JP7458880B2 - Power converter and control method for power converter - Google Patents

Description

The present invention relates to a power converter and a method of controlling the power converter.

A power conversion device is known that includes a plurality of DC-DC converters that respectively convert the output power of a plurality of solar cell modules (for example, Patent Document 1). In this power converter, the outputs of the DC-DC converters are connected in series, and the power converter outputs a voltage that is the sum of the output voltages of the DC-DC converters as an output voltage. Furthermore, in this power converter, each DC-DC converter is controlled so that the output power of the solar cell module is maximized.

Japanese Patent Application Publication No. 2018-38190 Japanese Patent Application Publication No. 2016-197994 Japanese Patent Application Publication No. 2013-252046 Japanese Patent Application Publication No. 2013-198385

In the power conversion device described in Patent Document 1, for example, when the output voltage of a specific DC-DC converter among a plurality of DC-DC converters fluctuates, other DC-DC converters are changed in order to maintain the output voltage of the power conversion device. Vary the output voltage of the DC converter. That is, there is a problem in that in order to maintain the output voltage of the power conversion device, the output voltage must be adjusted between the plurality of converters.

The problem to be solved by the present invention is to provide a power conversion device and a power conversion device control method that can maintain the output voltage of the power conversion device without adjusting the output voltage between a plurality of converters. be.

The present invention includes a plurality of first converters that convert power input from a plurality of power supplies, a first terminal connected to each output terminal of the plurality of first converters, and a second terminal connected to a load. 2 converters. In the present invention, the plurality of first converters are connected in parallel by respective output terminals of the first converters, and the second converter insulates between the first terminal and the second terminal. The above problem is solved by operating so that the voltage at the terminal and the voltage at the second terminal have a predetermined ratio.

According to the present invention, the output voltage of each of the first converters becomes a common output voltage among the plurality of first converters, and becomes equal to the voltage at the first terminal of the second converter. Since the voltage at the second terminal of the second converter is a voltage at a predetermined ratio to the common output voltage among the plurality of first converters, the power The output voltage of the converter can be maintained.

FIG. 1 is a block diagram showing an overview of a power conversion system according to this embodiment. FIG. 2A is an example of a circuit configuration of the first converter shown in FIG. 1. FIG. 2B shows another example of the circuit configuration of the first converter shown in FIG. FIG. 2C shows another example of the circuit configuration of the first converter shown in FIG. FIG. 2D shows another example of the circuit configuration of the first converter shown in FIG. FIG. 2E shows another example of the circuit configuration of the first converter shown in FIG. FIG. 2F shows another example of the circuit configuration of the first converter shown in FIG. FIG. 3 shows an example of a circuit configuration of the second converter shown in FIG. FIG. 4 shows an example of a circuit configuration of the power conversion system shown in FIG. FIG. 5 is a diagram for explaining MPPT control according to this embodiment. FIG. 6 is a diagram for explaining the operation of the power conversion device in the circuit configuration shown in FIG. FIG. 7 is a diagram for explaining a method of setting the turns ratio of the isolation transformer included in the second converter. FIG. 8 is a diagram for explaining problems in MPPT control using the hill-climbing method.

Embodiments of the present invention will be described below based on the drawings.

The power conversion system according to this embodiment will be outlined with reference to FIG. 1. FIG. 1 is a block diagram of a power conversion system 300 including a power conversion device 200 according to this embodiment. The power conversion system 300 includes multiple power sources 1 to 6, a load 7, and the power conversion device 200. In this embodiment, an example of six power sources (power sources 1 to 6) will be described, but the number of power sources in the power conversion system 300 may be multiple and is not limited to six.

The power conversion device 200 converts power input from a plurality of power sources 1 to 6, and supplies the converted power to a load 7. Power conversion device 200 is used, for example, in a charging system mounted on a vehicle. In the following description, the embodiment will be described with the power supplies 1 to 6 being solar cell modules and the load 7 being a battery (secondary battery). The power sources 1 to 6 are not limited to solar cell modules, and may be other power sources. The load 7 is not limited to a battery, but may be a device such as an air conditioner. Further, the power conversion device 200 does not necessarily need to be installed in a vehicle, and may be installed in another device other than the vehicle.

Power sources 1 to 6 are solar cell modules. A solar cell module is a module composed of multiple solar cell cells. A solar cell is an energy conversion element that absorbs the light energy of sunlight and converts the light energy of sunlight into electricity. An example of a solar cell module is a solar panel.

A solar cell module has multiple solar cells connected in series and multiple diodes connected in parallel to each solar cell. When silicon solar cells are used, the output voltage of each solar cell is 1V or less. In order to increase the output voltage of the solar cell module as a whole, the solar cell module is composed of multiple solar cells connected in series. The solar cell module outputs a voltage that is the sum of the output voltages of each solar cell.

The solar cell module is provided with a diode for bypassing the current flowing through the solar cell when the voltage generated by the solar cell is lower than a predetermined value. By connecting multiple solar cells in series, the solar cell module outputs a common current for each solar cell. For example, when the solar cell module is partially shaded and some solar cells are not irradiated with sunlight (so-called partial shading), the solar cell that is not irradiated with sunlight can generate less power than the solar cell that is irradiated with sunlight. Therefore, the solar cell that is not irradiated with sunlight can output less current than the solar cell that is irradiated with sunlight. If the bypass diode is not provided, the solar cell module can only output the current that the solar cell that is not irradiated with sunlight can output, and the output power of the solar cell module as a whole is significantly reduced. To solve this problem, the solar cell module is provided with a bypass diode connected in parallel with the solar cell. The bypass diode generates a current path that passes through the solar cell that is irradiated with sunlight and bypasses the solar cell that is not irradiated with sunlight. This suppresses the reduction in the output power of the solar cell module as a whole in partial shading.

The load 7 is a load such as a battery. The voltage generated by the power conversion device 200 is input to the load 7 . For example, if the load 7 is a battery mounted on a vehicle, the voltage of the battery fluctuates in a range of 240V to 400V.

The power conversion device 200 is a DC-DC converter that has a boost function that boosts the output voltage of the power supplies 1 to 6 to the voltage of the load 7 while controlling each of the power supplies 1 to 6 so that they can operate at the operating point where the most power can be generated. It is. Further, the power conversion device 200 is also a DC-DC converter having an insulation function of insulating between the power supplies 1 to 6 and the load 7.

The functions necessary for the power conversion device 200 will be described in the case where the power conversion system 300 is mounted on a vehicle, the power sources 1 to 6 are solar cell modules, and the load 7 is a battery mounted on the vehicle. Solar cell modules mounted on vehicles have an upper limit on their output voltage. Further, as described above, since the power that the solar cell module can generate varies depending on the amount of solar radiation, the output voltage of the solar cell module also varies depending on the amount of solar radiation. In order to efficiently supply the power generated by the solar cell module to the battery, the power conversion device 200 has a function to operate the solar cell module at an operating point where it can generate the most power, thereby maximizing the power input from the solar cell module. (MPPT function) is required. Furthermore, since there is a large difference between the power required by the battery and the power generated by each solar cell module, the power conversion device 200 needs to have a function to convert the power generated by each of the plurality of solar cell modules into power. be done. Furthermore, there is a large difference between the battery voltage and the output voltage per solar cell module. For this reason, the power conversion device 200 has a function to boost the output voltage of the solar cell module to the voltage of the battery (boost function), and a function to prevent current from flowing from the battery to the solar cell module. A function to insulate between the two (insulating function) is required.

A power conversion device according to the present invention includes a plurality of DC-DC converters that are provided corresponding to each of a plurality of power sources and converts power from each of the plurality of power sources, and a plurality of DC-DC converters that are connected to the plurality of DC-DC converters and a load. It consists of two DC-DC converters. In the following description, for convenience, the DC-DC converter connected to the power source will be referred to as a first converter, and one DC-DC converter connected to the first converter and a load will be referred to as a second converter. In the block diagram of FIG. 1, power conversion device 200 includes first converters 11 to 16 and second converter 17. In this embodiment, the plurality of first converters 11 to 16 realize the MPPT function and the function of converting the power generated by each of the plurality of solar cell modules, among the functions required by the power conversion device 200 described above. do. Further, the second converter 17 realizes a boost function and an insulation function among the functions required by the power conversion device 200 described above.

As shown in FIG. 1, in this embodiment, the power conversion device 200 includes a plurality of first converters 11 to 16 and a second converter 17. Each first converter is provided corresponding to the power supplies 1 to 6. Taking the first converter 11 as an example, the first converter 11 is provided corresponding to the power source 1, and power is input from the power source 1 to an input terminal of the first converter 11. Since the first converters 12 to 16 also have the same configuration as the first converter 11, the explanation for the first converter 11 will be used. Note that in the following description, "each of the plurality of first converters 11 to 16" may be read as "each of the first converters".

Each of the plurality of first converters 11 to 16 has a function (MPPT function) of controlling the power output from the power supply so that the corresponding power supply can operate at an operating point where it can generate the most power. Taking the first converter 11 as an example, the first converter 11 uses the MPPT function to operate the power supply 1 at an operating point that can generate the most power. The first converters 12 to 16 also operate their corresponding power supplies at operating points that can generate the most power. Since the MPPT functions of the first converters 12 to 16 are similar to the MPPT functions of the first converter 11, the explanation for the first converter 11 will be used.

Further, each of the plurality of first converters 11 to 16 is a buck-boost converter having a function of boosting or stepping down the voltage input from the corresponding power source (step-up/step-down function). Taking the first converter 11 as an example, the first converter 11 uses a step-up/down function to step up or step down the voltage input from the power supply 1 . The first converters 12 to 16 also step up or step down the voltage input from the corresponding power source. The buck-boost functions of the first converters 12 to 16 are similar to the buck-boost functions of the first converter 11, so the explanation for the first converter 11 will be used. Details of the step-up/down function will be described later.

Furthermore, the respective outputs of the plurality of first converters 11 to 16 are connected to each other. In the block diagram shown in FIG. 1, the output terminal of the first converter 11, the output terminal of the first converter 12, the output terminal of the first converter 13, the output terminal of the first converter 14, the output terminal of the first converter 15, and The output terminals of one converter 16 are connected to each other. As a result, the outputs of the plurality of first converters 11 to 16 are connected in parallel, and the plurality of first converters 11 to 16 are connected in parallel on the output side. Detailed connection relationships, circuit configuration and functions of the first converter will be described later.

The second converter 17 is provided between the first converters 11-16 and the load 7, and is connected to the first converters 11-16 and the load 7. The second converter 17 functions as a DC transformer under the control of the controller 100, which will be described later. The second converter 17 is a circuit that operates so that the input voltage and the output voltage are in a predetermined ratio. The detailed connection relationship, and the circuit configuration and functions of the second converter will be described later.

Controller 100 is a control device (also referred to as a control circuit) that controls a plurality of first converters 11 to 16 and second converter 17. The controller 100 includes, for example, a ROM (Read Only Memory) that stores programs for controlling the plurality of first converters 11 to 16 and the second converter 17, and a CPU (Central CPU) that executes the programs stored in the ROM. It consists of a processing unit) and a RAM (Random Access Memory) that functions as an accessible storage device. Note that the operating circuit may be an MPU (Micro Processing Unit), a DSP (Digital Signal Processor), an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), etc. instead of or in addition to the CPU (Central Processing Unit). can be used. As shown in FIG. 1, controller 100 outputs control signals to each of the plurality of first converters 11 to 16, and controls each first converter independently. Controller 100 also outputs a control signal to second converter 17 to control second converter 17 . Details of the control by the controller 100 will be described later. The above is an overview of the power conversion device 200 according to this embodiment.

Next, the circuit configuration of the first converter shown in FIG. 1 will be described using FIG. 2A as an example of the first converter 11 out of the multiple first converters 11 to 16. FIG. 2A is an example of the circuit configuration of the first converter shown in FIG. 1. In this embodiment, the first converters 12 to 16 have the same circuit configuration as the first converter 11, and the description of the first converter 11 is used.

As shown in FIG. 2A, the first converter 11 includes an input port 21 and an output port 31. The input port 21 includes a pair of input terminals 21a and 21b. The output port 31 includes a pair of output terminals 31a and 31b. The input terminal 21a is connected to the positive terminal of the power source 1 via a power line 41a, and the input terminal 21b is connected to the negative terminal of the power source 1 via a power line 41b. Further, the output terminal 31a is connected to the output line 51a, and the output terminal 31b is connected to the input terminal 21b and the negative terminal of the power supply 1 via the power supply line 41a.

As shown in FIG. 2A, the first converter 11 includes a step-up chopper circuit and a step-down chopper circuit. In the first converter 11, the series circuit of switching element _S1 and switching element _S2 and the series circuit of diode _D4 and switching element _S3 are connected via coil _L1 . A diode D ₁ is connected in parallel to the switching element S ₁ so that the conduction direction of the switching element S ₁ and the conduction direction of the diode are opposite to each other. A diode D ₂ is also connected in parallel to the switching element S 2 in the same connection relationship as that between the switching element S ₁ and _the diode D ₁ . A diode D ₃ is also connected in parallel to the switching element S 3 in the same connection relationship as that between the switching element S ₁ and _the diode D ₁ . IGBTs, MOSFETs, etc. are used for the switching elements S ₁ to S ₃ . The diodes D ₁ to D ₃ are parasitic diodes of rectifying elements or MOSFETs. The switching element S ₁ and the switching element S ₂ are connected in series between the power supply line 41a and the power supply line 41b, with the switching element S ₁ on the high potential side and the switching element S ₂ on the low potential side. The diode _D4 and the switching element _S3 are connected in series between the output line 51a and the power supply line 41b, with the diode _D4 on the high potential side and the switching element _S3 on the low potential side. One end of the coil _L1 is connected to a connection point _O1 between the switching element _S1 and the switching element _S2 . The other end of the coil _L1 is connected to a connection point _O2 between the diode _D4 and the switching element _S3 . Further, a smoothing capacitor 61 is connected between the power line 41a and the power line 41b, and the series circuit of the switching element _S1 and the switching element _S2 and the smoothing capacitor 61 are in a parallel relationship. In the example of FIG. 2A, the first converter 11 includes a boost chopper circuit including a coil L ₁ , a switching element S ₃ , and a diode D ₄ , a switching element S ₁ , a diode D ₂ , a coil L ₁ , and a diode D ₄ .

The circuit configuration of the first converter 11 is not limited to the chopper boost circuit and the chopper step-down circuit shown in FIG. 2A, but may be other circuit configurations. 2B to 2F are other examples of the circuit configuration of the first converter shown in FIG. 1. For example, as shown in FIG. 2B, the first converter 11 may have a configuration in which the switching element _S2 is replaced with a diode in the circuit configuration shown in FIG. 2A. For example, the first converter 11 may be configured with a SEPIC (Single Ended Primary Inductance Converter), as shown in FIG. 2C. For example, as shown in FIG. 2D, the first converter may be configured with a circuit that operates on the same principle as the SEPIC shown in FIG. 2C, but with the polarity of the output voltage reversed. For example, as shown in FIG. 2E, the first converter 11 may be a buck-boost type chopper circuit, and may be configured with a circuit in which the polarity of the output voltage is inverted. Further, for example, the first converter 11 may be configured with a ZETA converter, as shown in FIG. 2F.

Further, the first converter 11 is not limited to a so-called non-isolated converter in which the input port 21 and the output port 31 are electrically connected, as in the circuit configurations of FIGS. 2A to 2F, and 31 may be an insulation type converter in which an insulation transformer is provided between the converter and the converter. When an isolated converter is used as the first converter 11, input port 21 and output port 31 are isolated by an isolation transformer. Examples of the isolated converter used in the first converter 11 include a forward converter, a flyback converter, a full bridge converter, and a tapped inductor converter. Note that in this embodiment, the plurality of first converters 11 to 16 will be described as each having the same circuit, but the plurality of first converters 11 to 16 may include a plurality of types of circuits. The plurality of first converters 11 to 16 may be at least one circuit among the plurality of types of circuits listed as examples above, provided that the output voltage of each first converter has the same polarity.

Next, the circuit configuration of the second converter 17 will be explained using FIG. 3. FIG. 3 is an example of a circuit configuration of the second converter 17 shown in FIG. 1.

As shown in FIG. 3, the second converter 17 has ports 27 and 37. Port 27 is composed of a pair of terminals 27a and 27b. Port 37 is composed of a pair of terminals 37a and 37b. Terminal 27a is connected to line 47a, and terminal 27b is connected to line 47b. Terminal 37a is connected to line 47a, and terminal 37b is connected to line 47b. As described below, lines 47a and 47b are connected to output ports 31 to 36 of the first converters 11 to 16, respectively, and therefore the polarity of lines 47a and 47b corresponds to the circuit configuration of the first converter.

As shown in FIG. 3, the second converter 17 is configured with an LC series resonance type dual active bridge. The second converter 17 is an LLC converter composed of two coils (L) and one capacitor (C). The second converter 17 includes a primary circuit including a primary coil 57 and a secondary circuit including a secondary coil 67. The primary side circuit and the secondary side circuit are insulated.

The primary side circuit will be explained. As shown in FIG. 3, a series circuit of switching element _S5 and switching element _S6 and a series circuit of switching element _S7 and switching element _S8 are connected between line 47a and line 47b. . Taking the switching element _S5 as an example, a diode _D5 is connected in parallel to the switching element _S5 so that the conduction direction of the switching element _S5 and the conduction direction of the diode are opposite to each other. Diodes D ₆ to D ₈ are also connected in parallel to the switching elements S 6 to S ₈ in the same connection relationship as the connection relationship between the switching element S ₅ and the diode _{D 5} . IGBTs, MOSFETs, etc. are used for the switching elements S ₅ to S ₈ . The diodes D ₅ to D ₈ are parasitic diodes of rectifying elements or MOSFETs. The switching element _S5 and the switching element _S6 are connected in series between the line 47a and the line 47b, with the switching element _S5 on the high potential side and the switching element _S6 on the low potential side. The switching element _S7 and the switching element _S8 are connected in series between the line 47a and the line 47b, with the switching element _S7 on the high potential side and the switching element _S8 on the low potential side. Further, a coil C ₂ and a primary coil 57 are connected between the connection point O ₃ between the switching element S 5 and _the switching element S ₆ and the connection point O _{4 between the switching element S 7 and} the switching element S ₈ . are connected in series. The number of turns of the primary coil 57 is _n1 (unit: number of turns).

The secondary circuit will be described. As shown in FIG. 3, a series circuit of switching elements _S9 and _S10 and a series circuit of switching elements _S11 and _S12 are connected between the line 47a and the line 47b. Taking the switching element _S9 as an example, a diode D9 is connected in parallel to the switching element _S9 so that the conduction direction of the switching element _S9 and the conduction direction of the _diode are opposite to each other. Diodes _D10 to D12 are also connected in parallel to the switching elements S10 to _S12 in the same connection relationship as the connection relationship between _the switching element _S9 and the diode _D9 . IGBTs, MOSFETs, etc. are used for the switching elements _S9 to _S12 . The diodes _D9 to _D12 are rectifier elements or parasitic diodes _of MOSFETs. The switching elements _S9 and _S10 are connected in series between the lines 47a and 47b, with the switching element _S9 on the high potential side and the switching element _S10 on the low potential side. The switching elements _S11 and _S12 are connected in series between the lines 47a and 47b, with the switching element _S11 on the high potential side and the switching element _S12 on the low potential side. A secondary coil 67 is connected between a connection point _O5 between the switching elements _S9 and _S10 and a connection point _O6 between the switching elements _S11 and _S12 . The number of turns of the secondary winding 76 is _n2 (unit: number of turns). In this embodiment, the primary coil 57 and the secondary coil 67 function as an insulating transformer.

Next, the circuit configuration of the power conversion system 300 shown in FIG. 1 will be described using FIG. 4. FIG. 4 is an example of a circuit configuration of the power conversion system 300 shown in FIG. 1. In FIG. 4, the plurality of first converters 11 to 16 have the circuit configuration shown in FIG. 2A, and the second converter 17 has the circuit configuration shown in FIG. 3. Note that the controller 100 is omitted in FIG. 4.

As shown in FIG. 4, the input ports 21-26 of each first converter are connected to the corresponding power supplies 1-6. As shown in FIG. 4, the first converter 11 is connected to the power source 1 through an input port 21. As shown in FIG. Specifically, the input terminal 21a of the first converter 11 is connected to the positive terminal of the power supply 1, and the input terminal 21b of the first converter 11 is connected to the negative terminal of the power supply 1. Regarding the first converters 12 to 16, since the connection relationship between the first converter 11 and the power source 1 is the same, the explanation of the connection relationship between the first converter 11 and the power source 1 will be referred to.

Furthermore, the output ports 31 to 36 of each first converter are connected in parallel. Specifically, the output terminals 31a to 36a are connected by a wiring 81a. Further, the output terminals 31b to 36b are connected by a wiring 81b. The polarity of each output terminal is the same.

In addition, the output ports 31-36 of each of the first converters are connected to the port 27 of the second converter 17. Specifically, each of the output terminals 31a-36a is connected to the terminal 27a by a wiring 81. In addition, each of the output terminals 31b-36b is connected to the terminal 27b by a wiring 81b. The wiring 81 is composed of a pair of wiring 81a and wiring 81b, and is a wiring for connecting the multiple first converters 11-16 and the second converter 17.

In the circuit configuration shown in FIG. 4, each of the first converters is The output voltage becomes the common voltage between the first converters and the voltage at the port 27 of the second converter 17. Further, the output currents I _out1 to I _out6 of each first converter are summed, and the summed current is input to the second converter 17. Each of the plurality of first converters 11 to 16 transmits power from the plurality of power supplies 1 to 6 only in the direction of the port 27 of the second converter 17. In FIG. 4, the intermediate voltage V _mid indicates the output voltage common to each first converter (the voltage at port 27 of the second converter 17), and the current I _total indicates the sum of the output currents of each first converter. Indicates current.

Further, a port 37 of the second converter 17 is connected to the load 7. As shown in FIG. 4, the terminal 37a is connected to the positive terminal of the load 7 through a wiring 84a, and the terminal 37b is connected to the negative terminal of the load 7 through a wiring 84b. Wiring 84 is composed of a pair of wiring 84a and wiring 84b, and is wiring for connecting second converter 17 and load 7.

A smoothing capacitor 82 is provided between the multiple first converters 11-16 and the second converter 17. As shown in FIG. 4, the smoothing capacitor 82 is provided between the multiple first converters 11-16 and the second converter 17, and is connected between the wiring 81a and the wiring 81b. A smoothing capacitor 83 is provided between the second converter 17 and the load 7. As shown in FIG. 4, the smoothing capacitor 83 is provided between the second converter 17 and the load 7, and is connected between the wiring 84a and the wiring 84b.

Next, the control by the controller 100 and the operation of each circuit in the circuit configuration of the power conversion system 300 shown in FIG. 4 will be described.

The control of the first converter by the controller 100 and the operation of the first converter as a single circuit will be described again using FIG. 2A. The controller 100 outputs control signals to control terminals of the switching elements S ₁ to S ₃ to control on and off (also referred to as switching) of the switching elements S ₁ to S ₃ . Controller 100 independently controls each of switching elements S ₁ to S ₃ . For example, if the switching elements S ₁ to S ₃ shown in FIG. 2A are MOSFETs, the controller 100 switches each of the switching elements S ₁ to S ₃ by controlling the voltage to the gate terminal of each switching element. Hereinafter, the control of the first converter 11 by the controller 100 and the operation of the first converter 11 will be explained. Since it is similar to the converter 11, the explanation for the first converter 11 will be used.

The controller 100 operates the power source 1, which is a solar cell module, at an operating point where it can generate the most power, and controls the first converter 11 so that the power input from the power source 1 is maximized. In general MPPT control, the operating point where the power source 1 can generate the most power is searched for while detecting the current and voltage input from the power source 1 to the first converter 11. When the operating point is searched for, the power source 1 is operated at the searched operating point, and the input power from the power source 1 at a given point is maximized. In this embodiment, the controller 100 controls the first converter 11 so that the output power of the first converter 11 is maximized. This makes it possible to maximize the power input from the power source 1 to the first converter. The MPPT control according to this embodiment will be described later.

Further, the controller 100 controls the chopper boost circuit and the chopper step-down circuit that the first converter 11 has, thereby increasing or decreasing the input voltage of the first converter 11 . As shown in FIG. 2A, a current (input current I _in ) and a voltage (input voltage V _in ) are input to the first converter 11 from the power supply 1 via the input terminal 21 a and the input terminal 21 b. The first converter 11 boosts the input voltage using a boost chopper circuit. The first converter 11 outputs, as an output voltage V _out , a voltage obtained by boosting the input voltage V _in by causing the controller 100 to switch the switching element S ₃ . The step-up ratio of the first converter 11 is controlled by the on/off duty ratio of the switching element _S3 . The on/off duty ratio of the switching element _S3 is a ratio indicating the ratio of the on time of the switching element _S3 to the total time of the on time of the switching element _S3 and the off time of the switching element _S3 . Further, the first converter 11 steps down the input voltage using a step-down chopper circuit. The first converter 11 outputs, as an output voltage V _out , a voltage obtained by stepping down the input voltage V _in by causing the controller 100 to switch the switching element _S1 . The step-down ratio of the first converter 11 is controlled by the on/off duty ratio of the switching element _S1 . The on/off duty ratio of the switching element _S1 is a ratio indicating the ratio of the on time to the total time of the on time of the switching element _S1 and the off time of the switching element _S1 .

Next, the control of the second converter 17 by the controller 100 and the operation of the second converter 17 alone will be explained using FIG. 3 again. The controller 100 outputs control signals to control terminals of the switching elements S ₅ -S ₁₂ to control on and off of the switching elements S ₅ -S ₁₂ . Controller 100 independently controls each of switching elements S ₅ to S ₁₂ . For example, if the switching elements S ₅ -S ₁₂ shown in FIG. 3 are MOSFETs, the controller 100 switches each of the switching elements S ₅ -S ₁₂ by controlling the voltage to the gate terminal of each switching element.

Controller 100 controls second converter 17 so that second converter 17 functions as a DC transformer. As described above, the second converter 17 includes a primary side circuit and a secondary side circuit, which are insulated by an isolation transformer. The controller 100 synchronizes the on-time and off-time of each switching element with respect to the switching elements S ₅ to S ₁₂ and synchronizes the timing at which each switching element switches on and off with the resonant frequency of the isolation transformer of the second converter 17. Each switching element is controlled so that In other words, the controller 100 is configured such that the on time and the off time of the switching elements S ₅ to S ₁₂ of the second converter 17 are substantially the same, and the switching frequency is set to the resonance of the isolation transformer of the second converter 17. Each switching element is controlled so that the frequency is substantially the same as the frequency.

The second converter 17 is a resonant type converter. When a control signal from the controller 100 is input to each switching element of the second converter 17, each switching element of the second converter 17 has a terminal on the high potential side (for example, a drain terminal) and a terminal on the low potential side (for example, , source terminals) (for example, drain-source voltage) is turned on or off (ZVS: Zero Voltage Switching). Further, each switching element of the second converter 17 is turned on or off when the current flowing through the switching element is zero current (ZCS: Zero Current Switching). Such operation of the switching element is called soft switching, and can significantly reduce loss due to switching. The second converter 17 operates as a converter with little power conversion loss, that is, a highly efficient converter, in converting voltage V ₁ to voltage V ₂ or converting voltage V ₂ to voltage V ₁ . Thereby, the second converter 17 has an isolation transformer between the ports 27 and 37, and is a circuit that operates so that the relationship between the voltage of the port 27 and the voltage of the port 37 is a predetermined ratio, that is, It can operate as a DC transformer. The predetermined ratio is the ratio (turn ratio) between the winding n ₁ of the primary coil 57 and the winding n ₂ of the secondary coil 67. Note that the control method known at the time of filing of this application can be applied to the controller 100 as a method for soft switching each switching element of the second converter 17.

For example, when the winding n ₂ of the secondary coil 67 is made eight times the winding n ₁ of the primary coil 57 (n ₁ :n ₂ =1:8), the second converter 17 has a voltage V ₁ In the conversion from voltage V ₂ to voltage V 2 , the circuit operates as a booster circuit that outputs a voltage eight times the voltage V ₁ as voltage V ₂ . Further, the second converter 17 operates as a step-down circuit that outputs a voltage ⅛ times the voltage V ₂ as the voltage V ₁ in converting the voltage V ₂ to the voltage V ₁ .

Based on the operation of the first converter alone and the operation of the second converter 17 alone, regarding the control of the plurality of first converters 11 to 16 and the second converter 17 by the controller 100 and the operation as the power conversion device 200 , will be explained using FIG. 4 again.

The starting sequence and stopping sequence of the plurality of first converters 11 to 16 and second converter 17 will be explained. The winding ratio of the insulation transformer of the second converter 17 uses the above example (n ₁ :n ₂ =1:8).

In the circuit configuration shown in FIG. 4, controller 100 starts up second converter 17 earlier than the plurality of first converters 11-16. When power converter 200 is stopped, each switching element constituting the plurality of first converters 11 to 16 and switching elements S ₅ to S ₁₂ of second converter 17 are turned off. From this state, the controller 100 turns on and off the switching elements S ₅ -S ₁₂ of the second converter 17 while keeping each switching element configuring the plurality of first converters 11 - 16 off. As a result, the second converter 17 starts up earlier than the plurality of first converters 11 to 16. The voltage V _bat of the load 7 , which is a battery, is input to the second converter 17 , and the second converter 17 converts the voltage V _bat of the load 7 into a voltage at a predetermined ratio (for example, 1/8 of the voltage V _bat voltage) is output to port 27. When voltage is applied to the port 27 of the second converter 17, the controller 100 maintains control over the switching elements S ₅ to S ₁₂ of the second converter 17 and operates the second converter 17 as a DC transformer. The first converters 11 to 16 are turned on and off. The plurality of first converters 11 to 16 are activated, and each first converter converts the power of the corresponding power source and outputs it to the second converter 17. Thereby, the power conversion device 200 converts the power of the plurality of power sources 1 to 6 and supplies the converted power to the load 7.

The controller 100 also stops the second converter 17 later than the first converters 11 to 16. In a state in which the power conversion device 200 supplies power from the power sources 1 to 6 to the load 7, the switching elements constituting the first converters 11 to 16 and the switching elements S ₅ to S ₁₂ of the second converter 17 are turned on and off, respectively. From this state, the controller 100 turns off the switching elements constituting the first converters 11 to 16 while maintaining control over the switching elements S ₅ to S ₁₂ of the second converter 17 and operating the second converter 17 as a DC transformer. As a result, the first converters 11 to 16 stop earlier than the second converter 17. When power is no longer output from the first converters 11 to 16 to the second converter 17, the controller 100 turns off the switching elements S ₅ to S ₁₂ of the second converter 17 while keeping the switching elements constituting the first converters 11 to 16 turned off. As a result, the power conversion device 200 stops.

Next, the control of the multiple first converters 11 to 16 when both the multiple first converters 11 to 16 and the second converter 17 are activated will be described. In the circuit configuration shown in FIG. 4, the controller 100 switches each of the switching elements constituting the multiple first converters 11 to 16 in synchronization with a predetermined external signal. The predetermined external signal is an external signal that is unrelated to the power conversion device 200 and has a predetermined frequency. This makes it possible to synchronize the switching timing of each switching element among the multiple first converters 11 to 16. The predetermined frequency is not a particularly limited frequency, but a frequency experimentally determined according to the circuit configuration of the first converters 11 to 16 is used.

Next, MPPT control according to this embodiment will be explained using FIG. 5. FIG. 5 is a diagram for explaining MPPT control according to this embodiment. FIG. 5 shows a graph in which the horizontal axis is voltage and the vertical axis is current. In FIG. 5, C ₁ represents an example of the voltage-current characteristics of the power source 1 shown in FIG. 4, and C ₂ represents an example of the voltage-current characteristics of the power source 2 shown in FIG. 4. In this embodiment, power supplies 1 to 6 are solar cell modules. As described above, the power generated by the solar cell module fluctuates depending on the amount of solar radiation, so the power source 1 and the power source 2 exhibit different voltage-current characteristics. Further, when the amount of solar radiation to the solar cell module changes over time, the voltage-current characteristics C ₁ and C ₂ shown in FIG. 5 also change to the characteristics according to the amount of solar radiation. The operating point P _max1 indicates the operating point at which the power generated by the power source 1 is maximum in the voltage-current characteristic _C1 of the power source 1. The operating point P _max2 indicates the operating point at which the power generated by the power source 2 is maximum in the voltage-current characteristic _C2 of the power source 2.

In addition, in Fig. 5, the intermediate voltage V _mid corresponds to the intermediate voltage V _mid shown in Fig. 4. In the power conversion system 300 shown in Fig. 4, when the controller 100 starts up the second converter 17 earlier than the multiple first converters 11 to 16, an intermediate voltage V _mid having a predetermined ratio to the voltage V _bat of the load 7 is generated at the port 27 of the second converter 17. The predetermined ratio is the turns ratio (n ₁ :n ₂ ) of the isolation transformer of the second converter 17.

Here, the voltage of the load 7 will be explained. The speed at which the voltage of the battery changes due to charge and discharge is slower than the speed at which the generated power of the solar cell module changes due to changes in the amount of solar radiation, so in controlling the plurality of first converters 11 to 16, the battery is It can be considered as a voltage source. Since the intermediate voltage V _mid and the voltage of the load 7 have a predetermined ratio relationship, the intermediate voltage V _mid can be regarded as a constant voltage.

The controller 100 according to the present embodiment steps up or steps down the voltage input from each power source to each of the plurality of first converters 11 to 16 so that the output voltage becomes the intermediate voltage V _mid . In the example of FIG. 5, the controller 100 controls the first converter 11 to step up or step down the voltage input from the power supply 1 and output the intermediate voltage V _mid . When the intermediate voltage V _mid is output from the first converter 11, the controller 100 controls the first converter 11 so that the output current of the first converter 11 becomes maximum. In other words, the controller 100 controls the first converter 11 so that the output power of the first converter 11 is maximized under the conditions for outputting the intermediate voltage V _mid determined by the second converter 17.

For example, the controller 100 acquires information about the output current I _out1 and the output voltage V _out1 of the first converter 11 from a current sensor and a voltage sensor provided at the output port 31 of the first converter 11. The controller 100 operates the step-up chopper circuit or the step-down chopper circuit of the first converter 11 so that the output voltage V _out1 matches the intermediate voltage V _mid . Then, while detecting the output current I _out1 , the controller 100 switches each switching element constituting the first converter 11 so that the output current I _out1 becomes maximum. Thereby, the output power of the first converter 11 can be maximized in a state where the output voltage V _out1 of the first converter 11 is made equal to the intermediate voltage V _mid . Since the output power of the first converter 11 is maximized, the power input from the power supply 1 to the first converter 11 is also maximized, and as a result, the power supply 1 operates at the operating point P _max1 in the voltage-current characteristic _C1. . In the example of FIG. 5, since the voltage V _pmax1 corresponding to the operating point P _max1 of the power supply 1 is lower than the intermediate voltage V _mid , the controller 100 boosts the voltage V _pmax1 input from the power supply 1 while increasing the voltage at the first converter. The output current I _out1 of No. 11 is maximized.

Note that the buck-boost control and the control for maximizing the output current for the first converter 11 do not need to be performed in order; for example, the controller 100 may adjust the output voltage V _out1 to match the intermediate voltage V _mi while boosting or buckling the voltage. At the same time, the first converter 11 may be controlled so that the output current I _out1 is maximized.

Further, in the example of FIG. 5 , controller 100 controls first converter 12 in the same way as it controls first converter 11 . Specifically, controller 100 operates a step-up chopper circuit or a step-down chopper circuit of first converter 12. Then, while detecting the output current I _out2 , the controller 100 switches each switching element constituting the first converter 12 so that the output current I _out2 becomes maximum. Since the output power of the first converter 12 is maximized, the power input from the power supply 2 to the first converter 11 is also maximized, and as a result, the power supply 2 operates at the operating point P _max2 in the voltage-current characteristic _C2. . In the example of FIG. 5, since the voltage V _pmax2 corresponding to the operating point P _max2 of the power supply 2 is higher than the intermediate voltage V _mid , the controller 100 lowers the voltage V _pmax2 input from the power supply 2 while the first converter 12's output current I _out2 is maximized.

FIG. 6 is a diagram for explaining the operation of power conversion device 200 in the circuit configuration shown in FIG. 4. In FIG. 6, C ₁ to C ₆ indicate an example of the voltage-current characteristics of the power supplies 1 to 6 shown in FIG. 4. Note that C ₁ and C ₂ correspond to C ₁ and C ₂ shown in FIG. 5. Further, operating points P _max1 to P _max6 indicate operating points at which the generated power of the power supplies 1 to 6 is maximum in the voltage-current characteristics C ₁ to C ₆ of the power supplies 1 to 6, respectively.

As shown in the example of FIG. 6, each of the first converters corresponding to the power sources 1 to 6 outputs the maximum output current at that time while outputting the intermediate voltage V _mid by the controller 100. Taking the step-up operation as an example, for example, the first converter 11 steps up the voltage corresponding to the operating point P _max1 of the power source 1 to output the intermediate voltage V _min , while outputting the maximum output current I _out1 at that time. Taking the step-down operation as an example, the first converter 12 steps down the voltage corresponding to the operating point P _max2 of the power source 2 to output the intermediate voltage V _min , while outputting the maximum output current I _out2 at that time. Since the first converters 13 to 16 operate in the same manner as the first converter 11 or the first converter 12, the operation of each first converter and the output current at that time are similar to those of the first converter 11 or the first converter 12, and therefore the description of the operation of the first converter 11 or the first converter 12 is used. As shown in FIG. 6, even if the multiple power sources 1 to 6 have different voltage-current characteristics, the multiple power sources 1 to 6 can be operated at the operating points P _max1 to P _max6 at which the generated power is maximized.

Note that in the example of FIG. 6, the plurality of first converters 11 to 16 not only have different voltage step-up operations and step-down operations, but also have different step-up ratios and step-down ratios. Controller 100 switches the step-up ratio or step-down ratio by changing the on/off duty ratio of each switching element constituting the plurality of first converters 11 to 16.

In the circuit configuration shown in FIG. 4, since the outputs of the plurality of first converters 11 to 16 are connected in parallel, the output currents I _out1 to I _out6 of each first converter are summed. In the example of FIG. 6, the current I _total indicates the sum of output currents I _out1 to I _out6 output from each of the plurality of first converters 11 to 16. The current I _total in FIG. 6 corresponds to the current I _total shown in FIG. 4 .

When the current I _total is input to the second converter 17, the second converter 17 boosts the intermediate voltage V _mid to the voltage V _bat of the load 7 at a ratio determined by the winding ratio of the isolation transformer, while increasing the current I _bat is output to load 7.

Here, a method for setting the turns ratio of the isolation transformer of the second converter 17 in the power conversion system 300 shown in FIG. 4 will be described using FIG. 7. FIG. 7 is a diagram for explaining a method of setting the turns ratio of the isolation transformer included in the second converter 17. FIG. 7 corresponds to a block diagram of the power conversion system 300 shown in FIG. It is assumed that the power conversion system 300 uses the circuit configuration shown in FIG. 4 .

In this embodiment, the turns ratio (n ₁ :n ₂ ) of the isolation transformer of the second converter 17 is set according to the nominal maximum output operating voltage of the solar cell module and the voltage of the load 7, which is a battery. Specifically, the winding ratio of the isolation transformer is set to the ratio between the nominal maximum output operating voltage of the solar cell module and the voltage of the battery when the power storage rate is 50%. The nominal maximum output operating voltage of a solar cell module is the output voltage of the solar cell module when the solar cell module outputs maximum power. The battery's power storage rate is also called the battery's state of charge or battery's charging rate (SOC: State of Charge).

In the example of FIG. 7, it is assumed that the nominal maximum output operating voltage V _mpp of the solar cell module is 45V, the battery voltage V _bat is in the range of 240V to 400V, and the battery voltage V _bat is 360V when the SOC is 50%. In this case, the winding n ₂ of the secondary coil 67 is ₈ times as large as the winding n 1 of the primary coil 57 so that the intermediate voltage V _mid and the nominal maximum output operating voltage V _mpp of the solar cell module match. is set to Generally, in a buck-boost converter, the closer the buck-boost ratio is to 1, the more efficiently power can be converted. Therefore, each of the plurality of first converters 11 to 16 can output the voltage input from the corresponding power source as it is without stepping up or stepping down the voltage. This leads to increased power conversion efficiency. As in the example of FIG. 7, by setting the turns ratio of the isolation transformer of the second converter 17, it is possible to reduce the difference between the input voltage and the output voltage in the plurality of first converters 11 to 16. The step-up/down ratio can be brought close to 1. Thereby, the power conversion efficiency of the plurality of first converters 11 to 16 can be improved. Further, the second converter 17 functions as a DC transformer by soft switching of the switching elements S ₅ to S ₁₂ . Therefore, the power loss in the second converter 17 can be reduced, and the power input from the plurality of first converters 11 to 16 can be supplied to the load 7 with high efficiency. As a result, the power conversion efficiency of the entire power conversion device 200 can be improved, and the amount of power supplied to the load 7 can be increased.

As described above, the power conversion device 200 according to the present embodiment includes a plurality of first converters 11 to 16 that respectively convert power input from a plurality of power sources, and is connected to each of the output ports 31 to 36 of the first converter. and a second converter 17 having a port 27 connected to the load 7 and a port 37 connected to the load 7 . The plurality of first converters 11-16 are connected in parallel through output ports 31-36. The second converter 17 insulates between the port 27 and the port 37, and operates so that the voltage at the port 27 and the voltage at the port 37 are at a predetermined ratio. As a result, the output voltages V _out1 to V _out6 of the plurality of first converters 11 to 16 become the common intermediate voltage V _mid among the plurality of first converters 11 to 16. There is no need to adjust the output voltage between Further, since this intermediate voltage V _mid has a predetermined ratio with respect to the voltage V _bat of the load 7, the output voltage of the power conversion device 200 can be maintained. As a result, according to the power conversion device 200 according to the present embodiment, the output voltage of the power conversion device 200 can be maintained without adjusting the output voltage between the plurality of first converters 11 to 16.

Here, we will explain the action and effect of the power conversion device 200 of this embodiment by giving a power conversion device of a comparative example in which the outputs of multiple DC-DC converters are connected in series, unlike the power conversion device 200 of this embodiment, and the MPPT control in the power conversion device of this comparative example.

In the power conversion device according to the comparative example, a DC-DC converter is connected to each of the solar cell modules, and the output terminals of the DC-DC converters are connected to each other, thereby connecting the outputs of the plurality of DC-DC converters in series. ing. In the power conversion device according to the comparative example, each DC-DC converter increases the voltage of the solar cell module to the load, and operates each solar cell module at an operating point where the generated power is maximum. The power conversion device according to the comparative example outputs a voltage obtained by adding up the output voltages of each DC-DC converter to a load.

In the configuration of the power conversion device according to such a comparative example, when the power conversion device is connected to a load such as a battery that can be regarded as a constant voltage source, the ratio of the output voltage shared by each DC-DC converter is - It is proportional to the output power ratio of the DC converter. Therefore, in the power conversion device according to the comparative example, the output voltage of one DC-DC converter among the plurality of DC-DC converters is affected by the output power of the other DC-DC converters. For example, if the output power of the other DC-DC converters among the plurality of DC-DC converters changes, that is, if the operating point of the other DC-DC converters changes, the output power of one of the plurality of DC-DC converters changes. -The output voltage of the DC converter changes.

Due to the characteristics of a DC-DC converter, when the ratio between input voltage and output voltage changes, the power transmitted by the DC-DC converter changes even if the operation before and after the change is the same. Further, when the power source is a solar cell module, a change in the transmitted power of the DC-DC converter causes a change in the operating point of the solar cell module. Assume that, as in the above example, the transmission power of one DC-DC converter changes in response to a change in the operating point of the other DC-DC converters among the plurality of DC-DC converters. Even if the solar cell module is operating at the operating point where the power generated by one DC-DC converter is maximum before the change in the transmitted power, the operating point of the solar cell module will change due to the change in the transmitted power. moves from the operating point where is maximum. In other words, there is a problem in that due to changes in the operating points of other DC-DC converters among the plurality of DC-DC converters, a particular solar cell module cannot operate at the operating point where the generated power is maximum.

Furthermore, as for MPPT control in the power converter according to the comparative example, power generation is performed while sensors detect the current and voltage output from the solar cell module, that is, the input current and input voltage input to the DC-DC converter. An example of this is control that operates the solar cell module at the operating point where the power is maximum. An example of such MPPT control is the mountain climbing method.

FIG. 8 is a diagram for explaining the problem of MPPT control using the hill climbing method. FIG. 8 is an example of voltage-current characteristics when partial shading occurs on a solar cell module. FIG. 8 shows a graph with the horizontal axis being voltage and the vertical axis being power. For example, when partial shading occurs on a solar cell module, as shown in FIG. 8, two local maximum points, operating point _P1 and operating point _P2 , may appear in the power-voltage characteristics. In the example of the power-voltage characteristics shown in FIG. 8, the operating point at which the maximum power generation is achieved is operating point _P1 . For example, in the power-voltage characteristics before a predetermined time, if the operating point at which the maximum power generation is achieved is near operating point _P2 , in MPPT control using the hill climbing method, there is a risk that the operating point at which the maximum power generation is achieved is erroneously recognized as operating point _P2 without searching for operating point _P1 . To address such problems with the hill-climbing method, for example, in a conventional example (JP Patent Publication 2016-110524), the voltage or current of the voltage-current characteristic of the solar cell module is swept to appropriately search for the operating point that maximizes the power generation without erroneously recognizing the voltage-current characteristic that has multiple maximum points. This MPPT control is also called the scan method.

However, with the scanning method, while searching for the operating point that will maximize the power generation, the solar cell module operates at an operating point other than the operating point. As a result, with the scanning method, many opportunities to operate the solar cell module at the operating point that maximizes the power generation are lost. On the other hand, if the frequency of searching for an operating point is reduced in order to reduce such lost opportunities, as explained with reference to Figure 8, the opportunities to operate at an operating point that is mistakenly recognized as the maximum power generation increase, and the power generation of the solar cell module decreases. In other words, with the scanning method, there is a trade-off between the frequency of searching and the power generation, which poses the problem of requiring complex control.

In contrast, in this embodiment, the power supplies 1 to 6 are solar cell modules, and each of the plurality of first converters 11 to 16 is a circuit that operates so that the output power of each first converter is maximized. . Since the outputs of the plurality of first converters are connected in parallel, the output voltage among the plurality of first converters is common. Therefore, as in the power conversion device according to the comparative example, it is possible to prevent the transmission power of a specific first converter from changing due to changes in the operating point of other first converters among the plurality of first converters. I can do it. As a result, each of the first converters can operate each of the plurality of solar cells at an operating point where the generated power is maximum, and the power input from the plurality of solar cell modules can be increased.

Further, since the output voltage between the plurality of first converters is determined by the second converter 17, the output power of the first converter can be easily maximized without requiring control of the output voltage of the first converter. I can do it. By maximizing the output power of the first converter, each of the plurality of power supplies 1 to 6 will operate at the operating point where the generated power is maximum, as explained using FIGS. 4 and 5. . It becomes possible to solve the problem of misrecognition of operating points in the hill-climbing method without requiring complicated control such as in the scanning method.

Furthermore, in this embodiment, the second converter 17 includes an isolation transformer configured with a primary coil 57 connected to the port 27 and a secondary coil 67 connected to the port 37. The predetermined ratio in the operation of the second converter 17 is the ratio between the winding n ₁ of the primary coil 57 and the winding n ₂ of the secondary coil. As a result, it is possible to simply change the winding ratio between the winding n ₁ of the primary coil 57 and the winding n ₂ of the secondary coil without changing the circuit configuration of the plurality of first converters 11 to 16. , the power converter 200 can be easily designed to match the voltage range of the load 7. As a result, it is possible to provide a power conversion device 200 that can maintain the output voltage regardless of the voltage range of the load 7 without adjusting the output voltage between the plurality of first converters 11 to 16.

Additionally, in this embodiment, the power supplies 1 to 6 are solar cell modules, and each of the plurality of first converters 11 to 16 is a buck-boost converter that boosts or steps down the input voltage from the solar cell module. As a result, even if the intermediate voltage V _mid fluctuates due to the load 7 whose voltage fluctuates, such as a battery, the output voltage of each of the plurality of first converters 11 to 16 can be adjusted to the intermediate voltage V _mid . can. Since MPPT control can be continued even if the voltage of the load 7 fluctuates, the power input from the plurality of solar cell modules can be increased regardless of the fluctuation of the voltage of the load 7.

Further, in this embodiment, the power supplies 1 to 6 are solar cell modules, and the load 7 is a battery. The predetermined ratio in the operation of the second converter 17 is set to the ratio between the nominal maximum output operating voltage of the solar cell module and the voltage of the battery when the power storage rate SOC is 50%. As a result, the difference between the input voltage and the output voltage of each of the plurality of first converters 11 to 16 can be reduced, and the step-up/down ratio can be brought close to 1. As a result, buck-boost operation with less power loss becomes possible, and power conversion efficiency in the plurality of first converters 11 to 16 can be improved. In addition, when the nominal maximum output operating voltage of each solar cell module is different among the power supplies 1 to 6, the characteristics of the plurality of first converters 11 to 16 are adjusted to the characteristics of the solar cell module corresponding to each first converter. You can also set it. For example, each of the plurality of first converters 11 to 16 may be controlled in accordance with the solar cell module corresponding to each first converter. Further, for example, the circuit configuration of each of the plurality of first converters 11 to 16 may be changed in accordance with the characteristics of the solar cell module corresponding to each first converter. Furthermore, for example, the characteristics of the plurality of first converters 11 to 16 may be set in accordance with the characteristics of the solar cell module corresponding to each first converter by a combination of controlling each first converter and changing the circuit configuration. .

Furthermore, in the present embodiment, the power conversion device 200 includes a controller 100 that controls each of the plurality of first converters 11 to 16. Each of the plurality of first converters 11 to 16 has a switching element, and converts the power input from the plurality of power supplies 1 to 6 by turning on and off the switching element. The controller 100 switches the switching elements constituting the plurality of first converters 11 to 16 in synchronization with a predetermined external signal. This makes it possible to reduce the influence of disturbances on MPPT control between the plurality of first converters 11 to 16, compared to the case where each switching element constituting the plurality of first converters 11 to 16 switches asynchronously. This makes it possible to stabilize the operation of each first converter.

In addition, in the present embodiment, the controller 100 controls the switching elements constituting the plurality of first converters 11 to 16 so that the output currents I _out1 to I _out6 of each of the plurality of first converters 11 to 16 are maximized. switch. As a result, without providing a voltage sensor that detects the voltage input from the power supplies 1 to 6 and a current sensor that detects the current input from the power supplies 1 to 6, the power supplies 1 to 6 can be set at the operating point where the generated power is maximum. can be operated. As a result, the number of components such as sensors provided in the power conversion device 200 can be reduced. Furthermore, as described above, the solar cell module can be operated at the operating point where the generated power is maximum using a simple method without requiring complicated control like the scanning method. In addition to reducing the number of parts, the first converter can be made smaller because no complicated control is required.

Further, in this embodiment, the controller 100 controls the second converter 17. The second converter 17 includes an isolation transformer provided between ports 27 and 37, and switching elements S ₅ to S ₁₂ for controlling the current flowing through the isolation transformer. The controller 100 synchronizes the on-time and off-time of the switching elements S ₅ -S ₁₂ and synchronizes the switching timing of the switching elements S ₅ -S ₁₂ with _the resonant frequency of the isolation transformer. Control _S12 . As a result, the second converter 17 can be operated as a resonant converter that always performs soft switching, so the second converter 17 can operate with less power loss, and the power conversion efficiency of the second converter 17 can be improved. can.

Furthermore, in this embodiment, the controller 100 starts up the second converter 17 earlier than the plurality of first converters 11-16. In a state where the plurality of first converters 11 to 16 are not activated, a current path from the plurality of first converters 11 to 16 to the second converter 17 is not generated. In order to start the second converter 17 earlier than the plurality of first converters 11 to 16, at the timing when the second converter 17 is started, the plurality of first converters 11 to 16 are instantaneously connected to the second converter 17. Current flowing into the load 7 can be suppressed. As a result, it is possible to suppress pulsations in the power supplied to the load 7.

Additionally, in this embodiment, the controller 100 stops the second converter 17 later than the plurality of first converters 11-16. Since the plurality of first converters 11 to 16 stop earlier than the second converter 17 from the state where the power converter 200 is supplying power to the load 7, there is an instantaneous It is possible to suppress current from flowing into the load 7 from the plurality of first converters 11 to 16 via the second converter 17. As a result, it is possible to suppress pulsations in the power supplied to the load 7.

Additionally, in this embodiment, each of the plurality of first converters 11 to 16 transmits power only in the direction of the port 27 of the second converter 17 from the solar cell module. Thereby, it is possible to suppress the circulation of electric power among the plurality of first converters 11 to 16, and it is possible to improve the power conversion efficiency in each of the plurality of first converters 11 to 16.

Further, in this embodiment, each of the plurality of power supplies 1 to 6 is a solar cell module. A solar cell module includes a plurality of solar cells connected in series and a plurality of diodes connected in parallel with each of the solar cells. As a result, even if partial shading occurs on the solar cell module, the amount of decrease in generated power can be suppressed, so that the power input from the plurality of power sources 1 to 6 to the power converter 200 can be significantly reduced due to partial shading. The reduction can be suppressed.

Furthermore, in this embodiment, the load 7 is a battery. As a result, even if the voltage of the load 7 fluctuates due to charging and discharging of an electric charge, the output voltage from the power conversion device 200 can be maintained before and after the voltage fluctuation, and the maximum power input from the power sources 1 to 6 at each point in time can be supplied to the load 7 with high efficiency.

Note that the embodiments described above are described to facilitate understanding of the present invention, and are not described to limit the present invention. Therefore, each element disclosed in the above embodiments is intended to include all design changes and equivalents that fall within the technical scope of the present invention.

For example, in the embodiment described above, as the control of the plurality of first converters by the controller 100, an example of control is such that each switching element constituting the plurality of first converters 11 to 16 is switched in synchronization with a predetermined external signal. Although the explanation has been given above, it is not limited to this. For example, the controller 100 may switch each switching element constituting the plurality of first converters 11 to 16 so that the phases are different between the plurality of first converters 11 to 16. Since the ripples included in the output currents of the first converters 11 to 16 are out of phase between the first converters 11 to 16, it is possible to suppress the current I _total input to the second converter 17 from pulsating. As a result, the power conversion efficiency in the second converter 17 can be improved.

1 to 6...Power source 7...Loads 11 to 16...First converter 17...Second converter 21 to 26...Input ports 21a to 26a, 21b to 26b...Input terminals 27...Ports 27a, 27b...Terminals 31 to 36...Output ports 31a to 36a, 31b to 31b...Input terminal 37...Ports 37a, 37b...Terminals 81a, 81b...Wiring 82, 83...Smoothing capacitor 100...Controller 200...Power conversion device

Claims (13)

a plurality of first converters each converting power input from a plurality of power sources;
a second converter having a first terminal connected to each of the output terminals of the plurality of first converters, and a second terminal connected to a load;
a controller that controls the first converter,
The plurality of first converters are connected in parallel by the output terminal of each of the first converters,
The second converter insulates between the first terminal and the second terminal, and operates so that the voltage of the first terminal and the voltage of the second terminal are at a predetermined ratio ,
The power source is a solar cell module,
A power conversion device in which the load is a battery . The power conversion device according to claim 1, wherein the first converter is a circuit that operates so that the output power of the first converter is maximized. the second converter includes an isolation transformer including a primary coil connected to the first terminal and a secondary coil connected to the second terminal;
3. The power conversion device according to claim 1, wherein the predetermined ratio is a ratio between the number of turns of the primary coil and the number of turns of the secondary coil. 4. The power conversion device according to claim 1, wherein the first converter is a buck-boost converter that boosts or steps down the input voltage from the solar cell module. The predetermined ratio is set to a ratio between the output voltage of the solar cell module when the solar cell module outputs maximum power and the voltage of the battery when the power storage rate is 50%. 5. The power conversion device according to any one of 1 to 4. The first converter has a first switching element, and converts the power input from the power source by turning on and off the first switching element,
The power conversion device according to claim 1, wherein the controller switches the first switching element in synchronization with a predetermined external signal. The first converter has a first switching element, and converts the power input from the power source by turning on and off the first switching element,
The power conversion device according to claim 1, wherein the controller switches the plurality of first switching elements such that the plurality of first switching elements have different phases. The first converter has a first switching element, and converts the power input from the power source by turning on and off the first switching element,
The power conversion device according to claim 2, wherein the controller controls the first switching element so that the output current of the first converter is maximized. A controller for controlling the second converter,
the second converter includes an isolation transformer provided between the first terminal and the second terminal, and a second switching element for controlling a current flowing through the isolation transformer;
The power conversion device according to any one of claims 1 to 8, wherein the controller controls the second switching element so as to synchronize an on-time of the second switching element with an off-time of the second switching element and a timing for switching the second switching element on and off with a resonant frequency of the isolation transformer. A controller for controlling the second converter,
9. The power conversion device according to claim 1, wherein the controller starts the second converter earlier than the first converter and stops the second converter later than the first converter. The power conversion device according to claim 1, wherein the first converter transmits power only in the direction from the solar cell module to the first terminal. The power conversion device according to claim 1 , wherein the solar cell module includes a plurality of solar cells connected in series and a plurality of diodes connected in parallel with each of the solar cells. . a plurality of first converters connected in parallel by the output terminals of each of the first converters having an output terminal;
a second converter having a first terminal connected to each of the output terminals of the plurality of first converters and a second terminal connected to a load, and insulating between the first terminal and the second terminal;
A method for controlling a power conversion device, comprising: a controller that controls the first converter ;
The second converter operates such that the voltage at the first terminal and the voltage at the second terminal are in a predetermined ratio,
the load is a battery;
A method for controlling a power conversion device, wherein the controller controls the plurality of first converters so as to respectively convert power from a plurality of power sources that are solar cell modules .

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