JP2016127764A - Electric power converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power converter capable of increasing the electric power conversion efficiency in a wider range of electric power load than before.SOLUTION: A comparator (150) compares an effective value of an AC current (Iout1) and a setting value which is set by a setting section (140). When the comparison result by the comparator (150), the effective value of the AC current (Iout1) is equal to or smaller than the setting value, the switching command generation section (160) stops an inverter (2) from driving and outputs a stop instruction which represents that an inverter (1) only is driven to modulation wave generation sections (131 and 132), and outputs a gate block signal to a pulse generation section 112.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a power conversion device including a plurality of inverters.

  2. Description of the Related Art In recent years, a multi-phase power conversion device is known in which a plurality of inverters are connected in parallel to reduce the current flowing through each inverter in order to cope with an increase in output of the power conversion device. For example, in Non-Patent Document 1, two three-phase inverters are connected in parallel, SVPWM control is performed using a signal whose phase is not shifted in one inverter, and the phase is shifted 180 degrees in the other inverter. A grid-connected inverter that performs SVPWM control using the received signal is disclosed.

Dongsul Shin out of three people "Coupled Inductors for Parallel Operation of Interleaved Three-Phase Voltage Source Grid-Connected Inverters", Applied Power Electronics Conference and Exposition (APEC), 2013 Twenty-Eighth Annual IEEE Date of Conference: 17-21 March 2013, p. 2235-p. 2239

  However, in Non-Patent Document 1, the power conversion efficiency when two three-phase inverters are driven and the power conversion efficiency when only one three-phase inverter is driven may vary depending on the power load. It is not considered at all. Therefore, power conversion efficiency cannot be improved in a wide range of power load regions.

  The present disclosure provides a power conversion device that can improve power conversion efficiency in a wider range of power load than in the past.

A power conversion device according to an aspect of the present disclosure includes N (N is an integer of 2 or more) inverters that are connected in parallel to a power supply unit and convert DC power supplied from the power supply unit into AC power using a switching element. When,
A reactor for smoothing each of the N AC powers output from the N inverters;
An output unit that superimposes N AC powers smoothed by the reactor and outputs them to a load;
A carrier generation unit for generating N carrier signals corresponding to the N inverters and having a phase shifted by 360 degrees / N;
A modulation wave generation unit for generating N modulation wave signals for outputting a predetermined alternating current corresponding to the N inverters;
The N carrier signals and N modulated wave signals corresponding to the N carrier signals are compared to generate N PWM signals corresponding to the N inverters, and the N carrier signals are generated. A pulse generator for outputting to the inverter;
A current detector that detects current output from at least one of the N currents smoothed by the reactor or the output unit;
When the current detected by the current detection unit is less than or equal to a predetermined set value, the first to jth (j is an integer not less than 1 and not more than N−1) inverters among the N inverters are driven, and the (j + 1) th A switching control unit that outputs a stop instruction to stop driving the Nth inverter,
The carrier generation unit generates j carrier signals corresponding to the first to j-th inverters whose phases are shifted by 360 degrees / j when the stop instruction is output,
When the stop instruction is output, the pulse generator generates j carrier signals corresponding to the first to j-th inverters and j modulated wave signals corresponding to the first to j-th inverters. In comparison, j PWM signals corresponding to the first to j-th inverters are generated and output to the first to j-th inverters.

  According to the present disclosure, higher power conversion efficiency can be obtained in a wider range of power load than in the past.

It is a circuit diagram of the grid connection inverter apparatus to which the power converter device in Embodiment 1 was applied. It is a circuit diagram of the grid connection inverter apparatus to which the power converter device in a comparative example was applied. Section (a) is a graph showing the waveforms of AC currents Iout1 and Iout2 flowing through reactors 7 and 8 and the waveform of AC voltage Vout output to system power supply 10 in the power conversion device of FIG. Section (b) is a graph showing the waveform of AC current Iout flowing through reactor 7 and the waveform of AC voltage Vout output to system power supply 10 in the power conversion device of FIG. It is a graph which shows the experimental result which compared the power conversion efficiency of the power converter device of Embodiment 1, and the comparative example (power converter device of FIG. 2). It is a circuit diagram of the grid connection inverter apparatus to which the power converter device in Embodiment 2 was applied. It is a graph which shows the experimental result which compared the power conversion efficiency of the power converter device of Embodiment 2, and a comparative example. Section (a) is a graph showing the conduction loss and switching loss of the switches constituting the inverter. Section (b) is a graph showing reactor loss. It is a figure which shows the waveform at the time of the switching of the power converter device of Embodiment 3. FIG. It is a figure which shows the waveform at the time of the switching of the comparative example with respect to Embodiment 4. FIG. FIG. 10 is a diagram showing a waveform at the time of switching in the fourth embodiment. It is a circuit diagram of the grid connection inverter apparatus to which the power converter device in Embodiment 5 was applied. It is a circuit diagram of the grid connection inverter apparatus to which the power converter device in Embodiment 6 was applied. It is a figure which shows an example of the setting table which a setting part manages. It is a circuit diagram of the grid connection inverter apparatus to which the power converter device in Embodiment 8 was applied. It is a circuit diagram of the grid connection inverter apparatus with which the power converter device of Embodiment 9 was applied. It is a figure which shows the example of a switching of an inverter in the case of using the instantaneous value of alternating current.

(Background to one aspect of the present disclosure)
In recent years, with the widespread use of solar cells, development of power conditioners that link solar cells installed in homes or small-scale power plants with system power supplies has been actively conducted. The power conditioner converts the DC power generated by the solar cell into AC power and supplies it to the system power supply. For example, the AC power supplied to the system power supply has a ripple rate (harmonic content) within a certain value. A predetermined condition is imposed such that the effective value of the AC voltage is set to a certain value. Therefore, the power conditioner needs to perform power conversion so as to satisfy a predetermined condition.

  In view of this, the present inventor has focused on a multi-phase inverter (hereinafter referred to as a multi-phase inverter) in which a plurality of inverters are connected in parallel to a DC power source composed of a solar cell. And in a multiphase inverter, it discovered that a ripple could be reduced by shifting the phase of the carrier signal corresponding to each inverter at a predetermined interval.

  However, in the multiphase inverter, it has been found that high power conversion efficiency can be obtained in a region where the power load is high, but power conversion efficiency is lowered in a region where the power load is low compared to a normal inverter.

  In Non-Patent Document 1 described above, there is a disclosure of a multi-phase inverter, but it is not considered at all that the power conversion efficiency of the multi-phase inverter decreases in a region where the power load is low.

  An object of one embodiment of the present disclosure is to provide a power conversion device that can obtain high power conversion efficiency in a wider range of power load than in the past.

  Hereinafter, the power converter of one mode of the present disclosure will be specifically described.

(1) A power conversion device according to an aspect of the present disclosure is connected in parallel to a power supply unit, and converts DC power supplied from the power supply unit into AC power using a switching element (N is an integer of 2 or more) Inverters,
A reactor for smoothing each of the N AC powers output from the N inverters;
An output unit that superimposes N AC powers smoothed by the reactor and outputs them to a load;
A carrier generation unit for generating N carrier signals corresponding to the N inverters and having a phase shifted by 360 degrees / N;
A modulation wave generation unit for generating N modulation wave signals for outputting a predetermined alternating current corresponding to the N inverters;
The N carrier signals and N modulated wave signals corresponding to the N carrier signals are compared to generate N PWM signals corresponding to the N inverters, and the N carrier signals are generated. A pulse generator for outputting to the inverter;
A current detector that detects current output from at least one of the N currents smoothed by the reactor or the output unit;
When the current detected by the current detection unit is less than or equal to a predetermined set value, the first to jth (j is an integer not less than 1 and not more than N−1) inverters among the N inverters are driven, and the (j + 1) th A switching control unit that outputs a stop instruction to stop driving the Nth inverter,
The carrier generation unit generates j carrier signals corresponding to the first to j-th inverters whose phases are shifted by 360 degrees / j when the stop instruction is output,
When the stop instruction is output, the pulse generator generates j carrier signals corresponding to the first to j-th inverters and j modulated wave signals corresponding to the first to j-th inverters. In comparison, j PWM signals corresponding to the first to j-th inverters are generated and output to the first to j-th inverters.

  According to this configuration, the carrier signals corresponding to the N inverters are each shifted in phase by 360 degrees / N. Therefore, the ripple generated when the AC currents output from the N inverters are smoothed by the reactor is more likely to appear inverted between the AC currents. As a result, an alternating current in which ripples are canceled can be generated by superimposing the alternating currents output from the N inverters.

  Further, in a power conversion device including a plurality of inverters, when the power conversion efficiency when driving N inverters and the power conversion efficiency when driving j inverters are compared, in a region where the output power is low The latter has higher power conversion efficiency than the former, but as the output power is increased, this relationship is reversed, and the former has higher power conversion efficiency than the latter.

  In this aspect, N inverters are driven if the current detected by the current detector is larger than a predetermined set value, and only j inverters are driven if the current is equal to or less than the predetermined set value. . Therefore, by setting in advance a current value corresponding to output power whose power conversion efficiency is reversed as a set value, it is possible to improve power conversion efficiency in a wider range of output power than in the past.

(2) In the above aspect, when the N inverters are driven, each of the N currents smoothed by the reactor is L, and the current output from the output unit is N · L. Then
When the stop instruction is output, the modulation wave generator generates the j + 1 to 1st currents so that the Nj currents output from the j + 1st to 1st to Nth inverters gradually decrease from L to 0. First to first so that the modulation current signal corresponding to the N inverter is corrected and the j currents output from the first to jth inverters gradually increase from L to N · L / j. The modulated wave signal corresponding to the j inverter may be corrected.

  In this case, when the drive is switched from N inverters to j inverters, the modulation wave signal is corrected so that the output of the inverter whose drive is stopped gradually decreases from L to 0. In the inverter that continues to be driven, the modulation wave signal is corrected so that the output current gradually increases from L to N · L / j. Therefore, distortion occurring in the alternating current output to the load can be suppressed when switching the inverter.

(3) In the above aspect, when the N inverters are driven, each of the N currents smoothed by the reactor is L, and the current output from the output unit is N · L. Then
When the stop instruction is output, the modulated wave generating unit outputs N−j outputs from the j + 1 to Nth inverters within a certain period including a zero cross point of the AC voltage output from the output unit. The modulation wave signal corresponding to the (j + 1) th to (N) th inverters is corrected so that the current of the current decreases gradually from L to 0 or instantaneously, and j output from the first to jth inverters are corrected. The modulation wave signal corresponding to the first to jth inverters may be corrected so that the current increases gradually or instantaneously from L to N · L / j.

  In this case, switching of driving from N inverters to j inverters is performed within a certain period including a zero cross point. Then, the modulation wave signal is corrected so that the output current gradually or instantaneously decreases from L to 0 with respect to the inverter whose driving is stopped. Further, the modulation wave signal is corrected so that the output current increases gradually or instantaneously from L to N · L / j for the inverter that is continuously driven. Therefore, distortion occurring in the alternating current output to the load can be suppressed when switching the inverter.

(4) In the above aspect,
The current detection unit may detect any one of N currents smoothed by the reactor.

  In this case, it is possible to reduce the number of parts by reducing the number of parts by reducing the number of AC detection units to one.

(5) In the above aspect,
A voltage detection unit for detecting a DC voltage output from the power supply unit;
You may further provide the setting part which increases the said setting value as the detection voltage which the said voltage detection part detected increases.

  Inverters have increased switching losses as the input voltage increases. When the switching loss increases, the switching point at which the power conversion efficiency when N inverters are driven becomes higher than the power conversion efficiency when j inverters are driven shifts to the high load side. In this aspect, when the DC voltage output from the power supply unit is high, the set value is increased. Therefore, it is possible to switch driving between the N inverters and the j inverters at an optimal switching point.

  The power supply unit may be a solar cell or a DC / DC converter.

(6) A power conversion device according to another aspect of the present disclosure is provided.
N (N is an integer of 2 or more) inverters that are connected in parallel to the power supply unit and convert the DC power supplied from the power supply unit into AC power using a switching element;
A reactor for smoothing each of the N AC powers output from the N inverters;
An output unit that superimposes N AC powers smoothed by the reactor and outputs them to a load;
A carrier generation unit for generating N carrier signals corresponding to the N inverters and having a phase shifted by 360 degrees / N;
A modulation wave generation unit for generating N modulation wave signals for outputting a predetermined alternating current corresponding to the N inverters;
The N carrier signals and N modulated wave signals corresponding to the N carrier signals are compared to generate N PWM signals corresponding to the N inverters, and the N carrier signals are generated. A pulse generator for outputting to the inverter;
A DC / DC converter connected between the power supply unit and the N inverters;
When the duty ratio of the PWM signal for controlling the DC / DC converter is greater than or equal to a predetermined duty ratio, the first to jth (j is an integer from 1 to N-1) among the N inverters A switching control unit for driving the inverter and outputting a stop instruction for stopping the driving of the j + 1st to Nth inverters,
The carrier generation unit generates j carrier signals corresponding to the first to j-th inverters whose phases are shifted by 360 degrees / j when the stop instruction is output,
When the stop instruction is output, the pulse generator generates j carrier signals corresponding to the first to j-th inverters and j modulated wave signals corresponding to the first to j-th inverters. In comparison, j PWM signals corresponding to the first to j-th inverters are generated and output to the first to j-th inverters.

  When the DC voltage of the power supply unit decreases, the duty ratio of the DC / DC converter increases in order to maintain the input voltage of the inverter at a constant voltage. The power supply unit is, for example, a solar cell. Generally, when the amount of solar radiation decreases, the DC voltage decreases and the power supply capability decreases. When the duty ratio of the DC / DC converter increases, the output power of the inverter decreases, and the alternating current output from the inverter decreases.

  In this aspect, if the duty ratio of the DC / DC converter is smaller than the predetermined duty ratio, N inverters are driven, and if the duty ratio of the DC / DC converter is equal to or higher than the predetermined duty ratio, j inverters are driven. Only the inverter is driven. Therefore, by setting the DC / DC converter duty ratio corresponding to the output power whose power conversion efficiency is reversed as a predetermined duty ratio, the power conversion efficiency is improved in a wider range of output power than in the past. Can be made.

  (7) Moreover, in the said aspect, the effective value of an alternating current may be sufficient as the electric current detected by the said electric current detection part.

(8) Moreover, in the said aspect, the electric current detected by the said electric current detection part is an instantaneous value,
The switching control unit may perform a switching operation of the inverter to be driven at least once in one cycle of the alternating current output from the output unit.

  In this aspect, the switching point can be set more finely using the instantaneous value, and the power conversion efficiency can be improved.

(9) In the above aspect,
The N inverters may be single-phase inverters or three-phase inverters.

  In this case, even when a single-phase inverter or a three-phase inverter is used as the inverter, the same effects as those described above can be obtained.

(Embodiment 1)
FIG. 1 is a circuit diagram of a grid-connected inverter device to which the power conversion device according to Embodiment 1 is applied.

  As shown in FIG. 1, the grid-connected inverter device includes inverters 1 and 2, a DC power supply 3, a smoothing capacitor 4, current sensors 5 and 6, reactors 7 and 8, a filter capacitor 9, a system power supply 10, a control unit 11, And a voltage sensor 12. Reactor 7 includes two reactors 71 and 72, and reactor 8 includes two reactors 81 and 82. In FIG. 1, inverters 1 and 2, smoothing capacitor 4, current sensors 5 and 6, reactors 7 and 8, filter capacitor 9, and voltage sensor 12 constitute a power conversion device.

  The inverters 1 and 2 are connected to the DC power source 3 in parallel and are configured by a full-bridge single-phase inverter. Specifically, the inverters 1 and 2 include four switches SW1 to SW4. Inverters 1 and 2 constitute a multi-phase inverter.

  Since the inverters 1 and 2 have the same configuration, only the inverter 1 will be described below. The switches SW1 to SW4 are composed of n-type MOSFETs. The switches SW1 and SW2 have drains connected to the positive electrode of the DC power supply 3. The sources of the switches SW3 and SW4 are connected to the negative electrode of the DC power supply 3.

  The source of the switch SW1 is connected to the drain of SW3. The source of the switch SW2 is connected to the drain of the switch SW4. The connection point K1 between the switch SW1 and the switch SW3 is connected to the terminal T1 of the system power supply 10 via the reactor 71, and the connection point K2 between the switch SW2 and the switch SW4 is connected to the terminal T2 of the system power supply 10 via the reactor 72. Has been. In the inverter 2, the connection point K1 is connected to the terminal T1 of the system power supply 10 via the reactor 81, and the connection point K2 is connected to the terminal T2 of the system power supply 10 via the reactor 82.

  The inverter 1 switches on / off of the switches SW1 to SW4 according to the PWM signal output from the control unit 11, and converts the DC voltage supplied from the DC power supply 3 into a desired AC voltage. Here, the AC voltage employed by the system power supply 10 is employed as the desired AC voltage. As the AC voltage adopted by the system power supply 10, for example, a sine wave having a frequency of 50 Hz or 60 Hz is adopted. Therefore, the inverter 1 receives a PWM signal generated by comparing a modulated wave signal necessary for interconnection with the system power supply 10 with a carrier signal.

  In FIG. 1, an n-type MOSFET is used as the switch. However, a p-type MOSFET may be used, or an IGBT may be used.

  The smoothing capacitor 4 is connected in parallel with the DC power supply 3. Smoothing capacitor 4 suppresses fluctuations in DC voltage and stabilizes the input voltage of inverters 1 and 2. In the present embodiment, an electrolytic capacitor suitable for downsizing and cost reduction is employed as the smoothing capacitor 4.

  Reactors 71 and 72 smooth the pulsed AC power output from inverter 1 to generate sinusoidal AC power having a waveform corresponding to the modulated wave signal.

  Reactors 81 and 82 smooth the pulsed AC power output from inverter 2 and generate sinusoidal AC power having a waveform corresponding to the modulated wave signal.

  The current sensor 5 is provided between one end of the reactor 71 on the system power supply 10 side and the connection point K <b> 3, measures the alternating current Iout <b> 1 of the inverter 1 smoothed by the reactor 7, and outputs it to the control unit 11. The current sensor 6 is provided between one end of the reactor 81 on the system power supply 10 side and the connection point K <b> 4, measures the alternating current Iout <b> 2 of the inverter 2 smoothed by the reactor 8, and outputs it to the control unit 11.

  Connection points K3 and K4 superimpose AC power smoothed by reactors 71 and 72 and AC power smoothed by reactors 81 and 82, respectively. Connection points K3 and K4 are examples of output units. The filter capacitor 9 is connected between the terminal T1 and the terminal T2 of the system power supply 10, removes a high frequency component from the AC power superimposed at the connection points K3 and K4, and outputs it to the system power supply 10 and the load Z.

  The voltage sensor 12 is connected in parallel with the filter capacitor 9, measures the AC voltage Vout output from the filter capacitor 9, and outputs it to the control unit 11.

  The load Z is connected between the positive electrode and the negative electrode of the system power supply 10.

  The control unit 11 is configured by a microcontroller, for example, and controls the inverters 1 and 2. Specifically, the control unit 11 includes a pulse generation unit 110, a carrier generation unit 120, and a modulated wave generation unit 130. The pulse generation unit 110 includes a pulse generation unit 111 corresponding to the inverter 1 and a pulse generation unit 112 corresponding to the inverter 2. The carrier generation unit 120 includes a carrier generation unit 121 corresponding to the inverter 1 and a carrier generation unit 122 corresponding to the inverter 2. The modulated wave generator 130 includes a modulated wave generator 131 corresponding to the inverter 1 and a modulated wave generator 132 corresponding to the inverter 2.

  The modulated wave generator 131 is a modulated wave signal for obtaining a desired alternating current linked to the AC power supply 10 of the system. The modulated wave signal corresponding to the inverter 1 is converted into an alternating current Iout1 and an alternating voltage Vout. Generated and output to the pulse generator 111. In the present embodiment, system power supply 10 and load Z (depending on the amount of power generation and load Z, there may be power supply only to load Z, or power supply to load Z and reverse power flow to the system. The AC value of the target effective value is output to the system power supply 10 and the load Z. In the present embodiment, the number of inverters is two. Therefore, the modulation wave generation unit 131 is connected to the system power supply 10 and generates a modulation wave signal so that an AC current having an effective value that is 1/2 of the AC current Iout is output from the reactor 7.

  Similarly to the modulation wave generation unit 131, the modulation wave generation unit 132 generates a modulation wave signal corresponding to the inverter 2 using the alternating current Iout 2 and the AC voltage Vout and outputs the modulation wave signal to the pulse generation unit 112.

  The carrier generation unit 121 generates a carrier signal corresponding to the inverter 1 and outputs it to the pulse generation unit 111. As the carrier signal, a triangular wave having a frequency several hundred to several thousand times the frequency of the AC power adopted by the system power supply 10 can be adopted.

  The carrier generation unit 122 generates a carrier signal having the same amplitude and a phase shifted by 180 degrees with respect to the carrier signal generated by the carrier generation unit 121, and outputs the carrier signal to the pulse generation unit 112.

  The pulse generation unit 111 includes, for example, a comparator, compares the modulation wave signal generated by the modulation wave generation unit 131 with the carrier signal generated by the carrier generation unit 121, and generates a PWM signal corresponding to the inverter 1. Output to inverter 1. Specifically, the pulse generation unit 111 generates four PWM signals corresponding to the switches SW1 to SW4 that complementarily turn on / off the switches SW1 and SW4 and the switches SW2 and SW3. Output to the gate.

  For example, the pulse generation unit 112 includes a comparator, and similarly to the pulse generation unit 111, the modulation wave signal generated by the modulation wave generation unit 132 and the carrier signal generated by the carrier generation unit 122 are compared to correspond to the inverter 2. PWM signal to be generated is output to the inverter 2. Here, the phase of the carrier signal generated by the carrier generation unit 122 is shifted by 180 degrees with respect to the carrier signal generated by the carrier generation unit 121. Therefore, as will be described later, the ripples included in the two alternating currents are canceled by superimposing the alternating current Iout1 and the alternating current Iout2.

  FIG. 2 is a circuit diagram of a grid-connected inverter device to which the power conversion device in the comparative example is applied. In FIG. 2, the same components as those in FIG. In FIG. 2, the main difference from FIG. 1 resides in the inverter 1x. In order to obtain the AC power equal to that in FIG. 1, the inverter 1x has two switches SW1 to SW4 connected in parallel. Therefore, the alternating current Iout and the alternating voltage Vout having the same effective values as in FIG. In FIG. 2, the two inverters 81 and 82 and the connection points K3 and K4 that existed in FIG. 1 are omitted because the two inverters are not connected in parallel to the DC power source 3 as in FIG.

  Specifically, the drains and the sources of the switches SW1 and SW1 are connected. Similarly to the switch SW1, the other switches SW2 to SW4 have their drains and sources connected to each other. The drains of the switches SW 1 and SW 1 and the switches SW 2 and SW 2 are connected to the positive electrode of the DC power source 3, and the sources of the switches SW 3 and SW 3 and the switches SW 4 and SW 4 are connected to the negative electrode of the DC power source 3. The sources of the switches SW1 and SW1 are connected to the drains of the switches SW3 and SW3. The sources of the switches SW2 and SW2 are connected to the drains of the switches SW4 and SW4. A connection point K1 between the switches SW1 and SW1 and the switches SW3 and SW3 is connected to the terminal T1 of the system power supply 10 through the reactor 71, and a connection point K2 between the switches SW2 and SW2 and the switches SW4 and SW4 is connected through the reactor 72. Are connected to the terminal T2 of the system power supply 10.

  The switches SW1, SW1, SW2, SW2, SW3, SW3, and SW4, SW4 are simultaneously turned on / off. Specifically, a PWM signal output from a control unit (not shown) is input to each gate of the switches SW1, SW1 to SW4, SW4. When the switches SW1 and SW1 and the switches SW4 and SW4 are turned on, the switches SW2 and SW2 and the switches SW3 and SW3 are turned off. When the switches SW1 and SW1 and the switches SW4 and SW4 are turned off, the switches SW2 and SW2 are turned off. SW2 and switches SW3 and SW3 are turned on.

  The section (b) of FIG. 3 is a graph showing the waveform of the alternating current Iout flowing through the reactor 7 and the waveform of the alternating voltage Vout output to the system power supply 10 in the power conversion device of FIG. In section (b) of FIG. 3, the vertical axis represents voltage and current, and the horizontal axis represents time. In the section (b) of FIG. 3, the vicinity of the zero cross where the AC voltage Vout is 0 is shown in an enlarged manner.

  Here, a PWM signal is generated using a carrier signal having a frequency of 20 kHz, and the switches SW1, SW1 to SW4, SW4 are turned on / off. By turning on / off the switches SW1, SW1 to SW4, SW4, the pulsed AC power output from the inverter 1x is smoothed by the reactor 7. As a result, an alternating current Iout having a waveform corresponding to the modulated wave signal is generated. The alternating current Iout includes a ripple that varies in the order of the frequency of the carrier signal. This ripple is suppressed to some extent by the filter capacitor 9, but the amount of ripple removal by the filter capacitor 9 is limited. As a result, the AC voltage Vout is not as large as the AC current Iout, but includes ripples.

  Section (a) of FIG. 3 is a graph showing the waveforms of AC currents Iout1 and Iout2 flowing through reactors 7 and 8 and the waveform of AC voltage Vout output to system power supply 10 in the power conversion device of FIG. . In the section (a) of FIG. 3, the vertical axis and the horizontal axis are the same as those of the section (b) of FIG. 3, and the vicinity of the zero cross is shown enlarged.

  In the power conversion device of FIG. 1, the phase of the carrier signal generated by the carrier generation unit 122 is shifted by 180 degrees with respect to the carrier signal generated by the carrier generation unit 121. Therefore, when the alternating currents Iout1 and Iout2 at which the duty ratio of the PWM signal is 50% are near 0, the corresponding switches in the inverter 1 and the inverter 2 are alternately turned ON / OFF. Corresponding switches refer to switches having the same reference numerals in the inverter 1 and the inverter 2 such as the switch SW1 of the inverter 1 and the switch SW1 of the inverter 2.

  Therefore, the ripples are reversed between the alternating current Iout1 and the alternating current Iout2. As a result, the two alternating currents are superimposed at the connection points K3 and K4, so that the ripple is canceled and the alternating current Iout in which the ripple is suppressed is output to the system power supply 10. Accordingly, in the power conversion device of FIG. 1, the ripple of the AC voltage Vout is significantly suppressed as compared with the power conversion device of FIG. 2. Note that the ripple reduction effect is higher in the section where the duty ratio is close to 50%, that is, the section near the zero cross, but the ripple reduction effect is also obtained in the section where the duty ratio is other than 50%.

  The power conditioner for photovoltaic power generation is obliged to manufacture a device in accordance with the guidelines for connecting to the grid power supply 10. This guideline includes a rule that the ripple rate (harmonic content rate) of the alternating current output to the system power supply 10 must be a predetermined value or less.

  According to the present embodiment, since the phase of the carrier signal of inverter 1 and the carrier signal of inverter 2 is shifted by 180 degrees, the alternating current Iout has a significantly reduced ripple as compared with the power conversion device of FIG. Can be output to the system power supply 10. As a result, the waveform quality of the alternating current Iout output to the system power supply 10 can be improved.

  In addition, since the corresponding switches in the inverters 1 and 2 are alternately turned on / off, the ripples included in the current flowing through the smoothing capacitor 4 are canceled out and the ripples of the current flowing through the smoothing capacitor 4 can be reduced. The smoothing capacitor 4 is composed of an electrolytic capacitor, but the electrolytic capacitor self-heats due to ripples. This self-heating affects the life of the electrolytic capacitor. Therefore, by reducing the ripple, the number of electrolytic capacitors provided in large numbers can be reduced in consideration of the life of the electrolytic capacitor, and the cost can be reduced. Alternatively, by reducing the ripple, the added value of the product can be improved by extending the life of the electrolytic capacitor without changing the number.

  Next, the operation of the power conversion device according to the first embodiment will be briefly described. First, DC power supplied from the DC power source 3 is smoothed by the smoothing capacitor 4 and supplied to the inverters 1 and 2. When the DC voltage supplied from the DC power source 3 is E, the inverter 1 outputs the voltage of E to the reactor 7 when the switches SW1 and SW4 are on and the switches SW2 and SW3 are off. On the other hand, the inverter 1 outputs the voltage −E to the reactor 7 when the switches SW2 and SW3 are on and the switches SW1 and SW4 are off. As a result, a pulsed AC voltage whose voltage changes between + E and -E flows through the reactor 7. This pulsed AC voltage is smoothed by the reactor 7. As a result, the low-frequency component having a waveform corresponding to the modulation wave signal is superimposed with the high-frequency ripple component that increases with a constant slope in the + E interval and decreases with a constant slope in the -E interval. Is output from the reactor 7.

  On the other hand, like the inverter 1, the inverter 2 outputs a pulsed AC voltage whose voltage changes between + E and -E. Therefore, an alternating current Iout2 in which a high-frequency ripple component that increases with a constant slope in the + E interval and decreases with a constant slope in the −E interval is superimposed on the low-frequency component having a waveform corresponding to the modulation wave signal. Output from the reactor 8. Here, the phase of the carrier signal corresponding to the inverter 2 is shifted by 180 degrees with respect to the carrier signal corresponding to the inverter 1. Therefore, as shown in section (a) of FIG. 3, the phase shift between the ripple component in the alternating current Iout1 and the ripple component in the alternating current Iout2 approaches 180 degrees as the duty ratio approaches 50%.

  Therefore, by superimposing the alternating current Iout1 and the alternating current Iout2, the ripple is canceled out and the alternating current Iout in which the ripple is suppressed is output to the system power supply 10.

  FIG. 4 is a graph showing experimental results comparing the power conversion efficiencies of the power conversion device of the first embodiment and the comparative example (power conversion device of FIG. 2). In FIG. 4, the vertical axis indicates power conversion efficiency (%), and the horizontal axis indicates normalized output power. The normalized output power is a value obtained by dividing the actual output power (W) by the reference power. The power conversion efficiency is a value obtained by dividing the output power of the power conversion device by the input power. A curve 401 indicated by a solid line indicates the experimental result of the power conversion device according to the first embodiment, and a curve 402 indicated by an alternate long and short dash line indicates the experimental result of the comparative example of FIG.

  In the experiment of FIG. 4, the same type of switch was used in the power conversion device of the first embodiment and the power conversion device of the comparative example. Moreover, in the power converter device of Embodiment 1, four reactors of the same kind were used, and in the power converter device of the comparative example, two reactors of the same kind as the reactor of Embodiment 1 were used.

  In the experiment of FIG. 4, the frequency of the carrier signal was 16 kHz, the DC power supply was 330 V, and the modulation rate was 88% (equivalent to AC output 200 V). Further, a resistor was connected as the load Z without being connected to the system power supply 10.

  In both curves 401 and 402, the power conversion efficiency rapidly increased until the output power reached 2.0, and when the output power exceeded 2.0, the increase in power conversion efficiency became moderate. In the low load region where the output power is 3.5 or less, the curve 402 has a higher power conversion efficiency than the curve 401. However, in the high load region where the output power exceeds 3.5, this relationship is reversed. 401 had higher power conversion efficiency than curve 402. That is, in the high load region, the configuration of the first embodiment has higher power conversion efficiency than the configuration of the comparative example.

  And in output power 5.5, the power conversion efficiency improved 0.2%. Assuming that the output AC current Iout is the same between the configuration of the first embodiment and the configuration of the comparative example, the AC current per inverter in the configuration of FIG. This is because the copper loss of the reactor is halved. Details of the reason why the copper loss is halved will be described later. In addition, it is considered that the reduction of the loss in the smoothing capacitor 4 due to the reduction of the ripple of the current flowing through the smoothing capacitor 4 contributed to the improvement of the power conversion efficiency.

  Thus, according to the present embodiment, since the phase of the carrier signal of inverter 1 and the carrier signal of inverter 2 is shifted by 180 degrees, AC current Iout with high waveform quality with reduced ripple can be obtained. . Further, the ripple of the current flowing through the smoothing capacitor 4 is reduced, and high power conversion efficiency can be realized in a high load region.

(Embodiment 2)
FIG. 5 is a circuit diagram of a grid-connected inverter device to which the power conversion device according to Embodiment 2 is applied. The second embodiment is characterized in that it is determined whether to drive both inverters 1 and 2 or to stop driving one of the inverters according to the power load.

  5 differs from FIG. 1 in the configuration of the control unit 11. That is, the control unit 11 includes a setting unit 140, a comparator 150 (an example of a switching control unit), and a switching command generation unit 160 (an example of a switching control unit) in addition to the configuration of FIG. Setting unit 140 sets a setting value used when switching command generation unit 160 determines whether or not to drive one of inverters 1 and 2. Here, it is assumed that the drive of the inverter 2 is stopped.

  The comparator 150 compares the effective value of the alternating current Iout1 with the set value set by the setting unit 140. Specifically, the comparator 150 performs A / D conversion on the alternating current Iout1, calculates an effective value, compares the effective value with the set value, and outputs the comparison result to the switching command generation unit 160.

  When the comparison result indicates that the effective value of the alternating current Iout1 is equal to or less than the set value, the switching command generation unit 160 modulates a stop instruction indicating that the drive of the inverter 2 is stopped and only the inverter 1 is driven. The data is output to the generation units 131 and 132. In this case, the switching command generator 160 also outputs a gate block signal to the pulse generator 112.

  On the other hand, when the comparison result indicates that the effective value of AC current Iout1 is larger than the set value, switching command generation unit 160 drives inverters 1 and 2 without outputting a stop instruction and a gate block signal.

  When the modulation wave generation unit 131 receives a stop instruction from the switching command generation unit 160, the modulation wave generation unit 131 generates a modulation wave signal so that the effective value of the alternating current Iout1 becomes the effective value of the alternating current Iout, and outputs the modulation wave signal to the pulse generation unit 111. To do. Here, since the effective value of the alternating current Iout1 when the inverters 1 and 2 are driven is ½ of the effective value of the alternating current Iout, the modulation wave generating unit 131 sets the effective value of the alternating current Iout1 to 2 A modulated wave signal to be doubled is generated. As a result, the PWM signal that doubles the effective value of the alternating current Iout1 is output from the pulse generator 111.

  When receiving a stop instruction from the switching command generation unit 160, the modulation wave generation unit 132 generates a modulation wave signal that sets the alternating current Iout 2 to 0 and outputs the modulation wave signal to the pulse generation unit 112.

  When receiving the gate block signal, the pulse generator 112 turns off all the switches SW1 to SW4 of the inverter 2. Here, when the pulse generation unit 112 receives a modulated wave signal that sets Iout2 to 0, the PWM signal with a duty ratio of 50% is output to the inverter 2, so that the inverter 2 continues to be turned on / off. Therefore, the switching command generation unit 160 outputs a signal for turning off all the switches SW1 to SW4 of the inverter 2 from the pulse generation unit 112 by outputting a gate block signal to the pulse generation unit 112, and drives the inverter 2. It is completely stopped. Thereby, unnecessary power consumption in the inverter 2 is suppressed.

  As described above, when the effective value of the alternating current Iout1 is larger than the set value, AC power is supplied to the load Z by the inverters 1 and 2, but when the effective value of the alternating current Iout1 is less than the set value, the load is supplied from the inverter 2. The power supply to Z is stopped, and power is supplied from only the inverter 1 to the load Z.

  On the other hand, when only the inverter 1 is driven, the switching command generator 160 indicates that the comparison result by the comparator 150 indicates that ½ of the effective value of the alternating current Iout1 is larger than the set value. A restart instruction for restarting driving of the inverter 2 is output to the modulated wave generation units 131 and 132, and output of the gate block signal to the pulse generation unit 112 is stopped.

  Here, the comparator 150 compares 1/2 of the effective value of the alternating current Iout1 with the set value as follows. The effective value of the alternating current Iout1 when only the inverter 1 is driven is twice the effective value of the alternating current Iout1 when the inverters 1 and 2 are driven. On the other hand, the set value is set based on the case where the inverters 1 and 2 are driven. Therefore, when only inverter 1 is driven, comparator 150 compares 1/2 of the effective value of AC current Iout1 with the set value.

  When only the inverter 1 is driven and the modulation wave generator 131 receives a restart instruction, the modulation wave generator 131 generates a modulation wave signal for reducing the effective value of the alternating current Iout1 to ½ of the effective value of the alternating current Iout. Generated and output to the pulse generator 111. As a result, a PWM signal that causes the effective value of the alternating current Iout1 to be ½ of the effective value of the alternating current Iout is output from the pulse generator 111 to the inverter 1.

  When only the inverter 1 is driven and the modulation wave generator 132 receives a restart instruction, the modulation wave generator 132 generates a modulation wave signal for reducing the effective value of the alternating current Iout2 to ½ of the effective value of the alternating current Iout. Generated and output to the pulse generator 112.

  When the output of the gate block signal is stopped, the pulse generator 112 compares the modulated wave signal output from the modulated wave generator 132 with the carrier signal output from the carrier generator 122 to generate a PWM signal. The output of the PWM signal to the inverter 2 is resumed.

  In the present disclosure, the specific configuration of the setting unit 140 is not particularly limited. As an example, an effective value that is predetermined as an effective value of the alternating current Iout1 that switches from driving the inverters 1 and 2 to driving only the inverter 1 is set. A setting table that stores digital values can be used. Details of the setting table will be described later.

  FIG. 6 is a graph showing experimental results comparing the power conversion efficiencies of the power conversion device of the second embodiment and the comparative example (power conversion device of FIG. 2). In FIG. 6, a curve 601 indicates the power conversion efficiency of the second embodiment, and a curve 602 indicates the power conversion efficiency of the comparative example.

  In the curve 601, when the output power exceeds 3.5, switching from driving only the inverter 1 to driving the inverters 1 and 2 is performed. In the high load region where the output power is 3.5 or more in the curve 601, the power conversion efficiency is higher than that of the curve 602 in FIG. 6.

  Moreover, in the experimental result of FIG. 6, also in the low load area | region where output electric power is 3.5 or less, the power converter device of Embodiment 2 improved the power conversion efficiency compared with the power converter device of the comparative example. For example, when the output power is about 0.6, the power conversion device of the second embodiment has an approximately 1% increase in power conversion efficiency compared to the power conversion device of the comparative example.

  Hereinafter, the principle of improving the power conversion efficiency by switching the drive number of the inverter will be described with reference to FIG.

  Section (a) in FIG. 7 is a graph showing the conduction loss and switching loss of the switches constituting the inverter, the vertical axis shows the loss, and the horizontal axis shows the output power. (I) is a loss curve indicating conduction loss and switching loss when the power conversion device is driven to the rated output only by the inverter 1, and (ii) is the power conversion to the rated output by the inverter 1 and the inverter 2. These are conduction loss and switching loss when the device is driven.

  The switching loss is a loss that occurs when the switch is turned on and off. The conduction loss is a loss during the ON period of the switch.

  In both (i) and (ii), the switching loss gradually increases as the output power increases. In both (i) and (ii), the conduction loss is lower than the switching loss in the region where the output power is low, but since the increase rate is larger than the switching loss, the conduction loss is higher than the switching loss in the region where the output power is high. It is getting bigger.

  That is, in the region where the output power is low, the ratio of the switching loss to the total loss of the switch is high. However, the ratio of the conduction loss to the total loss of the switch increases as the output power increases.

  The conduction loss is estimated by the product of the square of the energization current of the switch and the on-resistance of the switch. Therefore, when a switch with low on-resistance is used, the conduction current is extremely low in the region where the output power is low, and thus the conduction loss is extremely low. In the region where the output power is high, the switch is greatly proportional to the square of the conduction current. To increase. If the output power is the same, in the case of (ii), the energization current of the switch is ½ compared to the case of (i).

  Here, the on-resistance of the switch is Ron, and the energization current of the switch in the case of (i) is ion. Also, (ii) has twice as many switches as (i). Therefore, in the case of (ii), the conduction loss of the switch is (ion / 2) ^ 2 * Ron * 2 = 1/2 * ion ^ 2 * Ron. On the other hand, the conduction loss of the switch in the case of (i) is (ion) ^ 2 * Ron.

  Therefore, in the region where the output power is high, the conduction loss is significantly lower in the case of (ii) than in the case of (i).

  On the other hand, the switching loss depends on the output capacity of the switch, the square of the applied voltage, and the carrier frequency, and does not change much according to the output power. Therefore, in the region where the output power is low (region where the current at ON / OFF is small), the ratio of the switching loss to the total loss of the switch is higher than the conduction loss. Furthermore, in the case of (ii), since the output capacity of the switch is doubled compared to the case of (i), the switching loss is increased. Therefore, the loss curve indicating the switching loss in the case of (ii) is higher by the substantially constant offset than the loss curve indicating the switching loss in the case of (i).

  In summary, in the region where the output power is low, the ratio of the switching loss is dominant, and (i) has a lower switching loss than (ii). Therefore, (i) has the total loss of the switch. Can be reduced. On the other hand, in the region where the output power is high, the conduction loss is dominant and the conduction loss of (ii) is lower than that of (i). Therefore, the total loss of the switch is higher in (ii) than in (i). Can be reduced.

  The section (b) in FIG. 7 is a graph showing the reactor loss, the vertical axis shows the loss, and the horizontal axis shows the output power. (I) is a loss curve when the power converter is driven to the rated output by only the inverter 1, and (ii) is a loss curve when the power converter is driven to the rated output by the inverter 1 and the inverter 2. It is. The reactor loss is roughly classified into a copper loss due to a fundamental wave component (frequency component of the modulated wave signal: 50 Hz or 60 Hz), a copper loss due to a ripple component (an integer multiple of the frequency of the carrier signal), and an iron loss.

  The copper loss is a loss based on the winding of the reactor, and is estimated by the product of the square of the energization current and the resistance component corresponding to the frequency of the current flowing through the reactor. Assuming that the output power is the same, in the case of (ii), the current flowing through the reactor is ½ compared to the case of (i).

  Here, the resistance of the reactor in the fundamental wave component is Rac, and the current of the fundamental wave component flowing in the reactor in the case of (i) is iac. In (ii), the number of reactors is twice that in (i). Therefore, in the case of (ii), the copper loss due to the fundamental wave component is (iac / 2) ^ 2 * Rac * 2 = 1/2 * iac * Rac. On the other hand, the copper loss due to the fundamental wave component in the case of (i) is (iac) ^ 2 * Rac.

  Therefore, in the region where the output power is high, the copper loss in the fundamental wave component is significantly lower in the case of (ii) than in the case of (i).

  The copper loss due to the ripple component is constant regardless of the output power because the ripple does not increase according to the output power. In (ii), the number of reactors is twice that in (i). Therefore, regardless of the output power, the copper loss due to the ripple component in (ii) is twice that in (i).

  The iron loss is a loss based on the core of the reactor, and is constant regardless of the output power, like the copper loss due to the ripple component. In (ii), the number of reactors is twice that in (i). Therefore, regardless of the output power, the iron loss in (ii) is twice that in the case of (i).

  In summary, in the region where output power is low, the ratio of copper loss and iron loss due to ripple components is dominant, and both losses are higher in (ii) than in (i). However, reactor loss can be reduced more than (ii). On the other hand, in the region where the output power is high, the ratio of the copper loss due to the fundamental wave component is dominant, and the copper loss is higher in (i) than in (ii). Reactor loss can be reduced more than i).

  Therefore, both the switch loss and the reactor loss are lower in the region (i) where the output power is low, and (ii) is lower in the region where the output power is high. Therefore, as shown in the result of FIG. 6, by switching between (i) and (ii) according to the output power, it is possible to improve the power conversion efficiency in a wider range of power load than in the past.

  Therefore, in the present embodiment, in (i) and (ii), the effective value of the alternating current Iout1 corresponding to the output power whose power conversion efficiency is reversed is set in advance as a setting value, and the effective value of the alternating current Iout1 is set. Is less than the set value, only the inverter 1 is driven, and when the effective value of the alternating current Iout1 is larger than the set value, the inverters 1 and 2 are driven.

  As a result, power conversion efficiency can be improved in a wider range of power load than in the past.

  Note that even if switching is performed by the power conversion device shown in FIG. 2, the switching loss due to the output capacity cannot be reduced in the low load region because two switches are connected in parallel. Furthermore, since the reactor current cannot be halved, the reactor loss cannot be reduced in a high load region.

  Next, the operation of the power conversion device according to the second embodiment will be briefly described. First, similarly to the first embodiment, driving of the inverters 1 and 2 is started. The comparator 150 starts monitoring the alternating current Iout1 through the current sensor 5. Then, it is assumed that the comparator 150 detects that the effective value of the alternating current Iout1 is equal to or less than the set value. In this case, the switching command generation unit 160 stops the drive of the inverter 2, outputs a stop instruction indicating that only the inverter 1 is driven to the modulation wave generation units 131 and 132, and the gate block to the pulse generation unit 112. Output a signal. Thereby, the drive of the inverter 2 is stopped and only the inverter 1 is driven. As a result, only the inverter 1 is driven in the low load region, and the power conversion efficiency is improved as compared with the case where the inverters 1 and 2 are driven.

  If the effective value of the alternating current Iout1 is not less than the set value during driving of the inverters 1 and 2, the driving of the inverters 1 and 2 is continued.

  On the other hand, it is assumed that comparator 150 detects that ½ of the effective value of AC current Iout1 has become larger than the set value while only inverter 1 is driven. In this case, the switching command generator 160 outputs a restart instruction for restarting driving of the inverter 2 to the modulated wave generators 131 and 132 and stops outputting the gate block signal to the pulse generator 112. As a result, the output of the PWM signal from the pulse generator 112 to the inverter 2 is resumed, and the inverters 1 and 2 are driven. As a result, in the high load region, the inverters 1 and 2 are driven, and the power conversion efficiency is increased as compared with the case where only the inverter 1 is driven.

(Embodiment 3)
The third embodiment is characterized in that the waveform of the alternating current Iout is smoothly changed when switching from driving the inverters 1 and 2 to driving only the inverter 1. In the present embodiment, the same components as those in the first and second embodiments are denoted by the same reference numerals and description thereof is omitted. Further, FIG. 5 is adopted as the circuit configuration of the present embodiment.

  FIG. 8 is a diagram illustrating a waveform at the time of switching of the power conversion device according to the third embodiment. The upper part of FIG. 8 is a graph showing the waveforms of the alternating current Iout and the modulated wave signal 801 of the alternating current Iout1, the vertical axis shows the current, and the horizontal axis shows the time. The lower part of FIG. 8 is a graph showing waveforms of the alternating current Iout1 and the alternating current Iout2, the vertical axis shows the current, and the horizontal axis shows the time. In addition, the waveform shown in FIG. 8 is a waveform by simulation.

  Until the time t1 (0.7 sec), the inverter 1 and the inverter 2 are driven. Therefore, the modulation wave signal 801 is a sine wave having an effective value of 13.75A. Note that the actual value on the vertical axis of the modulated wave signal 801 indicates a command value. The command value is a value that allows the inverter 1 to output an alternating current Iout1 indicating the value when the inverter 1 is driven using a PWM signal. Therefore, the modulated wave signal 801 does not actually have a current value indicated by the vertical axis of the graph. Hereinafter, for convenience of explanation, it is assumed that the modulated wave signal 801 has a value of the alternating current Iout1. The same applies to the modulated wave signal 802 (not shown) corresponding to the inverter 2.

  Since inverters 1 and 2 are driven until time t1, modulated wave signals 801 and 802 having an effective value of 13.75 A are output from modulated wave generators 131 and 132, respectively. Therefore, the inverters 1 and 2 respectively output AC currents Iout1 and Iout2 having an effective value of 13.75 A, and an AC current Iout having an effective value of 27.5 A is output to the system power supply 10.

  At time t <b> 1, the switching command generation unit 160 receives a comparison result indicating that the alternating current Iout <b> 1 is equal to or less than the set value from the comparator 150, and issues a stop instruction to stop the driving of the inverter 2 to the modulation wave generation units 131 and 132. Output.

  Modulated wave generating section 131 has an effective value that gradually increases from 13.75 A to 27.5 A over a transition period Tx (10 msec) from time t 1 to time t 2 (0.71 sec) when switching ends. Then, the modulated wave signal 801 is corrected. On the other hand, the modulated wave generator 132 corrects the modulated wave signal 802 (not shown) so that the effective value gradually decreases from 13.75 A to 0 A over the transition period Tx.

  The following modes can be adopted as specific examples of the processing to be changed gently. The modulated wave signal having an effective value of 13.75A output from the modulated wave generating unit 131 at time t1 is Sig1, and the modulated wave signal having an effective value to be output by the modulated wave generating unit 131 after switching is 27.5A as Sig2. To do. Then, the modulation wave generation unit 131 generates a signal of Sig1 * α + Sig2 * (1−α) as the modulation wave signal 801. It is assumed that the phases of Sig1 and Sig2 are aligned at time t1. At this time, the modulation wave generation unit 131 generates the modulation wave signal 801 so that the coefficient α gradually decreases from 1 to 0 in the transition period Tx. As a result, as shown in the lower part of FIG. 8, the waveform of the alternating current Iout1 gradually increases from a waveform (Sig1) having an effective value of 13.75A to a waveform (Sig2) having an effective value of 27.5A.

  On the other hand, the modulation wave generation unit 132 generates a signal of Sig1 * α as the modulation wave signal 802. At this time, the modulation wave generation unit 132 gradually decreases α similarly to the modulation wave generation unit 131. Thereby, as shown in the lower part of FIG. 8, the effective value of the alternating current Iout2 gradually decreases from 13.75 A to zero.

  At time t <b> 2 (0.71 sec), the switching command generation unit 160 outputs a gate block signal to the pulse generation unit 112. Thereby, the pulse generation unit 112 turns off the switches SW1 to SW4 of the inverter 2 and completely stops the driving of the inverter 2. As a result, only the inverter 1 is driven after time t2. As described above, the modulation wave signal 801 is gently raised and the modulation wave signal 802 is gently lowered, so that the drive of the inverters 1 and 2 is changed to the drive of only the inverter 1 without distorting the alternating current Iout. It is possible to switch. Moreover, it is possible to reduce the loss due to the output capacity by completely turning off the inverter 2.

  In the above description, 10 msec is employed as the transition period Tx. However, this is merely an example, and any value less than 10 msec may be employed, or any value greater than 10 msec may be employed. However, when the transition period Tx exceeds one cycle (1/50 sec or 1/60 sec) of the AC voltage defined by the system power supply 10, switching in units of one cycle cannot be performed. For example, only the inverter 1 is driven in the current cycle, and the inverters 1 and 2 cannot be driven in the next cycle. Therefore, the transition period Tx is preferably a period of one cycle or less of the AC voltage defined by the system power supply 10, and more preferably a period of ½ or less of this period with a margin. Moreover, as long as the transition period Tx of the inverter 1 and the inverter 2 is the same, it may be a period of one cycle or more of the AC voltage. In the example of FIG. 8, the transition period Tx is 10 msec. When the cycle of the AC voltage defined by the system power supply 10 is 1/50 sec (= 20 msec), a value that is ½ of the cycle is adopted. Yes.

(Embodiment 4)
The fourth embodiment is characterized in that when the drive of the inverters 1 and 2 is switched to the drive of only the inverter 1, the waveform of the alternating current Iout is smoothly changed in a certain period including the zero cross point of the alternating voltage Vout. .

  In addition, in this Embodiment, the same thing as Embodiment 1-3 is attached | subjected the same code | symbol, and description is abbreviate | omitted. Further, FIG. 5 is adopted as the circuit configuration of the present embodiment.

  FIG. 9 is a diagram showing waveforms at the time of switching in the comparative example with respect to the fourth embodiment. In the comparative example, in a period not including the zero cross point, the modulation wave signal 801 is gently increased, the modulation wave signal 802 (not shown) is instantaneously decreased, and the drive from the inverters 1 and 2 to the drive of only the inverter 1 is performed. Switching has been done. The waveform shown in FIG. 9 is a simulation waveform.

  The upper part of FIG. 9 is a graph showing the waveforms of the alternating current Iout and the modulated wave signal when the modulated wave signal 801 is gently raised and the modulated wave signal 802 is momentarily lowered in a period not including the zero cross point. Yes, the vertical axis represents current, and the horizontal axis represents time.

  The lower part of FIG. 9 is a graph showing the waveforms of the alternating current Iout1 and the alternating current Iout2, the vertical axis shows the current, and the horizontal axis shows the time.

  Until the time t1 (0.705 sec), the inverter 1 and the inverter 2 are driven. Therefore, the modulation wave signal 801 is a sine wave having an effective value of 13.75A.

  Since inverters 1 and 2 are driven until time t1, modulated wave signals 801 and 802 having an effective value of 13.75 A are output from modulated wave generators 131 and 132, respectively. Therefore, the inverters 1 and 2 respectively output AC currents Iout1 and Iout2 having an effective value of 13.75 A, and an AC current Iout having an effective value of 27.5 A is output to the system power supply 10.

  At time t <b> 1, the switching command generation unit 160 receives a comparison result indicating that the alternating current Iout <b> 1 is equal to or less than the set value from the comparator 150, and issues a stop instruction to stop the driving of the inverter 2 to the modulation wave generation units 131 and 132. Output.

  Modulated wave generating section 131 has an effective value that gradually increases from 13.75 A to 27.5 A over a transition period Tx (1 msec) from time t 1 to time t 2 (0.706 sec) when switching ends. Then, the modulated wave signal 801 is corrected. The method for correcting the modulated wave signal 801 is the same as that in the third embodiment.

  On the other hand, the modulated wave generator 132 corrects the modulated wave signal 802 so that the effective value sharply drops from 13.75 A to 0 A at time t1. As a result, as shown in the lower part of FIG. 9, the current value of the alternating current Iout2 is 0 A after time t1.

  At time t <b> 2, switching command generator 160 outputs the gate block signal to pulse generator 112. Thereby, the pulse generation unit 112 turns off the switches SW1 to SW4 of the inverter 2 and completely stops the driving of the inverter 2.

  As described above, in the comparative example, since the modulation wave signal 802 is switched instantaneously, the switching timing of the modulation wave signals 801 and 802 does not match the output timing of the gate block signal. In the comparative example, this switching is executed in a period not including the zero cross point. As a result, as shown in the upper part of FIG. 9, the waveform of the alternating current Iout is distorted in the transition period Tx.

  FIG. 10 is a diagram illustrating a waveform at the time of switching according to the fourth embodiment. Until the time t1 (0.7 sec), the inverter 1 and the inverter 2 are driven. Therefore, the modulation wave signal 801 is a sine wave having an effective value of 13.75A. The waveform shown in FIG. 10 is a simulation waveform.

  At time t <b> 1, the switching command generation unit 160 receives a comparison result indicating that the alternating current Iout <b> 1 is equal to or less than the set value from the comparator 150, and issues a stop instruction to stop the driving of the inverter 2 to the modulation wave generation units 131 and 132. Output.

  Modulated wave generator 131 corrects modulated wave signal 801 so that the effective value gradually increases from 13.75 A to 27.5 A over a transition period Tx (1 msec) from time t1 to time t2. . The method for correcting the modulated wave signal 801 is the same as that in the third embodiment.

  On the other hand, the modulated wave generator 132 corrects the modulated wave signal 802 so that the effective value sharply drops from 13.75 A to 0 A at time t1. As a result, as shown in the lower part of FIG. 9, the current value of the alternating current Iout2 is 0 A after time t1.

  At time t <b> 2, switching command generator 160 outputs the gate block signal to pulse generator 112. Thereby, the pulse generation unit 112 turns off the switches SW1 to SW4 of the inverter and completely stops the driving of the inverter 2.

  As described above, in the fourth embodiment, the modulated wave signals 801 and 802 are corrected in the same manner as in the comparative example, but the transition period Tx includes a zero cross point. Here, the transition period Tx is started when the AC voltage Vout reaches the zero cross point.

  Therefore, as shown in the upper part of FIG. 10, in the transition period Tx, distortion that appears in the comparative example can be prevented from appearing in the alternating current Iout. That is, in the fourth embodiment, even if the switching timing of the modulated wave signals 801 and 802 and the output timing of the gate block signal do not coincide with each other, the transition period Tx is set to the zero cross point. The distortion can be prevented from appearing.

  Note that the timing at which the comparator 150 detects that the alternating current Iout1 exceeds the set value does not necessarily match the zero cross point of the alternating voltage Vout. Therefore, after receiving the comparison result indicating that the AC current Iout1 exceeds the set value from the comparator 150, the switching command generation unit 160 monitors the AC voltage Vout and instructs to stop at the timing when the zero cross point first arrives. May be output from the modulation wave generation units 131 and 132 and the gate block signal may be output to the pulse generation unit 112.

  Thereby, the modulation wave generation units 131 and 132 can correct the modulation wave signals 801 and 802 with the zero cross point as a starting point.

  In the fourth embodiment, 1 msec is adopted as the transition period Tx. However, this is only an example, and as in the third embodiment, if the period is one cycle or less of the AC voltage defined by the system power supply 10, Any value may be adopted. In the example of FIG. 10, the alternating current Iout1 is gradually increased over the transition period Tx, and the alternating current Iout2 is sharply decreased at time t1, but this relationship may be reversed. That is, the alternating current Iout1 may be sharply increased at time t1, and the alternating current Iout2 may be gradually decreased over the transition period Tx.

  In the example of FIG. 10, the alternating current Iout1 may be gradually increased over the transition period Tx, and the alternating current Iout2 may be gradually decreased over the transition period Tx. In the example of FIG. 10, the alternating current Iout1 may be sharply increased at time t1, and the alternating current Iout2 may be sharply decreased at time t1.

(Embodiment 5)
FIG. 11 is a circuit diagram of a grid-connected inverter device to which the power conversion device according to the fifth embodiment is applied.

  11 differs from FIG. 1 in the position of the current sensor 5. That is, in FIG. 1, current sensors 5 and 6 are provided for each of the inverters 1 and 2. In FIG. 11, the current sensor 5 is connected between the filter capacitor 9 and the load Z. Therefore, in FIG. 11, the current sensor 6 is omitted.

  When the inverter 1 and the reactor 7 and the inverter 2 and the reactor 8 have a low impedance difference due to the on-resistance of the switches SW1 to SW4 and the resistance components of the reactors 7 and 8, the alternating current Iout1 output from the inverters 1 and 2 , Iout2 are substantially equal. Therefore, even if a current sensor is not provided for each of the inverters 1 and 2, by providing one current sensor 5 on the output side of the connection points K3 and K4, the current sensors 5 and 6 are provided for each inverter 1 and 2. The same effect as when provided is obtained. Therefore, in the present embodiment, one current sensor 5 is provided on the output side of the filter capacitor 9. Thereby, the number of parts can be reduced and the cost can be reduced.

  Since the current sensor 5 detects the alternating current Iout instead of the alternating current Iout1, the comparator 150 receives the alternating current Iout having an amplitude twice that of the alternating current Iout1. On the other hand, the set value managed by the setting unit 140 is set based on the effective value of the alternating current Iout1. Therefore, the comparator 150 may compare half the effective value of the alternating current Iout with the set value. Alternatively, the current sensor 5 may input an AC current that is ½ of the detected AC current Iout to the comparator 150.

(Embodiment 6)
FIG. 12 is a circuit diagram of a grid-connected inverter device to which the power conversion device according to the sixth embodiment is applied.

  12 differs from FIG. 1 in that a DC / DC converter 1200 is provided and the control unit 11 monitors the inverter input voltage Vdc1 of the inverters 1 and 2. The inverter input voltage Vdc1 may be monitored by providing a voltage sensor (not shown) in parallel with the smoothing capacitor 4.

  When a solar panel is employed as the DC power source 3, the input voltage Vdc2 changes according to the amount of solar radiation. Usually, the DC / DC converter 1200 provided between the solar panel and the inverters 1 and 2 is configured so that the inverter input voltage Vdc1 is linked to the system power supply 10 when the voltage output from the solar panel is low. The input voltage Vdc2 is boosted so that the necessary DC voltage is obtained.

  When the input voltage Vdc2 is high, the DC / DC converter 1200 is stopped, and the voltage output from the solar panel is input to the inverters 1 and 2 as they are. As the inverter input voltage Vdc1 output from the DC / DC converter 1200 increases, the switching loss in the switches SW1 to SW4 of the inverters 1 and 2 increases.

  The DC / DC converter 1200 includes a smoothing capacitor C12, a reactor L12, a switch SW12, and a diode D12. The smoothing capacitor C12 is connected in parallel with the DC power supply 3 and smoothes the input voltage Vdc2. Reactor L12 is connected between the positive electrode of DC power supply 3 and the drain of switch SW12. The switch SW12 is composed of, for example, an n-type MOSFET, and the source is connected to the negative electrode of the DC power supply 3. The diode D12 has an anode connected to the right end of the reactor L12 and the drain of the switch SW12, and a cathode connected to the upper end of the smoothing capacitor 4.

  First, when the switch SW12 is on, the right end of the reactor L12 is electrically connected to the negative electrode of the DC power supply 3, so that the current flowing through the reactor L12 increases. Here, when the switch SW12 is turned off, the current of the reactor L12 does not suddenly become 0, so that current is injected to the output side (inverters 1 and 2) via the diode D12. That is, when the switch SW12 is on, the energy stored in the reactor L12 is discharged to the output side at once. As a result, the input voltage Vdc2 is boosted to the inverter input voltage Vdc1 and applied to the smoothing capacitor 4.

  As shown in section (a) of FIG. 7, when the switching loss increases, the proportion of the switching loss in the total loss of the switch changes. Therefore, the switching point at which the power conversion efficiency is reversed changes between the case of driving only the inverter 1 (i) and the case of driving the inverters 1 and 2 (ii).

  Specifically, in section (a) of FIG. 7, both (i) and (ii) are switched because the switching loss shifts upward and the region where the switching loss is dominant with respect to the conduction loss increases. The point shifts to the high load side (right side).

  Therefore, in the present embodiment, inverters 1 and 2 are switched at an optimal switching point using inverter input voltage Vdc1 and alternating current Iout1.

  FIG. 13 is a diagram illustrating an example of the setting table T13 managed by the setting unit 140. The setting table T13 stores setting values corresponding to switching points according to the inverter input voltage Vdc1. In this example, the inverter input voltage Vdc1 has three ranges: a range (1) where the voltage is VA to VB, a range (2) where the voltage is greater than VB and less than VC, and a range (3) where the voltage is greater than VC and less than VD. It is divided into ranges. The setting values I1, I2, and I3 are associated with the ranges (1) to (3), respectively.

  The set values I1, I2, and I3 are effective values of the alternating current Iout1 corresponding to the optimum switching point when the inverter input voltage Vdc1 belongs to the ranges (1), (2), and (3), respectively. Experimentally determined values are used. Note that, as the inverter input voltage Vdc1 increases, the switching point shifts to the right side (the side with higher output power), so the set values I1 to I3 have a relationship of I3> I2> I1.

  For example, when the inverter input voltage Vdc1 belonging to the range (i) is input, the setting unit 140 sets the setting value I1 as the setting value. In this case, the comparator 150 drives only the inverter 1 if the effective value of the alternating current Iout1 is not more than the set value I1, and drives the inverters 1 and 2 if the effective value of the alternating current Iout1 is larger than the set value I1. Let

  Thus, in the present embodiment, since an appropriate set value is set according to the inverter input voltage Vdc1, even if the switching loss varies, the drive of the inverters 1 and 2 can be switched at an optimal switching point. . Therefore, the power conversion efficiency can be further improved.

  In FIG. 13, the inverter input voltage Vdc1 is divided into three ranges. However, this is only an example, and the inverter input voltage Vdc1 may be divided into two or any number of four or more. It may be. In this case, a setting value corresponding to the number of ranges of the inverter input voltage Vdc1 may be stored in the setting table T13.

(Embodiment 7)
The seventh embodiment is characterized in that the setting unit 140 sets a setting value corresponding to the input voltage Vdc2 input from the DC power supply 3 to the DC / DC converter 1200 instead of the inverter input voltage Vdc1. Note that the circuit configuration in this embodiment is the same as that in FIG.

  In the present embodiment, the setting table T13 stores setting values corresponding to switching points according to the input voltage Vdc2 instead of the inverter input voltage Vdc1. Therefore, the set values I1, I2, and I3 are effective values of the alternating current Iout1 corresponding to the optimum switching point when the input voltage Vdc2 belongs to the ranges (1), (2), and (3), respectively. Experimentally determined values are used. The other points are the same as in the sixth embodiment. The control unit 11 monitors the input voltage Vdc2. However, the input voltage Vdc2 may be monitored by connecting a voltage sensor (not shown) in parallel with the smoothing capacitor C12.

(Embodiment 8)
The eighth embodiment is characterized in that the number of inverters to be driven is switched in accordance with the duty ratio of the PWM signal input to the DC / DC converter 1200.

  FIG. 14 is a circuit diagram of a grid-connected inverter device to which the power conversion device according to the eighth embodiment is applied. 14 is different from FIG. 12 in that the control unit 11 further includes a pulse generation unit 170, a converter control unit 180, and a carrier generation unit 190.

  Converter control unit 180 monitors input voltage Vdc2 and controls inverter input voltage Vdc1 to a DC voltage necessary for connection to system power supply 10 at a constant level. Specifically, converter control unit 180 decreases the duty command signal of DC / DC converter 1200 as input voltage Vdc2 increases. On the other hand, converter control unit 180 increases the duty command signal as input voltage Vdc2 decreases. A DC modulated wave signal can be used as the duty command signal. The carrier generation unit 190 outputs a carrier signal that is a triangular wave having a constant amplitude and a constant period to the pulse generation unit 170.

  The pulse generator 170 compares the duty command signal with the carrier signal, generates a PWM signal, and outputs the PWM signal to the gate of the switch SW12.

  The DC power supply 3 is a solar cell. Generally, when the amount of solar radiation decreases, the generated DC voltage decreases, the input voltage Vdc2 decreases, and the power supply capability decreases. In this case, the duty command value is increased to compensate for the reduced power supply capability. When the duty command value of DC / DC converter 1200 is increased, the output power of the inverter is decreased, and the alternating current output by the inverter is decreased.

  Therefore, in the present embodiment, setting unit 140 sets the duty command value corresponding to the output power at which the power conversion efficiency is reversed as the set value.

  Then, when a comparison result indicating that the duty command value of DC / DC converter 1200 is equal to or less than a predetermined set value is output from comparator 150, switching command generation unit 160 drives the two inverters. . On the other hand, when a comparison result indicating that the duty command value of DC / DC converter 1200 is greater than a predetermined set value is output from comparator 150, switching command generation unit 160 drives only one inverter. . As a result, the power conversion efficiency can be improved in a wider range of output power than in the past.

  Further, in the present embodiment, the duty command value is divided into a plurality of ranges in the setting table T13, and the optimum duty command value is stored in each range.

  Therefore, setting unit 140 sets a setting value corresponding to the duty command value output from converter control unit 180 using the setting table. Then, setting unit 140 reads the duty command value corresponding to the duty command value from setting table T13, and sets the setting value in the same manner as in the sixth embodiment.

  Thus, in this Embodiment, the output current of an inverter can be estimated from a duty command value, and the switching operation | movement according to an output current can be performed.

  When the number of inverters is N (N is an integer equal to or greater than 2), if the duty ratio of the DC / DC converter 1200 is smaller than a predetermined set value, N inverters are driven and the DC / DC converter 1200 is driven. If the duty ratio is equal to or greater than a predetermined set value, j (j is an integer of 1 to N-1) inverters are driven.

(Embodiment 9)
FIG. 15 is a circuit diagram of a grid interconnection inverter device to which the power conversion device of the ninth embodiment is applied. 15 is different from FIG. 5 in that inverters 1 and 2 are each constituted by a three-phase inverter. Further, since inverters 1 and 2 are constituted by three-phase inverters, reactors 7 and 8 include three reactors 71 to 73 and 81 to 83, respectively.

  The inverters 1 and 2 are connected in parallel with the DC power source 3. Since the inverters 1 and 2 have the same configuration, only the inverter 1 will be described. The inverter 1 includes six switches SW1 to SW6. The switches SW1 and SW4 are U-phase switches, the switches SW2 and SW5 are V-phase switches, and the switches SW3 and SW6 are W-phase switches.

  The switches SW1 to SW6 are each configured by an n-type MOSFET, but the present embodiment is not limited to this, and a p-type MOSFET may be employed, or an IGBT may be employed.

  The drains of the switches SW1, SW2, and SW3 are connected to the positive electrode of the DC power supply 3, respectively. The sources of the switches SW4, SW5, and SW6 are connected to the negative electrode of the DC power supply 3. The source of the switch SW1 is connected to the drain of the switch SW4, the source of the switch SW2 is connected to the drain of the switch SW5, and the source of the switch SW3 is connected to the drain of the switch SW6.

  A connection point u between the switches SW1 and SW4 is connected to the reactor 71, a connection point v between the switches SW2 and SW5 is connected to the reactor 72, and a connection point w between the switches SW3 and SW6 is connected to the reactor 73. In inverter 2, connection points u, v, and w are connected to reactors 81, 82, and 83, respectively.

  Reactors 71, 72, and 73 smooth the AC power output from connection points u, v, and w of inverter 1, respectively, and output sinusoidal AC power having an amplitude corresponding to the pulse width.

  Reactors 81, 82, 83 smooth the AC power output from connection points u, v, w of inverter 2, respectively, and output sinusoidal AC power having an amplitude corresponding to the pulse width.

  The current sensor 51 is provided between one end of the reactor 71 on the system power supply 10 side and the connection point K <b> 3, measures the alternating current Iout_u <b> 1 smoothed by the reactor 71, and outputs it to the control unit 11. The current sensor 52 is provided between one end of the reactor 73 on the system power supply 10 side and the connection point K <b> 4, measures the alternating current Iout_w <b> 1 smoothed by the reactor 73, and outputs it to the control unit 11.

  The current sensor 53 is provided between one end of the reactor 81 on the system power supply 10 side and the connection point K <b> 3, measures the alternating current Iout_u <b> 2 smoothed by the reactor 81, and outputs it to the control unit 11. The current sensor 54 is provided between one end of the reactor 83 on the system power supply 10 side and the connection point K <b> 4, measures the alternating current Iout_w <b> 2 smoothed by the reactor 83, and outputs it to the control unit 11.

  The connection point K3 superimposes the U-phase AC power smoothed by the reactor 71 and the U-phase AC power smoothed by the reactor 81. The connection point K5 superimposes the V-phase AC power smoothed by the reactor 72 and the V-phase AC power smoothed by the reactor 82. The connection point K4 superimposes the W-phase AC power smoothed by the reactor 73 and the W-phase AC power smoothed by the reactor 83.

  The filter capacitor 91 is connected between the terminals Tu and Tv of the system power supply 10, removes a high frequency component from the AC power between the U and V phases, and outputs it to the system power supply 10 and the load Z. The filter capacitor 92 is connected between the terminals Tv and Tw of the system power supply 10, removes a high frequency component from the AC power between the V and W phases, and outputs it to the system power supply 10 and the load Z. The filter capacitor 93 is connected between the terminals Tu and Tw of the system power supply 10, removes a high frequency component from the AC power between the U and W phases, and outputs it to the system power supply 10 and the load Z.

  A voltage sensor (not shown) for measuring an AC voltage Vout_u between the U and V phases is connected in parallel to the filter capacitor 91, and an AC voltage Vout_v for measuring the AC voltage Vout_v between the V and W phases is connected to the filter capacitor 92. A voltage sensor (not shown) is connected in parallel, and a voltage sensor (not shown) for measuring the AC voltage Vout_w between the U and W phases is connected in parallel to the filter capacitor 93.

  The load Z is connected to the terminals Tu, Tv, Tw.

  The modulation wave generator 131 generates a modulation wave signal corresponding to the inverter 1, which is a modulation wave signal for outputting a desired AC current, using the AC currents Iout_u 1, Iout_w 1 and the AC voltages Vout_u, Vout_v, Vout_w. And output to the pulse generator 111.

  The modulation wave generator 132 generates a modulation wave signal corresponding to the inverter 2, which is a modulation wave signal for outputting a desired AC current, using the AC currents Iout_u 2, Iout_w 2 and the AC voltages Vout_u, Vout_v, Vout_w. And output to the pulse generator 112.

  As in FIG. 1, the pulse generator 111 compares the modulated wave signal generated by the modulated wave generator 131 with the carrier signal generated by the carrier generator 121 and generates a PWM signal corresponding to the inverter 1. Since 1 is a three-phase inverter, a PWM signal in which the phases of the U phase, the V phase, and the W phase are shifted by 120 degrees is generated.

  Specifically, the pulse generation unit 111 is a PWM signal whose phase is shifted by 120 degrees with respect to the switches SW1, SW2, and SW3, and turns on and off the switches SW1 and SW4 in a complementary manner. Are complementarily turned on / off, and a PWM signal for complementarily turning on / off the switches SW3 and SW6 is generated.

  Similar to the pulse generator 111, the pulse generator 112 generates a PWM signal corresponding to the inverter 2. Here, the phase of the carrier signal generated by the carrier generation unit 122 is shifted by 180 degrees with respect to the carrier signal generated by the carrier generation unit 121. Therefore, an alternating current in which ripples are canceled is obtained according to the same principle as in the first embodiment.

  The carrier generation unit 121, the carrier generation unit 122, the setting unit 140, the comparator 150, and the switching command generation unit 160 are the same as those in FIG.

  The comparator 150 monitors the alternating currents Iout_u1 and Iout_w1, compares both alternating currents with the set value set by the setting unit 140, and outputs the comparison result to the switching command generation unit 160.

  When the comparison result by the comparator 150 indicates that the effective value of at least one of the alternating currents Iout_u1 and Iout_w1 is less than or equal to the set value, the switching command generation unit 160 stops driving the inverter 2 and only the inverter 1 Is output to the modulated wave generators 131 and 132. In this case, the switching command generator 160 also outputs a gate block signal to the pulse generator 112. As a result, the drive of the inverter 2 is completely stopped as in FIG.

  On the other hand, in the case where only the inverter 1 is driven, the switching command generation unit 160 indicates that the comparison result by the comparator 150 is that the effective value of at least one of the alternating currents Iout_u1 and Iout_w1 is larger than the set value. In the case of indicating that it has become, the restart instruction for restarting the drive of the inverter 2 is output to the modulation wave generation units 131 and 132, and the output of the gate block signal to the pulse generation unit 112 is stopped. Thus, inverters 1 and 2 are driven in the same manner as in FIG. The reason for comparing half of the effective value with the set value is the same as in FIG.

  As described above, in the power conversion device according to the present embodiment, even when a three-phase inverter is employed as the inverters 1 and 2, the same effects as those of the first and second embodiments can be obtained.

(Modification 1)
In the above embodiment, the number of inverters is two, but the first modification is characterized in that the number of inverters is an arbitrary number equal to or greater than N (an integer greater than or equal to 2). In the following description, the N inverters are assumed to be single-phase inverters.

  In this case, the modulation wave generation unit 130 includes N modulation wave generation units 130_1 to 130_N corresponding to the N inverters. In addition, the carrier generation unit 120 includes N carrier generation units 120_1 to 120_N corresponding to N inverters. The pulse generation unit 110 includes N pulse generation units 110_1 to 110_N corresponding to N inverters.

  When N inverters are driven, each of the carrier generation units 120_1 to 120_N generates a carrier signal whose phase is shifted by 360 degrees / N. For example, when N = 3, the carrier generation units 120_2 and 120_3 generate carrier signals whose phases are shifted by 120 degrees and 240 degrees with respect to the carrier signals generated by the carrier generation unit 120_1, respectively.

  Modulated wave generators 130_1 to 130_N monitor AC currents Iout_1 to Iout_N and AC voltage Vout output from the corresponding inverters, respectively, and generate modulated wave signals for setting AC voltage Vout to a target effective value.

  Each of the pulse generators 110_1 to 110_N compares the modulated wave signals output from the corresponding modulated wave generators 130_1 to 130_N with the carrier signals output from the corresponding carrier generators 120_1 to 120_N, and outputs the PWM signal. Generate and output to the corresponding inverter.

  Comparator 150 compares the effective value of the alternating current (here, for convenience sake, alternating current Iout1) output from one inverter that is always driven among the N inverters with a set value.

  The switching command generation unit 160 drives the first to jth inverters when the comparison result indicating that the effective value of the alternating current Iout is equal to or less than the set value is received from the comparator 150 while the N inverters are being driven. And outputs a stop instruction to stop driving the j + 1st to Nth inverters. At this time, the switching command generator 160 outputs a gate block signal to the pulse generators 110_j + 1 to 110_N. J is an integer of 1 or more and N−1 or less.

  When the effective values of the alternating currents Iout_1 to Iout_N when N inverters are driven are L, the modulation wave generators 130_1 to 130_j corresponding to the first to jth inverters have an effective value from L to N · L. A modulated wave signal raised to / j is generated. On the other hand, modulated wave generators 130_j + 1 to 130_N corresponding to the (j + 1) th to Nth inverters generate modulated wave signals whose effective values are reduced from L to 0. As a result, the alternating currents Iout_1 to Iout_j output from the first to jth inverters are superimposed to generate an alternating current Iout having an effective value of N · L and output to the system power supply 10 before and after switching. The effective value of the alternating current Iout does not change.

  When the stop instruction is output from the switching command generator 160, the carrier generators 120_1 to 120_j each generate a carrier signal whose phase is shifted by 360 degrees / j.

  When a stop instruction is output from the switching command generator 160, the pulse generators 110_1 to 110_j respectively output modulated waves whose effective values have been increased from L to N · L / j, and carrier generators 120_1 to 120_j. The output carrier signal is compared, and a PWM signal corresponding to the first to jth inverters is generated. On the other hand, each of the pulse generators 110_j + 1 to 110_N stops outputting the PWM signal.

  Here, since the phase of the carrier signal is shifted by 360 degrees / j, the ripple is canceled by superimposing the alternating currents Iout_1 to Iout_j on the same principle as in the first embodiment.

  Thus, the first to jth inverters are driven, and the driving of the j + 1st to Nth inverters is stopped. For example, if the number of inverters is five and the number of inverters to be stopped is two, the carrier signals of the first to third inverters are signals whose phases are shifted by 120 degrees.

  On the other hand, when the j / N of the effective value of the alternating current Iout1 becomes larger than the set value from the comparator 150 during the driving of the first to j-th inverters, the switching command generation unit 160 A restart instruction for restarting the drive is output, and the output of the gate block signal to the pulse generators 110_j + 1 to 110_N is stopped. Here, the reason why the effective value j / N is compared with the set value is that the set value is set based on the effective value (L) of the alternating current Iout1 when N inverters are driven. Because.

  The modulated wave generators 130_1 to 130_j that have received the restart instruction generate a modulated wave signal whose effective value is reduced from N · L / j to L. On the other hand, the modulated wave generators 130_j + 1 to 130_N that have received the restart instruction generate a modulated wave signal whose effective value is increased from 0 to L. Thereby, the effective value of the alternating current Iout output to the system power supply 10 does not change before and after switching.

  As described above, even when the number of inverters is N, the same effect as in the first and second embodiments can be obtained.

(Modification 2)
In Modification 1, a single-phase inverter is used as the inverter, but a three-phase inverter may be used.

  In the first to eighth embodiments, a three-phase inverter may be employed as the inverters 1 and 2.

(Modification 3)
Moreover, in FIG. 1 etc., the full bridge type inverter was employ | adopted as a single phase inverter, However, A half bridge type inverter may be employ | adopted.

(Modification 4)
In the second and third embodiments, the comparator 150 compares the effective value of the alternating current with the set value. However, the present invention is not limited to this, and the instantaneous value of the alternating current may be compared with the set value. FIG. 16 is a diagram illustrating a switching example of the inverters 1 and 2 when using the instantaneous value of the alternating current. In FIG. 16, the waveform of the alternating current Iout is shown, the vertical axis indicates the current, and the horizontal axis indicates the time. In FIG. 16, for example, the instantaneous value of the alternating current Iout is input to the comparator 150 from the current sensor 5 as shown in FIG.

  At time t1, switching command generation unit 160 receives a comparison result indicating that AC current Iout has reached or exceeded threshold value IH1 from comparator 150, and drives inverters 1 and 2.

  At time t2, switching command generation unit 160 receives a comparison result indicating that AC current Iout has become equal to or lower than threshold value IH1 from comparator 150, and drives only inverter 1.

  At time t <b> 3, switching command generation unit 160 receives a comparison result indicating that AC current Iout has become equal to or lower than threshold value IH <b> 2 from comparator 150, and drives inverters 1 and 2.

  At time t4, the switching command generation unit 160 receives a comparison result indicating that the alternating current Iout has become equal to or higher than the threshold value IH2 from the comparator 150, and drives only the inverter 1.

  Thereafter, the above-described control is repeated at times t5, t6,. In addition, as the threshold values IH1 and IH2, for example, values having the same absolute value and IH1> 0 and IH2 <0 may be employed, or values having different absolute values may be employed.

  In this way, in the example of FIG. 16, if the alternating current Iout is within the range of the threshold value IH2 or more and the threshold value IH1 or less, the instantaneous value of the alternating current Iout is low, so that only the inverter 1 is driven and the alternating current Iout is If it is smaller than IH2 or larger than the threshold value IH1, since the instantaneous value of the alternating current Iout is high, the inverters 1 and 2 are driven. Thereby, a switching point can be set more finely and power conversion efficiency can be improved.

  In the example of FIG. 16, the inverter is switched four times in one cycle. In this case, it is desirable that the transition period Tx described in the third and fourth embodiments be ¼ or less of one cycle of the alternating current Iout.

(Modification 5)
In the second to ninth embodiments, it has been described that the comparator 150 calculates the effective value of the alternating current. However, the current sensors 5 and 6 may calculate the effective value of the alternating current.

  The present disclosure is useful for a power conditioner that links various power generation devices such as solar cells and a system power source.

DESCRIPTION OF SYMBOLS 1, 2 Inverter 3 DC power source 4 Smoothing capacitor 5, 6 Current sensor 7, 8 Reactor 9 Filter capacitor 10 System power supply 11 Control part 12 Voltage sensor 110, 111, 112 Pulse generation part 120, 121, 122 Carrier generation part 130, 131 , 132 Modulation wave generation unit 140 Setting unit 150 Comparator 160 Switching command generation unit 170 Pulse generation unit 180 Converter control unit 190 Carrier generation unit 1200 DC / DC converter

Claims (9)

N (N is an integer of 2 or more) inverters that are connected in parallel to the power supply unit and convert the DC power supplied from the power supply unit into AC power using a switching element;
A reactor for smoothing each of the N AC powers output from the N inverters;
An output unit that superimposes N AC powers smoothed by the reactor and outputs them to a load;
A carrier generation unit for generating N carrier signals corresponding to the N inverters and having a phase shifted by 360 degrees / N;
A modulation wave generation unit for generating N modulation wave signals for outputting a predetermined alternating current corresponding to the N inverters;
The N carrier signals and N modulated wave signals corresponding to the N carrier signals are compared to generate N PWM signals corresponding to the N inverters, and the N carrier signals are generated. A pulse generator for outputting to the inverter;
A current detector that detects current output from at least one of the N currents smoothed by the reactor or the output unit;
When the current detected by the current detection unit is less than or equal to a predetermined set value, the first to jth (j is an integer not less than 1 and not more than N−1) inverters among the N inverters are driven, and the (j + 1) th A switching control unit that outputs a stop instruction to stop driving the Nth inverter,
The carrier generation unit generates j carrier signals corresponding to the first to j-th inverters whose phases are shifted by 360 degrees / j when the stop instruction is output,
When the stop instruction is output, the pulse generator generates j carrier signals corresponding to the first to j-th inverters and j modulated wave signals corresponding to the first to j-th inverters. In comparison, the power conversion device generates j PWM signals corresponding to the first to j-th inverters and outputs the PWM signals to the first to j-th inverters. When the N inverters are driven, each of the N currents smoothed by the reactor is L, and the current output from the output unit is N · L.
When the stop instruction is output, the modulation wave generator generates the j + 1 to 1st currents so that the Nj currents output from the j + 1st to 1st to Nth inverters gradually decrease from L to 0. First to first so that the modulation current signal corresponding to the N inverter is corrected and the j currents output from the first to jth inverters gradually increase from L to N · L / j. The power conversion device according to claim 1, wherein the modulation wave signal corresponding to the j inverter is corrected. When the N inverters are driven, each of the N currents smoothed by the reactor is L, and the current output from the output unit is N · L.
When the stop instruction is output, the modulated wave generating unit outputs N−j outputs from the j + 1 to Nth inverters within a certain period including a zero cross point of the AC voltage output from the output unit. The modulation wave signal corresponding to the (j + 1) th to (N) th inverters is corrected so that the current of the current decreases gradually from L to 0 or instantaneously, and j output from the first to jth inverters are corrected. The power converter according to claim 1, wherein the modulation wave signal corresponding to the first to j-th inverters is corrected so that the current increases gradually or instantaneously from L to N · L / j.   The power converter according to any one of claims 1 to 3, wherein the current detection unit detects any one of N currents smoothed by the reactor. A voltage detection unit for detecting a DC voltage output from the power supply unit;
The power converter according to any one of claims 1 to 4, further comprising: a setting unit that increases the set value as a detection voltage detected by the voltage detection unit increases. N (N is an integer of 2 or more) inverters that are connected in parallel to the power supply unit and convert the DC power supplied from the power supply unit into AC power using a switching element;
A reactor for smoothing each of the N AC powers output from the N inverters;
An output unit that superimposes N AC powers smoothed by the reactor and outputs them to a load;
A carrier generation unit for generating N carrier signals corresponding to the N inverters and having a phase shifted by 360 degrees / N;
A modulation wave generation unit for generating N modulation wave signals for outputting a predetermined alternating current corresponding to the N inverters;
The N carrier signals and N modulated wave signals corresponding to the N carrier signals are compared to generate N PWM signals corresponding to the N inverters, and the N carrier signals are generated. A pulse generator for outputting to the inverter;
A DC / DC converter connected between the power supply unit and the N inverters;
When the duty ratio of the PWM signal for controlling the DC / DC converter is greater than or equal to a predetermined duty ratio, the first to jth (j is an integer from 1 to N-1) among the N inverters A switching control unit for driving the inverter and outputting a stop instruction for stopping the driving of the j + 1st to Nth inverters,
The carrier generation unit generates j carrier signals corresponding to the first to j-th inverters whose phases are shifted by 360 degrees / j when the stop instruction is output,
When the stop instruction is output, the pulse generator generates j carrier signals corresponding to the first to j-th inverters and j modulated wave signals corresponding to the first to j-th inverters. In comparison, the power conversion device generates j PWM signals corresponding to the first to j-th inverters and outputs the PWM signals to the first to j-th inverters.   The power converter according to claim 1, wherein the current detected by the current detector is an effective value of an alternating current. The current detected by the current detector is an instantaneous value,
6. The power conversion device according to claim 1, wherein the switching control unit performs a switching operation of the inverter to be driven at least once in one cycle of the alternating current output from the output unit.   The power converter according to claim 1, wherein the N inverters are single-phase inverters or three-phase inverters.