JP2020120578A - Electric power unit - Google Patents

Abstract

To provide an electric power unit capable of preventing element destruction due to surge voltage.SOLUTION: An electric power unit includes a series circuit of first switch element SW1 having a reactor 11 for connection with the output end of a rectifier circuit 2, and a diode D1 connected in anti-parallel, a backflow prevention diode D2 provided in an electrification path between a load and the first switch element, a second switch element SW2 connected in parallel with the backflow prevention diode, and a capacitor 12 connected in parallel with the load. In a booster circuit 10 having a step-up mode for boosting the output voltage of the rectifier circuit by on-off of the first switch element, and on-off of the second switch element of inverse phase from on-off of the first switch element, and a non-boost mode for outputting the output voltage of the rectifier circuit without boosting by continuing off of the first switch element, when the instantaneous value of a current flowing to the reactor is equal to or less than a set value, the step-up mode of the booster circuit is prohibited and the booster circuit is brought into the non-boost mode.SELECTED DRAWING: Figure 1

Description

The embodiment of the present invention relates to a power supply device mounted on, for example, an air conditioner or a heat source device having a refrigeration cycle.

The power supply device installed in an air conditioner or a heat source device having a refrigeration cycle is a full-wave rectifier circuit that rectifies the voltage of an AC power supply, a booster circuit that boosts the output voltage of this full-wave rectifier circuit, and the output of this booster circuit. It includes an inverter or the like that converts the voltage into an AC voltage having a predetermined frequency and supplies the AC voltage to the compressor motor. The booster circuit was connected to the output terminal of the full-wave rectifier circuit, a series circuit of a reactor and a switch element, a diode for preventing backflow provided in a conduction path between the load and the switch element, and connected between both ends of the load. It includes a capacitor and boosts the output voltage of the full-wave rectifier circuit when the switch element is turned on and off.

The backflow prevention diode in the booster circuit has a small voltage drop with respect to the current flowing in the forward direction. This voltage drop leads to power loss of the booster circuit and cannot be ignored in terms of energy saving.

As a countermeasure, a switch element (referred to as a second switch element), which has less power loss than the diode for preventing backflow, that is, a small on-resistance value, is connected in parallel to the diode, and this second switch element is connected to the switch element on the reactor side (first switch element). (1 switch element) is turned off when turned on and turned on when turned off, that is, the first and second switch elements are complementarily operated to reduce the period during which a forward current flows in the diode for preventing reverse current to reduce the diode. It is conceivable to reduce the power loss due to. MOSFETs are used as the first and second switch elements. In this case, if both switch elements are turned on at the same time, a short-circuit current will flow from the capacitor through both switch elements in the route that bypasses the backflow prevention diode.Therefore, when changing either switch element from off to on, A so-called dead time in which both switches are turned off is secured. Therefore, the current flows through the backflow prevention diode only during the dead time period of this very short time.

JP, 2009-38875, A

The current flowing through the reactor (referred to as reactor current) pulsates as the switch element turns on and off. In addition, when the load suddenly decreases due to a sudden change in the load condition of the refrigeration cycle or a sharp decrease in the number of revolutions of the compressor, and the current flowing through the load decreases, the level of the reactor current reaches "0 (zero)" or its vicinity. To descend.

Here, when the second switch element is switched from off to on while the level of the reactor current is dropping to or near "0", a reverse recovery current is generated in the diode element of the full-wave rectification circuit, which causes It was found that the reactor current Ia may fluctuate to the negative side (minus side). Specifically, when the second switch element is turned on while the reactor current level is decreasing to or near "0", the second switch element is a MOSFET capable of flowing current in both directions when turned on. Therefore, the boosted capacitor voltage applies a reverse voltage to the diode element of the full-wave rectifier circuit through the second switch element. Normally, the diode element does not flow current in the reverse direction, but if a reverse voltage is applied to the diode element that was flowing current in the forward direction, the reverse current (reverse recovery current) will flow to the diode element for a short period of time. Is called). After the reverse recovery current reaches the peak value, the temporal rate of change (di/dt) of the negative reactor current −Ia rapidly changes from negative to positive. At this time, a large counter electromotive force is generated in the reactor, and an excessive surge voltage due to the counter electromotive force is generated across the reactor. If an excessive voltage, which is the sum of the surge voltage and the capacitor voltage, is applied to the output end of the full-wave rectifier circuit, the diode element of the full-wave rectifier circuit may be destroyed.

An object of the embodiments of the present invention is to provide a power supply device capable of preventing the destruction of elements due to a surge voltage.

A power supply device according to a first aspect includes a rectifier circuit, a booster circuit, a current detection unit, and a control unit. The rectifier circuit rectifies the three-phase AC voltage. The booster circuit is a series circuit of a first switch element having a reactor connected to the output end of the rectifier circuit and a diode connected in antiparallel, and a backflow prevention provided in a conduction path between a load and the first switch element. Diode, a second switch element connected in parallel with the backflow prevention diode, and a capacitor connected in parallel with the load. The on/off of the first switch element and the on/off of the first switch element are opposite. A boost mode in which the output voltage of the rectifier circuit is boosted by turning on and off the phase of the second switch element, and a non-output mode in which the output voltage of the rectifier circuit is output without boosting by continuing to turn off the first switch element. It has a boost mode. The control means sets the booster circuit in the non-boosting mode when the instantaneous value Ia of the current detected by the current detecting means is equal to or less than the set value Ias while the booster circuit is in the boosting mode.

A power supply device according to a third aspect includes a rectifier circuit, a booster circuit, and a capacitor or a varistor connected to an output terminal of the rectifier circuit. The rectifier circuit rectifies the AC voltage. The booster circuit is a series circuit of a first switch element having a reactor connected to the output end of the rectifier circuit and a diode connected in antiparallel, and a backflow prevention provided in a conduction path between a load and the first switch element. Diode, a second switch element connected in parallel with the backflow prevention diode, and a capacitor connected in parallel with the load. The on/off of the first switch element and the on/off of the first switch element are opposite. The output voltage of the rectifier circuit is boosted by turning on and off the second switch element in phase. The capacitor or varistor connected to the output terminal of the rectifier circuit absorbs the surge voltage caused by the reverse recovery current generated in the diode element of the rectifier circuit.

The block diagram which shows the structure of 1st Embodiment. The figure which shows the waveform of the reactor current when there is no protection control of 1st Embodiment. The figure which expands and shows a part of waveform of FIG. The flowchart which shows the protection control of 1st Embodiment. The figure which shows the waveform of the reactor current in 1st Embodiment. The block diagram which shows the structure of 2nd Embodiment. The figure which shows the structure of the principal part of the modification of 2nd Embodiment. The figure which shows the structure of the principal part of another modification of 2nd Embodiment. The figure which shows the structure of the principal part of the further another modified example of each embodiment.

[1] First embodiment
As a first embodiment, a power supply device installed in an air conditioner having a refrigeration cycle will be described as an example.
As shown in FIG. 1, a diode bridge full-wave rectifier circuit 2 (hereinafter referred to as a full-wave rectifier circuit) is connected to a three-phase AC power source 1, and a booster circuit 10 is connected to an output terminal of the full-wave rectifier circuit 2. ing. The full-wave rectifier circuit 2 rectifies the three-phase AC voltage.

The booster circuit 10 is a series circuit of a reactor 11 and a switch element (first switch element) SW1 connected to the output terminal of the full-wave rectifier circuit 2, and a power supply path between the inverter 20 as a load and the first switch element SW1. Includes a backflow prevention diode D2 provided in, a switch element (second switch) SW2 connected in parallel to the backflow prevention diode D2, and a capacitor (electrolytic capacitor) 12 connected in parallel to the load. A boost mode in which the output voltage (DC voltage) of the full-wave rectifier circuit 2 is boosted by turning off (intermittent on) and turning on and off (intermittent on) the switch element SW2 having a phase opposite to the on and off of the switch element SW1, and There is a non-boosting mode in which the output voltage of the full-wave rectifier circuit 2 is output without being boosted by turning off the switch element SW1 (continuing turning off) and turning on the switch element SW2 (continuing turning on). The switch element SW1 is also referred to as a lower phase side switch element, and the switch element SW2 is also referred to as an upper phase side switch element.

The switch element SW1 is a semiconductor switch element having a small ON resistance, such as a super junction MOSFET, which includes a parasitic diode D1 connected in antiparallel with the switch element body, and is turned on/off by a drive signal S1 supplied from the controller 30. The switch element SW2 includes a parasitic diode D2 connected in anti-parallel with the switch element body, has a bidirectionality in which a current flows bidirectionally between the drain and source at the time of turning on, and has a power loss at the time of turning on the parasitic diode D2. The semiconductor switch element, which is smaller than the power loss due to the voltage drop in the forward direction, such as the switch element SW1, is a super-junction MOSFET having a small on-resistance, and is turned on by the drive signal S2 supplied from the controller 30. It is driven on and off in the opposite phase to off. The parasitic diode D2 of the switch element SW2 is used as it is as the backflow prevention diode D2.

An inverter 20, which is a load, is connected to the output terminal of the booster circuit 10. The inverter 20 converts the output voltage of the booster circuit 10 into an AC voltage by switching and outputs it as drive power to the motor 21. The motor 21 is a motor for driving the compressor 22 and is, for example, a brushless DC motor that is an inductive load, and operates by the output of the inverter 20.

The compressor 22 draws in the refrigerant, compresses it, and discharges it. One end of an outdoor heat exchanger 24 is connected to the refrigerant discharge port of the compressor 22 via a four-way valve 23, and the other end of the outdoor heat exchanger 24 is connected to one end of an indoor heat exchanger 26 via an expansion valve 25. Connected. The other end of the indoor heat exchanger 26 is connected to the refrigerant suction port of the compressor 22 via the four-way valve 23. The compressor 22, the four-way valve 23, the outdoor heat exchanger 24, the expansion valve 25, and the indoor heat exchanger 26 constitute a heat pump type refrigeration cycle of the air conditioner. The arrow in FIG. 1 indicates the flow of the refrigerant during cooling, and the high temperature refrigerant discharged from the compressor absorbs heat in the indoor heat exchanger 26 to cool the room and radiates heat in the outdoor heat exchanger 24. That is, the indoor heat exchanger 26 becomes a heat absorber, and the outdoor heat exchanger 24 becomes a radiator. By reversing the four-way valve 23, the flow of the refrigerant is reversed and heating operation can be performed. In this case, the indoor heat exchanger 26 radiates heat to warm the room, and the outdoor heat exchanger 24 absorbs heat.

A current sensor 13 for detecting a current (instantaneous value; referred to as a reactor current) Ia flowing in the reactor 11 is arranged in a conduction path between the positive side output end of the full-wave rectifier circuit 2 and the reactor 11 of the booster circuit 10. .. A current sensor 27 that detects a current (phase winding current) flowing in the motor 21 is arranged in a current path between the inverter 20 and the motor 21. The detection results of the current sensors 13 and 27 are supplied to the controller 30, and the output voltage (voltage across the capacitor 12) Vdc of the booster circuit 10 is detected by the controller 30.

The controller 30 includes a boost control unit 40, an inverter control unit 50, and a target value setting unit 51.

The step-up control unit 40 switches the step-up circuit 10 with a pulse width so that the output voltage Vdc of the step-up circuit 10 becomes the target value Vdcref and the input current (reactor current) Ia to the step-up circuit 10 becomes constant. Modulation (PWM) control is performed. The subtraction unit 41, the PI controller 42, the subtraction unit 43, the PI controller 44, the PWM signal generation unit 45, the carrier generation unit 46, and the switch drive control units (control means) 47 and 48. Including.

The subtraction unit 41 obtains a deviation ΔVdc between the output voltage Vdc of the booster circuit 10 and the target value Vdcref. The PI controller 42 obtains the current command value Iref for the input current (reactor current) Ia to the booster circuit 10 by the proportional/integral calculation using the deviation ΔVdc obtained by the subtraction unit 41 as an input. The subtraction unit 43 obtains a deviation ΔIa between the current command value Iref obtained by the PI controller 42 and the input current (detection current of the current sensor 13) Ia to the booster circuit 10. The PI controller 44 obtains a voltage command value Vref for pulse width modulation by a proportional/integral calculation using the deviation ΔIa obtained by the subtraction unit 43 as an input. The carrier generation unit 46 generates a triangular-wave carrier signal voltage Vc having a predetermined frequency. The PWM signal generation unit 45 performs pulse width modulation (voltage comparison) on the carrier signal voltage Vc generated by the carrier generation unit 46 with the voltage command value Vref obtained by the PI controller 44, thereby switching elements SW1 and W2 of the booster circuit 10. A pulsed PWM signal S0 for switching is generated.

The switch drive control unit 47 has the same phase as the PWM signal S0 generated by the PWM signal generation unit 45 when the target value Vdcref set by the target value setting unit 51 is equal to or higher than a predetermined value (at high/medium load). The drive signal S1 is generated and output for driving the switch element SW1. When the target value Vdcref set by the target value setting unit 51 is equal to or higher than a predetermined value (when the load is high/medium), the switch drive control unit 48 has a phase opposite to that of the PWM signal S0 generated by the PWM signal generation unit 45. The drive signal S2 is generated and output for driving the switch element SW2. The booster circuit 10 operates in the boosting mode by the output of the drive signals S1 and SW2.

Further, when the target value Vdcref set by the target value setting unit 51 is less than the predetermined value (when the load is low), the switch drive control unit 47 generates the drive signal S1 for continuously turning off the switch element SW1. Output. When the target value Vdcref set by the target value setting unit 51 is less than the predetermined value (when the load is low), the switch drive control unit 48 generates and outputs the drive signal S2 for continuously turning on the switch element SW2. .. Since the switch element SW1 is continuously turned off by the output of the drive signals S1 and SW2, boosting is not performed and the boosting circuit 10 is in the non-boosting mode.

In particular, the switch drive control units 47 and 48 are arranged so that the switch element SW2 is switched from on to off before the switch element SW1 is switched from off to on, that is, the timing and the switch at which the switch element SW1 is switched from off to on. In order to secure a so-called dead time in which both the switch elements SW1 and SW2 are in an off state with the timing when the element SW2 is switched from on to off, and after the switch element SW1 is switched from on to off. Both the switch elements SW1 and SW2 are turned off so that the switch element SW2 is switched from off to on, that is, between the timing when the switch element SW1 is switched from on to off and the timing when the switch element SW2 is switched from off to on. The drive signals S1 and S2 are generated so as to secure a so-called dead time for achieving the state.

Further, the switch drive control units 47 and 48 switch between the boosting mode and the non-boosting mode by the following method. The switch drive control units 47 and 48 switch to the boost mode when the effective value Iam of the reactor current Ia exceeds the set value Iams during the non-boosting mode. Further, when the effective value Iam of the reactor current Ia falls below the set value "Iams-α" during the boost mode, the mode is switched to the non-boosting mode. This is because, in the state where the effective current value is small, the inverter that drives the compressor originally does not require boosting, and on the contrary, boosting causes an increase in switching loss due to ON/OFF of the switch element SW2. This is because.

Further, when it is detected that the reactor current (instantaneous value) Ia falls below the set value Ias during the boosting mode, the switch drive control units 47 and 48 prohibit the boosting mode of the boosting circuit 10 and prohibit the boosting circuit. It includes protection control means for setting 10 to the non-boosting mode. The effective value Iam of the reactor current Ia is calculated from the instantaneous current value for several cycles of the AC power supply. The set value Iams is 12 A, for example, and the set value Ias is 3 A, for example. Further, “α” is a preset value set to function as a hysteresis for preventing frequent switching between the boost mode and the non-boosting mode, and for example, a large value of about 50% of the set value Ias=6A. Is set. The subtraction unit 41 and the PI controller 42 function as a voltage control system. The subtractor 43 and the PI controller 44 function as a current control system. By the voltage control system and the current control system, the booster circuit 10 is controlled so that the output voltage Vdc of the booster circuit 10 becomes the target value Vdcref and the input current (reactor current) Ia to the booster circuit 10 becomes constant. The switching is PWM controlled.

The inverter control unit 50 estimates the speed (rotation speed) of the motor 21 from the detection current (motor current) of the current sensor 27, and makes the estimated speed the target speed corresponding to the magnitude of the load (refrigeration load). The switching of the inverter 20 is PWM controlled. The target value setting unit 51 sets the minimum output voltage Vdc of the booster circuit 10 required for the output voltage of the inverter 20 to obtain the target speed as the target value Vdcref. That is, the target value Vdcref is determined by the load of the refrigeration cycle, is set low when the compressor 22 (motor 21) is in a low rotation state, that is, low, and increases as the compressor 22 rotates at higher speed (high load). The value is set.

The full-wave rectifier circuit 2, the booster circuit 10, the current sensor 13, the inverter 20, the current sensor 27, the controller 30, and the like constitute the power supply device of this embodiment.

Next, the control executed by the controller 30 will be described.
When the motor 21 rotates at a high/medium speed and under a high/medium load, the switch element SW1 is turned on/off, and the switch element SW2 is turned on/off in a phase opposite to the on/off state of the switch element SW1. As a result, the output voltage of the full-wave rectifier circuit 2 is boosted by the booster circuit 10 and supplied to the inverter 20. When the motor 21 rotates at a low speed and has a low load, the switch element SW1 is continuously turned off and the switch element SW2 is continuously turned on. As a result, the output voltage of the full-wave rectifier circuit 2 passes through the reactor 11 and the switch element SW2, and is supplied to the inverter 20 via the capacitor 12 without being boosted.

FIG. 2 shows a waveform of the reactor current Ia when it is assumed that there is no protection control means for the switch drive control units 47 and 48, and a part of this waveform is enlarged and shown in FIG.

That is, the level of the reactor current Ia drops to “0” or its vicinity as the load of the booster circuit 10 sharply decreases. When the switch element SW2 is turned on in the state where the level of the reactor current Ia drops to or near “0”, assuming that there is no protection control means for the switch drive control units 47 and 48, the switch element SW2 is Since it is a MOSFET, current may flow from the capacitor 12 toward the AC power supply 1.

In each diode element of the full-wave rectifier circuit 2, a current normally flows only in the forward direction. However, a MOSFET capable of flowing a current in both directions of the switch element body when turned on is used as the switch element SW2, and the voltage Vdc of the smoothing capacitor 12 is in a state of being boosted above the power supply voltage. Due to this, when the switch element SW2 is turned on when the level of the reactor current Ia is near “0”, since the switch element SW2 is a MOSFET capable of flowing current in both directions, the boosted voltage Vdc of the capacitor 12 is A reverse voltage is applied to each diode element of the full-wave rectifier circuit 2 through the switch element SW2. As a result, the reverse recovery current Ir starts to flow in the diode element of the full-wave rectifier circuit 2 in which the current has flowed in the forward direction until a short period of time, as shown by the broken line arrow in FIG. When the reverse recovery current Ir has finished flowing, the diode element of the full-wave rectification circuit 2 blocks the flow of the reverse recovery current Ir.

Even if the switch element SW2 is switched off while the reverse recovery current Ir is flowing in the diode element of the full-wave rectification circuit 2, the reverse recovery current Ir current is output from the negative side output end of the full-wave rectification circuit 2. It flows through the parasitic diode D1 of the switch element SW1 in the forward direction to the positive output terminal of the full-wave rectifier circuit 2 (reflux current).

Then, after the reverse recovery current reaches the peak value, the temporal change rate (di/dt) of the negative reactor current −Ia rapidly changes from negative to positive. At this time, a large counter electromotive force is generated in the reactor 11, and an excessive surge voltage resulting from the counter electromotive force is generated at both ends of the reactor 11. If an excessive voltage that is the sum of this surge voltage and the voltage Vdc of the capacitor 12 is applied to the output end of the full-wave rectifier circuit 2, the diode element of the full-wave rectifier circuit 2 may be destroyed.

In order to deal with this problem, the switch drive control units 47 and 48 execute the control shown in the flowchart of FIG. When the effective value Iam of the reactor current Ia is larger than the set value Iams (NO in step S1), the switch drive control units 47 and 48 execute the boosting operation of the booster circuit 10 (operation in the boosting mode) (step S2). .. With the execution of the boosting operation, the switch drive control units 47 and 48 return to the determination of step S1 on condition that the reactor current (instantaneous value) Ia is not equal to or less than the set value Ias (NO in step S3).

When the effective value Iam of the reactor current Ia falls below the set value Iams (YES in step S1), the switch drive control units 47 and 48 determine whether the booster circuit 10 is in the boosting operation (step S4). If the boosting operation is being performed (YES in step S4), the switch drive control units 47 and 48 compare the effective value Iam with the set value "Iams-α" (step S5). If the effective value Iam is not less than or equal to the set value "Iams-α" (NO in step S5), the switch drive control units 47 and 48 continue the boosting operation (step S2). However, if the effective value Iam has fallen to the set value “Iams−α” or less (YES in step S5), the switch drive control units 47 and 48 prohibit the boosting operation of the boosting circuit 10 and turn on the boosting circuit 10. The mode is switched to the non-boosting mode (step S6). Then, the switch drive control units 47 and 48 repeat the processing from the first step S1.

Specifically, when the air conditioning or the refrigeration load increases during the operation of the refrigeration cycle, the frequency of the output voltage of the inverter 20 increases, that is, the rotation speed of the compressor 22 increases, and the effective value Iam of the reactor current Ia increases. Is increased and exceeds the set value Iams, the boosting operation is started. After that, due to the operation of the refrigerating cycle, the air conditioning or the refrigerating load is lowered, the frequency output from the inverter 20 is lowered, the effective value Iam of the reactor current Ia is lowered, and the boosting is performed when the value falls below the set value “Iams−α”. The operation is completed and the non-boosting mode is set. The switching between the boost mode and the non-boosting mode here is intended to improve efficiency. It should be noted that α of the set value “Iams−α” is a hysteresis value, and it is desirable to set it to a considerably large value, for example, about 50% of the set value Ims. By securing this hysteresis value α, frequent occurrence of switching between the boosting mode and the non-boosting mode is prevented.

On the other hand, for example, when the load suddenly decreases due to the shift to the defrosting operation in which the four-way valve 23 of the refrigeration cycle reverses, the power consumed on the inverter 20 side decreases and the reactor current Ia decreases. Therefore, during the boosting operation, when the reactor current (instantaneous value) Ia drops below the set value Ias due to a sudden decrease in the load of the compressor 22 (YES in step S3), the switch drive control units 47 and 48 cause the boosting circuit 10 to operate. The boosting mode is prohibited and the boosting circuit 10 is set to the non-boosting mode (step S6).

In this way, by prohibiting the boosting switching when the reactor current Ia falls below the set value Ias, as shown in FIG. 5, the subsequent fall of the reactor current Ia subsides at “0” level, The current Ia does not swing to the negative side.

Since the negative reactor-Ia does not flow, even when the switch element SW2 is switched from OFF to ON, the boosted voltage Vdc of the capacitor 12 causes a reverse voltage to each diode element of the full-wave rectifier circuit 2 through the switch element SW2. The situation of joining can be prevented. Therefore, the reverse recovery current Ir does not flow through the diode element of the full-wave rectifier circuit 2, and the generation of the surge voltage due to the reverse recovery current Ir can be prevented. That is, an excessive voltage, which is the sum of the surge voltage and the voltage Vdc of the capacitor 12, is not applied to the output end of the full-wave rectifier circuit 2, and the diode element in the full-wave rectifier circuit 2 can be prevented from being destroyed.

As described above, there is a mode switching control for switching to the non-boosting mode when the effective value Iam of the reactor current Ia drops below the set value “Iams−α” during the boosting mode in order to improve efficiency. The control is to switch between the boosting mode and the non-boosting mode in the steady state for the purpose of improving efficiency, and it takes several cycles of the AC power supply to detect (update) the effective value Iam of the reactor current Ia. Become. For this reason, in the normal mode switching control, it is not possible to respond to the sudden drop of the reactor current (instantaneous value) Ia to “0” or its vicinity due to the rapid decrease of the load as described above, It is not possible to switch from boost mode to non-boost mode. Therefore, in step S3, the boosting mode and the non-boosting mode are switched based on the instantaneous value of the reactor current Ia (step S6).

Further, in the present embodiment, in the non-boosting mode, the switch element SW2 is kept on, and the current is prevented from flowing to the backflow prevention diode D2 as much as possible to improve the efficiency. However, if a device with a large rating is adopted as the backflow prevention diode D2 and it is possible to flow a current of a certain amount, the reactor current (instantaneous value) Ia drops below the set value Ias during the boost mode. Only in the non-boosting mode (step S6) at the time (YES in step S3), the switch element SW2 is continuously turned off to allow the current to flow through the backflow prevention diode D2 to completely generate the reverse current in the reactor 11. May be blocked. That is, depending on the rating of the backflow prevention diode D2, the operation of the switch element SW2 may be on or off if at least the switch element SW1 is kept off.

[2] Second embodiment
In the second embodiment, instead of the protection control of the switch drive control units 47 and 48 in the first embodiment, a capacitor 61 is connected to the output end of the full-wave rectifier circuit 2 as shown in FIG. Other configurations are the same as those in the first embodiment.

The surge voltage generated when the negative reactor current −Id flows is generated by the disappearance of the negative reactor current −Id. Therefore, a capacitor 61 is connected to the output terminal of the full-wave rectification circuit 2 so that the surge voltage energy generated when a negative reactor current −Id flows is absorbed by the capacitor 61. Therefore, an excessive voltage will not be applied to the output terminal of the full-wave rectifier circuit 2, and thus the destruction of the elements of the full-wave rectifier circuit 2 can be prevented.

The capacitance of the capacitor 61 needs to be selected in consideration of the absorption amount of the surge voltage generated by the negative reactor current −Id and so as not to cause resonance with the substrate or the parasitic inductance in the circuit. Specifically, when the capacitance of the capacitor 61 is large, a parasitic inductance with the switch element SW1 or LC resonance with the parasitic diode D1 occurs, and a resonance current flows at the timing when the switch element SW1 switches to cause a switch element SW1. Will increase the loss. Since the allowable loss varies depending on the characteristics of the semiconductor switch element and the heat radiation structure of the system to be incorporated, it is necessary to select the capacitor 61 having the optimum capacity in consideration of them. Hereinafter, this selection will be described.

Energy E _L accumulated in the reactor 11 when a current flows in the reactor 11 is expressed by the following equation (1). L is the inductance of the reactor 11, and i _L is the reverse current (negative reactor current −Id) flowing in the reactor 11.
E _L =1/2×L×i _L ² ... Formula (1)
It is sufficient to determine the capacitance C of the capacitor 61 so that the energy stored in the energy E _L and the capacitor 61 are balanced.

The initial energy Ec0 stored in the capacitor 61 before absorption of the surge voltage is represented by the following equation (2). Energy Ec1 accumulated in the capacitor 61 after absorbing the surge voltage is expressed by the following equation (3). V is the initial voltage of the capacitor 61, and ΔV is the allowable voltage jump when a surge voltage occurs.
Ec0=1/2×C×V ² ……Equation (2)
Ec1=1/2×C×(V+ΔV) ²
=1/2×C×V ² +C×V×ΔV+1/2×C×ΔV ² (3)
The charging energy Ec= of the capacitor 61 is expressed by the following equation (4).
Ec=Ec1-Ec0=C×V×ΔV+1/2×C×ΔV ² (4)
Assuming that all of the energy E _L stored in the reactor 11 is charged in the capacitor 61, the formula (1)=the formula (4), which can be replaced by the following formula (5).
1/2×L×i _L ² =C×V×ΔV+1/2×C×ΔV ² (5)
For example, assuming that the inductance L of the reactor 11 is 0.5 mH, the reverse current flowing through the reactor 11 is 4 A, the initial voltage V of the capacitor 61 is 400 V, and the allowable voltage jump ΔV at the time of surge voltage generation is 100 V, these are given by the formula (5). When fitted on the left side, the following formula (6) is obtained.
1/2 x L x i _L ² = 1/2 x 0.5 x 10 ^-3 x 4 ² = 4.00 [ml] (Equation 6)
If the right side of the equation (5) is expanded based on the equation (6), 0.1 μF can be obtained as the capacitance C of the capacitor 61 as in the following equation (7).

C=(4.00×10 ^-3 )/(V×ΔV+1/2×ΔV)
= (4.00×10 ^-3 )/(400×100+100)≒0.1[ml]……Equation (7)
[3] Modification of Second Embodiment As shown in the main part of FIG. 7, in the second embodiment, a resistor 62 is inserted and connected in a conduction path between the full-wave rectifier circuit 2 and the capacitor 61. Good. In addition to selecting the capacitor 60 having the optimum capacity as in the second embodiment, by forming an RC snubber circuit by connecting the capacitor 60 and the resistor 62 in series, even if resonance occurs, It is possible to suppress an increase in EMI (Electro Magnetic Interference) noise.

As shown in the main part in FIG. 8, in the second embodiment, a resistor 62 is inserted and connected in the energization path between the full-wave rectifier circuit 2 and the capacitor 61, and a diode 63 is connected in parallel to the resistor 62. It may be configured. The capacitor 60, the resistor 62, and the diode 63 form an RDC snubber circuit. With this configuration, the power loss of the resistor 62 can be reduced.

In the second embodiment, the capacitor 61 for absorbing the surge voltage caused by the negative reactor current −Ia is connected to the output terminal of the full-wave rectification circuit 2, but instead of the capacitor 61, the surge voltage is absorbed. You may connect the varistor of. Even if a reverse recovery current is generated by the negative reactor current −Ia and a surge voltage resulting from the reverse recovery current Ir is generated across the reactor 11, an excessive voltage that is the sum of the surge voltage and the voltage Vdc of the capacitor 12 is It is absorbed by the varistor and does not add to the output end of the full-wave rectifier circuit 2. Therefore, the breakdown of the diode element in the full-wave rectification circuit 2 can be prevented.

Further, in order to obtain higher efficiency, as shown in FIG. 9, instead of the switch element SW2 of each of the above-described embodiments, a series circuit of a switch element (previous stage switch element) SW2 and a switch element (second stage switch element) SW3. May be provided, and the diode D4 for backflow prevention may be connected in parallel to the series circuit. The switch elements SW2 and SW3 are turned on and off in synchronization with each other by the drive signal S2. The series circuit of the switch elements SW2 and SW3 is formed by connecting the switch elements SW2 and SW3 in series in mutually opposite directions. The high efficiency switching circuit for suppressing the reverse recovery current of the parasitic diode D3 of the switch element SW3 is a diode for preventing backflow. It is formed with D4. The high-efficiency switching circuit corresponds to the semiconductor switch circuit described in Japanese Unexamined Patent Publication No. 2015-156795, and effectively suppresses the reverse recovery current of the parasitic diode (also called a freewheeling diode) D3 of the switch element SW3. As a result, the loss is reduced and the switching speed is increased. By adopting this high-efficiency switching circuit, higher efficiency can be obtained as compared with the above embodiments.

The above embodiments and modifications are presented as examples, and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, rewritings, and changes can be made without departing from the spirit of the invention. These embodiments are included in the scope of the invention, and are included in the invention described in the claims and an equivalent range thereof.

DESCRIPTION OF SYMBOLS 1... Three-phase AC power supply, 2... Full wave rectification circuit, 10... Booster circuit, 11... Reactor, 12... Capacitor, 13... Current sensor, D2... Reverse current blocking diode, SW1... Switch element (first switch element), SW2...Switch element (second switch element), 20...Inverter, 30...Controller, 40...Boost control section, 45...PWM signal generation section, 47,48...Switch drive control section, 50...Inverter control section, 51...Target Value setting section

Power apparatus according to claim 1 includes a rectifier circuit, a booster circuit, a capacitor connected or varistor to the output terminal of the rectifier circuit. The rectifier circuit rectifies the AC voltage. The booster circuit is a series circuit of a first switch element having a reactor connected to the output end of the rectifier circuit and a diode connected in antiparallel, and a backflow prevention provided in a conduction path between a load and the first switch element. Diode, a second switch element connected in parallel with the backflow prevention diode, and a capacitor connected in parallel with the load. The on/off of the first switch element and the on/off of the first switch element are opposite. The output voltage of the rectifier circuit is boosted by turning on and off the second switch element in phase. The capacitor or varistor connected to the output terminal of the rectifier circuit absorbs the surge voltage caused by the reverse recovery current generated in the diode element of the rectifier circuit.

C=(4.00×10 ^-3 )/(V×ΔV+1/2×ΔV)
= (4.00 × 10 ^-3 )/(400 × 100 + 100) ≒ 0.1 [ μF ] ……Equation (7)
[3] Modified Example of Second Embodiment As shown in the main part of FIG. 7, in the second embodiment, a resistor 62 is inserted and connected in a conduction path between the full-wave rectifier circuit 2 and the capacitor 61. Good. In addition to selecting the capacitor 60 having the optimum capacity as in the second embodiment, by forming an RC snubber circuit by connecting the capacitor 60 and the resistor 62 in series, even if resonance occurs, It is possible to suppress an increase in EMI (Electro Magnetic Interference) noise.

Claims (9)

A rectifier circuit that rectifies the three-phase AC voltage,
A series circuit of a first switch element having a reactor connected to the output terminal of the rectifier circuit and a diode connected in anti-parallel, a backflow prevention diode provided in a conduction path between a load and the first switch element, A second switch element connected in parallel to the backflow prevention diode; and a capacitor connected in parallel to the load, wherein the first switch element is turned on/off and the first switch element is turned on/off in the opposite phase. There are a boost mode in which the output voltage of the rectifier circuit is boosted by turning on and off two switch elements, and a non-boost mode in which the output voltage of the rectifier circuit is output without boosting by continuing to turn off the first switch element. Booster circuit,
Current detection means for detecting the current flowing through the reactor,
Control means for setting the booster circuit to a non-boosting mode when the instantaneous value Ia of the current detected by the current detecting means is equal to or less than the set value Ias in the boosting mode of the booster circuit;
A power supply device comprising: When the effective value Iam of the current Ia detected by the current detection unit is equal to or higher than the set value Iams, the control unit sets the booster circuit to the boost mode, and the effective value Iam is lower than the set value Iams. The power supply device according to claim 1, wherein when the voltage is lower than or equal to -α, the boosting mode of the boosting circuit is prohibited and the boosting circuit is set to the non-boosting mode. A rectifier circuit that consists of a diode element and rectifies AC voltage,
A series circuit of a first switch element having a reactor connected to the output terminal of the rectifier circuit and a diode connected in anti-parallel, a backflow prevention diode provided in a conduction path between a load and the first switch element, A second switch element connected in parallel to the backflow prevention diode; and an electrolytic capacitor connected in parallel to the load, wherein the first switch element is turned on and off and the first switch element is turned on and off. A booster circuit for boosting the output voltage of the rectifier circuit by turning on and off the second switch element;
A capacitor or a varistor connected to the output terminal of the rectifying circuit,
Equipped with
The capacitor or the varistor absorbs a surge voltage caused by a reverse recovery current generated in a diode element of the rectifier circuit,
A power supply device characterized by the above. The power supply device according to claim 3, further comprising a resistor that is inserted and connected to a current path between the rectifier circuit and the capacitor. The power supply device according to claim 4, further comprising a diode connected in parallel with the resistor. The second switch element is a MOSFET including a parasitic diode, and the power loss at the time of turning on is smaller than the power loss due to the forward voltage drop of the parasitic diode.
The backflow prevention diode is a parasitic diode of the second switch element,
The power supply device according to claim 1, wherein the power supply device is a power supply device. The said load is an inductive load, The power supply device as described in any one of Claim 1 thru|or 6 characterized by the above-mentioned. The power supply device according to claim 7, wherein the inductive load is an inverter connected to an output end of the booster circuit and a DC brushless motor for driving a compressor that operates by an output of the inverter. The second switch element is a series circuit of a front stage switch element and a rear stage switch element,
The booster circuit is a series circuit of a first switch element having a reactor connected to an output terminal of the rectifier circuit and a diode connected in antiparallel, and a reverse current provided in a conduction path between a load and the first switch element. A protection diode, a series circuit of the front-stage and rear-stage switches connected in parallel to the backflow prevention diode, and a capacitor connected in parallel to the load. , A boosting mode in which the output voltage of the rectifier circuit is boosted by turning on and off the front-stage and rear-stage switch elements that are opposite in phase to the off state, and the output voltage of the rectifier circuit is boosted by continuing to turn off the first switch element. Has a non-boosting mode that outputs without
The power supply device according to claim 1 or 2, wherein:

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