JP6833546B2 - Power converter and power conversion method - Google Patents

Description

Embodiments of the present invention relate to power conversion devices and power conversion methods.

There is a DC feeder system as one of the systems that supply electric power to the overhead wire (feeder) of a DC electric railway. The overhead wire (key wire) has a large increase / decrease in the amount of travel of the train and the regenerative energy returned from the train (regenerative vehicle) to the AC power supply system, and the load fluctuates sharply.

In addition, in a DC power supply system, it is common to generate DC using a diode rectifier, so in order to return regenerative energy to the AC power supply system, it is necessary to install a regenerative inverter, and the regenerative current of the regenerative vehicle must be installed. If there is not enough load around the regenerative vehicle to absorb it, the regenerative vehicle will expire.

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 electric power between two DC power supply circuits, it is known that a power conversion device such as a DCDC converter is inserted and connected between the two DC power supply circuits (see, for example, Patent Document 1). ).

However, since the conventional DCDC converter is used for a hybrid electric vehicle having a relatively small voltage fluctuation, it cannot be applied to a DC feeder system having a large voltage fluctuation.

For overhead wires (wires) with large voltage fluctuations, for example, a power supply circuit using a series resonance circuit consisting of a capacitor and a transformer is provided in the power converter to insulate it from the overhead wires (wires), and then the power converter 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 the inverter connected in series with the storage battery to charge and discharge the storage battery to perform power distribution with the overhead wire. ..

Japanese Unexamined Patent Publication No. 2012-44801

However, in addition to the large voltage fluctuation of the wire, some storage batteries also have a large internal resistance, and when the voltage of the wire rises beyond the amount of change in the added voltage, the capacitor and transformer, which are the power supplies for series addition, It is conceivable that an overcurrent flows through the resonance circuit of the above and the circuit including the inverter in the subsequent stage fails (damages).

The problem to be solved by the present invention is that when a series resonant circuit consisting of a capacitor and a transformer is used as a power supply circuit for voltage addition, overcurrent is prevented and continuous operation is possible without failure. The purpose is 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 drives the first switching circuit or the second switching circuit according to the fluctuation of the voltage of the DC transmission line to generate the first voltage. The second power supply circuit has 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 to adjust the second voltage to obtain 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 maximum output voltage of the first voltage and the second voltage.

It is a figure which shows the circuit structure of the power conversion apparatus of one Embodiment. It is a figure which shows the state that an overcurrent flows in the circuit of a power conversion apparatus.

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

As shown in FIG. 1, the power conversion device 10 of the embodiment is one of the DC power supply systems that mutually supply power to and from the overhead wire of a DC electric railway (hereinafter referred to as "DC power supply 1"). Two devices, 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. It has 6 and a control unit 9 that controls 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 control unit 9. 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.

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

A capacitor 4 is connected to terminals 1a and 1b of the DC electric wire 1, and a DC voltage generated between the electric wire and the rail is applied in the case of 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 control unit 9. PT is an abbreviation for instrument transformer (Potential Transformer).

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

The power supply circuit 5 has two full bridge circuits (a first switching circuit 51 and a second switching circuit 54) and a resonance type insulation circuit in which a transformer 52 and a capacitor 53 as a capacitance element are connected in series.

The two full-bridge circuits (first switching circuit 51 and second switching circuit 54) are single-phase full-bridge circuits, and for example, an IGBT element or the like is used. The element constituting the bridge circuit is not limited to the IGBT element, and may be, for example, a MOSFET.

The first switching circuit 51 is a circuit that generates electric power to charge the storage battery 2. The second switching circuit 54 is a circuit that generates electric power to charge the capacitor 3. The capacitor 3 is connected in parallel to the storage battery 2. 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 control unit 9.

The resonance type insulation circuit is one 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 fluctuation of the voltage of the DC transmission line 1 to transfer electric power between the storage battery 2 (and the capacitor 3) and the DC transmission line 1. This is a first power supply circuit that generates a first voltage for distribution.

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 control unit 9 makes a first switching circuit so that the first switching circuit 51 connected to the capacitor 7 switches. The operation of controlling 51 to lower the second voltage is performed.

On the contrary, when the second voltage of the capacitor 7 becomes lower than the first voltage of the capacitor 3, the control unit 9 sets the second switching circuit so that the second switching circuit 54 connected to the capacitor 3 switches. 54 is controlled, electric power is sent from the storage battery 2 to the capacitor 7, and an operation of increasing the second voltage is performed.

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 has a third switching circuit 61 that generates a second voltage applied to the capacitor 7. The power supply circuit 6 is a second power supply circuit (series inverter circuit) that adds a 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 3a, 4a, and 7a of each circuit to adjust the second voltage and adjust the DC transmission line. It controls the flow of current between 1 and 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 wire 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 voltage. 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, in the control unit 9, the voltage of the DC wire 1 (detection voltage of the voltage detector 4a) is the first voltage of the storage battery 2 (condenser 3) (detection voltage of the voltage detector 3a) and the second voltage of the capacitor 7. When it becomes larger than the sum with 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, and 61 may not be completely stopped, but the switching operation may be suppressed.

Then, when the voltage of the DC electric wire 1 becomes smaller than the sum of the maximum output voltage of the first voltage and the second voltage, the control unit 9 drives the first to third switching circuits 51, 54, 61. To resume. If the operations of the first to third switching circuits 51, 54, and 61 are suppressed, the normal operation is restored.

In addition, the power conversion device 10 has a capacitor 4, a reactor 8 and the like connected in parallel to the DC electric wire 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 configured by a circuit as well as a single element such as the reactor 8.

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

Hereinafter, the operation of the power conversion device 10 of this embodiment will be described.
For example, consider a case where the voltage of the DC wire 1 rises due to the influence of load fluctuations and the voltage from the DC wire 1 is charged to the storage battery 2.
In this case, the control unit 9 causes electric power to flow through the series power supply circuit 5 according to the ratio between the voltage of the difference between the voltage of the storage battery 2 and the voltage of the DC electric wire 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 wire 1 is 1000 V, the difference is 500 V. For the power supply circuit 5, 1/2 of the power flowing in from the DC wire 1 is the power supply circuit 5. It will flow to the storage battery 2 through a path through the (resonant circuit).

Here, the case where the output voltage of the power supply circuit 5 is equal to both the upper bridge circuit and the lower bridge circuit will be described.

In other words. When the voltage of the capacitor 3 is 500V, the output of the bridge circuit in the upper stage of the series power supply circuit 5 is the device specification in which 500V is output to the capacitor 7, that is, the transformation ratio of the transformer 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 this power converter can even 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, if the voltage on the DC wire 1 side exceeds 1000 V, the current cannot be controlled with respect to the reactor 8.

At this time, an overcurrent flows in the series power supply circuit 5 according to the ratio of the voltages of the capacitors 7 and 3 as in the operation described above.

Normally, assuming that the inverter circuit of the power supply circuit 6 has a dead time and 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 is possible.

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

If the voltage on the DC wire 1 side is larger than the sum of the voltage on the storage battery 2 side and the maximum voltage that can be added to this voltage (output voltage of the power supply circuit 6), the current control for the reactor 8 cannot be performed in the same manner. , An uncontrolled current flows through the power supply circuit 5 as a converter, an overcurrent occurs, and an overcurrent flows along the route of reference numerals A → B → C as shown in FIG. 2, and switching forming a full bridge. There is a risk that the semiconductor element (switching element) of the circuit will fail (damage).

Therefore, in the power conversion device 10 of the present embodiment, the control unit 9 has a certain condition (the following (first voltage, second voltage) from the relationship between the voltage on the DC wire 1 side and the voltage on the storage battery 2 side (first voltage, second voltage). When the condition of the equation 1) is satisfied, the gate block is performed on the first to third switching circuits 51, 54, 61.

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

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

Actually, the accuracy of the voltage detectors 3a, 4a, and 7a is also a problem, and in consideration of this, a lower value 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 conditions (Equation 1) are set in the control unit 9.

Voltage of DC wire 1> Maximum voltage that the power converter can output ... (Equation 1)
When the condition of the condition (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.

This makes it possible to prevent an overcurrent in the power supply circuit 5 due to a voltage rise.

Further, when the above condition (Equation 1) is no longer 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 feeder system for DC electric railways. Specifically, the DC electric wire 1 is a train line, and the voltage of the train line rises as the train regenerates. If the voltage rises in the normal range, the above condition (Equation 1) is not satisfied, and the storage battery 2 can be charged with regenerative power.

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

There is also the idea that the maximum voltage that can be output as a device should be designed to be high, but in this case, it is necessary to increase the withstand voltage of the elements of the switching circuits of the power supply circuits 5 and 6 as the voltage of the capacitor 7 increases. Therefore, it also leads to an increase in switching loss. An increase in switching loss is not a good thing 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 conversion device using a switching element having a low withstand voltage, and it is possible to configure a power conversion device having a small loss, a low capacity, and a low cost.

As described above, according to this embodiment, the control unit 9 performs the first to third switching when the voltage of the DC power supply 1 becomes larger than the sum of the sum of the maximum output voltage of the first voltage and the second voltage. Since the drive of the circuits 51, 54, and 61 is stopped and the drive is restarted when the voltage becomes smaller, the power supply circuit 5 is connected to the capacitor 53 in order to mutually supply the power between the DC electric wire 1 and the storage battery 2. When a series resonance circuit composed of a transformer 52 is used, it prevents an overcurrent generated in the power supply circuit 5 due to an excessive voltage rise on the DC wire 1 side, and has low loss and low capacity that enables continuous operation without failure. A (small) and low cost power converter 10 can be provided.

Although embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. This novel embodiment can be implemented in various other embodiments, and various omissions, replacements, and changes can be made without departing from the gist of the invention. This embodiment and its modifications are included in the scope and gist of the invention, and are also included in the scope of the invention described in the claims and the equivalent scope thereof.

Further, 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 above program is stored in a computer-readable electronic medium: electronic media. The function of the present invention may be realized by the computer by having the computer read the program from the electronic medium. Examples of electronic media include recording media such as CD-ROMs, flash memories, removable media: removable media, and the like. Further, the present invention may be realized by distributing and storing the components in different computers connected via a network and communicating each component between the functioning computers.

1 ... DC 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 unit, 10 ... Power converter, 11 ... Resistor, 51 ... First switching circuit, 52 ... Transformer, 53 ... Capacitor, 54 ... Second switching circuit, 61 ... Third switching circuit.

Claims (4)

It has 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, and the first switching circuit responds to fluctuations in the voltage of the DC transmission line. A first power supply circuit that drives a switching circuit or the second switching circuit to generate a first voltage, and
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.
The first to third switching circuits are controlled based on the voltage of the DC transmission line and the first voltage to adjust the second voltage between the DC transmission line and the first and second power supply circuits. Equipped with a control unit that controls the flow of current
The control unit
The second voltage that can be added to the first power supply circuit is obtained from the voltage and transformation ratio of the DC transmission line and the dead time when the third switching circuit is switched.
The control unit
A power conversion device that stops the switching operation of 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. A first switching circuit that generates power to charge the first power storage element, a second switching circuit that generates power to charge the second power storage element connected in parallel to the first power storage element, and the first switching circuit. It has an insulation circuit that insulates and connects the second switching circuit and the second switching circuit, and a third power storage element, and drives the first switching circuit or the second switching circuit according to fluctuations in the voltage of the DC transmission line. A first power supply circuit that generates a first voltage for circulating electric power between the first power storage element and the second power storage element and the DC transmission line.
A third switching circuit for generating a second voltage applied to said third storage element, first adding the second voltage generated by the driving of the third switching circuit to a voltage of said first power storage element 2 power supply circuit and
The first to third switching circuits are controlled based on the voltage of the DC transmission line and the first voltage to adjust the second voltage between the DC transmission line and the first and second power supply circuits. Equipped with a control unit that controls the flow of current
The control unit
A power conversion device that stops the switching operation of 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. The control unit
After the switching operation is stopped, when the voltage of the DC transmission line becomes smaller than the sum of the sum of the first voltage and the maximum output voltage of the second voltage, the switching of the first to third switching circuits is performed. The power conversion device according to any one of claims 1 and 2, wherein the operation is restarted. It has 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, and the first switching circuit responds to fluctuations in the voltage of the DC transmission line. The first power supply circuit that drives the switching circuit or the second switching circuit to generate the first voltage and the third switching circuit, and the second voltage generated by driving the third switching circuit is the first voltage. The second power supply circuit to be added to the voltage, the voltage of the DC transmission line, and the first to third switching circuits are controlled based on the first voltage to adjust the second voltage to adjust the DC transmission line and the said. In a power conversion method in a power conversion device including a control unit that controls the flow of current between the first and second power supply circuits.
The control unit
The second voltage that can be added to the first power supply circuit is obtained from the voltage and transformation ratio of the DC transmission line and the dead time when the third switching circuit is switched.
The control unit
A power conversion method for stopping the switching operation of 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.

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