JP4708266B2 - Bidirectional power conversion device and power conversion operation switching method thereof - Google Patents

Description

  The present invention relates to a bidirectional power conversion device that performs mutual power conversion between a DC distribution network and an AC distribution network, and a method for switching the power conversion operation thereof.

  Conventionally, a bidirectional power converter is disposed between a DC distribution network in which a plurality of DC power sources and a plurality of DC loads are connected, and an AC distribution network in which a commercial power source and a plurality of AC loads are connected. There has been a technique for stabilizing the supply voltage of a DC power distribution network by performing mutual power conversion with a power converter (see, for example, Patent Document 1).

  FIG. 4 is a block diagram showing a configuration of a bidirectional power converter according to the prior art. Referring to FIG. 4, the bidirectional power converter 1 is connected to both the DC distribution network 6 and the AC distribution network 10. A DC load 7, a fuel cell 8, and a photovoltaic power generation 9 are connected to the DC distribution network 6. The fuel cell 8 and the photovoltaic power generation 9 are DC power sources. An AC load 11 is connected to the AC distribution network 10. Further, a commercial power source 12 is connected to the AC power distribution network 10 at a connection point with the bidirectional power converter 1. As an example, the commercial power source 12 is of AC 200V.

  Here, the power conversion operation from the direct current to the alternating current of the bidirectional power conversion device 1 is referred to as an inverter operation, and the power conversion operation from the alternating current to the direct current is referred to as a rectification operation. A state where neither the inverter operation nor the rectifying operation is performed is referred to as a standby operation. The bidirectional power conversion device 1 shifts to the inverter operation when the DC distribution network voltage supplied from the DC power source to the DC load 7 increases, and shifts to the rectification operation when the DC distribution network voltage decreases, thereby reducing the DC distribution network voltage. Stabilize.

  The bidirectional power conversion device 1 includes a bidirectional conversion unit 2, an operation switching control device 3, a DC voltage / current measuring device 4, and an AC voltage / current measuring device 5.

  The bidirectional conversion unit 2 performs an inverter operation, a rectifying operation, or a standby operation in accordance with an instruction from the operation switching control device 3. In the inverter operation, the bidirectional conversion unit 2 converts the power of the DC distribution network 6 into AC and supplies it to the AC distribution network 10. In the rectification operation, the bidirectional conversion unit 2 converts the power of the AC distribution network 10 into a direct current and supplies the direct current to the DC distribution network 6. In the standby operation, the bidirectional conversion unit 2 performs neither the inverter operation nor the rectification operation.

  The DC voltage / current measuring device 4 measures the DC distribution network voltage Vdc supplied by the DC distribution network 6 and the DC output current Idc from the bidirectional conversion unit 2 and notifies the operation switching control device 3 of the measured values.

  The AC voltage / current measuring instrument 5 measures the DC distribution network voltage Vac supplied by the AC distribution network 10 and the AC output current Iac from the bidirectional conversion unit 2 and notifies the operation switching control device 3 thereof.

  The operation switching control device 3 sets the DC distribution network voltage Vdc within the range between the maximum voltage VH and the minimum voltage VL (VL ≦ VL) based on the measured value notified from the DC voltage / current measuring device 4 and the AC voltage / current measuring device 5. The inverter operation, the rectification operation, or the standby operation is selected so as to maintain Vdc ≦ VH) and the bidirectional power conversion apparatus 1 is instructed.

  FIG. 5 is a flowchart showing the operation of the conventional bidirectional power converter. This operation is mainly based on control from the operation switching control device 3 to the bidirectional conversion unit 2.

  Referring to FIG. 5, when the bidirectional power conversion device 1 starts operation, it first enters a standby operation (step 901). In the standby operation, the bidirectional power converter 1 determines whether the DC distribution network voltage Vdc is equal to or higher than the maximum voltage VH (step 902).

  If the DC distribution network voltage Vdc is equal to or higher than the maximum voltage VH, the bidirectional power converter 1 starts an inverter operation (step 903) so that the DC distribution network voltage Vdc becomes VT satisfying VL <VT <VH. Power conversion from direct current to alternating current is performed (step 904).

  Subsequently, the bidirectional power converter 1 determines whether or not the AC output current Iac is greater than or equal to the minimum AC output current Imac (step 905). If AC output current Iac is equal to or greater than minimum AC output current Imac, bidirectional power conversion device 1 returns to step 904 and continues the inverter operation.

  When the power supply / demand balance in the DC distribution network is balanced and the AC output current Iac falls below the minimum AC output current Imac, the bidirectional power conversion device 1 returns to Step 901 and shifts to a standby operation.

  In step 902, if the DC distribution network voltage Vdc is smaller than the maximum voltage VH, the bidirectional power converter 1 determines whether or not the DC distribution network voltage Vdc is less than or equal to the minimum voltage VL (step 906).

  If the DC distribution network voltage Vdc is equal to or lower than the minimum voltage VL, the bidirectional power converter 1 starts a clear flow operation (step 907) so that the DC distribution network voltage Vdc becomes VT that satisfies VL <VT <VH. Power conversion from AC to DC is performed (step 908).

  Subsequently, the bidirectional power converter 1 determines whether or not the DC output current Idc is greater than or equal to the minimum DC output current Imdc (step 909). If the DC output current Idc is equal to or greater than the minimum DC output current Imdc, the bidirectional power converter 1 returns to Step 908 and continues the rectification operation.

  When the power supply / demand balance in the DC distribution network is balanced and the AC output current Idc falls below the minimum DC output current Imdc, the bidirectional power converter 1 returns to Step 901 and shifts to a standby operation.

  FIG. 6 is a timing chart showing an operation example of a conventional bidirectional power converter. Referring to FIG. 6, bidirectional power conversion device 1 continues the standby operation while DC distribution network voltage Vdc is within the range of VL <Vdc <VH. In the stand-by operation, neither direct current to alternating current conversion nor alternating current to direct current conversion is performed, so the direct current output current Idc and the alternating current output current Iac are zero.

  Thereafter, when the DC distribution network voltage Vdc rises and reaches the maximum voltage VH, the bidirectional power converter 1 shifts to an inverter operation. When shifting to the inverter operation, the AC output current Iac becomes equal to or greater than the minimum AC output current Imac. By continuing the inverter operation, the AC output current Iac gradually decreases, and when the AC output current Imac falls below the minimum AC output current Imac, the bidirectional power conversion device 1 returns to the standby operation again.

This time, when the DC distribution network voltage Vdc decreases and reaches the minimum voltage VL, the bidirectional power converter 1 shifts to a rectifying operation. When shifting to the rectifying operation, the DC output current Idc becomes equal to or greater than the minimum DC output current Imdc. By continuing the rectifying operation, the DC output current Idc gradually decreases, and when the DC output current Imdc falls below the minimum DC output current Imdc, the bidirectional power conversion device 1 returns to the standby operation again.
JP 2000-341881 A

  However, in the above-described conventional technology, when switching the operation mode from the standby operation to the inverter operation, the DC distribution network voltage Vdc is reduced due to the delay caused by the measurement time of the DC distribution network voltage and the time required to start the bidirectional conversion unit 2. The maximum voltage VH, which is the upper limit of the specified range, may be exceeded.

  In the above-described prior art, when the operation mode is switched from the standby operation to the rectification operation, the DC distribution network voltage Vdc may be below the minimum voltage VL that is the lower limit of the specified range due to the delay.

  FIG. 7 is a timing chart showing a state when the DC distribution network voltage of the conventional bidirectional power converter exceeds the specified range.

  Referring to FIG. 7, the DC distribution network voltage Vdc is equal to or higher than the maximum voltage VH, and it takes a delay time ΔTH from when the bidirectional power conversion apparatus 1 decides the transition from the standby operation to the inverter operation until the actual transition. . Due to the delay time ΔTH, the DC distribution network voltage Vdc continues to exceed the maximum voltage VH, and an overshoot voltage of the voltage ΔVH appears.

  In addition, the DC power distribution network voltage Vdc is equal to or lower than the minimum voltage VL, and a delay time ΔTL is required from when the bidirectional power conversion device 1 determines the transition from the standby operation to the rectification operation until the actual transition. Due to the delay time ΔTL, the DC distribution network voltage Vdc continues to be lower than the minimum voltage VL, and an undershoot voltage of the voltage ΔVL appears.

  The objective of this invention is providing the bidirectional | two-way power converter device which can suppress the deviation from the regulation range of a DC distribution network voltage at the time of transfer of an operation mode.

In order to achieve the above object, the bidirectional power conversion device of the present invention provides:
A bidirectional power converter connected between a DC power distribution network to which a DC power supply and a DC load are connected, and an AC distribution network to which an AC power supply and an AC load are connected, and performs mutual power conversion and supply,
Inverter operation for converting direct current power of the direct current distribution network to alternating current and supplying the alternating current distribution network, rectification operation for converting electric power of the alternating current distribution network to direct current and supplying the direct current distribution network, and the inverter A bidirectional conversion unit that operates in either a standby operation in which neither the operation nor the rectifying operation is performed;
A DC measuring unit for measuring a DC distribution network voltage supplied by the DC distribution network;
The change rate of the DC distribution network voltage is calculated from the DC distribution network voltage measured by the DC measurement unit, and the waiting time is calculated using the change rate and a delay time required for the operation of the bidirectional conversion unit. An inverter operation threshold voltage lower than an upper limit of a specified range used for determination of transition from operation to the inverter operation, and a rectification operation threshold voltage higher than a lower limit of the specified range used for determination of transition from the standby operation to the rectification operation. An operating voltage calculating device for calculating;
The bidirectional conversion unit is shifted from the standby operation to the inverter operation by determination using the DC distribution network voltage measured by the DC measurement unit and the inverter operation threshold voltage calculated by the operating voltage calculation device, An operation switching control device that shifts the bidirectional converter from the standby operation to the rectification operation based on the determination using the DC distribution network voltage and the rectification operation threshold voltage.

  Therefore, according to the present invention, since the operation mode is shifted with the threshold value calculated from the change rate and the delay time, the operation mode is shifted while the DC distribution network voltage shows an expected fluctuation while it is within the specified range. It is possible to suppress the DC distribution network voltage from deviating from the specified range.

  In addition, the operating voltage calculation device is preliminarily determined from a response characteristic from the standby operation to the inverter operation of the bidirectional conversion unit, where the upper limit value of the DC distribution network voltage is VH and the lower limit value is VL. The delay time is ΔTH, the delay time predetermined from the response characteristic from the standby operation to the rectifying operation is ΔTL, the change rate of the DC distribution network voltage is dVdc / dt, and the inverter operation threshold voltage is (VH). -ΔTH · dVdc / dt), and the threshold voltage for rectification operation may be obtained by (VL-ΔTL · dVdc / dt).

Moreover, it further has an AC measuring unit for measuring an AC output current supplied from the bidirectional conversion unit to the AC distribution network,
The direct current measurement unit further measures a direct current output current supplied from the bidirectional conversion unit to the direct current distribution network,
In the standby operation, the operation switching control device shifts to the inverter operation when the DC distribution network voltage becomes equal to or higher than the inverter operation threshold voltage, and the rectification operation when the DC distribution network voltage becomes lower than the rectification operation threshold voltage. In the inverter operation, when the DC output current measured by the DC measurement unit falls below a predetermined threshold value, the operation returns to the standby operation, and the AC output measured by the AC measurement unit in the rectification operation. When the current falls below a predetermined threshold, the standby operation may be returned.

  According to the present invention, since the operation mode is shifted with the threshold value calculated from the rate of change and the delay time, the operation mode can be shifted while the DC distribution network voltage is within the specified range, and the DC distribution network voltage is defined. Deviation from the range can be suppressed.

  Embodiments for carrying out the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a block diagram showing a configuration of a bidirectional power converter according to an embodiment of the present invention. Referring to FIG. 1, the bidirectional power converter 20 is connected to both the DC distribution network 6 and the AC distribution network 10. A DC load 7, a fuel cell 8, and a photovoltaic power generation 9 are connected to the DC distribution network 6. The fuel cell 8 and the photovoltaic power generation 9 are DC power sources. An AC load 11 is connected to the AC distribution network 10. Further, a commercial power source 12 is connected to the AC power distribution network 10 at a connection point with the bidirectional power converter 1. As an example, the commercial power source 12 is of AC 200V.

  Here, the power conversion operation from the direct current to the alternating current of the bidirectional power conversion device 20 is referred to as an inverter operation, and the power conversion operation from the alternating current to the direct current is referred to as a rectification operation. A state where neither the inverter operation nor the rectifying operation is performed is referred to as a standby operation. The bidirectional power converter 20 shifts to the inverter operation when the DC distribution network voltage supplied from the DC power source to the DC load 7 increases, and shifts to the rectification operation when the DC distribution network voltage decreases, thereby changing the DC distribution network voltage. Stabilize.

  The bidirectional power conversion device 20 includes a bidirectional conversion unit 2, an operation switching control device 22, a DC voltage / current measurement device 4, an AC voltage / current measurement device 5, and an operation voltage calculation device 21.

  The bidirectional conversion unit 2 performs an inverter operation, a rectifying operation, or a standby operation in accordance with an instruction from the operation switching control device 22. In the inverter operation, the bidirectional conversion unit 2 converts the power of the DC distribution network 6 into AC and supplies it to the AC distribution network 10. In the rectification operation, the bidirectional conversion unit 2 converts the power of the AC distribution network 10 into a direct current and supplies the direct current to the DC distribution network 6. In the standby operation, the bidirectional conversion unit 2 performs neither the inverter operation nor the rectification operation.

  The DC voltage / current measuring device 4 measures the DC distribution network voltage Vdc supplied from the DC distribution network 6 and the DC output current Idc from the bidirectional conversion unit 2, and the DC distribution network voltage Vdc and the DC output current Idc. Is notified to the operation switching control device 22 and the DC distribution network voltage Vdc is notified to the operation voltage calculation device 21.

  The AC voltage / current measuring instrument 5 measures the DC distribution network voltage Vac supplied by the AC distribution network 10 and the AC output current Iac from the bidirectional conversion unit 2 and notifies the operation switching control device 3 thereof.

  The operating voltage calculation device 21 uses the DC distribution network voltage Vdc measured by the DC voltage / current measuring device 4 to determine the inverter operation threshold voltage VH ′ used for determining the transition from the standby operation to the inverter operation or the standby operation to the rectification operation. A rectification operation threshold voltage VL ′ used for determination of transition is calculated and notified to the operation switching control device 22.

  In the calculation of the inverter operation threshold voltage VH ′, the operation voltage calculation device 21 first starts direct current at an arbitrary time sufficiently short with respect to the delay time ΔTH required for switching the bidirectional conversion unit 2 from the standby operation to the inverter operation. A change rate (DC voltage time change rate) ΔV / Δt of the distribution network voltage Vdc is calculated. For example, if the delay time ΔTH of the bidirectional conversion unit 2 is about 10 milliseconds, the operating voltage calculation device 21 may calculate the DC voltage time change rate ΔV / Δt for about 1 millisecond. The delay time ΔTH can be set from the switching response characteristic from the standby operation to the inverter operation.

  Then, assuming that the upper limit of the specified range for maintaining the DC distribution network voltage Vdc is the maximum voltage VH, the operating voltage calculation device 21 uses the DC voltage time change rate ΔV / Δt, and uses the inverter operation start voltage VH ′ = VH−ΔTH × ΔV / Δt is calculated.

  In calculating the rectification operation threshold voltage VL ′, the operation voltage calculation device 21 firstly has an arbitrary time sufficiently short with respect to the delay time ΔTL required to switch the bidirectional conversion unit 2 from the standby operation to the rectification operation. The change rate (DC voltage time change rate) ΔV / Δt of the DC distribution network voltage Vdc is calculated. For example, if the delay time of the bidirectional conversion unit 2 is about 10 milliseconds, the operating voltage calculation device 21 may calculate the DC voltage time change rate ΔV / Δt for about 1 millisecond. The delay time ΔTL can be set from the switching response characteristic from the standby operation to the rectification operation.

  Then, assuming that the lower limit of the prescribed range for maintaining the DC distribution network voltage Vdc is the minimum voltage VL, the operating voltage calculation device 21 uses the DC voltage time change rate ΔV / Δt, and uses the inverter operation start voltage VL ′ = VL. -ΔTL × ΔV / Δt is calculated.

  If the delay time ΔTL from the standby operation to the rectification operation is approximately the same as the delay time ΔTH from the standby operation to the inverter operation, the calculation of the inverter operation threshold voltage VH ′ and the calculation of the rectification operation threshold voltage VL ′ are performed. The calculation of the DC voltage time change rate ΔV / Δt can be the same.

  The operation switching control device 22 includes the measured value notified from the DC voltage / current measuring device 4 and the AC voltage / current measuring device 5, the inverter operation threshold voltage VH ′ and the rectification operation threshold voltage VL ′ notified from the operation voltage calculation device 21. Based on the above, the inverter operation, the rectifying operation, or the standby operation is selected, and the bidirectional power converter 1 is instructed.

  FIG. 2 is a flowchart showing the operation of the bidirectional power converter according to this embodiment. This operation is mainly based on the control from the operation switching control device 22 to the bidirectional conversion unit 2.

  Referring to FIG. 2, when the bidirectional power converter 20 starts operation, it first enters a standby operation (step 101). In the standby operation, the bidirectional power converter 20 determines whether or not the DC distribution network voltage Vdc is equal to or higher than the maximum voltage VH ′ (step 102).

  If the DC distribution network voltage Vdc is equal to or higher than the maximum voltage VH ′, the bidirectional power converter 20 starts an inverter operation (step 103) so that the DC distribution network voltage Vdc becomes VT satisfying VL <VT <VH. Then, power conversion from DC to AC is performed (step 104).

  Subsequently, the bidirectional power converter 20 determines whether or not the AC output current Iac is greater than or equal to the minimum AC output current Imac (step 105). If AC output current Iac is greater than or equal to minimum AC output current Imac, bidirectional power conversion device 20 returns to step 104 and continues the inverter operation.

  When the power supply / demand balance in the DC distribution network is balanced and the AC output current Iac falls below the minimum AC output current Imac, the bidirectional power converter 20 returns to Step 101 and shifts to a standby operation.

  In step 102, if the DC distribution network voltage Vdc is smaller than the maximum voltage VH ', the bidirectional power converter 20 determines whether or not the DC distribution network voltage Vdc is less than or equal to the minimum voltage VL' (step 106).

  If the DC distribution network voltage Vdc is equal to or lower than the minimum voltage VL ′, the bidirectional power conversion device 20 starts a clear current operation (step 107) so that the DC distribution network voltage Vdc becomes VT that satisfies VL <VT <VH. Then, power conversion from AC to DC is performed (step 108).

  Subsequently, the bidirectional power converter 20 determines whether or not the DC output current Idc is greater than or equal to the minimum DC output current Imdc (step 109). If the DC output current Idc is equal to or greater than the minimum DC output current Imdc, the bidirectional power converter 20 returns to Step 108 and continues the rectification operation.

  When the power supply / demand balance in the DC distribution network is balanced and the AC output current Idc falls below the minimum DC output current Imdc, the bidirectional power converter 20 returns to Step 101 and shifts to a standby operation.

  FIG. 3 is a graph showing a transient fluctuation of the DC distribution network voltage when the operation mode of the bidirectional power converter according to the present embodiment is switched. According to the present embodiment, when the operation mode is switched, while the fluctuations predicted from the delay time set in advance from the response characteristics and the change rate of the DC distribution network voltage are indicated, the DC distribution network voltage is within the specified range. The switching of the operation mode is determined using a threshold value set so that the operation mode can be switched. Therefore, as shown in FIG. 3, the bidirectional power conversion device of the present embodiment can maintain the DC distribution network voltage in a range between the maximum voltage VH and the minimum voltage VL, and can be stably operated.

It is a block diagram which shows the structure of the bidirectional | two-way power converter device by one Embodiment of this invention. It is a flowchart which shows operation | movement of the bidirectional | two-way power converter device by this embodiment. It is a graph which shows the transient fluctuation of the DC distribution network voltage at the time of operation mode switching of the bidirectional power converter by this embodiment. It is a block diagram which shows the structure of the bidirectional | two-way power converter device by a prior art. It is a flowchart which shows operation | movement of the conventional bidirectional | two-way power converter device. It is a timing chart which shows the operation example of the conventional bidirectional | two-way power converter device. It is a timing chart which shows a mode when the DC distribution network voltage of the conventional bidirectional | two-way power converter device exceeds a regulation range.

Explanation of symbols

2 Bidirectional Conversion Unit 4 DC Voltage Current Measuring Device 5 AC Voltage Current Measuring Device 6 DC Distribution Network 7 DC Load 8 Fuel Cell 9 Solar Power Generation 10 AC Distribution Network 11 AC Load 12 Commercial Power Supply 20 Bidirectional Power Converter 21 Operating Voltage Calculation device 22 Operation switching control device 101-109 steps

Claims (6)

A bidirectional power converter connected between a DC power distribution network to which a DC power supply and a DC load are connected, and an AC distribution network to which an AC power supply and an AC load are connected, and performs mutual power conversion and supply,
Inverter operation for converting direct current power of the direct current distribution network to alternating current and supplying the alternating current distribution network, rectification operation for converting electric power of the alternating current distribution network to direct current and supplying the direct current distribution network, and the inverter A bidirectional conversion unit that operates in either a standby operation in which neither the operation nor the rectifying operation is performed;
A DC measuring unit for measuring a DC distribution network voltage supplied by the DC distribution network;
The change rate of the DC distribution network voltage is calculated from the DC distribution network voltage measured by the DC measurement unit, and the waiting time is calculated using the change rate and a delay time required for the operation of the bidirectional conversion unit. An inverter operation threshold voltage lower than an upper limit of a specified range used for determination of transition from operation to the inverter operation, and a rectification operation threshold voltage higher than a lower limit of the specified range used for determination of transition from the standby operation to the rectification operation. An operating voltage calculating device for calculating;
The bidirectional conversion unit is shifted from the standby operation to the inverter operation by determination using the DC distribution network voltage measured by the DC measurement unit and the inverter operation threshold voltage calculated by the operating voltage calculation device, An bidirectional power conversion device comprising: an operation switching control device that shifts the bidirectional converter from the standby operation to the rectification operation based on the determination using the DC distribution network voltage and the rectification operation threshold voltage.   The operating voltage calculation device sets an upper limit value of a specified range of the DC distribution network voltage to VH and a lower limit value to VL, and determines a predetermined delay from a response characteristic from the standby operation to the inverter operation of the bidirectional conversion unit. Let ΔTH be the time, ΔTL be a delay time determined in advance from the response characteristic from the standby operation to the rectification operation, and let the rate of change of the DC distribution network voltage be dVdc / dt, and the inverter operation threshold voltage be (VH−ΔTH). The bidirectional power converter according to claim 1, wherein the bidirectional power conversion device is obtained by (dVdc / dt) and the rectification operation threshold voltage is obtained by (VL−ΔTL · dVdc / dt). An AC measuring unit for measuring an AC output current supplied from the bidirectional conversion unit to the AC distribution network;
The direct current measurement unit further measures a direct current output current supplied from the bidirectional conversion unit to the direct current distribution network,
In the standby operation, the operation switching control device shifts to the inverter operation when the DC distribution network voltage becomes equal to or higher than the inverter operation threshold voltage, and the rectification operation when the DC distribution network voltage becomes lower than the rectification operation threshold voltage. In the inverter operation, when the DC output current measured by the DC measurement unit falls below a predetermined threshold value, the operation returns to the standby operation, and the AC output measured by the AC measurement unit in the rectification operation. The bidirectional power converter according to claim 1 or 2, wherein when the current falls below a predetermined threshold value, the standby operation is resumed. In a bidirectional power conversion device connected between a DC power distribution network to which a DC power supply and a DC load are connected and an AC distribution network to which an AC power supply and an AC load are connected, and performing mutual power conversion and supply, the DC power distribution Inverter operation for converting the DC power of the network to AC and supplying it to the AC distribution network, Rectification operation for converting the power of the AC distribution network to DC and supplying it to the DC distribution network, the inverter operation and the A power conversion operation switching method for switching between a standby operation in which neither rectification operation is performed,
Measure the DC distribution network voltage supplied by the DC distribution network,
From the measured DC distribution network voltage, the rate of change of the DC distribution network voltage is calculated,
Using the rate of change, the inverter operation threshold voltage used for determining the transition from the standby operation to the inverter operation, and the rectification operation threshold voltage used for determining the transition from the standby operation to the rectification operation are calculated,
Transition from the standby operation to the inverter operation by the determination using the DC distribution network voltage and the inverter operation threshold voltage,
A power conversion operation switching method in which the standby operation is shifted to the rectification operation by determination using the DC distribution network voltage and the rectification operation threshold voltage.   The upper limit value of the specified range of the DC distribution network voltage is VH, the lower limit value is VL, a delay time predetermined from the response characteristic from the standby operation to the inverter operation is ΔTH, and the standby operation is switched to the rectification operation. The inverter operation threshold voltage is obtained by (VH−ΔTH · dVdc / dt), where ΔTL is a predetermined delay time from response characteristics, the rate of change of the DC distribution network voltage is dVdc / dt, and the rectification operation threshold voltage is obtained. The power conversion operation switching method according to claim 4, wherein the value is calculated by (VL−ΔTL · dVdc / dt). Measuring the AC output current supplied from the bidirectional conversion unit to the AC distribution network and the DC output current supplied from the bidirectional conversion unit to the DC distribution network;
In the standby operation, when the DC distribution network voltage is equal to or higher than the inverter operation threshold voltage, the inverter operation is performed, and when the DC distribution network voltage is lower than the rectification operation threshold voltage, the rectification operation is performed, and the inverter operation is performed. 6. The power according to claim 4, wherein when the DC output current falls below a predetermined threshold, the standby operation is resumed, and when the AC output current falls below a predetermined threshold in the rectifying operation, the standby operation is resumed. Conversion operation switching method.

Images