JP2005085088A - Electric power converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power converter allowing improvement of power conversion efficiency by reducing DC-DC output voltage of a DC-DC converter to reduce switching loss of an inverter device. <P>SOLUTION: This electric power converter has a controller 4 having: the DC-DC converter 2 boosting DC battery voltage VB supplied from a fuel cell 9 to the DC-DC output voltage VD; the inverter device 3 switching the DC-DC output voltage VD by a PWM signal SPWM of a high-frequency carrier frequency to generate inverter output voltage VC; and a voltage reduction means 7 generating a variable output voltage correction instruction value Vα, and reducing the DC-DC output voltage VD of the DC-DC converter 2 in a light load. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a power converter that converts a direct current output of a fuel cell into an alternating current and operates in an interconnected manner with a system power supply, and particularly reduces the output voltage of the DC-DC converter or the switching carrier frequency of an inverter device at a light load. The present invention relates to a power conversion device that reduces the switching loss of an inverter device and improves power conversion efficiency.

  In recent years, a distributed power source obtained by converting a DC power source of a photovoltaic power generation or a fuel cell into an AC power source and a system power source (commercial power sources: 50 Hz / 60 Hz, 100 V / 200 V) are connected to each other, and household devices ( When a distributed power source cannot be covered by a distributed power source, a distributed power source system that supplies a system power source to drive a household device (load) has been put into practical use.

  A conventional power converter includes a DC-DC converter that boosts a DC power supply of a fuel cell and converts it into a DC-DC DC output, and a DC-DC DC output of the DC-DC converter that is connected to a system power supply (commercial power supply: 50 Hz). / 60 Hz, 100 V / 200 V) and an inverter device that outputs an alternating current at a frequency matched with the frequency.

  On the other hand, since power conversion devices using fuel cells cannot currently operate a reverse power flow (charging) to the grid side, the power consumed by household devices such as daytime or midnight (for example, refrigerators) In a small time zone, the generated power of the fuel cell or power conversion device must be suppressed so that a reverse power flow (charging) does not occur from the power conversion device to the grid (commercial power supply) side.

In addition, as disclosed in “Patent Document 1” (system interconnection type inverter device), a conventional power conversion device uses a booster circuit unit (DC− Inverter main circuit section that boosts the voltage by a DC converter and converts the boosted DC power supply to AC power supply so that the difference between the output voltage of the booster circuit section and the peak value of the system power supply (commercial power supply) is constant Control and suppress the loss of the switching element of the inverter main circuit section, and increase the power conversion efficiency.
Japanese Patent Laid-Open No. 10-14112

  Conventional power converters have a configuration in which a DC-DC converter outputs a rated output voltage, an inverter device drives a switching element at a rated carrier frequency, and outputs an alternating current. , Refrigerators, etc.) that output alternating current when the load is light, the power generation of the fuel cell must be suppressed to prevent reverse power flow to the system power supply (commercial power supply), and the household equipment used The work to adjust the power to suit the needs becomes complicated.

  Further, at the time of a light load, it is indispensable to take measures to prevent the reverse power flow to the system power supply (commercial power supply) by consuming surplus power that is not used in household devices (for example, a refrigerator) with a resistor or the like.

  On the other hand, among the distributed power systems such as fuel cells, a system with a small capacity of about 1 kW (kilowatt) has a great improvement in power conversion efficiency even if the switching loss of the inverter device is slightly improved.

  The conventional power conversion device disclosed in “Patent Document 1” (system-connected inverter device) suppresses the loss of the switching element of the inverter circuit in a photovoltaic power generation system in which the generated power of the DC power source is relatively large, Although the conversion efficiency can be increased, in a power conversion device using a fuel cell with a small amount of power generated by a DC power source, the loss of the switch element cannot be suppressed to the minimum, and an increase in power conversion efficiency cannot be expected.

  The present invention has been made to solve such problems, and a first object is to reduce the switching loss of the inverter device by reducing the DC-DC output voltage of the DC-DC converter at the time of light load. An object of the present invention is to provide a power conversion device that improves power conversion efficiency.

  A second object is to provide a power conversion device that lowers the carrier frequency of the inverter device at the time of light load to reduce switching loss and improve power conversion efficiency.

  In order to solve the above problems, a power conversion device according to the present invention converts a direct current output of a fuel cell into an alternating current, and performs a DC-DC conversion device, an inverter device, and a control device that are interconnected with a system power supply. The control device includes a voltage lowering unit that lowers the output voltage of the DC-DC converter at a light load.

  The power conversion device according to the present invention is a power conversion device including a DC-DC conversion device, an inverter device, and a control device that convert the direct current output of the fuel cell into alternating current and is interconnected with the system power supply. Since the voltage reduction means for reducing the output voltage of the DC-DC converter at the time of light load is provided, the output voltage can be reduced by reducing the duty ratio of the drive pulse of the DC-DC converter.

  Further, the voltage reduction means according to the present invention, when detecting the output power and the system voltage, the voltage value storage means for storing the correction coefficient corresponding to the output power and the DC-DC output voltage command value corresponding to the system voltage, Correction for reading the corresponding correction coefficient and the corresponding DC-DC output voltage command value from the voltage value storage means, calculating the product of the correction coefficient and the DC-DC output voltage command value, and outputting the DC-DC output voltage correction command value Command value calculating means, and changing the DC-DC output voltage of the DC-DC converter.

  The voltage reduction means according to the present invention includes a voltage value storage means for storing a correction coefficient corresponding to the output power and a DC-DC output voltage command value corresponding to the system voltage, and a voltage value when the output power and the system voltage are detected. A correction command value for reading a corresponding correction coefficient and a corresponding DC-DC output voltage command value from the storage means, calculating a product of the correction coefficient and the DC-DC output voltage command value, and outputting a DC-DC output voltage correction command value Since the calculation means is provided and the DC-DC output voltage of the DC-DC converter is changed, the output voltage can be reduced based on the DC-DC output voltage correction command value at a light load.

  Furthermore, the voltage value storage means according to the present invention stores a correction coefficient that changes linearly with respect to the output power at light load.

  The voltage value storage means stores a correction coefficient that changes stepwise with respect to the output power at light load.

  Furthermore, the voltage value storage means according to the present invention stores a correction coefficient that changes exponentially with respect to the output power at light load.

  The voltage value storage means according to the present invention stores a correction coefficient that changes linearly with respect to output power at light load, stepwise with respect to output power at light load, or exponentially changes with respect to output power at light load. Therefore, the DC-DC output voltage correction command value can be set with a degree of freedom.

  The control device according to the present invention further includes a distortion determination unit that compares the measured output current distortion rate with the specified distortion rate, and the DC-DC output voltage correction command value is within a range in which the output current distortion rate does not exceed the specified distortion rate. Is output.

  The control device according to the present invention includes a distortion determination unit that compares the measured output current distortion rate with a specified distortion rate, and outputs a DC-DC output voltage correction command value within a range in which the output current distortion rate does not exceed the specified distortion rate. Therefore, the output voltage can be reduced to a range not exceeding the specified distortion rate and output.

  The power conversion device according to the present invention is a power conversion device including a DC-DC conversion device, an inverter device, and a control device that converts a direct current output of a fuel cell into alternating current and is connected to a system power supply. Is characterized by comprising a frequency lowering means for lowering the switching carrier frequency of the inverter device at the time of light load.

  The power conversion device according to the present invention is a power conversion device including a DC-DC conversion device, an inverter device, and a control device that convert the direct current output of the fuel cell into alternating current and is interconnected with the system power supply. Since the frequency reduction means for reducing the switching carrier frequency of the inverter device at the time of light load is provided, the switching carrier frequency of the switching element of the inverter device can be reduced.

  Furthermore, the frequency lowering means according to the present invention comprises frequency storage means for storing a carrier frequency command value corresponding to the output power, and when detecting the output power, reads the corresponding carrier frequency command value from the frequency storage means and The switching carrier frequency of the device is changed.

  The frequency reduction means according to the present invention includes frequency storage means for storing a carrier frequency command value corresponding to the output power, and when detecting the output power, reads the corresponding carrier frequency command value from the frequency storage means to Since the switching carrier frequency is changed, the switching carrier frequency of the switching element of the inverter device can be reduced.

  The frequency storage means according to the present invention stores a carrier frequency command value that changes linearly with respect to the output power.

  Furthermore, the frequency storage means according to the present invention stores a carrier frequency command value that changes stepwise with respect to the output power.

  The frequency storage means according to the present invention stores a carrier frequency command value that varies exponentially with respect to the output power.

  The frequency storage means according to the present invention stores the carrier frequency command value linearly with respect to the output power, stepwise with respect to the output power, or exponentially changing with respect to the output power. It can be set with a degree.

  Furthermore, the control device according to the present invention includes a distortion determination unit that compares the measured output current distortion rate with the specified distortion rate, and outputs the carrier frequency command value within a range where the output current distortion rate does not exceed the specified distortion rate. It is characterized by.

  The control device according to the present invention includes a distortion determination unit that compares the measured output current distortion rate with the specified distortion rate, and outputs the carrier frequency command value in a range in which the output current distortion rate does not exceed the specified distortion rate. The switching element of the device can be driven to a switching carrier frequency that does not exceed the specified distortion rate.

  The power conversion device according to the present invention is a power conversion device including a DC-DC conversion device, an inverter device, and a control device that converts a direct current output of a fuel cell into alternating current and is connected to a system power supply. Is characterized by comprising voltage reduction means for reducing the output voltage of the DC-DC converter and frequency reduction means for reducing the switching carrier frequency of the inverter device at light load.

  The power conversion device according to the present invention is a power conversion device including a DC-DC conversion device, an inverter device, and a control device that convert the direct current output of the fuel cell into alternating current and is interconnected with the system power supply. Since the voltage reduction means for reducing the output voltage of the DC-DC converter at the time of light load and the frequency reduction means for reducing the switching carrier frequency of the inverter device are provided, the output voltage of the DC-DC converter and the inverter device The switching carrier frequency of the switching element can be lowered.

  Furthermore, the control device according to the present invention is characterized by comprising sequence means for setting the operation order of the voltage reduction means and the frequency reduction means.

  Since the control device according to the present invention includes the sequence means for setting the operation order of the voltage reduction means and the frequency reduction means, it reduces either the output voltage of the DC-DC converter or the switching carrier frequency of the inverter device. The other can then be lowered.

  The power conversion device according to the present invention is a power conversion device including a DC-DC conversion device, an inverter device, and a control device that convert the direct current output of the fuel cell into alternating current and is interconnected with the system power supply. Since voltage reduction means for reducing the output voltage of the DC-DC converter at light load is provided, the output voltage can be lowered by reducing the duty ratio of the drive pulse of the DC-DC converter, and switching of the inverter device Loss can be reduced and power conversion efficiency can be improved.

  Further, the voltage reduction means according to the present invention, when detecting the output power and the system voltage, the voltage value storage means for storing the correction coefficient corresponding to the output power and the DC-DC output voltage command value corresponding to the system voltage, Correction for reading the corresponding correction coefficient and the corresponding DC-DC output voltage command value from the voltage value storage means, calculating the product of the correction coefficient and the DC-DC output voltage command value, and outputting the DC-DC output voltage correction command value Since the command value calculating means is provided and the DC-DC output voltage of the DC-DC converter is changed, the output voltage can be reduced based on the DC-DC output voltage correction command value at a light load, and the inverter device Switching loss and power conversion efficiency can be improved.

  Furthermore, the voltage value storage means according to the present invention stores a correction coefficient that changes linearly with respect to the output power, changes stepwise with respect to the output power, or changes exponentially with respect to the output power. The correction command value can be set with a degree of freedom, and an output voltage reduced to a predetermined voltage value can be output.

  The control device according to the present invention further includes a distortion determination unit that compares the measured output current distortion rate with the specified distortion rate, and the DC-DC output voltage correction command value is within a range where the output current distortion rate does not exceed the specified distortion rate. Therefore, the output voltage can be reduced to a range that does not exceed the specified distortion rate, and the switching loss of the inverter device can be greatly reduced to improve the power conversion efficiency.

  Furthermore, the power conversion device according to the present invention is a power conversion device including a DC-DC conversion device, an inverter device, and a control device that convert a direct current output of a fuel cell into an alternating current and that are connected to a system power supply. Has a frequency lowering means that lowers the switching carrier frequency of the inverter device at light load, so the switching carrier frequency of the switching element of the inverter device can be lowered, reducing the switching loss and improving the power conversion efficiency can do.

  The frequency reduction means according to the present invention further comprises frequency storage means for storing a carrier frequency command value corresponding to the output power, and when detecting the output power, reads the corresponding carrier frequency command value from the frequency storage means to Since the switching carrier frequency of the device is changed, the switching carrier frequency of the switching element of the inverter device can be lowered, and the switching loss can be reduced to improve the power conversion efficiency.

  Furthermore, since the frequency storage means according to the present invention stores a carrier frequency command value that is linear with respect to the output power, stepwise with respect to the output power, or exponentially changing with respect to the output power, the carrier frequency command value Can be set with a degree of freedom, and the switching element of the inverter device can be driven with a desired frequency characteristic.

  In addition, the control device according to the present invention includes a distortion determination unit that compares the measured output current distortion rate with the specified distortion rate, and outputs the carrier frequency command value within a range where the output current distortion rate does not exceed the specified distortion rate. Thus, the switching element of the inverter device can be driven to a switching carrier frequency that does not exceed the specified distortion rate, and the switching loss of the inverter device can be greatly reduced to improve the power conversion efficiency.

  Furthermore, the power conversion device according to the present invention is a power conversion device including a DC-DC conversion device, an inverter device, and a control device that convert a direct current output of a fuel cell into an alternating current and that are connected to a system power supply. Is provided with a voltage reducing means for reducing the output voltage of the DC-DC converter and a frequency reducing means for reducing the switching carrier frequency of the inverter device at the time of a light load, so that the output voltage of the DC-DC converter and the inverter The switching carrier frequency of the switching element of the device can be lowered, the switching loss of the inverter device can be reduced to the maximum, and the power conversion efficiency can be further improved.

  Further, since the control device according to the present invention includes the sequence means for setting the operation order of the voltage reduction means and the frequency reduction means, either the output voltage of the DC-DC converter or the switching carrier frequency of the inverter device is obtained. The power conversion efficiency can be reduced by maximizing the switching loss of the entire device by the synergistic effect of lowering the switching loss due to the lower output voltage and lowering the switching loss due to the lowering of the switching carrier frequency. Can be further improved.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a block diagram of an embodiment of a power converter according to the present invention. Note that the present invention reduces the output voltage by reducing the duty ratio of the drive pulse for driving the switching element of the DC-DC conversion device based on the DC-DC output voltage command value when the device is lightly loaded. The switching loss of the switching element of the apparatus is reduced and the power conversion efficiency is improved.

  In FIG. 1, the power conversion device 1 includes a DC-DC conversion device 2, an inverter device 3, a control device 4, an AC filter 5, and a circuit breaker 6, and boosts the direct-current battery voltage VB generated by the fuel cell 9. It converts into DC-DC output voltage VD, converts the converted DC-DC output voltage VD into an alternating current synchronized with the frequency (50 Hz / 60 Hz) of the system power supply (commercial power supply), and converts the AC power supply into an electric appliance in the home ( A distributed power source to be supplied to a load L1, a load L2, or a load L3 of a refrigerator, an air conditioner, a personal computer, a TV, a microwave oven, a microwave oven, etc.) is configured and constructed so as to be connected to a system power source (commercial power source).

  The DC-DC converter 2 generates a high-frequency pulse by switching a DC battery voltage VB supplied from the fuel cell 9 via input terminals A and B with a switching element at a relatively high frequency on the primary side of the transformer. Then, a high frequency pulse boosted from the secondary side of the transformer is output and smoothed by the electrolytic capacitor C2 to obtain a DC DC-DC output voltage VD.

  For the generation of the high frequency pulse, the switching element is driven on / off with the drive pulse based on the output voltage correction command value Vα supplied from the control device 4. The DC-DC output voltage VD is adjusted by changing the on-pulse width or on-time (corresponding to the duty ratio) of the drive pulse.

  The inverter device 3 is constituted by a bridge circuit of switching elements, and the DC-DC output voltage VD smoothed by the electrolytic capacitor C2 is PWM-driven by the PWM signal based on the carrier frequency command value VF supplied from the control device 4. Then, an output current IO synchronized with the frequency (50 Hz or 60 Hz) of the system power supply is output.

  The control device 4 is composed of various arithmetic functions, processing functions, memory, etc. based on a microprocessor, generates a variable output voltage correction command value Vα, and the DC-DC of the DC-DC converter 2 at a light load. A voltage reduction means 7 which is a converter control means for reducing the output voltage VD, and an inverter control means 8 for generating a rated carrier frequency command value VF are provided.

  Further, the control device 4 has a function of detecting the inverter output voltage VC, the output current IO, and the system voltage VAC, and calculates the output power and the output current distortion rate.

  Furthermore, when an abnormality occurs in the power conversion device 1, the control device 4 switches from the power conversion device 1 to the system power source VAC without driving the system power source VAC, and drives the load L1, the load L2, or the load L3. Therefore, a switch control signal CS for turning off the switches s1 to s3 of the circuit breaker 6 is generated.

  Further, the control device 4 calculates the distortion rate (DI) of the output current IO and monitors it so as not to exceed the specified distortion rate (DK). Note that the control device 4 detects and controls parameters such as a direct current, an output direct current divided current, and an internal control voltage in order to realize various protection functions.

  FIG. 2 is a block diagram showing the principal part of an embodiment of the voltage drop means according to the present invention. In FIG. 2, the voltage lowering means 7 includes a voltage value storage means 10 for storing a correction coefficient K corresponding to the output power PO and a DC-DC output voltage command value Vr corresponding to the system voltage VAC, output power PO and system voltage. When VAC is detected, the corresponding correction coefficient K and the corresponding DC-DC output voltage command value Vr are read from the voltage value storage means 11, and the product of the correction coefficient K and the DC-DC output voltage command value Vr is calculated. A correction command value calculating means 11 for outputting a DC output voltage correction command value Vα;

  The correction command value calculating means 10 takes in the output power PO and the system voltage VAC, accesses the voltage value storage means 11, reads out the correction coefficient K and the output voltage correction command value Vr, and corrects the correction coefficient K and the output voltage correction command value Vr. The calculated output voltage correction command value Vα (= K × Vr) is supplied to the DC-DC converter 2 to change the DC-DC output voltage VD.

  The voltage value storage means 11 is composed of a fixed memory such as a ROM, a rewritable memory such as an EEPROM, a correspondence table of the load factor β and the correction coefficient K corresponding to the output power PO, the system voltage VAC and the output voltage command. When the correspondence table of the values Vr is stored and accessed from the correction command value calculation means 10, the corresponding correction coefficient K and output voltage command value Vr are provided to the correction command value calculation means 10 from the correspondence table.

  FIG. 3 is a characteristic diagram of an embodiment of the correspondence table according to the present invention. (A) is a characteristic diagram of load factor β-correction coefficient K, and (b) is a characteristic diagram of system voltage VAC-output voltage command value Vr. (A) In the figure, when the load factor β at which the output power PO reaches the rating is 100%, the correction factor K is 1.0, but the load factor β when the output power PO is light load is 30%. Then, the correction coefficient K is as small as 0.95.

  (B) In the figure, the output voltage command value Vr is also reduced as the system voltage VAC decreases. The system voltage VAC is generally in the vicinity of 100 VAC (volts), but varies somewhat depending on the region. Occurs and the voltage value changes.

  In other words, the voltage lowering means 7 sets the correction coefficient K to be lower as the load factor β is lowered at a light load, lowers the output voltage correction command value Vα, and sets the DC-DC output voltage VD of the DC-DC converter 2. Reduce.

  As described above, the voltage reduction means 7 according to the present invention includes the voltage value storage means 11 for storing the correction coefficient K corresponding to the output power PO and the DC-DC output voltage command value Vr corresponding to the system voltage VAC, and the output power. When PO and the system voltage VAC are detected, the corresponding correction coefficient K and the corresponding DC-DC output voltage command value Vr are read from the voltage value storage means 11, and the product of the correction coefficient K and the DC-DC output voltage command value Vr is calculated. Correction command value calculation means 10 for calculating and outputting a DC-DC output voltage correction command value Vα (= K × Vr), and changing the DC-DC output voltage VD of the DC-DC converter 2. At the time of load, the output voltage can be lowered based on the DC-DC output voltage correction command value, the switching loss of the inverter device can be reduced, and the power conversion efficiency can be improved.

  FIG. 4 is a correction coefficient storage state diagram of one embodiment of the voltage value storage means according to the present invention. (A) The figure shows a linear characteristic of the correction coefficient K with respect to the output power PO at light load, (b) The figure shows the step characteristic of the correction coefficient K with respect to the output power PO at light load, and (c) the figure is light. At the time of load, the correction coefficient K represents an exponential characteristic with respect to the output power PO.

  The correction coefficient K is 1.0 with respect to the rating of the output power PO, and the correction coefficient K with respect to the output power PO at the time of light load is E1 characteristic linear, E2 characteristic steps k1 to k5, and E3 characteristic. Since it can be set to exponentially decreasing characteristics, the correction coefficient K can be set freely, and the DC-DC output voltage VD of the DC-DC converter 2 is optimally set according to the light load state. can do.

  Thus, the voltage value storage means 11 according to the present invention is linear with respect to the output power PO at light load, stepwise with respect to the output power PO at light load, or output power PO at light load. Since the correction coefficient K that changes exponentially is stored, the DC-DC output voltage correction command value Vα can be set with a degree of freedom, and the output voltage reduced to a predetermined voltage value can be output. .

  In this embodiment, the correction value data table is prepared in advance in the voltage value storage unit and the correction coefficient is read out. However, the linear value, step function, or exponential function formula is stored in the voltage value storage unit in advance. May be stored, an arithmetic expression may be read, a parameter may be given, and a correction coefficient may be obtained by calculation.

  FIG. 5 is a block diagram showing an embodiment of the DC-DC output voltage control of the DC-DC converter according to the present invention. In FIG. 5, the DC-DC converter 2 includes a transformer T, a MOSFET-Q, a resistor R, a diode D, a choke coil L, and a drive pulse generator 12. The drive pulse generator 12 generates a relatively high frequency drive pulse SD with the duty ratio adjusted by the output voltage correction command value Vα supplied from the voltage lowering means 7, and supplies the drive pulse SD to the gate of the MOSFET-Q. .

  The MOSFET-Q turns on / off the battery voltage VB on the primary side of the transformer T with the drive pulse SD supplied from the drive pulse generator 12 to generate a relatively high frequency pulse. The voltage is boosted through the transformer T, and the boosted relatively high frequency pulse is output to the secondary side. The boosted relatively high-frequency pulse is rectified by a rectifier circuit constituted by a diode D and a choke coil L, and then smoothed by an electrolytic capacitor C2 to become a DC-DC output voltage VD.

  FIG. 6 is an explanatory diagram of duty change according to an embodiment of the drive pulse according to the present invention. (A) The figure shows the drive pulse waveform at the time of rating, and (b) the figure shows the drive pulse waveform at the light load. (A) In the figure, the duty ratio of the drive pulse SD at the time of rating is represented by pulse on width TON1 ÷ one cycle Ta.

  (B) In the figure, since the duty ratio of the drive pulse SD at light load is expressed by pulse on width TON2 ÷ one cycle Ta, the duty ratio at light load is smaller than the duty ratio at the time of rating. The boosted relatively high frequency pulse generated by turning on / off Q also has the same short pulse-on width waveform as drive pulse SD, and the DC-DC output voltage VD smoothed by electrolytic capacitor C2 is lowered.

  In the present embodiment, the drive pulse generator 12 is provided in the DC-DC converter 2, but may be provided in the controller 4.

  FIG. 7 is a block diagram of an embodiment of the distortion determination means according to the present invention. In FIG. 7, the distortion determination means 13 is provided inside the control device 4. The distortion determination means 13 has a comparison / determination function, detects an output current IO in the control device 4, and outputs an output calculated from a fundamental component and a harmonic component (for example, up to an nth-order harmonic component) of the output current IO. When the current distortion rate DI is supplied, the output current distortion rate DI is compared with a preset specified distortion rate DK. If the output current distortion rate DI exceeds the specified distortion rate DK (DI> DK), a determination signal is sent. HO is provided to the voltage drop means 7.

  When the determination signal HO is provided from the distortion determination means 13, the voltage reduction means 7 outputs a correction coefficient k4 that is one rank higher in the case of the correction coefficient k5 shown in FIG. The DC-DC output voltage VD is increased so as to improve the distortion rate DI and satisfy the specified distortion rate DK. The DC-DC converter 2 tends to increase the output current distortion rate DI when the DC-DC output voltage VD is lowered.

  As described above, the control device 4 according to the present invention includes the distortion determination means 13 that compares the measured output current distortion rate DI with the specified distortion rate DK, and the output current distortion rate DI does not exceed the specified distortion rate DK (DK). > DI) Since the DC-DC output voltage correction command value Vα is output in the range, the output voltage VD can be reduced to a range not exceeding the specified distortion rate DK and the switching loss of the inverter device 3 can be greatly increased. The power conversion efficiency can be improved by lowering.

  As described above, the control device 4 according to the present invention includes the voltage reduction means 7 for reducing the output voltage VD of the DC-DC converter 2 at the time of light load. The output voltage VD can be lowered by lowering the duty ratio of SD, the switching loss of the inverter device 2 can be reduced, and the power conversion efficiency can be improved.

  The AC filter 5 filters the pulsed inverter output current IO from the inverter device 3 to remove harmonic components, and converts a sinusoidal alternating current that matches the frequency (50 Hz or 60 Hz) of the system power source into a single-phase two-wire. An expression (AC voltage 100V) or a single-phase three-wire system (AC voltage 200V) is connected between output terminals D and E, between output terminals D and E, between output terminals C and D, or output terminals C, E is supplied to a load L1, a load L2 or a load L3 respectively connected between E.

  The circuit breaker 6 is composed of switches s1 to s3. When an abnormality occurs on the apparatus main body and the system power supply side, the circuit breaker 6 interrupts the switches s1 to s3 by the switch control signal CS from the control apparatus 4, and the apparatus main body is connected to the system power supply VAC. Disconnect from.

  FIG. 8 is a block diagram of another embodiment of the power converter according to the present invention. The present invention reduces the switching loss of the switching element of the inverter device by lowering the switching carrier frequency of the PWM signal that drives the switching element of the inverter device based on the carrier frequency command value VF when the device is lightly loaded. , To improve power conversion efficiency.

  In FIG. 8, the power conversion device 14 includes a DC-DC conversion device 2, an inverter device 3, a control device 15, an AC filter 5, and a circuit breaker 6. Note that the power conversion device 14 has only the configuration in which the control device 15 includes the converter control means 16 and the frequency reduction means 17, and the power conversion in which the control device 4 shown in FIG. 1 includes the voltage reduction means 7 and the inverter control means 8. Different from device 1.

  The control device 15 is composed of various arithmetic functions, processing functions, memory, etc. based on a microprocessor, and generates converter control means 16 that generates a rated output voltage command value Vr, variable carrier frequency command value VF, A frequency reduction means 17 that is an inverter control means for reducing the switching carrier frequency of the PWM signal SPWM of the inverter device 3 at the time of light load is provided.

  The control device 15 has a function of detecting the inverter output voltage VC, the output current IO, and the system voltage VAC, and calculates the output power and the output current distortion rate.

  Further, when an abnormality occurs in the power conversion device 14, the control device 15 switches from the power conversion device 14 to the system power supply VAC without driving the system power supply VAC, and drives the load L1, the load L2, or the load L3. Therefore, the switch control signal CS for turning off the switches s1 to s3 of the circuit breaker 6 is generated.

  Further, the control device 15 calculates the distortion rate (DI) of the output current IO and monitors it so as not to exceed the specified distortion rate (DK). Note that the control device 15 also detects and controls parameters such as a direct current, an output-side direct current divided current, and an internal control voltage in order to realize various protection functions.

  FIG. 9 is a block diagram showing the principal part of one embodiment of the frequency reducing means according to the present invention. In FIG. 9, the frequency lowering unit 17 includes an output unit 18 and a frequency storage unit 19.

  The output means 18 has a memory access function, takes in the output power PO, accesses the voltage frequency storage means 19, reads the carrier frequency command value F, and outputs the carrier frequency command value VF (= carrier frequency command value F) as an inverter device. 3, the switching carrier frequency of the PWM signal SPWM for driving the switching element of the inverter device 3 is changed.

  The frequency storage means 19 is composed of a fixed memory such as a ROM and a rewritable memory such as an EEPROM, stores a correspondence table of carrier frequency command values F corresponding to the output power PO in advance, and is accessed from the output means 18. The corresponding carrier frequency command value F is provided to the output means 18 from the correspondence table.

  FIG. 10 is a characteristic diagram of an embodiment of the correspondence table according to the present invention. In FIG. 10, the carrier frequency command value VF is set to the rating (corresponding to the rated frequency) when the output power PO is near the rating (rated load), and the switching carrier frequency is lowered when the output power PO is in the light load region. The carrier frequency command value F is set to decrease.

  In other words, the frequency lowering means 17 sets the carrier frequency command value F to be low as the output power PO decreases at the time of light load, and provides the low carrier frequency command value VF to the inverter device 3 to set the switching carrier frequency of the PWM signal SPWM. It controls to drive a switching element (inverter bridge) by reducing.

  Thus, the frequency reduction means 17 according to the present invention includes the frequency storage means 19 for storing the carrier frequency command value F corresponding to the output power PO, and the carrier frequency command corresponding to the output power PO from the frequency storage means 19. Since the value F is read and the switching carrier frequency of the inverter device 3 is changed, the switching carrier frequency of the switching element of the inverter device can be lowered, and the switching loss can be reduced to improve the power conversion efficiency.

  FIG. 11 is a carrier frequency command value storage state diagram of one embodiment of the frequency storage means according to the present invention. (A) The figure shows the linear characteristic of the carrier frequency command value F with respect to the output power PO at light load, and (b) shows the step characteristic of the carrier frequency command value F with respect to the output power PO at light load. In the figure, the carrier frequency command value F represents an exponential characteristic with respect to the output power PO at a light load.

  The carrier frequency command value F for the rated capacity of the output power PO is the rated frequency. Since the carrier frequency command value F can be set to the G1 characteristic linear, the G2 characteristic steps F1 to F5, and the G3 characteristic exponentially decreasing characteristics with respect to the output power PO at light load, the carrier frequency command value F can be set freely, and the switching carrier frequency of the PWM signal SPWM of the inverter device 3 can also be optimally set according to the light load state.

  Thus, the frequency storage means 19 according to the present invention stores the carrier frequency command value F that varies linearly with respect to the output power PO, stepwise with respect to the output power PO, or exponentially with respect to the output power PO. Therefore, the carrier frequency command value F can be set with a degree of freedom, and the switching element of the inverter device 3 can be driven with a desired frequency characteristic.

  In the present embodiment, a data table of carrier frequency command values is prepared in advance in the frequency storage means and the carrier frequency command values are read out. However, linear functions, step functions or exponential functions are previously stored in the frequency storage means. The calculation formula may be stored, the calculation formula may be read, a parameter is given, and the carrier frequency command value may be obtained by calculation.

  FIG. 12 is a block diagram showing an embodiment of the carrier frequency control of the inverter device according to the present invention. In FIG. 12, the inverter device 3 includes switching elements such as MOSFETs Q1 to Q4 and IGBTs (Insulated Gate Bipolar Transistors) -Q1 to Q4 that constitute an inverter bridge, and a PWM signal generator 20. The PWM signal generator 20 generates a PWM signal SPWM based on the carrier frequency command value VF and the PWM command value supplied from the frequency reduction means 17, and MOSFETs Q1-Q4 and IGBT-Q1-Q4 are generated by the PWM signal SPWM. Is controlled to reduce the switching loss of the switching element by lowering the switching carrier frequency at light load.

  FIG. 13 is a waveform diagram of an embodiment of a PWM signal according to the present invention. In FIG. 13, the PWM signal generator 20 uses a PWM signal SPWM of PWM (Pulse Width Modulation) in which a carrier frequency command value VF corresponding to a sine wave indicated by a broken line is lowered at a light load. Since Q4 is driven, the switching loss of switching elements Q1-Q4 can be reduced.

  Although the PWM signal generator 20 is provided in the inverter device 3 in the present embodiment, it may be provided in the control device 15.

  FIG. 14 is a block diagram showing an embodiment of the distortion determination means according to the present invention. In FIG. 14, the distortion determination means 21 is provided inside the control device 15. The distortion determination means 21 has a comparison / determination function, detects an output current IO in the control device 15, and outputs an output calculated from a fundamental component and a harmonic component (for example, up to an nth-order harmonic component) of the output current IO. When the current distortion rate DI is supplied, the output current distortion rate DI is compared with a preset specified distortion rate DK. If the output current distortion rate DI exceeds the specified distortion rate DK (DI> DK), a determination signal is sent. HO is provided to the frequency reduction means 17.

  When the determination signal HO is provided from the distortion determination means 21, the frequency reduction means 17 outputs a correction coefficient F4 that is one rank higher in the case of the correction coefficient F5 shown in FIG. The switching carrier frequency of the PWM signal SPWM of the PWM signal generator 20 shown in FIG. 12 is increased so as to improve the distortion rate DI and satisfy the specified distortion rate DK. The inverter device 3 tends to increase the output current distortion ratio DI when the switching carrier frequency is lowered.

  As described above, the control device 15 according to the present invention includes the distortion determination means 21 that compares the measured output current distortion rate DI with the specified distortion rate DK, and the output current distortion rate DI does not exceed the specified distortion rate DK (DI). Since the carrier frequency command value VF is output in the <DK) range, the switching elements Q1 to Q4 of the inverter device 3 can be driven down to the switching carrier frequency in a range not exceeding the specified distortion rate DK. The power conversion efficiency can be improved by greatly reducing the switching loss.

  As described above, the control device 15 according to the present invention includes the frequency lowering means 17 for lowering the switching carrier frequency of the inverter device 3 at the time of light load, so the switching carriers of the switching elements Q1 to Q4 of the inverter device 3 are provided. The frequency can be lowered, the switching loss can be reduced, and the power conversion efficiency can be improved.

  FIG. 15 is a block diagram of another embodiment of the power converter according to the present invention. Note that the present invention reduces the output voltage by reducing the duty ratio of the drive pulse for driving the switching element of the DC-DC conversion device based on the DC-DC output voltage command value when the device is lightly loaded. The switching loss of the switching element of the device is reduced, the power conversion efficiency is improved, and the switching carrier frequency of the PWM signal for driving the switching element of the inverter device is reduced based on the carrier frequency command value VF, thereby The switching loss of the switching element is reduced and the power conversion efficiency is improved.

  In FIG. 15, the power conversion device 22 includes a DC-DC conversion device 2, an inverter device 3, a control device 23, an AC filter 5, and a circuit breaker 6. The power conversion device 22 is different from the power conversion device 1 shown in FIG. 1 and the power conversion device 14 shown in FIG. 8 only in the configuration in which the control device 23 includes the voltage reduction means 7 and the frequency reduction means 17.

  The control device 23 includes the voltage lowering unit 7 shown in FIG. 2 and the frequency lowering unit 17 shown in FIG. 9, generates a variable output voltage correction command value Vα at a light load, and the DC of the DC-DC converter 2 -The DC output voltage VD is lowered, and a variable carrier frequency command value VF is generated, and the switching carrier frequency of the PWM signal SPWM of the inverter device 3 is lowered.

  Further, the control device 23 has a function of detecting the inverter output voltage VC, the output current IO, and the system voltage VAC, and calculates the output power and the output current distortion rate.

  Further, when an abnormality occurs on the power conversion device 22 and the system power supply side, the control device 23 switches from the power conversion device 22 to the system power supply VAC without affecting the system power supply VAC, and loads L1, L2 or load. In order to drive L3, a switch control signal CS is generated to turn off the switches s1 to s3 of the circuit breaker 6.

  Further, the control device 23 calculates the distortion rate (DI) of the output current IO and monitors it so as not to exceed the specified distortion rate (DK).

  Furthermore, the control device 23 includes a sequence unit that defines the operation order of the voltage reduction unit 7 and the frequency reduction unit 17.

  Since the control device 23 includes the voltage reduction means 7, the DC-DC output voltage VD of the DC-DC conversion device 2 can be increased or decreased, so that the output voltage is reduced based on the output voltage correction command value Vα at light load. It is possible to reduce the switching loss of the inverter device 3 and improve the power conversion efficiency.

  Moreover, the control apparatus 23 can reduce the switching carrier frequency of the switching elements Q1-Q4 of the inverter apparatus 3 by providing the frequency reduction means 17, and can reduce switching loss and improve power conversion efficiency. Can do.

  FIG. 16 is a block diagram showing the principal part of one embodiment of the sequence means according to the present invention. In FIG. 16, a sequence means 24 is provided in the control device 23, and the order signal CK 1 is supplied to the voltage reduction means 7, and the order signal CK 2 is supplied to the frequency reduction means 17, and the voltage reduction means 7 and the frequency reduction means 17 Control the order of movement.

  When the sequence means 24 detects the output power PO, it outputs the sequence signal CK1 to operate the voltage reduction means 7 first, and then outputs the sequence signal CK2 to operate the frequency reduction means 17. Alternatively, the voltage lowering unit 7 may be operated after the frequency lowering unit 17 is operated.

  Thus, since the control device 23 according to the present invention includes the sequence means 24 for setting the operation order of the voltage reduction means 7 and the frequency reduction means 17, the output voltage VD of the DC-DC conversion device 3 and the inverter device 3 are set. One of the switching carrier frequencies can be lowered and then the other can be lowered, and the switching of the entire apparatus can be performed by the synergistic effect of the switching loss reduction due to the reduction of the output voltage VD and the switching loss reduction due to the reduction of the switching carrier frequency. The power conversion efficiency can be further improved by maximally reducing the loss.

  FIG. 17 is a block diagram showing an embodiment of the distortion determination means according to the present invention. In FIG. 17, the distortion determination means 25 is provided in the control device 23, detects the output current IO in the control device 15, and generates a fundamental wave component and a harmonic component (for example, up to the nth harmonic component) of the output current IO. When the output current distortion rate DI calculated from the above is supplied, the output current distortion rate DI is compared with a preset specified distortion rate DK, and when the output current distortion rate DI exceeds the specified distortion rate DK (DI> DK). Supplies the determination signal HO to the voltage reduction means 7 and the frequency reduction means 17.

  When the determination signal HO is provided from the distortion determination means 25, the voltage reduction means 7 outputs a correction coefficient k4 that is one rank higher in the case of the correction coefficient k5 shown in FIG. The DC-DC output voltage VD is increased so as to improve the distortion rate DI and satisfy the specified distortion rate DK. The DC-DC converter 2 tends to increase the output current distortion rate DI when the DC-DC output voltage VD is lowered.

  On the other hand, when the determination signal HO is provided from the distortion determination means 25, the frequency reduction means 17 outputs a correction coefficient F4 that is one rank larger in the case of the correction coefficient F5 shown in FIG. The switching carrier frequency of the PWM signal SPWM of the PWM signal generator 20 shown in FIG. 12 is increased so as to improve the output current distortion rate DI and satisfy the specified distortion rate DK. The inverter device 3 tends to increase the output current distortion ratio DI when the switching carrier frequency is lowered.

  When the sequence means 24 shown in FIG. 16 operates the voltage reduction means 7, the distortion determination means 25 supplies the determination signal HO to the voltage reduction means 7, and the sequence means 24 causes the frequency reduction means 17 to When operating, the determination signal HO is supplied to the voltage lowering means 7. Thereby, the distortion determination means 25 controls the output current distortion ratio DI so as not to exceed the specified distortion ratio DK even when the voltage reduction means 7 and the frequency reduction means 17 operate, and the switching elements Q1 to Q1 of the inverter device 3 are controlled. The switching loss of Q4 can be reduced and the power conversion efficiency can be improved to the maximum.

  As described above, the control device 23 according to the present invention has the voltage reduction means 7 for reducing the output voltage VD of the DC-DC converter 2 and the frequency reduction for reducing the switching carrier frequency of the inverter device 3 at light load. Since the means 17 is provided, the output voltage VD of the DC-DC converter 2 and the switching carrier frequency of the switching elements Q1 to Q4 of the inverter device 3 can be reduced, and the switching loss of the inverter device can be reduced to the maximum. The power conversion efficiency can be further improved.

  The power conversion device according to the present invention can reduce the DC-DC output voltage or reduce the switching carrier frequency to reduce the switching loss and improve the power conversion efficiency at the time of light load. Not only can it be applied to any power conversion device such as solar power generation.

Block diagram of an embodiment of a power converter according to the present invention Block diagram of main part of one embodiment of voltage drop means according to the present invention The characteristic diagram of one embodiment of the correspondence table according to the present invention One embodiment of voltage value storage means according to the present invention Correction coefficient storage state diagram Configuration diagram of one embodiment of DC-DC output voltage control of a DC-DC converter according to the present invention Duty change explanatory drawing of one Embodiment of the drive pulse which concerns on this invention Block diagram of one embodiment of distortion determination means according to the present invention Block diagram of another embodiment of the power converter according to the present invention Block diagram of essential parts of an embodiment of frequency reducing means according to the present invention The characteristic diagram of one embodiment of the correspondence table according to the present invention One embodiment of frequency storage means according to the present invention Carrier frequency command value storage state diagram Configuration diagram of one embodiment of carrier frequency control of an inverter device according to the present invention Waveform diagram of one embodiment of a PWM signal according to the present invention Block diagram of one embodiment of distortion determination means according to the present invention Block diagram of another embodiment of the power converter according to the present invention Block diagram of essential parts of one embodiment of sequence means according to the present invention Block diagram of one embodiment of distortion determination means according to the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,14,22 Power converter 2 DC-DC converter 3 Inverter apparatus 4,15,23 Control apparatus 5 AC filter 6 Circuit breaker 7 Voltage reduction means 8 Inverter control means 9 Fuel cell 10 Correction command value calculation means 11 Voltage value Storage means 12 Drive pulse generator 13, 21, 25 Distortion determination means 16 Converter control means 17 Frequency reduction means 18 Output means 19 Frequency storage means 20 PWM signal generator 24 Sequence means C1, C2 Electrolytic capacitors s1, s2, s3 switch T Transformer Q MOSFET
VB Battery voltage VD DC-DC output voltage VC Inverter output voltage VAC System power supply (voltage)
K Correction coefficient Vα Output voltage correction command value Vr Output voltage command value F, VF Carrier frequency command value SD Drive pulse PO Output power IO Output current DI Output current distortion rate DK Specified distortion rate SPWM PWM signal CK1, CK2 Sequence signal

Claims (14)

In a power converter provided with a DC-DC converter, an inverter device, and a control device that converts the direct current output of the fuel cell into an alternating current and operates in an interconnected manner with the system power supply.
The said control apparatus is provided with the voltage reduction means to reduce the output voltage of the said DC-DC converter at the time of light load, The power converter device characterized by the above-mentioned. The voltage lowering means stores voltage value storage means for storing a correction coefficient corresponding to output power and a DC-DC output voltage command value corresponding to system voltage, and when detecting output power and system voltage, the voltage value storage means Correction command value calculating means for reading out the corresponding correction coefficient and the corresponding DC-DC output voltage command value, calculating the product of the correction coefficient and the DC-DC output voltage command value, and outputting the DC-DC output voltage correction command value The power converter according to claim 1, further comprising: changing a DC-DC output voltage of the DC-DC converter. 3. The power conversion apparatus according to claim 2, wherein the voltage value storage means stores a correction coefficient that changes linearly with respect to output power at light load. 3. The power conversion apparatus according to claim 2, wherein the voltage value storage means stores a correction coefficient that changes stepwise with respect to output power at light load. 3. The power conversion apparatus according to claim 2, wherein the voltage value storage means stores a correction coefficient that changes exponentially with respect to output power at light load. The control means includes distortion determination means for comparing the measured output current distortion rate with a specified distortion rate, and outputs a DC-DC output voltage correction command value within a range where the output current distortion rate does not exceed the specified distortion rate. The power converter according to claim 1, wherein In a power converter provided with a DC-DC converter, an inverter device, and a control device that converts the direct current output of the fuel cell into an alternating current and operates in an interconnected manner with the system power supply.
The said control apparatus is provided with the frequency reduction means to reduce the switching carrier frequency of the said inverter apparatus at the time of light load, The power converter device characterized by the above-mentioned. The frequency reduction means includes frequency storage means for storing a carrier frequency command value corresponding to output power, and when the output power is detected, reads the corresponding carrier frequency command value from the frequency storage means to switch the inverter device. The power conversion apparatus according to claim 7, wherein the carrier frequency is changed. 9. The power converter according to claim 8, wherein the frequency storage means stores a carrier frequency command value that changes linearly with respect to output power at light load. 9. The power converter according to claim 8, wherein the frequency storage means stores a carrier frequency command value that changes stepwise with respect to output power at light load. 9. The power converter according to claim 8, wherein the frequency storage means stores a carrier frequency command value that changes exponentially with respect to output power at light load. The control means includes distortion determination means for comparing the measured output current distortion rate with a specified distortion rate, and outputs a carrier frequency command value in a range where the output current distortion rate does not exceed the specified distortion rate. Item 8. The power conversion device according to Item 7. In a power converter provided with a DC-DC converter, an inverter device, and a control device that converts the direct current output of the fuel cell into an alternating current and operates in an interconnected manner with the system power supply.
The control device includes: a voltage reduction unit that reduces an output voltage of the DC-DC converter at a light load; and a frequency reduction unit that reduces a switching carrier frequency of the inverter device. Conversion device. 14. The power conversion apparatus according to claim 13, wherein the control device includes a sequence unit that sets an operation order of the voltage reduction unit and the frequency reduction unit.

Images