Power supply device and air conditioner

Abstract

Provided are a power supply device and the like for suppressing disturbance in a waveform of a power supply current. A power supply device (100) comprises: a power factor improvement circuit (20) that has a switching element (22) and a reactor (21) provided in a current path through the switching element (22), and that improves the power factor at the time of converting an AC voltage applied from an AC power supply (E1) into a DC voltage; a smoothing capacitor (30) connected to the output side of the power factor improvement circuit (20); and a control unit (70) that outputs a prescribed pulse signal to the switching element (22). The control unit (70) sets the pulse cycle of the pulse signal to be less than a prescribed stability critical cycle. The stability critical cycle is calculated on the basis of: a load state coefficient in which the operation states of a motor (M1) and an inverter circuit (40) that receive power supply through the smoothing capacitor (30) are reflected in a prescribed manner; a DC voltage of the smoothing capacitor (30); and an inductance value of the reactor (21).

Description

Power supply unit and air conditioner

[0001] The present disclosure relates to a power supply device and the like.

[0002] A known technology for improving the power factor when converting AC voltage to DC voltage is disclosed in, for example, Patent Document 1. Patent Document 1 describes that "a coefficient is set in accordance with load state information indicating the operating state of the load, and the product of this coefficient and the power supply current information is calculated, and a duty ratio that defines the operation of the switching element is created based on this product."

[0003] Patent No. 2809463

[0004] For example, if the inductance of the DC reactor is reduced to reduce costs, or if the switching frequency during power factor correction is lowered to improve efficiency, the waveform of the power supply current becomes more likely to be disturbed. With regard to suppressing such disturbance of the waveform of the power supply current, there is room for improvement in the technology described in Patent Document 1.

[0005] Therefore, an object of the present disclosure is to provide a power supply device or the like that suppresses disturbances in the waveform of the power supply current.

[0006] In order to solve the above-mentioned problems, the power supply device according to the present disclosure includes a power factor correction circuit having a switching element and a reactor provided in a current path via the switching element, and which improves the power factor when an AC voltage applied from an AC power source is converted into a DC voltage, a smoothing capacitor connected to the output side of the power factor correction circuit, and a control unit which outputs a predetermined pulse signal to the switching element, wherein the control unit sets the pulse period of the pulse signal to be less than a predetermined stability limit period, and the stability limit period is calculated based on a load state coefficient which reflects in a predetermined manner the operating state of a load receiving power supply via the smoothing capacitor, the DC voltage of the smoothing capacitor, and the inductance value of the reactor.

[0007] According to the present disclosure, it is possible to provide a power supply device or the like that is adapted to suppress disturbance in the waveform of the power supply current.

[0008] 1 is a configuration diagram of a power supply device according to a first embodiment. FIG. 2 is an explanatory diagram showing a current flow when a switching element of a power factor correction circuit is in an on state during a period when the polarity of the voltage of the AC power supply is positive in the power supply device according to the first embodiment. FIG. 3 is an explanatory diagram showing a current flow when a switching element of a power factor correction circuit is in an off state during a period when the polarity of the voltage of the AC power supply is positive in the power supply device according to the first embodiment. FIG. 4 is an explanatory diagram related to detection of a power supply current and a timer count value in the power supply device according to the first embodiment. FIG. 5 is a diagram showing a simulation result when the pulse period of a PWM signal is shorter than the stability limit period in the power supply device according to the first embodiment. FIG. 6 is a configuration diagram of a power supply device according to a second embodiment. FIG. 7 is an explanatory diagram showing a current flow when magnetic energy is stored in a reactor during a period when the polarity of the voltage of the AC power supply is positive in the power supply device according to the second embodiment. FIG. 8 is an explanatory diagram showing a current flow when magnetic energy is released from a reactor during a period when the polarity of the voltage of the AC power supply is positive in the power supply device according to the second embodiment. FIG. 9 is a configuration diagram of an air conditioner according to a third embodiment. FIG. 10 is a diagram showing a simulation result when the pulse period of a PWM signal is longer than the stability limit period in a power supply device according to a comparative example.

[0009] First Embodiment Configuration of Power Supply Device Fig. 1 is a configuration diagram of a power supply device 100 according to a first embodiment. The power supply device 100 shown in Fig. 1 is a device that converts an AC voltage applied from a single-phase AC power supply E1 into a predetermined DC voltage. As shown in Fig. 1, the power supply device 100 includes a rectifier circuit 10, a power factor correction circuit 20, a smoothing capacitor 30, a DC voltage detection unit 50, a power supply current detection unit 60, and a control unit 70.

[0010] An inverter circuit 40 (load) is connected to the output side of the power supply device 100. The inverter circuit 40 is a power converter that converts the DC voltage applied from the power supply device 100 into a predetermined AC voltage. The AC voltage on the output side of the inverter circuit 40 is applied to the windings of a motor M1 (load). The motor M1 is an electric motor that is driven by the AC voltage applied from the inverter circuit 40. For example, a permanent magnet synchronous motor is used as this motor M1, but other types of motors can also be used.

[0011] The rectifier circuit 10 converts AC voltage applied from a single-phase AC power source E1 into DC voltage (pulsating DC voltage). In the example of Fig. 1, the rectifier circuit 10 is configured as a diode bridge for full-wave rectification. The rectifier circuit 10 is configured such that a series connection of diodes D1 and D2 and another series connection of diodes D3 and D4 are connected in parallel with each other.

[0012] The cathode of diode D1 is connected to the positive DC line K1. The anode of diode D1 is connected to the cathode of the other diode D2. The anode of diode D2 is connected to the negative DC line K2. The same applies to the series connection of diodes D3 and D4. The connection point between diodes D1 and D2 is connected to one terminal of AC power supply E1 via wiring K3. The connection point between the other diodes D3 and D4 is connected to the other terminal of AC power supply E1 via wiring K4.

[0013] The power factor correction circuit 20 is a circuit for correcting the power factor when converting the AC voltage applied from the AC power source E1 into a DC voltage. The power factor correction circuit 20 also has a function of boosting the DC voltage after rectification by the rectifier circuit 10. In the example of Fig. 1, the power factor correction circuit 20 is configured as a boost chopper including a reactor 21, a switching element 22, and a diode 23.

[0014] The reactor 21 is an element that stores power from the AC power supply E1 as magnetic energy and releases this magnetic energy in response to the on / off switching of the switching element 22. As shown in Fig. 1 , the reactor 21 is provided on the positive DC line K1. More specifically, the reactor 21 is provided on the positive DC line K1 between the rectifier circuit 10 and a connection point between the switching element 22 and the DC line K1. From another perspective, the reactor 21 is provided on a current path (see the dashed arrows in Figs. 2A and 2B ) that passes through the switching element 22.

[0015] The switching element 22 is an element for switching a current path by switching on and off. For example, an insulated gate bipolar transistor (IGBT) is used as the switching element 22. The type of the switching element 22 is not limited to an IGBT, and a metal-oxide-semiconductor field-effect transistor (MOSFET) or a bipolar transistor may also be used. The gate of the switching element 22 is connected to the control unit 70 via a wiring. The collector of the switching element 22 is connected to the positive DC line K1, and the emitter is connected to the negative DC line K2.

[0016] The diode 23 is an element that allows current to flow from the reactor 21 toward the smoothing capacitor 30 and blocks current flow in the opposite direction. As shown in FIG. 1 , the diode 23 is provided on the positive DC line K1. Specifically, the diode 23 is provided between the connection point between the positive DC line K1 and the switching element 22 and the connection point between the DC line K1 and the smoothing capacitor 30. The anode of the diode 23 is connected to the reactor 21 via the positive DC line K1. The cathode of the diode 23 is connected to the positive electrode of the smoothing capacitor 30 and the input side of the inverter circuit 40 via the positive DC line K1.

[0017] The smoothing capacitor 30 is an element that smoothes the DC voltage on the output side of the power factor correction circuit 20. As shown in Fig. 1, the smoothing capacitor 30 is connected to the output side of the power factor correction circuit 20. Specifically, the positive electrode of the smoothing capacitor 30 is connected to the positive DC line K1, and the negative electrode is connected to the negative DC line K2. For example, an electrolytic capacitor or a film capacitor is used as the smoothing capacitor 30.

[0018] The inverter circuit 40 is a power converter that converts the DC voltage of the smoothing capacitor 30 into a predetermined AC voltage and applies this AC voltage to the motor M1. Although not shown, the inverter circuit 40 is configured such that a first leg, a second leg, and a third leg, each of which is configured with a pair of switching elements connected in series, are connected in parallel to the smoothing capacitor 30. For example, an IGBT or a MOSFET is used as such a switching element. In the first leg, the connection point between the pair of switching elements is connected to the windings of the motor M1 via wiring. The same applies to the remaining second leg and third leg.

[0019] The DC voltage detection unit 50 detects the DC voltage of the smoothing capacitor 30. In other words, the DC voltage detection unit 50 detects the DC voltage on the output side of the power factor correction circuit 20. The detected values ​​of the DC voltage detection unit 50 are outputted from time to time to the control unit 70. The power supply current detection unit 60 detects the power supply current of the AC power supply E1 and is provided on the wiring K3. The detected values ​​of the power supply current detection unit 60 are outputted from time to time to the control unit 70.

[0020] The control unit 70 outputs a predetermined PWM signal (pulse signal) to the switching element 22 by PWM control (Pulse Width Modulation) based on the detection values ​​of the DC voltage detection unit 50 and the power supply current detection unit 60. The control unit 70 is, for example, a microcomputer (not shown), which reads out a program stored in a ROM (Read Only Memory) and loads it into a RAM (Random Access Memory), and a CPU (Central Processing Unit) executes various processes.

[0021] As shown in FIG. 1 , the control unit 70 includes a duty ratio calculation unit 71 and a PWM signal generation unit 72. The duty ratio calculation unit 71 calculates a duty ratio for switching the switching element 22 on and off based on the detection value of the power supply current detection unit 60, etc. The PWM signal generation unit 72 generates a predetermined PWM signal (pulse signal) based on the duty ratio calculated by the duty ratio calculation unit 71. Here, the "duty ratio" (on-duty) refers to the ratio of the on-time to one cycle (pulse cycle) of the switching element 22. The PWM signal generated by the PWM signal generation unit 72 is output to the switching element 22.

[0022] The control unit 70 controls each switching element (not shown) of the inverter circuit 40 in a predetermined manner by PWM control based on the detected values ​​of the DC voltage detection unit 50 and the power supply current detection unit 60, as well as the detected value of the bus current of the DC line K2. Note that the control method for the inverter circuit 40 is well known, and therefore a detailed description thereof will be omitted.

[0023] 2A is an explanatory diagram showing the flow of current when the switching element 22 of the power factor correction circuit 20 is in the ON state during a period when the polarity of the voltage of the AC power supply E1 is positive. The dashed arrow in FIG. 2A indicates the flow of current. When the switching element 22 is in the ON state during a period when the polarity of the voltage of the AC power supply E1 is positive, current flows from the AC power supply E1 sequentially through the diode D1, the reactor 21, the switching element 22, and the diode D4, as shown by the dashed arrow in FIG. 2A. As a result, magnetic energy is stored in the reactor 21. Furthermore, the charge stored in the smoothing capacitor 30 is supplied to the inverter circuit 40 and the motor M1.

[0024] 2B is an explanatory diagram showing the current flow when the switching element 22 of the power factor correction circuit 20 is in the off state during a period when the polarity of the voltage of the AC power source E1 is positive. When the switching element 22 switches from the on state (see FIG. 2A ) to the off state (see FIG. 2B ), the magnetic energy stored in the reactor 21 is released, and charge is stored in the smoothing capacitor 30. That is, as shown by the dashed arrows in FIG. 2B , current flows from the AC power source E1 sequentially through the diode D1, the reactor 21, the diode 23, the smoothing capacitor 30, and the diode D4. As a result, the DC voltage of the smoothing capacitor 30 becomes higher than the DC voltage on the output side of the rectifier circuit 10. The DC voltage thus boosted is converted to a predetermined AC voltage by the inverter circuit 40, and this AC voltage is applied to the windings of the motor M1.

[0025] 2A and 2B show the current flow during the period when the voltage polarity of the AC power supply E1 is positive. However, during the period when the voltage polarity is negative, the current flows in the same manner as during the period when the voltage polarity is positive, except that the current flows sequentially through the diodes D2 and D3 of the rectifier circuit 10.

[0026] <Regarding constant boost ratio control> The control unit 70 shown in Fig. 1 controls the switching element 22 so as to boost the DC voltage at a predetermined boost ratio (i.e., performs constant boost ratio control). Here, the "boost ratio" is the ratio of the DC voltage on the output side of the power factor correction circuit 20 (the DC voltage of the smoothing capacitor 30) to the DC voltage on the input side of the power factor correction circuit 20. When the boost ratio is a, the relationship of the following equation (1) is established. Note that K included in equation (1) ｐ is a predetermined load condition coefficient, and i ｓ is the instantaneous value of the power supply current.

[0027]

[0028] Further, the conduction ratio d (on-duty) of the switching element 22 of the power factor correction circuit 20 is expressed by the following equation (2).

[0029]

[0030] In this way, the flow ratio calculation unit 71 (see FIG. 1) calculates the load condition coefficient Kｐ and the detected value of the power supply current detection unit 60 (see FIG. 1) (instantaneous value i ｓ ) and the current conduction ratio d when switching on / off the switching element 22 (see FIG. 1) is calculated based on the above equation (2). Note that when the current conduction ratio d is calculated based on the equation (2), the effective value I ｓ is expressed by the following formula (3): ｍ is the amplitude of the power supply voltage, and E ｄ is the DC voltage of the smoothing capacitor 30, and ω is the angular frequency in electrical angle.

[0031]

[0032] Therefore, by having the conduction ratio calculation unit 71 (see FIG. 1) calculate the conduction ratio d based on the above-mentioned equation (2), it is possible to improve the power factor so that the waveform of the power supply current becomes a sinusoidal waveform synchronized with the power supply voltage.

[0033] Furthermore, by transforming equation (3), the following equation (4) is obtained. Note that V included in equation (4) ｓ is the effective value of the power supply voltage.

[0034]

[0035] For example, the rotation speed of the motor M1 increases, and the DC voltage E ｄ As the value of increases, the load condition coefficient K ｐ In this way, the load condition coefficient K ｐ The "load state information" that indicates the operating state of the inverter circuit 40 (load) and the motor M1 (load) is reflected in a predetermined manner. The "load state information" includes the effective value I ｓ and the DC voltage E of the smoothing capacitor 30 ｄ and the effective value of the power supply voltage V ｓ The control unit 70 controls the DC voltage E ｄ The load condition coefficient K is controlled based on PI control (or PID control) so that the load condition coefficient K approaches a predetermined target value. ｐ This adjusts the DC voltage E ｄ can be maintained close to a predetermined target value.

[0036] <Regarding the PWM Pulse Period> Using a reactor 21 with a small inductance in the power supply device 100 (see FIG. 1) can reduce costs, but on the other hand, this can easily cause the waveform of the power supply current to become distorted when the DC voltage or load state changes suddenly. After extensive research into this issue, the inventors discovered that the power supply current can be stabilized by setting the pulse period used to control the switching element 22 of the power factor correction circuit 20 to be less than a predetermined stability limit period. The derivation of this stability limit period will be described in detail below.

[0037] FIG. 3 is an explanatory diagram relating to power supply current detection and timer count values. The horizontal axis of each graph in FIG. 3 represents time. The solid line at the top of FIG. 3 shows a rough outline of the power supply current. In reality, the power supply current fluctuates minutely from moment to moment (see, for example, the power supply current waveform in FIG. 4 ). The dashed arrows at the top of FIG. 3 are lines sequentially connecting the power supply current values ​​detected at each predetermined pulse period ΔT. The hatched triangles G1 and G2 indicate the timing at which the control unit 70 (see FIG. 1 ) reads the detection value of the power supply current detection unit 60 (see FIG. 1 ).

[0038] The lower part of Figure 3 shows the change in the timer count value under PWM control. As shown in Figure 3, the timer count value is set to change in a triangular wave shape. That is, in the first half (ΔT / 2) of the pulse period ΔT under PWM control, the timer count value increases linearly with time, and in the second half (ΔT / 2), the timer count value decreases linearly with time. Although not shown in Figure 3, during one pulse period ΔT, the switching element 22 (see Figure 1) is turned on at a predetermined conduction ratio d and then switched off.

[0039] As shown in FIG. s (n-1), i s (n), i s (n+1), i s (n+2), i s(n+3), ... indicate the power supply current for each half cycle (ΔT / 2) in PWM control. The open triangle G3 in Fig. 3 indicates the timing when the conduction ratio set by the control unit 70 (see Fig. 1) is reflected in the PWM control.

[0040] As shown in FIG. s (n) to i s (n+1) is the section A, and i s (n+1) to i s If (n+2) is section B, the rate of change of the power supply current in section A is expressed by the following equation (5). Note that ΔT included in equation (5) is the pulse period in PWM control. Also, v s (n) is the power supply current i s (n) is the instantaneous value of the power supply voltage at the time of detection. L is the inductance value of the reactor 21 (see FIG. 1), and E d is the DC voltage of the smoothing capacitor 30, and K p is the load condition coefficient.

[0041]

[0042] Similarly, the rate of change of the power supply current in section B of FIG. 3 is expressed by the following equation (6).

[0043]

[0044] Adding and rearranging both sides of equation (5) and equation (6) yields equation (7) below.

[0045]

[0046] Furthermore, when Z-transform is performed on equation (7), the following equation (8) is obtained.

[0047]

[0048] Since the stability condition is satisfied when the pole in the denominator of equation (8) is greater than 1, the stability condition is expressed by the following equation (9).

[0049]

[0050] Therefore, the stability limit period ΔT is a threshold value that is a criterion for determining whether or not the power supply current can be stabilized. stable is expressed by the following equation (10): stable is the DC voltage E of the smoothing capacitor 30 ｄ and a load condition coefficient K that reflects the operating conditions of the inverter circuit 40 (load) and the motor M1 (load) in a predetermined manner. p and the value of the inductance L of the reactor 21 (see FIG. 1).

[0051]

[0052] When switching on / off the switching element 22 of the power factor correction circuit 20 (see FIG. 1), the period of the PWM pulse is set to a predetermined stability limit period ΔT stable The inventors have found that the power supply current can be stabilized by setting the pulse period of the PWM signal (pulse signal) to be less than the predetermined stability limit period ΔT stable The control unit 70 sets the stability limit period ΔT stable When deriving the value of , the value of equation (10) may be calculated from time to time, or a predetermined data table (not shown) may be used. In the above-described configuration, as shown in FIG. 3, the current detection and the reflection of the conduction ratio are performed for each PWM period, in other words, for each PWM valley. However, if there is room for the calculation load factor, it is also possible to perform the current detection and the reflection of the conduction ratio for each PWM half period, in other words, for each PWM peak and valley. In this way, by performing the current detection and the reflection of the conduction ratio for each PWM peak and valley, the stability limit period ΔT stable It is possible to double the amount.

[0053] Also, the stability limit period ΔT stable It is advisable to repeat the update of the stability limit period ΔT in the pulse period of the PWM signal (pulse signal). This allows the stability limit period ΔT to be updated even in a transient state such as a sudden change in the DC voltage or load state. stableis updated every moment, which can prevent the power supply current from becoming unstable. Note that the case where the value of the stability limit period is repeatedly maintained is also included in the "update" of the stability limit period. stable The updating of may be repeated at a period that is a predetermined multiple (a natural number multiple of 2 or more) of the pulse period of the PWM signal (pulse signal). Even in this case, it is possible to suppress instability of the power supply current in a transient state.

[0054] For example, when the control unit 70 increases the rotation speed of the motor M1, the DC voltage E ｄ Since the stability limit period ΔT stable The value of the stability limit period ΔT stable The value of the stability limit period ΔT stable The pulse period of the PWM signal is adjusted within a predetermined range of less than 1 / 2.

[0055] FIG. 8 shows a power supply device according to a comparative example, in which the pulse period of the PWM signal is equal to or exceeds the stability limit period ΔT stable 8 is a diagram showing the results of a simulation when the time is longer than 1 / 2. The horizontal axis of each simulation result in FIG. 8 represents time. The vertical axis of each simulation result represents, from the top of the page in FIG. 8, voltage (DC voltage and power supply voltage), power supply current, and duty ratio (on-duty). The frequency of the PWM pulse is 12 [kHz], the inductance of the reactor 21 (see FIG. 1) is 3.5 [mH], the DC voltage is 300 [V], and the load condition coefficient K p The simulation was carried out with the stability limit period ΔT set to 0.33. stable The value of this stability limit period ΔT stable The value corresponds to a frequency of 14.1 kHz.

[0056] In the comparative example of FIG. 8, the frequency of the PWM pulse (12 kHz) is equal to the stability limit period ΔT stable In other words, the pulse period (83.3 μs) in PWM control is lower than the frequency (14.1 kHz) corresponding to the stability limit period ΔTstable (70.9 μs). As a result, the waveform of the power supply current is disturbed, and the transition of the PWM pulse current ratio is also disturbed. In this way, the PWM pulse period is longer than the stability limit period ΔT stable It was confirmed that when the voltage is higher than this, the power supply current becomes unstable.

[0057] FIG. 4 shows the power supply device according to the first embodiment, in which the pulse period of the PWM signal is equal to or less than the stability limit period ΔT stable 4 is a diagram showing the results of a simulation when the stability limit period ΔT is shorter than 16 [kHz]. The horizontal and vertical axes in FIG. 4 are the same as those in the comparative example (see FIG. 8). The simulation conditions are the same as those in the comparative example, except that the PWM pulse frequency is 16 [kHz]. In this case, the period corresponding to the pulse frequency (16 [kHz]) in PWM control is 62.5 [μs], so the stability limit period ΔT stable (70.9 μs). As a result, the power supply current has a stable waveform, and the PWM pulse conduction ratio is also stable. In this way, the PWM pulse period is set to the stability limit period ΔT stable It was confirmed that by setting the value to less than this, the power supply current and other factors become stable.

[0058] <Effects> According to the first embodiment, the load condition coefficient K p and DC voltage E ｄ and the value of the inductance L of the reactor 21 (see FIG. 1), the control unit 70 (see FIG. 1) calculates a predetermined stability limit period ΔT stable The control unit 70 calculates the pulse period when performing PWM control as the stability limit period ΔT stable This makes it possible to stabilize the feedback loop from power supply current detection to PWM signal output. Therefore, even if a small inductance element is used as reactor 21 (see FIG. 1) or the frequency of the PWM pulse is lowered to reduce the number of switching operations per unit time, it is possible to stably boost the DC voltage while suppressing disturbances in the power supply current waveform.

[0059] Furthermore, suppressing the disturbance of the power supply current waveform also suppresses power supply current harmonics, making it possible to operate in compliance with power supply harmonics regulations. Even in a transient state where the DC voltage or load state changes suddenly, the control unit 70 calculates the pulse period from moment to moment within the stability limit period ΔT stable By setting the value of the power supply current to less than 1 / f, it is possible to prevent the waveform of the power supply current from being disturbed. In this way, according to the first embodiment, it is possible to appropriately boost the DC voltage while stabilizing the power supply current.

[0060] Second Embodiment A power supply device 100A (see FIG. 5) according to a second embodiment is configured to include a power factor correction circuit 20A (see FIG. 5) having switching elements Q1 to Q4 (see FIG. 5) instead of the rectifier circuit 10 (see FIG. 1) and power factor correction circuit 20 (see FIG. 1) described in the first embodiment. The second embodiment differs from the first embodiment in the location of the reactor 24 (see FIG. 5) used to boost the DC voltage and correct the power factor. The rest of the second embodiment is similar to the first embodiment. Therefore, only the differences from the first embodiment will be described, and overlapping portions will not be described.

[0061] Fig. 5 is a configuration diagram of a power supply device 100A according to the second embodiment. As shown in Fig. 5, the power supply device 100A includes a power factor correction circuit 20A, a smoothing capacitor 30, a DC voltage detection unit 50, a power supply current detection unit 60, and a control unit 70. An inverter circuit 40 is connected to the output side of the power supply device 100A.

[0062] The power factor correction circuit 20A converts the AC voltage applied from the AC power source E1 into a DC voltage, and also has the function of boosting the DC voltage and correcting the power factor. As shown in Fig. 5, the power factor correction circuit 20A includes switching elements Q1 to Q4 and a reactor 24.

[0063] The switching elements Q1 to Q4 are connected in a bridge configuration. Specifically, a first leg formed by connecting the switching elements Q1 and Q2 in series and a second leg formed by connecting the switching elements Q3 and Q4 in series are connected in parallel to the smoothing capacitor 30. For example, MOSFETs are used as the switching elements Q1 to Q4, but other types of switching elements such as IGBTs and bipolar transistors may also be used. Furthermore, different types of elements may be used for the switching elements Q1 and Q2 of the first leg and the switching elements Q3 and Q4 of the second leg. The switching elements Q1 to Q4 are switched on and off in a predetermined manner by the control unit 70.

[0064] Each of the switching elements Q1 to Q4 has an internal parasitic diode (reference numeral not shown). The parasitic diode is a pn junction portion that exists between the source and drain of each switching element. In the example of FIG. 5, the drain of the switching element Q1 is connected to the positive DC line K1. The source of the switching element Q1 is connected to the drain of the other switching element Q2 via a wiring. The source of the switching element Q2 is connected to the negative DC line K2. The same applies to the switching elements Q3 and Q4 of the second leg.

[0065] The connection point between the switching elements Q1 and Q2 is connected to one terminal of the AC power supply E1 via a wire K3, and the connection point between the other switching elements Q3 and Q4 is connected to the other terminal of the AC power supply E1 via a wire K4.

[0066] The reactor 24 is an element that stores power from the AC power supply E1 as magnetic energy and releases this magnetic energy in response to the on / off switching of the switching elements Q1 to Q4. In the example of Fig. 5, the reactor 24 is provided on the wiring K4. That is, the reactor 24 is provided in a current path (see the dashed arrows in Figs. 6A and 6B) that passes through a predetermined switching element.

[0067] 6A is an explanatory diagram showing the flow of current when magnetic energy is stored in the reactor 24 during a period when the polarity of the voltage of the AC power supply E1 is positive. The dashed arrows in FIG. 6A indicate the flow of current. When the switching elements Q1 and Q3 are turned on while the remaining switching elements Q2 and Q4 are maintained in the off state during a period when the polarity of the voltage of the AC power supply E1 is positive, current flows as shown by the dashed arrows in FIG. 6A. That is, current flows from the AC power supply E1 sequentially through the switching elements Q1 and Q3 and the reactor 24. As a result, magnetic energy is stored in the reactor 24. Furthermore, the charge stored in the smoothing capacitor 30 is supplied to the inverter circuit 40 and the motor M1.

[0068] 6B is an explanatory diagram showing the flow of current when magnetic energy is being released from reactor 24 during a period when the polarity of the voltage of AC power supply E1 is positive. When switching element Q3 is switched to the off state and switching element Q4 is switched to the on state while switching element Q1 is maintained in the on state (see FIGS. 6A and 6B), current flows as shown by the dashed arrow in FIG. 6B. That is, current flows from AC power supply E1 through switching element Q1, smoothing capacitor 30, switching element Q4, and reactor 24 in this order.

[0069] As a result, the magnetic energy stored in the reactor 24 is released and an electric charge is stored in the smoothing capacitor 30, thereby boosting the DC voltage of the smoothing capacitor 30. The DC voltage thus boosted is converted into a predetermined AC voltage by the inverter circuit 40, and this AC voltage is applied to the windings of the motor M1.

[0070] 6A and 6B have described the current flow during periods when the voltage polarity of AC power supply E1 is positive, but although not shown, current flows during periods when the voltage polarity is negative as follows. That is, when magnetic energy is stored in reactor 24, switching elements Q2 and Q4 are turned on, while the remaining switching elements Q1 and Q3 are maintained in the off state. Also, when magnetic energy is released from reactor 24, switching elements Q2 and Q3 are turned on, while the remaining switching elements Q1 and Q4 are turned off.

[0071] When switching on / off the switching elements Q1 to Q4, the control unit 70 (see FIG. 5) adjusts the pulse period of the PWM signal (pulse signal) to a predetermined stability limit period ΔT stable This makes it possible to stably boost the DC voltage and improve the power factor while suppressing disturbances in the power supply current.

[0072] <Effects> According to the second embodiment, the control unit 70 controls the switching elements Q1 to Q4 in a predetermined manner, thereby reducing loss during boosting compared to the first embodiment, and thus achieving higher efficiency. Furthermore, even when a reactor 24 (see FIG. 5) with a small inductance is used, the control unit 70 adjusts the pulse period of the PWM signal to the predetermined stability limit period ΔT stable By setting the value to less than this, it is possible to suppress the disturbance of the waveform of the power supply current and to stably boost the DC voltage.

[0073] Third Embodiment In the third embodiment, an air conditioner W1 (see FIG. 7) including the power supply device 100 (see FIG. 1) configured as described in the first embodiment will be described. Note that the configuration and processing content of the power supply device 100 are the same as those in the first embodiment, and therefore description thereof will be omitted.

[0074] FIG. 7 is a configuration diagram of an air conditioner W1 according to a third embodiment. The solid arrows in FIG. 7 indicate the flow of refrigerant in the heating cycle. The dashed arrows in FIG. 7 indicate the flow of refrigerant in the cooling cycle. The air conditioner W1 is a device that performs air conditioning, such as cooling and heating. As shown in FIG. 7 , the air conditioner W1 includes, as components provided in the outdoor unit U1, a compressor 91, an outdoor heat exchanger 92, an outdoor fan 93, an expansion valve 94, and a four-way valve 95. The air conditioner W1 also includes, as components provided in the indoor unit U2, an indoor heat exchanger 96 and an indoor fan 97.

[0075] Although not shown in Fig. 7, the air conditioner W1 is equipped with the power supply device 100 (see Fig. 1) and inverter circuit 40 (see Fig. 1) described in the first embodiment. The power supply device 100 and the inverter circuit 40 are mounted on a circuit board (not shown) of the outdoor unit U1.

[0076] The compressor 91 is a device that compresses a low-temperature, low-pressure gas refrigerant and discharges it as a high-temperature, high-pressure gas refrigerant. Although not shown in Fig. 7, an accumulator for separating the refrigerant into gas and liquid is connected to the suction side of the compressor 91. The "load" of the power supply device 100 (see Fig. 1) includes the inverter circuit 40 (see Fig. 1) and the motor M1 (see also Fig. 1). The motor M1 is a drive source for the compressor 91 and is connected to the output side of the inverter circuit 40 (see Fig. 1).

[0077] The outdoor heat exchanger 92 is a heat exchanger in which heat is exchanged between the refrigerant flowing through its heat transfer tubes and the outside air sent in from the outdoor fan 93. The outdoor fan 93 is a fan that sends the outside air to the outdoor heat exchanger 92. The outdoor fan 93 has an outdoor fan motor 93a that serves as a drive source, and is installed near the outdoor heat exchanger 92.

[0078] The expansion valve 94 is a valve that reduces the pressure of the refrigerant condensed in the "condenser" (one of the outdoor heat exchanger 92 and the indoor heat exchanger 96). The refrigerant reduced in pressure by the expansion valve 94 is guided to the "evaporator" (the other of the outdoor heat exchanger 92 and the indoor heat exchanger 96). The indoor heat exchanger 96 is a heat exchanger that exchanges heat between the refrigerant flowing through its heat transfer tube (not shown) and indoor air (air in the air-conditioned room) sent in by an indoor fan 97. The indoor fan 97 is a fan that sends indoor air to the indoor heat exchanger 96. The indoor fan 97 is equipped with an indoor fan motor 97a that serves as a drive source, and is installed near the indoor heat exchanger 96.

[0079] The four-way valve 95 switches the refrigerant flow path depending on the operating mode of the air conditioner W1. For example, during cooling operation (see the dashed arrow in FIG. 7 ), the refrigerant circulates sequentially through the compressor 91, the outdoor heat exchanger 92 (condenser), the expansion valve 94, and the indoor heat exchanger 96 (evaporator). During heating operation (see the solid arrow in FIG. 7 ), the refrigerant circulates sequentially through the compressor 91, the indoor heat exchanger 96 (condenser), the expansion valve 94, and the outdoor heat exchanger 92 (evaporator). Air that has exchanged heat with the refrigerant flowing through the indoor heat exchanger 96 is then blown out of the indoor unit U2 into the air-conditioned room.

[0080] <Effects> According to the third embodiment, the air conditioner W1 is equipped with a power supply unit 100 (see Figure 1) having the same configuration as that of the first embodiment, which makes it possible to reduce the cost of the air conditioner W1 and improve its performance and reliability.

[0081] <<Modifications>> The power supply device 100, 100A and the air conditioner W1 according to the present disclosure have been described above in various embodiments, but are not limited to these descriptions and various modifications can be made. For example, while the various embodiments have described a case in which the power supply current detection unit 60 (see FIG. 1) is provided on the wiring K3 (see FIG. 1), this is not limiting. That is, the power supply current detection unit 60 may be provided on another wiring K4 (see FIG. 1) instead of the wiring K3. Furthermore, the power supply current detection unit 60 may be provided between the rectifier circuit 10 and the power factor correction circuit 20 on the positive DC line K1 or the negative DC line K2.

[0082] In addition, in each embodiment, the power supply device 100 (see FIG. 1) is connected to a single-phase AC power supply E1 (see FIG. 1), but this is not limiting. For example, each embodiment can also be applied to a case where the power supply device 100 is connected to a three-phase AC power supply.

[0083] In addition, in each embodiment, the control unit 70 performs constant step-up ratio control, but this is not limiting. For example, each embodiment can also be applied to a case where the power supply voltage of the AC power supply E1 is detected, the control unit 70 generates a current command so that the power supply voltage and the power supply current are in phase with each other at every moment, and a PWM signal is output based on this current command.

[0084] In addition, in each embodiment, the case where the stability limit period is calculated based on equation (10) has been described, but this is not limiting. For example, the value obtained by multiplying equation (10) by a predetermined coefficient (a positive coefficient smaller than 1) may be set as the stability limit period. Alternatively, the value obtained by subtracting a predetermined value (a positive value) from equation (10) may be set as the stability limit period.

[0085] Furthermore, in each embodiment, the inverter circuit 40 (see FIG. 1) and the motor M1 (see FIG. 1) are described as being used as the "load" of the power supply device 100, but this is not limiting, and other types of loads may be used as appropriate.

[0086] Furthermore, in the third embodiment, a configuration has been described in which the power supply device 100 (see FIG. 1) is electrically connected to the motor M1 of the compressor 91 (see FIG. 7) via the inverter circuit 40 (see FIG. 1), but the present invention is not limited to this. For example, the power supply device 100 may be electrically connected to the outdoor fan motor 93a (load) via the inverter circuit 40. Furthermore, the power supply device 100 may be electrically connected to the motor M1 of the compressor 91 and also to the outdoor fan motor 93a via the inverter circuit 40.

[0087] Furthermore, in the third embodiment (see FIG. 7 ), a configuration in which the air conditioner W1 includes a four-way valve 95 has been described, but this is not limiting. That is, the four-way valve 85 may be omitted as appropriate to configure an air conditioner dedicated to cooling or heating. Furthermore, the third embodiment (see FIG. 7 ) can be applied to various types of air conditioners, such as commercial air conditioners and multi-air conditioners for buildings, in addition to room air conditioners. Furthermore, each embodiment can be applied to various devices, such as air conditioning and hot water supply systems, water heaters, and refrigerators.

[0088] Furthermore, the embodiments can be combined as appropriate. For example, the second and third embodiments may be combined so that the motor M1 of the compressor 91 (see FIG. 7) is driven by a power supply device 100A (see FIG. 5) including switching elements Q1 to Q4 (second embodiment) (third embodiment).

[0089] Furthermore, each embodiment has been described in detail to clearly explain the present disclosure, and is not necessarily limited to having all of the described configurations. Furthermore, it is possible to add, delete, or replace part of the configuration of each embodiment with other configurations. Furthermore, the above-described mechanisms and configurations are those considered necessary for explanation, and do not necessarily represent all mechanisms and configurations of the product.

[0090] REFERENCE SIGNS LIST 10 Rectifier circuit 20, 20A Power factor correction circuit 21 Reactor 22 Switching element 23 Diode 30 Smoothing capacitor 40 Inverter circuit (load) 50 DC voltage detection unit 60 Power supply current detection unit 70 Control unit 71 Conduction ratio calculation unit 72 PWM signal generation unit 91 Compressor 92 Outdoor heat exchanger 93 Outdoor fan 94 Expansion valve 95 Four-way valve 96 Indoor heat exchanger 97 Indoor fan 100, 100A Power supply device E1 AC power supply M1 Motor (load) Q1, Q2, Q3, Q4 Switching element W1 Air conditioner

Claims

1. A power factor improvement circuit having a switching element and a reactor provided in a current path through the switching element, for improving the power factor when converting an AC voltage applied from an AC power supply into a DC voltage; a smoothing capacitor connected to the output side of the power factor improvement circuit; and a control unit that outputs a predetermined pulse signal to the switching element, wherein the control unit sets a pulse period in the pulse signal to be less than a predetermined stability limit period, and the stability limit period is calculated based on a load state coefficient in which an operating state of a load receiving power supply through the smoothing capacitor is reflected in a predetermined manner, a DC voltage of the smoothing capacitor, and an inductance value of the reactor.

2. The power supply device according to claim 1, wherein the stability limit period is calculated based on the formula (10). Here, ΔT included in the formula (10) stable is the stability limit period, L is the inductance value of the reactor, and K p is the load state coefficient.

3. The power supply device according to claim 1, characterized in that the update of the stability limit period is repeated at the pulse period or at a period that is a predetermined multiple of the pulse period.

4. The power supply device according to claim 1, characterized in that the load state coefficient is adjusted based on PI control so as to bring the DC voltage of the smoothing capacitor closer to a predetermined target value.

5. An air conditioner comprising the power supply device according to any one of claims 1 to 4, an inverter circuit that converts a DC voltage applied from the power supply device into a predetermined AC voltage, and a motor driven by the AC voltage applied from the inverter circuit, further comprising a compressor, an outdoor heat exchanger, an expansion valve, and an indoor heat exchanger, wherein the load includes the inverter circuit and the motor, and the motor is a drive source of the compressor.

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