Power Conversion Circuit

Abstract

To provide a power conversion circuit which can suppress voltage between switching elements and can reduce noise.SOLUTION: A power conversion circuit 1 comprises: a switching element Q1; a first resonance circuit 2 connected between the switching element Q1 and a load; a second resonance circuit L4 and C4; and a third resonance circuit L5 and C5. The second resonance circuit L4 and C4 is connected between a first terminal of the switching element Q1 and ground potential. The third resonance circuit L5 and C5 is connected between a second terminal of the switching element Q1 and the ground potential.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Voltage resonant power conversion circuits, including class E, perform low-loss switching by using zero-voltage switching, which turns on the switching element when the voltage across it is zero. This allows the drive frequency of the switching element to be increased, making it possible to miniaturize passive components such as inductors and capacitors.

[0003] However, voltage resonance increases the voltage across the switching elements. This requires the use of switching elements with high voltage resistance, which increases the cost of the switching elements and conduction loss. Therefore, by adding an LC series resonant circuit with a resonant frequency higher than the drive frequency in parallel with the switching elements, the peak voltage can be suppressed. This allows the switching elements to have a lower voltage resistance, resulting in lower costs and reduced conduction loss. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2017-184500 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, the power conversion circuit of Patent Document 1 does not achieve the noise suppression effect of reducing the number of filter stages, which is a problem for power converters that operate at high frequencies and high voltages. Therefore, multiple noise filters are required, which leads to an increase in the size and cost of the power conversion circuit. Furthermore, noise is generated by the LC series resonant circuit connected in parallel with the switching element.

[0006] An object of the present invention is to provide a power conversion circuit that can suppress the voltage between switching elements and reduce noise. [Means for solving the problem]

[0007] The power conversion circuit according to the present invention includes a switching element, a first resonant circuit connected between the switching element and a load, a second resonant circuit, and a third resonant circuit. The second resonant circuit is connected to a first terminal of the switching element and a ground potential. The third resonant circuit is connected to a second terminal of the switching element and a ground potential. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a power conversion circuit that can suppress the voltage between switching elements and reduce noise. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a circuit diagram of a power conversion circuit according to a first embodiment of the present invention. [Figure 2] Fig. 2(a) is a configuration diagram of a power conversion circuit according to the first embodiment. Fig. 2(b) is a circuit diagram that functions as a peak voltage suppressor. Fig. 2(c) is a diagram showing the outflow of common mode current to a peak voltage suppression resonant circuit. Fig. 2(d) is a diagram showing the filter characteristics of the peak voltage suppression resonant circuit. [Figure 3] FIG. 3 is a circuit diagram of a power conversion circuit according to a second embodiment of the present invention. [Figure 4] FIG. 4 is a circuit diagram of a power conversion circuit according to a third embodiment of the present invention. [Figure 5] FIG. 5 is a diagram showing filter characteristics with and without magnetic coupling between two inductors of a peak voltage suppression resonant circuit in a power conversion circuit according to a third embodiment of the present invention. [Figure 6] FIG. 6 is a diagram showing an example of the implementation of a peak voltage suppression resonant circuit. [Figure 7]FIG. 7 is a circuit diagram of a power conversion circuit according to a fourth embodiment of the present invention. [Figure 8] FIG. 8 is a circuit diagram of a power conversion circuit according to a fifth embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, power conversion circuits according to several embodiments of the present invention will be described in detail with reference to the drawings. The same or corresponding parts in the drawings of the power conversion circuits according to the embodiments will be designated by the same reference numerals, and their description will be omitted.

[0011] (First embodiment) 1 is a circuit diagram of a power conversion circuit according to a first embodiment of the present invention. The power conversion circuit 1 according to the first embodiment converts power supplied from an input power supply connected to the input side into a predetermined power by turning on and off a switching element Q1, and supplies the converted power to a load connected to the output side.

[0012] The power conversion circuit 1 is a class E power conversion circuit and includes a class E inverter circuit 11 and a rectifier circuit (not shown). The class E inverter circuit 11 includes choke coils L1 and L2, a switching element Q1, a capacitor C1 connected in parallel with the switching element Q1, and an LC resonant circuit 2. The class E inverter circuit 11 generates a high-frequency AC current by repeatedly turning the switching element Q1 on and off at a high frequency and a high voltage. The rectifier circuit rectifies the high-frequency current generated by the class E inverter circuit 11.

[0013] A choke coil L1 is connected between an input positive terminal P of an input power supply, which is a DC power supply, and one end of the switching element Q1. A choke coil L2 is connected between an input negative terminal N of the input power supply and the other end of the switching element Q1.

[0014] One end of the switching element Q1 is connected to one end of the choke coil L1, and the other end is connected to one end of the choke coil L2. The switching element Q1 is configured by a unipolar transistor such as a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor). The switching element Q1 switches between on and off operation in response to an on / off control signal from the control unit 5.

[0015] The capacitor C1 may be a separate component capacitor, or may not be arranged as a separate component by utilizing the parasitic capacitance of the MOSFET used as the switching element Q1.

[0016] The rectifier circuit may be a so-called class E rectifier, which has a diode, a rectifier-side shunt capacitor connected in parallel with the diode, and an output choke inductor, or a so-called class D rectifier, which consists of four bridge-connected diodes.

[0017] The higher the operating frequency of a power conversion circuit, the smaller the inductance and capacitance values ​​required for passive components such as inductors and capacitors used, making it possible to reduce the size of the power conversion circuit.

[0018] The LC resonant circuit 2 is made up of an inductor L3 and a capacitor C3, and the resonant frequency of the inductor L3 and the capacitor C3 is approximately the same as the drive frequency of the switching element Q1, and forms a first resonant circuit.

[0019] In the LC resonant circuit 2, when the switching element Q1 is off, the inductor L3 and capacitor C3 resonate to increase the voltage of the switching element Q1 in a sinusoidal manner, and when the switching element Q1 turns, the voltage decreases sinusoidally to near zero or to zero. At this time, turning on the switching element Q1 reduces the turn-on loss to zero.

[0020] Since so-called zero voltage switching can be performed, it is possible to reduce losses even when the drive frequency is increased, and the power conversion circuit can be made smaller.

[0021] (Characteristic configuration of the first embodiment) A characteristic feature of the first embodiment is the provision of a peak voltage suppression resonant circuit 3 that resonates to suppress the peak voltage of the switching element Q1. The peak voltage suppression resonant circuit 3 is made up of a series resonant circuit of an inductor L4 and a capacitor C4, and a series resonant circuit of an inductor L5 and a capacitor C5.

[0022] In a series resonant circuit of an inductor L4 and a capacitor C4, one end of the inductor L4 is connected to one end of the choke coil L1 and one end of the switching element Q1, and the other end of the inductor L4 is connected to one end of the capacitor C4, the other end of which is connected to a ground potential P1.

[0023] In a series resonant circuit of an inductor L5 and a capacitor C5, one end of the inductor L5 is connected to one end of the choke coil L2 and the other end of the switching element Q1, and the other end of the inductor L5 is connected to one end of the capacitor C5, the other end of which is connected to a ground potential P1.

[0024] A series resonant circuit consisting of inductor L4 and capacitor C4 constitutes a second resonant circuit, and a series resonant circuit consisting of inductor L5 and capacitor C5 constitutes a third resonant circuit.

[0025] The inductance value of inductor L4 is the same as the inductance value of inductor L5. The capacitance value of capacitor C4 is the same as the capacitance value of capacitor C5. The inductance values ​​of inductors L4 and L5 are sufficiently small compared to the inductance values ​​of choke coils L1 and L2.

[0026] Next, the operation of the power conversion circuit according to the first embodiment will be described with reference to FIG. 2. The power conversion circuit shown in FIG. 2(a) becomes the equivalent circuit shown in FIG. 2(b) as a function of suppressing the peak voltage of the switching element Q1. An inductor L and a capacitor C are connected across the switching element Q1. The resonant frequency f LC is expressed by equation (1).

[0027] f LC =1 / {2π(LC) 1 / 2}…(1)

[0028] resonance frequency f LC is the driving frequency f for turning on and off the switching element Q1 SW It is a higher frequency than

[0029] Next, with reference to FIG. 2(c), the function of the peak voltage suppression resonant circuit 3 to suppress the peak voltage of the switching element Q1 and the noise filtering function of the peak voltage suppression resonant circuit 3 and the choke coils L1 and L2 to suppress noise will be described.

[0030] First, we will explain the peak voltage suppression function of the peak voltage suppression resonant circuit 3. Since inductors L4 and L5 are connected in series between choke coils L1 and L2, the inductance value is 2L. Furthermore, since capacitors C4 and C5 are connected in series between choke coils L1 and L2, the capacitance value is C / 2.

[0031] Multiplying the inductance 2L by the capacitance C / 2 results in LC, with a resonant frequency of f LC is expressed by equation (1), and the resonant circuit in this case is the series resonant circuit shown in Figure 2(b). The peak voltage suppression resonant circuit 3 is formed as a resonant circuit between the switching elements Q1, so it can suppress the peak voltage of the switching element Q1. This allows the switching element Q1 to have a lower withstand voltage, lower cost, and lower loss.

[0032] Next, a description will be given of the filtering function of suppressing noise by the peak voltage suppression resonant circuit 3 and the choke coils L1 and L2. Noise is generated by the switching of the switching element Q1 and the LC resonant circuit 2.

[0033] A choke coil L1, an inductor L4, and a capacitor C4 are connected between the input positive terminal P and the ground potential P1. A choke coil L2, an inductor L5, and a capacitor C5 are connected between the input negative terminal N and the ground potential P1. The choke coils L1 and L2 have the same inductance value, which is denoted as Lc.

[0034] In the power conversion circuit 1, a common mode current flows to the ground potential P1 via parasitic capacitance due to the switching element Q1 and other elements. The common mode current flows through the capacitor C4 and inductor L4 and is suppressed by the choke coil L1. The common mode current also flows through the capacitor C5 and inductor L5 and is suppressed by the choke coil L2. The choke coils L1 and L2 function as a common mode choke coil.

[0035] The choke coil L1, inductor L4, and capacitor C4 function as a low-pass filter. The choke coil L2, inductor L5, and capacitor C5 function as a low-pass filter. The inductance values ​​of inductors L5 and L6 are sufficiently small compared to the inductance values ​​of choke coils L1 and L2. Therefore, if inductors L5 and L6 are ignored, the cutoff frequency fc of each low-pass filter is determined by the choke coil L1 (or L2) and capacitor C4 (or C5), and is expressed by the following equation (2):

[0036] fc=1 / {2π(L1C4) 1 / 2}…(2)

[0037] Since the inductance value of the choke coil L1 is sufficiently larger than the inductance value of the inductor L4, the cutoff frequency fc of the low-pass filter is set to the resonant frequency fLC The frequency is sufficiently lower than the cutoff frequency fc. In the frequency characteristics shown in Figure 2(d), the cutoff frequency fc is located at a position where the gain of the frequency characteristics is attenuated by 3 dB from 0 dB. The higher the frequency is above the cutoff frequency fc, the better the attenuation characteristics of the low-pass filter become, and the greater the effect of suppressing noise becomes.

[0038] (Effects of the power conversion circuit according to the first embodiment) In the power conversion circuit according to the first embodiment, the peak voltage suppression resonant circuit 3 is formed as a resonant circuit between the switching elements Q1, thereby suppressing the peak voltage of the switching element Q1. The peak voltage suppression resonant circuit 3 also functions as a noise filter that cuts common-mode current. This reduces the number of filter stages due to the noise suppression effect, enabling the power conversion circuit 1 to be made smaller and less expensive.

[0039] Also, the driving frequency f SW Higher resonant frequency f LC By providing a second resonant circuit and a third resonant circuit having the above, not only is the voltage between the switching elements suppressed, but it also functions as a noise filter. This not only realizes lower voltage resistance / low cost and lower loss of the switching elements, but also reduces the number of filter stages due to the noise suppression effect, making it possible to reduce the size and cost of the power conversion circuit.

[0040] In addition, in the E-class power conversion circuit, the driving frequency f SW Higher resonant frequency f LC By providing the second and third resonant circuits having these, the voltage between the switching elements is suppressed. In addition, the peak voltage suppression resonant circuit 3 and choke coils L1 and L2 also function as a noise filter that cuts common mode current. This not only achieves lower voltage resistance / low cost and lower loss for the switching element Q1, but also reduces the number of filter stages due to the noise suppression effect, allowing for smaller and less costly power conversion circuits.

[0041] In addition, the second and third resonant circuits are formed by connecting an inductor and a capacitor in series, which makes tuning easy.Furthermore, the switching elements can be made lower voltage / lower cost, and the number of filter stages can be reduced due to the low loss and noise suppression effect, which allows for a smaller and less expensive power conversion circuit.

[0042] (Second embodiment) Fig. 3 is a circuit diagram showing a power conversion circuit according to a second embodiment of the present invention. The power conversion circuit of Fig. 3 constitutes a high-frequency class E PFC (power factor correction) circuit, and an input power supply outputs AC to the power conversion circuit 1a. Compared to Fig. 1, the high-frequency class E PFC circuit is characterized in that the switching elements are made up of at least two switch groups Q1 and Q2 connected in series.

[0043] The other configurations are the same as those shown in FIG. 1, so only the configuration and operation of the switch groups Q1 and Q2 will be explained here.

[0044] The switch group Q1, Q2 consists of a series circuit of a switching element Q1 and a switching element Q2. One end of the switching element Q1 is connected to one end of the choke coil L1, and one end of the switching element Q2 is connected to one end of the choke coil L2. The on and off operations of the switching elements Q1 and Q2 are controlled by the control unit 5a.

[0045] The voltage input to the class E PFC circuit is an AC voltage, and depending on the polarity of the AC voltage, the control unit 5a switches one of the switching elements Q1 and Q2 and turns the other on, thereby enabling PFC operation and improving the power factor.

[0046] Although the input voltage is AC and the operation of the two switching elements Q1 and Q2 differ from those of the power conversion circuit according to the first embodiment, the noise suppression effect is the same as that of the power conversion circuit according to the first embodiment.

[0047] (Effects of the power conversion circuit according to the second embodiment) According to the power conversion circuit of the second embodiment, in the E-class PFC power conversion circuit, the drive frequency f SW Higher resonant frequency f LC By providing the second and third resonant circuits having these, the voltage between the switching elements is suppressed. In addition, the peak voltage suppression resonant circuit 3 and choke coils L1 and L2 also function as a noise filter that cuts common mode current. This not only achieves lower voltage resistance / low cost and lower loss for the switching elements Q1 and Q2, but also reduces the number of filter stages due to the noise suppression effect, allowing for smaller and less costly power conversion circuits.

[0048] (Third embodiment) 4 is a circuit diagram of a power conversion circuit according to a third embodiment of the present invention. The power conversion circuit according to the third embodiment is characterized in that the inductor L4a of the second resonant circuit L4a, C4 and the inductor L5a of the third resonant circuit L5a, C5 are magnetically coupled.

[0049] Normal mode current flows through a loop LP1 of A → L4a → C4 → P1 → C5 → L5a → B. For this reason, magnetic coupling in normal mode reinforces the magnetic fluxes of inductors L4a and L5a.

[0050] On the other hand, the common mode current passes through the ground potential P1 via the parasitic capacitance C6 of the switching element Q1 and flows in a loop LP2 from C4 to L4a to A and C5 to L5a to B. In this case, the magnetic coupling in the common mode cancels out the magnetic flux of the inductors L4a and L5a.

[0051] Therefore, the driving frequency f of the switching element Q1 SW Normal mode resonance frequency f LC_N and normal mode resonance frequency f LC_N Common mode resonance frequency f LC_C It has.

[0052] Normal mode resonance frequency f LC_N is expressed by equation (3).

[0053] f LC_N =1 / {2π(L _N C) 1 / 2}>f SW …(3)

[0054] L _N is the inductance value when the magnetic fluxes of the inductors L4a and L5a are reinforced.

[0055] The common mode resonance frequency is expressed by equation (4).

[0056] f LC_C =1 / {2π(L _ C) 1 / 2}>f SW …(4)

[0057] L _ C is the inductance value when the magnetic flux of inductors L4a and L5a is cancelled out.

[0058] 5 is a diagram showing the filter characteristics of two inductors in a peak voltage suppression resonant circuit of a power conversion circuit according to a third embodiment of the present invention, with and without magnetic coupling. The resonant frequency at which the peak voltage is suppressed is higher with magnetic coupling than without magnetic coupling.

[0059] This not only enables the switching element Q1 to have a lower breakdown voltage, lower cost, and lower loss, but also enables noise suppression effects to be achieved in even higher frequency bands, reducing the number of filter stages and enabling the power conversion circuit to be made smaller and less expensive.

[0060] Figure 6 shows an example implementation of the peak voltage suppression resonant circuit in Figure 4. Figure 6 shows a loop LP2 of common mode current and a loop LP1 of normal mode current that flow through core 6 made of magnetic material. Inductors L4a and L5a are magnetically coupled using core 6 made of magnetic parts, and are installed so that the magnetic coupling in normal mode reinforces magnetic fluxes, while the magnetic coupling in common mode cancels out the magnetic fluxes.

[0061] (Effects of the power conversion circuit according to the third embodiment) In the power conversion circuit according to the third embodiment, the inductance components of the second resonant circuit and the third resonant circuit are magnetically coupled to each other, and the magnetic coupling in the normal mode is formed so as to reinforce the magnetic fluxes, while the magnetic coupling in the common mode is formed so as to cancel the magnetic fluxes. SW Normal mode resonance frequency f LC_N and normal mode resonance frequency f LC_N Common mode resonance frequency f LC_C This allows for lower voltage resistance, lower cost, and lower loss in the switching elements, while also providing noise suppression effects in higher frequency bands, reducing the number of filter stages and enabling the miniaturization and cost reduction of power conversion circuits.

[0062] In addition, the inductance components of the second and third resonant circuits are magnetically coupled using the core 6 made of a magnetic part, so that the desired normal mode resonant frequency f LC_N Furthermore, the shortest possible length enables noise suppression to be achieved in higher frequency bands, reducing the number of filter stages and enabling the miniaturization and cost reduction of power conversion circuits.

[0063] (Fourth embodiment) 7 is a circuit diagram of a power conversion circuit according to a fourth embodiment of the present invention. The power conversion circuit comprises a high-frequency class E PFC circuit having switch groups Q1 and Q2, a capacitor C1 connected in parallel to the switch groups Q1 and Q2, choke coils L1 and L2, and series LC resonant circuits L3a, C3a, L3b, and C3b.

[0064] One end of the choke coil L2 and one end of the switching element Q2 are connected to one end of the heat dissipation member 7a via a capacitance C7 formed by the parasitic capacitance of the switching element Q2 and the parasitic capacitance of the heat dissipation member 7a, and the other end of the heat dissipation member 7a is connected to one end of the inductor L7.

[0065] One end of the choke coil L1 and one end of the switching element Q1 are connected to one end of the heat dissipation member 7b via a capacitance C8 formed by the parasitic capacitance of the switching element Q1 and the parasitic capacitance of the heat dissipation member 7b, and the other end of the heat dissipation member 7b is connected to one end of the inductor L8.

[0066] The heat dissipation members 7a and 7b are made of, for example, heat sinks. The heat dissipation member 7a dissipates heat generated in the switching element Q2, and the heat dissipation member 7b dissipates heat generated in the switching element Q1.

[0067] (Effects of the power conversion circuit according to the fourth embodiment) According to the power conversion circuit of the fourth embodiment, the electrostatic capacitances C7 and C8 parasitic on the heat dissipation members 7a and 7b and the switch groups Q1 and Q2 are utilized as capacitor components of the peak voltage suppression resonant circuit 3, thereby reducing the number of capacitors to be implemented and reducing costs.

[0068] (Fifth embodiment) Fig. 8 is a circuit diagram of a power conversion circuit according to a fifth embodiment of the present invention. The power conversion circuit according to the fifth embodiment differs from the power conversion circuit according to the fourth embodiment shown in Fig. 7 in that one end of an insulating heat conductive member 8a is connected to one end of a choke coil L2 and one end of a switching element Q2, and the other end of the heat conductive member 8a is connected to one end of a heat dissipation member 7a.

[0069] One end of insulating heat conduction member 8b is connected to one end of choke coil L1 and one end of switching element Q1, and the other end of heat conduction member 8b is connected to one end of heat dissipation member 7b. Heat conduction members 8a and 8b are insulating and therefore have a capacitance component.

[0070] (Effects of the power conversion circuit according to the fifth embodiment) According to the power conversion circuit of the fifth embodiment, by providing thermally conductive members 8a and 8b between the heat dissipation members 7a and 7b and the switch groups Q1 and Q2, the number of capacitors to be mounted can be reduced, thereby reducing costs, by utilizing the thermally conductive members 8a and 8b as capacitor components of the peak voltage suppression resonant circuit 3. In addition, heat can be dissipated from the switching elements Q1 and Q2.

[0071] Although the power conversion circuits according to the first embodiment to the fifth embodiment are provided with two choke coils L1 and L2, only one of the choke coils L1 and L2 may be provided.

[0072] Furthermore, the present invention is not limited to the power conversion circuits according to the first to fifth embodiments, and any number of the power conversion circuits according to the first to fifth embodiments may be used in combination. [Explanation of symbols]

[0073] 1 Power conversion circuit 2 LC resonant circuit 3,3b Peak voltage suppression resonant circuit 5,5a Control section 6 cores 7a, 7b Heat dissipation member 8a, 8b Heat conductive member 11 E-class inverter circuit Q1, Q2 switching elements L1, L2 choke coil L3, L4, L5, L7, L8 inductors C1~C5 Shunt capacitors

Claims

1. A power conversion circuit including a switching element, a capacitor connected in parallel with the switching element, and a first resonant circuit connected between the switching element and a load, a second resonant circuit connected to the first terminal of the switching element and to a ground potential; a third resonant circuit connected to the second terminal of the switching element and to the ground potential;

2. The power conversion circuit according to claim 1 , wherein the second resonant circuit and the third resonant circuit have a resonant frequency higher than a drive frequency of the switching element.

3. At least one choke coil connected to a plurality of input terminals and the switching element; the first resonant circuit including an inductor and a capacitor connected to at least one end of the switching element; 2. The power conversion circuit according to claim 1, which is a high frequency class E circuit having a

4. the switching element is a group of at least two series-connected switches; a capacitor connected in parallel to the group of switches; at least one choke coil connected between the plurality of input terminals and the switching element; the first resonant circuit consisting of an inductor and a capacitor connected to at least one end of the group of switches; 2. The power conversion circuit according to claim 1, which is a high frequency class E power factor correction circuit having:

5. 5. The power conversion circuit according to claim 1, wherein the second resonant circuit and the third resonant circuit are formed by connecting an inductor and a capacitor in series.

6. 6. The power conversion circuit according to claim 5, wherein the inductance components of the inductors of the second resonant circuit and the third resonant circuit are magnetically coupled to each other, and the magnetic coupling in normal mode is formed so as to reinforce magnetic fluxes, and the magnetic coupling in common mode is formed so as to cancel out magnetic fluxes.

7. 7. The power conversion circuit according to claim 6, wherein the inductance components of the inductors of the second resonant circuit and the third resonant circuit are magnetically coupled to each other using a magnetic part.

8. 6. The power conversion circuit according to claim 5, wherein the capacitor components of the second resonant circuit and the third resonant circuit are parasitic capacitances formed by a heat dissipation member and the switching element.

9. 9. The power conversion circuit according to claim 8, further comprising an insulating heat-conducting member disposed between the heat-dissipating member and the switching element.

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