JP2023008064A - Power conversion device - Google Patents

Abstract

To provide a power conversion device which can improve a power conversion efficiency without operation an electric leakage breaker.SOLUTION: A power conversion device 10A that is connected to power generation means 21 and 22, and performs a power supply to a load via a distribution board, comprises: DC/DC converters 11 and 12; a bidirectional inverter 15; a leakage current detection part 18; and a control part 17A that switches a driving system of the bidirectional inverter 15 with a bipolar drive system and a unipolar driving system. The control part 17A switches it to the unipolar driving system if a detection value of the leakage current detection part 18 is smaller than a first threshold value when driving the bidirectional inverter 15 with the bipolar driving system. On the other hand, if the detection value of the leakage current detection part 18 is a second threshold value or larger when the bidirectional inverter 15 is driven by the unipolar driving system, the control part switches it to the unipolar driving system.SELECTED DRAWING: Figure 1

Description

The present invention relates to power converters.

FIG. 3 shows a power conversion device 10C described in Patent Document 1. As shown in FIG. The power conversion device 10C is a hybrid power storage device connectable to the solar cells 21 and 22, and includes step-up DC/DC converters 11 and 12, a storage battery 13, a bidirectional DC/DC converter 14, a capacitor C1, It includes a bidirectional inverter 15, a relay circuit 16, and a control section 17C.

FIG. 4 shows a circuit diagram of the bidirectional inverter 15. As shown in FIG. The bidirectional inverter 15 includes DC terminals T11 and T12, switching elements Q1 to Q4, diodes D1 to D4 connected in parallel to the switching elements Q1 to Q4 in opposite directions, coils L1 and L2, and a filter composed of a capacitor C2. A circuit and AC terminals T13 and T14. The DC terminals T11 and T12 are connected to the capacitor C1, and the AC terminals T13 and T14 are connected to the relay circuit 16. A connection point between the switching element Q2 and the switching element Q4 is a, and a connection point between the switching element Q1 and the switching element Q3 is b.

As a drive system for the bidirectional inverter 15, there are generally a bipolar drive system shown in FIG. 5 and a unipolar drive system shown in FIG. 5A and 6A show the carrier signal and the command signal (the first command signal and the second command signal in FIG. 6). 5(B) and 6(B) show the output voltage across ab of the bidirectional inverter 15, and FIG. 5(C) and FIG. 6(C) show the output current across ab.

In the case of the bipolar drive system, the control unit 17C compares the carrier signal and the command signal to generate a PWM signal, and turns on/off the switching elements Q1 to Q4 based on the generated PWM signal and its inverted signal. On the other hand, in the case of the unipolar driving method, the control unit 17C compares the carrier signal and the first command signal to generate the first PWM signal, and based on the first PWM signal and its inverted signal, switches the switching elements Q2 and Q2. Q4 is turned on/off, the carrier signal is compared with the second command signal to generate a second PWM signal, and the switching elements Q1 and Q3 are turned on/off based on the second PWM signal and its inverted signal. .

For example, when performing a power conversion operation (DC/AC conversion operation) in the direction from the DC terminals T11 and T12 to the AC terminals T13 and T14 in the unipolar drive system, when the minus side of the sine wave is output from the AC terminals T13 and T14, , a step-down chopper operation is performed by the switching element Q1 and the diode D3, the switching element Q2 is always off, and the switching element Q4 is always on. When the plus side of the sine wave is output from the AC terminals T13 and T14, the switching element Q2 and the diode D4 perform a step-down chopper operation, the switching element Q1 is always off, and the switching element Q3 is always on.

When the power conversion operation (AC/DC conversion operation) is performed in the direction from the AC terminals T13 and T14 to the DC terminals T11 and T12 in the unipolar driving method, when the positive side of the sine wave is input to the AC terminals T13 and T14, switching Element Q4 and diode D2 perform boost chopper operation, and switching elements Q1 and Q3 are always turned off. When the negative side of the sine wave is input to the AC terminals T13 and T14, the switching element Q3 and the diode D1 perform a step-up chopper operation, and the switching elements Q2 and Q4 are always turned off.

FIG. 7A shows the output voltage, ground voltage and leakage current of the bidirectional inverter 15 in the bipolar drive system. FIG. 7B shows the output voltage, ground voltage and leakage current of the bi-directional inverter 15 in the unipolar drive system.

In the bipolar drive system, switching loss occurs in the switching elements Q1 to Q4, so the power conversion efficiency is lower than in the unipolar drive system. can be reduced. The unipolar drive system has a larger voltage to ground and leakage current than the bipolar drive system, but the number of switching elements Q1 to Q4 to be turned on/off at high frequencies is halved, so power conversion efficiency can be improved.

By the way, the capacitive component to ground of the solar cells 21 and 22 connected to the power converter 10C varies depending on the type and structure of the solar cells 21 and 22, and may suddenly increase when wet due to rain or the like. If the capacitance component is large, the leakage current will be large, so there is a problem that the earth leakage breaker installed on the switchboard in the home will operate and the power supply to the domestic load connected via the switchboard will be stopped. occur.

As the solar cells 21 and 22, by using a solar cell with a small capacitive component with respect to the ground or a solar cell whose capacitive component does not easily increase even if it gets wet with rain or the like, the bidirectional inverter 15 is driven by a unipolar drive system, and an earth leakage breaker is provided. power conversion efficiency can be improved without operating the

However, a general power converter is required to be able to connect various solar cells. For this reason, in the conventional power conversion device 10C, the bidirectional inverter 15 is always driven by the bipolar drive method so as to cope with the solar cells 21 and 22 having a large leakage current, even if the power conversion efficiency is sacrificed. Do not operate the earth leakage breaker.

JP 2019-134602 A

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object thereof is to provide a power converter capable of improving power conversion efficiency without operating an earth leakage breaker.

In order to solve the above problems, the power converter according to the present invention includes:
A power conversion device connected to at least one power generation means and supplying power to a load via a switchboard,
a DC/DC converter connected to the power generating means;
an inverter that converts a DC voltage input from the DC/DC converter side into an AC voltage and outputs the AC voltage to the switchboard side;
a leakage current detection unit that detects leakage current in a power line connecting the inverter and the switchboard;
a control unit that switches the driving method of the inverter between a bipolar driving method and a unipolar driving method,
The control unit
switching from the bipolar drive system to the unipolar drive system when the detection value of the leakage current detection unit is smaller than a first threshold when the inverter is driven by the bipolar drive system,
When the inverter is driven by the unipolar drive method and the detection value of the leakage current detection unit is equal to or greater than a second threshold value larger than the first threshold value, the unipolar drive method is switched to the bipolar drive method. It is characterized by

In this configuration, a leakage current detection unit for detecting leakage current is provided, and when the leakage current is small, the inverter is driven by the unipolar driving method, and when the leakage current is large, the inverter is driven by the bipolar driving method. Therefore, according to this configuration, it is possible to improve the power conversion efficiency without operating the earth leakage breaker.

In the power converter,
The control unit
controlling the DC/DC converter so that the input voltage of the inverter is maintained at a first voltage value when the inverter is driven by the bipolar drive method;
configured to control the DC/DC converter so that the input voltage of the inverter is maintained at a second voltage value smaller than the first voltage value when the inverter is driven by the unipolar driving method; can.

In the power converter,
It is preferable that the control unit drives the inverter by the bipolar driving method when starting the operation of the inverter.

The power converter,
a storage means;
a bidirectional DC/DC converter that charges and discharges the storage means;
further comprising
The inverter is a bi-directional inverter and can be configured to be connected to the DC/DC converter and the bi-directional DC/DC converter.

The power converter,
further comprising opening/closing means provided between the power generating means and the DC/DC converter for disconnecting electrical connection between the power generating means and the DC/DC converter when in an open state;
The opening/closing means is interposed in both a positive side power line and a negative side power line connecting the power generation means and the DC/DC converter,
The control unit
When the power generating means is not generating power, the opening/closing means may be placed in the open state and the inverter may be driven by the unipolar driving method.

ADVANTAGE OF THE INVENTION According to this invention, the power converter device which can improve power conversion efficiency can be provided, without operating an earth leakage breaker.

1 is a block diagram of a power converter according to a first embodiment; FIG. It is a block diagram of a power conversion device according to a second embodiment. 1 is a block diagram of a conventional power conversion device; FIG. It is a circuit diagram of a bidirectional inverter. It is various waveform diagrams of a bipolar drive system, (A) is a carrier signal and a command signal, (B) is an output voltage, and (C) is a waveform diagram of an output current. It is various waveform diagrams of a unipolar drive system, (A) is a carrier signal and a 1st and 2nd command signal, (B) is an output voltage, (C) is a waveform diagram of an output current. It is a figure which shows an output voltage, a ground voltage, and a leakage current, (A) is a figure of a bipolar drive system, (B) is a figure of a unipolar drive system.

An embodiment of a power converter according to the present invention will be described below with reference to the accompanying drawings.

[First embodiment]
FIG. 1 shows a power converter 10A according to the first embodiment of the present invention. The power conversion device 10A is a hybrid power storage device that can be connected to solar cells 21 and 22 (corresponding to the “power generating means” of the present invention), and includes terminals T1 to T8, step-up DC/DC converters 11 and 12, A storage battery 13, a bidirectional DC/DC converter 14, a capacitor C1, a bidirectional inverter 15, a relay circuit 16, a control section 17A, and a leakage current detection section 18 are provided.

Terminals T1 and T2 are connected to the positive and negative sides of solar cell 21, respectively. Terminals T3 and T4 are connected to the positive and negative sides of solar cell 22, respectively. The terminals T5 and T6 are connected to a commercial power system and connected to domestic loads via a distribution board (not shown) provided with an earth leakage breaker (including a distribution board). Terminals T7 and T8 are connected to stand-alone output lines. A home load (for example, a home appliance such as a refrigerator) that is to be preferentially operated during a power failure in the commercial power system is connected to the isolated output line.

DC/DC converter 11 is connected to terminals T1 and T2 via breaker BR1. The breaker BR1 is normally on (closed). The DC/DC converter 11 boosts the DC power generation voltage input from the solar cell 21 under the control of the control unit 17A and outputs the voltage to the bidirectional inverter 15 side.

DC/DC converter 12 is connected to terminals T3 and T4 via breaker BR2. The breaker BR2 is normally on (closed). Under the control of the control unit 17A, the DC/DC converter 12 boosts the DC power generation voltage input from the solar cell 22 and outputs the voltage to the bidirectional inverter 15 side.

The storage battery 13 corresponds to the "storage means" of the present invention, and includes at least one battery unit and a battery management system (BMS) attached to the battery unit. The battery management system acquires battery information (for example, the amount of stored electricity) of the battery unit and transmits it to the control unit 17A. Note that the battery management system may be included in the control unit 17A.

The bidirectional DC/DC converter 14 has one DC end connected to the storage battery 13 and the other DC end connected to the bidirectional inverter 15 via the capacitor C1. The bidirectional DC/DC converter 14 performs charge/discharge operation of the storage battery 13 under the control of the control unit 17A.

The bidirectional inverter 15 has a DC end connected to the DC/DC converters 11 and 12 and a bidirectional DC/DC converter 14 via a capacitor C1, and has an AC end connected to the relay circuit 16 . The bidirectional inverter 15 is driven by switching between a bipolar drive system and a unipolar drive system under the control of the control section 17A, and performs DC/AC conversion operation and AC/DC conversion operation.

As shown in FIG. 4, the bidirectional inverter 15 includes DC terminals T11 and T12, switching elements Q1 to Q4, diodes D1 to D4 connected in parallel to the switching elements Q1 to Q4 in opposite directions, coils L1, It comprises a filter circuit consisting of L2 and capacitor C2, and AC terminals T13 and T14. The DC terminals T11 and T12 are connected to the capacitor C1, and the AC terminals T13 and T14 are connected to the relay circuit 16.

Relay circuit 16 includes relays S1 to S6. Relays S1 and S2 are interposed in power lines connecting bidirectional inverter 15 and terminals T5 and T6. Relays S3 and S4 are interposed in power lines connecting the bidirectional inverter 15 and the terminals T7 and T8 via the relays S1 and S2. Relays S5 and S6 are interposed in power lines that connect bidirectional inverter 15 and terminals T7 and T8 without relays S1 and S2.

The relays S1 to S6 are switched between an ON state (closed state) and an OFF state (open state) under the control of the control section 17A. For example, when the commercial power system is energized, the relays S1 to S4 are turned on and the relays S5 and S6 are turned off. turn on.

The leakage current detection unit 18 is provided in the power line connecting the bidirectional inverter 15 and the terminals T5 and T6 (the power line connecting the bidirectional inverter 15 and the switchboard), and detects the leakage current in the power line. do. Leakage current detection unit 18 outputs a detection value (current value) of the detected leakage current to control unit 17A.

Control unit 17 A controls DC/DC converters 11 and 12 , bidirectional DC/DC converter 14 , bidirectional inverter 15 and relay circuit 16 . The control section 17A may be configured by an analog control circuit, may be configured by a digital control circuit using a microcontroller or the like, or may be configured by a circuit combining an analog control circuit and a digital control circuit. may be

The control unit 17A switches the driving method of the bidirectional inverter 15 between the bipolar driving method and the unipolar driving method. Since the bipolar drive system and the unipolar drive system are the same as in the prior art (for example, see FIGS. 5 to 7), descriptions thereof are omitted here.

When starting the operation of the bidirectional inverter 15, the control unit 17A drives it by the bipolar driving method. The bipolar drive system has a smaller AC component of the voltage to ground than the unipolar drive system, and can reduce leakage current.

When the detection value of the leakage current detector 18 is smaller than the first threshold when the bidirectional inverter 15 is driven by the bipolar drive method, the control unit 17A sets the bidirectional inverter 15 to the bipolar drive method. to the unipolar drive system. When the detection value of the leakage current detection unit 18 is equal to or greater than the first threshold, the control unit 17A maintains the bipolar driving method.

When the bidirectional inverter 15 is driven by the unipolar drive method and the detection value of the leakage current detection unit 18 is equal to or greater than a second threshold that is larger than the first threshold, the control unit 17A drives the bidirectional inverter 15. The method is returned to the bipolar drive method. When the detected value of the leakage current detector 18 is smaller than the second threshold, the controller 17A maintains the unipolar driving method.

For example, in the switchboard described above, the earth leakage breaker operates when the earth leakage current reaches 30 [mA]. Then, in the power conversion device 10A, at the time of evaluation (for example, at the time of evaluation before product shipment), the difference in leakage current between when the bidirectional inverter 15 is driven by the bipolar drive method and when it is driven by the unipolar drive method is It is 15 [mA]. In this case, for example, the first threshold can be set to 10 [mA] and the second threshold can be set to 27 [mA] (=10 [mA]+15 [mA]+α). The second threshold is larger than the value obtained by adding the difference (15 [mA]) to the first threshold in consideration of the leakage current increase (+α) due to the capacitance component of the solar cells 21 and 22 with respect to the ground. It is preferably smaller than the operating voltage value (30 [mA]) at which the breaker operates.

When the bi-directional inverter 15 is driven by the unipolar drive method, the solar cells 21 and 22 get wet due to rain or the like, and the capacitive components of the solar cells 21 and 22 to the ground increase, resulting in an increase in leakage current, and the leakage current is detected. When the detection value of the unit 18 reaches the second threshold value (for example, 27 [mA]), the control unit 17A switches the driving method of the bidirectional inverter 15 to the bipolar driving method. After that, the solar cells 21 and 22 dry, the capacitance component to the ground of the solar cells 21 and 22 decreases, the leakage current decreases, and the detection value of the leakage current detection unit 18 reaches the first threshold value (eg, 10 [mA]). ), the control unit 17A switches the driving method of the bidirectional inverter 15 to unipolar driving.

When the bidirectional inverter 15 is driven by the bipolar drive method, the control unit 17A controls the DC voltage so that the input voltage of the bidirectional inverter 15 (the voltage across the capacitor C1) is maintained at a predetermined first voltage value. /DC converters 11 and 12 and a bidirectional DC/DC converter 14 are controlled. On the other hand, when the bidirectional inverter 15 is driven by the unipolar driving method, the control unit 17A maintains the input voltage of the bidirectional inverter 15 at a predetermined second voltage value smaller than the first voltage value. DC/DC converters 11 and 12 and bidirectional DC/DC converter 14 are controlled.

For example, in the unipolar drive system and the bipolar drive system, the input voltage of the bidirectional inverter 15 (the voltage across the capacitor C1) is fixed to the same value (eg, 200 [V]), and the same duty (eg, 90 [%] ) to drive the bidirectional inverter 15, the resulting output voltages are as follows. That is, in the unipolar driving method, 200[V]×0.9=180[V], while in the bipolar driving method, (200[V]×0.9)−(200[V]×0.1) = 160 [V].

When the bidirectional inverter 15 is driven by the bipolar drive system, the input voltage of the bidirectional inverter 15 must be 225 [V] in order to obtain the same output voltage (180 [V]) as in the unipolar drive system. However, if the input voltage is fixed at 225 [V] and the bidirectional inverter 15 is driven by the unipolar driving method, the difference between the input voltage and the output voltage will increase, resulting in a decrease in power conversion efficiency.

Therefore, in the present embodiment, the first voltage value is the lowest voltage value (for example, 225 [ V]). The second voltage value is set to the lowest voltage value (for example, 200 [V]) that minimizes the difference between the input voltage and the output voltage of the bidirectional inverter 15 and obtains the desired output voltage in the unipolar driving method. do.

As a result, in the power conversion device 10A according to the present embodiment, the leakage current is monitored by the leakage current detection unit 18, and the driving method of the bidirectional inverter 15 is switched according to the magnitude of the leakage current. , the power conversion efficiency of the bidirectional inverter 15 is improved, and operation of the earth leakage breaker provided on the switchboard can be avoided.

Furthermore, in the power conversion device 10A according to the present embodiment, the input voltage of the bidirectional inverter 15 (the voltage across the capacitor C1) is changed to the input voltage and the output voltage of the bidirectional inverter 15 according to the driving method of the bidirectional inverter 15. difference is minimized and the voltage is controlled to the minimum voltage value at which a desired output voltage can be obtained, so that the power conversion efficiency can be improved.

[Second embodiment]
FIG. 2 shows a power converter 10B according to a second embodiment of the present invention. The power converter 10B differs from the first embodiment in that it includes a first opening/closing means RL1 and a second opening/closing means RL2, and that the control section 17B controls the first opening/closing means RL1 and the second opening/closing means RL2. However, other points are common to the first embodiment.

The first opening/closing means RL1 is, for example, a relay, and is interposed in both the plus side power line and the minus side power line connecting the solar cell 21 and the DC/DC converter 11 . Both of the first opening/closing means RL1 are simultaneously switched between an open state (OFF state) and a closed state (ON state) under the control of the control unit 17B. Disconnect electrical connections.

The second opening/closing means RL2 is, for example, a relay, and is interposed in both the plus side power line and the minus side power line that connect the solar cell 22 and the DC/DC converter 12 . Both of the second opening/closing means RL2 are simultaneously switched between an open state (OFF state) and a closed state (ON state) under the control of the control unit 17B. Disconnect electrical connections.

When the solar cells 21 and 22 do not generate power for a predetermined time (when the voltage generated by the solar cells 21 and 22 is not applied to the terminals T1 and T2), the controller 17B controls the first opening/closing means RL1 and the second opening/closing means. RL2 is opened and the bi-directional inverter 15 is driven by the unipolar driving method. In this case, the driving method of the bidirectional inverter 15 is fixed to the unipolar driving method regardless of the detection value of the leakage current detection unit 18 .

In the power conversion device 10B according to the present embodiment, by disconnecting the solar cells 21 and 22 when the solar cells 21 and 22 do not generate power for a predetermined time, it is possible to avoid inputting leakage current from the solar cells 21 and 22. can do. For example, when the solar cells 21 and 22 are not generating power, even if the leakage current increases due to an increase in the capacitance component to the ground of the solar cells 21 and 22, the driving method of the bidirectional inverter 15 is bipolar driving. Since the system is not switched (because the unipolar drive system is maintained), it is possible to avoid a decrease in power conversion efficiency.

[Modification]
Although the embodiments of the power converter according to the present invention have been described above, the present invention is not limited to the above embodiments.

A power conversion device of the present invention is a power conversion device that is connected to power generation means and supplies power to a load via a switchboard, and comprises a DC/DC converter and a DC voltage input from the DC/DC converter side. is converted into an AC voltage and output, a leakage current detection unit for detecting leakage current, and a control unit for switching the drive method of the inverter between the bipolar drive method and the unipolar drive method. can be changed. For example, the power conversion device of the present invention may be a photovoltaic power generation device.

The control unit of the present invention switches the bipolar drive method to the unipolar drive method when the detection value of the leakage current detection unit is smaller than the first threshold while the inverter is being driven by the bipolar drive method, and the inverter is switched to the unipolar drive method. If the detection value of the leakage current detection unit is equal to or greater than the second threshold value, which is larger than the first threshold value while driving in the drive method, the configuration can be changed as appropriate if the unipolar drive method is switched to the bipolar drive method. .

The first threshold value and the second threshold value can be appropriately set as long as they are values smaller than the operating voltage value at which the earth leakage breaker of the switchboard operates. It is preferable that the control unit performs switching control with hysteresis so that switching between the bipolar driving method and the unipolar driving method does not frequently occur in a short time in the vicinity of the first threshold value and the second threshold value.

10A, 10B power converters 11, 12 DC/DC converter 13 storage battery 14 bidirectional DC/DC converter 15 bidirectional inverter 16 relay circuits 17A, 17B control unit 18 leakage current detection units 21, 22 solar cell

Claims (5)

A power conversion device connected to at least one power generation means and supplying power to a load via a switchboard,
a DC/DC converter connected to the power generating means;
an inverter that converts a DC voltage input from the DC/DC converter side into an AC voltage and outputs the AC voltage to the switchboard side;
a leakage current detection unit that detects leakage current in a power line connecting the inverter and the switchboard;
a control unit that switches the driving method of the inverter between a bipolar driving method and a unipolar driving method,
The control unit
switching from the bipolar drive system to the unipolar drive system when the detection value of the leakage current detection unit is smaller than a first threshold when the inverter is driven by the bipolar drive system,
When the inverter is driven by the unipolar drive method and the detection value of the leakage current detection unit is equal to or greater than a second threshold value larger than the first threshold value, the unipolar drive method is switched to the bipolar drive method. A power conversion device characterized by: The control unit
controlling the DC/DC converter so that the input voltage of the inverter is maintained at a first voltage value when the inverter is driven by the bipolar drive method;
controlling the DC/DC converter such that the input voltage of the inverter is maintained at a second voltage value smaller than the first voltage value when the inverter is driven by the unipolar driving method; The power converter according to claim 1, characterized in that. 3. The power conversion apparatus according to claim 1, wherein the control unit drives the inverter by the bipolar drive method when starting the operation of the inverter. a storage means;
a bidirectional DC/DC converter that charges and discharges the storage means;
further comprising
The power converter according to any one of claims 1 to 3, wherein the inverter is a bidirectional inverter and is connected to the DC/DC converter and the bidirectional DC/DC converter. further comprising opening/closing means provided between the power generating means and the DC/DC converter for disconnecting electrical connection between the power generating means and the DC/DC converter when in an open state;
The opening/closing means is interposed in both a positive side power line and a negative side power line connecting the power generation means and the DC/DC converter,
The control unit
5. The power converter according to any one of claims 1 to 4, wherein when the power generating means does not generate power, the opening/closing means is set to the open state and the inverter is driven by the unipolar driving method. Device.

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