JP2015130759A - Electric power conversion system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power conversion system capable of ensuring the safety of circuit components by preventing abnormal rise of output voltage from the converter due to sharp reduction of load.SOLUTION: In a heat-pump refrigerant cycle, when a four-way valve does not switch any flow path, a converter is operated in a mode including pressure rise; and when the four-way valve switches the flow path, the converter is operated in a mode including no pressure rise.

Description

  The present invention relates to a power converter that converts the voltage of an AC power source into DC and converts the converted DC voltage into an AC voltage having a predetermined frequency.

  There is known a power conversion device that converts the voltage of an AC power source into DC by a converter, applies the converted DC voltage to a smoothing capacitor, converts the voltage of the smoothing capacitor into an AC voltage having a predetermined frequency by an inverter, and outputs the AC voltage. .

  Further, as a converter that converts the voltage of the AC power supply into DC, there is a boost converter that has a reactor, a diode, and a switching element and boosts and converts the voltage of the AC power supply into DC.

JP2011-229342A JP 2010-110172 A

  When driving the compressor motor of the heat pump refrigeration cycle with the output of the inverter, the pressure applied to the compressor motor is switched when the flow path of the four-way valve in the heat pump refrigeration cycle is switched. Fluctuates greatly and the load on the inverter decreases rapidly. With this sudden decrease in load, the output voltage of the converter may rise abnormally and exceed the smoothing capacitor's withstand voltage.

  An object of the present embodiment is to provide a power conversion device that can prevent an abnormal increase in the output voltage of a converter due to a sudden decrease in load, thereby ensuring the safety of circuit components.

  The power converter of claim 1 includes a converter, a smoothing capacitor, an inverter, and control means. The converter includes a reactor, a diode connected to the AC power supply through the reactor, and a switching element connected in parallel to the diode, and boosts and DC converts the voltage of the AC power supply. The smoothing capacitor is connected to the output terminal of the converter. The inverter converts the voltage of the smoothing capacitor into an AC voltage having a predetermined frequency, and outputs the converted AC voltage as drive power for the compressor motor of the heat pump refrigeration cycle. The control means operates the converter in a mode with pressure increase when there is no switching of the flow path of the four-way valve in the heat pump refrigeration cycle, and operates the converter in a mode without pressure increase when switching the flow path of the four-way valve.

The block diagram which shows the structure of one Embodiment of this invention. The flowchart which shows the control of the same embodiment. The figure which shows the pulsation of the load torque in the same embodiment. The figure which shows the relationship between the operation | movement of the four-way valve in the same embodiment, and the commutation mode of a converter. The figure which shows the relationship between the input voltage and input current to the converter in the same embodiment, and the output voltage of a converter.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
As shown in FIG. 1, a converter 2 is connected to phase lines R, S, and T of a commercial three-phase AC power source 1, and a smoothing capacitor 4 is connected to the output terminal of the converter 2. An inverter 5 is connected to the smoothing capacitor 4, and a load such as a brushless DC motor (also called a permanent magnet synchronous motor) 6 phase winding Lu. Lv. Lw is connected.

  An inverter 7 is connected to the smoothing capacitor 4, and a motor 105 </ b> M of an outdoor fan 105 described later is connected to the output terminal of the inverter 7.

  The converter 2 includes reactors 21, 22 and 23, a bridge circuit of diodes 31 a to 36 b connected to the three-phase AC power supply 1 through the reactors 21, 22 and 23, and switching elements connected in parallel to the diodes 31 a to 36 b For example, it has MOSFETs 31 to 36 and boosts and DC converts the voltage of the three-phase AC power supply 1. For example, an AC voltage of 100V is converted into a DC voltage of about 300V.

  The bridge circuit of the diodes 31a to 36b includes a series circuit of diodes 31a and 32a, a series circuit of diodes 33a and 34a, and a series circuit of diodes 35a and 36a. The interconnection point of the diodes 31a and 32a is connected to the R phase of the three-phase AC power supply 1, the interconnection point of the diodes 33a and 34a is connected to the S phase of the three-phase AC power supply 1, and the interconnection point of the diodes 35a and 36a. Is connected to the T phase of the three-phase AC power source 1. The diodes 31a to 36b are parasitic diodes of the MOSFETs 31 to 36.

  The inverter 5 includes MOSFETs 51, 52 connected in series, and a U-phase series circuit, MOSFETs 53, 54 connected in series to the phase winding Lu of the brushless DC motor 6. The MOSFETs 53, 54 are connected in series. Are connected in series to the phase winding Lv of the brushless DC motor 6, MOSFETs 55 and 56 are connected in series, and the connection point of the MOSFETs 55 and 56 is connected to the phase winding Lw of the brushless DC motor 6. A series circuit for W phase connected is included, and the voltage of the smoothing capacitor 4 is converted into a three-phase AC voltage having a predetermined frequency by switching of each MOSFET and output from the interconnection point of each MOSFET. The MOSFETs 51 to 56 include parasitic diodes 51a to 56a.

  The brushless DC motor 6 includes a stator having three phase windings Lu, Lv, and Lw connected in a star shape, and a rotor having a permanent magnet. The rotor rotates due to the interaction between the magnetic field generated by the current flowing through the phase windings Lu, Lv, and Lw and the magnetic field created by the permanent magnet.

  The brushless DC motor 6 is a drive motor (compressor motor) of the compressor 100 and is accommodated in a case of the compressor 100. The compressor 100 sucks and compresses the refrigerant, and discharges the compressed refrigerant. An outdoor heat exchanger 102 is connected to the refrigerant discharge port of the compressor 100 via a four-way valve 101, and an indoor heat exchanger 104 is connected to the outdoor heat exchanger 102 via an electric expansion valve 103. The refrigerant suction port of the compressor 100 is connected to the indoor heat exchanger 104 via the four-way valve 101 by piping. An outdoor fan 105 is disposed in the vicinity of the outdoor heat exchanger 102, and an indoor fan 106 is disposed in the vicinity of the indoor heat exchanger 104.

  The inverter 7 converts the voltage of the smoothing capacitor 4 into an AC voltage having a predetermined frequency by switching, and outputs the converted AC voltage as drive power to the motor 105M of the outdoor fan 105.

  The outdoor fan 105 supplies outside air to the outdoor heat exchanger 102 and supplies cooling air (outside air) to the heat sink 10 that is a heat radiating member to which the converter 2 and the inverter 5 are mounted. The indoor fan 106 circulates the air in the air-conditioned room through the indoor heat exchanger 104.

  During cooling, the refrigerant discharged from the compressor 100 flows to the outdoor heat exchanger 102 through the four-way valve 101, and the refrigerant flowing to the outdoor heat exchanger 102 releases heat to the outside air, as indicated by solid arrows. And condense. The refrigerant that has passed through the outdoor heat exchanger 102 is decompressed by the electric expansion valve 103 and flows to the indoor heat exchanger 104. The refrigerant that has flowed into the indoor heat exchanger 104 evaporates by taking heat from the indoor air, and is sucked into the compressor 100 through the four-way valve 101.

  During heating, the flow path of the four-way valve 101 is switched, so that the refrigerant discharged from the compressor 1 flows to the indoor heat exchanger 104 through the four-way valve 101 as indicated by the broken arrow, and the indoor heat exchange is performed. The refrigerant flowing into the vessel 104 releases heat into the room and condenses. The refrigerant that has passed through the indoor heat exchanger 104 is decompressed by the electric expansion valve 103 and flows to the outdoor heat exchanger 102. The refrigerant that has flowed into the outdoor heat exchanger 102 evaporates by drawing up heat from the outside air, and is sucked into the compressor 100 through the four-way valve 101.

  Current sensors 71, 72, 73 for detecting input current are disposed in the energization path between the three-phase AC power source 1 and the reactors 21, 22, 23. Current sensors 81, 82, 83 for detecting an output current (phase winding current) are disposed in a current path between the output end of the inverter 5 and the brushless DC motor 6. The detection results of these current sensors are supplied to the control unit 90.

  Connected to the control unit 90 is a remote control type operating device (referred to as a remote controller) 91 for setting operating conditions, a converter 2, an inverter 5, an inverter 7, a four-way valve 101, an electric expansion valve 103, and a motor 106M of an indoor fan 106. The

The control unit 90 has the following means (1) and (2) as main functions.
(1) First control means for operating the converter 2 in a mode without boosting to start the inverter 5 when starting the brushless DC motor 6 (thermo-on) and then operating the converter 2 in a mode with boosting.

  (2) Second control means for operating the converter 2 in a mode with boost when the flow path of the four-way valve 101 is not switched, and operating the converter 2 in a mode without boost when switching the flow path of the four-way valve 101.

  Specifically, the first control means (1), when starting up the brushless DC motor 6, starts up the inverter 5 while operating the converter 2 in the non-boosting mode and sets the rotational position of the brushless DC motor 6. The MOSFETs 51 to 56 of the inverter 5 are turned on and off by a PWM signal having a pulse width corresponding to the estimated rotational position, and the converter 2 is operated in a mode with a boost after the estimation of the rotational position is stabilized.

  Further, the first control means detects a torque current component Iq corresponding to torque pulsation (also referred to as torque ripple) of the brushless DC motor 6, and determines the brushless DC motor 6 according to the average value Iqa of the detected torque current component Iq. The torque correction amount for the torque is determined, torque pulsation control is performed to adjust the on / off duty of the PWM signal according to the determined torque correction amount, and the determined torque correction amount is set to a predetermined value (for example, Iqa / 2) It is determined that the estimation of the rotational position is stable when the value drops below. The average value Iqa of the torque current component Iq corresponds to the average torque necessary to maintain the designated rotational speed.

  The mode with step-up of the converter 2 is a PWM rectification mode in which MOSFETs corresponding to a plurality of phases (two phases or three phases) of the three-phase AC power supply 1 among the MOSFETs 31 to 36 of the converter 2 are turned on / off by a PWM signal. (2-phase PWM rectification mode or 3-phase PWM rectification mode). The mode without boost of the converter 2 is a diode rectification mode in which the MOSFETs 31 to 36 of the converter 2 are not turned on or off, or a MOSFET corresponding to one phase of the three-phase AC power supply 1 among the MOSFETs 31 to 36 of the converter 2 is PWM signal. This is a PWM rectification mode (one-phase PWM rectification mode) which is turned on and off by the above.

Next, the control executed by the control unit 90 will be described with reference to the flowchart of FIG.
When the thermostat is ON based on the comparison between the room temperature (the temperature detected by the room temperature sensor) and the set temperature of the remote controller 91 (YES in step 201), the control unit 90 determines that the brushless DC motor 6 needs to be activated. Then, the inverter 5 is started while the converter 2 is operated in the diode rectification mode (or the one-phase PWM rectification mode) without boosting (step 202).

  In the diode rectification mode operation without boosting, current flows from the three-phase AC power source 1 through the reactor 21 and the positive-side diode 31a to the smoothing capacitor 4 in a phase in which the R-phase voltage of the three-phase AC power source 1 is at a positive level. The current passing through the smoothing capacitor 4 first returns to the S phase of the three-phase AC power supply 1 through the negative diode 34a and the reactor 22, and then, as the phase of the R phase voltage advances, the negative diode 36a and the reactor 23 are changed. A path that passes through and returns to the T phase of the three-phase AC power source 1 is formed.

  In the phase in which the S-phase voltage of the three-phase AC power supply 1 is at a positive level, a current flows from the three-phase AC power supply 1 through the reactor 22 and the positive diode 33a to the smoothing capacitor 4, and the current passing through the smoothing capacitor 4 is first The phase returns to the T phase of the three-phase AC power source 1 through the negative side diode 36a and the reactor 23. Next, as the phase of the S phase voltage advances, the R phase of the three-phase AC power source 1 passes through the negative side diode 32a and the reactor 21. A path back to is formed.

  In a phase where the T-phase voltage of the three-phase AC power supply 1 is at a positive level, a current flows from the three-phase AC power supply 1 through the reactor 23 and the positive diode 35a to the smoothing capacitor 4, and the current passing through the smoothing capacitor 4 is first It returns to the R phase of the three-phase AC power source 1 through the negative side diode 32a and the reactor 21, and then the S phase of the three-phase AC power source 1 passes through the negative side diode 34a and the reactor 22 as the phase of the T phase voltage advances. A path back to is formed.

  In the phase where the R-phase input voltage, the S-phase input voltage, and the T-phase input voltage are at negative levels, the operation pattern is basically the same as that of the positive level period, except that the positive and negative signs are opposite. Therefore, the detailed description is abbreviate | omitted.

  As the inverter 5 is started, the control unit 90 estimates the rotational position of the rotor (also referred to as the rotor speed) in the brushless DC motor 6 based on the detected currents of the current sensors 81, 82, and 83, and carries a carrier signal having a predetermined frequency. (Triangular wave signal) A PWM signal is generated by pulse width modulation (voltage comparison between a carrier signal and a sine wave signal) with a sine wave signal having a voltage level corresponding to the estimated rotational position. The MOSFETs 51 to 56 of the inverter 5 are driven on and off.

  Incidentally, in the torque of the brushless DC motor 6, as shown in FIG. 3, pulsations corresponding to the suction stroke, the compression stroke, and the discharge stroke of the compressor 100 as a load are generated every cycle. This torque pulsation (also referred to as torque ripple) appears as vibration and noise of the compressor 100.

  In order to deal with this problem, the control unit 90 detects the torque current component Iq corresponding to the torque pulsation of the brushless DC motor 6 from the detected currents of the current sensors 81, 82, 83, and the average value of the detected torque current component Iq. A torque correction amount for the torque of the brushless DC motor 6 corresponding to the rotational position of the brushless DC motor 6 is determined according to Iqa, and the on / off duty of the generated PWM signal is determined according to the determined torque correction amount. adjust.

  Note that while the amount of torque correction that is likely to occur in a state where the rotational speed is small is large, a period during which the current flowing through the phase winding of the brushless DC motor 6 is small occurs, and an error occurs in rotational position estimation during that period. When the converter 2 is operated in the PWM rectification mode with step-up in a situation where an error occurs in the rotational position estimation, a pulsation close to the switching cycle of the inverter 5 is superimposed on the output voltage (DC voltage) of the converter 2, resulting in the rotational position. The estimation error increases.

  Therefore, the control unit 90 compares the determined torque correction amount with a predetermined value (for example, Iqa / 2) to determine whether or not the torque pulsation control is stable (step 203).

  When the torque correction amount is equal to or greater than the predetermined value, the control unit 90 determines that the torque pulsation control is not in the stable range, and thus determines that the rotational position estimation is not sufficiently stable. (NO in step 203), the operation of the diode rectification mode of the converter 2 is continued.

  When the torque correction amount falls below a predetermined value, the control unit 90 determines that the torque pulsation control has entered the stable range, and thus determines that the rotational position estimation is stable (in step 203). YES), the operation of converter 2 is switched from the diode rectification mode to the two-phase or three-phase PWM rectification mode (step 204).

  In the PWM rectification mode, the control unit 90 performs pulse width modulation (voltage comparison between the carrier signal and the sine wave signal) on the carrier signal (triangular wave signal) having a predetermined frequency with the sine wave signal, thereby generating the PWM signals Du, Dv, and Dw. The MOSFETs 31 to 36 of the converter 2 are turned on and off by the generated PWM signals Du, Dv, and Dw. The sine wave signals Du, Dv, and Dw are synchronized with the period of the R-phase voltage, S-phase voltage, and T-phase voltage of the three-phase AC power supply 1, and are generated based on the detection results of the current sensors 71, 72, and 73. .

  In this case, a current flows from the three-phase AC power source 1 through the reactor 21 and the positive-side diode 31a to the smoothing capacitor 4 in a phase where the R-phase voltage of the three-phase AC power source 1 becomes a positive level. Is first returned to the S phase of the three-phase AC power supply 1 through the negative diode 34a and the reactor 22, and then the three-phase AC power supply 1 through the negative diode 36a and the reactor 23 as the phase of the R phase voltage advances. A path is formed to return to the T phase. In addition to this operation, the MOSFET 32 is repeatedly turned on and off in accordance with the PWM signal Du generated by the control unit 90. When the MOSFET 32 is turned on, the interconnection point of the diodes 31 a and 32 a is electrically connected to the negative output terminal of the converter 2, and the short circuit path through the reactor 21, the MOSFET 32, the negative diode 34 a and the reactor 22 with respect to the three-phase AC power supply 1. Is formed. By forming this short circuit, energy (charge) is stored in the reactors 21 and 22. The energy stored in the reactors 21 and 22 is supplied to the smoothing capacitor 4 when the MOSFET 32 is turned off. By this energy supply, the voltage is boosted.

  In the phase where the S-phase voltage of the three-phase AC power source 1 is at a positive level, current flows from the three-phase AC power source 1 through the reactor 22 and the positive diode 33a to the smoothing capacitor 4, and the current passing through the smoothing capacitor 4 is first The phase returns to the T phase of the three-phase AC power source 1 through the negative side diode 36a and the reactor 23. Next, as the phase of the S phase voltage advances, the R phase of the three-phase AC power source 1 passes through the negative side diode 32a and the reactor 21. A path back to is formed. In addition to this operation, the MOSFET 34 is repeatedly turned on and off in accordance with the PWM signal Dv generated by the control unit 90. When the MOSFET 34 is turned on, the interconnection point of the diodes 33 a and 34 a is electrically connected to the negative output terminal of the converter 2, and the short-circuit path through the reactor 22, the MOSFET 34, the negative diode 36 a and the reactor 23 with respect to the three-phase AC power supply 1. Is formed. By forming this short circuit, energy (charge) is stored in the reactors 22 and 23. The energy stored in the reactors 22 and 23 is supplied to the smoothing capacitor 4 when the MOSFET 34 is turned off. By this energy supply, the voltage is boosted.

  In the phase where the T-phase voltage of the three-phase AC power supply 1 is at a positive level, a current flows from the three-phase AC power supply 1 through the reactor 23 and the positive diode 35a to the smoothing capacitor 4, and the current passing through the smoothing capacitor 4 is It returns to the R phase of the three-phase AC power source 1 through the negative side diode 32a and the reactor 21, and then the S phase of the three-phase AC power source 1 passes through the negative side diode 34a and the reactor 22 as the phase of the T phase voltage advances. A path back to is formed. In addition to this operation, the MOSFET 36 is repeatedly turned on and off according to the PWM signal Dw generated by the control unit 90. When the MOSFET 36 is turned on, the interconnection point of the diodes 35 a and 36 a is electrically connected to the negative output terminal of the converter 2, and the short-circuit path through the reactor 23, MOSFET 36, negative diode 32 a and reactor 21 with respect to the three-phase AC power supply 1. Is formed. By forming this short circuit, energy (charge) is stored in the reactors 23 and 21. The energy stored in the reactors 23 and 21 is supplied to the smoothing capacitor 4 when the MOSFET 36 is turned off. By this energy supply, the voltage is boosted.

  In the phase where each of the R-phase input voltage, the S-phase input voltage, and the T-phase input voltage is at a negative level, the MOSFETs 31, 33, and 35 connected in parallel with the positive diodes 31a, 33a, and 35a are repeatedly turned on and off. Regarding the operation associated with turning on / off of the MOSFETs 31, 33, and 35, the operation pattern is basically the same as that of the positive level period, except that the sign is opposite. Therefore, the detailed description is abbreviate | omitted.

  On the other hand, the controller 90 turns on the four-way valve 101 during heating, and the refrigerant discharged from the compressor 100 passes through the four-way valve 101, the indoor heat exchanger 104, the electric expansion valve 103, the outdoor heat exchanger 102, and the four-way valve 101. Thus, a heating passage returning to the compressor 100 is formed. During this heating, frost gradually adheres to the surface of the outdoor heat exchanger 102 that functions as an evaporator.

  Therefore, the control unit 90 detects the amount of frost formation on the outdoor heat exchanger 102 from the temperature of the outdoor heat exchanger 102 (detected temperature of the heat exchanger temperature sensor), the outside air temperature, etc. during heating (YES in step 205). Then, the necessity of defrosting is determined from the detected amount of frost formation (step 206).

  When the amount of frost formation is equal to or greater than a certain amount, the control unit 90 turns on the defrost signal and turns on the inverter 5 as shown in FIG. 4 under the determination that the defrost is necessary (YES in Step 206). Is reduced (step 207). When the output frequency F drops below the set value Fa, which is an allowable condition for switching the flow path of the four-way valve 101 (YES in step 208), the control unit 90 changes the converter 2 from the PWM rectification mode to the diode rectification mode. Switching (step 209). After this switching, the control unit 90 turns off the four-way valve 101 to switch the refrigerant flow in the heat pump refrigeration cycle from the heating flow path to the defrost flow path (so-called reverse cycle defrost flow path) (step 210). .

  When the defrosting flow path is formed, the high-temperature refrigerant discharged from the compressor 100 is directly supplied to the outdoor heat exchanger 102 through the four-way valve 101, and the heat of the high-temperature refrigerant is supplied to the outdoor heat exchanger 102. Arrived frost is removed.

  After turning off the four-way valve 101, the control unit 90 returns the output frequency F of the inverter 5 to the increasing direction (step 211), and when the output frequency F increases to a set value Fb (> Fa) or more (step) In step 212, the operation of the converter 2 is switched from the diode rectification mode to the two-phase or three-phase PWM rectification mode. Along with this switching, the control unit 90 sets the output frequency F of the inverter 5 to an arbitrary value optimum for the defrost load. In this case, since the converter 2 is operating in the PWM rectification mode with step-up, an output for obtaining a sufficient defrosting capability can be obtained from the inverter 5.

  Thereafter, when it is determined that the outdoor heat exchanger 102 is no longer frosted due to a rise in the temperature of the outdoor heat exchanger 102 or a decrease in the compressor current, the control unit 90 determines that the defrosting has been completed. (YES in step 214), the defrost signal is turned off to reduce the output frequency F of the inverter 5 (step 215). Then, control unit 90 switches the operation of converter 2 from the PWM rectification mode to the diode rectification mode (step 217) when the output frequency F decreases to less than the set value Fa (YES in step 216). After this switching, the control unit 90 turns on the four-way valve 101 to switch the refrigerant flow from the defrosting channel to the original heating channel (step 218).

  After the four-way valve 101 is turned on, the control unit 90 returns the output frequency F of the inverter 5 to the increasing direction (step 219), and when the output frequency F increases to the set value Fb (> Fa) or more (step) 220 (YES), the operation of converter 2 is switched from the diode rectification mode to the two-phase or three-phase PWM rectification mode (step 221). Along with this switching, the control unit 90 sets the output frequency F of the inverter 5 to an arbitrary value optimum for the heating load (difference between the room temperature and the set temperature). In this case, since the converter 2 operates in the PWM rectification mode with step-up, an output for obtaining a sufficient heating capacity can be obtained from the inverter 5.

  Subsequently, the control unit 90 monitors the thermo-off based on the comparison between the room temperature and the set temperature (step 222). When it is not thermo-off (NO in step 222), the control unit 90 returns to step 205 and determines whether or not the operation mode is heating. When the thermostat is off (YES in step 222), the control unit 90 stops the operation of the converter 2 and the inverter 5 to interrupt the operation of the brushless DC motor 6, and returns to step 201 to monitor the thermo-on.

  When the flow path of the four-way valve 101 is switched, the load on the inverter 5 is suddenly reduced. When the load rapidly decreases, as shown in FIG. 5, the input currents Ir, Is, It to the converter 2 are greatly reduced (the input voltages Vr, Vs, Vt to the converter 2 are not changed), and the output voltage of the converter 2 There is a possibility that Vdc abnormally rises to about 400 V and exceeds the withstand voltage of the smoothing capacitor 4.

  However, in this embodiment, since the converter 2 is switched to the diode rectification mode without boosting before the flow path of the four-way valve 101 is switched, even if the load suddenly decreases as the flow path of the four-way valve 101 is switched, The output voltage Vdc of the converter 2 does not rise abnormally. Thereby, the overvoltage exceeding a withstand voltage is not added to the smoothing capacitor 4, and the safety | security of circuit components including the smoothing capacitor 4 can be ensured.

[Modification]
Cooling air is supplied from the outdoor fan 105 to the heat sink 10 on which the converter 2 and the inverter 5 are mounted. When the outdoor fan 105 is not in operation, the cooling air is not supplied to the heat sink 10, so that cooling of the converter 2 and the inverter 5 may not be sufficient.

  Therefore, the control unit 90 stops the operation of the outdoor fan 105. For example, during defrosting, if sufficient defrosting capability can be obtained without the boosting action of the converter 2, the controller 2 rectifies the diode 2 with less heat generation. Operate in mode or one-phase PWM rectification mode.

  Since the heat generation of the converter 2 is caused by a switching loss, the diode rectification mode without switching or the one-phase PWM rectification with fewer switching times than when operating in the two-phase or three-phase PWM rectification mode with many switching times. Less when operating in mode.

  In this way, when the outdoor fan 105 is not operating, the converter 2 is operated in a mode that generates little heat, so that even if the cooling air is not supplied to the heat sink 10, insufficient cooling does not occur.

  In the above embodiment, the case where the load is the brushless DC motor 6 has been described as an example. However, the load is not limited and can be applied to various electric devices.

  In addition, the said embodiment and modification are shown as an example and are not intending limiting the range of invention. The novel embodiments and modifications can be implemented in various other forms, and various omissions, rewrites, and changes can be made without departing from the spirit of the invention. In these embodiments and modifications, the scope of the invention is included in the gist, and is included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 1 ... Three-phase alternating current power supply, 2 ... Converter, 4 ... Smoothing capacitor, 5 ... Inverter, 6 ... Brushless DC motor (load) 21, 22, 23 ... Reactor, 31a-36a ... Diode, 31-36 ... MOSFET (switching) Element) 51-56 MOSFET (switching element), 71, 72, 73 ... current sensor, 81, 82, 83 ... current sensor, 90 ... control unit, 91 ... remote control, 100 ... compressor, 101 ... four-way valve, DESCRIPTION OF SYMBOLS 102 ... Outdoor heat exchanger, 103 ... Electric expansion valve, 104 ... Indoor heat exchanger, 105 ... Outdoor fan, 106 ... Indoor fan

Claims (6)

A converter having a reactor, a diode connected to the AC power supply through the reactor, a switching element connected in parallel to the diode, and boosting and converting the voltage of the AC power supply;
A smoothing capacitor connected to the output of the converter;
An inverter that converts the voltage of the smoothing capacitor into an alternating voltage of a predetermined frequency, and outputs the converted alternating voltage as drive power for the compressor motor of the heat pump refrigeration cycle;
Control means for operating the converter in a mode with pressure increase when there is no flow switching of the four-way valve in the heat pump refrigeration cycle, and for operating the converter in a mode without pressure increase when switching the flow path of the four-way valve;
A power conversion device comprising: The converter has a plurality of switching elements corresponding to each phase of the AC power supply,
The control means includes
When there is no switching of the flow path of the four-way valve, the switching elements corresponding to a plurality of phases of the AC power supply among the switching elements of the converter are operated in a PWM rectification mode that is turned on / off by a PWM signal,
When switching the flow path of the four-way valve, a diode rectification mode in which each switching element of the converter is not turned on or off, or a switching element corresponding to one phase of the AC power supply among the switching elements of the converter is turned on by a PWM signal. Operate in PWM rectification mode to turn off,
The power conversion device according to claim 1. A heat dissipation member for the converter and the inverter;
An outdoor fan for supplying outside air to the outdoor heat exchanger of the heat pump refrigeration cycle and supplying cooling air to the heat radiating member;
The control means operates the converter in a mode without boosting when switching the flow path of the four-way valve, and operates the converter in a mode without boost when the outdoor fan is not operating.
The power conversion device according to claim 1. The control means, upon starting the compressor motor, operates the converter in a mode without boost to start the inverter, and then operates the converter in a mode with boost.
The power conversion device according to any one of claims 1 to 3, wherein: When starting the compressor motor, the control means starts the inverter while operating the converter in a mode without boosting, estimates the rotational position of the compressor motor, and outputs a pulse width corresponding to the estimated rotational position. The switching element of the inverter is driven on and off by the PWM signal, and the converter is operated in the step-up mode after the estimation of the rotational position is stabilized.
The power conversion device according to claim 4. The control means detects a torque current component corresponding to the torque pulsation of the compressor motor, determines a torque correction amount for the torque of the compressor motor according to the detected torque current component, and sets the determined torque correction amount to the determined torque correction amount. In response, the on / off duty of the PWM signal is adjusted, and it is determined that the estimation of the rotational position is stable when the determined torque correction amount falls below a predetermined value.
The power conversion device according to claim 5.

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