JP5817225B2 - Power converter - Google Patents

Description

  The present invention relates to a power converter such as an uninterruptible power supply (UPS), a voltage sag compensator, a photovoltaic power conditioner (an inverter for photovoltaic power generation), and in particular, an AC output voltage to ground is ungrounded. It is related with the power converter device which suppresses becoming balance.

  FIG. 3 is a schematic diagram illustrating an example of a conventional inverter device 10 for photovoltaic power generation. The inverter device 10 for photovoltaic power generation is a power conversion device that converts a DC voltage generated by the solar battery panel 1 into an AC voltage by the inverter circuit 3 and supplies power to the power supply system 4.

  In the inverter device 10 for photovoltaic power generation, the DC voltage varies depending on the illuminance from the sun with respect to the solar cell panel 1 and the power (that is, generated power) supplied from the inverter circuit 3 to the power supply system 4. In order to operate the inverter circuit 3 efficiently with respect to the fluctuation of the DC voltage, generally, a boost chopper circuit 2 is provided between the solar cell panel 1 and the inverter circuit 3 as shown in FIG. .

JP 2007-68385 A

  As shown in FIG. 3, the photovoltaic power generation inverter device 10 uses the negative pole of the boost chopper circuit 2 and the negative pole of the inverter circuit 3 as a common (connected by a common line). Since the solar cell panel 1 has a stray capacitance with respect to the ground, the solar cell panel 1 is in a state in which the positive electrode and the negative electrode are grounded by several [μF] capacitors 5 and 5, and is balanced with respect to the ground. It becomes a state.

  When a normal chopper operation is performed in the boost chopper circuit 2 in this state, the ground voltage between the negative pole and the positive pole in the DC voltage of the inverter circuit 3 becomes unbalanced, and as shown in FIG. A DC component (offset) is added to the ground voltage of the output voltage. For this reason, the AC output voltage of the inverter circuit 3 is increased in ground voltage by the amount of the DC component (offset) added to the positive pole side, and it is necessary to increase the dielectric strength of the inverter device 10 for photovoltaic power generation.

  FIG. 5 is a schematic diagram illustrating another example of a conventional inverter device 20 for photovoltaic power generation. The thin-film solar cell panel 1 may ground the negative pole on the DC side due to restrictions. In this case, as shown in FIG. 5, one point on the DC side is grounded. As a result, as shown in FIG. 6, a direct current component (offset) is further added to the positive side of the alternating current output voltage of the inverter circuit 3, and the ground voltage of the alternating current output voltage is further unbalanced with respect to the ungrounded state. Become.

  As described above, it is a problem to provide a power conversion device in which the ground voltage of the AC output voltage in the inverter circuit is suppressed from becoming unbalanced.

  The present invention has been devised in view of the above-described conventional problems, and one aspect thereof is a power conversion device that converts DC power output from a DC power source having a stray capacitance to the ground into AC power, A boost chopper circuit that boosts a DC voltage output from the power supply; and an inverter circuit that converts the DC voltage output from the boost chopper circuit into an AC voltage. The negative pole of the DC power supply is grounded, and the boost chopper circuit The positive electrode and the positive electrode of the inverter circuit are connected by a common line.

  The boost chopper circuit may control the duty ratio so that 2Ep = Ec, where Ep is the output DC voltage of the DC power supply and Ec is the DC voltage of the inverter circuit.

  The step-up chopper circuit has a capacitor connected in parallel to the solar cell panel, one end of the step-up reactor connected to the negative electrode side of the capacitor, and the other end side of the step-up reactor and the positive electrode of the capacitor A configuration in which a switching element is connected may be used.

  For the power conversion device, an inverter device for photovoltaic power generation (power conditioner for photovoltaic power generation), an uninterruptible power supply device (UPS), a sag compensation device, or the like may be applied.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the power converter device which suppressed the imbalance of the alternating current output voltage of an inverter circuit.

It is the schematic which shows an example of the inverter apparatus for solar power generation in embodiment. It is a graph which shows the alternating current output voltage of the inverter apparatus for photovoltaic power generation in embodiment. It is the schematic which shows an example of the inverter apparatus for photovoltaic power generation in the past. It is a graph which shows the alternating current output voltage of the inverter apparatus for photovoltaic power generation shown in FIG. It is the schematic which shows the other example of the conventional inverter apparatus for photovoltaic power generation. It is a graph which shows the alternating current output voltage of the inverter apparatus for photovoltaic power generation shown in FIG.

  An object of the present invention is to balance the ground voltage of an AC output voltage in a power conversion device (for example, an inverter device for photovoltaic power generation) as much as possible (to a target waveform).

  As shown in FIG. 5, when the negative pole of the boost chopper circuit 2 and the inverter circuit 3 is connected as a common (with a common line), a DC component (offset) is added to the plus side to the ground voltage of the AC output voltage. . In addition, when the DC negative electrode of the solar cell panel 1 is grounded, a DC component (offset) is added to the positive voltage to the ground voltage of the AC output voltage. From these two conditions, the inverter device 30 for photovoltaic power generation in the present invention is proposed.

  Specifically, the positive poles of the boost chopper circuit 2 and the inverter circuit 3 are connected as a common (with a common line). Further, when the ground potential is zero V, the average potential from the ground at the DC side positive pole of the inverter circuit 3 is P, and the average potential from the ground at the DC side negative pole of the inverter circuit 3 is N, P = | It is controlled so that N |

  Hereinafter, a power converter according to an embodiment of the present invention will be described in detail with reference to FIGS.

[Embodiment]
FIG. 1 is a schematic diagram showing a power conversion device (for example, an inverter device for photovoltaic power generation: hereinafter referred to as an inverter device for photovoltaic power generation) 30 in the present embodiment.

  The photovoltaic power generation inverter device 30 is inserted between the solar cell panel 1 and the power supply system 4, converts the DC power output from the solar cell panel 1 into AC power, and outputs the AC power to the power supply system 4.

  As shown in FIG. 1, an inverter device 30 for photovoltaic power generation in this embodiment is interposed between a boost chopper circuit 2 connected to a solar cell panel 1 and the boost chopper circuit 2 and a power supply system 4. Inverter circuit 3. A smoothing capacitor C2 is interposed between the step-up chopper circuit 2 and the inverter circuit 3.

  Since the solar cell panel 1 has a stray capacitance with respect to the ground, the positive electrode and the negative electrode are grounded by several [μF] capacitors 5 and 5.

  The step-up chopper circuit 2 is a general step-up chopper circuit including a capacitor C1, a step-up reactor L, and two switching elements Sw1 and Sw2 connected in series. In order to operate the inverter circuit 3 efficiently, the DC voltage is boosted. Note that the switching elements Sw1 and Sw2 in this embodiment are obtained by connecting a self-extinguishing semiconductor element (for example, IGBT) and a freewheel diode in antiparallel.

  In the step-up chopper circuit 2, a capacitor C1 is connected in parallel to the solar cell panel 1, and one end of a step-up reactor L is connected to the negative electrode side of the capacitor C1. A switching element Sw2 is connected between the other end side of the boosting reactor L and the positive side of the capacitor C1, and the switching element Sw1 is interposed between the switching element Sw2 and the smoothing capacitor C2.

  In the step-up chopper circuit 2, the energy output from the capacitor C1 is stored in the step-up reactor L when the switching element Sw2 is on. When the switching element Sw2 is off, the energy accumulated in the boosting reactor L and the energy output from the capacitor C1 are supplied to the smoothing capacitor C2.

  As described above, the voltage supplied from the capacitor C1 can be boosted to a predetermined voltage by controlling the ratio of the on-state time and the off-state time of the switching element Sw2 (that is, determining the duty ratio). it can.

  The smoothing capacitor C2 smoothes the output of the boost chopper circuit 2 and the input voltage of the inverter circuit 3.

  The inverter circuit 3 is not particularly limited, but in this embodiment, a general three-phase voltage source inverter is used as shown in FIG.

  The inverter 30 for photovoltaic power generation according to the present embodiment is a circuit in which the positive polarity side of the boost chopper circuit 2 and the inverter circuit 3 is connected as a common (with a common line), and the negative polarity side of the solar cell panel 1 is grounded. is there. The control method, characteristics, and the like of the boost chopper circuit 2 are the same as those in the case where the negative pole side is connected as a common (with a common line) as shown in FIGS.

  Here, the average potential from the ground in the positive electrode portion on the DC side of the inverter circuit 3 is P, and the average potential from the ground in the negative electrode portion is N, and as shown in FIG. Is Ep and the DC voltage of the inverter circuit 3 is Ec, the potential of P is Ep and the potential of N is Ep-Ec. Therefore, the DC component (offset) voltage added to the AC output voltage of the inverter circuit 3 can be expressed as Ep-Ec / 2.

  When 2Ep = Ec where the potential is P = | N | (ie, Ep = | Ep−Ec |), the imbalance between the negative and positive ground voltages in the DC voltage of the inverter circuit 3 is eliminated. The Therefore, in the inverter device 30 for photovoltaic power generation in this embodiment, the boost chopper circuit 2 is controlled so that 2Ep = Ec (determining the duty ratio), whereby the AC output voltage output from the inverter circuit 3 is reduced. It becomes possible to suppress imbalance in the ground voltage.

  FIG. 2 is a graph showing the AC output voltage of the photovoltaic power generation inverter device 30 in the present embodiment. As shown in FIG. 2, the photovoltaic power generation inverter device 30 in the present embodiment eliminates the unbalance of the ground voltage in the AC output voltage of the inverter circuit 3. As a result, the maximum voltage with respect to the ground is relaxed, and the dielectric strength can be suppressed.

  As described above, according to the inverter device 30 for photovoltaic power generation in the present embodiment, the boost chopper circuit 2 and the inverter circuit 3 are provided when the boost chopper circuit 2 is provided and the negative electrode of the solar battery panel 1 is grounded. By using a circuit in which the positive pole of the inverter circuit 3 is connected to a common (connected by a common line), it is possible to eliminate an imbalance in the ground voltage of the AC output voltage of the inverter circuit 3.

  Moreover, by eliminating the imbalance in the ground voltage of the AC output voltage of the inverter circuit 3, the maximum voltage with respect to the ground is relaxed, and the dielectric strength can be suppressed.

       Although the present invention has been described in detail only for the specific examples described above, it is obvious to those skilled in the art that various changes and modifications are possible within the scope of the technical idea of the present invention. Such variations and modifications are naturally within the scope of the claims.

  For example, in the embodiment, the power conversion device 30 to which the three-phase voltage type inverter circuit 3 is applied has been described in detail, but inverter circuits having other configurations are also applicable.

  The step-up chopper circuit 2 is not limited to the configuration described in the embodiment. For example, the switching element Sw1 may be replaced with a diode.

  Furthermore, in the embodiment, an inverter device for photovoltaic power generation is applied to the power conversion device 30, but the power conversion device 30 includes an uninterruptible power supply (UPS), a voltage sag compensator, a power conditioner for photovoltaic power generation, and the like. Various power converters can be applied.

1 ... Solar panel (DC power supply)
2 ... Boost chopper circuit 3 ... Inverter circuit 4 ... Power supply system 10, 20, 30 ... Power converter (inverter device for photovoltaic power generation)
C1 ... Capacitor C2 ... Smoothing capacitor L ... Reactor for boosting Sw1, Sw2 ... Switching element

Claims (1)

A power conversion device for photovoltaic power generation that converts DC power output from a DC power supply having a stray capacitance to the ground into AC power,
A step-up chopper circuit that boosts the DC voltage output from the DC power supply;
An inverter circuit for converting a DC voltage output from the boost chopper circuit into a three-phase AC voltage;
A smoothing capacitor for smoothing a DC voltage between the boost chopper circuit and the inverter circuit;
With
Ground the negative pole of the DC power supply, connect the positive pole of the boost chopper circuit and the positive pole of the inverter circuit with a common line,
The step-up chopper circuit is
A capacitor connected in parallel to the solar panel;
A boosting reactor having one end connected to the negative electrode side of the capacitor;
First and second switching elements connected between the other end side of the boosting reactor and the positive electrode of the capacitor, and between the other end side of the boosting reactor and the negative electrode side of the smoothing capacitor,
A power converter that controls the duty ratio so that 2Ep = Ec, where Ep is the output DC voltage of the DC power supply and Ec is the DC voltage of the inverter circuit.

Images