JP7313231B2 - DC power supply, motor drive and air conditioner - Google Patents

Description

The present invention relates to a DC power supply device, a motor drive device, and an air conditioner that convert AC power into DC power.

Conventionally, there is a DC power supply device that includes a rectifier circuit using a switching element that is a semiconductor switch such as a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) instead of a rectifier diode, and a current detection circuit on the AC power supply side of the rectifier circuit. Patent Literature 1 discloses a technique in which a DC power supply device controls opening and closing of a switching element in synchronization with the timing at which a current flows through a parasitic diode of the switching element, thereby reducing conduction loss. In the DC power supply device described in Patent Document 1, in synchronous rectification control, the current value of the DC current flowing in the rectifier circuit detected by the current detection circuit is used to control the opening and closing of the switching element, and the absolute value of the current value Switches opening and closing according to the timing when it exceeds the current threshold. As a result, the DC power supply device described in Patent Literature 1 efficiently performs synchronous rectification control.

JP 2012-143154 A

However, in the circuit configuration of the DC power supply device described in Patent Document 1, when a load is connected between the current detection circuit and the rectifier circuit in parallel with the rectifier circuit, the current detection circuit detects the total current value of the DC current value flowing through the rectifier circuit and the DC current value flowing through the load. In this case, the detected value of the current detection circuit becomes larger than the current value of the DC current flowing through the rectifier circuit, the timing at which the detected value exceeds the current threshold set for the rectifier circuit deviates from the expected timing, and the opening/closing timing of the switching element differs from the expected timing. Therefore, in a general circuit configuration in which an AC power supply is connected to the front stage of the rectifier circuit and a capacitor is connected to the rear stage of the rectifier circuit, there is a problem that if the voltage across the capacitor exceeds the power supply voltage of the AC power supply, an inappropriate regenerative current may flow from the capacitor to the AC power supply.

The present invention has been made in view of the above, and it is an object of the present invention to obtain a DC power supply device that can stably operate a rectifier circuit using a switching element when a load is connected in parallel with the rectifier circuit.

In order to solve the above-described problems and achieve the object, a DC power supply device according to the present invention includes a rectifier circuit that uses a plurality of switching elements to rectify AC power output from an AC power supply and outputs the rectified DC power to a first load, a parallel load connection between the AC power supply and the rectifier circuit that allows a second load to be connected in parallel with the rectifier circuit, and a current that flows through the rectifier circuit and the second load when the second load is connected to the parallel load connection between the AC power supply and the parallel load connection. and a control unit capable of controlling the connection between the parallel load connection unit and the second load when the parallel load connection unit and the second load are connectable, and controlling the operation of the switching element based on the value detected by the current detection unit. The control unit controls the operation of the switching element according to the state of the second load when the second load is connected to the parallel load connection unit.

ADVANTAGE OF THE INVENTION The DC power supply device which concerns on this invention is effective in the ability to operate|move a rectifier circuit stably even when load is connected in parallel with the rectifier circuit using a switching element.

1 is a diagram showing a configuration example of a DC power supply device according to Embodiment 1; FIG. 4 is a diagram showing current waveforms of currents flowing in the DC power supply device according to Embodiment 1 and on/off timings of switching elements; FIG. 4 is a flowchart showing an operation of setting a current threshold value used for synchronous rectification control by the DC power supply according to Embodiment 1; FIG. 2 is a diagram showing an example of a hardware configuration that realizes a control unit included in the DC power supply device according to Embodiment 1; 5 is a flow chart showing an operation of setting a current threshold value used for synchronous rectification control by the DC power supply according to Embodiment 2; FIG. 11 shows a configuration example of a DC power supply device according to Embodiment 3; FIG. 10 is a diagram showing current waveforms of currents flowing in the DC power supply device according to Embodiment 3 and on/off timings of switching elements; FIG. 11 shows a configuration example of a DC power supply device according to Embodiment 4; FIG. 11 is a diagram showing a configuration example of a motor drive device according to Embodiment 5; The figure which shows the structural example of the air conditioner which concerns on Embodiment 6.

BEST MODE FOR CARRYING OUT THE INVENTION A DC power supply device, a motor drive device, and an air conditioner according to embodiments of the present invention will be described below in detail with reference to the drawings. In addition, this invention is not limited by this embodiment.

Embodiment 1.
FIG. 1 is a diagram showing a configuration example of a DC power supply device 100 according to Embodiment 1 of the present invention. DC power supply 100 is connected to AC power supply 1 and load 10 . The AC power supply 1 supplies AC power to the DC power supply device 100 . The AC power supply 1 is a general commercial power supply, but is not limited to this. Let the direction of the arrow of the power supply voltage Vs of the AC power supply 1 shown in FIG. 1 be the positive pole. The load 10 is, for example, a compressor, a motor that drives a fan, or an inverter that drives a motor, but is not limited to these. The DC power supply 100 converts AC power output from the AC power supply 1 into DC power and outputs the DC power to the load 10 . In the following description, load 10 may be referred to as a first load.

A configuration of the DC power supply device 100 will be described. DC power supply 100 includes current detection unit 2 , reactor 3 , rectifier circuit 4 , capacitor 9 , control unit 11 , parallel load connection unit 12 , switch 14 , and load 15 . The DC power supply device 100 may include a switch for shutting off the AC power supply 1, i.e., a breaker, between the AC power supply 1 and the current detection unit 2, for power on/off switching purposes and forcible shutdown during overcurrent.

The current detection section 2 is installed between the AC power supply 1 and the parallel load connection section 12 . Current detection unit 2 detects a current value of current Is, which is the sum of current Ir flowing through rectifier circuit 4 and current Il flowing through load 15 when load 15 is connected to parallel load connection unit 12 . The current detection unit 2 detects the value of the current Is, which is the current Ir flowing through the rectifier circuit 4 when the load 15 is not connected to the parallel load connection unit 12 . Regarding the current Is, the current Ir, and the current Il, the direction of the arrow shown in FIG. 1 is the positive direction. Note that the current Is is sometimes referred to as a primary current. The current detection unit 2 is composed of, for example, a current detection element such as a current transformer or a shunt resistor, and an amplifier that converts the detection value of the current Is detected by the current detection element into a voltage within a range that can be handled by the control unit 11 and outputs the voltage, but the configuration of the current detection unit 2 is not limited to this.

The reactor 3 is inserted to improve the power factor, and by inserting the reactor 3, it is possible to improve the power factor by extending the conduction period of the current Is output from the AC power supply 1. Further, as described in FIG. 5 of Patent Document 1, by performing switching to short-circuit the reactor 3 to the AC power supply 1, it is possible to further improve the power factor and boost the output voltage (DC voltage) of the rectifier circuit 4.

The rectifier circuit 4 includes switching elements S1 to S4. The switching elements S1-S4 are, for example, semiconductor switches 5-8 such as MOSFETs. Diodes 5a to 8a are connected to the semiconductor switches 5 to 8, respectively. The diodes 5a to 8a may be parasitic diodes present in the MOSFETs, or may be diodes that are separately connected. The switching elements S1 to S4 are turned on and off by the controller 11 . The rectifier circuit 4 performs power conversion using switching elements S1 to S4. Specifically, the rectifier circuit 4 rectifies the AC power output from the AC power supply 1 and outputs the rectified DC power to the load 10 via the capacitor 9 . The rectifier circuit 4 is configured as a bridge rectifier by the diodes 5a to 8a when the switching elements S1 to S4 are all off. In the rectifier circuit 4, when a current flows through the diodes 5a-8a, the conversion efficiency is lowered due to the forward loss and recovery loss of the diodes 5a-8a.

Here, the switching elements S1 to S4 are semiconductor elements using silicon, and switching elements using wide bandgap semiconductors such as silicon carbide (SiC) and gallium nitride (GaN). As the switching elements S1 to S4, superjunction MOSFETs or the like are used in addition to MOSFETs. Materials such as silicon and silicon carbide (SiC) are also used for the diodes 5a to 8a. Diodes 5a to 8a may be ordinary rectifier diodes, fast recovery diodes with good recovery characteristics, Schottky barrier diodes, or the like.

The capacitor 9 is a capacitor for smoothing the voltage of the DC power after power conversion by the rectifier circuit 4 . Capacitor 9 is, for example, an electrolytic capacitor. A load 10 is connected across the capacitor 9 .

The control unit 11 controls operations of the switching elements S1 to S4 included in the rectifier circuit 4 based on the current value of the current Is detected by the current detection unit 2 . In the following description, the current value of the current Is detected by the current detector 2 may be referred to as a detected value. In the present embodiment, the control unit 11 controls the on/off of the switching elements S1 and S2 of the rectifier circuit 4 based on the polarity of the power supply voltage Vs of the AC power supply 1, and the current value of the current Is of the AC power supply 1, i.e., controls the on/off of the switching elements S3 and S4 of the rectifier circuit 4 based on the value detected by the current detection unit 2. Also, the control unit 11 controls the operation of the load 10 based on the detection value of the current detection unit 2 . Further, the control unit 11 controls on/off of the switch 14 . That is, the control unit 11 can control the connection between the parallel load connection unit 12 and the load 15 by turning on/off the switch 14 when the parallel load connection unit 12 and the load 15 are connectable. In addition, in the DC power supply device 100 shown in FIG. 1, the control unit 11 directly controls the rectifier circuit 4 and the load 10, but this is an example and the present invention is not limited to this. DC power supply device 100 may include a drive section for driving rectifier circuit 4 and a drive section for driving load 10 . In this case, the control section 11 generates a control signal and outputs it to each driving section. Each drive unit generates and outputs a drive signal based on the control signal acquired from the control unit 11 .

The parallel load connection section 12 is a connection section to which a load 15 can be connected via a switch 14 in parallel with the rectifier circuit 4 between the current detection section 2 and the reactor 3 . The parallel load connection unit 12 is, for example, a pattern, a connector, or the like provided so as to be connectable to the load 15 via the switch 14 on the board on which the DC power supply device 100 is mounted.

The switch 14 is a switch such as a breaker for controlling whether or not to connect the load 15 in parallel with the rectifier circuit 4 . The switch 14 is a switch that can be turned on and off by the control unit 11 between the parallel load connection unit 12 and the load 15 .

Load 15 comprises an inductance component 16 and a resistance component 17 . The load 15 is, for example, a component that can be optionally connected to the DC power supply 100 . A load 15 is connected to the parallel load connection 12 via a switch 14 . In DC power supply device 100 , switch 14 and load 15 are connected in parallel to rectifier circuit 4 after current detection unit 2 . In the following description, load 15 may be referred to as a second load.

Next, the operation of the DC power supply device 100 will be described. In the DC power supply device 100, the control unit 11 controls on/off of the switching elements S3 and S4 of the rectifier circuit 4 based on the detection value of the current detection unit 2 as described above. Specifically, the control unit 11 turns on either the switching element S3 or the switching element S4 during a period in which the absolute value of the detection value of the current detection unit 2 is equal to or greater than the current threshold. However, as shown in FIG. 1, the current detection unit 2 detects the current value of the current Ir flowing through the rectifier circuit 4 as the current value of the current Is when the load 15 is not connected. Therefore, the current detection unit 2 cannot detect only the current value of the current Ir flowing through the rectifier circuit 4 when the load 15 is connected. In this case, the current Is includes the current Il in addition to the current Ir. Therefore, even if the control unit 11 compares the detected value of the current Is with the current threshold set for the current Ir flowing through the rectifier circuit 4, it is not possible to accurately determine the timing when the current Ir becomes equal to or greater than the current threshold and the timing when the current Ir becomes less than the current threshold.

Here, when it is assumed that the DC power supply device 100 is used in an electric product such as an air conditioner, the load 15 connected as an option is a previously assumed and known component. In the DC power supply device 100 , the connection of the load 15 can be operated by the control unit 11 controlling the ON/OFF of the switch 14 . Therefore, when the load 15 is connected inside the DC power supply device 100, the control unit 11 sets a current threshold for comparison with the detected value of the current Is detected by the current detection unit 2 according to the characteristics of the load 15, that is, the type of the load 15. The control unit 11 holds in advance a default current threshold value used for synchronous rectification control, and when the load 15 is connected, the current threshold value for the detection value of the current detection unit 2 is changed from the default current threshold value. When the load 15 is connected to the parallel load connection section 12 via the switch 14 , the control section 11 controls the operation of the switching elements S 1 to S 4 of the rectifier circuit 4 according to the state of the load 15 .

FIG. 2 is a diagram showing current waveforms of currents flowing in the DC power supply device 100 according to Embodiment 1 and timings of turning on and off the switching elements S1 to S4. In FIG. 2, the first stage shows the power supply voltage Vs of the AC power supply 1, the second stage shows the current Ir flowing through the rectifier circuit 4, the third stage shows the current Il flowing through the load 15, and the fourth stage shows the current Is flowing from the AC power supply 1 to the current detection unit 2. As before, current Is = current Ir + current Il. In FIG. 2, the 5th row shows a power supply polarity signal representing the polarity of the power supply voltage Vs of the AC power supply 1, and the 6th to 9th rows show drive signals from the control section 11 to the switching elements S1 to S4. For example, the control unit 11 can acquire the power polarity signal from a detector (not shown) that detects the polarity of the power supply voltage Vs of the AC power supply 1, but the method of acquiring the power polarity signal is not limited to this. Also, in FIG. 2, a to f indicate current thresholds, and A to N indicate timings related to the control of the control section 11. FIG. The current threshold a for the current Ir and the current threshold d for the current Is are the same value, and the current threshold b for the current Ir and the current threshold e for the current Is are the same value.

When the switch 14 is turned on by the control signal and the load 15 is connected in parallel with the rectifier circuit 4, the control unit 11 changes the current thresholds d and e for the current Is to the current thresholds c and f as shown in FIG. The current threshold c is the larger absolute value of the current Is at the timings C and E when the timings at which the current Ir overlaps with the original current threshold a are the signal switching timings C and E. Similarly, the current threshold f is the larger absolute value of the current Is at the timings I and K when the timings at which the current Ir overlaps with the original current threshold b are the signal switching timings I and K.

As shown in FIG. 2, the phase of the current Il is delayed by the influence of the inductance component 16 of the load 15 and other inductance components, and the phase of the current Is is also delayed compared to the phase of the power supply voltage Vs. Also, the current Is increases compared to the current Ir because it is the sum of the currents Ir and Il. On the premise of such a situation, the case where the polarity of the power supply voltage Vs of the AC power supply 1 is positive, that is, only the half cycle will be extracted and explained. As a condition for preventing unnecessary regeneration from the output side of the rectifier circuit 4 to the input side, it is necessary to set the drive signal of the switching element S4 to H signal when the current Ir is flowing, and to set the drive signal of the switching element S4 to L signal when the current Ir is not flowing. As a method of satisfying the above conditions, the current Is is observed at timings C and E, which are the original switching timings of the drive signal for the switching element S4, and the one with the larger absolute value is set as the current threshold. However, it is assumed that the phase of the current Ir does not lag behind the phase of the power supply voltage Vs by 90 degrees or more. As a result, the switching element S4 is turned on during the period when the current Ir is flowing in the appropriate direction, and is turned off during the period when the current Ir is not flowing. As a result, since unnecessary regeneration is not performed, the DC power supply device 100 can perform low-loss and stable power conversion.

As shown in FIG. 2, before the AC power supply 1 is turned on, the switching elements S1 to S4 are in a high impedance state between the drain and source because the L signal is input as the drive signal. Since the switching elements S1 to S4 are H-active, when the H signal is input, the impedance between the drain and the source is low when the switching element is ON, and when the L signal is input, the impedance between the drain and the source is high when the switching element is OFF. When the AC power supply 1 is turned on and the polarity of the power supply is positive, an H signal is input from the control section 11 to the switching element S1 as a drive signal at timing A after the dead time has elapsed.

When the current Is begins to flow in the positive direction, the current Ir flows through the diodes 5a and 8a in the rectifier circuit 4 until the current Is reaches or exceeds the positive current threshold value c, causing loss due to the diodes 5a and 8a. In the DC power supply 100, an H signal is input from the control section 11 to the switching element S4 as a drive signal at timing B when the current Is becomes equal to or greater than the current threshold value c in FIG. That is, in FIG. 1, the switching elements S1 and S4 are on, and the switching elements S2 and S3 are off. In the rectifier circuit 4, since the current Ir flows between the drain and source of the semiconductor switches 5, 8 of the switching elements S1, S4, no loss occurs due to the diodes 5a, 8a. In the DC power supply device 100, an L signal is input as a drive signal from the control section 11 to the switching element S4 at the timing D when the current Is becomes less than the current threshold value c in FIG. That is, in FIG. 1, the switching element S4 is turned off. In the rectifier circuit 4, since the current Ir flows through the diodes 5a and 8a until it reaches 0 A, a loss occurs due to the diodes 5a and 8a.

In DC power supply 100, a dead time is provided in order to prevent parts from being broken due to arm short-circuiting when the power supply polarity of AC power supply 1 changes from positive to negative. At timing F, an L signal is input from the control section 11 to the switching element S1 as a driving signal, and the switching element S1 is turned off. At timing G after the dead time has elapsed, an H signal is input from the control section 11 to the switching element S2 as a drive signal, and the switching element S2 is turned on. As a result, the on/off states of the switching elements S1 and S2 are reversed.

When the current Is begins to flow in the negative direction, the current Ir flows through the diodes 6a and 7a in the rectifier circuit 4 until the current Is drops below the negative current threshold value f. In the DC power supply device 100, an H signal is input as a drive signal from the control section 11 to the switching element S3 at timing H when the current Is becomes equal to or less than the current threshold value f in FIG. That is, in FIG. 1, the switching elements S2 and S3 are on, and the switching elements S1 and S4 are off. In the rectifier circuit 4, since the current Ir flows between the drain and source of the semiconductor switches 6, 7 of the switching elements S2, S3, no loss occurs due to the diodes 6a, 7a. In the DC power supply device 100, an L signal is input as a drive signal from the control section 11 to the switching element S3 at timing J when the current Is exceeds the current threshold value f in FIG. That is, in FIG. 1, the switching element S3 is turned off. In the rectifier circuit 4, since the current Ir flows through the diodes 6a and 7a until it reaches 0 A, a loss occurs due to the diodes 6a and 7a.

In DC power supply 100, a dead time is provided in order to prevent parts from being destroyed due to arm short-circuiting when the power supply polarity of AC power supply 1 changes from negative to positive. At timing L, an L signal is input from the control section 11 to the switching element S2 as a driving signal, and the switching element S2 is turned off.

DC power supply 100 repeatedly performs the above operation while driving load 10 . As a result, the DC power supply device 100 can avoid unnecessary regenerative operation from the output side of the rectifier circuit 4 to the input side, and perform AC/DC power conversion stably and with high efficiency.

In DC power supply 100 , control unit 11 prestores a current threshold corresponding to the characteristics of load 15 , that is, the type of load 15 . As for the current threshold, the designer of the DC power supply 100 or the like sets the current threshold for each load 15 based on the operation of the DC power supply 100 when the assumed load 15 is connected. Specifically, if the current threshold when the load 15 is not connected is Ith1 and the current threshold when the load 15 is connected is Ith2, then "Ith2=Ith1+ΔI". Alternatively, ΔI=0 when the load 15 is not connected, and ΔI>0 when the load 15 is connected. The designer of the DC power supply 100 may set a plurality of current thresholds for each load 15 by simulation or actual measurement according to the voltage value and frequency of the power supply voltage Vs from the AC power supply 1, the operating state of the rectifier circuit 4, the operating state of the load 10, etc., and cause the control unit 11 to hold them.

If the control unit 11 controls the switching element S4 based on the result of comparing the current Is detected by the current detection unit 2 with the current threshold d corresponding to the current threshold a for the original current Ir, the control unit 11 turns on the switching element S4 at the timing M when the current Is becomes equal to or greater than the current threshold d, and turns off the switching element S4 at the timing F when the current Is becomes less than the current threshold d. Similarly, if the controller 11 controls the switching element S3 based on the result of comparing the value of the current Is detected by the current detector 2 with the current threshold e corresponding to the current threshold b for the original current Ir, the controller 11 turns on the switching element S3 at the timing N when the current Is becomes equal to or less than the current threshold e, and turns off the switching element S3 at the timing L when the current Is exceeds the current threshold e. In the present embodiment, control unit 11 changes the current threshold for comparison with current Is according to the characteristics of load 15, that is, the type of load 15, as described above. As a result, the control unit 11 can avoid turning on the switching element S4 between the timing M and the timing F, and avoid turning on the switching element S3 between the timing N and the timing L.

The above operation of the DC power supply device 100 will be described using a flowchart. FIG. 3 is a flow chart showing the operation of setting the current threshold used for synchronous rectification control by the DC power supply 100 according to the first embodiment. In the DC power supply 100, the control unit 11 determines whether or not the load 15 is connected to the parallel load connection unit 12 via the switch 14, that is, to the preceding stage of the rectifier circuit 4 (step ST1). When the load 15 is connected (step ST1: Yes), the control unit 11 changes the current threshold value according to the type of the connected load 15 (step ST2). When the load 15 is not connected (step ST1: No), the controller 11 does not change the current threshold (step ST3) and uses the default current threshold.

Next, the hardware configuration of the control unit 11 included in the DC power supply device 100 will be described. FIG. 4 is a diagram showing an example of a hardware configuration that implements the control unit 11 included in the DC power supply device 100 according to Embodiment 1. As shown in FIG. Control unit 11 is realized by processor 201 and memory 202 .

The processor 201 is a CPU (Central Processing Unit, central processing unit, processor, arithmetic unit, microprocessor, microcomputer, processor, DSP (Digital Signal Processor)), or system LSI (Large Scale Integration). The memory 202 can be non-volatile or volatile semiconductor memory such as RAM (Random Access Memory), ROM (Read Only Memory), flash memory, EPROM (Erasable Programmable Read Only Memory), EEPROM (Registered Trademark) (Electrically Erasable Programmable Read-Only Memory). Moreover, the memory 202 is not limited to these, and may be a magnetic disk, an optical disk, a compact disk, a mini disk, or a DVD (Digital Versatile Disc).

As described above, according to the present embodiment, in the DC power supply device 100, when the load 15 is connected in parallel with the rectifier circuit 4 before the rectifier circuit 4 using the switching elements S1 to S4, the current threshold for the detection value of the current detection unit 2 that detects the total current flowing through the rectifier circuit 4 and the load 15 is changed according to the characteristics of the load 15. Thus, the DC power supply device 100 can stably operate the rectifier circuit 4 even when the value detected by the current detection unit 2 changes with respect to the current value of the current Ir flowing through the rectifier circuit 4 . The DC power supply device 100 can avoid disturbance of the output voltage, ringing, etc. caused by inadvertent regeneration of the rectifier circuit 4 from the capacitor 9 to the AC power supply 1, and can perform stable and low-loss AC/DC power conversion.

Note that the DC power supply device 100 can be applied not only to the rectifier circuit 4 used when converting AC power obtained from the AC power supply 1, which is a commercial power supply, into DC power, but also to other rectifier circuits. The same applies to the DC power supply devices of the subsequent embodiments.

In addition, since the parallel load connection part 12 of the DC power supply device 100 is a pattern, a connector, or the like that is provided so as to be connectable to the load 15 via the switch 14 on the substrate on which the DC power supply device 100 is mounted, it is possible to use the same substrate without the switch 14 and the load 15. Thereby, the DC power supply device 100 can use a common substrate regardless of the presence or absence of the load 15 .

Further, the DC power supply device 100 can be configured without the switch 14 by short-circuiting the pattern portion where the switch 14 is mounted. In this case, the control unit 11 in the DC power supply 100 uses a current threshold in advance according to the type of the load 15 when the load 15 is connected, and uses a preset current threshold in advance when the load 15 is not connected.

Embodiment 2.
In Embodiment 1, control unit 11 previously holds a current threshold corresponding to the type of load 15 connected to parallel load connection unit 12 . Embodiment 2 describes a case where the control unit 11 calculates the current threshold each time the current threshold is changed.

The configuration of the DC power supply device 100 of the second embodiment is the same as that of the first embodiment. In the second embodiment, the current threshold value setting operation by the control unit 11 is different from that in the first embodiment. FIG. 5 is a flow chart showing the operation of setting the current threshold used for synchronous rectification control by the DC power supply 100 according to the second embodiment. In DC power supply 100, control unit 11 checks whether load 15 is connected to parallel load connection unit 12 via switch 14, that is, to the preceding stage of rectifier circuit 4 (step ST11). When the load 15 is connected (step ST11: Yes), the control unit 11 compares the absolute value of the first detection value of the current detection unit 2 at the first timing when the absolute value of the current Ir flowing through the rectifier circuit 4 becomes equal to or greater than the original current threshold and the absolute value of the second detection value of the current detection unit 2 at the second timing when the absolute value of the current Ir flowing through the rectification circuit 4 becomes less than the original current threshold (step ST12). In the example of FIG. 2, timings C and I correspond to the first timing, and timings E and K correspond to the second timing. The first timing is the timing at which the control unit 11 turns on the switching element according to the detection value of the current detection unit 2 when the load 15 is not connected to the parallel load connection unit 12 via the switch 14 . The second timing is the timing at which the control unit 11 turns off the switching element according to the detection value of the current detection unit 2 when the load 15 is not connected to the parallel load connection unit 12 via the switch 14 .

When the absolute value of the first detection value is larger (step ST12: Yes), the control unit 11 changes the current threshold to the absolute value of the first detection value (step ST13). When the absolute value of the second detection value is larger (step ST12: No), the control unit 11 changes the current threshold to the absolute value of the second detection value (step ST14). For example, the control unit 11 can obtain the first timing and the second timing by temporarily turning off the switch 14 and acquiring the current Is of the current detection unit 2 when the load 15 is not connected, that is, the current Ir. In this way, the control unit 11 sets the larger one of the absolute value of the detection value at the first timing and the absolute value of the detection value at the second timing as the current threshold, and controls the operation of the switching elements S3 and S4 based on the current threshold. When the load 15 is not connected (step ST11: No), the controller 11 does not change the current threshold (step ST15) and uses the default current threshold.

The method of determining the current threshold of the control unit 11 in the second embodiment is the same as the method of setting the current threshold in advance by the designer of the DC power supply device 100 in the first embodiment. In Embodiment 1, the current threshold is set in advance for each load 15, but the actual current waveform may differ even for the same type of load 15 depending on variations in the components that make up the load 15. In the second embodiment, the DC power supply 100 sets the current threshold value based on the actual current value, so that AC/DC power conversion can be performed more stably and efficiently.

As described above, according to the present embodiment, when the load 15 is connected in parallel with the rectifier circuit 4 before the rectifier circuit 4 using the switching elements S1 to S4, the DC power supply device 100 calculates and changes the current threshold for the detection value of the current detection unit 2 that detects the total current flowing through the rectifier circuit 4 and the load 15. As a result, DC power supply 100 can operate rectifier circuit 4 more stably than in the first embodiment. The DC power supply 100 can perform more stable AC/DC power conversion with lower loss than in the first embodiment.

Embodiment 3.
In Embodiments 1 and 2, the position of parallel load connecting portion 12 , that is, the position where load 15 is connected is between current detecting portion 2 and reactor 3 . In Embodiment 3, the position of the parallel load connection portion 12 , that is, the position where the load 15 is connected is between the reactor 3 and the rectifier circuit 4 . Specifically, the case of Embodiment 1 will be described as an example.

FIG. 6 is a diagram showing a configuration example of a DC power supply device 100a according to the third embodiment. DC power supply 100a differs from DC power supply 100 of Embodiment 1 in that the position of parallel load connecting section 12 is changed from the front stage of reactor 3 to the rear stage. That is, in the DC power supply device 100a, the rectifier circuit 4 and the load 15 are connected in parallel after the reactor 3. FIG. In DC power supply 100a, since load 15 is connected after reactor 3, current Il is expected to be affected by reactor 3 and lag in phase.

FIG. 7 is a diagram showing current waveforms of respective currents flowing in the DC power supply device 100a according to the third embodiment and timings of turning on and off the respective switching elements S1 to S4. The operation of the control unit 11 in the DC power supply 100a is the same as the operation of the control unit 11 in the DC power supply 100 of the first embodiment. However, when the current Il of the first embodiment shown in FIG. 2 and the current Il of the third embodiment shown in FIG. 7 are compared, the current Il of the third embodiment shown in FIG. 7 lags behind the current Il of the first embodiment shown in FIG. 2 in peak timing. As a result, when comparing the current Is of the first embodiment shown in FIG. 2 and the current Is of the third embodiment shown in FIG. 7, similarly, the current Is of the third embodiment lags behind the current Is of the first embodiment in peak timing. However, by the same method as in the first embodiment, the designer of the DC power supply 100a or the like can set the current threshold for each load 15 based on the operation of the DC power supply 100a when the assumed load 15 is connected. The DC power supply 100a can set the current threshold by the same procedure as the flowchart of the operation of the DC power supply 100 in the first embodiment shown in FIG.

As described above, according to the present embodiment, the DC power supply device 100a can obtain the same effect as in the first and second embodiments even when the load 15 is connected in parallel with the rectifier circuit 4 before the rectifier circuit 4 using the switching elements S1 to S4 and after the reactor 3.

Embodiment 4.
In Embodiments 1 to 3, since the control unit 11 can control the on/off of the switch 14, it was possible to determine whether or not the load 15 was connected. In the fourth embodiment, a case of using a switch that is manually turned on and off by the user will be described.

FIG. 8 is a diagram showing a configuration example of a DC power supply device 100b according to the fourth embodiment. DC power supply 100b is obtained by replacing switch 14 with switch 14a in DC power supply 100 of the first embodiment. In the configuration shown in FIG. 8, the controller 11 cannot determine whether the switch 14a is on or off. In this case, the user of the DC power supply device 100b provides the control section 11 with information on the ON/OFF state of the switch 14a, so that the control section 11 can perform the same control as in the first to third embodiments.

As described above, according to the present embodiment, even when the DC power supply device 100b includes the switch 14a instead of the switch 14, the same effects as in the first to third embodiments can be obtained by acquiring information on the on/off state of the switch 14a from the user.

Embodiment 5.
Embodiment 5 describes a motor drive device including DC power supply device 100 described in Embodiment 1. FIG. The DC power supply 100 described in Embodiment 1 will be described as an example, but the DC power supply 100 of Embodiment 2, the DC power supply 100a of Embodiment 3, and the DC power supply 100b of Embodiment 4 are also applicable.

FIG. 9 is a diagram showing a configuration example of the motor driving device 101 according to the fifth embodiment. A motor drive device 101 drives a motor 42 as a load. Motor drive device 101 includes DC power supply device 100 of Embodiment 1, inverter 41 , motor current detector 44 , and inverter controller 43 . Inverter 41 corresponds to load 10 connected to DC power supply 100 . Inverter 41 drives motor 42 by converting DC power supplied from DC power supply 100 into AC power and outputting the AC power to motor 42 . An example in which the load of the motor drive device 101 is the motor 42 is described, but this is only an example, and the device connected to the inverter 41 may be a device to which AC power is input, and may be a device other than the motor 42.

The inverter 41 is a circuit in which switching elements such as IGBTs (Insulated Gate Bipolar Transistors) are configured in a three-phase bridge configuration or a two-phase bridge configuration. The switching elements used in inverter 41 are not limited to IGBTs, and may be switching elements made of wide bandgap semiconductors, IGCTs (Integrated Gate Commutated Thyristors), FETs (Field Effect Transistors), or MOSFETs.

A motor current detector 44 detects a current flowing between the inverter 41 and the motor 42 . The inverter control unit 43 uses the current detected by the motor current detection unit 44 to generate a PWM (Pulse Width Modulation) signal for driving the switching elements in the inverter 41 so that the motor 42 rotates at a desired rotation speed, and applies it to the inverter 41. Inverter control unit 43 is realized by a processor and a memory, similar to control unit 11 . The inverter control unit 43 of the motor drive device 101 and the control unit 11 of the DC power supply device 100 may be realized by one circuit.

When DC power supply device 100 is used in motor drive device 101 , bus voltage Vdc required for controlling inverter 41 changes according to the operating state of motor 42 . In general, the higher the rotation speed of the motor 42, the higher the output voltage of the inverter 41 needs to be. The upper limit of the output voltage of inverter 41 is limited by the input voltage to inverter 41 , that is, bus voltage Vdc, which is the output of DC power supply 100 . A region where the output voltage from the inverter 41 exceeds the upper limit limited by the bus voltage Vdc and saturates is called an overmodulation region.

In such a motor driving device 101, it is not necessary to boost the bus voltage Vdc in the low rotation range of the motor 42, that is, in the range in which the overmodulation region is not reached. On the other hand, when the motor 42 rotates at a high speed, the overmodulation region can be shifted to a higher speed side by increasing the bus voltage Vdc. As a result, the operating range of the motor 42 can be expanded to the high rotation side.

Also, if it is not necessary to expand the operating range of the motor 42, the number of windings on the stator of the motor 42 can be increased accordingly. By increasing the number of turns of the windings, the motor voltage generated across the windings increases in the low rotation region, and the current flowing through the windings decreases accordingly, so the loss caused by the switching operation of the switching elements in the inverter 41 can be reduced. The number of turns of the windings of the motor 42 is set to an appropriate value in order to obtain both the effects of expanding the operating range of the motor 42 and improving the loss in the low rotation region.

As described above, according to the present embodiment, by using the DC power supply device 100, uneven heat generation between the arms can be reduced, and the motor drive device 101 with high reliability and high output can be realized.

Embodiment 6.
Embodiment 6 describes an application example of the motor drive device 101 described in Embodiment 5. FIG.

FIG. 10 is a diagram showing a configuration example of an air conditioner 700 according to Embodiment 6. As shown in FIG. Air conditioner 700 is an example of a refrigeration cycle device, and includes motor drive device 101 and motor 42 of the fifth embodiment. Air conditioner 700 includes compressor 81 incorporating compression mechanism 87 and motor 42 , four-way valve 82 , outdoor heat exchanger 83 , expansion valve 84 , indoor heat exchanger 85 , and refrigerant pipe 86 . The air conditioner 700 is not limited to a separate type air conditioner in which the outdoor unit is separated from the indoor unit, and may be an integrated air conditioner in which the compressor 81, the indoor heat exchanger 85, and the outdoor heat exchanger 83 are provided in one housing. The motor 42 is driven by a motor drive device 101 .

A compression mechanism 87 that compresses refrigerant and a motor 42 that operates the compression mechanism 87 are provided inside the compressor 81 . A refrigeration cycle device is configured by circulating the refrigerant through the compressor 81, the four-way valve 82, the outdoor heat exchanger 83, the expansion valve 84, the indoor heat exchanger 85, and the refrigerant pipe 86. Note that the components included in air conditioner 700 can also be applied to equipment such as a refrigerator or freezer that includes a refrigeration cycle device.

In the sixth embodiment, the case where the motor 42 is used as the driving source of the compressor 81 and the motor driving device 101 drives the motor 42 has been described. However, the motor 42 may be applied to the drive source for driving the indoor unit fan and the outdoor unit fan (not shown) provided in the air conditioner 700 and the motor 42 may be driven by the motor drive device 101 . Alternatively, the motor 42 may be applied to the drive source of the indoor blower, the outdoor blower, and the compressor 81 , and the motor 42 may be driven by the motor drive device 101 .

Here, since the four-way valve 82, the expansion valve 84, etc. in FIG. 10 are driven by a built-in motor, they are electric actuators and require a power source as a drive source. As a power generation method, for example, a means of connecting the power supply device 91 in FIG. At this time, the power supply device 91, the four-way valve 82, and the expansion valve 84 correspond to the load 15 described above. Further, the power consumption of the outdoor unit is dominated by the power consumption of the compressor 81 and the built-in motor 42, and the motor driving device 101 serving as the power source handles large power conversion. Therefore, even if a highly efficient power conversion circuit is mounted, a large loss will occur, and cooling will be required to prevent thermal destruction of the semiconductor element. Therefore, as shown in FIG. 10, for example, even when an external cooling fan 92 is installed, a power supply is required, and power may be supplied from a power supply device 91 as shown in FIG. The air cooling fan 92 corresponds to the load 15 described above.

In the air conditioner 700 that also performs heating, the indoor heat exchanger 85 may be frosted during heating at extremely low temperatures. In order to prevent this, for example, an anti-freezing heater 93 as shown in FIG. 10 may be installed. This applies not only to the air conditioner 700, but also to refrigerators, for example. In refrigerators in particular, since the defrosting operation of the air conditioner 700 cannot be performed, the proportion of the heater 93 mounted is relatively high. Even when power is supplied to the heater 93 from the power supply device 91, the heater 93 corresponds to the load 15 described above.

In the first embodiment and the like, it has been explained that the switching method of the switching elements S1 to S4 is appropriately changed according to the state of the load 15. FIG. Specifically, in the sixth embodiment, the switching method of the switching elements S1 to S4 is appropriately changed according to the state of the front-stage load corresponding to the load 15 such as the four-way valve 82, the expansion valve 84, the air cooling fan 92, and the heater 93. As a result, the DC power supply device 100, the motor driving device 101, etc. can be operated stably and with high efficiency.

Here, in FIG. 10, power is supplied to the cooling fan 92, the heater 93, and the like via the power supply device 91, but the present invention is not limited to this. For example, the air conditioner 700 may be configured to supply power directly from the AC power supply 1 to the air cooling fan 92 and the heater 93 without going through the power supply device 91 . In addition, in the air conditioner 700, description of operating means such as switches and relays for the four-way valve 82, the expansion valve 84, the cooling fan 92, the heater 93, etc. is omitted, but they may be inserted as appropriate. Moreover, although the four-way valve 82, the expansion valve 84, the air cooling fan 92, the heater 93, etc. are described as the load 15, these are examples in the sixth embodiment, and other load devices and actuators may be used.

As described above, according to the present embodiment, even when the air conditioner 700 includes the power supply device 91, the air cooling fan 92, the heater 93, etc., the DC power supply device 100, the motor drive device 101, etc. can be stably and highly efficiently operated.

The configuration shown in the above embodiment shows an example of the contents of the present invention, and can be combined with another known technique, and part of the configuration can be omitted or changed without departing from the gist of the present invention.

1 AC power supply 2 Current detection unit 3 Reactor 4 Rectifier circuit 5 to 8 Semiconductor switch 5a to 8a Diode 9 Capacitor 10, 15 Load 11 Control unit 12 Parallel load connection unit 14, 14a Switch 16 Inductance component 17 Resistance component 41 Inverter 42 Motor 43 Inverter control unit 44 Motor current detection unit 81 Compressor 82 Four-way valve 8 3 outdoor heat exchanger, 84 expansion valve, 85 indoor heat exchanger, 86 refrigerant pipe, 87 compression mechanism, 91 power supply device, 92 air cooling fan, 93 heater, 100, 100a, 100b DC power supply device, 101 motor drive device, 700 air conditioner, S1 to S4 switching elements.

Claims (5)

a rectifier circuit that uses a plurality of switching elements to rectify AC power output from an AC power supply and outputs the rectified DC power to a first load;
a parallel load connection unit capable of connecting a second load in parallel with the rectifier circuit between the AC power supply and the rectifier circuit;
a current detection unit for detecting a current value of a current flowing through the rectifier circuit and the second load when the second load is connected to the parallel load connection unit between the AC power supply and the parallel load connection unit, and detecting a current value of a current flowing through the rectification circuit when the second load is not connected to the parallel load connection unit;
a control unit capable of controlling the connection between the parallel load connection unit and the second load when the parallel load connection unit and the second load are connectable, and for controlling the operation of the switching element based on the value detected by the current detection unit;
with
When the second load is connected to the parallel load connection unit, the control unit controls the operation of the switching element according to the state of the second load.
DC power supply. When the second load is not connected to the parallel load connection portion, the timing for turning on the switching element according to the detected value is defined as a first timing, and the timing for turning off the switching element according to the detected value is defined as second timing,
The control unit uses the larger one of the absolute value of the detection value at the first timing and the absolute value of the detection value at the second timing as a current threshold, and controls the operation of the switching element based on the current threshold.
The DC power supply device according to claim 1 . a switch that can be switched on and off by the control unit between the parallel load connection unit and the second load;
The DC power supply device according to claim 1 or 2 , comprising: A motor drive device for driving a motor,
A DC power supply device according to any one of claims 1 to 3 ;
an inverter that converts the DC power output from the DC power supply into AC power and outputs the AC power to the motor;
A motor drive device comprising: a motor;
a motor driving device according to claim 4 ;
air conditioner.

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