JP2016152655A - Power conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power conversion device capable of improving conversion efficiency.SOLUTION: The power conversion device includes a bridge circuit, an inductor and a control unit. The bridge circuit connects in parallel a first and a second switch connected in series, a third and a fourth switch connected in series, and a capacitor. The inductor is connected in series to an AC power source and a load between the junction of the first and second switches and the junction of the third and the fourth switches. The control unit switches on and off either one of the first and second switches selected according to the polarity of the power voltage of the AC power source, in such a manner that the duty of a rectangular voltage generated at the junction of the first and second switches becomes constant, and also switches on the fourth or the third switch in a period while the first or the second switch is switched on.SELECTED DRAWING: Figure 1

Description

  Embodiments described herein relate generally to a power conversion apparatus.

  The power conversion device converts an AC voltage obtained from an AC power source into a DC voltage having a different voltage and supplies power to a load. In a circuit that converts an AC voltage of an AC power source into a DC voltage, the AC power flowing in the AC power source is best in the form of a sine wave having the same phase as the AC power source voltage, and harmonic noise is less generated. A circuit that converts the input current to a sine wave is called a PFC (Phase Factor Collection: power factor corrector).

  FIG. 11 shows a configuration example of a totem pole PFC as an example of a conventional PFC. The circuit in FIG. 11 controls circuit current (power supply current) and charge accumulation in the capacitor C1 by controlling on / off of the switches S1 and S2. The circuit current can be controlled by PWM (Pulse Width Modulation) that changes the pulse width of the switching signal for turning on and off the switches S1 and S2 in accordance with the phase of the power supply voltage. FIG. 12 shows an example of conventional PWM control. In the PWM control shown in FIG. 12, the pulse widths of the switching signals of the switches S1 and S2 change greatly. For example, when the voltage Vs1 of the AC power supply is low, the time for turning on the switches S1 and S2 becomes long, and when the voltage Vs1 of the AC power supply is high, the time for turning on the switches S1 and S2 becomes short. When the pulse width of the switching signal fluctuates greatly, it becomes difficult to apply the circuit operation to another application or improve the conversion efficiency.

JP 2014-39418 A

  The problem to be solved by the present invention is to provide a power conversion device capable of improving the conversion efficiency.

  According to the embodiment, the power conversion device includes a bridge circuit, an inductor, and a control unit. The bridge circuit connects first and second switches connected in series, third and fourth switches connected in series, and a capacitor in parallel. The inductor is connected in series to the AC power source and the load between the connection point of the first and second switches and the connection point of the third and fourth switches. The control unit is configured so that the duty of the rectangular voltage generated at the connection point of the first and second switches, which is selected according to the polarity of the power supply voltage of the AC power supply, is constant. The fourth or third switch is turned on within a period during which the first or second switch is turned on.

FIG. 1 is a diagram illustrating a configuration example of the power conversion device according to the first embodiment. FIG. 2 is a block diagram illustrating a configuration example of a control unit in the power conversion apparatus according to the first embodiment. FIG. 3A is a diagram illustrating an example of a triangular wave, a first PWM threshold value, and a second PWM threshold value. FIG. 3B shows an example of a gate drive signal generated by the first PWM. FIG. 3C shows an example of a gate drive signal generated by the second PWM. FIG. 3D shows an example of circuit current. FIG. 3E shows an example of a voltage generated at the U point. FIG. 4A shows the waveform of the power supply voltage for half a cycle. FIG. 4B shows an example of a triangular wave, a first PWM threshold value, and a second PWM threshold value. FIG. 4C shows the waveform of the gate drive signal generated by the first PWM. FIG. 4D shows the waveform of the gate drive signal generated by the second PWM. FIG. 4E shows the waveform of the circuit current. FIG. 4F shows the waveform of the voltage generated at the point U. Fig.5 (a) shows the waveform for two periods in the alternating voltage from an alternating current power supply. FIG. 5B shows a gate drive signal of the first switch. FIG. 5C shows the gate drive signal of the second switch. FIG. 5D shows the gate drive signal of the fourth switch as a sub switch for the first switch. FIG. 5E shows the gate drive signal of the third switch as a sub switch for the second switch. FIG. 6 is a diagram illustrating a first configuration example of the power conversion device according to the second embodiment. FIG. 7 is a diagram illustrating a second configuration example of the power conversion device according to the second embodiment. FIG. 8 is a diagram illustrating a third configuration example of the power conversion device according to the second embodiment. FIG. 9 is a block diagram illustrating a configuration example of a control unit in the power conversion apparatus according to the second embodiment. FIG. 10 is a diagram illustrating a modification of the power conversion device illustrated in FIG. 1. FIG. 11 is a diagram illustrating an example of a conventional PFC. FIG. 12 is a diagram illustrating an example of PWM control for the PFC of FIG.

Hereinafter, embodiments will be described with reference to the drawings.
(First embodiment)
FIG. 1 is a diagram illustrating a configuration example of a power conversion device 1 according to the first embodiment.
The power conversion device 1 is a power supply device that converts an AC voltage from an AC power source into a DC voltage. For example, the power conversion device 1 can be realized as an AC adapter having a connector connected to an AC power source and a connector connected to a load. In the configuration example shown in FIG. 1, the power conversion device 1 is connected to an AC power source 2 as an input power source. The power converter 1 is connected to a load 3 that outputs a DC voltage converted from an AC voltage of the AC power supply 2. The power conversion device 1 includes switches S1, S2, S3, S4, a capacitor C1, a first inductor L1, an AC voltage detection unit 11, a circuit current detection unit 12, a boost detection unit 13, and a control unit 15.

  Four S1, S2, S3, and S4 are bridge-connected. The first switch S1 and the second switch S2 are connected in series. The third switch S3 and the fourth switch S4 are connected in series. The first and second switches S1 and S2 connected in series and the third and fourth switches S3 and S4 connected in series are connected in parallel to form a closed loop. Furthermore, the first and second switches S1 and S2 connected in series, the third and fourth switches S3 and S4 connected in series, and the capacitor C1 are connected in parallel.

  The switches S1, S2, S3 and S4 can be realized by semiconductor switches. For example, the switches S1, S2, S3, and S4 are realized by a switch module including MOSFET, GaN, SiC, and other composite transistors. In the present embodiment, description will be made assuming that the switches S1, S2, S3, and S4 are configured by N-type MOSFETs. The N-type MOSFETs as the switches S1, S2, S3, and S4 operate as switches from the drain to the source. That is, the switches S1, S2, S3, and S4 are turned on when the signal (gate drive signal) applied to the gate is at a high (H) level, and are turned off when the signal is at a low (L) level. Further, the switches S1, S2, S3, and S4 are always in a conductive state from the source to the drain by the parasitic diode regardless of the gate drive signal.

  The switch S1 connects the source to the drain of the switch S2. The switch S1 connects the drain to the drain of the switch S3. The switch S3 connects the source to the drain of the switch S4. Switch S2 connects the source to the source of switch S4. With these connections, the switches S1, S2, S3, and S4 form a closed loop and a bridge circuit.

  Here, in the configuration shown in FIG. 1, a connection point between the source of the switch S1 and the drain of the switch S2 is a U point, and a connection point between the source of the switch S3 and the drain of the switch S4 is a V point. The AC power supply 2, the inductor L1, and the circuit current detection unit 12 are connected in series between the U point and the V point of the bridge circuit. In addition, the connection of these each part is not limited to a specific order.

  The AC voltage detection unit 11 detects an AC power supply voltage Vs1 input from the AC power supply 2 to the power conversion device 1. The AC voltage detector 11 outputs a detection signal Vs1 indicating an instantaneous value of the power supply voltage from the AC power supply 2 to the controller 15. For example, the AC voltage detection unit 11 is connected in parallel to both ends of the AC power supply 2.

  The circuit current detection unit 12 detects a circuit current Is1 as a power supply (input) current that flows to the AC power supply 2 (or may be referred to as an inductor current that flows through the first inductor L1). The circuit current detection unit 12 outputs a detection value Is1 indicating an instantaneous value of the circuit current to the control unit 15. The circuit current detection unit 12 functions as a current detection unit. The circuit current detection unit 12 is connected in series between the UVs, and detects a current flowing between the UVs. For example, the circuit current detection unit 12 may be connected between the AC power supply 2 and the point V, may be connected between the AC power supply 2 and the first inductor L1, or may be connected to the first inductor L1. You may connect between U points.

  The capacitor C1 is connected between the drain of the switch S1 and the source of the switch S2 (between the drain of the switch S3 and the source of the switch S4). The capacitor C1 is connected in parallel to a U-side half bridge composed of switches S1 and S2 connected in series and a V-side half bridge composed of switches S3 and S4 connected in series. The capacitor C1 and the four switches S1, S2, S3, S4 constitute an H bridge.

The boost detection unit 13 detects a voltage (bridge capacitor voltage) Vs2 applied to the capacitor C1. The boost detection unit 13 outputs a detection signal Vs2 indicating an instantaneous value of the capacitor voltage to the control unit 15. The boost detection unit 13 is connected in parallel to both ends of the capacitor C1.
The load 3 is connected to both ends of the capacitor C1. The load 3 may be a resistance load or a combination of a circuit that performs voltage conversion and a load.

  The control unit 15 receives the detection signal Vs1 from the AC voltage detection unit 11, the detection value Is1 from the circuit current detection unit 12, and the detection signal Vs2 from the boost detection unit 103. The control unit 15 outputs gate drive signals P1, P2, P3, and P4 for the switches S1, S2, S3, and S4. Gate drive signals P1, P2, P3, and P4 are signals that turn on and off the switches S1, S2, S3, and S4, respectively. Here, it is assumed that the gate drive signals P1, P2, P3, and P4 are pulse signals that turn on the switches S1, S2, S3, and S4 at the H level and turn them off at the L level.

  The control unit 15 controls the switches S1 and S2 as main switches and the switches S3 and S4 as sub switches of the switches S1 and S2. In the control of the conventional totem pole PFC, the pulse width of the gate drive signal changes drastically according to the voltage phase of the AC power supply Vac. When the pulse width changes drastically, the voltage at the point U (equal to the voltage across the switch S2) is a rectangular pulse, but its duty changes drastically. In order to alleviate such duty fluctuation, the control unit 15 of the power conversion device 1 according to the present embodiment controls the switches S3 and S4 as sub switches. For example, the control unit 15 turns on the switch S4 with the gate drive signal P4 having a pulse width narrower than that of the gate drive signal P1 in synchronization with the pulse of the gate drive signal P1 of the switch S1. Further, the control unit 15 turns on the switch S3 with the gate drive signal P3 having a pulse width narrower than that of the gate drive signal P2 in synchronization with the pulse of the gate drive signal P2 of the switch S2.

Next, the structure of the control part 15 in the power converter device 1 is demonstrated.
FIG. 2 is a block diagram illustrating an example of a configuration (function) included in the control unit 15 in the power conversion device 1 according to the first embodiment.
The control unit 15 includes a first absolute value conversion unit 21, a first amplification factor adjustment unit 22, a first bias point correction unit 23, a multiplication unit 24, a second amplification factor adjustment unit 25, and a second bias point. Correction unit 26, polarity determination unit 27, average value calculation unit 28, first difference output unit 29, reference voltage setting unit 30, second absolute value conversion unit 31, third amplification factor adjustment unit 32, second A differential output unit 33, a triangular wave generation unit 34, a first PWM generation unit 35, a second PWM generation unit 36, and a selector unit 37 are provided. Each of these units may be realized by hardware or software. For example, some or all of the above-described units may be realized by a DSP.

  The first absolute value converting unit 21 outputs a signal obtained by converting an input signal into an absolute value. The first absolute value conversion unit 21 receives the detection signal (detected value of the power supply voltage) Vs1 from the AC voltage detection unit 11, and converts the input power supply voltage value to an absolute value. For example, if the detection signal Vs1 is −1.41, the first absolute value converting unit 21 outputs +1.41. The first absolute value converting unit 21 supplies the absolute value of the power supply voltage value to the first gain adjusting unit 22 and the second gain adjusting unit 25.

  The first amplification factor adjustment unit 22 adjusts the value of the power supply voltage that has been converted to the absolute value by the first absolute value conversion unit 21 with the first amplification factor. For example, the first amplification factor adjustment unit 22 converts an input value (power supply voltage value) of 1.41 into a value of 0.9. The first amplification factor adjustment unit 22 supplies the value adjusted with the first amplification factor to the first bias point correction unit 23.

  The first bias point correction unit 23 adds the first bias value to the input value from the first amplification factor adjustment unit 22. For example, the first bias point correction unit 23 adds a bias value of 0.05 to an input value of 0.9 to obtain 0.95. The first bias point correction unit 23 supplies the multiplication unit 24 with the value to which the first bias value has been added.

  The second amplification factor adjustment unit 25 adjusts the value of the power supply voltage that has been converted to the absolute value by the first absolute value conversion unit 21 with the second amplification factor. For example, when the absolute value of the power supply voltage is 1.41 and the second amplification factor is 0.5, the second amplification factor adjustment unit 25 sets the adjustment value to 1.41 × 0.5 = 0.7. The second amplification factor adjustment unit 25 supplies the adjustment value adjusted by the second amplification factor to the second bias point correction unit 26.

  The second bias point correction unit 26 adds the second bias value to the adjustment value input from the second amplification factor adjustment unit 25. For example, the second bias point correction unit 26 adds a bias value of 0.2 to an input value of 0.7 to obtain 0.9. The second bias point correction unit 26 supplies a value to which the second bias value is added to the second PWM generation unit 36. Note that a reference voltage may be set for the second bias value. This can be realized by providing a difference output unit that outputs a difference between the second bias value and the reference voltage to the PWM generation unit 36.

  Further, the detection signal (detected value of the power supply voltage) Vs <b> 1 of the AC voltage detection unit 11 is also input to the polarity determination unit 27. The polarity determination unit 27 determines whether the value of the power supply voltage from the AC power supply 2 is positive or negative. The polarity determination unit 27 supplies a signal indicating the polarity determination result to the selector unit 37. For example, the polarity determination unit 27 outputs “1” to the selector unit 37 if the value of the power supply voltage is positive, and outputs “0” to the selector unit 37 if it is negative. That is, if the frequency of the AC voltage of the AC power supply 2 is 50 Hz, the polarity determination unit 27 alternately outputs “1” and “0” in synchronization with 50 Hz.

  The average value calculation unit 28 inputs the detection signal (detection value of the capacitor voltage) Vs2 of the boost detection unit 13. The boost detection unit 13 detects the voltage value at both ends of the capacitor C1 as the detection signal Vs2. If the frequency of the AC power supply 2 is 50 Hz, the voltage of the capacitor C1 includes a ripple voltage having a double 100 Hz component. The average value calculation unit 28 calculates the average value of the voltage for one cycle of the power supply frequency. The average value calculation unit 28 supplies the calculated average value to the first difference output unit 29.

  The first difference output unit 29 outputs a difference value between the average value calculated by the average value calculation unit 28 and the value of the reference voltage set by the reference voltage setting unit 30. For example, assuming that the voltage across the capacitor C1 fluctuates at 410V ± 50V, the detection signal Vs2 of the boost detection unit 13 is assumed to be 4.1 ± 0.5. In this case, the average value calculation unit 28 outputs a value of 4.1 as the average value of the detection signal Vs2. If the output value of the average value calculation unit 28 is 4.1 and the value set by the reference voltage setting unit 30 is 4.0, the first difference output unit 29 outputs 0.1 as the difference value. The first difference output unit 29 supplies the difference value to the multiplication unit 24.

  The multiplication unit 24 outputs a value obtained by multiplying the output value from the first bias point correction unit 23 and the difference value from the first difference output unit 29. For example, if one input is 0.95 and the other input is 0.1, the multiplication unit 24 outputs 0.95 × 0.1 = 0.095 as the multiplication result. The multiplication unit 24 supplies the multiplication result to the second difference output unit 33.

  The detection signal (detection value of the circuit current) Is1 of the circuit current detection unit 12 is input to the second absolute value conversion unit 31. The second absolute value converting unit 31 outputs a signal obtained by converting the value of the input signal into an absolute value. The second absolute value converting unit 31 receives the circuit current value Is1 and converts the input circuit current value into an absolute value. For example, if the circuit current value Is1 is −1.2, the second absolute value converting unit 31 outputs 1.2 as an absolute value. The second absolute value conversion unit 31 supplies the absolute value of the circuit current value to the third amplification factor adjustment unit 32.

  The third amplification factor adjustment unit 32 adjusts the value of the power supply current absolute valued by the second absolute value conversion unit with the third amplification factor. For example, when the absolute value of the power supply current is 1.2 and the third amplification factor is 0.5, the third amplification factor adjustment unit 32 outputs 0.6 as the adjustment value. The third amplification factor adjustment unit 32 supplies the adjustment value adjusted by the third amplification factor to the second difference output unit 33.

  The second difference output unit 33 outputs the difference between the input value from the multiplication unit 24 and the adjustment value from the third amplification factor adjustment unit 32. For example, when values of 0.095 and 0.6 are input, the second difference output unit 33 outputs 0.095−0.6 = −0.505. The difference output unit 33 supplies the difference value to the first PWM generation unit 35.

  The triangular wave generating unit 34 generates a triangular wave that becomes a carrier signal for the first and second PWM control. The triangular wave generation unit 34 generates a triangular wave having a predetermined frequency in the range of the maximum value 1 and the minimum value−1. The frequency of the triangular wave generated by the triangular wave generator 34 is, for example, 20 kHz. The triangular wave generation unit 34 outputs the generated triangular wave to the first PWM generation unit 35 and the second PWM generation unit 36.

  The first PWM generator 35 generates a first PWM signal from the output value from the second difference output unit 33 and the triangular wave from the triangular wave generator 34. That is, the first PWM generation unit 35 sets the output value from the second difference output unit 33 as the first PWM threshold value. The first PWM generation unit 35 sets the first PWM signal to the H level (1) when the magnitude of the triangular wave is larger than the output value from the second difference output unit 33. The first PWM generation unit 35 sets the first PWM signal to L level (1) when the magnitude of the triangular wave is equal to or smaller than the output value from the second difference output unit 33. For example, if the output value of the second difference output unit 33 is −0.505, the first PWM generation unit 35 outputs 1 when the triangular wave is −0.505 or more, and is −0.505 or less. In this case, 0 is output. The first PWM generation unit 35 supplies the generated first PWM signal to the selector unit 37.

  The second PWM generator 36 generates a second PWM signal from the output value from the second bias point corrector 26 and the triangular wave from the triangular wave generator 34. That is, the second PWM generation unit 36 sets the output value from the second bias point correction unit 26 as the second PWM threshold value. When the triangular wave is larger than the output value from the second bias point correction unit 26, the second PWM generation unit 36 sets the second PWM signal to the H level (1). The second PWM generation unit 36 sets the second PWM signal to L level (0) when the triangular wave is equal to or less than the output value from the second bias point correction unit 26. For example, when the output value of the second bias point correction unit 26 is 0.9, the second PWM generation unit 36 outputs 1 when the triangular wave is 0.9 or more, and when the output value is 0.9 or less. 0 is output. The second PWM generation unit 36 supplies the generated second PWM signal to the selector unit 37.

The selector unit 37 selects the output destination of the first PWM signal and the second PWM signal according to the output value of the polarity determination unit 27. For example, when the output value of the polarity determination unit 27 is 1, the selector unit 37 outputs the output of the first PWM generation unit 35 as P2, and outputs the output of the second PWM generation unit 36 as P3. Further, when the output value of the polarity determination unit 27 is 0, the selector unit 37 outputs the output of the first PWM generation unit 35 as P1, and outputs the output of the second PWM generation unit 36 as P4.
With the above operation, the rectangular voltage generated at the connection point (point U) of the switches S1 and S2 as the main switch is maintained at a substantially constant duty regardless of the phase of the AC power supply 2.

Next, the gate drive signal for each switch generated by the control unit 15 will be described.
FIGS. 3A to 3E are diagrams illustrating waveforms of signals by the first and second PWM controls in the power conversion device 1 according to the first embodiment.
FIG. 3A is a diagram illustrating an example of the triangular wave Sc for generating the PWM, the first PWM threshold Th1, and the second PWM threshold Th2, where the horizontal axis is time. FIG. 3B is a diagram illustrating an example of the gate drive signal P2 based on the first PWM threshold. FIG. 3C is a diagram illustrating an example of the gate drive signal P3 based on the second PWM threshold. FIG. 3D is a diagram showing an example of a circuit current (power supply current) detection signal IS1 and its average current. FIG. 3E shows an example of a voltage generated at the U point.

  3A to 3E are cases where the power supply voltage of the AC power supply 2 is a low voltage in the vicinity of the zero cross. The selector unit 37 of the control unit 15 outputs the signals P2 and P3 and pauses the signals P1 and P4 if the detection signal Vs1 of the power supply voltage is positive (if the output of the polarity determination unit 27 is 1). State. Therefore, FIGS. 3A to 3E show the waveforms of the respective signals when the power supply voltage detection signal Vs1 is positive.

  In general, when the power supply voltage is low, even if only the switch S2 is turned on, the slope indicating the increasing rate of the current Is1 is small. For example, when the power supply voltage of the AC power supply 2 is 10V, the voltage applied to the inductor L1 is 10V. That is, the power supply current Is1 increases only with a slope having a magnitude corresponding to the power supply voltage Vs1. The smaller the slope of the current Is1, the wider the pulse width of the gate drive signal P2 and the longer the on state of the main switch S2 is, in order to set the current value to a predetermined value. That is, when the current is controlled only by the main switches S2 and S1, the duty ratio between the on and off of the gate drive signals P2 and P1 becomes extremely biased.

  As shown in FIG. 3B, the control unit 15 according to the present embodiment performs control so that the duty ratio between on and off of the main switch S2 is approximately 50%. That is, the control unit 15 performs control so that the pulse width of the gate drive signal P2 for the main switch S2 is approximately 50%. Further, as shown in FIG. 3C, the control unit 15 controls the switch S3, which is a sub-switch of the switch S2, in synchronization with the switch S2. That is, the control unit 15 sets the gate drive signal P3 of the switch S3 to a pulse synchronized with the gate drive signal P2.

  For example, at time Ta, the triangular wave Sc exceeds the first PWM threshold Th1. Therefore, the control unit 15 sets the gate drive signal P2 to the H level and turns on the switch S2 (main switch). When the switch S2 is turned on, the power supply current Is1 starts to increase.

  At time Tb, the triangular wave Sc exceeds the second PWM threshold Th2 that is larger than the first PWM threshold. Therefore, the control unit 15 sets the gate drive signal P3 of the switch S3 to the H level and turns on the switch S3. When the switch S3 is turned on, a voltage (for example, 400 V) of the capacitor C1 is additionally applied to the inductor L1. That is, when the switches S2 and S3 are turned on, a voltage (410V) obtained by adding the power supply voltage (10V) and the capacitor voltage (400V) is applied to the inductor L1. As a result, the current Is1 increases with a slope corresponding to the potential difference obtained by adding the power supply voltage and the capacitor voltage. As the slope of the current Is1 increases, the time until the current Is1 reaches a predetermined current value is significantly shortened.

  At time Tc, the triangular wave Sc falls below the second PWM threshold Th2. For this reason, the control unit 15 sets the gate drive signal P3 to the L level and turns off the third switch S3. If the switch S2 is turned off while the switch S2 remains on, the voltage applied to the inductor L1 is again only 10V. When the voltage applied to the inductor L1 is only the power supply voltage, the current Is1 has a gentle slope indicating the increase rate.

At time Td, the triangular wave Sc falls below the first PWM threshold Th1. Therefore, the control unit 15 sets the gate drive signal P2 to the L level and turns off the switch S2. When both the switches S2 and S3 are turned off, the current flowing through the inductor L1 flows to the capacitor C1 via the body diode of the switch S1 instead of via the switch S2. As a result, the voltage of the capacitor C1 increases. In exchange for the charge accumulation in the capacitor C1, the current flowing through the inductor L1 decreases.
By the operation as described above, the control unit of the power conversion device can set the rectangular voltage generated at the point U to a substantially constant duty regardless of the phase of the AC power supply.

Next, each signal in the half cycle of the power supply voltage of the AC power supply 2 will be described.
4A to 4F show each signal in a half cycle of the power supply voltage from the AC power supply with the horizontal axis as time. FIG. 4A is a diagram illustrating a waveform of the power supply voltage for a half cycle. FIG. 4B shows an example of a triangular wave Sc for generating PWM corresponding to FIG. 4A, a first PWM threshold Th1, and a second PWM threshold Th2. FIG. 4C shows the waveform of the gate drive signal P2 corresponding to FIG. FIG. 4D shows the waveform of the gate drive signal P3 corresponding to FIG. FIG. 4 (e) shows the waveform of the circuit current detection signal Is1 corresponding to the gate drive signals P2 and P3 of FIGS. 4 (c) and 4 (d). FIG. 4F shows the waveform of the voltage generated at the point U.

  In the next half cycle of the power supply voltage of the AC power supply 2, the polarity of the voltage Vs1 is inverted. For this reason, the gate drive signals P2 and P3 are paused (L level), and the gate drive signals P1 and P4 have waveforms shown in FIGS. 4B and 4C.

  As shown in FIG. 4B, the second PWM threshold Th2 changes according to the phase of the power supply voltage. As shown in FIG. 4D, the gate drive signal P3 of the switch S3 as the sub switch is generated by the second PWM control based on the second PWM threshold Th2. For example, when the value of the power supply voltage is low, the second PWM threshold Th2 is also small, so that the gate drive signal P3 has a wide pulse width. When the value of the power supply voltage is high, the second PWM threshold Th2 is also increased, so that the gate drive signal P3 has a narrow pulse width.

  On the other hand, the gate drive signal P2 of the switch S2 as the main switch is generated by the first PWM control based on the first PWM threshold Th1, as shown in FIG. 4C. As shown in FIG. 4B, the first PWM threshold Th1 is substantially flat regardless of the value of the power supply voltage of the AC power supply 2. For this reason, the gate drive signal P2 generated by the first PWM control based on the first PWM threshold is maintained at a substantially constant duty within the period of the AC power supply. Therefore, as shown in FIG. 4F, the voltage generated at the point U on the switch S2 side has a rectangular waveform with a substantially constant duty that repeats a predetermined value alternately.

Next, the waveform of each gate drive signal in two cycles of the power supply voltage will be described.
FIG. 5A shows a waveform for two cycles in the AC voltage from the AC power supply 2. FIG. 5B shows the gate drive signal P1 of the switch (main switch) S1. FIG. 5C shows the gate drive signal P2 of the switch (main switch) S2. FIG. 5D shows a gate drive signal P4 of the switch S4 as a sub switch for the switch S1. FIG. 5E shows a gate drive signal P3 of the switch S3 as a sub switch for the switch S2.

  The control unit 15 selects one of the switches S1 and S2 as the main switch according to the phase of the power supply voltage of the AC power supply 2. The control unit 15 outputs a pulse signal as the gate drive signal P1 or P2 to the selected main switch. The gate drive signals P1 and P2 given to the switches S1 and S2 are generated by the first PWM control and become signals with a substantially constant pulse width.

  The switch S4 functions as a sub switch of the switch S1. The gate drive signal P4 given to the switch S4 is generated by the second PWM control. The gate drive signal P4 is a pulse signal whose pulse width is changed within a period during which the switch S1 is turned on (a period synchronized with the gate drive signal P1). For this reason, while the main switch S1 is inactive, the sub switch S4 is also inactive.

  The switch S3 functions as a sub switch of the switch S2. The gate drive signal P3 given to the switch S3 is generated by the second PWM control. The gate drive signal P3 is a pulse signal whose pulse width is changed within a period during which the switch S2 is on (a period synchronized with the gate drive signal P2). For this reason, while the main switch S2 is inactive, the sub switch S3 is also inactive.

  As described above, the power conversion device according to the first embodiment includes the bridge circuit in which four switches are bridge-connected and the control unit. The control unit controls the two main switches on the point side that generate a voltage to be supplied to the load in the bridge circuit with a pulse signal whose duty is substantially constant. Further, the control unit controls two switches other than the main switch by PWM according to the phase of the power supply voltage. Thereby, the power converter according to the first embodiment can be controlled so that the power source (circuit) current is in phase with the power source voltage and the duty of the rectangular voltage supplied to the load is substantially constant. As a result, the power conversion device according to the first embodiment can achieve power conversion with good power factor and low current harmonics, and can reduce the number and size of the input filter.

(Second Embodiment)
Next, a second embodiment will be described.
The power conversion device according to the second embodiment has a load circuit such as an inverter circuit. 2nd Embodiment demonstrates the structural example of the power converter device which connected load circuits, such as an inverter circuit, to the power converter device demonstrated in 1st Embodiment.

FIG. 6 is a diagram illustrating a first configuration example of the power conversion device 101 according to the second embodiment.
A power conversion device 101 shown in FIG. 6 is obtained by connecting an inverter circuit 121 and an output voltage detection unit 122 to the bridge circuit of the power conversion device 1 shown in FIG. The power conversion device 101 connects an inverter circuit 121 between the drain and source of the main switch S2. The control unit 115 of the power conversion device 101 controls the duty of the rectangular voltage generated at the point U to be substantially constant by the same control as that of the power conversion device 1 described in the first embodiment.

  For example, in the conventional power supply circuit shown in FIG. 11, the rectangular voltage generated at the point U has a large variation in duty. In general, since the inverter circuit is frequency controlled, it is desirable that the duty of the output voltage to be input is fixed at 50% in principle. If the inverter is operated with a rectangular voltage whose duty fluctuates significantly as an input, the output of the inverter fluctuates according to the phase of the power supply voltage. In other words, the inverter cannot be connected unless the duty of the rectangular voltage is constant.

  Since the power converter 101 has a rectangular voltage with a substantially constant duty at the point U, the inverter circuit 121 can be connected without the inverter driving components (semiconductor switch, drive circuit). With such a configuration, the power conversion device 101 can simplify and reduce the size of the circuit. Further, the power conversion device 101 can be expected to improve conversion efficiency and reduce costs by having a simple circuit configuration.

FIG. 7 is a diagram illustrating a second configuration example of the power conversion device 201 according to the second embodiment.
A power conversion device 201 illustrated in FIG. 7 is a circuit example in which the inverter circuit 121 illustrated in FIG. 6 is replaced with specific components.
The power conversion device 201 has a configuration in which a second capacitor C2, a second inductor L2, and an output voltage detection unit 221 are added to the power conversion device 1 shown in FIG. The power conversion device 201 includes a control unit 215 instead of the control unit 115. In the power converter 201, the configuration other than the second capacitor C2, the second inductor L2, the output voltage detector 221 and the controller 215 is the same as that of the power converter 1 described in the first embodiment. Therefore, detailed description is omitted.

  The power conversion device 201 connects the second capacitor C2, the second inductor L2, and the load 3 in series between the drain and the source of the main switch S2. The second capacitor C2 and the second inductor L2 constitute an inverter circuit.

  Further, the output voltage detection unit 221 detects the value Vs3 of the output (load) voltage due to the output (high frequency alternating current) of the inverter. The output voltage detection unit 221 outputs the detection signal Vs3 to the control unit 215. The output voltage detector 221 may be anything that can detect the output status to the load. For example, the output power detection unit 221 may be replaced with one that detects current, or may be replaced with one that detects power.

  The inverter circuit is driven by a rectangular voltage (for example, 0V and 400V) generated at the point U. The second inductor L2 limits the current by a current limiting action. The current supplied to the load 3 is controlled by an inverter circuit. Further, the current limiting action of the second inductor L2 depends on the frequency. Therefore, if the frequency is controlled, the output of the inverter circuit can be controlled. On the other hand, the PWM that determines the input (circuit) current Is1 has no dependency on the frequency. For this reason, even if the frequency is varied in order to control the current supplied to the load 3, there is no influence on the waveform control (power factor control) of the input current Is1.

FIG. 8 shows a third configuration example of the power conversion device 301 according to the second embodiment.
The power conversion device 301 shown in FIG. 8 includes a circuit that generates an isolated DC voltage by applying an inverter circuit. The power conversion device 301 can be applied to, for example, a switching power supply.

  In addition to the configuration of the power conversion device 1 shown in FIG. 1, the power conversion device 301 includes a second capacitor C2, a second inductor L2, a transformer T1, diodes D1 and D2, a third capacitor C3, and an output voltage detection. Part 321. The power conversion device 301 includes a control unit 315 instead of the control unit 15. In the power conversion device 301, the configuration other than the second capacitor C2, the second inductor L2, the transformer T1, the diodes D1 and D2, the third capacitor C3, the output voltage detection unit 321 and the control unit 215 is the first configuration. Since it is the same as that of the power converter device 1 demonstrated in embodiment, detailed description shall be abbreviate | omitted.

  The second capacitor C2, the second inductor L2, and the primary winding Tp of the transformer T1 are connected in series between the drain and the source of the main switch S2. The secondary winding Ts of the transformer T1 is composed of windings Ts1 and Ts2 having a center tap. The diodes D1 and D2 are connected in directions to alternately rectify currents flowing through the windings Ts1 and Ts2, respectively. The third capacitor C3 stores the current rectified by the diodes D1 and D2. The capacitor C3 has both ends connected to the load 3.

  The output voltage detector 321 detects the output voltage (load voltage) Vs3 as the voltage across the third capacitor C3. The output voltage detection unit 321 may be anything that can detect the output status to the load 3. For example, the output power detection unit 321 may be replaced with one that detects current, or may be replaced with one that detects power.

  The power converter 301 can arbitrarily change the output voltage by adjusting the turns ratio of the transformer T. For example, when the voltage across the first capacitor C1 is 400V, for example, a 24V output can be taken out if the ratio of the secondary winding Ts to the primary winding Tp of the transformer T is sufficiently small. The output voltage includes a ripple component. For this reason, when precise regulation is required, the detection signal Vs3 of the output voltage detection unit 321 is fed back to the control unit 315. By feeding back the detection signal Vs3 as the output voltage value, the control unit 315 can control to stabilize the output voltage.

FIG. 9 is a block diagram illustrating a configuration example of the control unit 315 of the power conversion device 301.
9 has a configuration in which a control function based on the detection signal Vs3 is added to the configuration (function) shown in FIG. For this reason, as for the control unit 315 shown in FIG. 9, those that can be realized by the same operation as the configuration shown in FIG.

  As illustrated in FIG. 9, the control unit 315 has a configuration in which a third difference output unit 341, a reference voltage setting unit 342, and a frequency generation unit 343 are added to the configuration of the control unit 15 illustrated in FIG. 2. In addition, the triangular wave generation unit 34 of the control unit 315 can set the frequency of the triangular wave to be generated to the frequency generated by the frequency generation unit 343. The detection signal Vs3 of the output voltage detection unit 321 is input to the third difference output unit 341.

  The reference voltage setting unit 342 sets a reference voltage value for the output voltage. The reference voltage setting unit 342 supplies the reference voltage value to the third difference output unit 341. However, when the output power detection unit 321 is replaced with a current detection unit, the reference voltage setting unit 342 also sets the value of the reference current. Further, when the output power detection unit 321 is replaced with a power detection unit, the reference voltage setting unit 342 is also replaced with one that sets the value of the reference power.

  The third difference output unit 341 outputs a difference value between the output voltage detection signal Vs3 from the output voltage detection unit 321 and the reference voltage value from the reference voltage setting unit 342. For example, when the reference voltage value is 24 and the detection signal Vs3 is 24.2, the third difference output unit 341 outputs 0.2 as the difference value. However, the third difference output unit 341 calculates a difference value by subtracting the value of the reference voltage from the detection signal Vs3. In this case, if the third difference output unit 341 is a positive value, it means that the detected value of the output voltage is higher than the value of the reference voltage. The third difference output unit 341 inputs the calculated difference value to the frequency generation unit 343.

  The frequency generation unit 343 determines a frequency according to the difference value. The frequency generation unit 343 supplies the determined frequency to the triangular wave generation unit 34. For example, when the difference value output from the third difference output unit 341 is positive, the frequency generation unit 343 increases the frequency of the triangular wave generated by the triangular wave generation unit 34. Further, when the difference value output from the third difference output unit 341 is negative, the frequency generation unit 343 reduces the frequency of the triangular wave generated by the triangular wave generation unit 34.

  For example, when the output voltage is larger than the reference voltage, the control unit 315 increases the frequency of the triangular wave as the carrier signal used for the first and second PWM control. When the frequency of the carrier signal is increased, the current limiting action of the second inductor L2 becomes stronger. When the current limiting action of the second inductor L2 becomes stronger, the amount of current supplied to the load 3 decreases. When the amount of current supplied to the load 3 decreases, the output voltage decreases and approaches the value of the reference voltage.

When the output voltage is smaller than the reference voltage, the control unit 315 decreases the frequency of the triangular wave used for the first and second PWM controls. When the frequency of the carrier signal is lowered, the current limiting action of the second inductor L2 becomes weaker. When the current limiting action of the second inductor L2 becomes weak, the amount of current supplied to the load 3 increases. When the amount of current supplied to the load 3 increases, the output voltage rises and approaches the reference voltage.
As described above, according to the control unit shown in FIG. 9, the output voltage can be controlled without affecting the control described in the first embodiment.

  As described above, the power conversion device according to the second embodiment provides a PFC circuit that can connect an inverter circuit by omitting circuit components for inverter operation. That is, the power conversion device according to the second embodiment can realize inverter control with a simple circuit configuration and a PFC function with a high power factor and a low input current harmonic.

Further, the power conversion device according to the second embodiment can separate the PFC function and the inverter output control function. That is, the power conversion device according to the second embodiment can perform PFC control and inverter output control as controls that do not interfere with each other. In addition, since the power conversion device according to the second embodiment does not require circuit components (drive circuit or semiconductor switch) for inverter operation, the power conversion efficiency is also improved.
From the above, the power conversion device according to the second embodiment can achieve small size, low cost, and high efficiency while satisfying specifications required for power conversion such as a switching power supply.

  In the second embodiment, the power conversion apparatus to which the inverter circuit having the basic configuration as shown in FIGS. 7 and 8 is connected has been described. However, the power conversion device according to the second embodiment is not limited to the configuration shown in FIGS. 7 and 8, and other inverter circuits may be mounted. Furthermore, in the power conversion device described in the second embodiment, the load circuit may not be an inverter. The power conversion device described in the second embodiment may be anything as long as the load circuit is a circuit that drives the load using a rectangular voltage generated at the point U.

  As described above, the power conversion device according to each embodiment can achieve both the PFC function and the output voltage control function by controlling a circuit having a small number of components with four switches. In addition, since the power conversion device according to each embodiment can realize power conversion with a single-stage circuit instead of a multi-stage circuit, it is possible to prevent a reduction in efficiency that occurs when a multi-stage circuit passes.

  In addition, the power conversion device according to each embodiment can use not only the inverter output but also the boosted voltage of the PFC as an output. As described above, the power conversion device according to each embodiment can be widely used because it is widely used and can be realized at a small size and at a low cost.

In addition, the control part of the power converter device which concerns on each embodiment is not limited to the structure of FIG. 2 or FIG. As long as the control unit is configured to adjust the on / off of the sub switches (switches S4, S3) according to the control target value by PWM or the like while suppressing the duty fluctuation of the pulses for turning on / off the main switches (switches S1, S2). good.
In each embodiment, a PWM generation method using a triangular wave has been described. However, the PWM generation method is not limited to the one using a triangular wave. The PWM generation method may be generated using, for example, a sawtooth wave. In addition, the second PWM signal may be generated using a delay time based on the first PWM signal.

  Further, the first inductor L1 in the power conversion device shown in FIG. 1, FIG. 6, FIG. 7 or FIG. 8 may be composed of a plurality of elements. That is, in the power converter shown in FIG. 1, FIG. 6, FIG. 7, or FIG. 8, a plurality of inductors may be connected in series between the UVs.

  For example, FIG. 10 shows a power conversion device 1 ′ as a modification of the power conversion device 1 shown in FIG. A power conversion device 1 ′ illustrated in FIG. 10 has a configuration example in which the first inductor L1 in the power conversion device 1 illustrated in FIG. 1 is replaced with two inductors L1a and L1b. In the power converter 1 ′ shown in FIG. 10, one end of the inductor L1a is connected to the point U, and one end of the inductor L1b is connected to the point V. As shown in FIG. 10, even when there are a plurality of inductors connected between the UVs, the control and circuit operations described in the first or second embodiment can be similarly realized.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 1, 101, 201, 301, 1 '... Power converter, 15, 115, 215, 315 ... Control part, C1 ... 1st capacitor, C2 ... 2nd capacitor, L1 ... 1st inductor, L2 ... 2nd inductor, S1 ... second switch, S2 ... second switch, S3 ... third switch, S4 ... fourth switch, T ... transformer, Tp ... primary winding, Ts ... secondary winding.

Claims (5)

A bridge circuit in which a first and a second switch connected in series, a third and a fourth switch connected in series, and a capacitor are connected in parallel;
An inductor connected in series with an AC power source and a load between a connection point of the first and second switches and a connection point of the third and fourth switches;
Either the first or second switch selected according to the polarity of the power supply voltage of the AC power supply is turned on / off so that the duty of the rectangular voltage generated at the connection point of the first and second switches is constant. And a controller that turns on the fourth or third switch within a period in which the first or second switch is turned on;
A power conversion device comprising: The controller turns on the first or second switch by turning on the fourth or third switch with a fourth or third switching signal having a pulse width corresponding to the phase of the power supply voltage. Reducing the degree of pulse width modulation of the first or second switching signal;
The power conversion device according to claim 1, wherein: The control unit generates the first and second switching signals by a first PWM control, and the second and third switching signals have a pulse width that varies according to the phase of the power supply voltage. Generated by PWM control,
The power conversion device according to claim 2, wherein And a load circuit connected between a connection point of the first and second switches and a connection point of the third and fourth switches and supplying an output voltage to a load.
The power conversion device according to claim 1, wherein the power conversion device is a power conversion device. Output detection means for detecting voltage, current or power supplied from the inverter circuit as the load circuit to the load;
Controlling the frequency of the voltage generated at the connection point of the first and second switches according to the detection value obtained by the output detection means;
The power conversion device according to claim 4, wherein

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