation of the first to third switching circuits when a voltage of the DC transmission line becomes larger than a sum of the first voltage and the maximum output voltage of the second voltage.

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