JP2023093953A - Grid interconnection system - Google Patents

Abstract

To prevent an inrush current in a grid interconnection system.SOLUTION: A grid interconnection system includes: a power conversion device that converts a DC voltage of a DC power supply into a three-phase AC voltage; a grid interconnection relay provided between the power conversion device and a power system; a voltage sensor that detects three-phase voltages respectively on the power system side of the grid interconnection relay; and a control device that controls operation of the grid interconnection relay based on a detection value obtained by the voltage sensor. The grid interconnection relay has a first-phase relay provided on a first-phase voltage line, a second-phase relay provided on a second-phase voltage line, and a third-phase relay provided on a third-phase voltage line. The control device closes the first-phase relay and the second-phase relay when the first-phase voltage and the second-phase voltage are equal to each other, and closes the third-phase relay when the third-phase voltage becomes zero thereafter.SELECTED DRAWING: Figure 2

Description

The technology disclosed in this specification relates to a system interconnection system for connecting a DC power supply to a three-phase AC power system.

Patent Literature 1 discloses a grid interconnection system. This grid connection system includes a power conversion device that converts a DC voltage of a DC power supply into a single-phase AC voltage, and a grid connection relay provided between the power conversion device and the power grid. In this type of system, when the grid connection relay is closed and the power converter and the power grid are electrically connected, an excessive rush current may occur. In relation to this, in the grid interconnection system of Patent Document 1, inrush current is suppressed by monitoring the voltage on both sides of the grid interconnection relay and closing the grid interconnection relay when the difference is within the allowable range. is configured to

JP 2016-100963 A

The grid interconnection system of Patent Document 1 connects a DC power supply to a single-phase AC power system, and when connecting a DC power supply to a three-phase AC power system, the technology described in Patent Document 1 is used. It is difficult to adopt as it is. For example, when the grid interconnection system of Patent Document 1 is applied to a power system from a DC power supply to a three-phase AC power system, the power system side and It is necessary to provide voltage sensors for detecting the three-phase voltage on both sides of the power converter, and the increase in cost due to these sensors poses a problem. In addition, these sensors must be connected to a battery or the like in the DC circuit as a power supply, and if the voltage or capacity of the power supply is low, the three-phase voltage may not be detected. There is In view of the above, the present specification provides a novel and useful technique capable of suppressing rush power in a grid interconnection system that connects a DC power supply to a three-phase AC power system.

The technology disclosed in this specification is embodied in a grid interconnection system for connecting a DC power supply to a three-phase AC power system. In this grid interconnection system, a power conversion device that converts the DC voltage of the DC power supply into a three-phase AC voltage, a grid interconnection relay provided between the power conversion device and the power system, and the grid connection A voltage sensor for detecting a three-phase voltage on the power system side of the system relay, and a control device for controlling the operation of the system interconnection relay based on the detected value by the voltage sensor. The system interconnection relays include a first relay provided on the first-phase voltage line, a second relay provided on the second-phase voltage line, and a third relay provided on the third-phase voltage line. and The controller closes (i.e. conducts) the first relay and the second relay when the first phase voltage and the second phase voltage are equal to each other, and then closes the third relay. Closing the third relay when the phase voltage is zero. Here, the U phase, the V phase and the W phase may be assigned in any way to the first phase, the second phase and the third phase.

According to the configuration described above, it is possible to significantly suppress rush power compared to the case where the first relay, the second relay and the third relay are closed at the same time.

In one embodiment of the present technology, the grid interconnection system may further include a filter circuit provided between the power conversion device and the grid interconnection relay and having a reactor and a capacitor. Generally, in a configuration in which this type of filter circuit exists, an excessive inrush current is likely to occur in the reactor or capacitor at the timing when the grid connection relay is closed. The present technology can be suitably adopted for such a configuration, and can significantly reduce the inrush current.

1 is a circuit diagram showing the configuration of a grid interconnection system 10 of an embodiment; FIG. 4 is a flowchart showing control operations executed by the control device 30; 3 is a graph showing time-measured changes in current and voltage in each part of the grid interconnection system 10 when the control operation shown in FIG. 2 is executed. FIG. 4 is an enlarged view of part IV (a period of 0.57 seconds to 0.60 seconds) in the graph of FIG. 3; FIG. 4 is an enlarged view of a portion V (a period of 0.67 seconds to 0.70 seconds) in the graph of FIG. 3; As a comparative example with respect to FIGS. 3 to 5, graphs showing time-measured changes in current and voltage in each part of the grid interconnection system 10 when three relays 18u, 18v, and 18w are closed at the same time. FIG. 7 is an enlarged view of a VII portion (a period of 0.57 seconds to 0.60 seconds) in the graph of FIG. 6;

A grid interconnection system 10 of an embodiment will be described with reference to the drawings. The grid interconnection system 10 is a device for connecting a DC power supply 2 to a three-phase AC power system 6, and can be employed, for example, in an electric vehicle. By employing the grid interconnection system 10 in an electric vehicle, for example, electric power can be supplied from the stopped electric vehicle to the electric power system 6 of a general power distribution company. However, the grid interconnection system 10 of the present embodiment is not limited to the DC power supply 2 mounted on an electric vehicle, and can be applied to a stationary DC power supply 2 as well. Note that the DC power supply 2 is not particularly limited, but may be, for example, a secondary battery, a fuel cell, or a solar panel.

As shown in FIG. 1 , the grid interconnection system 10 includes a power conversion device 14 , a filter circuit 16 , a grid interconnection relay 18 , a voltage sensor 20 , a transformer 22 and a controller 30 .

The power converter 14 is electrically connected to the DC power supply 2 . Although not particularly limited, a main relay 4 is provided between the DC power supply 2 and the power conversion device 14 to electrically connect and disconnect the two. The power converter 14 has a plurality of switching elements 14s, and can convert the DC voltage of the DC power supply 2 into a three-phase AC voltage. Although it is an example, the power converter 14 in this embodiment has six switching elements 14s, and these switching elements 14s constitute a three-phase inverter circuit. The plurality of switching elements 14s perform power conversion from direct current to alternating current by PWM (Pulse Width Modulation) control. The grid interconnection system 10 may further include a DC-DC converter in addition to the three-phase inverter circuit.

The filter circuit 16 is provided on the output side (AC circuit side) of the power converter 14 . The filter circuit 16 eliminates or suppresses pulsation caused by PWM control from the three-phase AC power output by the power conversion device 14 . Although not particularly limited, the filter circuit 16 in this embodiment is a so-called LC-type filter, and has reactors 16r and capacitors 16c provided in voltage lines 24u, 24v, and 24w of respective phases. Note that the power conversion device 14 does not necessarily require the filter circuit 16 .

The grid connection relay 18 is provided on voltage lines 24u, 24v, and 24w that connect the filter circuit 16 and the transformer 22, and is interposed between the power converter 14 and the power grid 6. FIG. The grid connection relay 18 has a plurality of relays 18u, 18v, and 18w, and can electrically connect and disconnect between the power conversion device 14 and the power grid 6 . The plurality of relays 18u, 18v, and 18w includes a first relay 18u provided on the U-phase voltage line 24u, a second relay 18v provided on the V-phase voltage line 24v, and a W-phase voltage line 24w. and a third relay 18w provided. As an example, these relays 18u, 18v, and 18w are normally-off contact relays.

Voltage sensor 20 detects the voltage of each phase of the three-phase AC power between power converter 14 and power system 6 . In particular, the voltage sensor 20 in this embodiment detects the voltage Vu of the U-phase voltage line 24u with respect to the neutral line and the voltage Vv of the V-phase voltage line 24v with respect to the neutral line on the power system 6 side of the grid connection relay 18. , and the voltage Vw of the W-phase voltage line 24w with respect to the neutral line, respectively. A specific configuration of the voltage sensor 20 is not particularly limited. Voltage sensor 20 is connected to control device 30 via a signal line (not shown), and a value detected by voltage sensor 20 is input to control device 30 .

The transformer 22 is provided between the grid connection relay 18 and the electric power system 6, and prohibits direct conduction between them (that is, without electromagnetic induction). Note that the transformer 22 is not necessarily required.

The control device 30 controls the operation of the grid connection relay 18 . As described above, the control device 30 is connected to the voltage sensor 20 and can control the operation of the grid connection relay 18 based on the value detected by the voltage sensor 20 . Note that the control device 30 may be configured by a dedicated control unit, or may be configured by various control units mounted on the electric vehicle. Alternatively, control device 30 may be arranged outside the electric vehicle and connected to the electric vehicle by wireless communication.

Control of the system interconnection relay 18 by the control device 30 will be described with reference to FIG. 2 . As shown in FIG. 2, the control device 30 starts the process of connecting the DC power supply 2 to the power system 6, that is, the process of system interconnection based on its own judgment or an instruction from another person (YES in S12). ). In this case, control device 30 does not close system interconnection relay 18 immediately, and waits until V-phase voltage Vv and W-phase voltage Vw become equal to each other (NO in S14). Then, when the V-phase voltage Vv and the W-phase voltage Vw are equal to each other (YES in S14), the control device 30 controls the second relay 18v provided on the V-phase voltage line 24v and the W-phase voltage Vw. The third relay 18w provided on the voltage line 24w is closed (conducted) (S16).

Thereafter, control device 30 waits until U-phase voltage Vu becomes zero (NO in S18). When U-phase voltage Vu becomes zero (YES in S18), controller 30 closes first relay 18u provided on U-phase voltage line 24u (S20). Here, between the timing (S16) at which the two relays 18v and 18w are closed and the timing (S20) at which the last relay 18u is closed, there is an interval between the timing (S20) at which the last relay 18u is closed in order to wait for the transient fluctuations in the voltage and current to subside. , a predetermined waiting time may be provided.

As described above, in the grid interconnection system 10 of this embodiment, the three relays 18u, 18v, and 18w of the grid interconnection relay 18 are not closed at the same time when the grid is interconnected. As a result, the rush current flowing through the switching element 14s and the reactor 16r and the rush current flowing through the capacitor 16c are significantly suppressed. In this regard, one specific example will be described with reference to FIGS. 3-7.

3 to 5 show simulation results of changes over time occurring in voltage and current of each part when grid interconnection is executed according to this embodiment. In this simulation, the second relay 18v and the third relay 18 are simultaneously closed within the period of the VI section (0.57 seconds to 0.60 seconds) in FIG. 3, and the V section (0 0.67 seconds to 0.70 seconds), the first relay 18u is closed. FIG. 4 shows an enlarged view of the IV part, and FIG. 5 shows an enlarged view of the V part.

On the other hand, FIGS. 6 and 7 show, as a comparative example, simulation results of changes over time occurring in the voltage and current of each part when the three relays 18u, 18v, and 18w are closed at the same time. In this simulation, the three relays 18u, 18v, 18w are closed simultaneously within the period of part VII (0.57 seconds to 0.60 seconds) in FIG. FIG. 6 shows the VII section in an enlarged manner.

In FIGS. 3 to 7, the graph (a) shows the change over time of the DC voltage on the DC power supply 2 side of the power converter 14. FIG. Graph (b) shows the change over time of the U-phase voltage before being filtered by the filter circuit 16 . The graph of (c) is the current of each phase before being filtered by the filter circuit 16, and shows the change over time of the current flowing through the switching element 14s and the reactor 16r. A graph (d) shows changes over time in the voltage of each phase after being filtered by the filter circuit 16 . The graph (e) shows changes over time in the current of each phase after being filtered by the filter circuit 16 . A graph (f) shows the change over time of the current flowing through the capacitor 16c.

As shown in FIGS. 3 and 4, according to this embodiment, at the timing when the two relays 18v and 18w are closed, the current (c) flowing through the switching element 14s and the reactor 16r and the current (f ), a certain amount of inrush current is generated, but the peak value is suppressed to a relatively low level. For example, referring to FIG. 4, the peak value in the graph of (c), that is, the peak value of the current flowing through the switching element 14s and the reactor 16r, is 400 amperes or less, and the peak value in the graph of (f), that is, the capacitor 16c The peak value of the current flowing through is also suppressed to 80 amperes or less.

Also, as shown in FIGS. 3 and 5, even at the timing when the first relay 18u is closed, a significant increase in the current (f) flowing through the capacitor 16c can be seen, but the peak value is also suppressed to 80 amperes or less. It is

On the other hand, in the comparative examples shown in FIGS. 6 and 7, at the timing when the three relays 18u, 18v, and 18w are closed, the current (c) flowing through the switching element 14s and the reactor 16r and the current (c) flowing through the capacitor 16c At (f), generation of a relatively large inrush current can be seen. For example, referring to FIG. 7, the peak value in the graph of (c), that is, the peak value of the current flowing through the switching element 14s and the reactor 16r exceeds 600 amperes, and the peak value in the graph of (f), that is, the capacitor The peak value of current through 16c is also over 600 Amps.

As described above, in the grid interconnection system 10 of the present embodiment, when the V-phase voltage and the W-phase voltage become equal to each other, the second relay 18v and the second relay 18w are closed, and then U It is configured to close the third relay 18u when the phase voltage is zero. This makes it possible to significantly suppress the rush power at the time of system interconnection, as compared with the case where the three relays 18u, 18v, and 18w are closed at the same time.

In the grid interconnection system 10 of the present embodiment, first, the second relay 18v provided on the V-phase voltage line 24v and the third relay 18w provided on the W-phase voltage line 24w are closed. The first relay 18u provided on the U-phase voltage line 24u is closed. However, this order is an example and is not particularly limited. The V phase in the present embodiment is an example of the first phase in the technology disclosed in the present specification, and the W phase in the present example is an example of the second phase in the technology disclosed in the present specification. The U phase in the example is an example of the first phase in the technology disclosed in this specification.

As another embodiment, first, when the U-phase voltage and the V-phase voltage become equal to each other, the first relay 18u provided on the U-phase voltage line 24u and the first relay 18u provided on the V-phase voltage line 24v The second relay 18v may be closed. Then, when the W-phase voltage becomes zero thereafter, the third relay 18w provided on the W-phase voltage line 24w may be closed. There is no particular limitation among the U-phase, V-phase, and W-phase, provided that two of the three relays 18u, 18v, and 18w are closed first, and then the remaining one is closed. good.

Although the embodiments of the present technology have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above. The technical elements described in this specification or in the drawings exhibit technical usefulness either singly or in various combinations, and are not limited to the combinations described in the claims as filed. In addition, the techniques exemplified in this specification or drawings achieve a plurality of purposes at the same time, and achieving one of them has technical utility in itself.

2: DC power supply, 4: Main relay, 6: Electric power system, 10: Grid interconnection system, 14: Power converter, 16: Filter circuit, 18: Grid interconnection relay, 18u: First relay, 18v: Second Relay 18w: Third relay 20: Voltage sensor 22: Transformer 24u: U-phase voltage line 24v: V-phase voltage line 24w: W-phase voltage line 30: Control device

Claims (2)

A system interconnection system for connecting a DC power supply to a three-phase AC power system,
a power conversion device that converts the DC voltage of the DC power supply into a three-phase AC voltage;
a system interconnection relay provided between the power conversion device and the power system;
a voltage sensor that detects three-phase voltages on the power system side of the grid connection relay;
a control device that controls the operation of the grid connection relay based on the value detected by the voltage sensor;
with
The system interconnection relays include a first relay provided on the first-phase voltage line, a second relay provided on the second-phase voltage line, and a third relay provided on the third-phase voltage line. and
The controller closes the first relay and the second relay when the first phase voltage and the second phase voltage are equal to each other, after which the third phase voltage is zero. closing the third relay when
Grid-connected system. The grid interconnection system according to claim 1, further comprising a filter circuit provided between said power converter and said grid interconnection relay and having a reactor and a capacitor.

Images