JP2007159370A - Bidirectional power conversion device with reverse power flow prevention function - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a bidirectional power conversion device with a reverse power flow prevention function, capable of suppressing time lag at switching of reverse power flow prevention operation and voltage transition fluctuation to an AC power distribution network, and capable of reducing energy loss. <P>SOLUTION: A reverse power flow prevention output control circuit 13, if a commercial output current detected by a commercial output current detection circuit 14 underruns a reverse power flow set current value Ism (A), lowers an AC output voltage by controlling switching pattern of a converter 27 of a bidirectional power conversion unit 11 so that the commercial output current does not underrun Ism (A). Thus, power conversion amount from a DC power distribution network 18 to an AC power distribution network 19 is reduced, to prevent reverse power flow. An excessive power in the DC power distribution network 18 is stored in a DC voltage stabilizing battery 12 connected to the DC power distribution network 18, being parallel to the bidirectional conversion unit 11. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention is connected to a DC distribution network in which a plurality of DC power supplies and a plurality of DC loads are connected, and an AC distribution network in which a commercial power supply and a plurality of AC loads are connected, and between the DC distribution network and the AC distribution network. It is related with the bidirectional | two-way power converter device which performs mutual power supply between.

  For example, Patent Literature 1 and Patent Literature 2 disclose a reverse power flow prevention device in a private power generation facility that is connected to a grid. In Patent Document 1, when the load is reduced, the output on the power generator side is also reduced. Further, Patent Document 2 performs control to immediately stop a distributed power source such as solar power generation when commercial power is interrupted.

  FIG. 5 shows a conventional example of a power supply system using such a power generator with a reverse power flow prevention function. The power generator with a reverse flow prevention function includes an AC generator 3, a commercial output power detector 4, a dummy resistance power detector 5, a reverse flow prevention control circuit 6, an output control controller 7, a dummy resistor input circuit 8, and a dummy resistor 9. The power supply is connected to the commercial power supply 1 for the AC load 2.

When the amount of power generated by the AC generator 3 becomes excessive relative to the AC load 2 due to the decrease in the AC load 2, the reverse power flow prevention control circuit 6 calculates the reverse power flow energy from the detected value of the commercial output power detector 4. Then, a signal for turning on the dummy resistor 9 corresponding to the reverse power flow amount is sent to the dummy resistor making circuit 8. In parallel with this, a signal for suppressing the power generation amount of the AC generator 3 is sent to the output controller 7. Thereafter, when the output of the AC generator 3 decreases and the output of the commercial power source detected by the commercial output power detector 4 becomes larger than the power consumption of the dummy resistor detected by the dummy resistance power detector 5, the reverse power flow prevention is performed. The control circuit 6 sends a signal for opening the dummy resistor to the dummy resistor input circuit 8.
JP-A-7-123596 Japanese Patent Laid-Open No. 11-41818

  However, in the conventional power generator with the reverse flow prevention function described above, a dummy resistor connected in parallel to the AC load via the switch is necessary to prevent the reverse flow, and a relay is connected to the switch for connecting the dummy resistor. Therefore, there is a problem that a time lag occurs at the time of switching the reverse power flow preventing operation, and the introduction of the dummy resistor causes a transient voltage fluctuation to the AC distribution network, and the power consumption of the dummy resistor is all lost.

  An object of the present invention is to provide a bidirectional power conversion device with a reverse power flow prevention function capable of suppressing a time lag at the time of switching a reverse power flow prevention operation and a voltage transient fluctuation to an AC distribution network and capable of reducing energy loss. is there.

  In order to achieve the above object, a bidirectional power converter of the present invention includes a bidirectional power conversion unit that performs mutual power conversion between AC and DC, and a commercial power that detects a current flowing from a commercial power source to the AC power distribution network. Comparing the detected current of the output current detection circuit and the commercial output current detection circuit with the reverse power flow setting current value, when the former falls below the latter, an output suppression signal is output to the bidirectional power conversion unit, and the bidirectional power conversion unit A reverse flow prevention output control circuit for reducing the alternating current output and preventing reverse flow, and a DC voltage stabilizing battery for absorbing surplus current of the DC distribution network during the reverse flow prevention operation.

  When the commercial output current detected by the commercial output current detection circuit falls below the reverse flow setting current value Ism (A), the reverse flow prevention output control circuit prevents the commercial output current from dropping below Ism (A). By reducing the AC output voltage by controlling the switching pattern of the converter, the amount of power conversion from the DC distribution network to the AC distribution network is reduced, and reverse power flow is prevented. Also, if the amount of power generated by the DC power supply and the DC load do not decrease, surplus power is generated in the DC distribution network, but the surplus power in the DC distribution network is stabilized by the DC voltage connected to the DC distribution network in parallel with the bidirectional conversion unit. Store in battery. This eliminates the need for switching with dummy resistors compared to a conventional power generation device having a reverse power flow prevention function, so there is no time lag when switching the reverse power flow prevention operation, suppressing transient voltage fluctuations, Energy loss can be reduced during reverse power flow prevention operation.

  According to the present invention, in the reverse power flow prevention control of the bidirectional power converter, the time lag at the time of switching the reverse power flow prevention operation and the voltage transient fluctuation to the AC distribution network are suppressed, and the surplus power generation amount at the time of the reverse power flow operation is reduced to the direct current. Energy loss can be reduced by storing the battery in a voltage stabilizing battery.

  Next, embodiments of the present invention will be described with reference to the drawings.

  Referring to FIG. 1, a bidirectional power converter 10 with a reverse power flow prevention function according to the present embodiment is connected to a DC distribution network 18 having a DC voltage V0 (V), an AC distribution network 19 having an AC200 (V), and a commercial power supply 1. Has been. The DC distribution network 18 includes a plurality of DC power sources such as the solar power generation device 15 and the fuel cell 16 and a plurality of DC loads 17. The AC power distribution network 19 includes a plurality of AC loads 2 and a commercial power source 1. The bidirectional power converter 10 includes a bidirectional conversion unit 11, a commercial output current detection circuit 14, a reverse power flow prevention output control circuit 13, and a DC voltage stabilizing battery 12. The bidirectional conversion unit 11 includes a converter 27 on the DC distribution network 18 side and an inverter 28 on the AC distribution network 19 side. A space between the converter 27 and the inverter 28 is referred to as Vlink 29. As shown in FIG. 2, the converter 27 of the bidirectional conversion unit 11 includes a switch 20, a diode 21, an inductance 22, a capacitor 23, an input voltage detection circuit 24, an input voltage control circuit 25, and a reverse flow prevention output suppression circuit 26. Has been. Note that FIG. 1 actually includes a plurality of bidirectional conversion units 11. Whether the number of the bidirectional conversion units 11 is one or more, the AC output reduction in the bidirectional conversion units 11 can be performed independently for preventing reverse power flow.

  The bidirectional power converter 10 is in a standby operation state in which power is not exchanged between the DC power distribution network 18 and the AC power distribution network 19 when the voltage of the DC power distribution network 18 satisfies Vh ≧ V0 ≧ Vl. , Vlink 29 is maintained at Vr (V) by the converter 27 and the inverter 28. When the voltage Vdc of the DC distribution network 18 exceeds Vh (V), the bidirectional power converter 10 changes from the DC distribution network 18 to the AC distribution network 19 so as to lower the voltage Vdc of the DC distribution network 18 to V0 (V). Transition to inverter operation to send power. When the voltage Vdc of the DC distribution network 18 falls below Vl (V), the bidirectional power conversion apparatus 10 moves from the AC distribution network 19 to the DC distribution network 18 so as to raise the voltage Vdc of the DC distribution network 18 to V0 (V). Transition to rectification operation to send power.

  Next, the operation of the bidirectional power converter 10 of the present embodiment will be described with reference to FIG.

1) During normal inverter operation In order to lower the voltage Vdc of the DC distribution network 18, the inverter output of the bidirectional power conversion apparatus 10 during inverter operation for performing power conversion from DC to AC is increased in proportion to the voltage of Vlink. Become. Further, the switching on time Ton of the converter 27 is proportional to the output voltage of the converter 27. Therefore, as the difference between the voltage Vdc of the DC distribution network 18 and the target voltage V0 is larger, control is performed to decrease the output voltage of the converter 27, and the amount of power conversion from the DC system to the AC system is increased.

  When the voltage Vdc of the DC distribution network 18 exceeds Vh (V) (step 101), the inverter operation from DC to AC is started (step 102), and the commercial output current Ics detected by the commercial output current detection circuit 14 is started. Is output to the reverse flow prevention output control circuit 13. The on time Ton of the switch 20 of the converter 27 is initialized to 0 (step 103). Ton 'is obtained by multiplying the difference between the voltage Vdc and the voltage V0 by a constant γ and adding Ton to the difference (step 104). The reverse flow prevention output control circuit 13 compares Ics with the reverse flow set current (Ism (A)) including a margin that does not cause reverse flow (step 105). When Ics is larger than Ism, Ton ′ is set to Ton (step 106), the switching signal Ton is transmitted from the input voltage control circuit 25 to the switch 20 (step 107), and the process returns to step 104.

2) At the time of reverse flow prevention control operation When the voltage Vdc of the DC distribution network 18 is high, the bidirectional AC output increases, and when the commercial output current decreases, the reverse flow occurs when the AC load is small. Therefore, the switching on-time of the converter 27 is controlled so as to be inversely proportional to the difference between the reverse flow threshold current Ism and the commercial output current Ics, thereby reducing the bidirectional AC output.

  When Ics detected by the commercial output current detection circuit 14 decreases and Ics falls below Ism (A) (in the case of NO at step 105), Ton 'is set to Ton "(step 108) and X (n) is set to 0. (Step 109) Next, the difference between Ics and Ism is multiplied by a constant κ, and X (n) is added to this to obtain X (n + 1) (Step 110). X (n) is set (step 111), Xn (n) multiplied by Ton "is set as Ton (step 112), and the switching signal Ton is transmitted from the input voltage control circuit 25 to the switch 20 (step 113). The above steps 110 to 113 are repeated until X (n) becomes 1 or more. When X (n) becomes 1 or more, the process returns to step 103.

  Note that the DC voltage stabilizing battery 12 is a storage battery having a rated voltage that does not become fully charged with a charging capacity of about 75% even when the bidirectional power converter 10 is in the standby state of the DC voltage V0 (V). An example of the relationship between the DC charging voltage and the charging capacity of the DC voltage stabilizing battery 12 is shown in FIG. The DC voltage stabilizing battery 12 is connected in parallel with the bidirectional conversion unit 11 on the DC distribution network 18 side in the bidirectional power converter 10. When the reverse power flow preventing operation of the bidirectional power converter 10 is activated, if the AC load 2 or the DC load 17 decreases, the amount of power generation in the DC distribution network 18 becomes excessive, and the voltage of the DC distribution network 18 increases. To do. Along with this, the DC voltage stabilizing battery 12 starts charging, and suppresses the voltage increase of the DC distribution network 18. On the other hand, the power stored in the DC voltage stabilizing battery 12 is consumed by the DC load 17 or the AC load 2 by discharging when the voltage of the DC distribution network 18 is reduced, thereby preventing the reverse power flow prevention operation. The surplus power at the time can be used effectively. When the DC voltage stabilizing battery 12 is, for example, a sealed lead-acid battery, the voltage of a single battery is 1.6V when the battery has a capacity of 0% and 2.23V when the capacity is 100%. Control means (not shown) for setting the rectifying operation start voltage VL and the inverter operation start voltage VH of the bidirectional power converter 10 so that each voltage of the battery 12 does not deviate from this voltage range is bidirectional. It may be provided in the power converter 10.

It is a figure which shows the structure of one Embodiment of the bidirectional | two-way power converter device with a reverse power flow prevention function by this invention. It is a figure which shows the structure of the converter of a bidirectional | two-way conversion unit. It is explanatory drawing of converter control of a bidirectional | two-way power conversion unit. It is a figure which shows the charge amount characteristic of the DC distribution network voltage and the battery for DC voltage stabilization. It is a figure which shows the structure of the conventional alternating current generator with a reverse power flow prevention function.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Commercial power supply 2 AC load 3 AC generator 4 Commercial output power detector 5 Dummy resistance power detector 6 Reverse power flow prevention control circuit 7 Output control controller 8 Dummy resistance input circuit 9 Dummy resistor 10 Bidirectional power converter 11 Bidirectional conversion Unit 12 DC voltage stabilization battery 13 Reverse power flow prevention output control circuit 14 Commercial output current detection circuit 15 Wind power generator 16 Fuel cell 17 DC load 18 DC distribution network 19 AC distribution network 20 Switch 21 Diode 22 Inductance 23 Capacitor 24 Input voltage detection Circuit 25 Output voltage control circuit 26 Reverse power flow prevention output control circuit 27 Converter 28 Inverter 29 Vlink

Claims (5)

Bidirectional power connected to a DC distribution network to which a plurality of DC power supplies and a plurality of DC loads are connected, and to an AC distribution network to which a commercial power supply and a plurality of AC loads are connected to perform mutual power conversion between AC and DC A conversion device,
A bidirectional power conversion unit that performs mutual power conversion between AC and DC; and
A commercial output current detection circuit for detecting a current flowing from the commercial power source to the AC distribution network;
The detected current of the commercial output current detection circuit is compared with a reverse power flow setting current value, and when the former falls below the latter, an output suppression signal is output to the bidirectional power conversion unit, and the AC output of the bidirectional power conversion unit is A reverse flow prevention output control circuit that reduces and prevents reverse flow;
A bidirectional power converter comprising: a DC voltage stabilizing battery that absorbs surplus current of the DC distribution network during reverse power flow prevention operation.   The bidirectional power conversion device according to claim 1, comprising a plurality of the bidirectional power conversion units.   The battery of the rated voltage which does not become a full charge is used as the DC voltage stabilizing battery when the DC distribution network voltage increases due to a decrease in DC load or AC load during reverse power flow prevention control. Bi-directional power converter.   4. The bidirectional power according to claim 1, further comprising control means for controlling a DC distribution network voltage maintained by the bidirectional power converter to a voltage range in which the DC voltage stabilizing battery is not fully charged. 5. Conversion device.   The bidirectional conversion unit includes a converter connected to a DC distribution network and an inverter connected to an AC distribution network, and the converter reduces an AC output of the bidirectional power conversion unit by a switching operation. 2. The bidirectional power converter according to 1.

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