JP2018107895A - Power converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a power converter having high conversion efficiency regardless of characteristic variations in a switching element of an inverter circuit.SOLUTION: A power converter (20) for converting DC power from an external power source to supply AC power, includes: a conversion efficiency calculation unit (13) for calculating conversion efficiency (η) on the basis of an inverter circuit (1) having a booster circuit (7), a smoothing capacitor (8), switches (9a, 9b), and switching elements (2a, 2b, 2c, 2d), an input voltage (V), an input current (I), an output voltage (V), and an output current (I); a drain voltage measurement unit (14) for measuring and acquiring a drain voltage of the switching elements (2a, 2b, 2c, 2d); and a gate voltage generation unit (19) for generating a gate voltage of the switching elements (2a, 2b, 2c, 2d) using the conversion efficiency (η) and the drain voltage.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a power conversion device that converts DC power from an external power source and supplies AC power.

  Conventionally, the configuration disclosed in Patent Document 1 can be exemplified as a power conversion device that converts DC power generated by a solar cell and supplies AC power. The power conversion device disclosed in Patent Document 1 includes a booster circuit that boosts the output voltage from the solar cell, and an inverter circuit that converts AC power synchronized with the system power supply. This inverter circuit includes a switching element, an inductor that is a reactor for a filter disposed at the subsequent stage of these switching elements, and a capacitor that is disposed at the subsequent stage of these inductors. And a switching element produces | generates the alternating voltage which is an output of an inverter circuit by pulse width modulation (PWM: Pulse Width Modulation) control by turning on / off by control of the gate voltage which is an output voltage from a gate drive circuit.

Japanese Patent Laid-Open No. 2002-10495

  However, according to the above-described conventional technology, the conversion efficiency of the power converter is affected by variations in characteristics of the switching elements. Therefore, there is a problem that it is difficult to increase the conversion efficiency of the power conversion device.

  The present invention has been made in view of the above, and an object of the present invention is to obtain a power conversion device having high conversion efficiency regardless of variations in characteristics of switching elements of an inverter circuit.

  In order to solve the above-described problems and achieve the object, the present invention provides a power conversion device that converts DC power from an external power source and supplies AC power, and includes an inverter circuit having a plurality of switching elements; A conversion efficiency calculation unit that calculates conversion efficiency based on the input voltage and input current, and the output voltage and output current, and measures the voltage between the drain and the source of each of the plurality of switching elements to determine the drain voltage A drain voltage measurement unit to be acquired, and a gate voltage generation unit that generates a gate voltage of each of the plurality of switching elements using the conversion efficiency and each of the plurality of drain voltages.

  According to the present invention, there is an effect that it is possible to obtain a power conversion device with high conversion efficiency regardless of variations in characteristics of switching elements of the inverter circuit.

The figure which shows the power converter device which concerns on Embodiment 1 of this invention, and one structural example of the periphery The flowchart which shows an example of a process until conversion efficiency last value is calculated at the time of starting in the power converter device shown in FIG. The flowchart which shows an example of a process until the gate voltage of a switching element is produced | generated in the power converter device shown in FIG. The flowchart which shows an example of the process of calculation and adjustment of the gate voltage of a switching element in the power converter device shown in FIG. The figure which shows the change of ON resistance with respect to the gate voltage in Si-MOSFET and SiC-MOSFET applicable to the switching element of the power converter device shown in FIG.

  Below, the power converter concerning an embodiment of the invention is explained in detail based on a drawing. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
FIG. 1 is a diagram illustrating a configuration example of a power conversion apparatus and surroundings according to Embodiment 1 of the present invention. A solar cell 6 that is an external power source that outputs DC power is connected to the input of the power conversion device 20 shown in FIG. 1, and the system 10 is connected to the output of the power conversion device 20.

  The system 10 is a single-phase AC power supply, and the AC power output from the power converter 20 is synchronized with the system 10.

  A power conversion device 20 shown in FIG. 1 includes a booster circuit 7, a smoothing capacitor 8, switches 9a and 9b, an inverter circuit 1, an input power measurement unit 11, an output power measurement unit 12, and a conversion efficiency calculation unit 13. A drain voltage measuring unit 14 and a gate voltage generating unit 19.

  The booster circuit 7 boosts the output voltage of the solar cell 6. The smoothing capacitor 8 smoothes the output voltage from the booster circuit 7. The inverter circuit 1 includes switching elements 2a, 2b, 2c, and 2d, reactors 3a and 3b, a capacitor 4, and gate drive circuits 5a, 5b, 5c, and 5d. Here, the switching elements 2a, 2b, 2c, and 2d are MOSFETs (Metal Oxide Field Effect Transistors) formed of silicon, that is, Si-MOSFETs. The reactors 3a and 3b are filter circuit reactors. The capacitor 4 is a filter circuit capacitor. The switches 9a and 9b are arranged in parallel with each other and switch the connection state between the power conversion device 20 and the system 10.

The input power measurement unit 11 includes a voltage measurement unit 111, a current measurement unit 112, and a power calculation unit 113. Voltage measurement unit 111 obtains the input voltage V _i by measuring the voltage of the solar cell 6. The current measuring unit 112 measures the current of the P bus on the output side of the solar cell 6 and acquires the input current I _i . The power calculation unit 113 calculates the input power P _i from the product of the input voltage V _i acquired by the voltage measurement unit 111 and the input current I _i acquired by the current measurement unit 112. Here, the formula for calculating the input power is P _i = V _i × I _i .

The output power measurement unit 12 includes a voltage measurement unit 121, a current measurement unit 122, and a power calculation unit 123. Voltage measuring unit 121 acquires the output voltage V _o by measuring the voltage of the capacitor 4. The current measuring unit 122 measures the current of the P bus on the output side of the inverter circuit 1 and acquires the output current _Io . The power calculation unit 123 calculates the output power P _o from the product of the output voltage V _o acquired by the voltage measurement unit 121 and the output current I _o acquired by the current measurement unit 122. Here, the calculation formula of the output power is P _o = V _o × I _o .

The conversion efficiency calculation unit 13 receives the input power P _i and the output power P _o and calculates the conversion efficiency η. Here, the formula for calculating the conversion efficiency is η = P _o / P _i .

The drain voltage measuring unit 14 measures drain voltages with reference to the sources of the switching elements 2a, 2b, 2c, and 2d to obtain drain voltages V _DSa , V _DSb , V _DSc , and V _DSd .

The gate voltage generation unit 19 receives the conversion efficiency η calculated by the conversion efficiency calculation unit 13 and the drain voltages V _DSa , V _DSb , V _DSc , V _DSd acquired by the drain voltage measurement unit 14 and inputs the switching elements 2 a, Gate voltages V _GSa , V _GSb , V _GSc , and V _GSd are generated and output with reference to the sources of 2b, 2c, and 2d. Gate voltage _V GSa the gate voltage generator 19 is _{output, V GSb, V GSc, V} GSd the gate driving circuit 5a, 5b, 5c, are input to 5d. Each of the gate drive circuits 5a, 5b, 5c and 5d _controls the gate voltage of each of the switching elements 2a, 2b, 2c and 2d based on each of the gate voltages _VGSa , _VGSb , _VGSc and _VGSd .

The gate voltage generation unit 19 includes a gate voltage command value calculation unit 15, a gate voltage circuit 16, a conversion efficiency previous value storage unit 17, and a gate voltage command value previous value storage unit 18. The gate voltage command value calculation unit 15 includes a conversion efficiency η, a conversion efficiency previous value η _o , drain voltages V _DSa , V _DSb , V _DSc , and V _DSd , and gate voltage command previous values V _GSao , V _GSbo , Based on each of V _GSco and V _GSdo , each of the gate voltage command values is calculated. The gate voltage circuit 16 outputs the respective gate voltages V _GSa , V _GSb , V _GSc , V _GSd according to each of the gate voltage command values calculated by the gate voltage command value calculation unit 15. The previous conversion efficiency value storage unit 17 stores at least the previous conversion efficiency value η _o which is the previous conversion efficiency. The gate voltage command value previous value accumulation unit 18 accumulates at least each of the previous gate voltage command previous values _VGSao , _VGSbo , _VGSco , and _VGSdo .

Note that the previous gate voltage command previous values V _GSao , V _GSbo , V _GSco , and V _GSdo at the time of startup of the power conversion device 20 are initial values. This initial value may be appropriately set to a theoretical value that maximizes the conversion efficiency η according to the circuit.

  The power conversion device 20 shown in FIG. 1 changes the gate voltage of the switching elements 2a, 2b, 2c, and 2d so as to increase the conversion efficiency η, and breaks down the breakdown voltage between the drain and the source as the gate voltage increases. Works to prevent.

FIG. 2 is a flowchart illustrating an example of processing until the conversion efficiency previous value ηo is calculated at the time of startup in the power conversion device 20 illustrated in FIG. 1. First, start the process, the conversion efficiency calculation unit 13, the input power _{P i} and the output power _{P o,} calculates the conversion efficiency eta (S1). Next, the gate voltage command value calculation unit 15 sets the conversion efficiency η as the previous conversion efficiency value ηo (S2), and ends the process.

  FIG. 3 is a flowchart showing an example of processing until the gate voltage of the switching element 2a is generated in the power conversion device 20 shown in FIG. Note that the process shown in FIG. 3 is executed a plurality of times at regular time intervals during the operation of the power conditioner including the solar battery 6. That is, the previous value in the previous value storage unit 17 of the conversion efficiency and the previous value storage unit 18 of the gate voltage command value is a value in the previous process.

First, start the process, the gate voltage command value calculating unit 15, a value obtained by adding the gate voltage change amount [Delta] V _a of the switching element 2a to the gate voltage previous value _{V GSAO} a command value of the gate voltage _{V GSa} (S11) . Next, the conversion efficiency calculation unit 13 calculates the conversion efficiency η from the input power P _i and the output power P _o (S12). Next, the gate voltage command value calculation unit 15 compares the conversion efficiency η, which is the current value, with the previous conversion efficiency value η _o from the previous conversion value storage unit 17, and whether η> η _o is satisfied. Is determined (S13). When η> η _o is not satisfied (S13: No), the gate voltage command value calculation unit 15 inverts the sign of the gate voltage change amount ΔV _a of the switching element 2a (S14).

Note that the gate voltage change amount ΔV _a of the switching element 2a may be appropriately set according to the components so that the change efficiency η is increased.

That is, when the conversion efficiency η of the current value is larger than the conversion efficiency η _{o of the} previous value, the conversion efficiency is improved as compared with the previous time due to the increase of the gate voltage, and thus the gate voltage change amount ΔV _{a of the} switching element 2a. Is added to further improve the conversion efficiency. However, when the conversion efficiency η of the current value is not larger than the conversion efficiency η _{o of the} previous value, the conversion efficiency is lower than the previous value due to the increase of the gate voltage. By adding the gate voltage change amount ΔV _a , the conversion efficiency is improved.

Next, the gate voltage command value calculation unit 15 acquires the drain voltage V _DSa of the switching element 2a from the drain voltage measurement unit 14 (S15). The gate voltage command value calculating section 15 determines whether the drain voltage _{V DSa} is 80% or less of the drain voltage maximum rated voltage _{V DSmax} a set value (S16). Here, in consideration of general derating in semiconductor components, the set value to be compared is set to 80% of the drain voltage maximum rated voltage V _DSmax , but this ratio may be set as appropriate according to the components. When the drain voltage V _DSa is 80% or less of the drain voltage maximum rated voltage V _DSmax (S16: Yes), the processing is ended as it is. When the drain voltage V _DSa is not 80% or less of the drain voltage maximum rated voltage V _DSmax which is the set value (S16: No), the absolute value of the gate voltage change amount ΔV _a of the switching element 2a is 2 from the gate voltage V _GSa. The value obtained by subtracting the double is set as the gate voltage V _GSa (S17), and the process is ended.

The gate voltage command value calculation unit 15 outputs the command value of the gate voltage V _{GSa thus} determined to the gate voltage circuit 16, and the gate voltage circuit 16 outputs the gate voltage V _GSa according to the command value, The gate drive circuit 5a _turns on and off the switching element 2a by controlling the gate voltage of the switching element 2a based on the gate voltage _VGSa .

As described above, the gate voltage of the switching element 2a is controlled, that is, the gate voltage _VGSa is calculated and adjusted. And this process should just be performed in order about each of switching element 2a, 2b, 2c, 2d.

FIG. 4 is a flowchart illustrating an example of processing for calculating and adjusting the gate voltages of the switching elements 2a, 2b, 2c, and 2d in the power conversion device 20 illustrated in FIG. In FIG. 4, first, the processing is started, and the gate voltage _VGSa is calculated and adjusted as shown in FIG. 4 (S21), and the gate voltage _VGSb is calculated and adjusted in the same manner (S22). The gate voltage _VGSc is calculated and adjusted (S23), the gate voltage _VGSd is calculated and adjusted in the same manner (S24), and the calculation returns to the calculation and adjustment of the gate voltage _VGSa to repeat the series of operations.

  As described above, according to the present embodiment, the gate voltage of each switching element can be controlled so as to improve the conversion efficiency based on the comparison result between the previous value and the current value of the conversion efficiency. Conversion efficiency can be improved.

  FIG. 5 is a diagram showing a change in on-resistance with respect to the gate voltage in the Si-MOSFET and the SiC-MOSFET applicable to the switching elements 2a, 2b, 2c, and 2d of the power conversion device 20 shown in FIG. The SiC-MOSFET is a MOSFET formed of silicon carbide.

  As shown in FIG. 5, the ON resistance can be reduced by increasing the gate voltage in both the Si-MOSFET and the SiC-MOSFET. As described above, in both the Si-MOSFET and the SiC-MOSFET, it is possible to improve the conversion efficiency by reducing the on-resistance by increasing the gate voltage, but if the gate voltage is increased, noise is generated by high-speed switching. There is a risk, and this noise contributes to a decrease in conversion efficiency. Therefore, even if the gate voltage of the MOSFET is simply increased, the conversion efficiency cannot always be improved. Further, the on-resistance with respect to the gate voltage may vary in the MOSFET, and this variation may hinder further improvement in conversion efficiency. That is, in the prior art, due to variations in the characteristics of the switching elements in the inverter circuit, the gate voltage may not match the voltage value that can maximize the conversion efficiency as the power converter, Further improvement of the conversion efficiency may be hindered.

  According to the present embodiment, it is possible to obtain a power conversion device with high conversion efficiency regardless of variations in characteristics of switching elements of the inverter circuit.

  In this embodiment, since the drain voltage of the switching element of the inverter circuit is controlled so as not to exceed the set value based on the maximum rated voltage of the drain voltage, breakdown withstand voltage between the drain and the source can be prevented. .

  In the present embodiment, switching elements 2a, 2b, 2c, and 2d are preferably SiC-MOSFETs. When the switching elements 2a, 2b, 2c and 2d are SiC-MOSFETs, the on-resistance when the gate voltage is increased is further reduced as compared with the case where the switching elements 2a, 2b, 2c and 2d are Si-MOSFETs. Therefore, switching loss can be further suppressed. Therefore, conversion efficiency can be further improved by using switching elements 2a, 2b, 2c, and 2d as SiC-MOSFETs and controlling the gate voltage as described above. Furthermore, since the switching loss due to the increase in the switching speed accompanying the increase in the gate voltage can be reduced, the conversion efficiency can be further improved in this respect.

  The configuration described in the above embodiment shows an example of the contents of the present invention, and can be combined with another known technique, and can be combined with other configurations without departing from the gist of the present invention. It is also possible to omit or change the part.

  1 inverter circuit, 2a, 2b, 2c, 2d switching element, 3a, 3b reactor, 4 capacitor, 5a, 5b, 5c, 5d gate drive circuit, 6 solar cell, 7 booster circuit, 8 smoothing capacitor, 9a, 9b switch, 10 systems, 11 input power measurement unit, 12 output power measurement unit, 13 conversion efficiency calculation unit, 14 drain voltage measurement unit, 15 gate voltage command value calculation unit, 16 gate voltage circuit, 17 conversion efficiency previous value accumulation unit, 18 Gate voltage command value previous value accumulation unit, 19 Gate voltage generation unit, 20 Power converter, 111, 121 Voltage measurement unit, 112, 122 Current measurement unit, 113, 123 Power calculation unit.

Claims (3)

A power conversion device that converts DC power from an external power source and supplies AC power,
An inverter circuit having a plurality of switching elements;
A conversion efficiency calculation unit that calculates conversion efficiency based on the input voltage and input current, and the output voltage and output current;
A drain voltage measuring unit that obtains a drain voltage by measuring a voltage between a drain and a source of each of the plurality of switching elements;
A power conversion device comprising: a gate voltage generation unit configured to generate a gate voltage of each of the plurality of switching elements using the conversion efficiency and each of the plurality of drain voltages.   The power conversion device according to claim 1, wherein the gate voltage generation unit controls the gate voltage of each of the switching elements such that each of the plurality of drain voltages is equal to or lower than a set value.   The power converter according to claim 1, wherein the plurality of switching elements are MOSFETs formed of SiC.

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