JP2014183612A - Dc-dc conversion apparatus, power conversion apparatus, dispersed power supply system, and control method for dc-dc conversion apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a DC-DC conversion apparatus, performing continuous operation of a power conversion apparatus even when an instantaneous drop in a system voltage occurs and rapidly recovering output power of the power conversion apparatus when the system voltage recovers, capable of accommodating it even if an output status of a DC power supply changes suddenly during an instantaneous drop.SOLUTION: After an instantaneous drop in a system voltage occurs, a control section, upon detecting that an output voltage of a DC-DC converter section 211 is below a threshold value for recovery determination, determines the system voltage to have recovered and, while the output voltage of the DC-DC converter section 211 is below the threshold value for recovery determination, increases a width of a pulse signal driving switching elements Q1, Q2 to raise the output voltage of the DC-DC converter section 211.

Description

  The present invention relates to a power conversion device.

  Conventionally, there is a power conditioner (power conversion device) that outputs AC power by connecting a distributed power source such as a solar cell to a commercial power system using a DC power source. In such a power conditioner, continuous operation is performed even when an instantaneous voltage drop (hereinafter referred to as “instantaneous drop”), which is a phenomenon in which the voltage drops instantaneously in the system voltage, and promptly when the system voltage returns. It is required to restore the output power.

  As a power conditioner as described above, for example, Patent Document 1 includes a DC / DC converter, monitors the output voltage Vdc of the DC / DC converter, and when the output voltage Vdc exceeds a preset upper limit value, A power conditioner is disclosed that determines that an instantaneous drop in the system voltage has occurred and switches to the instantaneous drop mode. Further, the power conditioner has a function of determining that the system voltage has been restored when the output voltage Vdc falls below a preset lower limit value, and returning to the normal mode.

  In the power conditioner, the DC input current Iin is changed so that the output voltage Vdc matches a preset target value in the voltage sag mode, and the DC input current is returned from the voltage sag mode to the normal mode. Control is performed to return the command value of Iin to the command value immediately before the occurrence of the instantaneous drop.

JP 2012-55036 A

  With the power conditioner disclosed in Patent Document 1, continuous operation can be performed even when a system voltage drop occurs, and output power can be quickly returned when the system voltage is restored from the voltage drop.

  However, if the DC power source is, for example, a solar cell, the amount of solar radiation may suddenly decrease during the sag and the power generation amount of the solar cell may decrease. When returning from the low mode to the normal mode, there is a problem that the DC input current Iin cannot be controlled to the command value even if the command value of the DC input current Iin is returned to the command value immediately before the instantaneous drop.

  Accordingly, the present invention provides a DC / DC conversion that can continue the operation of the power conversion device even when a system voltage drop occurs, and can quickly restore the output power of the power conversion device when the system voltage is restored. An object of the present invention is to provide a DC / DC converter that can cope with a sudden change in the output status of a direct current power supply during an instantaneous drop.

In order to achieve the above object, the present invention can connect a DC power source on the input side and an inverter device connected to the output side on the output side, respectively, and a DC / DC converter unit having at least one switching element;
A DC / DC converter comprising: a control unit that drives and controls the DC / DC converter unit;
When the control unit detects that the output voltage of the DC / DC converter unit exceeds a threshold for determining a sag, a determination is made that a system voltage sag has occurred, and power is continuously output from the inverter device. As described above, while the output voltage of the DC / DC converter unit is higher than the voltage drop determination threshold, the pulse signal width for driving the switching element is reduced to reduce the output voltage of the DC / DC converter unit. Control
Thereafter, when the control unit detects that the output voltage of the DC / DC converter unit has fallen below the return determination threshold, the control unit determines that the system voltage has been recovered, and the output voltage of the DC / DC converter unit is While the value is below the determination threshold, the width of the pulse signal that drives the switching element is widened to increase the output voltage of the DC / DC converter unit.

  Further, in the above configuration, when the control unit detects that the output voltage of the DC / DC converter unit exceeds the threshold value for determining the voltage drop, the output voltage of the DC / DC converter unit is used for determining the voltage drop. While the threshold value is exceeded, the width of the pulse signal for driving the switching element may be reduced according to the amount by which the output voltage of the DC / DC converter unit exceeds the threshold value for determining the instantaneous drop or by a fixed amount. Good.

  In any one of the configurations described above, when the control unit detects that the output voltage of the DC / DC converter unit has fallen below the return determination threshold, the output voltage of the DC / DC converter unit determines the return determination. The width of the pulse signal for driving the switching element may be widened according to the amount by which the output voltage of the DC / DC converter section is below the return determination threshold value or while the output voltage is below the return threshold value. Good.

In any one of the above configurations, the DC power supply is a solar cell,
The control unit performs MPPT control (maximum power point tracking control) at normal time,
Further, when the control unit has not detected that the output voltage of the DC / DC converter unit has exceeded the instantaneous voltage drop determination threshold value, the output voltage of the DC / DC converter unit sets the return determination threshold value. When it falls below, it is good also as a structure which does not perform control which expands the width | variety of the pulse signal which drives the said switching element.

In any one of the above configurations, the DC power source is a secondary battery or a fuel cell,
The control unit performs constant power control or constant current control in normal times,
Further, when the control unit has not detected that the output voltage of the DC / DC converter unit has exceeded the instantaneous voltage drop determination threshold value, the output voltage of the DC / DC converter unit sets the return determination threshold value. When it falls below, it is good also as a structure which does not perform control which expands the width | variety of the pulse signal which drives the said switching element.

  The present invention also includes a DC / DC converter having any one of the above-described configurations, and an inverter device connected to the grid connected to the output side of the DC / DC converter unit included in the DC / DC converter. Let it be a power converter.

  In addition, the present invention provides a distributed power supply system including the power conversion device configured as described above and a DC power supply connected to the input side of the power conversion device.

Further, the present invention can connect a DC power source on the input side and an inverter device connected to the output side on the output side, respectively, and a DC / DC conversion device including a DC / DC converter unit having at least one switching element. Control method,
A first determination step of determining that an instantaneous drop in the system voltage has occurred when detecting that the output voltage of the DC / DC converter unit exceeds a threshold for determining an instantaneous drop;
After the first determination step, the switching element is driven while the output voltage of the DC / DC converter unit exceeds the threshold for determination of instantaneous drop so that electric power is continuously output from the inverter device. A first control step for performing control to reduce the output voltage of the DC / DC converter by reducing the pulse signal width;
After the first control step, when detecting that the output voltage of the DC / DC converter unit has fallen below the return determination threshold value, a second determination step for determining that the system voltage has returned;
After the second determination step, while the output voltage of the DC / DC converter unit is below the return determination threshold, the pulse signal for driving the switching element is widened to output the DC / DC converter unit. And a second control step for performing control to increase the voltage.

  According to the present invention, a DC / DC converter capable of continuously operating the power converter even when a system voltage drop occurs, and quickly returning the output power of the power converter when the system voltage is restored. However, even if the output status of the DC power supply suddenly changes during the voltage sag, it can be dealt with.

It is a block diagram of the distributed power supply system which concerns on one Embodiment of this invention. It is a figure which shows the FRT (Fault Ride Through) requirement prescribed | regulated by the grid connection rule (in the case of 20% or more of residual voltages). It is a figure which shows the FRT (Fault Ride Through) requirement prescribed | regulated by the grid connection rule (in the case of less than 20% of remaining voltage). It is a figure which shows an example of each part waveform of the power conditioner which concerns on one Embodiment of this invention when the instantaneous drop of a system voltage generate | occur | produces.

  An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of a distributed power supply system for grid connection according to an embodiment of the present invention. A distributed power supply system 10 shown in FIG. 1 includes a DC power supply 1 and a power conditioner 2.

  The power conditioner 2 is a power conversion device that is connected to the commercial power system 3 and converts the DC power output from the DC power source 1 into AC power and outputs the AC power. When the DC power source 1 that is a distributed power source is configured by, for example, a solar battery, the distributed power source system 10 corresponds to a solar power generation system. The DC power source 1 may be a power generation device that uses renewable energy other than solar cells, or may be a fuel cell or a storage battery.

  The power conditioner 2 includes a DC / DC conversion device 21 and an inverter device 22. The DC / DC converter 21 includes a DC / DC converter unit 211, a DC / DC converter control microcomputer 212, and drivers 213 and 214.

  The DC / DC converter unit 211 is a so-called half-bridge type DC / DC converter circuit using LLC resonance.

  As shown in FIG. 1, the DC / DC converter unit 211 includes an input capacitor C0, switching elements Q1 and Q2, a voltage resonance capacitor Cv, a current resonance capacitor Cr, a transformer Tr0, a capacitor C1, a diode D1 and D2, a smoothing capacitor C2, and an output voltage detection circuit A1 are provided.

  A rectifier circuit including diodes D1 and D2 and a capacitor C1 is connected to the secondary side of the transformer Tr0. A smoothing capacitor C2 is connected to the output side of the rectifier circuit, and the input side of the inverter device 22 is connected to the output side of the smoothing capacitor C2.

  The transformer Tr0 is a loosely coupled transformer, and includes a leakage inductance and an excitation inductance (not shown), and the leakage inductance corresponds to a resonant inductor that contributes to current series resonance.

  The switching elements Q1 and Q2 formed of MOSFETs have antiparallel diodes connected between the drain and source. The antiparallel diode may be a parasitic diode (built-in diode) or an externally connected diode.

  The positive side of the DC power source 1 is connected to one end of the input capacitor C0, and the negative side of the DC power source 1 is connected to the other end of the input capacitor C0. A group in which switching elements Q1 and Q2 are connected in series is connected in parallel with input capacitor C0.

  One end of the voltage resonance capacitor Cv is connected to the drain of the switching element Q1, and one end of the current resonance capacitor Cr is also connected. The other end of the current resonance capacitor Cr is connected to one end of the primary winding of the transformer Tr0. The other end of the primary winding of the transformer Tr0 is connected to the other end of the voltage resonance capacitor Cv, and is also connected to a connection point between the source of the switching element Q1 and the drain of the switching element Q2.

  An output terminal of a driver 214 which is a gate driving circuit for switching the switching element Q1 is connected to the gate of the switching element Q1, and a gate driving circuit for switching the switching element Q2 is connected to the gate of the switching element Q2. The output terminal of a certain driver 213 is connected. When the DC / DC converter control microcomputer 212 outputs a drive signal to the driver 214, the switching element Q1 is driven by the driver 214. Further, the DC / DC converter control microcomputer 212 outputs a drive signal to the driver 213, whereby the switching element Q <b> 2 is driven by the driver 213.

  When the switching elements Q1 and Q2 are complementarily pulse-driven including the dead time, the DC / DC converter unit 211 converts the DC power output from the DC power source 1 into DC power of a predetermined voltage, and the inverter device 22 Output to.

  The inverter device 22 to which the commercial power system 3 is connected on the output side converts the DC power output from the DC / DC converter unit 211 into AC power and outputs the AC power. The inverter device 22 may be configured by, for example, a so-called two-level inverter device or three-level inverter device.

Further, the output voltage detection circuit A1, in which both ends of the smoothing capacitor C2 are connected to the input, outputs the detection signal of the output voltage Vdc (for example, the detection signal is 5.0V when Vdc = 450V) to the DC.
/ Output to DC converter control microcomputer 212. The DC / DC converter control microcomputer 212 monitors the output voltage Vdc of the DC / DC converter unit 211 by monitoring the output of the output voltage detection circuit A1.

  Although the power conditioner 2 which concerns on this embodiment is the above structures, the instantaneous drop of the system voltage of the commercial power grid 3 is demonstrated here. The upper part of Fig. 2A and Fig. 2B shows the behavior of the grid voltage when a voltage sag occurs. The operation continuation requirements (FRT (Fault Ride Through)) when a voltage sag occurs that the power conditioner must satisfy (Requirements) are shown in the lower part corresponding to the upper part of FIGS. 2A and 2B.

  In the upper part of FIG. 2A, when the voltage before the voltage drop is 100%, the voltage drops to 20% or more and a voltage sag occurs, and within 1 second from the voltage sag, the system voltage reaches 100%. Indicates return. When such a system voltage sag and recovery occur, as shown in the lower part of FIG. 2A, the FRT requirement is that the power conditioner is continuously operated when the system sag occurs, and 0.1% from the time when the system voltage recovers. It is required to restore the inverter output to 80% or more before the voltage drop within 2 seconds.

  In the upper part of FIG. 2B, when the system voltage is 100% of the voltage before the voltage drop, the voltage drops to a voltage of less than 20% and a voltage sag occurs. It shows that it returned to%. When such a system voltage dip and recovery occur, as shown in the lower part of FIG. 2B, the FRT requirement is that the power conditioner continues to operate or is gate-blocked when the sag occurs and the system voltage is restored. It is required to restore the inverter output to 80% or more before the voltage drop within 0.2 seconds.

  The power conditioner 2 according to the present embodiment can perform control that satisfies the FRT requirement, which will be described next. The DC power supply 1 will be described as a solar cell.

  FIG. 3 shows an example of each waveform of the output voltage Vdc of the DC / DC converter 211 and the output current of the power conditioner 2 when an instantaneous drop in the system voltage occurs (when the voltage drops to 20% before the voltage drop). This will be described below with reference to FIG. Note that the specific voltage values described below are merely examples.

  First, during the normal operation of the DC / DC converter 21, the DC / DC converter control microcomputer 212 controls the input voltage (operating point) so as to maximize the input power from the solar cell (DC power supply 1). Control (maximum power point tracking control) is performed. As a technique for MPPT control, for example, a so-called hill climbing method can be employed. In the hill-climbing method, the input voltage is sequentially changed in the direction in which the input power increases, and the input voltage that maximizes the input power is searched. The input voltage is changed by changing the width of the pulse signal that drives the switching elements Q1 and Q2.

  During the normal operation of the DC / DC converter 21, the inverter device 22 controls the output power so that the output voltage Vdc of the DC / DC converter unit 211 (= the input voltage of the inverter device 22) is a constant voltage. In the example of FIG. 3, since the constant voltage is 380V, the output voltage Vdc is controlled to 380V on average. In FIG. 3, the output voltage Vdc includes a ripple component because it is influenced by the AC on the system side.

  Note that the inverter device 22 always performs control such that the output voltage Vdc becomes a constant voltage as described above, even after the occurrence of an instantaneous voltage drop described below.

  During normal operation, the DC / DC converter control microcomputer 212 monitors the output voltage Vdc based on the output of the output voltage detection circuit A1, and when the instantaneous voltage decreases, the system voltage decreases and the output power of the inverter device 22 rapidly increases. When it is detected that the output voltage Vdc has exceeded a certain threshold value (threshold drop determination threshold) by the drop, it is determined that an instantaneous drop in the system voltage has occurred. Then, the DC / DC converter control microcomputer 212 sequentially drives the switching elements Q1 and Q2 according to the amount by which the output voltage Vdc exceeds the threshold while the output voltage Vdc exceeds the threshold for determination of instantaneous drop. Reduce the width of the signal. More specifically, as the amount by which the output voltage Vdc exceeds the threshold value is larger, the amount of reduction of the pulse signal width is increased, and the pulse signal width is reduced by the amount of reduction. Note that the pulse signal width may be reduced step by step until the pulse signal width is reduced by the reduction amount, or may be reduced at a stroke instead of stepwise. When the output voltage Vdc is equal to or lower than the threshold for determination of instantaneous drop, the control for reducing the pulse width is stopped.

  Thereby, it becomes control which suppresses the input current of the DC / DC converter part 211, and can suppress the raise of the output voltage Vdc. In the example of FIG. 3, the threshold is set to 400V, and when the output voltage Vdc exceeds 400V, the output voltage Vdc is reduced by reducing the pulse signal width, and thereafter, the average voltage is a constant voltage of about 390V. Electric power is continuously output from the power conditioner 2 even during a sag.

  Further, when it is detected that the output voltage Vdc has exceeded the threshold for determining the instantaneous drop, the pulse width reduction amount corresponding to the detected Vdc is determined based on the correspondence relationship between the threshold value of Vdc and the pulse width reduction amount, While Vdc is higher than the threshold for determination of instantaneous drop, an embodiment may be adopted in which the pulse width is sequentially reduced by a fixed amount of the determined pulse width reduction amount. When the threshold value of Vdc is set finely, the correspondence relationship may be defined by a table.

  The microcomputer 212 for DC / DC converter control monitors the output voltage Vdc by the output of the output voltage detection circuit A1 after the instantaneous drop of the system voltage, and the inverter device 22 in the subsequent stage outputs the output current when the system voltage is restored. When it is detected that the output voltage Vdc has fallen below a certain threshold value (recovery determination threshold value) in an attempt to extract a large amount of power to maintain, it is determined that the system voltage has recovered. Then, while the output voltage Vdc is below the return determination threshold value, the DC / DC converter control microcomputer 212 sequentially drives the switching elements Q1 and Q2 according to the amount by which the output voltage Vdc falls below the threshold value. Increase the width of. More specifically, as the amount by which the output voltage Vdc falls below the threshold value is larger, the amount of expansion of the pulse signal width is increased, and the pulse signal width is increased by the amount of expansion. It should be noted that it may be expanded stepwise until the pulse signal width is increased by the amount of expansion, or it may be expanded at once rather than stepwise. When the output voltage Vdc is equal to or higher than the return determination threshold, the control for increasing the pulse width is stopped.

  Thereby, it becomes control which increases the input current of the DC / DC converter part 211, The output voltage Vdc can be raised rapidly, As a result, the output electric power of the power conditioner 2 can be returned rapidly. In the example of FIG. 3, the output voltage Vdc decreases when the system voltage is restored. However, when the voltage falls below 350 V, which is the threshold value, the pulse signal width is widened, so the output voltage Vdc quickly increases to about 380 V. The output current of the inverter 2 is also restored to the same level as before the occurrence of the instantaneous drop.

  Further, when it is detected that the output voltage Vdc has fallen below the return determination threshold value, a pulse width expansion amount corresponding to the detected Vdc is determined based on the correspondence relationship between the Vdc threshold value and the pulse width expansion amount, and Vdc While the value is lower than the return determination threshold value, an embodiment may be adopted in which the pulse width is sequentially increased by a certain amount of the determined pulse width extension amount. When the threshold value of Vdc is set finely, the correspondence relationship may be defined by a table.

  The DC / DC converter control microcomputer 212 returns to the normal operation of performing the MPPT control after expanding the pulse signal width as described above.

  As described above, according to the present embodiment, the operation of the power conditioner 2 can be continued even when the voltage drop of the system voltage occurs, and when the system voltage is restored, the output power of the power conditioner 2 is quickly restored. So that FRT requirements can be met.

  Furthermore, in the present embodiment, even when the amount of solar cell power generation is reduced due to a sudden decrease in the amount of solar radiation during the instantaneous drop in the system voltage, the output voltage Vdc corresponding to the return of the system voltage is reduced. Since it is a value, it is possible to operate without problems.

  Further, in the present embodiment, when the output voltage Vdc falls below the return determination threshold, triggered by the fact that the output voltage Vdc once exceeds the instantaneous drop determination threshold, the above-described pulse signal width is controlled to be widened. If it is not detected that the threshold value for low determination has been exceeded, the control is not performed if the threshold value for return determination is not reached.

  When normal MPPT control is performed without causing an instantaneous drop in the system voltage, and the output voltage Vdc is controlled to a constant voltage and the output voltage Vdc falls below the return determination threshold value due to a ripple component, When the control for widening the pulse signal width is performed, the input voltage deviates from the optimum operating point in MPPT control (interference with MPPT control). However, in the present embodiment, since the control for widening the pulse signal width is not performed in such a case, the interference with the MPPT control as described above can be avoided.

  The embodiment of the present invention has been described above, but the embodiment can be variously modified within the scope of the gist of the present invention.

  For example, the DC / DC converter unit 211 can be configured as a full-bridge circuit or a non-insulated DC / DC converter.

  Furthermore, the DC power source 1 may be a power generation device that uses renewable energy other than solar cells, or may be a fuel cell or a storage battery. In the case of a fuel cell or a storage battery (secondary battery), the input constant power control or the constant current control is used, so that it can be similarly applied to power control other than MPPT control. In this case, as described above, when the output voltage Vdc is not detected to exceed the instantaneous drop determination threshold and is below the return determination threshold, the control for widening the pulse signal width is not performed. Interference with constant power control or constant current control can be avoided.

DESCRIPTION OF SYMBOLS 1 DC power supply 2 Power conditioner 3 Commercial power system 10 Distributed power supply system 21 DC / DC conversion device 22 Inverter device 211 DC / DC converter part 212 DC / DC converter control microcomputer 213, 214 Driver C0 Input capacitor Q1, Q2 Switching element Cv voltage resonance capacitor Cr current resonance capacitor Tr0 transformer C1 capacitor D1, D2 diode C2 smoothing capacitor A1 output voltage detection circuit

Claims (5)

A DC power source can be connected to the input side, and an inverter device connected to the grid can be connected to the output side, and a DC / DC converter unit having at least one switching element;
A DC / DC converter comprising: a control unit that drives and controls the DC / DC converter unit;
When the control unit detects that the output voltage of the DC / DC converter unit exceeds a threshold for determining a sag, a determination is made that a system voltage sag has occurred, and power is continuously output from the inverter device. As described above, while the output voltage of the DC / DC converter unit is higher than the voltage drop determination threshold, the pulse signal width for driving the switching element is reduced to reduce the output voltage of the DC / DC converter unit. Control
Thereafter, when the control unit detects that the output voltage of the DC / DC converter unit has fallen below the return determination threshold, the control unit determines that the system voltage has been recovered, and the output voltage of the DC / DC converter unit is While the threshold value for determination is below, the width of the pulse signal that drives the switching element is widened to increase the output voltage of the DC / DC converter unit,
A DC / DC converter characterized by the above.   When the control unit detects that the output voltage of the DC / DC converter unit has exceeded the threshold value for determining a voltage sag, while the output voltage of the DC / DC converter unit exceeds the threshold value for determining a sag voltage The width of a pulse signal for driving the switching element is reduced in accordance with an amount by which an output voltage of the DC / DC converter unit exceeds the threshold for determining a voltage sag or by a constant amount. The DC / DC converter described in 1. When the control unit detects that the output voltage of the DC / DC converter unit has fallen below the return determination threshold value, while the output voltage of the DC / DC converter unit is below the return determination threshold value, The width of the pulse signal for driving the switching element is increased according to the amount by which the output voltage of the DC / DC converter unit is lower than the return determination threshold, or by a certain amount.
The DC / DC conversion apparatus according to claim 1 or 2, wherein: The DC power source is a solar cell,
The control unit performs MPPT control (maximum power point tracking control) at normal time,
Further, when the control unit has not detected that the output voltage of the DC / DC converter unit has exceeded the instantaneous voltage drop determination threshold value, the output voltage of the DC / DC converter unit sets the return determination threshold value. 4. The DC / DC converter according to claim 1, wherein when the value is lower, control for increasing a width of a pulse signal for driving the switching element is not performed. 5.   A DC / DC converter according to any one of claims 1 to 4, a system-connected inverter device connected to an output side of a DC / DC converter unit included in the DC / DC converter, The power converter provided with.

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