JP5604754B2 - Inverter - Google Patents

Description

  The present invention relates to a method for controlling a power conditioner.

  Conventionally, a photovoltaic power generation system includes a power conditioner that converts the generated power of a solar cell into alternating current power and supplies the alternating current power to the system side, and various power conditioners have been developed (for example, patent documents). 1, Patent Document 2).

Japanese Patent Laid-Open No. 2001-258160 (FIGS. 5, 6, 8, etc.) JP 2007-68385 A (Fig. 10 etc.)

  Here, in the conventional power conditioner, when the system side is grounded, problems such as high-frequency noise current may flow due to the influence of the stray capacitance on the ground potential of the solar cell. Hereinafter, the cause of the high-frequency noise current flowing will be described.

  The power conditioner includes a DC / DC converter that boosts DC power from a solar cell and an inverter that converts DC power from the DC / DC converter into AC power. For example, when the output voltage of the DC / DC converter is 380 V and this is called a DC bus voltage, when the inverter that converts the DC power from the DC / DC converter into AC power is switched, the DC bus voltage is grounded on the system side. The DC bus voltage viewed from the ground potential fluctuates from 0V to 380V. The DC bus is connected to the solar cell, and the voltage from the DC bus to the solar cell varies greatly with respect to the ground potential at the switching speed of the inverter (for example, 20 kHz). Leakage current (high frequency noise current) flows.

  In recent years, in order to cope with CO2 reduction, the idea of using the power of solar power generation as it is without converting it into AC is progressing. In this concept, a method of connecting the DC bus at the output of the DC / DC converter to the DC power supply system is adopted. However, the DC power supply system includes a storage battery that is the source of DC power, an AC / DC converter that converts AC power from the system side to DC power, an air conditioner as a load, a TV, etc., and a power conditioner is connected. Then, the stray capacitance with respect to the ground potential further increases, causing a problem that high-frequency noise current flows.

  In addition, there is a method of reducing the high frequency noise current by adopting the double carrier method and reducing the high frequency noise current as in Patent Document 1, and the high frequency noise current can be reduced in a configuration including a solar cell, a DC / DC converter and an inverter. FIG. 4 shows a waveform example of the DC bus voltage Vdc and the output AC voltage Vac of the power conditioner of Patent Document 1. However, when connected to a DC power supply system, the stray capacitance with respect to the ground potential may increase and a high frequency noise current may be generated. Further, as in Patent Document 2, there is a method in which the same voltage is generated up and down although the sign is different with the booster circuit and the inductor centered on the ground potential. However, according to switching, fluctuations in the DC bus voltage could not be suppressed, and high-frequency noise current could not be suppressed.

  In view of the above problems, an object of the present invention is to provide a power conditioner that can suppress fluctuations in a DC bus voltage and suppress generation of a high-frequency noise current even when a DC power supply system is connected.

To achieve the above object, the present invention provides a power conditioner comprising: a DC / DC converter; and an inverter that converts a DC voltage output from the DC / DC converter into an AC voltage and supplies the AC voltage to the system side.
The inverter has a switching circuit unit having a first upper and lower arm and a second upper and lower arm connected in parallel to the output line of the DC / DC converter, and a first end connected to a connection point of the first upper and lower arm. An inductor, a first capacitor having one end connected to the other end of the first inductor, a second capacitor having one end connected to the other end of the first capacitor, and one end connected to the other end of the second capacitor A second inductor having the other end connected to a connection point of the second upper and lower arms,
A connection point between the first capacitor and the second capacitor is grounded, and voltages of the same magnitude with different positive and negative are applied to the output line of the DC / DC converter,
The first upper arm of the first upper and lower arms, the second lower arm of the second upper and lower arms, and the first lower arm of the first upper and lower arms and the second upper arm of the second upper and lower arms are alternately and alternately set in pairs. The control unit further includes a control unit that performs on / off control and simultaneously controls on / off of one pair while maintaining the other pair in an off state.

  According to such a configuration, the DC bus voltage is not connected to the ground potential on the system side, the fluctuation of the DC bus voltage can be suppressed, and the DC power supply system is connected to the DC bus at the output of the DC / DC converter. Even in this case, generation of high-frequency noise current can be suppressed.

  Moreover, the said structure WHEREIN: The said inverter is good also as a structure provided with the 3rd capacitor | condenser connected in series, and a 4th capacitor | condenser connected to the ground in the front | former stage of the said switching circuit part. Thereby, the DC bus voltage can be stabilized.

  In any of the above-described configurations, a solar cell may be connected to the input of the DC / DC converter. Thereby, generation | occurrence | production of a high frequency noise current can be suppressed even when a direct-current power feeding system is connected to a photovoltaic power generation system.

  According to the power conditioner of the present invention, fluctuations in the DC bus voltage can be suppressed, and generation of high-frequency noise current can be suppressed even when a DC power supply system is connected.

It is a figure which shows one structural example of the power conditioner which concerns on this invention, and the direct-current power feeding system connected to this. It is a figure which shows the switching pattern of each switch element in an inverter. It is a figure which shows an example of the output voltage and DC bus voltage of an inverter. It is a figure which shows the example of a waveform of the DC bus voltage and output AC voltage of the conventional power conditioner.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a configuration example of a power conditioner according to the present invention and a DC power supply system connected to the power conditioner.

  The power conditioner 1 converts the output power of the solar cell DC / DC converter 2 that boosts the output power of the solar cell 11 to 380 V, and the output power of the solar cell DC / DC converter 2 into AC power and supplies it to the system side. And an inverter 3. A direct current power supply system 12 is connected to the output of the solar cell DC / DC converter 2 via a direct current bus 4.

  The DC power supply system 12 includes a DC bus 4, a system AC / DC converter 5, a storage battery 6, a storage battery DC / DC converter 7, a DC drive air conditioner 8, a DC drive TV 9, and a DC drive refrigerator 10. Is done. The DC bus 4 includes a system AC / DC converter 5 that converts AC power on the system side into DC power to be supplied, a storage battery DC / DC converter 7 that charges and discharges the storage battery 6, a DC drive air conditioner 8, A DC drive TV 9 and a DC drive refrigerator 10 are connected.

  Hereinafter, a more specific configuration of the power conditioner 1 will be described.

  The solar cell DC / DC converter 2 is a so-called current resonance type insulating converter. The DC / DC converter controller 2F alternately turns on and off the main switch element 2A and the auxiliary switch element 2B to drive the subsequent high-frequency transformer 2D. The high-frequency transformer 2D is a leakage transformer having a leakage inductance, and the turns ratio is in the range of 1.5 to 2 times. Soft switching of the main switch element 2A and the auxiliary switch element 2B is achieved using current resonance between the leakage inductance component of the transformer and the resonance capacitor 2C. The main switch element 2A and the auxiliary switch element 2B are alternately driven by a PFM (pulse frequency modulation) method in which the drive frequency is variable in the range of 15 kHz to 70 kHz. Further, since the secondary voltage rectifier circuit 2E is provided on the secondary side of the high frequency transformer 2D, the secondary winding voltage boosted by the high frequency transformer 2D is further converted to a double DC voltage 380V.

  The inverter 3 includes a 100 μF capacitor 3J, a 100 μF capacitor 3K, a switching circuit unit 3L, a 2.5 mH inductor 3E, a 10 μF capacitor 3F, a 10 μF capacitor 3G, a 2.5 mH inductor 3H, And an inverter control unit 3I.

  One end of the capacitor 3J and one end of the capacitor 3K are connected to the output of the solar cell DC / DC converter 2, and the connection point between the other end of the capacitor 3J and the other end of the capacitor 3K is grounded.

  A switching circuit unit 3L is provided after the capacitors 3J and 3K. The switching circuit unit 3L includes a first upper and lower arm composed of switch elements 3A and 3B composed of IGBTs (insulated gate bipolar transistors) and a second upper and lower arm composed of switch elements 3C and 3D composed of IGBTs. Composed. Switching control of each switch element is performed by the inverter control unit 3I.

  A connection point between the switch element 3A and the switch element 3B is connected to one end of the inductor 3E, and the other end of the inductor 3E is connected to one end of the capacitor 3F. A connection point between the switch element 3C and the switch element 3D is connected to one end of the inductor 3H, and the other end of the inductor 3H is connected to one end of the capacitor 3G. The connection point between the capacitor 3F and the capacitor 3G is grounded.

  Capacitor 3J and capacitor 3K equally divide the output voltage 380V of solar cell DC / DC converter 2 so that the voltage on capacitor 3J side is 190V and the voltage on capacitor 3K side is -190V.

  Here, the switching pattern of each switch element in the switching circuit unit 3L is shown in FIG. 2A shows a switching pattern of the switch element 3A, FIG. 2B shows a switching pattern of the switch element 3B, FIG. 2C shows a switching pattern of the switch element 3C, and FIG. These show the switching pattern of the switch element 3D, respectively. Each switch element is turned off when the gate-emitter voltage is V0 and turned on when V1.

  As the switching pattern of each switch element, the switch element 3A (first upper arm), the switch element 3D (second lower arm), the switch element 3B (first lower arm), and the switch element 3C (second upper arm) are paired. At the same time, ON / OFF control is performed. More specifically, the switch element 3A and the switch element 3D are simultaneously turned on / off by PWM (Pulse Width Modulation) control during a period of 8.3 ms that is a half cycle of 60 Hz, and the switch element 3B and the switch element 3C are turned off during that period. It is said. In the next 8.3 ms period, the switch element 3B and the switch element 3C are simultaneously turned on / off by PWM control, and the switch element 3A and the switch element 3D are turned off during that period.

  By such switching control, as shown in FIG. 3, the output voltage Vac1 (FIG. 1) on the inductor 3E side becomes a sine wave from 0 V to 140 V in the on / off control period of the switch element 3A and the switch element 3D, and the switch element 3B In the ON / OFF control period of the switch element 3C, it becomes a sine wave from 0V to -140V, and an AC voltage is supplied to the system side. Waveform).

  Further, the switch element 3A and the switch element 3D and the switch element 3B and the switch element 3C are paired and controlled to be turned on and off at the same time. For example, when the switch element 3A and the switch element 3D are turned on at the same time, Current flows so that -190 V is generated at one end of the inductor 3H and the DC bus voltages Vdc1 and Vdc2 (FIG. 1) do not become 0V. As shown in FIG. 3, the DC bus voltage Vdc1 is 190V and Vdc2 is Stabilizes at -190V. Thereby, even when the DC power supply system 12 is connected, generation of high-frequency noise current can be suppressed (for example, when only the switch element 3A is turned on, current flows through the path from the switch element 3A to the switch element 3D). The DC bus voltage Vdc1 becomes 0V).

  Further, the DC bus voltage can be stabilized by setting the capacitances of the capacitor 3J and the capacitor 3K to 100 μF. Note that the capacity may be larger than 100 μF.

  The switching element of the switching circuit unit 3L is not limited to the IGBT, but may be a MOSFET or a field effect transistor made of a nitride semiconductor.

  As mentioned above, although embodiment of this invention was described, embodiment can be variously changed if it is in the range of the meaning of this invention.

DESCRIPTION OF SYMBOLS 1 Power conditioner 2 DC / DC converter for solar cells 3 Inverter 4 DC bus 5 System | strain AC / DC converter 6 Storage battery 7 DC / DC converter for storage batteries 8 DC drive air conditioner 9 DC drive TV
10 DC-driven refrigerator 11 Solar cell 12 DC power supply system

Claims (2)

In a power conditioner comprising: a DC / DC converter; and an inverter that converts a DC voltage output from the DC / DC converter into an AC voltage and supplies the AC voltage to the system side.
The inverter has a switching circuit unit having a first upper and lower arm and a second upper and lower arm connected in parallel to the output line of the DC / DC converter, and a first end connected to a connection point of the first upper and lower arm. An inductor, a first capacitor having one end connected to the other end of the first inductor, a second capacitor having one end connected to the other end of the first capacitor, and one end connected to the other end of the second capacitor A second inductor having the other end connected to a connection point of the second upper and lower arms,
A connection point between the first capacitor and the second capacitor is grounded, and voltages of the same magnitude with different positive and negative are applied to the output line of the DC / DC converter,
The first upper arm of the first upper and lower arms and the second lower arm of the second upper and lower arms, and the first lower arm of the first upper and lower arms and the second upper arm of the second upper and lower arms, respectively, A control unit that simultaneously performs on / off control of the pair of signals and maintains the other state in an off state alternately for each half cycle of the output sine wave;
A power conditioner , wherein a solar cell can be connected to the input of the DC / DC converter, and a DC power supply system can be connected to the output of the DC / DC converter .   2. The power conditioner according to claim 1, wherein the inverter includes a third capacitor and a fourth capacitor connected in series and grounded at a connection point, in a preceding stage of the switching circuit unit.

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