PFC circuit

Abstract

To disperse a heat load of a plurality of switching elements, and to suppress a temperature rise caused by an increase in switching loss due to high frequency.SOLUTION: The PFC circuit includes a first switching element, a second switching element, a third switching element, and a fourth switching element, and improves a power factor of power input from an AC power supply, wherein a control mode is switched to a first mode, a second mode, a third mode, and a fourth mode in accordance with a state of a sinusoidal AC voltage input from the AC power supply, the control mode is switched from the first mode to the second mode, from the second mode to the third mode, from the third mode to the fourth mode, and from the fourth mode to the first mode, and each switching element is changed to a different state in each mode.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a PFC circuit. [Background technology]

[0002] Patent Document 1 discloses that in a totem-pole single-phase PFC converter, the voltage of a low-frequency node, one of the two poles of the AC power supply to which an inductor is not connected, is linearly controlled at the timing when the polarity of the input of the AC power supply is reversed. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 7279715 Publication Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the configuration described in Patent Document 1, the load of switching loss is unevenly distributed among multiple switching elements, and therefore, when the drive frequency is increased, switching loss increases in switching elements with high loads, which may cause the temperature to exceed the heat resistance limit.

[0005] The present invention has been made in consideration of the above circumstances, and aims to provide a PFC circuit that can distribute the thermal load of multiple switching elements and suppress the temperature rise that accompanies an increase in switching loss due to higher frequencies. [Means for solving the problem]

[0006] The present invention provides a PFC circuit that improves the power factor of power input from the AC power supply, the PFC circuit comprising: a first arm in which a first switching element having a first diode connected in parallel and a second switching element having a second diode connected in parallel are connected in series at a first connection point; and a second arm that is provided in parallel with the first arm and in which a third switching element having a third diode connected in parallel and a fourth switching element having a fourth diode connected in parallel are connected in series at a second connection point; one end of an input terminal of an AC power supply is connected to the first connection point and the other end of the input terminal of the AC power supply is connected to the second connection point; a control mode is switched to any one of a first mode, a second mode, a third mode, and a fourth mode depending on the state of a sinusoidal AC voltage applied, the control mode is switched from the first mode to the second mode, from the second mode to the third mode, from the third mode to the fourth mode, and from the fourth mode to the first mode, and the first switching element, the second switching element, the third switching element, and the fourth switching element change to different states in the first mode, the second mode, the third mode, and the fourth mode, respectively. [Effects of the Invention]

[0007] In the present invention, the thermal load of a plurality of switching elements can be distributed, and the temperature rise that accompanies an increase in switching loss due to higher frequencies can be suppressed. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram schematically illustrating a PFC circuit according to an embodiment. [Figure 2] FIG. 2 is a diagram for explaining the relationship between the state of the sinusoidal wave input voltage and the control mode. [Figure 3] FIG. 3 is a diagram for explaining the first mode and the third mode. [Figure 4] FIG. 4 is a diagram for explaining the second mode and the fourth mode. [Figure 5]FIG. 5 is a flowchart showing a control mode switching flow. DETAILED DESCRIPTION OF THE INVENTION

[0009] The PFC circuit according to the embodiment of the present invention will be specifically described below, but the present invention is not limited to the embodiment described below.

[0010] 1 is a diagram schematically illustrating a PFC circuit according to an embodiment. A PFC (Power Factor Correction) circuit 1 corrects the power factor of AC power input from an AC power source 2, converts the AC power into DC power, and outputs it. The PFC circuit 1 is electrically connected to the AC power source 2. The AC power source 2 is connected to an input terminal (AC terminal) of the PFC circuit 1.

[0011] The PFC circuit 1 rectifies and boosts the AC power from which noise has been removed by the filter circuit 3 and outputs it to a smoothing capacitor C2, while also improving the power factor by making the input voltage closer to a sine wave. The filter circuit 3 includes a capacitor C1 and an inductor L. The smoothing capacitor C2 smooths the voltage of the DC power output from the PFC circuit 1. The DC power smoothed by the smoothing capacitor C2 is supplied to a power conversion circuit such as a DC / DC converter or inverter.

[0012] The PFC circuit 1 is a single-phase totem-pole PFC having four switching elements SW1 to SW4. The PFC circuit 1 includes a first arm 10 and a second arm 20. The first arm 10 and the second arm 20 are connected in parallel.

[0013] The first arm 10 is an arm in which a first switching element SW1 and a second switching element SW2 are connected in series at a first connection point P1. The first switching element SW1 is the upper arm, and the second switching element SW2 is the lower arm. A first diode D1 is connected in parallel to the first switching element SW1. A second diode D2 is connected in parallel to the second switching element SW2. One end of an input terminal of an AC power supply 2 is connected to the first connection point P1.

[0014] The second arm 20 is an arm in which the third switching element SW3 and the fourth switching element SW4 are connected in series at the second connection point P2. The third switching element SW3 is the upper arm, and the fourth switching element SW4 is the lower arm. A third diode D3 is connected in parallel to the third switching element SW3. A fourth diode D4 is connected in parallel to the fourth switching element SW4. The other end of the input terminal of the AC power supply 2 is connected to the second connection point P2.

[0015] Each of the switching elements SW1 to SW4 is configured by a MOSFET. Each of the switching elements SW1 to SW4 of the PFC circuit 1 performs a switching operation in response to a command signal from a control device.

[0016] The PFC circuit 1 is capable of high-frequency operation and is configured to realize a PFC control method with a compact circuit configuration. Specifically, the PFC circuit 1 is configured to uniformly distribute the heat load of the first to fourth switching elements SW1 to SW4, thereby suppressing the effects of temperature rise that accompanies increased switching loss due to higher frequencies.

[0017] As shown in FIG. 2, the PFC circuit 1 switches the control mode among a first mode, a second mode, a third mode, and a fourth mode depending on the state of a sinusoidal AC voltage (hereinafter referred to as a sinusoidal input voltage) input from an AC power supply 2.

[0018] In the first mode, the first switching element SW1 performs rectification, the second switching element SW2 performs switching, the third switching element SW3 is inactive, and the fourth switching element SW4 is always on. As shown in Fig. 2, the control mode of the PFC circuit 1 is the first mode in state A where the sine wave input voltage is positive. As shown in Fig. 3, the PFC circuit 1 operates in the first mode when the polarity of one end of the input terminal of the AC power supply 2 is positive.

[0019] In the second mode, the first switching element SW1 performs switching operation, the second switching element SW2 performs rectification operation, the third switching element SW3 is always on, and the fourth switching element SW4 is inactive. As shown in Figure 2, the control mode of the PFC circuit 1 is the second mode in state B where the sinusoidal wave input voltage is negative. As shown in Figure 4, the PFC circuit 1 operates in the second mode when the polarity of the other end of the input terminal of the AC power supply 2 is positive.

[0020] In the third mode, the first switching element SW1 is always on, the second switching element SW2 is inactive, the third switching element SW3 is in switching operation, and the fourth switching element SW4 is in rectifying operation. As shown in Figure 2, the control mode of the PFC circuit 1 is the third mode in state C where the sine wave input voltage is positive. As shown in Figure 3, the PFC circuit 1 operates in the third mode when the polarity of one end of the input terminal of the AC power supply 2 is positive.

[0021] In the fourth mode, the first switching element SW1 is inactive, the second switching element SW2 is always on, the third switching element SW3 is in rectification operation, and the fourth switching element SW4 is in switching operation. As shown in Fig. 2, the control mode of the PFC circuit 1 is the fourth mode in state D where the sinusoidal wave input voltage is negative. As shown in Fig. 4, the PFC circuit 1 operates in the fourth mode when the polarity of the other end of the input terminal of the AC power supply 2 is positive.

[0022] 5 is a flow chart showing a control mode switching flow. The control shown in FIG.

[0023] The control device operates the PFC circuit 1 in the first mode (step S1). In step S1, the PFC circuit 1 is controlled to operate in the first mode in state A where the sinusoidal wave input voltage is positive.

[0024] The control device determines whether the sinusoidal input voltage has inverted from positive to negative (step S2). In step S2, it is determined whether the state of the sinusoidal input voltage has transitioned from state A to state B.

[0025] If it is determined that the sinusoidal wave input voltage has not inverted from positive to negative (step S2: No), this control routine returns to step S1.

[0026] If it is determined that the sinusoidal wave input voltage has reversed from positive to negative (step S2: Yes), the control device operates the PFC circuit 1 in the second mode (step S3). In step S3, the PFC circuit 1 is controlled to operate in the second mode in state B where the sinusoidal wave input voltage is negative.

[0027] The control device determines whether the sinusoidal input voltage has reversed from negative to positive (step S4). In step S4, it is determined whether the state of the sinusoidal input voltage has transitioned from state B to state C.

[0028] If it is determined that the sinusoidal wave input voltage has not reversed from negative to positive (step S4: No), this control routine returns to step S3.

[0029] If it is determined that the sinusoidal wave input voltage has reversed from negative to positive (step S4: Yes), the control device operates the PFC circuit 1 in the third mode (step S5). In step S5, the PFC circuit 1 is controlled to the third mode in state C where the sinusoidal wave input voltage is positive.

[0030] The control device determines whether the sinusoidal input voltage has inverted from positive to negative (step S6). In step S6, it is determined whether the state of the sinusoidal input voltage has transitioned from state C to state D.

[0031] If it is determined that the sinusoidal wave input voltage has not inverted from positive to negative (step S6: No), this control routine returns to step S5.

[0032] If it is determined that the sinusoidal wave input voltage has reversed from positive to negative (step S6: Yes), the control device operates the PFC circuit 1 in the fourth mode (step S7). In step S7, the PFC circuit 1 is controlled to the fourth mode in state D where the sinusoidal wave input voltage is negative.

[0033] The control device determines whether the sinusoidal input voltage has reversed from negative to positive (step S8). In step S8, it is determined whether the state of the sinusoidal input voltage has transitioned from state D to state A.

[0034] If it is determined that the sinusoidal wave input voltage has not reversed from negative to positive (step S8: No), this control routine returns to step S7.

[0035] If it is determined that the sinusoidal wave input voltage has reversed from negative to positive (step S8: Yes), this control routine returns to step S1.

[0036] In this way, the control mode of the PFC circuit 1 switches from the first mode to the second mode, from the second mode to the third mode, from the third mode to the fourth mode, and from the fourth mode to the first mode. In other words, the control mode switches in the order of the first mode, the second mode, the third mode, and the fourth mode, and then switches from the fourth mode back to the first mode, forming a loop.

[0037] A conventional totem-pole PFC circuit does not distinguish between states A and C shown in Figure 2, nor between states B and D. In a conventional configuration, the circuit transitions in the following order for one cycle of the sinusoidal input voltage: state A, state B, state A, state B. Therefore, for one cycle of the sinusoidal input voltage, the first switching element of the conventional configuration changes state in the following order: rectification, switching, rectification, switching. Similarly, the second switching element of the conventional configuration changes state in the following order: switching, rectification, switching, rectification. The third switching element of the conventional configuration changes state in the following order: pause, always-on, pause, always-on. The fourth switching element of the conventional configuration changes state in the following order: always-on, pause, always-on, pause. In a conventional totem-pole PFC circuit, the thermal load is unevenly distributed between the first and second switching elements.

[0038] In contrast, in the PFC circuit 1, the state of each of the switching elements SW1 to SW4 changes every quarter cycle of one cycle of the sinusoidal input voltage. The cycles of each mode are the same. As the first switching element SW1 transitions between the first to fourth modes, its state changes in the order of rectification operation, switching operation, always-on, and pause. As the second switching element SW2 transitions between the first to fourth modes, its state changes in the order of switching operation, rectification operation, pause, and always-on. As the third switching element SW3 transitions between the first to fourth modes, its state changes in the order of pause, always-on, switching operation, and rectification operation. As the fourth switching element SW4 transitions between the first to fourth modes, its state changes in the order of always-on, pause, rectification operation, and switching operation. In the PFC circuit 1, the thermal load of each of the switching elements SW1 to SW4 can be uniformly distributed.

[0039] As described above, according to the embodiment, the heat load of the four switching elements SW1 to SW4 is uniformly distributed, and the temperature rise effect of increased switching loss due to higher frequencies can be suppressed. This makes it possible to raise the upper limit of the drive frequency. In addition, passive components such as coils can be made smaller. [Explanation of symbols]

[0040] 1 PFC circuit 2 AC power supply 10 First Arm 20 Second Arm D1 to D4 1st to 4th diodes P1 First connection point P2 Second connection point SW1 to SW4: First to fourth switching elements

Claims

[Claim 1] a first arm in which a first switching element having a first diode connected in parallel and a second switching element having a second diode connected in parallel are connected in series at a first connection point; a second arm provided in parallel with the first arm, in which a third switching element having a third diode connected in parallel and a fourth switching element having a fourth diode connected in parallel are connected in series at a second connection point; one end of an input terminal of an AC power supply is connected to the first connection point, and the other end of the input terminal of the AC power supply is connected to the second connection point; and the PFC circuit corrects a power factor of power input from the AC power supply, a control mode is switched to one of a first mode, a second mode, a third mode, and a fourth mode according to a state of a sinusoidal AC voltage input from the AC power supply; the control mode is switched from the first mode to the second mode, from the second mode to the third mode, from the third mode to the fourth mode, and from the fourth mode to the first mode; The first switching element, the second switching element, the third switching element, and the fourth switching element change to different states in the first mode, the second mode, the third mode, and the fourth mode, respectively. A PFC circuit comprising:

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