JP2016171680A - Power conversion device, air conditioner having the same, and power conversion method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly efficient and highly reliable power conversion device etc.SOLUTION: A power conversion device 1 includes: a rectifier circuit D; a reactor L1 provided on a wiring ha which connects an AC power G to the rectifier circuit D; a smoothing capacitor C1; switching elements Q3, Q4 connected in parallel with diodes D3, D4; a current detector 11 which detects current flowing through the wiring ha; and a converter controller 18 which controls the switching elements Q3, Q4. Based on the detected value of the current detector 11, the converter controller 18 switches between synchronous rectification control to switch on/off the switching elements Q3, Q4, synchronously with the polarities of the voltage of the AC power G, and control to switch the switching element Q3 or the switching element Q4 included in a short-circuit current path through the reactor L1.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a power conversion device that converts AC voltage to DC voltage.

Trains, automobiles, air conditioners, and the like are equipped with power conversion devices (DC power supply devices) that convert AC voltage to DC voltage. And the direct-current voltage output from a power converter device is converted into the alternating voltage of a predetermined frequency with an inverter, and this alternating voltage is applied to loads, such as a motor.
In such a power conversion device, it is required to suppress harmonics in accordance with the harmonic current regulation, and to improve power conversion efficiency to save energy.

For example, Patent Document 1 describes a power conversion device that includes a rectifier circuit in which two of the diodes constituting a full-wave rectifier circuit are replaced with MOSFETs, and MOSFET drive means for driving each MOSFET. Yes.
In the technique described in Patent Document 1, one MOSFET is kept on and the other MOSFET is kept off while the voltage of the AC power supply is in a positive half cycle. In addition, during the half cycle in which the voltage of the AC power source is negative, one MOSFET is kept off and the other MOSFET is kept on.

JP 2007-110869 A

By the way, in a high load region where the power consumption of the load is large, a large current flows through the MOSFET, and the loss (that is, the amount of generated heat) increases in proportion to the square of the current. Further, the MOSFET has a characteristic that the on-resistance increases as the temperature increases.
In the technique described in Patent Document 1, on / off of the MOSFET is uniformly controlled regardless of the magnitude of the current flowing through the MOSFET. Therefore, there is a possibility that the temperature rise of the MOSFET and the increase of the on-resistance may cause a decrease in energy efficiency or the destruction of the element of the MOSFET.

  Then, this invention makes it a subject to provide a highly efficient and highly reliable power converter device etc.

In order to solve the above-described problems, the present invention provides a synchronous rectification control in which a current is passed through a smoothing capacitor by turning on / off a switching element in synchronization with the polarity of the voltage of an AC power supply, and a short circuit via a reactor. The control for switching the switching element included in the current path is switched based on the detection value of the load detection unit.
Details will be described in an embodiment for carrying out the invention.

  ADVANTAGE OF THE INVENTION According to this invention, a highly efficient and highly reliable power converter device etc. can be provided.

It is a lineblock diagram of the power converter concerning a 1st embodiment of the present invention. It is the table | surface which put together the correspondence of the operation area | region, the load state, the control mode, and the main objective. It is explanatory drawing which shows the magnitude relationship of each load state. It is a flowchart which shows the process which a power converter device performs. It is explanatory drawing which shows the flow of an electric current when a power supply voltage is contained in a positive half cycle at the time of power activation. It is explanatory drawing which shows the time change of the power supply voltage at the time of synchronous rectification control (at the time of light load (intermediate)), a circuit current, and the drive pulse of a switching element. It is explanatory drawing which shows the flow of an electric current when a power supply voltage is contained in a positive half cycle at the time of synchronous rectification control (at the time of light load (intermediate)). It is explanatory drawing which shows the time change of the power supply voltage, circuit current, and the drive pulse of a switching element at the time of synchronous rectification and circuit short circuit control (at the time of light load (rated), medium load, and high load). It is explanatory drawing which shows the flow of an electric current when a power supply voltage is contained in a positive half cycle at the time of synchronous rectification and circuit short circuit control (light load (rated), medium load, and high load). It is explanatory drawing which shows the time change of the power supply voltage at the time of circuit short circuit control (1st protection area), a circuit current, and the drive pulse of a switching element. It is explanatory drawing which shows the flow of an electric current when a power supply voltage is contained in a positive half cycle at the time of circuit short-circuit control (1st protection area). It is a block diagram of the power converter device which concerns on 2nd Embodiment of this invention. It is explanatory drawing which shows the flow of an electric current when a power supply voltage is contained in a positive half cycle at the time of power activation. It is explanatory drawing which shows the flow of an electric current when a power supply voltage is contained in a positive half cycle at the time of synchronous rectification control. It is explanatory drawing which shows the flow of an electric current when a power supply voltage is contained in a positive half cycle at the time of synchronous rectification and circuit short circuit control. It is explanatory drawing which shows the flow of an electric current when a power supply voltage is contained in a positive half cycle at the time of circuit short-circuit control. It is a block diagram of the power converter device which concerns on 3rd Embodiment of this invention. It is explanatory drawing which shows the relationship between the temperature of a switching element, and the threshold value of an electric current. It is a flowchart which shows the process which a power converter device performs. It is a block diagram of the power converter device which concerns on 4th Embodiment of this invention. It is explanatory drawing which shows the flow of an electric current when a power supply voltage is contained in a positive half cycle at the time of power activation. It is explanatory drawing which shows the flow of an electric current when a power supply voltage is contained in a negative half cycle at the time of power activation. It is explanatory drawing which shows the flow of an electric current when a power supply voltage is contained in a positive half cycle at the time of synchronous rectification control (at the time of light load (intermediate)). It is explanatory drawing which shows the flow of an electric current when a power supply voltage is contained in a negative half cycle at the time of synchronous rectification control (at the time of light load (intermediate)). It is explanatory drawing which shows the flow of an electric current when a power supply voltage is contained in a positive half cycle at the time of switching control (at the time of light load (rated), medium load, and high load). It is explanatory drawing which shows the flow of an electric current when a power supply voltage is contained in a negative half cycle at the time of switching control (at the time of light load (rated), medium load, and high load). It is explanatory drawing which shows the operation principle of partial switching control. It is explanatory drawing of high-speed switching control, (a) is explanatory drawing which shows the relationship of the duty of each switching element, (b) It is explanatory drawing which shows the relationship between the instantaneous value of a power supply voltage, and the instantaneous value of a circuit current. (C) is explanatory drawing which shows the duty of a switching element in the case where the delay part of the current phase by a reactor is not considered in the half cycle when a power supply voltage is positive, and the case where the delay part of a current phase is considered. It is a block diagram of the air conditioner which concerns on 5th Embodiment of this invention.

<< First Embodiment >>
<Configuration of power converter>
FIG. 1 is a configuration diagram of a power conversion device 1 according to the first embodiment.
The power converter 1 is a converter that converts an AC voltage supplied from an AC power source G into a DC voltage and outputs the DC voltage to a load H (an inverter, a motor, or the like). The power conversion device 1 has an input side connected to the AC power supply G and an output side connected to the load H.

  As shown in FIG. 1, the power conversion device 1 includes a rectifier circuit D, a reactor L1, a smoothing capacitor C1, switching elements Q3 and Q4, a current detection unit 11, a current comparison unit 12, and an AC voltage detection unit. 13, a zero cross determination unit 14, a load detection unit 15, a load comparison unit 16, a DC voltage detection unit 17, and a converter control unit 18.

  The rectifier circuit D is a diode bridge circuit that full-wave rectifies the current flowing from the AC power supply G through the wirings ha and hb. The rectifier circuit D has four diodes D1 to D4 connected in a bridge shape.

The anode of the diode D1 is connected to the cathode of the diode D3, and the connection point P1 is connected to the AC power supply G via the wiring ha. The wiring ha has one end connected to the AC power source G and the other end connected to the connection point P1.
The anode of the diode D2 is connected to the cathode of the diode D4, and the connection point P2 is connected to the AC power source G via the wiring hb. The wiring hb has one end connected to the AC power supply G and the other end connected to the connection point P2.

The reactor L1 stores electric power supplied from the AC power source G as energy, and further boosts the energy by releasing this energy. The reactor L1 is provided on the wiring ha that connects the AC power supply G and the rectifier circuit D.
The smoothing capacitor C1 smoothes the voltage applied from the rectifier circuit D to obtain a DC voltage, and is connected to the output side of the rectifier circuit D via the wirings hc and hd. That is, the smoothing capacitor C1 has a positive side connected to the cathodes of the diodes D1 and D2, and a negative side connected to the anodes of the diodes D3 and D4.

  The switching elements Q3 and Q4 are, for example, MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors), and are controlled to be turned on / off by a command from the converter control unit 18 described later. Note that the use of MOSFETs as the switching elements Q3 and Q4 has advantages in that power consumption can be reduced and switching can be performed at high speed.

One switching element Q3 is connected in parallel to the diode D3. More specifically, the source of the switching element Q3 (MOSFET) is connected to the anode of the diode D3, and the drain is connected to the cathode of the diode D3.
The other switching element Q4 is connected in parallel to the diode D4 (the connection relationship with the diode D4 is the same as that of the switching element Q3).

  The switching element Q3 has a parasitic diode D31 therein. The parasitic diode D31 is a pn junction portion that exists between the source and drain of the switching element Q3 (MOSFET). Similarly, the switching element Q4 has a parasitic diode D41 therein.

  As diode D3 connected in parallel to switching element Q3, a diode whose forward voltage is smaller than the forward voltage of parasitic diode D31 of switching element Q3 is preferably selected. Thereby, when the switching element Q3 is turned off, the current flowing through the parasitic diode D31 having a large loss can be reduced, and the heat generation of the switching element Q3 can be suppressed. The same can be said for the diode D4 connected in parallel to the switching element Q4.

The current detection unit 11 (load detection unit) detects a current (load) flowing through the wirings ha and hb, and is provided in the wiring hb. Although FIG. 1 shows the case where a transformer is used as the current detection unit 11, a shunt resistor, a Hall element, or the like may be used.
The current comparison unit 12 is a comparator (comparator) that compares the detection value of the current detection unit 11 with a predetermined threshold value. The threshold value to be compared with the detection value of the current detection unit 11 will be described later. Current comparison unit 12 outputs the comparison result to converter control unit 18.

The AC voltage detector 13 detects an AC voltage applied from the AC power supply G, and is connected to the wirings ha and hb. The AC voltage detection unit 13 outputs the detected value to the zero cross determination unit 14.
The zero cross determination unit 14 has a function of determining whether the value of the AC voltage detected by the AC voltage detection unit 13 is switched (that is, whether the zero cross point has been reached). For example, the zero-cross determination unit 14 outputs a signal “1” to the converter control unit 18 during a period in which the power supply voltage is positive, and a signal “0” to the converter control unit 18 during a period in which the power supply voltage is negative. Is output.

  The load detection unit 15 is a shunt resistor, for example, and has a function of detecting a current (load) supplied to the load H. If the load H is a motor, the load detection unit 15 may detect the rotational speed of the motor and estimate the current value (load) from this rotational speed. The load detection unit 15 outputs the detected value to the load comparison unit 16.

  The load comparison unit 16 is a comparator (comparator) that compares the detection value of the load detection unit 15 with a predetermined threshold value. The threshold value to be compared with the detection value of the load detection unit 15 will be described later. The load comparison unit 16 outputs the comparison result to the converter control unit 18.

  The DC voltage detector 17 detects the voltage (DC voltage) of the smoothing capacitor C1, and its positive side is connected to the wiring hc and its negative side is connected to the wiring hd. DC voltage detection unit 17 outputs the detected value to converter control unit 18. Note that the detection value of the DC voltage detection unit 17 is used to determine whether or not the voltage value applied to the load H has reached a predetermined target value.

  The converter control unit 18 is, for example, a microcomputer (not shown), reads a program stored in a ROM (Read Only Memory) and develops it in a RAM (Random Access Memory), and a CPU (Central Processing Unit) Various processes are executed. Converter control unit 18 controls on / off of switching elements Q <b> 1 to Q <b> 4 based on information input from current comparison unit 12, zero cross determination unit 14, load comparison unit 16, and DC voltage detection unit 17. The processing executed by converter control unit 18 will be described later.

<Control mode of power converter>
FIG. 2 is a table summarizing the correspondence relationship between the operation area, the load state, the control mode, and the main purpose. The operation region of the power conversion device 1 is divided into a “steady region” and a “protection region” based on the size of the load (for example, the detection value of the current detection unit 11: see FIG. 1). Here, the “steady region” is an operation region when a device including the power conversion device 1 is operating normally. The “protection area” is an operation area when the current flowing through the power conversion device 1 becomes abnormally large due to load fluctuation or the like. Next, the load state shown in FIG. 2 will be described with reference to FIG.

FIG. 3 is an explanatory diagram showing the magnitude relationship of each load state. As shown in FIG. 3, the load is greater in the “protection area” than in the “steady area”, and each area is divided by a threshold value I2 (second threshold value).
The “steady region” is divided into “light load (intermediate)”, “light load (rated)”, “medium load”, and “high load” based on the magnitude of the load. Although not shown in FIG. 3, the “steady region” also includes “at power-on” (see FIG. 2), which is a transient load state immediately after power-on.
As shown in FIG. 3, the load increases in the order of “light load (intermediate)”, “light load (rated)”, “medium load”, and “high load”. “Light load (rated)” is divided by a threshold value I1 (first threshold value).

  Incidentally, “light load (rated)”, “medium load”, and “high load” are actually divided by threshold values and fine control is performed according to the load state. Assume that the region is greater than or equal to the threshold value I1 and less than the threshold value I2.

2 is a transient load state immediately after the power is turned on, as described above, and the switching elements Q3 and Q4 (see FIG. 1) are in the off state.
“Light load (intermediate)” is an area where the load is relatively small, and is also called an intermediate area. By the way, in air conditioners (room air conditioners), the low loss and high efficiency of this “light load (intermediate)” greatly affect the improvement of APF (Annual Performance Factor). In the present embodiment, synchronous rectification control is performed at “light load (intermediate)” to increase the efficiency of the power conversion device 1. The synchronous rectification control will be described later.

“Light load (rated)” is a region where the load is relatively large, and is also called a rated region. The operating efficiency at this “light load (rated)” also greatly affects the APF of the air conditioner, as with the above “light load (intermediate)”.
“Medium load” and “High load” are regions where the load is larger than “Light load (rated)”. In particular, in the “high load” region, the output is maximized within the range in which the power conversion device 1 is normally driven.
In the “light load (rated)”, “medium load”, and “high load” regions, synchronous rectification and short circuit control are performed mainly for high-efficiency operation, harmonic suppression, and boosting. The synchronous rectification / circuit short-circuit control will be described later.

The “first protection region” is a load state when the current flowing in the circuit becomes abnormally large due to load fluctuation or the like. When the magnitude of the load is included in the “first protection region”, the circuit short-circuit control is executed. Circuit short-circuit control will be described later.
The “second protection area” is an area having a larger load than the “first protection area”. That is, the “second protection region” is a case where the temperature of the switching elements Q3 and Q4 does not decrease even when the circuit short-circuit control is performed in the “first protection region”, or the current does not settle and the current further increases. Load condition. In this case, the load H (motor) is decelerated or stopped in order to prevent the switching elements Q3 and Q4 from being destroyed.
As shown in FIG. 3, the “first protection area” and the “second protection area” are separated by a threshold value I3 (third threshold value).

Note that the number of threshold values (three threshold values I1, I2, and I3 in FIG. 3) and the magnitude of the threshold values are appropriately set based on prior experiments and simulations.
Further, for the determination of the load state, the detection value of the current detection unit 11 (see FIG. 1) may be used, or the detection value of the load detection unit 15 (see FIG. 1) may be used. For example, when the load H (see FIG. 1) includes an inverter and a motor, the current value detected by the load detection unit 15, the rotational speed of the motor, and the like are detected as the load. Then, the load comparison unit 16 (see FIG. 1) specifies which of the regions shown in FIG. 3 includes this load.
Below, the case where a load state (refer FIG. 2) is specified based on the detected value of the electric current detection part 11 (refer FIG. 1) as an example is demonstrated.

<Operation of power converter>
FIG. 4 is a flowchart illustrating processing executed by the power conversion device 1.
In step S101, the power conversion device 1 determines whether or not a power-on command is input from the outside (for example, a remote controller). When a power-on command is input (S101: Yes), the process of the power conversion device 1 proceeds to step S102. On the other hand, when the power-on command is not input (S101: No), the power conversion apparatus 1 repeats the process of step S101.
In step S102, the power conversion apparatus 1 performs power-on.

(1. When power is turned on)
FIG. 5 is an explanatory diagram showing the flow of current when the power supply voltage is included in the positive half cycle when the power is turned on. Since no drive signal is input to the switching elements Q3 and Q4 at the moment of turning on the power, the switching elements Q3 and Q4 are in the off state. Further, since the electric charge is not charged in the smoothing capacitor C1 before the power is turned on, an inrush current flows at the moment when the power is turned on. It is preferable to select the switching elements Q3 and Q4 with a sufficient current capacity so that element breakdown does not occur due to this inrush current.

  During the period of the positive half cycle of the power supply voltage, a current flows in the direction indicated by the arrow in FIG. That is, current flows in the order of AC power supply G → reactor L1 → diode D1 → smoothing capacitor C1 → diode D4 and switching element Q4 (parasitic diode D41) → AC power supply G. The current from the negative side of the smoothing capacitor C1 is shunted to the diode D4 and the parasitic diode D41.

In step S <b> 103 of FIG. 4, the power conversion device 1 reads the detection value I (load) of the current detection unit 11 by the current comparison unit 12.
In step S104, the power converter 1 determines whether or not the detection value I read in step S103 is less than a threshold value I2 (second threshold value). That is, the power converter 1 determines whether or not the detected current value I is included in the “steady region” (see FIG. 3).

When the input current is less than the threshold value I2 (S104: Yes), the process of the power conversion device 1 proceeds to step S105.
In step S105, the power converter 1 determines whether or not the detection value I read in step S103 is less than the threshold value I1 (first threshold value) by the current comparison unit 12. That is, the power converter 1 determines whether or not the detected current value I is included in the region of “light load (intermediate)” (see FIG. 3).

When the detection value I is less than the threshold value I1 (S105: Yes), the process of the power conversion device 1 proceeds to step S106.
In step S <b> 106, the power conversion device 1 performs synchronous rectification control by the converter control unit 18. Here, the synchronous rectification control is a control in which a current is passed through the smoothing capacitor C1 by turning on / off the switching elements Q3 and Q4 in synchronization with the polarity of the voltage of the AC power supply G.

(2. Synchronous rectification control)
FIG. 6 is an explanatory diagram showing temporal changes in the power supply voltage, the circuit current flowing through the wirings ha and hb, and the driving pulses of the switching elements Q3 and Q4 during synchronous rectification control (light load (intermediate)).
During the period of the positive half cycle of the power supply voltage (see FIG. 6A), converter control unit 18 turns off switching element Q3 (see FIG. 6C) and turns on switching element Q4 (see FIG. 6C). (Refer FIG.6 (d)). In the period of the negative half cycle of the power supply voltage, the switching elements Q3 and Q4 are switched on / off. Thus, switching elements Q3 and Q4 are alternately turned on / off in synchronization with the zero cross point of the power supply voltage.
Incidentally, the polarity (positive / negative) of the voltage of the AC power supply G is determined by the zero cross determination unit 14.

  FIG. 7 is an explanatory diagram showing the flow of current when the power supply voltage is included in the positive half cycle during synchronous rectification control (light load (intermediate)). As indicated by an arrow in FIG. 7, current flows in the order of AC power supply G → reactor L1 → diode D1 → smoothing capacitor C1 → switching element Q4 → AC power supply G in the period of the positive half cycle of the power supply voltage.

  Although the switching element Q4 and the diode D4 are connected in parallel, when the switching element Q4 is turned on, a current flows to the switching element Q4 side where the voltage drop (voltage drop) is small. In other words, since almost no current flows through the diode D4 having a large voltage drop, it is possible to achieve low loss and high efficiency.

  If the reactor L1 (see FIG. 7) is not provided, the current flows only during a short period in which the AC voltage exceeds the voltage of the smoothing capacitor C1 (see FIG. 7). The rate is lowered. On the other hand, in this embodiment, by providing the reactor L1, as shown in FIG.6 (b), an energization area can be extended and a power factor can be improved.

After performing the synchronous rectification control in step S106 of FIG. 4, the process of the power converter 1 proceeds to step S107. In step S107, the power conversion apparatus 1 determines whether or not a stop command is input from the outside (for example, a remote controller).
When a stop command is input from the outside (S107: Yes), the power conversion device 1 stops the supply of DC power (S108) and ends the process (END). On the other hand, when the stop command is not input from the outside (S107: No), the process of the power converter device 1 returns to step S103.

When the detected current value I is greater than or equal to the threshold value I1 in step S105 (S105: No, I1 ≦ I <I2), that is, the detected current value I is “light load (rated)”, “medium load”, And “high load” (see FIG. 3), the process of the power conversion apparatus 1 proceeds to step S109.
In step S <b> 109, the power conversion apparatus 1 performs synchronous rectification / circuit short-circuit control by the converter control unit 18. Here, the synchronous rectification / circuit short-circuit control is control in which one of the switching elements Q3 and Q4 included in the short-circuit current path (see FIG. 9) via the reactor L1 is turned on and the other is switched. The “short-circuit current” is a current that flows from the AC power supply G without passing through the smoothing capacitor C1 and returns to the AC power supply G.

(3. Synchronous rectification and short circuit control)
FIG. 8 shows the power supply voltage, the circuit current flowing through the wirings ha, hb, etc., and the drive pulse time of the switching elements Q3, Q4 at the time of synchronous rectification / circuit short-circuit control (light load (rated), medium load, high load). It is explanatory drawing which shows a change. In the synchronous rectification / circuit short-circuit control, the switching elements Q3 and Q4 are alternately switched (see FIGS. 8C and 8D), and the above-described synchronous rectification control (see FIGS. 6C and 6D). ))).

During the period of the positive half cycle of the power supply voltage (see FIG. 8A), the converter control unit 18 switches on / off the switching element Q3 by a predetermined number of times and a predetermined pulse width (see FIG. 8C). ), The switching element Q4 is turned on (see FIG. 8D).
Further, during the period of the half cycle in which the power supply voltage is negative (see FIG. 8A), converter control unit 18 turns on switching element Q3 (see FIG. 8C) and switches switching element Q4 (see FIG. 8C). (Refer FIG.8 (d)).

  In the present embodiment, as an example, a case where switching is performed by repeatedly turning on / off twice immediately after the positive / negative of the power supply voltage is switched (see FIGS. 8C and 8D) is shown. The number of times can be set as appropriate.

FIG. 9 is an explanatory diagram showing the flow of current when the power supply voltage is included in the positive half cycle during synchronous rectification / circuit short-circuit control (light load (rated), medium load, and high load).
When the switching element Q3 is in the ON state during the positive half cycle period of the power supply voltage (see FIG. 8C), the power factor correction current Is (short circuit current) indicated by the arrow in FIG. 9 flows. That is, the power factor correction current Is flows in the order of AC power supply G → reactor L1 → switching element Q3 → switching element Q4 → AC power supply G.

As the power factor correction current Is flows in this way, the degree of distortion of the current waveform can be reduced, and the current waveform can be made closer to a sine wave (see FIG. 8B). That is, the power factor of the power converter 1 can be improved. Moreover, the harmonic contained in a circuit current can be suppressed by making a current waveform close to a sine wave.
Note that the phase of the circuit current can be adjusted by adjusting the delay at the time of switching (delay time from switching between positive and negative to the start of switching) and the on-time.

Further, the DC voltage (the voltage of the smoothing capacitor C1) can be boosted by the power factor correction current Is flowing through the reactor L1 and the switching elements Q3 and Q4. When the inductance of the reactor L1 and Ls, if power factor correction current Is flows through the reactor L1, the reactor L1 is stored the energy represented by _{P L = 1/2 * Ls} * Is 2.
For example, during the period of the positive half cycle of the power supply voltage, by turning on the switching elements Q3 and Q4, the power factor correction current Is flows and energy is stored in the reactor L1. Thereafter, when switching element Q3 is turned off, a current flows through smoothing capacitor C1 due to the energy stored in reactor L1, and the DC voltage of smoothing capacitor C1 is boosted.

  Thus, the power factor can be improved, the harmonics can be suppressed, and the voltage can be boosted by the synchronous rectification / circuit short-circuit control. Further, since the switching element Q4 is kept in the ON state during the period of the positive half cycle of the power supply voltage (see FIG. 8D), the current flows to the switching element Q4 bypassing the diode D4. Therefore, a large loss does not occur in the diode D4, and the efficiency of the power conversion device 1 can be increased.

Returning again to FIG. 4, the description will be continued. After performing synchronous rectification and circuit short-circuit control in step S109, the process of the power converter 1 proceeds to step S107.
When the detected current value I is greater than or equal to the threshold value I2 in step S104 (S104: No), that is, when the detected current value I is included in the “protection area” (see FIG. 3), The process proceeds to step S110.

  In step S110, the power converter 1 determines whether the current detection value I is less than the threshold I3 (third threshold) by the current comparison unit 12, that is, the current detection value I is “first protection region” ( It is determined whether it is included in FIG. When the detected current value I is less than the threshold value I3 (S110: Yes, I2 ≦ I <I3), the processing of the power conversion device 1 proceeds to step S111. On the other hand, when the detected current value I is equal to or greater than the threshold value I3 (S110: No), the processing of the power conversion device 1 proceeds to step S113 described later.

  In step S <b> 111, the power conversion device 1 performs circuit short-circuit control by the converter control unit 18. Here, the circuit short-circuit control is control in which one of the switching elements Q3 and Q4 included in the short-circuit current path (see FIG. 11) via the reactor L1 is turned off and the other is switched.

(4. Short circuit control)
FIG. 10 is an explanatory diagram showing temporal changes in the power supply voltage, the circuit current flowing through the wirings ha and hb, and the drive pulses of the switching elements Q3 and Q4 during the circuit short-circuit control (first protection region). The switching element Q4 is turned off in the positive half cycle of the power supply voltage (see FIG. 10D), and the switching element Q3 is turned off in the negative half cycle (see FIG. 10C). However, this is different from the case of synchronous rectification / circuit short-circuit control (see FIGS. 8C and 8D).

During the period of the positive half cycle of the power supply voltage (see FIG. 10A), the converter control unit 18 switches on / off the switching element Q3 by a predetermined number of times and a predetermined pulse width (see FIG. 10C). ), And the switching element Q4 is turned off (see FIG. 10D).
Further, during the period of the half cycle in which the power supply voltage is negative (see FIG. 10A), converter control unit 18 turns off switching element Q3 (see FIG. 10C) and switches switching element Q4 (see FIG. 10C). (Refer FIG.10 (d)).

  FIG. 11 is an explanatory diagram showing a current flow when the power supply voltage is included in the positive half cycle during the circuit short-circuit control (first protection region). During the period of the positive half cycle of the power supply voltage, when the switching element Q3 is on (see FIG. 10C), a current (short-circuit current) flows in the direction indicated by the arrow in FIG. That is, current flows in the order of AC power supply G → reactor L1 → switching element Q3 → diode D4 and switching element Q4 (parasitic diode D41) → AC power supply G.

  Note that MOSFETs (switching elements Q3 and Q4) have higher on-resistance as the temperature rises. Further, in the “first protection region” (see FIG. 3) where a large current flows in the circuit, the switching elements Q3 and Q4 tend to generate heat. If a large current flows through the switching elements Q3 and Q4, the heat generation of the switching elements Q3 and Q4 and the increase in on-resistance may cause a thermal runaway.

  Therefore, in this embodiment, in the “first protection region” (see FIG. 3) in which a large current flows in the circuit, only the circuit short-circuit control is performed without performing the synchronous rectification control. Thereby, the steady current flowing through the switching elements Q3 and Q4 can be reduced, and the heat generation of the switching elements Q3 and Q4 can be suppressed. Further, as shown in FIG. 10B, the circuit current can be made close to a sine wave by the above switching, and the DC voltage of the smoothing capacitor C1 can be boosted.

  In step S112 of FIG. 4, the power conversion device 1 determines whether or not the detection value I of the current detection unit 11 is less than the threshold value I2, that is, the current detection value I is “steady region” (step S111). (See FIG. 3). When the detected current value I is less than the threshold value I2 (S112: Yes), the process of the power conversion device 1 proceeds to step S105. On the other hand, when the detected current value I is greater than or equal to the threshold value I2 (S112: No), the process of the power conversion apparatus 1 proceeds to step S113.

  In step S113, the power converter 1 performs protection control. For example, when the load is a motor, the power conversion device 1 decelerates or stops the motor. Although not shown in FIG. 4, for example, in step S <b> 113, the power conversion device 1 decelerates the motor, and if the current does not decrease even after the motor decelerates, the motor is stopped. Further, when the current decreases due to the above-described deceleration, the process proceeds to step S111 and the circuit short-circuit control is performed.

<Effect>
According to the present embodiment, in the “light load (intermediate)” region where the current flowing through the circuit is small (S105: Yes), synchronous rectification control is performed to actively flow current through the switching elements Q3 and Q4 (S106). ), A large loss can be avoided in the diodes D3 and D4. Therefore, high efficiency of the power conversion device 1 can be achieved.

  Further, in the regions of “light load (rated)”, “medium load”, and “high load” where the current flowing through the circuit is relatively large (S105: No), by performing synchronous rectification / circuit short-circuit control (S109), While improving a power factor, a harmonic can be suppressed and further pressure | voltage rise can be performed.

Further, in the “first protection region” where the current flowing through the circuit is very large (S110: Yes), the circuit can be boosted while suppressing the heat generation of the switching elements Q3 and Q4 by performing the circuit short-circuit control (S111). .
Further, if the current value does not become small even when the deceleration operation is performed (S110: No, S112: No), the protection elements (S113) can surely prevent the switching elements Q3 and Q4 from being destroyed.

  Thus, in this embodiment, the efficiency of the power conversion device 1 can be improved by selectively executing the control modes of the switching elements Q3 and Q4 according to the load state (the magnitude of the current value). At the same time, the reliability can be improved.

<< Second Embodiment >>
The second embodiment is different from the first embodiment in that switching elements Q1 and Q2 (see FIG. 12) are added, but the other configurations are the same as those of the first embodiment. Further, the flow of processing executed by the power conversion device 1A (see FIG. 4) is the same as that in the first embodiment. Therefore, a different part from 1st Embodiment is demonstrated and description is abbreviate | omitted about the overlapping part.

FIG. 12 is a configuration diagram of a power conversion device 1A according to the second embodiment.
The power conversion device 1A includes switching elements Q1 and Q2 (for example, MOSFETs) in addition to the configuration described in the first embodiment. As shown in FIG. 12, the switching element Q1 is connected in parallel to the diode D1. More specifically, the source of the switching element Q1 (MOSFET) is connected to the anode of the diode D1, and the drain is connected to the cathode of the diode D1.
The switching element Q2 is connected in parallel to the diode D2 (the connection relationship with the diode D2 is the same as that of the switching element Q1).

  Next, the current flow in the synchronous rectification control, the synchronous rectification / circuit short-circuit control, and the circuit short-circuit control when the power is turned on will be described.

(1. When power is turned on)
FIG. 13 is an explanatory diagram showing the flow of current when the power supply voltage is included in the positive half cycle when the power is turned on. When the power is turned on (S102: see FIG. 4), the switching elements Q1 to Q4 are all in the off state. In the period of the positive half cycle of the power supply voltage, AC power supply G → reactor L1 → diode D1 and switching element Q1 (parasitic diode D11) → smoothing capacitor C1 → diode D4 and switching element Q4 (parasitic diode D41) → AC power supply G Current flows sequentially. The description of the period of the half cycle in which the power supply voltage is negative is omitted.

(2. Synchronous rectification control)
FIG. 14 is an explanatory diagram showing the flow of current when the power supply voltage is included in the positive half cycle during synchronous rectification control. When performing synchronous rectification control (S106: refer to FIG. 4), converter control unit 18 controls switching elements Q1 to Q4 as follows. That is, converter control unit 18 turns on switching elements Q1 and Q4 and turns off switching elements Q2 and Q3 during the period of a half cycle in which the power supply voltage is positive. Then, as shown in FIG. 14, a current flows in the order of AC power supply G → reactor L1 → switching element Q1 → smoothing capacitor C1 → switching element Q4 → AC power supply G.
In the period of a half cycle in which the power supply voltage is negative, switching elements Q2 and Q3 are turned on, and switching elements Q1 and Q4 are turned off.

  When synchronous rectification control is performed in this way, a current flows through the switching elements Q1 to Q4, and a current hardly flows through the diodes D1 to D4. In particular, during the synchronous rectification control as in the first embodiment (see FIG. 7), current does not flow through the diode D1 having a large loss, but current flows through the switching element Q1 (see FIG. 14). Therefore, the loss and efficiency can be further reduced as compared with the first embodiment.

(3. Synchronous rectification and short circuit control)
FIG. 15 is an explanatory diagram showing a current flow when the power supply voltage is included in the positive half cycle during the synchronous rectification / circuit short-circuit control. When performing synchronous rectification / circuit short-circuit control (S109: see FIG. 4), the converter control unit 18 controls the switching elements Q1 to Q4 as follows. In other words, the converter control unit 18 switches the switching element Q3 at a predetermined number of times and with a predetermined pulse width during the positive half cycle of the power supply voltage, turns on the switching element Q4, and turns off the switching elements Q1 and Q2. To do. Then, when switching element Q3 is on, a current (short-circuit current) flows in the order of AC power supply G → reactor L1 → switching element Q3 → switching element Q4 → AC power supply G.

Note that, during the half cycle in which the power supply voltage is negative, the switching element Q3 is turned on, the switching element Q4 is switched, and the switching elements Q1, Q2 are turned off.
By performing synchronous rectification / circuit short-circuit control in this way, it is possible to improve power factor, suppress harmonics, and boost voltage as described in the first embodiment.

(4. Short circuit control)
FIG. 16 is an explanatory diagram showing the flow of current when the power supply voltage is included in the positive half cycle during circuit short-circuit control. When performing the circuit short-circuit control (S111: see FIG. 4), the converter control unit 18 controls the switching elements Q1 to Q4 as follows. That is, converter control unit 18 switches switching element Q3 at a predetermined number of times and with a predetermined pulse width, and turns off switching elements Q1, Q2, and Q4 during a period in which the power supply voltage is a positive half cycle. Then, when switching element Q3 is turned on, current flows in the order of AC power supply G → reactor L1 → switching element Q3 → switching element Q4 (parasitic diode D41) → AC power supply G as shown in FIG.

Note that, in the period of a half cycle in which the power supply voltage is negative, the switching elements Q1, Q2, and Q3 are turned off, and the switching element Q4 is switched.
By performing the circuit short-circuit control in this way, as described in the first embodiment, it is possible to suppress the heat generation of the switching elements Q1 to Q4 while boosting the DC voltage of the smoothing capacitor C1.

<Effect>
According to the present embodiment, it is possible to increase the efficiency of the power conversion device 1A by selectively executing the control modes of the switching elements Q1 to Q4 according to the load state (current value magnitude). , Can increase its reliability.
In the synchronous rectification control, no current flows through the diodes D1 to D4 having a large loss, and a current flows through the switching elements Q1 to Q4 having a small loss. Thereby, the loss in the circuit can be suppressed, and the energy efficiency can be further increased as compared with the first embodiment.

«Third embodiment»
The third embodiment is different from the first embodiment in that the power conversion device 1B (see FIG. 17) includes the temperature detection units T3 and T4 and the storage unit 19, but the rest is the same as the first embodiment. is there. Therefore, a different part from 1st Embodiment is demonstrated and description is abbreviate | omitted about the overlapping part.

FIG. 17 is a configuration diagram of a power conversion device 1B according to the third embodiment.
The power conversion device 1B includes temperature detection units T3 and T4 and a storage unit 19 in addition to the configuration described in the first embodiment.
The temperature detector T3 detects the temperature of the switching element Q3. For example, the temperature detection unit T3 detects the temperature of a container (not shown) in which the switching element Q3 is stored as the temperature of the switching element Q3. It should be noted that the temperature of the radiating fin (not shown) installed in the switching element Q3 and the temperature around the switching element Q3 may be indirectly detected as the temperature of the switching element Q3. The temperature detection unit T3 outputs the detected value to the current comparison unit 12.
Similarly, the temperature detection unit T4 detects the temperature of the switching element Q4 and outputs the detected value to the current comparison unit 12.

  The storage unit 19 stores information (see FIG. 18) indicating the correspondence between the temperatures of the switching elements Q3 and Q4 and the thresholds I21 and I31 related to current. As the storage unit 19, a semiconductor storage device, a magnetic disk device, an optical disk device, or the like can be used.

  FIG. 18 is an explanatory diagram showing the relationship between the temperature of the switching elements Q3 and Q4 and the threshold value of the circuit current. The horizontal axis in FIG. 18 represents the temperatures (element temperatures) of the switching elements Q3 and Q4 detected by the temperature detectors T3 and T4. The vertical axis represents the circuit current detected by the current detection unit 11.

The threshold value I21 (second threshold value) is a threshold value that divides the “steady region” (see FIG. 2) described in the first embodiment and the “first protection region” (see FIG. 2).
The threshold value I31 (third threshold value) is a threshold value that divides the “first protection region” (see FIG. 2) described in the first embodiment and the second protection region (see FIG. 2). As shown in FIG. 18, at each temperature, the threshold value I31 is set to a value larger than the threshold value I21.

As shown in FIG. 18, the threshold value I21 and the threshold value I31 are set such that each threshold value decreases as the temperature of the switching elements Q3 and Q4 increases. This is because the on-resistance of the switching elements Q3 and Q4 (MOSFET) changes in a positive characteristic with respect to the temperature, and the higher the temperature of the switching elements Q3 and Q4, the greater the amount of heat generation and the more likely the thermal runaway occurs. is there.
Note that the information shown in FIG. 18 is created by a prior experiment or simulation and stored in the storage unit 19 in advance. Note that the thresholds I21 and I31 may be specified as a function related to temperature, or may be stored in the storage unit 19 as a map.

  The current comparison unit 12B illustrated in FIG. 17 compares the threshold value corresponding to the temperature of the switching elements Q3 and Q4 input from the temperature detection units T3 and T4 with the detection value of the current detection unit 11. Current comparison unit 12 then outputs the comparison result to converter control unit 18.

FIG. 19 is a flowchart showing an operation flow of the power conversion apparatus 1B. In addition, the same step number as FIG. 4 was attached | subjected about the part which overlaps with the flowchart of FIG. 4 demonstrated in 1st Embodiment.
After reading the detection value I of the current detection unit 11 in step S103, the power conversion device 1B reads the detection values of the temperature detection units T3 and T4 in step S201.

In step S202, the power conversion device 1B specifies threshold values I21 and I31 corresponding to the temperature read in step S201 by the current comparison unit 12B. For example, when the detected value of the temperature detection unit T3 is the temperature T _α , as shown in FIG. 18, a current threshold I21 _α (second threshold) corresponding to the temperature T _α and a threshold I31 _α (third Threshold).
In step S202 of FIG. 19, it is preferable to preferentially use thresholds I21 and I31 corresponding to the higher temperature among the detection values of the temperature detectors T3 and T4 (the same applies to S110a described later). This is because thermal runaway on the high temperature side of the switching elements Q3 and Q4 can be reliably prevented.

  In the present embodiment, the threshold value I1 (not shown in FIG. 18) is a fixed value regarding the temperature, but information regarding the threshold value I1 may be added to the correspondence information shown in FIG. In this case, the threshold value I1 is set to be smaller than the threshold value I21 (see FIG. 18) at each temperature, and the threshold value I1 becomes smaller as the temperature of the switching elements Q3 and Q4 becomes higher.

  In step S104a of FIG. 19, the power conversion apparatus 1B determines whether or not the detected current value I read in step S103 is less than the threshold value I21 specified in step S202. That is, the power conversion device 1B determines whether or not the state specified by the element temperature and the current detection value is included in the “steady region” illustrated in FIG. Steps S105 to S109 are the same as those in the first embodiment, and a description thereof will be omitted.

  In step S110a, the power conversion apparatus 1B determines whether the detected current value I read in step S103 is less than the threshold value I31 specified in step S202. That is, the power conversion device 1B determines whether or not the point specified by the element temperature and the current detection value is included in the “first protection region” illustrated in FIG. Steps S111 to S113 are the same as those in the first embodiment, and a description thereof will be omitted.

<Effect>
In the present embodiment, the control mode is determined based on the comparison result between the threshold values I21 and I31 corresponding to the temperatures of the switching elements Q3 and Q4 and the detected current value I. Therefore, the control mode can be switched at a timing more appropriate than in the first embodiment.
When the thresholds I21 and I31 are kept constant regardless of the temperatures of the switching elements Q3 and Q4, the thresholds I21 and I31 are set to a small value with a certain margin so as not to cause thermal runaway. Then, there is a possibility of switching to protection control such as deceleration of the load H (motor) even though the temperatures of the switching elements Q3 and Q4 are not so high.

On the other hand, in the present embodiment, since the optimum threshold values I21 and I31 are set corresponding to the temperatures of the switching elements Q3 and Q4 (see FIG. 18), the protection control is not performed prematurely. Therefore, the energy efficiency of the power conversion device 1B can be further increased as compared with the first embodiment.
Further, by referring to the information shown in FIG. 18, the protection control can be executed at an optimal timing before the switching elements Q3 and Q4 reach thermal destruction. Therefore, the thermal destruction of switching elements Q3 and Q4 can be reliably prevented, and the reliability of power conversion device 1B can be improved.

<< Fourth Embodiment >>
The power conversion device 1C (see FIG. 20) according to the fourth embodiment omits the switching element Q3 and the diode D4 from the power conversion device 1 (see FIG. 1) according to the first embodiment, and further in the first embodiment. Instead of the described diode D2 (see FIG. 1), a switching element Q2 (FIG. 20) is provided. Further, the power conversion device 1C (see FIG. 20) according to the fourth embodiment is different from the first embodiment in that the current control gain adjustment unit 20 and the step-up ratio control unit 21 are provided. Other points are the same as in the first embodiment (see FIGS. 1 to 4). Therefore, a different part from 1st Embodiment is demonstrated and description is abbreviate | omitted about the overlapping part.

FIG. 20 is a configuration diagram of a power conversion device 1C according to the fourth embodiment.
The power conversion device 1C includes a bridge circuit J, a reactor L1, a smoothing capacitor C1, a current detection unit 11, a current comparison unit 12, an AC voltage detection unit 13, a zero cross determination unit 14, and a load detection unit 15. , A load comparison unit 16, a DC voltage detection unit 17, a converter control unit 18, a current control gain adjustment unit 20, and a boost ratio control unit 21.

The bridge circuit J has a function of full-wave rectifying current flowing from the AC power supply G via the wirings ha and hb, and a function of boosting with the reactor L1. The bridge circuit J has a configuration in which a pair of diodes D1 and D3 connected in series and a pair of switching elements Q2 and Q4 connected in series are connected in parallel.
The switching elements Q2, Q4 are, for example, MOSFETs, and are controlled to be turned on / off by a command from the converter control unit 18. The drain of the switching element Q2 is connected to the positive side of the smoothing capacitor C1, and the source is connected to the drain of the other switching element Q4. The source of the switching element Q4 is connected to the negative side of the smoothing capacitor C1.

  The connection point P1 between the pair of diodes D1 and D3 is connected to the AC power supply G via the wiring ha. A connection point P2 between the pair of switching elements Q2 and Q4 is connected to the AC power supply G via the wiring hb.

Current control gain adjustment unit 20, based on the step-up ratio of the effective value I _s and the DC voltage of the circuit current a, and has a function of adjusting the current control gain K _p. At this time, by controlling K _p × I _s to a constant value, the DC voltage is boosted a times with respect to the voltage (effective value) of the AC power supply G. The step-up ratio control unit 21 selects (determines) the DC voltage step-up ratio 1 / a based on the detection value of the load detection unit 15 and outputs the selection result to the converter control unit 18. The processing executed by the current control gain adjustment unit 20 and the step-up ratio control unit 21 will be described later.

  Further, unlike the first embodiment (see FIG. 1), the fourth embodiment has no diode connected in parallel with the switching elements Q2 and Q4, and the current is divided between the diode and the parasitic diode of the switching element. It is not configured to do. Therefore, hereinafter, the synchronous rectification / circuit short-circuit control described in the first embodiment and the circuit short-circuit control are collectively referred to as “switching control”.

(1. When power is turned on)
FIG. 21 is an explanatory diagram showing the flow of current when the power supply voltage is included in the positive half cycle when the power is turned on. When the power is turned on (S102: see FIG. 4), the switching elements Q2 and Q4 are both turned off. In the period of the positive half cycle of the power supply voltage, current flows in the order of AC power supply G → reactor L1 → diode D1 → smoothing capacitor C1 → switching element Q4 (parasitic diode D41) → AC power supply G.

  FIG. 22 is an explanatory diagram showing the flow of current when the power supply voltage is included in the negative half cycle when the power is turned on. During the half cycle of the negative power supply voltage, current flows in the order of AC power supply G → switching element Q2 (parasitic diode D21) → smoothing capacitor C1 → diode D3 → reactor L1 → AC power supply G.

(2. Synchronous rectification control)
FIG. 23 is an explanatory diagram showing the flow of current when the power supply voltage is included in the positive half cycle during synchronous rectification control (light load (intermediate)). When the detection value I (load) of the current detection unit 11 is less than the threshold value I1 (first threshold value) (S105: Yes, see FIG. 4), the converter control unit 18 performs synchronous rectification control (S106).
When performing synchronous rectification control, converter control unit 18 turns on / off switching elements Q2, Q4 in synchronization with the polarity of the voltage of AC power supply G. That is, converter control unit 18 turns on switching element Q4 and turns off switching element Q2 during the period of the positive half cycle of the power supply voltage. Then, as shown in FIG. 23, a current flows in the order of AC power supply G → reactor L1 → diode D1 → smoothing capacitor C1 → switching element Q4 → AC power supply G.

  FIG. 24 is an explanatory diagram showing a current flow when the power supply voltage is included in a negative half cycle during synchronous rectification control (light load (intermediate)). Converter control unit 18 turns on switching element Q2 and turns off switching element Q4 during the half cycle of a negative power supply voltage. Then, as shown in FIG. 24, current flows in the order of AC power supply G → switching element Q2 → smoothing capacitor C1 → diode D3 → reactor L1 → AC power supply G.

  By performing synchronous rectification control in this way, a current flows through the switching element Q2 or the switching element Q4, so that a reduction in loss and an increase in efficiency can be achieved.

(3. Switching control)
Further, when the detection value I (load) of the current detection unit 11 is equal to or greater than the threshold value I1 (first threshold value), the converter control unit 18 performs the above-described “switching control”. Specifically, when detection value I is equal to or greater than threshold value I1 and less than threshold value I4, converter control unit 18 performs partial switching control. When detected value I is equal to or greater than threshold value I4 and less than threshold value I2, converter control unit 18 executes high-speed switching control. The threshold value I4 (I1 <I4 <I2) is a threshold value used as a reference when determining whether to perform partial switching control or high-speed switching control, and is set in advance. The partial switching control and the high speed switching control will be described later.

FIG. 25 is an explanatory diagram showing the flow of current when the power supply voltage is included in the positive half cycle during switching control (light load (rated), medium load, and high load).
When performing switching control, converter control unit 18 alternately turns on / off switching elements Q2 and Q4. That is, the converter control unit 18 switches the switching element Q2 at a predetermined number of times and with a predetermined pulse width during the period of the positive half cycle of the power supply voltage. When the switching element Q2 is in the on state, the converter control unit 18 . Then, when the switching element Q2 is turned on, a current (short-circuit current) flows in the order of AC power supply G → reactor L1 → diode D1 →→ switching element Q2 → AC power supply G.

  FIG. 26 is an explanatory diagram showing the flow of current when the power supply voltage is included in the negative half cycle during switching control (light load (rated), medium load, and high load). When the switching element Q4 is on during the half cycle of the negative power supply voltage, a current (short circuit current) flows in the order of AC power supply G → switching element Q4 → diode D3 → reactor L1 → AC power supply G. As described above, since the switching elements Q2 and Q4 are alternately turned on / off, the switching element Q2 is turned off when the switching element Q4 is turned on.

(3-1. Partial switching control)
The partial switching control is a control for boosting the DC voltage and improving the power factor by switching the switching elements Q2 and Q4 multiple times (that is, short-circuiting) with a predetermined delay and duty within a half cycle of the power supply voltage. It is. Compared with the case of the high-speed switching control described later, the switching loss can be reduced because the switching frequency of the switching elements Q2 and Q4 is small.
In order to cause the short circuit current (power factor correction current) to flow through the main circuit, the converter control unit 18 switches the switching element Q2 according to the polarity of the voltage Vs of the AC power supply G, as in the case of the synchronous rectification control (full wave rectification). , Q4 is switched. For example, in the positive half cycle of the power supply voltage, the converter control unit 18 turns on the switching elements Q2 and Q4 alternately and then turns off the switching elements Q2 and Q4 until switching to the negative half cycle.

When the switching element Q2 or the switching element Q4 is switched and the short-circuit current _Isp flows through the main circuit, the energy W represented by the following (Equation 1) is stored in the reactor L1. L ₁ is the inductance of reactor L1.

  Thereafter, switching element Q2 or switching element Q4 is turned off, so that the energy stored in reactor L1 is released to smoothing capacitor C1, and the DC voltage is boosted.

  FIG. 27 is an explanatory diagram showing the operation principle of partial switching control. In the explanatory diagram shown in FIG. 27, the horizontal axis represents time, and the vertical axis represents power supply voltage Vs (positive half cycle), sine wave ideal current (circuit current), and driving pulses of switching elements Q2 and Q4. , Shows. As shown in “ideal current” in FIG. 27, the circuit current is ideally sinusoidal with respect to the power supply voltage Vs. This ideal current is obtained by the current control gain adjustment unit 20 based on, for example, the detection value of the load detection unit 15 and the determination result of the zero cross determination unit 14.

For example, the point P1 on the ideal current is considered, and the tangent slope (rate of change with time) at this point P1 is set to di (P1) / dt. Next, after giving a predetermined delay from time t = 0 [s], the slope of the circuit current when the switching element Q2 is turned on during the on time of ton1_Q2 is set to di (ton1) / dt. Thereafter, the current gradient when the switching element Q2 is turned off at time toff1_Q2 is set to di (toff1) / dt. At this time, the converter control unit 18 turns on the switching elements Q2 and Q4 so that the average value of di (ton1) / dt and di (toff1) / dt is equal to the slope di (P1) / dt at the point P1. / Set the timing to turn off.
Similarly, the current gradient at the point P2 is set to di (P2) / dt. The slope of the current when the switching element Q2 is turned on for the time of ton2_Q2 is set to di (ton2) / dt, and the slope of the current when turned off for the time of toff2_Q2 is set to di (toff2) / dt. As in the case of the point P1, the converter control unit 18 performs switching so that the average value of di (ton2) / dt and di (toff2_Q2) / dt is equal to the slope di (P2) / dt at the point P2. The timing for turning on / off the elements Q2 and Q4 is set. Thereafter, this is repeated.

  It should be noted that the timing for alternately turning on / off switching elements Q2, Q4 in the positive half cycle of the power supply voltage may be set, for example, at the start of the positive half cycle, or on / off of switching elements Q2, Q4. The next timing may be set every time it is turned off.

  In the example shown in FIG. 27, converter control unit 18 turns on switching element Q2 and turns off switching element Q4 in the section of ton1_Q2 (= toff1_Q4). Then, converter control unit 18 turns off switching element Q2 and turns on switching element Q4 in the interval toff1_Q2 (= ton2_Q4). In this way, converter control unit 18 turns on / off switching elements Q2, Q4 alternately in time. This is because synchronous rectification is performed while performing a circuit short-circuit operation. That is, in this embodiment, synchronous rectification is performed while performing boosting by partial switching and power factor correction operation. Thereby, power conversion can be performed with high efficiency.

  It should be noted that the closer to the ideal sine wave, the more the switching frequency of the switching element Q2. That is, the power factor is improved as the number of times of switching is increased, and the harmonic current can be reduced.

(3-1. High-speed switching control)
The high-speed switching control is a control for boosting the DC voltage and improving the power factor by switching the switching elements Q2 and Q4 at a predetermined frequency. In the period of the positive half cycle of the power supply voltage, the converter control unit 18 turns on the switching element Q2 and turns off the switching element Q4 to flow a short-circuit current, and then turns off the switching element Q2 and turns on the switching element Q4. To perform synchronous rectification. In this way, converter control unit 18 turns on / off switching elements Q2 and Q4 alternately at a predetermined frequency.

Similarly, in the period of the half cycle in which the power supply voltage is negative, the switching element Q4 is turned on and the switching element Q2 is turned off to allow a short-circuit current to flow, and then the switching element Q4 is turned off and the switching element Q2 is turned on. Synchronous rectification is performed at
Incidentally, the instantaneous current i _s flowing through the circuit is expressed by the following (Equation 2). Here, V _s is the effective value of the supply voltage, K _p is the current control gain, V _d is the DC voltage, the ω is the angular frequency.

  By arranging the above (Equation 2), the following (Equation 3) is obtained.

Further, the instantaneous current i _s, can be expressed by the following (Equation 4).

Based on (Formula 3) and (Formula 4), the current control gain _Kp is expressed by the following (Formula 5).

From (Equation 5), the relationship shown by the following (Equation 6) is established. Here, I _s is the effective value of the circuit current, a is a step-up ratio.

  In addition, in the half cycle in which the power supply voltage is positive, the on-duty d of the switching element Q2 (in the half cycle in which the power supply voltage is negative, the on-duty of the switching element Q4) is expressed by the following (Equation 7).

As K _p · _{I s} is constant, and adjusting the current control gain _{K p} by the current control gain adjustment unit 20, converter control unit 18 on the basis of the current control gain _{K p} is the switching elements Q2, Q4 ON / by controlling the off can boost the a times the ((equation 6), (see equation 7)), the power supply voltage of the run value V _s. The step-up ratio a is set (controlled) by the step-up ratio control unit 21 based on the load detected by the load detection unit 15. That is, the larger the load, the larger the step-up ratio a is set.

  FIG. 28A is an explanatory diagram showing the relationship of the duty of the switching elements Q2 and Q4 in the high-speed switching control. As described above, during the execution of the high-speed switching control, the switching elements Q2 and Q4 are alternately turned on / off, and the duty (conductivity) is controlled as shown in FIG.

  FIG. 28B is an explanatory diagram showing the relationship between the instantaneous value vs of the power supply voltage and the instantaneous value is of the circuit current in the high-speed switching control. As shown in FIGS. 28A and 28B, in the half cycle in which the power supply voltage is positive, the duty of the switching element Q2 that performs the switching operation for flowing the short-circuit current is set to a smaller value as the instantaneous current is is larger. (See (Equation 7)). The duty of the switching element Q4 on the side where synchronous rectification is performed has a characteristic opposite to that of the switching element Q2. That is, the relationship shown by the following (Formula 8) and (Formula 9) is established.

  Further, as shown in FIG. 28 (b), when the relationship between the instantaneous value vs of the power supply voltage and the instantaneous value is of the circuit current is seen, the circuit current is controlled in a sine wave shape, so that the power factor is relatively high. It has become. FIG. 28B assumes a state in which the inductance of the reactor L1 is relatively small and there is almost no phase delay of the current with respect to the power supply voltage. If the inductance of reactor L1 is relatively large and the current phase is delayed with respect to the voltage phase, the duty of switching elements Q2 and Q4 is set in consideration of the current phase as shown in FIG. You only have to set it.

  By performing high-speed switching control in this way, the circuit current can be approximated to a sine wave to reduce the harmonic current, and the power factor can be improved. Further, by alternately turning on / off switching elements Q2 and Q4, boosting and synchronous rectification can be performed, and high efficiency can be achieved in power conversion.

<Effect>
According to the present embodiment, by performing synchronous rectification control or switching control according to the size of the load, power factor can be improved, harmonics can be suppressed, and voltage can be boosted, and higher efficiency can be achieved. Can do.
In the first embodiment (see FIG. 1), since a reverse recovery current is generated in the diode D2 during the circuit short-circuit operation, a high-speed diode having a relatively short reverse recovery time is used as the diode D2 in order to reduce the loss. It is desirable to use it. However, since the high-speed diode has a relatively large forward voltage drop, the conduction loss tends to increase accordingly.
In contrast, in the present embodiment, a trr high-speed type switching element (MOSEFT) having a relatively short reverse recovery time is used as the switching elements Q2 and Q4, so that the switching loss is reduced. Therefore, conduction loss can be reduced. Therefore, it is possible to reduce the loss when power conversion is performed.

«Fifth embodiment»
5th Embodiment demonstrates the air conditioner W provided with the power converter device 1 demonstrated in 1st Embodiment. In addition, about the structure (refer FIG. 1) of the power converter device 1 and the process (refer FIG. 4) which the power converter device 1 performs, it is the same as that of 1st Embodiment. Therefore, a different part from 1st Embodiment is demonstrated and description is abbreviate | omitted about the overlapping part.

FIG. 29 is a configuration diagram of an air conditioner W according to the fifth embodiment.
The air conditioner W includes a power conversion device 1, an inverter 2, a motor 3, and an air conditioning circuit (a compressor 41, an outdoor heat exchanger 42, an expansion valve 43, an indoor heat exchanger 44, and the like). .

The inverter 2 is a power converter that converts the DC voltage applied from the power converter 1 into an AC voltage based on, for example, PWM control (Pulse Width Modulation).
The motor 3 is an electric motor (for example, a three-phase synchronous motor) that is driven by an AC voltage input from the inverter 2.
The compressor 41 is a device that compresses the refrigerant, and is driven by the rotation of the motor 3.
The outdoor heat exchanger 42 is a heat exchanger for performing heat exchange between the indoor air sent from the outdoor fan F1 and the refrigerant.
The expansion valve 43 is a decompressor for expanding and decompressing the refrigerant flowing from the outdoor heat exchanger 42 or the indoor heat exchanger 44.
In the example shown in FIG. 29, the power converter 1, the inverter 2, the motor 3, the compressor 41, the outdoor heat exchanger 42, and the outdoor fan F1 are installed in the outdoor unit U1.

The indoor heat exchanger 44 is a heat exchanger for performing heat exchange between indoor air sent from the indoor fan F2 and the refrigerant, and is installed in the indoor unit U2.
In an air-conditioning circuit in which the compressor 41, the outdoor heat exchanger 42, the expansion valve 43, and the indoor heat exchanger 44 are sequentially connected in an annular manner via the pipe i, the refrigerant is circulated by a known heat pump cycle. Yes. The air conditioner W may be for cooling or for heating. Moreover, you may provide the four-way valve (not shown) which switches the direction through which a refrigerant | coolant flows between the time of cooling and the time of heating.

  Although not shown in FIG. 29, as one of the protection controls described in the first embodiment (S113: see FIG. 4), the rotational speed of the outdoor fan F1 may be increased. As a result, since the outside air is sent from the outdoor fan F1 toward the radiation fins (not shown) installed in the switching elements Q3 and Q4 (see FIG. 1), the heat radiation of the switching elements Q3 and Q4 can be promoted. it can.

<Effect>
According to this embodiment, since the air conditioner W includes the power conversion device 1, the air conditioner W having high energy efficiency (that is, APF) and high reliability can be provided.

≪Modification≫
As mentioned above, although each embodiment demonstrated the power converter device 1 etc. which concern on this invention, this invention is not limited to these description, A various change can be made.
For example, in the first embodiment (see FIG. 1), the configuration in which the switching elements Q3 and Q4 are connected in parallel to the diodes D3 and D4 has been described, but the present invention is not limited to this. That is, a configuration in which switching elements are connected in parallel to the diodes D1 and D2 shown in FIG. 1 and no switching elements are connected in parallel to the diodes D3 and D4 may be employed. Note that the control method of each switching element is the same as that in the first embodiment (see FIG. 4), and thus the description thereof is omitted.

Moreover, you may use super junction MOSFET or SiC-MOSFET with small ON resistance as switching element Q1-Q4. Thereby, the energy loss of the power converter device 1 can be further reduced, and the loss and efficiency can be reduced.
Moreover, although each embodiment demonstrated the case where switching element Q1-Q4 was MOSFET, it is not restricted to this. For example, bipolar transistors may be used as the switching elements Q1 to Q4, or IGBTs (Insulated-Gate-Bipolar-Transistors) may be used.
For example, when bipolar transistors are used as the switching elements Q2 and Q4 described in the fourth embodiment (see FIG. 20), the collector of the switching element Q2 is connected to the positive side of the smoothing capacitor C1, and the emitter of the switching element Q2 is connected. What is necessary is just to connect to the collector of switching element Q4 and to connect the emitter of switching element Q4 to the negative side of smoothing capacitor C1.

  In each embodiment, for example, as illustrated in FIG. 1, the case where the current detection unit 11 is provided in the wiring hb connecting the AC power supply G and the rectifier circuit D has been described, but the present invention is not limited thereto. That is, instead of the current detection unit 11, a shunt resistor (current detection unit) may be provided on the drain side or the source side of the switching elements Q3 and Q4. As a result, the current flowing through the switching elements Q3 and Q4 can be accurately detected, and the control mode can be switched at an optimal timing.

Moreover, although 1st Embodiment demonstrated the case where a control mode was determined based on the comparison result of the detected value I of the electric current detection part 11, and threshold value I1, I2, I3, it is not restricted to this. For example, the control mode may be switched as follows by setting the threshold value relating to the current (load) to only the threshold value I1. That is, when the detection value of the current detection unit 11 is less than the threshold value I1, the above-described synchronous rectification control is executed (see FIG. 6). When the detection value is equal to or greater than the threshold value I1, the short-circuit current path through the reactor L1 The included switching element Q3 (or switching element Q4) may be switched (see FIGS. 8 and 10).
Even in such control, loss reduction and high efficiency can be achieved by synchronous rectification control, and power factor improvement, harmonic suppression, boosting, and the like can be performed by switching. The “switching” described above may be synchronous rectification / circuit short-circuit control (see FIG. 8), circuit short-circuit control (see FIG. 10), or “4” in the fourth embodiment. This corresponds to “switching control”. The control method described above can also be applied to the second to fifth embodiments.

  Further, for example, the thresholds related to the current are only thresholds I1 and I2, and when the detection value I of the current detection unit 11 is equal to or greater than the threshold I1 and less than the threshold I2, the synchronous rectification / circuit short-circuit control is executed (see FIG. 8). Circuit short-circuit control may be executed when the threshold value is greater than or equal to I2 (see FIG. 10).

Moreover, although each embodiment demonstrated the case where control mode was switched based on the detected value of the electric current detection part 11 (refer FIG. 1), it is not restricted to this. That is, a “load” having a positive correlation with the current flowing in the wirings ha and hb (see FIG. 1) is detected by the load detection unit 15 (see FIG. 1), and the control mode is based on the magnitude of this “load”. May be switched.
Specifically, the control mode may be switched based on the comparison result between the output voltage of the smoothing capacitor C1 (see FIG. 1) and a plurality of threshold values. Since the output voltage increases as the load increases, the relationship between the load area divided by a plurality of threshold values and the output voltage is the same as in FIG.

  Also, the current value of the inverter 2 (see FIG. 29) on the output side of the smoothing capacitor C1 (see FIG. 1), the rotational speed of the motor 3 (see FIG. 29) connected to the inverter 2, or the modulation rate of the motor 3 Based on this, the control mode may be switched. The above-described “modulation rate” is a ratio of the effective value of the applied voltage (line voltage) of the motor 3 to the DC voltage of the inverter 2. As the load increases, the current flowing through the inverter 2 (the rotation speed of the motor 3 and the modulation rate) also increases. Therefore, the relationship between the load region divided by a plurality of threshold values and the current flowing through the inverter 2 (the rotational speed and modulation rate of the motor 3) is the same as that in FIG.

Moreover, although 5th Embodiment demonstrated the case where the detected value (load) of the electric current detection part 11 was used when switching the control mode regarding the power converter device 1 with which the air conditioner W (refer FIG. 29) is provided. Not limited to this. For example, the load may be detected based on the difference between the detected value of a room temperature thermistor (not shown) installed in the indoor unit U2 (see FIG. 29) and the set temperature of the air conditioner W. In this case, the larger the difference between the room temperature and the set temperature, the higher the load of the power conversion device 1 and the greater the output of the air conditioner W.
Further, based on the size of the load, converter control unit 18 performs the above-described synchronous rectification control and control for switching switching element Q3 (or switching element Q4) included in the short-circuit current path via reactor L1. You may make it switch.

  Moreover, each embodiment can be combined suitably. For example, the second embodiment and the third embodiment liquid are combined, a temperature detection unit is provided for each of the switching elements Q1 to Q4, and the detection value of each temperature detection unit and the magnitude of the load (for example, circuit current) The control mode may be switched based on this. In addition, about the process which the power converter device 1 performs, since it is the same as that of 3rd Embodiment (refer FIG. 19), description is abbreviate | omitted.

  Further, for example, the current control gain adjustment unit 20 (see FIG. 20) and the boost ratio control unit 21 (see FIG. 20) described in the fourth embodiment are combined with the power conversion device 1 (see FIG. 1) of the first embodiment. ) And on / off of the switching elements Q3 and Q4 (see FIG. 1) may be controlled based on the method described in the fourth embodiment. Specifically, when performing the partial switching control, the converter control unit 18 always turns on the switching element Q4 during the period of the positive half cycle of the power supply voltage Vs, and turns the switching element Q3 a plurality of times with a predetermined delay and duty. Switch. Further, when performing the high-speed switching control, the converter control unit 18 always turns on the switching element Q4 and switches the switching element Q3 at a predetermined frequency during the period of the positive half cycle of the power supply voltage Vs. Thus, partial switching control and high-speed switching control can also be applied in synchronous rectification / circuit short-circuit control and circuit short-circuit control. Similarly, the fourth embodiment can be applied to the second and third embodiments.

  Moreover, the power converter 1 (refer FIG. 29) is combined with 3rd Embodiment and 5th Embodiment and based on the detected value of temperature detection part T3, T4 (refer FIG. 17) installed in switching element Q3, Q4. ) Control mode may be switched. Further, without directly detecting the temperature of the switching elements Q3 and Q4, the detected value of an outside temperature thermistor (not shown) installed in the outdoor unit U1 (see FIG. 29) is used to switch the switching elements Q3 and Q3. You may detect the temperature of Q4 indirectly. For example, when performing a cooling operation, the higher the outside air temperature, the larger the load, and the switching elements Q3 and Q4 are more likely to rise in temperature. Therefore, in this case, the threshold values II21 and I31 (see FIG. 18) corresponding to the outside air temperature are set to relatively small values.

  In the fourth embodiment, the case where the partial switching control and the high-speed switching control are switched based on the size of the load has been described. However, the present invention is not limited to this. That is, when the switching value between the partial switching control and the high-speed switching control is not performed and the detection value I of the current detection unit 11 is not less than the threshold value I1 and less than the threshold value I2, only the partial switching control may be performed. Only switching may be performed. When the detection value I (load magnitude) enters the first protection region (see FIG. 3), the switching loss is reduced by reducing the number of switchings, thereby preventing thermal destruction of the element. Can do. Further, when the magnitude of the load enters the second protection region (see FIG. 3), the device may be decelerated or stopped.

Moreover, although 5th Embodiment demonstrated the case where the power converter device 1 was mounted in the air conditioner W (refer FIG. 20), it is not restricted to this. For example, you may mount the power converter device 1 in the charging equipment to a battery, a refrigerator, a water heater, a washing machine, a vehicle.
Moreover, although each embodiment demonstrated the case where the alternating voltage of the single phase alternating current power supply G was converted into a direct voltage by the power converter device 1, it is not restricted to this. For example, each embodiment can also be applied when converting an AC voltage supplied from a three-phase AC power source into a DC voltage.

  Each of the above-described embodiments is described in detail for easy understanding of the present invention, and is not necessarily limited to the one having all the configurations described. A part of the configuration of one embodiment can be replaced with the configuration of another embodiment. Further, the configuration of another embodiment can be added to the configuration of a certain embodiment. In addition, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

  Each of the above-described configurations, functions, processing units, processing means, and the like may be realized by hardware by designing a part or all of them, for example, by an integrated circuit. Further, the mechanisms and configurations are those that are considered necessary for the explanation, and not all the mechanisms and configurations on the product are necessarily shown.

1, 1A, 1B, 1C Power converter 11 Current detection unit (load detection unit)
12, 12B Current comparison unit (control unit)
13 AC voltage detection unit 14 Zero cross determination unit (control unit)
15 Load detection unit 16 Load comparison unit (control unit)
17 DC voltage detection unit 18 Converter control unit (control unit)
DESCRIPTION OF SYMBOLS 19 Memory | storage part 20 Current control gain adjustment part 21 Boost ratio control part 2 Inverter 3 Motor 41 Compressor (air-conditioning circuit)
42 Outdoor heat exchanger (air conditioning circuit)
43 Expansion valve (air conditioning circuit)
44 Indoor heat exchanger (air conditioning circuit)
i Piping (air conditioning circuit)
G AC power source C1 Smoothing capacitor D Rectifier circuit D1, D2, D3, D4 Diode ha Wiring L1 Reactor Q1, Q2, Q3, Q4 Switching element T3, T4 Temperature detector W Air conditioner

Claims (12)

A rectifier circuit having a plurality of diodes connected in a bridge shape and rectifying a current from an AC power supply;
A reactor provided in a wiring connecting the AC power supply and the rectifier circuit;
A smoothing capacitor connected to the output side of the rectifier circuit and smoothing the voltage applied from the rectifier circuit to a DC voltage;
Among the plurality of diodes, a diode having a cathode connected to the positive side of the smoothing capacitor, and / or a switching element connected in parallel to each of a diode having an anode connected to the negative side of the smoothing capacitor,
A load detection unit for detecting a load having a positive correlation with the magnitude of the current flowing in the wiring;
A control unit for controlling the switching element,
The controller is
Synchronous rectification control for flowing current through the smoothing capacitor by turning on / off the switching element in synchronization with the polarity of the voltage of the AC power supply;
A power converter that switches between switching the switching element included in a short-circuit current path via the reactor based on a detection value of the load detection unit. The controller is
When the detection value of the load detection unit is less than a first threshold, the synchronous rectification control is executed,
The power conversion device according to claim 1, wherein when the detection value of the load detection unit is equal to or greater than the first threshold value, the switching element included in a short-circuit current path via the reactor is switched. The controller is
One of the two switching elements included in the short-circuit current path through the reactor when the detection value of the load detection unit is equal to or greater than the first threshold and less than a second threshold greater than the first threshold. Executes synchronous rectification and short circuit control that switches on the other,
When the detection value of the load detection unit is equal to or greater than the second threshold, one of the two switching elements included in the path is turned off and circuit short-circuit control is performed to switch the other. Item 3. The power conversion device according to Item 2. The controller is
The protection control for decelerating or stopping the motor on the output side of the smoothing capacitor is executed when the detection value of the load detection unit is equal to or greater than a third threshold value greater than the second threshold value. The power converter device described in 1. A temperature detector for directly or indirectly detecting the temperature of the switching element;
A storage unit in which at least the second threshold value and the third threshold value are stored in association with the temperature of the switching element,
The control unit reads the second threshold value and the third threshold value corresponding to the temperature detected by the temperature detection unit from the storage unit, and compares the detection value of the load detection unit with each threshold value. The power converter according to claim 4, wherein: The load detector is
Detecting the output voltage of the smoothing capacitor, the current value of the inverter connected to the smoothing capacitor, the rotational speed of the motor connected to the inverter, or the modulation rate related to the voltage of the motor as the magnitude of the load. The power conversion device according to claim 1. The power converter according to claim 1, wherein the switching element is a MOSFET, a source is connected to an anode of the diode, and a drain is connected to a cathode of the diode. The power converter according to claim 7, wherein a forward voltage of the diode is smaller than a forward voltage of a parasitic diode included in the switching element connected in parallel to the diode. The power converter according to claim 7, wherein the MOSFET is a super junction MOSFET or a SiC-MOSFET. A pair of diodes connected in series and a pair of switching elements connected in series are connected in parallel, and a connection point of the pair of diodes and a connection point of the pair of switching elements are respectively A bridge circuit connected to an AC power source;
A reactor provided in a wiring connecting the AC power supply and the bridge circuit;
A smoothing capacitor connected to the output side of the bridge circuit and smoothing a voltage applied from the bridge circuit to a DC voltage;
A load detection unit for detecting a load having a positive correlation with the magnitude of the current flowing in the wiring;
A control unit for controlling the switching element,
The controller is
Synchronous rectification control for flowing current through the smoothing capacitor by turning on / off the switching element in synchronization with the polarity of the voltage of the AC power supply;
The switching control for alternately turning on and off the pair of switching elements a plurality of times in each of positive and negative half cycles of the voltage of the AC power supply is switched based on a detection value of the load detection unit. Power conversion device. The power conversion device according to any one of claims 1 to 10,
An inverter that converts a DC voltage applied from the power converter to an AC voltage;
A motor driven by an AC voltage applied from the inverter, and
An air conditioner comprising an air conditioning circuit in which a compressor driven by the rotation of the motor, an outdoor heat exchanger, an expansion valve, and an indoor heat exchanger are sequentially connected in an annular manner through a pipe. Machine. A rectifier circuit having a plurality of diodes connected in a bridge shape and rectifying a current from an AC power supply;
A reactor provided in a wiring connecting the AC power supply and the rectifier circuit;
A smoothing capacitor connected to the output side of the rectifier circuit and smoothing the voltage applied from the rectifier circuit to a DC voltage;
Among the plurality of diodes, a diode having a cathode connected to the positive side of the smoothing capacitor, and / or a switching element connected in parallel to each of a diode having an anode connected to the negative side of the smoothing capacitor,
A load detection unit for detecting a load having a positive correlation with the magnitude of the current flowing in the wiring;
A power conversion method executed by a power conversion device comprising:
Synchronous rectification control for flowing current through the smoothing capacitor by turning on / off the switching element in synchronization with the polarity of the voltage of the AC power supply;
A control method for switching the switching element included in the short-circuit current path through the reactor based on a detection value of the load detection unit.

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