Power converters and air conditioners

Abstract

To provide a compact power converter and air conditioner with excellent power conversion efficiency. [Solution] The power converter comprises a smoothing capacitor, an active filter, a passive filter, and a switching control unit. The active filter has a first rectifier, an inductor, and a first switching element that switches between a current path passing through the first rectifier, the inductor, and the smoothing capacitor, and a current path passing through the first rectifier, the inductor, and not through the smoothing capacitor, and operates / stops according to an instruction signal. The passive filter has a second rectifier and a reactor, and at least a part of the second rectifier and the reactor are connected in parallel with the active filter between the AC power supply and the smoothing capacitor. The switching control unit outputs an instruction signal to operate the active filter when the load is above a threshold, and outputs an instruction signal to stop the active filter when the load is below a threshold.

Description

Technical Field

[0001] The present invention relates to a power conversion device that converts an AC power supply into DC and an air conditioner equipped with the same.

Background Art

[0002] Conventionally, a power conversion device (so-called converter) that converts power from an AC power supply into DC has been known. Such a power conversion device is used for applications such as supplying DC power to an inverter mounted on an air conditioner. In addition, the power conversion device is often configured using a PFC (Power Factor Correction) circuit to improve the power factor.

[0003] Patent Document 1 describes a power supply device provided with an active filter (interleaved circuit) that improves the power factor by the operation of a switching element and a passive filter that improves the power factor using an AC reactor between an AC power supply and an inverter. This power supply device is provided with a relay for bypassing the AC reactor during active filter operation. This relay is connected, together with the AC reactor, between the branch point on the input side of the active filter and the passive filter and the AC power supply. With such a configuration, either the active filter or the passive filter can be selected and used according to the load magnitude, so that, for example, the power conversion efficiency during low load can be improved.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In configurations using relays, as described in Patent Document 1, the resistance component of the relays can cause energy loss during active filter operation. Furthermore, space is required on the circuit board to accommodate the relays, making it difficult to miniaturize the device.

[0006] In view of the above circumstances, the object of the present invention is to provide a compact power conversion device with excellent power conversion efficiency, and an air conditioner equipped with the same. [Means for solving the problem]

[0007] To achieve the above objective, a power conversion device according to one embodiment of the present invention is a power conversion device that converts an AC voltage from an AC power source into a DC voltage and supplies it to a load, and comprises a smoothing capacitor, an active filter, a passive filter, and a switching control unit. The active filter includes a first rectifier that rectifies the output voltage of the AC power supply, an inductor, and a first switching element that switches between a current path including the AC power supply that passes through the first rectifier, the inductor, and the smoothing capacitor, and a current path that passes through the first rectifier and the inductor but not through the smoothing capacitor, by switching control, and operates / stops according to an input instruction signal. The passive filter includes a second rectifier that rectifies the output voltage of the AC power supply and a reactor, and at least a part of the second rectifier and the reactor are connected in parallel with the active filter between the AC power supply and the smoothing capacitor. The switching control unit detects the magnitude of the load and, if the magnitude of the load is greater than or equal to a threshold, outputs the instruction signal to instruct the operation of the active filter. If the magnitude of the load is less than the threshold, it outputs the instruction signal to instruct the stopping of the active filter.

[0008] In this power converter, an active filter comprising a first rectifier, an inductor, and a first switching element is configured between the AC power supply and the smoothing capacitor. Furthermore, at least a portion of the second rectifier and a reactor are connected in parallel with the active filter to form a passive filter. The active filter operates / stops according to an instruction signal corresponding to the load magnitude. This allows for switching between the active and passive filters without the use of switching elements such as relays, enabling the realization of a compact power converter with excellent power conversion efficiency.

[0009] The first rectifier may be a bridge rectifier circuit. In this case, one end of the reactor may be connected to the positive terminal of the smoothing capacitor. The second rectifier may also include a first diode connected in the forward direction from one output terminal of the AC power supply toward the other end of the reactor, and a second diode connected in the forward direction from the other output terminal of the AC power supply toward the other end of the reactor. This makes it possible to configure a second rectifier section using part of the bridge rectifier circuit. As a result, the number of components in the passive filter is reduced, allowing for a smaller circuit.

[0010] The first rectifier may be a bridge rectifier circuit. In this case, one end of the reactor may be connected to the positive terminal of the smoothing capacitor. The second rectifier may also include a second switching element connected between one output terminal of the AC power supply and the other end of the reactor, and a third switching element connected between the other output terminal of the AC power supply and the other end of the reactor. For example, a diode does not allow current to flow unless the forward voltage is exceeded, resulting in energy loss. However, by using switching elements, it is possible to avoid such losses and improve power conversion efficiency.

[0011] The first rectifier may include a pair of input terminals connected to the AC power supply, a pair of positive and negative output terminals, a third diode connected in the forward direction from one input terminal toward the positive output terminal, a fourth diode connected in the forward direction from the other input terminal toward the positive output terminal, a fourth switching element connected between one input terminal and the negative output terminal, and a fifth switching element connected between the other input terminal and the negative output terminal. By replacing diodes with switching elements in a bridge-structured circuit in this way, it becomes possible to improve the power conversion efficiency of an active filter.

[0012] When the active filter is stopped, the impedance of the path connecting the first rectifier and the smoothing capacitor may be greater than the impedance of the path connecting the second rectifier and the smoothing capacitor. This makes it possible to switch from an active filter to a passive filter by utilizing the difference in impedance.

[0013] An air conditioner according to one embodiment of the present invention comprises a power converter that converts an AC voltage from an AC power source to a DC voltage, an inverter that converts the DC voltage from the power converter to an AC voltage, a motor driven by the AC voltage from the inverter, and a motor control device that controls the inverter so that the motor is driven according to a given rotational speed. The power converter includes a smoothing capacitor, a first rectifier that rectifies the output voltage of the AC power supply, an inductor, and a first switching element that switches by switching control between a current path including the AC power supply that passes through the first rectifier, the inductor, and the smoothing capacitor, and a current path that passes through the first rectifier and the inductor but does not pass through the smoothing capacitor, and an active filter that operates / stops according to an input instruction signal, a second rectifier that rectifies the output voltage of the AC power supply, and a reactor, wherein at least a part of the second rectifier and the reactor are connected in parallel with the active filter between the AC power supply and the smoothing capacitor, and a switching control unit that detects the magnitude of the load of the inverter, outputs an instruction signal to instruct the operation of the active filter if the magnitude of the load is greater than or equal to a threshold, and outputs an instruction signal to instruct the stop of the active filter if the magnitude of the load is less than the threshold. [Effects of the Invention]

[0014] As described above, the present invention makes it possible to provide a compact power converter with excellent power conversion efficiency, and an air conditioner equipped with the same. The effects described herein are not necessarily limited, and any of the effects described in this disclosure may be provided. [Brief explanation of the drawing]

[0015] [Figure 1] This is a block diagram showing an example configuration of an outdoor unit of an air conditioner equipped with a power conversion device according to the first embodiment. [Figure 2] Figure 1 is a circuit diagram showing an example configuration of the power conversion device. [Figure 3] Figure 2 is a circuit diagram showing the equivalent circuit of the power converter shown. [Figure 4] This is a circuit diagram showing an example configuration of a power conversion device according to the second embodiment. [Figure 5] This is a circuit diagram showing an example configuration of a power conversion device according to the third embodiment. [Figure 6]It is a circuit diagram showing a configuration example of a power conversion device cited as a comparative example.

Embodiments for Carrying Out the Invention

[0016] Hereinafter, embodiments of the present invention will be described while referring to the drawings.

[0017] <First Embodiment> [Configuration of Air Conditioner] FIG. 1 is a block diagram showing a configuration example of an outdoor unit of an air conditioner equipped with a power conversion device according to the first embodiment. The block diagram shown in FIG. 1 illustrates a configuration example of the outdoor unit of the air conditioner 1. The air conditioner 1 includes a power conversion device 100, an inverter 2, a motor 3, and a motor control device 4.

[0018] [[ID=二十]]The power conversion device 100 converts an AC voltage from an AC power source 5 into a DC voltage. That is, the power conversion device 100 functions as a converter. The AC power source 5 is an AC power line that supplies power to the air conditioner 1 and outputs an AC voltage at a predetermined voltage (for example, AC100V, etc.). The power conversion device 100 converts this AC voltage into a DC voltage and supplies it to the inverter 2. Therefore, the inverter 2 is a load for the power conversion device 100. The configuration of the power conversion device 100 will be described in detail later.

[0019] The inverter 2 converts the DC voltage from the power conversion device 100 into an AC voltage. Specifically, the inverter 2 generates an AC voltage for driving the motor 3 from the DC voltage based on a control signal from the motor control device 4 and supplies it to the motor 3. The motor 3 is a power source for driving a compressor that compresses refrigerant and is driven by the AC voltage from the inverter 2. As the motor 3, for example, a permanent magnet synchronous motor (PMSM (Permanent Magnet Synchronous Motor)) is used. Note that the specific configurations of the inverter 2 and the motor 3 are not limited.

[0020] The motor control device 4 controls the inverter so that the motor is driven according to a given rotational speed. Here, the rotational speed given to the motor control device 4 is, for example, a rotational speed command value output from a higher-level controller (not shown) that controls the operation of the air conditioner 1. As shown in Figure 1, the motor control device 4 receives a rotational speed signal from the inverter 2 indicating the rotational speed of the motor 3. The motor control device 4 outputs a drive signal to the inverter 2 so that, for example, the rotational speed matches the rotational speed command value. The drive signal is a PWM-modulated pulse signal (PWM signal), and the voltage output from the inverter 2 to the motor is controlled by varying the duty cycle of this PWM signal. The motor control device 4 may also be capable of outputting the rotational speed of the motor 3 and the duty cycle of the PWM signal.

[0021] [Configuration of the power converter] The power converter 100 includes a smoothing capacitor 7, an active filter 10, a passive filter 30, and a switching control unit 40. The power converter 100 also has input terminals 8a and 8b connected to the AC power supply 5, and positive output terminals 9a and negative output terminals 9b connected to the inverter 2. Input terminal 8a is connected to one power line 5a of the AC power supply 5, and input terminal 8b is connected to the other power line 5b of the AC power supply 5. In this embodiment, one power line 5a and the other power line 5b of the AC power supply 5 correspond to one output terminal and the other output terminal of the AC power supply.

[0022] The smoothing capacitor 7 is a capacitor that smooths the voltage rectified by the active filter 10 or the passive filter 30 in the power converter 100. The smoothing capacitor 7 is connected between the positive output terminal 9a and the negative output terminal 9b.

[0023] The active filter 10 and the passive filter 30 are filters that adjust the waveform of the current input from the AC power supply 5 (hereinafter referred to as the input current), and function as a PFC (Power Factor Correction) circuit that improves the power factor in the power converter 100. The active filter 10 is an active PFC circuit that adjusts the waveform of the input current by switching control. The passive filter 30 is a passive (also called a static) PFC circuit that adjusts the waveform of the input current by a reactor 34, which will be described later.

[0024] Here, the power factor is the ratio of the power actually supplied from, for example, the AC power source 5 to the power effectively used by the power converter 100. Generally, in a converter such as the power converter 100, for example, by providing a smoothing capacitor 7, a phase shift may occur between the waveform of the AC voltage supplied from the AC power source 5 and the waveform of the input current, or the waveform of the input current may deviate from the sine wave waveform of the AC voltage. In this way, when the waveforms of the AC voltage and the input current do not match, the power factor decreases.

[0025] The active filter 10 and the passive filter 30 are connected to a common smoothing capacitor 7 and function together with the smoothing capacitor 7 as a filter (PFC circuit) that shapes the waveform of the input current to improve the power factor. Therefore, the smoothing capacitor 7 can also be said to be an element that constitutes the active filter 10 and the passive filter 30.

[0026] The active filter 10 includes a first rectifier 11, an interleaving circuit 14, a DC voltage detection unit 15, and a switching control unit 16. The interleaving circuit 14 includes inductors 17a and 17b, switching elements 18a and 18b, and diodes 19a and 19b. Switching elements 18a and 18b correspond to the first switching elements that constitute the active filter, and inductors 17a and 17b correspond to the inductors that constitute the active filter.

[0027] The first rectifier unit 11 rectifies the output voltage of the AC power supply. Specifically, the first rectifier unit 11 rectifies the AC voltage input from a pair of input terminals 12a and 12b and outputs it from a pair of output terminals (positive output terminal 13a and negative output terminal 13b). One input terminal 12a of the first rectifier unit 11 is connected to the input terminal 8a of the power converter 100, and the other input terminal 12b is connected to the input terminal 8b of the power converter 100 via an input current detection unit 41, which will be described later. Any circuit capable of rectifying an AC voltage can be used as the first rectifier unit 11. Typically, a full-wave rectifier circuit (bridge circuit) is used, but it is not limited to this, and half-wave rectifier circuits, voltage doubler rectifier circuits, Cockcroft-Walton circuits, etc. may also be used.

[0028] Inductor 17a is connected to the anode of diode 19a, and inductor 17b is connected to the anode of diode 19b. The inductors 17a and diode 19a connected in series, and the inductors 17b and diode 19b connected in series, are connected in parallel to each other between the positive output terminal 13a of the first rectifier unit 11 and the positive output terminal 9a of the power converter 100. The negative output terminal 13b of the first rectifier unit 11 is connected to the negative output terminal 9b of the power converter 100.

[0029] Switching elements 18a and 18b are elements that switch ON / OFF according to an input switching signal. For example, MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors) are used as switching elements 18a and 18b, but other switching elements can also be used. Switching element 18a is connected between the connection point of the inductor 17a and the anode of the diode 19a and the negative output terminal 9b, and switching element 18b is connected between the connection point of the inductor 17b and the anode of the diode 19b and the negative output terminal 9b. Switching element 18a is controlled ON / OFF by switching signal a, and switching element 18b is controlled ON / OFF by switching signal b.

[0030] Furthermore, in the active filter 10, the circuit composed of inductor 17a, switching element 18a, and diode 19a, and the circuit composed of inductor 17b, switching element 18b, and diode 19b, each function as a boost chopper type circuit (boost circuit). Therefore, the active filter 10 (interleaved circuit 14) becomes a two-phase interleaved type PFC circuit in which two boost circuits are connected in parallel. Note that when only one boost circuit is used (see Figure 3), the active filter 10 becomes a boost chopper type PFC circuit.

[0031] The DC voltage detection unit 15 detects the voltage between the positive output terminal 9a and the negative output terminal 9b of the power converter 100 and outputs it as a DC voltage signal. Therefore, the DC voltage signal is a signal that monitors the output voltage of the power converter 100. Any voltage sensor can be used as the DC voltage detection unit 15.

[0032] The switching control unit 16 outputs switching signal a and switching signal b to control the operation of switching elements 18a and 18b. Switching signal a and switching signal b are signals with opposite phases to each other, and each signal is PWM modulated. In this embodiment, the switching control unit 16 receives a DC voltage signal from the DC voltage detection unit 15, an input current signal representing the value of the input current from the input current detection unit 41 (described later), and an operation instruction signal from the switching determination unit 42.

[0033] In the control operation of switching elements 18a and 18b by the switching control unit 16, for example, the duty cycles of switching signal a and switching signal b are determined so that the DC voltage signal becomes the target voltage, and the instantaneous value of the input current (input current signal) is monitored so that the input current becomes sinusoidal. Pulse signals with these duty cycles are then output as switching signal a and switching signal b.

[0034] The control operation of switching elements 18a and 18b may be feedback control that references either a DC voltage signal or an input current signal, or it may be control that does not reference either signal. For example, a predetermined duty cycle may be set according to the circuit characteristics of the active filter 10 and the required target voltage. Also, if the DC voltage signal is not referenced, it is not necessary to provide the DC voltage detection unit 15.

[0035] The operation instruction signal input to the switching control unit 16 is a signal that indicates whether or not to perform control operations on switching elements 18a and 18b, and is a signal that instructs the operation / stop of the active filter 10. For example, the state in which PWM-modulated switching signals a and b are generated is the operating state of the active filter 10, and the state in which switching signals a and b are not generated is the stopped state of the active filter 10.

[0036] If the operation instruction signal is a signal that instructs the active filter 10 to operate, the switching control unit 16 outputs switching signal a and switching signal b. On the other hand, if the operation instruction signal is a signal that instructs the active filter 10 to stop, the switching control unit 16 does not output switching signal a and switching signal b, but outputs a stop signal that turns off switching elements 18a and 18b. In this way, the active filter 10 operates / stops according to the input operation instruction signal. In this embodiment, the operation instruction signal corresponds to an instruction signal.

[0037] As shown in Figure 1, when the switching element 18a is OFF, the positive output terminal 13a of the first rectifier 11 is connected to the negative output terminal 9b of the power converter 100 via the inductor 17a, diode 19a, and smoothing capacitor 7. When the switching element 18a is ON, the positive output terminal 13a of the first rectifier 11 is connected to the negative output terminal 9b of the power converter 100 via the inductor 17a and the switching element 18a. In other words, the switching element 18a switches between a current path that passes through the first rectifier 11, inductor 17a, and smoothing capacitor 7 (the path when the switching element 18a is OFF) and a path that passes through the first rectifier 11 and inductor 17a but not through the smoothing capacitor 7 (the path when the switching element 18a is ON) by switching control.

[0038] Similarly, when the switching element 18b is OFF, the positive output terminal 13a of the first rectifier unit 11 is connected to the negative output terminal 9b of the power converter 100 via the inductor 17b, diode 19b, and smoothing capacitor 7. When the switching element 18b is ON, the positive output terminal 13a of the first rectifier unit 11 is connected to the negative output terminal 9b of the power converter 100 via the inductor 17b and the switching element 18b. In other words, the switching element 18b switches between a current path that passes through the first rectifier unit 11, inductor 17b, and smoothing capacitor 7 (the path when the switching element 18b is OFF) and a path that passes through the first rectifier unit 11 and inductor 17b but not through the smoothing capacitor 7 (the path when the switching element 18b is ON) by switching control.

[0039] With this configuration, when the switching element 18a is turned OFF, the current generated by the energy stored in the inductor 17a during the period when the switching element 18a was ON is supplied to the smoothing capacitor 7. Similarly, when the switching element 18b is turned OFF, the current generated by the energy stored in the inductor 17b during the period when the switching element 18b was ON is supplied to the smoothing capacitor 7.

[0040] Generally, when current flows through an inductor, the current changes continuously and does not momentarily become zero or reverse polarity. Therefore, regardless of the voltage of the smoothing capacitor 7, the current flowing through inductors 17a and 17b is supplied to the smoothing capacitor 7. This continues even when the voltage of the smoothing capacitor 7 becomes greater than the voltage on the AC power supply 5 side. This makes it possible to perform a boost operation that raises the voltage between the positive output terminal 9a and the negative output terminal 9b of the power converter 100 (the output voltage of the power converter 100) to a level higher than the peak voltage of the AC power supply 5.

[0041] Furthermore, in the interleaved circuit 14, switching signal a and switching signal b are signals that are in opposite phases to each other. As a result, the ripple currents generated by inductors 17a and 17b are also in opposite phases and cancel each other out. This makes it possible to miniaturize the noise filter (not shown) used to suppress the ripple current, or to configure the circuit without a noise filter. In addition, having two current paths allows for the dispersion of heat generated in inductors 17a and 17b and switching elements 18a and 18b, and enables miniaturization of each element. The interleaved circuit 14 may be configured as a circuit with two or more interleaved systems.

[0042] The passive filter 30 includes a second rectifier 31 and a reactor 34. In this embodiment, the passive filter 30 is configured such that the second rectifier 31 and the reactor 34 are connected in parallel with the active filter 10 between the AC power supply 5 and the smoothing capacitor 7.

[0043] The second rectifier 31 rectifies the output voltage of the AC power supply 5. In this embodiment, the second rectifier 31 is configured separately from the first rectifier 11. The second rectifier 31 rectifies the AC voltage input from a pair of input terminals 32a and 32b and outputs it from a pair of output terminals (positive output terminal 33a and negative output terminal 33b). Any circuit capable of rectifying an AC voltage can be used as the second rectifier 31. Typically, a full-wave rectifier circuit (bridge circuit) is used, but it is not limited to this, and half-wave rectifier circuits, voltage doubler rectifier circuits, Cockcroft-Walton circuits, etc. may also be used.

[0044] The reactor 34 is an inductor provided in the passive filter 30. In this disclosure, the inductor provided in the passive filter 30 is referred to as the "reactor." Also, as described above, the inductors (inductors 17a and 17b) provided in the active filter 10 are referred to as the "inductors." The reactor 34, together with the smoothing capacitor 7, constitutes a filter that adjusts the waveform of the input current. This enables power factor improvement and suppression of high-frequency noise (emission countermeasures) by the passive filter 30.

[0045] The inductance Lac of the reactor 34 is set to be greater than the inductance of the inductor provided in the active filter 10. Also, in the active filter 10, the inductance Lint of the interleaving inductor (inductor 17a or inductor 17b) is smaller than the inductance Lchop of the boost chopper inductor. This is because the current path is more distributed in the interleaving method than in the boost chopper method. From these points, the magnitude of each inductance is Lac > Lchop > Lint.

[0046] As shown in Figure 1, the power converter 100 has connection points 37a to 37d that connect the active filter 10 and the passive filter 30 in parallel. Connection point 37a is formed in the path connecting the input terminal 8a of the power converter 100 and one input terminal 12a of the first rectifier unit 11, and connection point 37b is formed in the path connecting the input current detection unit 41 and the other input terminal 12b of the first rectifier unit 11. In addition, connection point 37c is formed in the path connecting one end of the smoothing capacitor 7 and the positive output terminal 9a of the power converter 100, and connection point 37d is formed in the path connecting the other end of the smoothing capacitor 7 and the negative output terminal 9b of the power converter 100.

[0047] In the example shown in Figure 1, one input terminal 32a of the second rectifier unit 31 is connected to connection point 37a via reactor 34, and from connection point 37a is connected to input terminal 8a of power converter 100 (one power line of AC power supply 5). The other input terminal 32b of the second rectifier unit 31 is connected to connection point 37b, and from connection point 37b is connected to input terminal 8b of power converter 100 (the other power line of AC power supply 5) via input current detection unit 41. The positive output terminal 33a of the second rectifier unit 31 is connected to connection point 37c, and from connection point 37c is connected to one end of smoothing capacitor 7 (positive output terminal 9a of power converter 100). The negative output terminal 33b of the second rectifier unit 31 is connected to connection point 37d, and from connection point 37d is connected to the other end of smoothing capacitor 7 (negative output terminal 9b of power converter 100).

[0048] Furthermore, the reactor 34 is located on the current path of the passive filter 30, which is branched off from the current path connected to the AC power supply 5. More specifically, the location of the reactor 34 is not limited as long as it is on a path connected in parallel with the active filter 10 and carrying both positive and negative currents. This point will be explained in detail with reference to Figure 2.

[0049] Thus, the power converter 100 is equipped with an active filter 10 and a passive filter 30 connected in parallel to each other. Note that there are no elements provided to switch the current paths flowing through the active filter 10 and the passive filter 30.

[0050] The switching control unit 40 switches the operation and stopping of the active filter 10 according to the magnitude of the load to which the power converter 100 is connected. Specifically, the switching control unit 40 detects the magnitude of the load and outputs an operation instruction signal to instruct the operation of the active filter 10 if the magnitude of the load is greater than or equal to a threshold, and outputs an operation instruction signal to instruct the stopping of the active filter 10 if the magnitude of the load is less than the threshold. As described above, the operation instruction signal is a signal that instructs whether or not the switching operation of the switching elements 18a and 18b of the active filter 10 is performed, and is output to the switching control unit 16.

[0051] In the power converter 100, when the active filter 10 is activated, the passive filter 30 becomes inactive, and active filter control is performed. Conversely, when the active filter 10 is stopped, the passive filter 30 becomes active, and passive filter control is performed. In other words, by switching the operation and stopping of the active filter 10, it is possible to switch between using the active filter 10 and the passive filter 30. In this respect, it can be said that the switching control unit 40 switches between the active filter 10 and the passive filter 30 according to the magnitude of the load. The operation of switching between the active filter 10 and the passive filter 30 will be described later with reference to Figure 3, etc.

[0052] In this embodiment, the switching control unit 40 includes an input current detection unit 41 and a switching determination unit 42. The input current detection unit 41 is a current sensor that is installed in the input current path common to the active filter 10 and the passive filter 30 (here, between the input terminal 8b and the connection point 37b) and detects the current value (instantaneous value) of the input current. As the input current detection unit 41, a current sensor that utilizes electromagnetic induction such as a current transformer, or a current sensor that detects current from the voltage of a load resistor can be used. The current value detected by the input current detection unit 41 is output to the switching determination unit 42 and the switching control unit 16.

[0053] The switching determination unit 42 calculates the load magnitude from the detection result of the input current detection unit 41 and performs a threshold determination on the load magnitude. Then, according to the result of the threshold determination, it outputs an operation instruction signal that instructs the active filter 10 to operate or stop. Here, the load magnitude is calculated from the instantaneous value of the input current detected by the input current detection unit 41. In the threshold determination, it is determined whether the effective value of the input current is equal to or greater than a predetermined threshold (for example, 4 amperes).

[0054] For example, if the effective value of the input current is greater than or equal to a threshold, an operation instruction signal is output to instruct the active filter 10 to operate (switching operation), as this indicates that the load is greater than or equal to the threshold. Conversely, if the effective value of the input current is less than the threshold, an operation instruction signal is output to instruct the active filter 10 to stop, as this indicates that the load is less than the threshold. As a result, when the load is greater than or equal to the threshold, the active filter 10, which is capable of boosting voltage, operates and supplies a relatively large amount of power. When the load is less than the threshold, boosting voltage is unnecessary, so the passive filter 30 operates and supplies a relatively small amount of power. This prevents unnecessary boosting voltage operation and avoids wasted power loss due to losses in the switching elements 18a and 18b and heat generation in the inductors 17a and 17b. Furthermore, if the load is above a threshold and a relatively large amount of power is supplied, resulting in high harmonic noise, the active filter 10, which has a high power factor correction and high-frequency noise suppression effect, is selected. If the load is below a threshold and a relatively small amount of power is supplied, resulting in low harmonic noise, the passive filter 30, which has no switching loss, is selected. Thus, an appropriate converter (either the active filter 10 or the passive filter 30) can be used depending on the load size.

[0055] The method for determining the load magnitude is not limited. Parameters representing the load magnitude may include, for example, the rotational speed of the motor 3 output from the motor control device 4 or the duty cycle of the PWM signal. For example, the active filter 10 may be instructed to operate when the rotational speed of the motor 3 is above a predetermined threshold (e.g., 300 revolutions / minute), and to stop when the rotational speed of the motor 3 is below the predetermined threshold. Similarly, the active filter 10 may be instructed to operate when the duty cycle of the PWM signal is above a predetermined threshold, and to stop when the duty cycle of the PWM signal is below the predetermined threshold.

[0056] Furthermore, two thresholds, an upper threshold and a lower threshold, may be set as predetermined thresholds. For example, it is possible to control the active filter 10 to operate when the duty cycle of the PWM signal output from the motor control device 4 exceeds the upper threshold (e.g., 95%), and to stop the active filter 10 when the duty cycle of the PWM signal falls below the lower threshold (e.g., 10%). Note that control using upper and lower thresholds may also be applied to other parameters (such as the effective value of the input current or the rotational speed of the motor 3). For example, if a single threshold is used, the filter may switch frequently if the load remains close to the threshold for an extended period. However, by using two thresholds, the frequency of filter switching can be suppressed, and the operation of the power converter 100 can be stabilized.

[0057] Figure 2 is a circuit diagram showing an example configuration of the power converter 100 shown in Figure 1. Figure 2 shows a specific example configuration of the first rectifier unit 11 and the second rectifier unit 31 described above. Here, the DC voltage detection unit 15 and the switching control unit 16 and the switching control unit 40 that constitute the active filter 10 are omitted.

[0058] As shown in Figure 2, the first rectifier section 11 of the active filter 10 is a full-wave rectifier circuit having four rectifier diodes 20a, 20b, 20c, and 20d, and is configured as a bridge rectifier circuit. Specifically, the cathodes of rectifier diode 20a and 20c are connected to each other, and the anodes of rectifier diode 20b and 20d are connected to each other. In addition, the cathode of rectifier diode 20b is connected to the anode of rectifier diode 20a, and the cathode of rectifier diode 20d is connected to the anode of rectifier diode 20c.

[0059] The connection point between rectifier diodes 20a and 20b is one input terminal 12a of the first rectifier unit 11 and is connected to one power line 5a of the AC power supply 5. The connection point between rectifier diodes 20c and 20d is the other input terminal 12b of the first rectifier unit 11 and is connected to the other power line 5b of the AC power supply 5. The connection point between the cathodes of rectifier diodes 20a and 20c is the positive output terminal 13a of the first rectifier unit 11 and is connected to inductors 17a and 17b of the interleaving circuit 14. The connection point between the anodes of rectifier diodes 20b and 20d is the negative output terminal 13b of the first rectifier unit 11 and is connected to the negative output terminal 9b of the power converter 100.

[0060] In the active filter 10 shown in Figure 2, the switching element 18a is connected to the negative output terminal 9b via a resistive component 22a, and the switching element 18b is connected to the negative output terminal 9b via a resistive component 22b. Here, the resistive components 22a and 22b are, for example, the parasitic resistances of the switching elements 18a and 18b, respectively.

[0061] The second rectifier section 31 of the passive filter 30 is a full-wave rectifier circuit having four rectifier diodes 35a, 35b, 35c, and 35d, and is configured as a bridge rectifier circuit. Specifically, the cathodes of rectifier diode 35a and 35c are connected to each other, and the anodes of rectifier diode 35b and 35d are connected to each other. In addition, the cathode of rectifier diode 35b is connected to the anode of rectifier diode 35a, and the cathode of rectifier diode 35d is connected to the anode of rectifier diode 35c.

[0062] The connection point between rectifier diodes 35a and 35b becomes one input terminal 32a of the second rectifier unit 31 and is connected to one power line 5a of the AC power supply 5 via the reactor 34 and connection point 37a. The connection point between rectifier diodes 35c and 35d becomes the other input terminal 32b of the second rectifier unit and is connected to the other power line 5b of the AC power supply 5 via connection point 37b. The connection point between the cathodes of rectifier diodes 35a and 35c becomes the positive output terminal 33a of the second rectifier unit 31 and is connected to one end of the smoothing capacitor 7 (positive output terminal 9a of the power converter 100) via connection point 37c. The connection point between the anodes of rectifier diodes 35b and 35d becomes the negative output terminal 33b of the second rectifier unit 31 and is connected to the other end of the smoothing capacitor 7 (negative output terminal 9b of the power converter 100) via connection point 37d.

[0063] As shown in Figure 2, in this embodiment, the second rectifier 31 is provided in parallel with the first rectifier 11. In this case, the connection position of the reactor 34 may be either on the input side or the output side of the second rectifier 31. Here, locations where the reactor 34 can be provided are schematically illustrated by regions 38a to 38d. For example, in Figure 2, the reactor 34 is provided between one input terminal 32a of the second rectifier 31 and the connection point 37a (region 38a). However, it is not limited to this, and the reactor 34 may also be provided between the other input terminal 32b of the second rectifier 31 and the connection point 37b (region 38b). Furthermore, the reactor 34 may be provided between the positive output terminal 33a of the second rectifier 31 and the connection point 37c (region 38d). Furthermore, the reactor 34 may also be provided between the negative output terminal 33b of the second rectifier 31 and the connection point 37d (region 38c).

[0064] Figure 3 is a circuit diagram showing the equivalent circuit of the power converter shown in Figure 2. The power converter 100a shown in Figure 3 is a simplified circuit configuration of the power converter 100 shown in Figure 2, and includes an active filter 10a and a passive filter 30a.

[0065] As shown in Figure 3, the rectifier circuits mounted on the active filter 10a and passive filter 30a (corresponding to the first rectifier section 11 and second rectifier section 31 in Figure 2) are, for example, bridge circuits composed of four diodes, with only the two diodes that allow current to pass through when the voltage of the AC power supply 5 is positive shown. Furthermore, the active filter 10a is a diagram of only one of the two boost circuits that constitute the interleaved active filter 10 shown in Figure 1. In this case, the active filter 10a can be considered a boost chopper type PFC circuit. It is also possible to use the power converter 100a as an actual circuit. In this case, the power converter 100a functions as a converter that can switch between the active filter 10a and the passive filter 30a when the voltage of the AC power supply 5 is positive. In this respect, the power converter 100a can also be said to be one embodiment of this embodiment.

[0066] The active filter 10a includes rectifier diodes 20e and 20f, an inductor 17, a switching element 18, and a diode 19. The anode of rectifier diode 20e is connected to one power line of the AC power supply 5 via input terminal 8a. The cathode of rectifier diode 20e is connected to the anode of diode 19 via inductor 17. The cathode of diode 19 is connected to one end of smoothing capacitor 7 and the positive output terminal 9a. The cathode of rectifier diode 20f is connected to the other power line of the AC power supply 5 via input terminal 8b. The anode of rectifier diode 20f is connected to the other end of smoothing capacitor 7 and the negative output terminal 9b. The switching element 18 is connected between the connection point between inductor 17 and the anode of diode 19 and the negative output terminal 9b (the other end of smoothing capacitor 7). In this way, in the active filter 10a, the rectifier diodes 20e and 20f constitute a rectifier circuit corresponding to the first rectifier section 11 when the voltage of the AC power supply 5 is a positive voltage. The inductor 17, switching element 18, and diode 19 constitute a boost circuit. The switching element 18 can be switched ON / OFF by a switching signal.

[0067] The passive filter 30a includes rectifier diodes 35e and 35f, and a reactor 34. The anode of rectifier diode 35e is connected to one power line of the AC power supply 5 via input terminal 8a from connection point 37a on the anode side of rectifier diode 20e. The cathode of rectifier diode 35e is connected to one end of smoothing capacitor 7 via reactor 34 from connection point 37c on the path connecting the cathode of diode 19 and the positive output terminal 9a. The cathode of rectifier diode 35f is connected to the other power line of the AC power supply 5 via input terminal 8b from connection point 37b on the cathode side of rectifier diode 20f. The anode of rectifier diode 35f is connected to the other end of smoothing capacitor 7 from connection point 37d on the path connecting the switching element 18 and the negative output terminal 9b. In this way, in the passive filter 30a, the rectifier diodes 35e and 35f constitute a rectifier circuit corresponding to the second rectifier section 31 when the voltage of the AC power supply 5 is a positive voltage.

[0068] Referring to Figure 3, the operation of the active filter 10a and the passive filter 30a, and the operation when each filter switches, will be explained.

[0069] In the following, the input current path in the active filter 10a will be referred to as the active line, and the mode in which the active filter 10a operates will be referred to as the active operating mode. Similarly, the input current path in the passive filter 30a will be referred to as the passive line, and the mode in which the passive filter 30a operates will be referred to as the passive operating mode. The passive operating mode is the active non-operating mode in which the active filter 10a does not operate.

[0070] Furthermore, the output voltage of the AC power supply 5 is denoted as Vac, and the output voltage of the power converter 100 (here, power converter 100a) is denoted as Vdc. The output voltage Vdc is the DC voltage between the positive output terminal 9a and the negative output terminal 9b, and is the voltage across the smoothing capacitor 7.

[0071] The output voltage Vac of the AC power supply 5 is assumed to be an AC voltage with an effective value of 100[V] and a frequency of 50[Hz]. Of course, the present invention is also applicable when using an AC power supply 5 that outputs other AC voltages. Furthermore, the following explanation will mainly describe the case where the output voltage Vac of the AC power supply 5 is a positive voltage. Note that the same explanation can be applied when the output voltage Vac is a negative voltage by configuring the rectifier circuits of each filter to invert the negative voltage before outputting it.

[0072] [Active filter operation] In active operation mode, a switching signal is input to the switching element 18 of the active filter 10a to control the ON / OFF state of the switching element 18. This causes the switching operation of the switching element 18 to switch ON / OFF at a predetermined switching frequency fsw. This switching operation enables a voltage boost operation, as described below. As a result, the output voltage Vdc becomes higher than the output voltage Vac of the AC power supply 5, and becomes a DC voltage in the range of, for example, 280[V] to 400[V]. The switching frequency fsw of the active filter 10a is, for example, 10[kHz].

[0073] When the switching element 18 is ON, the input current passes through the AC power supply 5, rectifier diode 20e, inductor 17, switching element 18, rectifier diode 20f in that order, and returns to the AC power supply 5. This is the path 43a (solid line path in Figure 3). At this time, current flows in the positive direction (from the AC power supply 5 side to the load side) through the inductor 17, and energy is stored in the inductor 17. Path 43a is the active line when the switching element 18 is ON.

[0074] When the switching element 18 is OFF, the path of the input current is the path 43b (the dotted path in FIG. 3) that passes through the AC power supply 5, the rectifying diode 20e, the inductor 17, the diode 19, the smoothing capacitor 7, and the rectifying diode 20f in this order and returns to the AC power supply 5 again. At this time, the current flowing through the inductor 17 is supplied to the subsequent smoothing capacitor 7, and the charge is accumulated in the smoothing capacitor 7. The path 43b is the active line when the switching element 18 is OFF.

[0075] In this way, in the active operation mode, by repeating the ON / OFF of the switching element 18, the voltage across the smoothing capacitor 7 (output voltage Vdc) increases. Note that in the switching period (1 / fsw) of the switching element 18, when the switching element 18 is OFF, regardless of the magnitude and direction of the voltage across the inductor 17, a current flows transiently in the positive direction due to the action of the inductor 17. Therefore, even when the output voltage Vdc becomes larger than the peak voltage of the output voltage Vac of the AC power supply 5, during the period when the switching element 18 is OFF, the current is supplied to the smoothing capacitor 7 through the inductor 17. As a result, the step-up operation becomes possible. Note that since Vac < Vdc, the current flowing through the inductor 17 during the period when the switching element 18 is OFF decreases compared to the current when the switching element 18 is ON.

[0076] During the operation of the active filter 10a, the voltage at the subsequent stage of the inductor 17 (output voltage Vdc) is stepped up to a high voltage (for example, 400 [V]). Therefore, no current flows from the AC power supply 5 with an effective value of 100 [V] through the passive filter 30a. That is, in the active operation mode, the passive filter 30a does not function.

[0077] [Operation of Passive Filter] In passive operation mode (active non-operation mode), a signal to turn off the switching element 18 of the active filter 10a (hereinafter referred to as the OFF signal) is input. In this case, the switching element 18 remains in the OFF state, and current flows to the passive filter 30a side, as will be described later.

[0078] When the passive filter 30a is operating, the input current passes through the AC power supply 5, rectifier diode 35e, reactor 34, smoothing capacitor 7, and rectifier diode 35f in that order, and returns to the AC power supply 5 via path 43c (the dashed line path in Figure 3). In passive operation mode, the smoothing capacitor 7 is charged by the input current passing through path 43c. Path 43c is a passive line formed by the passive filter 30a.

[0079] The voltage across the smoothing capacitor 7 is, for example, the peak voltage of the output voltage Vac of the AC power supply 5. Here, the effective value of the output voltage Vac of the AC power supply 5 is 100[V], and its peak voltage is (100 × sqrt(2))[V]. Here, sqrt(2) is the square root of 2 (≈1.4). Therefore, the output voltage Vdc of the power converter 100a in passive operation mode is approximately 140[V]. In reality, the voltage will be the voltage after subtracting the losses due to the voltage drop across the rectifier diodes 35e and 35f. In any case, the output voltage Vdc in passive operation mode will be lower than the output voltage Vdc in active operation mode with boost operation.

[0080] [Switching from passive operation mode to active operation mode] First, let's explain the switching from passive operation mode to active operation mode. This switching is performed using the voltage generated by the boost operation of the active filter 10a, for example.

[0081] When the active operation mode is started, the control signal input to the switching element 18 during passive operation mode is switched from an OFF signal to a switching signal. As a result, the active filter 10a starts the switching operation of switching the switching element 18 ON / OFF. Consequently, the voltage on the positive terminal line connected to the smoothing capacitor 7 in the active filter 10a (the line connected from the inductor 17 through the diode 19 to the positive terminal output terminal 9a) is boosted to a high voltage.

[0082] The voltage on the positive terminal line connected to the smoothing capacitor 7 is higher than, for example, the peak voltage of the output voltage Vac of the AC power supply 5 (for example, 140V) (for example, 400V). Therefore, in the passive line (path 43c) passing through the passive filter 30a, no current flows from the rectifier diode 35e to the smoothing capacitor 7 via the reactor 34. In this way, the active filter 10a performs a boost operation, automatically preventing current from flowing through the passive filter 30a. In other words, by inputting a switching signal, the passive operation mode is automatically switched to the active operation mode.

[0083] [Switching from active operation mode to passive operation mode] Next, we will explain how to switch from active operation mode to passive operation mode. This switching is performed by utilizing the difference in impedance between, for example, the active filter 10a and the passive filter 30a.

[0084] When the active filter 10a is stopped, the line from the rectifier diode 20e of the active filter 10a to the smoothing capacitor 7 is connected to the inductor 17 and diode 19. On the other hand, the line from the rectifier diode 35e of the passive filter 30a to the smoothing capacitor 7 is connected to the reactor 34. A rectified current attempts to flow through the smoothing capacitor 7 from the cathodes of the rectifier diodes 20e and 35e. Here, the rectified current is a DC current whose direction (positive or negative) does not change. Therefore, among the elements (inductor 17, diode 19, and reactor 34) placed on the path of the rectified current in the active filter 10a and the passive filter 30a, the impedance to the rectified current should mainly be considered to be the impedance (resistive component) of diode 19. For example, in the active filter 10a, a voltage drop occurs due to the impedance of diode 19. As a result, the output voltage of the active filter 10a is lower than the output voltage of the passive filter 30a. For this reason, in the active line (path 43b) when the active filter 10a is stopped, no current flows from the rectifier diode 20e through diode 19 to the smoothing capacitor 7.

[0085] Thus, in this embodiment, when the active filter 10a is stopped, the impedance of the path connecting the first rectifier (here, the rectifier diode 20e) and the smoothing capacitor 7 is configured to be greater than the impedance of the path connecting the second rectifier (here, the rectifier diode 35e) and the smoothing capacitor 7. This makes it possible to switch from the active filter 10a to the passive filter 30a by utilizing the difference in impedance.

[0086] For example, when starting passive operation mode, the control signal input to the switching element 18 during active operation mode switches from a switching signal to an OFF signal. As a result, the switching element 18 remains in the OFF state in the active filter 10a, and the active filter 10a enters a stopped state. In this case, since the boost operation is eliminated, the voltage on the positive side line connected to the smoothing capacitor 7 decreases in accordance with power consumption. This eliminates the high-voltage condition that was causing current not to flow through the passive filter 30a.

[0087] As mentioned above, the impedance of path 43b as seen from the rectifier diode 20e of the active filter 10a is greater than the impedance of path 43c as seen from the rectifier diode 35e of the passive filter 30a. Therefore, when the active filter 10a is stopped, current flows through the passive line (path 43c), which has a relatively lower impedance, making it possible to operate the passive filter 30a. In other words, by switching the switching signal to the OFF signal and maintaining the stop of operation of the active filter 10a, the active operation mode is automatically switched to the passive operation mode.

[0088] The operation of the active filter 10a and passive filter 30a described above can be interpreted as the operation of the active filter 10 and passive filter 30 of the power converter 100 shown in Figure 1. That is, in the power converter 100 as well, if switching signals a and b are input to the switching elements 18a and 18b, the input current path switches from the passive filter 30 to the active filter 10, enabling the active operation mode. Also, if switching signals a and b are switched to OFF signals, the input current path switches from the active filter 10 to the passive filter 30, enabling the passive operation mode.

[0089] Thus, the inventors focused on the differences in output voltage and impedance due to the operation of the active filter 10 and the passive filter 30 (active filter 10a and passive filter 30a), and found a configuration that allows for automatic switching of each filter without the need for switching elements such as relays, by moving the position of the reactor 34 to the passive filter 30 (passive filter 30a) side. This makes it possible to realize a compact power conversion device with excellent power conversion efficiency.

[0090] Furthermore, the reactor 34 of the passive filter 30 has a larger impedance when an unrectified AC current flows through it compared to when a rectified current flows through it. For this reason, it is preferable to place the reactor 34 between the second rectifier unit 31 and the smoothing capacitor 7 (regions 38c and 38d) rather than between the second rectifier unit 31 and the AC power supply 5 (regions 38a and 38b shown in Figure 2). This makes it possible to easily switch from active operation mode to passive operation mode using the impedance of the inductors 19a and 19b (inductor 19 in Figure 3) that constitute the active filter 10.

[0091] In the power converter 100 according to this embodiment, an active filter 10 is configured between the AC power supply 5 and the smoothing capacitor 7, including a first rectifier 11, inductors 17a and 17b, and switching elements 18a and 18b. A second rectifier 31 and a reactor 34 are connected in parallel with the active filter 10 to form a passive filter 30. The active filter 10 operates / stops according to an instruction signal corresponding to the load magnitude. This makes it possible to switch between the active filter 10 and the passive filter 30 without using switching elements such as relays, enabling the realization of a compact power converter with excellent power conversion efficiency.

[0092] Figure 6 is a circuit diagram showing an example configuration of a power converter as a comparative example. The power converter 101 shown in Figure 6 comprises an active filter 110 configured as an interleaved PFC circuit, a passive filter 130 with an AC reactor 134 on the input side, a relay element 135 for bypassing the AC reactor 134, and a smoothing capacitor 7. The AC reactor 134 is a coil (inductance element) provided for power factor correction and high-frequency noise countermeasures.

[0093] The active filter 110 is provided with a bridge rectifier circuit 111 and an interleaving circuit 114, while the passive filter 130 is provided with a bridge rectifier circuit 131. The bridge rectifier circuit 111 and the interleaving circuit 114 are configured in the same way as the first rectifier section 11 and the interleaving circuit 14 shown in Figure 2, and the bridge rectifier circuit 131 is configured in the same way as the second rectifier section 31 shown in Figure 2.

[0094] A pair of power lines 5a and 5b of the AC power supply 5 are connected to branching points 45a and 45b. A pair of input terminals 12a and 12b of the bridge rectifier circuit 111 and a pair of input terminals 32a and 32b of the bridge rectifier circuit 131 are connected to each branching point 45a and 45b, respectively. An AC reactor 134 and a relay element 135 are connected in parallel to the path from one of the power lines 5a of the AC power supply 5 to branching point 45a.

[0095] In the power converter 101, active control (interleaved control) and passive control can be switched by switching the ON / OFF state of the relay element 135. For example, the power converter 101 detects the load, and if the detected load is above a predetermined threshold, the relay element 135 is turned ON to bypass the AC reactor 134 and activate the active filter 110. In Figure 6, as an example of the path during active operation, path 43p when one of the switching elements is ON is shown with a solid line. This enables rectification of the input current (operation of the bridge rectifier circuit 111), as well as voltage boosting and power factor correction (operation of the interleaved circuit 114). Conversely, if the detected load is below a predetermined threshold, the relay element 135 is turned OFF and the passive filter 130 is activated. In Figure 6, path 43q during passive operation is shown with a dotted line. This allows current to flow through the AC reactor 134, enabling rectification (by the action of the bridge rectifier circuit 131) and power factor correction (by the action of the AC reactor 134).

[0096] Thus, in the power converter 101, when using the active filter 110, the relay element 135 was made conductive to bypass the AC reactor 134, but the relay element 135 was the cause of power loss. For example, the relay element 135, which switches the path of a large current, has a mechanical switch part, and the loss due to contact resistance in the switch part was large. In addition, space was required on the circuit board to place the relay element, which hindered the miniaturization of the circuit.

[0097] In contrast, in the power converter 100 according to this embodiment, the reactor 34 constituting the passive filter 30 is not provided on a path shared with the active filter 10, but is provided in a path branched off to the passive filter 30 side. By positioning the reactor 34 on the passive filter 30 side in this way, the active line and the passive line can be separated without providing relay elements 135, etc., as shown in Figure 6. Since relay elements are unnecessary, it is possible to eliminate losses that occur when the input current passes through relay elements, for example. In addition, it is possible to reduce component costs and to miniaturize the device by reducing the component area.

[0098] <Second Embodiment> A power conversion device according to a second embodiment of the present invention will now be described. In the following description, parts that are similar to the configuration and operation of the power conversion device 100 described in the above embodiment will be omitted or simplified.

[0099] Figure 4 is a circuit diagram showing an example configuration of a power converter according to the second embodiment. In this embodiment, a circuit configuration in which part of the rectifier circuits of the active filter and the passive filter are common will be described. The power converter 200 shown in Figure 4 is, for example, a modified version of the power converter 100 shown in Figure 2, mainly by changing the configuration of the passive filter 30. As shown in Figure 4, the power converter 200 has an active filter 210, a passive filter 230, and a smoothing capacitor 7.

[0100] The active filter 210 has a first rectifier section 211 and an interleaving circuit 214, and is configured similarly to the active filter 10 shown in Figure 2, for example. The first rectifier section 211 is a full-wave rectifier circuit having four rectifier diodes 20a, 20b, 20c, and 20d, and is configured as a bridge rectifier circuit. The interleaving circuit 214 has inductors 17a and 17b, switching elements 18a and 18b, and diodes 19a and 19b, forming an interleaved boost circuit. In addition to the interleaving circuit 214, a boost chopper type circuit as shown in Figure 3 may be used as the active filter 210.

[0101] The passive filter 230 includes a second rectifier 231 and a reactor 234. The second rectifier 231 is a full-wave rectifier circuit consisting of four rectifier diodes, including rectifier diodes 50a and 50b and rectifier diodes 20c and 20d of the first rectifier 211. In this embodiment, rectifier diode 50a corresponds to the first diode, and rectifier diode 50b corresponds to the second diode.

[0102] The power converter 200 has three connection points 37a to 37c for connecting the active filter 210 and the passive filter 230 in parallel. Connection point 37a is formed in the path connecting the input terminal 8a of the power converter 200 to one input terminal 12a of the first rectifier 211, and connection point 37b is formed in the path connecting the input terminal 8b of the power converter 200 to the other input terminal 12b of the first rectifier 211. Connection point 37c is formed in the path connecting one end (positive terminal) of the smoothing capacitor 7 to the positive output terminal 9a of the power converter 200. In this embodiment, connection point 37d, which is provided in Figures 1 and 2, etc., is not formed.

[0103] As shown in Figure 4, one end of the reactor 234 is connected to the positive terminal of the smoothing capacitor 7. The rectifier diode 50a is connected in the forward direction from one power line 5a of the AC power supply 5 toward the other end of the reactor 234. The rectifier diode 50b is connected in the forward direction from the other power line 5b of the AC power supply 5 toward the other end of the reactor 234.

[0104] Specifically, the anode of rectifier diode 50a is connected to one passive line (connection point 37a) branched in parallel from the AC power supply 5, and the anode of rectifier diode 50b is connected to the other passive line (connection point 37b). The cathodes of rectifier diode 50a and rectifier diode 50b are connected to each other, and a reactor 234 is connected between the connection point of each cathode and the connection point 37c on the smoothing capacitor 7 side.

[0105] Here, we will explain the current path (passive line) in the passive filter 230. The path 43d indicated by the solid arrow in Figure 4 is the current path when the output voltage Vac of the AC power supply 5 is positive. The path 43e indicated by the dotted arrow is the current path when the output voltage Vac of the AC power supply 5 is negative.

[0106] For example, when the output voltage Vac is positive, the input current output from the AC power supply 5 to the input terminal 8a passes through connection point 37a, rectifier diode 50a, reactor 234, connection point 37c, smoothing capacitor 7, and rectifier diode 20d of the first rectifier unit 211 in that order, and then returns to the AC power supply 5 from the input terminal 8b (path 43d). In other words, the rectifier diode 20d of the first rectifier unit 211 constitutes a passive line.

[0107] Furthermore, when the output voltage Vac is negative, the input current output from the AC power supply 5 to the input terminal 8b passes through connection point 37b, rectifier diode 50b, reactor 234, connection point 37c, smoothing capacitor 7, and rectifier diode 20b of the first rectifier unit 211 in that order, and then returns to the AC power supply 5 from the input terminal 8a (path 43e). In other words, the rectifier diode 20b of the first rectifier unit 211 constitutes a passive line.

[0108] Furthermore, the reactor 234 of the passive filter 230 is positioned after the rectifier diodes 50a and 50b located in the branched path. This makes it possible to improve the power factor by supplying current to the reactor 234 when the polarity of the output voltage Vac is positive or negative, as shown in paths 43d and 43e.

[0109] The above configuration in the passive filter 230 can be described as replacing a commonly used diode bridge circuit with four diodes with a circuit with two diodes. As a result, two of the four rectifier diodes 20a to 20d that make up the diode bridge circuit (first rectifier section 211) of the active filter 210, namely rectifier diodes 20b and 20d in the lower arm, can be used as rectifier diodes in the lower arm of the passive filter 230.

[0110] As described above, the passive filter 230 according to this embodiment has a configuration in which a part of the second rectifier section 231 (rectifier diodes 50a and 50b) and the reactor 234 are connected in parallel with the active filter 210 between the AC power supply 5 and the smoothing capacitor 7. This makes it possible to configure the second rectifier section 231 using a part of the first rectifier section 211 which is configured as a bridge rectifier circuit. As a result, the number of components in the passive filter 230 is reduced, and the circuit can be made smaller.

[0111] For example, in the comparative example shown in Figure 6, a diode bridge circuit is provided for both the active filter 110 and the passive filter 130. Because two sets of diode bridge circuits are included, a large amount of space on the circuit board is required. Furthermore, space is needed for the relay element 135, making it difficult to miniaturize the device.

[0112] In contrast, in the power conversion device 200 according to this embodiment, the passive filter 230 is composed of two rectifier diodes 50a and 50b. This makes it possible to reduce component costs compared to, for example, the case where two sets of diode bridge circuits are provided, and to achieve miniaturization of the substrate and device by reducing the component area.

[0113] <Third Embodiment> Figure 5 is a circuit diagram showing an example configuration of a power converter according to the third embodiment. In this embodiment, a rectifier circuit using switching elements is used as the rectifier circuit for the active filter and the passive filter. The power converter 300 shown in Figure 5 is, for example, a modified version of the power converter 200 shown in Figure 4, with changes to the configuration of the first rectifier section 211 of the active filter 210 and the second rectifier section 231 of the passive filter 230. As shown in Figure 5, the power converter 300 includes an active filter 310, a passive filter 330, a rectifier control unit 340, and a smoothing capacitor 7.

[0114] The active filter 310 includes a first rectifier 311 and an interleaving circuit 314. Of these, the interleaving circuit 314 is configured in the same way as, for example, the interleaving circuit 214 shown in Figure 4 (or the interleaving circuit 14 shown in Figure 2). Alternatively, a boost chopper type circuit as shown in Figure 3 may be used instead of the interleaving circuit 314.

[0115] The first rectifier section 311 is configured as a bridge rectifier circuit using both diodes and switching elements. The first rectifier section 311 is a full-wave rectifier circuit having two rectifier diodes 60a and 60b and two rectifier switching elements 61a and 61b. Note that the rectifier diodes 60a and 60b correspond to the rectifier diodes 20a and 20c of the first rectifier section 211 shown in Figure 4.

[0116] The rectifier switching elements 61a and 61b are, for example, switching elements such as MOSFETs, and their ON / OFF state is switched according to a control signal from the rectifier control unit 340, which will be described later. Figure 5 shows the body diodes (also called parasitic diodes) of the MOSFETs for the rectifier switching elements 61a and 61b. The body diodes can be considered as diodes connected in the forward direction from the source side to the drain side.

[0117] As shown in Figure 5, the rectifier diode 60a is connected in the forward direction from one input terminal 12a to the positive output terminal 13a, and the rectifier diode 60b is connected in the forward direction from the other input terminal 12b to the positive output terminal 13a. The rectifier switching element 61a is connected between one input terminal 12a and the negative output terminal 13b, and the rectifier switching element 61b is connected between the other input terminal 12b and the negative output terminal 13b. In this embodiment, the rectifier diode 60a corresponds to the third diode, and the rectifier diode 60b corresponds to the fourth diode. The rectifier switching element 61a corresponds to the fourth switching element, and the rectifier switching element 61b corresponds to the fifth switching element.

[0118] Thus, the first rectifier unit 311 has a configuration in which the rectifier diode 20b is replaced with a rectifier switching element 61a and the rectifier diode 20d is replaced with a rectifier switching element 61b, as shown in Figure 4. This can be described as replacing a diode bridge circuit with four diodes with a circuit in which two diodes are placed on the upper arm and two switching elements (MOSFETs) are placed on the lower arm.

[0119] The passive filter 330 includes a second rectifier 331 and a reactor 334. The second rectifier 331 is a full-wave rectifier circuit consisting of four rectifier switching elements, including rectifier switching elements 62a and 62b and rectifier switching elements 61a and 61b of the first rectifier 311. In this embodiment, rectifier switching element 62a corresponds to the second switching element, and rectifier switching element 62b corresponds to the third switching element.

[0120] As shown in Figure 5, one end of the reactor 334 is connected to the positive terminal of the smoothing capacitor 7. The rectifier switching element 62a is connected between one power line 5a of the AC power supply 5 and the other end of the reactor 334. The rectifier switching element 62b is connected between the other power line 5b of the AC power supply 5 and the other end of the reactor 334.

[0121] Thus, the second rectifier unit 331 has a configuration in which the rectifier diode 50a is replaced with a rectifier switching element 62a and the rectifier diode 50b is replaced with a rectifier switching element 62b, as shown in the second rectifier unit 231 in Figure 4. This can be described as replacing the two diodes that function as the upper arm in the passive line with two switching elements (MOSFETs).

[0122] Furthermore, the reactor 334 of the passive filter 330 is positioned downstream of the rectifier switching elements 62a and 62b located in the branch path. This makes it possible to improve the power factor by supplying current to the reactor 334 when the polarity of the output voltage Vac is positive or negative, similar to the case in Figure 4.

[0123] The rectifier control unit 340 generates a control signal to control the ON / OFF state of each rectifier switching element provided in the first rectifier unit 311 and the second rectifier unit 331. The control signal is a square wave that includes, for example, an ON level to turn on the rectifier switching element and an OFF level to turn off the rectifier switching element, and the frequency of the control signal is set to the power supply frequency (e.g., 50 Hz).

[0124] For example, in passive operation mode, when the output voltage Vac of the AC power supply 5 is positive, the rectifier switching elements 62a and 61b are set to ON so that current flows along path 43f, and the rectifier switching elements 62b and 61a are set to OFF. Also, when the output voltage Vac of the AC power supply 5 is negative, the rectifier switching elements 62b and 61a are set to ON so that current flows along path 43g, and the rectifier switching elements 62a and 61b are set to OFF. This makes it possible to operate the passive filter 330 in the same way as in Figure 4.

[0125] Even when the active filter 310 is operating, each rectifier switching element is controlled in the same manner as described above. This makes it possible to properly perform the rectification function of the active filter 310. Note that in active operation mode, it is not necessary to operate the passive filter 330, so control of rectifier switching elements 62a and 62b is not required.

[0126] Generally, when a forward voltage is applied to a diode, current will flow once a certain voltage Vf is exceeded. Vf varies depending on the element, but below Vf, current cannot flow, resulting in a loss in terms of power conversion efficiency. Furthermore, diodes also possess resistance when conducting, where current flows when a voltage above Vf is applied. Therefore, in a diode bridge circuit using, for example, four diodes, the losses due to the diode's Vf and resistance during conduction may be significant.

[0127] In contrast, in the power conversion device 300 according to this embodiment, some of the rectifier diodes are replaced with switching elements. For example, in a switching element configured using a MOSFET, the threshold voltage required for current to begin flowing is lower than that of the diode's Vf, making it possible to flow current over a wider voltage range. Also, the resistance during conduction is lower for a MOSFET than for a rectifier diode. This makes it possible to reduce losses due to the diode's Vf and losses due to resistance during conduction. In this way, it is possible to improve power conversion efficiency by using switching elements such as MOSFETs.

[0128] For example, in the active filter 310, the first rectifier section 311 is provided with two rectifier switching elements 61a and 61b. As a result, in the active operation mode, the input current passes through the rectifier switching elements 61a and 61b, making it possible to reduce power loss compared to when diodes are used. In the passive filter 330, the bridge structure of the second rectifier section 331 is composed of four switching elements (rectifier switching elements 62a and 62b and rectifier switching elements 61a and 61b). As a result, power loss can be significantly reduced in the passive operation mode. This makes it possible to improve power conversion efficiency in both the active and passive operation modes.

[0129] Furthermore, switching elements such as MOSFETs can be made smaller in size than diodes. Therefore, in the power conversion device 300 according to this embodiment, replacing each diode in the diode bridge circuit with a switching element makes it possible to reduce the size of the substrate and the device.

[0130] <Other Embodiments> The present invention is not limited to the embodiments described above, and various other embodiments can be realized.

[0131] In the example shown in Figure 5, two rectifier diodes 60a and 60b were used as elements constituting the upper arm of the first rectifier section 311. For example, the two rectifier diodes 60a and 60b may also be replaced with switching elements. Alternatively, a rectifier switching element may be provided only on the passive filter 330 side. In this case, the first rectifier section 311 may be constructed entirely using diodes. Furthermore, the locations where a rectifier switching element is applied are not limited.

[0132] The above embodiment mainly described a power conversion device that supplies DC voltage to the inverter of an air conditioner. However, it is not limited to this, and the power conversion device of the present invention can be applied to any device that uses DC voltage, such as home appliances, automobiles, and industrial machinery.

[0133] It is also possible to combine at least two of the feature features of the present technology described above. In other words, the various feature features described in each embodiment may be combined arbitrarily, regardless of the specific embodiment. Furthermore, the various effects described above are merely examples and not limiting, and other effects may also be exhibited. [Explanation of symbols]

[0134] 1…Air conditioner 5…AC power supply 7…Smoothing Capacitor 10, 10a, 210, 310… Active filters 11, 211, 311...first rectifier 14, 214, 314… Interleaved circuits 17, 17a, 17b... Inductors 18, 18a, 18b… Switching elements 19, 19a, 19b…diodes 30, 30a, 230, 330… Passive filters 31, 231, 331...Second rectifier 34, 234, 334… Reactor 40…Switching control unit 50a, 50b... Rectifier diodes 61a, 61b, 62a, 62b... Rectifier switching elements 100, 100A, 200, 300... Power converter

Claims

1. A power conversion device that converts AC voltage from an AC power source into DC voltage and supplies it to a load, A smoothing capacitor, An active filter comprising: a first rectifier for rectifying the output voltage of the AC power supply; an inductor; and a first switching element that switches by switching control between a current path including the AC power supply that passes through the first rectifier, the inductor, and the smoothing capacitor, and a path that passes through the first rectifier, the inductor, and not through the smoothing capacitor, and which operates / stops according to an input instruction signal, A passive filter comprising a second rectifier that rectifies the output voltage of the AC power supply and a reactor, wherein at least a part of the second rectifier and the reactor are connected in parallel with the active filter between the AC power supply and the smoothing capacitor, A switching control unit that detects the magnitude of the load, outputs an instruction signal to instruct the operation of the active filter if the magnitude of the load is greater than or equal to a threshold, and outputs an instruction signal to instruct the stopping of the active filter if the magnitude of the load is less than the threshold. A power conversion device equipped with the following features.

2. A power conversion device according to claim 1, The first rectifier section is a bridge rectifier circuit, One end of the reactor is connected to the positive terminal of the smoothing capacitor. The second rectifier unit includes a first diode connected in the forward direction from one output terminal of the AC power supply toward the other terminal of the reactor, and a second diode connected in the forward direction from the other output terminal of the AC power supply toward the other terminal of the reactor. Power converter.

3. A power conversion device according to claim 1, The first rectifier section is a bridge rectifier circuit, One end of the reactor is connected to the positive terminal of the smoothing capacitor. The second rectifier unit includes a second switching element connected between one output terminal of the AC power supply and the other terminal of the reactor, and a third switching element connected between the other output terminal of the AC power supply and the other terminal of the reactor. Power converter.

4. A power conversion device according to claim 1, The first rectifier unit includes a pair of input terminals connected to the AC power supply, a pair of positive and negative output terminals, a third diode connected in the forward direction from one input terminal to the positive output terminal, a fourth diode connected in the forward direction from the other input terminal to the positive output terminal, a fourth switching element connected between one input terminal and the negative output terminal, and a fifth switching element connected between the other input terminal and the negative output terminal. Power converter.

5. A power conversion device according to any one of claims 1 to 4, When the active filter is stopped, the impedance of the path connecting the first rectifier and the smoothing capacitor is greater than the impedance of the path connecting the second rectifier and the smoothing capacitor. Power converter.

6. An air conditioner comprising: a power converter that converts AC voltage from an AC power source to DC voltage; an inverter that converts DC voltage from the power converter to AC voltage; a motor driven by the AC voltage from the inverter; and a motor control device that controls the inverter so that the motor is driven according to a given rotational speed, The aforementioned power converter is A smoothing capacitor, An active filter comprising: a first rectifier for rectifying the output voltage of the AC power supply; an inductor; and a first switching element that switches by switching control between a current path including the AC power supply that passes through the first rectifier, the inductor, and the smoothing capacitor, and a path that passes through the first rectifier, the inductor, and not through the smoothing capacitor, and which operates / stops according to an input instruction signal, A passive filter comprising a second rectifier that rectifies the output voltage of the AC power supply and a reactor, wherein at least a part of the second rectifier and the reactor are connected in parallel with the active filter between the AC power supply and the smoothing capacitor, A switching control unit that detects the load on the inverter, outputs an instruction signal to instruct the active filter to operate if the load is greater than or equal to a threshold, and outputs an instruction signal to instruct the active filter to stop if the load is less than the threshold. has Air conditioner.

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