Ripple current cancellation device

Abstract

To provide a ripple current cancellation device that can be retrofitted to a DC / DC converter.SOLUTION: A ripple current cancellation device 2 according to the present invention includes coils 22, 23 constituting a magnetic coupling portion LC, a terminal S1 connected to one end of the coil 22 via a capacitor C1, a terminal S2 connected to the other end of the coil 23 via a capacitor C2, a terminal S3 commonly connected to the other end of the coil 22 and one end of the coil 23, and an auxiliary inductance LS inserted between one end of the coil 23 and the terminal S3.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a ripple current cancellation device. [Background technology]

[0002] The ripple current superimposed on the output current of a switching power supply can cause increased noise, reduced efficiency, excess heat generation, electromagnetic interference with other devices, etc. Therefore, in conventional switching power supplies, many measures have been taken to minimize the ripple current.

[0003] Non-Patent Document 1 discloses an example of such a device. In the switching power supply of this document, a ripple current cancellation circuit including a coupling reactor and an auxiliary inductor is installed in parallel with the output inductor. In this way, the ripple current can be reduced. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Michael J. Schutten et al., "Ripple Current Cancellation Circuit," IEEE (Institute of Electrical and Electronics Engineers) Xplore, February 19, 2003, pp. 464-470 Summary of the Invention [Problem to be solved by the invention]

[0005] Incidentally, when implementing the ripple current cancellation circuit described in Non-Patent Document 1, a configuration as shown in Fig. 4 has been used up until now. That is, a coil 101 separate from the output inductor L1 is wound around a toroidal core 100 that constitutes the winding core of the output inductor L1, and the coil 101 and the output inductor L1 form a coupled reactor. The symbols in Fig. 4 (excluding the toroidal core 100 and the coil 101) are based on the example in Non-Patent Document 1.

[0006] However, according to the configuration of FIG. 4, since the switching power supply incorporates a ripple current cancellation circuit, it is necessary to design the switching power supply including the ripple current cancellation circuit. Therefore, a ripple current cancellation circuit as a device that can be retrofitted to the switching power supply has been demanded.

[0007] The above circumstances are the same for any DC / DC converter (power conversion device) including a switching power supply. Therefore, one of the objects of the present invention is to provide a ripple current cancellation device that can be retrofitted to a DC / DC converter.

Means for Solving the Problems

[0008] The ripple current cancellation device according to the present invention includes a first coil and a second coil that constitute a magnetic coupling portion, a first terminal connected to one end of the first coil via a first capacitor, a second terminal connected to the other end of the second coil via a second capacitor, a third terminal commonly connected to the other end of the first coil and one end of the second coil, and an auxiliary inductance inserted between one end of the second coil and the third terminal.

Effects of the Invention

[0009] According to the ripple current cancellation device of the present invention, it is possible to provide a ripple current cancellation device that can be retrofitted to a DC / DC converter.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0012] FIG. 1 is a diagram showing the configuration of a switching power supply 1 and a ripple current canceling device 2 according to the present embodiment. Further, FIG. 2 is a diagram showing the coil shown in FIG. 1 represented by circuit symbols. These figures also show a DC power supply 3 and a load 4 connected to the switching power supply 1. The load 4 is, for example, a battery for an electric vehicle or solar power generation.

[0013] As shown in FIGS. 1 and 2, the switching power supply 1 includes a full-bridge circuit 10, an output reactor L L and an output capacitor C out and is a DC / DC converter configured to include. The switching power supply 1 is configured to have six terminals T1 to T6 as external terminals. Among these, terminals T1 and T2 are the input terminals of the switching power supply 1 and are connected to the high-side terminal and the low-side terminal of the DC power supply 3, respectively. Further, terminals T3 and T4 are the output terminals of the switching power supply 1 and are connected to the high-side terminal and the low-side terminal of the load 4, respectively. Regarding terminals T5 and T6, they will be described later.

[0014] The full-bridge circuit 10 is composed of four switches S1A, S2A, S1B, and S2B. These switches S1A, S2A, S1B, and S2B are each one-way switches composed of a semiconductor element such as a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) or an IGBT (Insulated Gate Bipolar Transistor), and a diode connected in parallel with this semiconductor element. The on / off states of the switches S1A, S2A, S1B, and S2B are controlled by a control device (not shown).

[0015] The switches S1A and S2A correspond to the first leg of the full-bridge circuit 10, and the switches S1B and S2B correspond to the second leg of the full-bridge circuit 10. Also, the switches S1A and S1B correspond to the upper arm of the full-bridge circuit 10, and the switches S2A and S2B correspond to the lower arm of the full-bridge circuit 10.

[0016] The high-side input terminal of the full-bridge circuit 10 is connected to terminal T1, and the low-side input terminal is connected to terminal T2. Also, the output terminal of the first leg of the full-bridge circuit 10 is connected to terminal T3 via the output reactor L L and the output terminal of the second leg of the full-bridge circuit 10 is connected to terminal T4.

[0017] The output reactor L L is an inductor connected between the output terminal of the first leg of the full-bridge circuit 10 and terminal T3, and plays a role in reducing the ripple current in the output voltage and improving the stability of the output voltage. Hereinafter, the inductance of the output reactor L L may be denoted as "L L ". As shown in FIG. 1, the output reactor L L can be configured by winding the coil 12 around the core 11. FIG. 1 shows an example where the core 11 is a toroidal core, but the core 11 may be a core other than a toroidal core. Also, the output capacitor C outis a capacitor connected between terminal T3 and terminal T4, and plays roles such as reducing the ripple current and noise in the output voltage and improving the stability of the output voltage.

[0018] Output reactor L L The input terminal and output terminal of are respectively connected to terminals T5 and T6. Thus, in the switching power supply 1, an external device can be connected in parallel with the output reactor L L In the following description, the wiring connecting the output terminal of the output reactor L L to terminal T3 and the connection point with terminal T6 are referred to as node n1, the current flowing from the output reactor L L into node n1 is i1, and the current flowing from node n1 toward terminal T3 is i L which is so called.

[0019] The ripple current cancellation device 2 is composed of a magnetic coupling part L C , an auxiliary inductance L S , and capacitors C1 and C2. In addition, the ripple current cancellation device 2 is configured to have three terminals S1 to S3 as external terminals. Terminals S1, S2, and S3 are respectively connected to terminals T5, T6, and T4 of the switching power supply 1.

[0020] The magnetic coupling part L C is a coupling reactor or transformer formed by in-phase coupling of two coils 22 and 23. The two coils 22 and 23 are wound in the same direction around a core 21 that does not form the magnetic core of the output reactor L L . The illustrated inductance L m is the exciting inductance of the magnetic coupling part L C . For the core 21, although an example of a toroidal core is shown in FIG. 1, it may be a core other than a toroidal core. The number of turns of the coils 22 and 23 are respectively n p , n s respectively. The core 21 is composed of, for example, Finemet (registered trademark), a nano-crystalline soft magnetic core material.

[0021] One end of coil 22 is connected to terminal S1 via capacitor C1. The other end of coil 23 is connected to terminal S2 via capacitor C2. The other end of coil 22 and one end of coil 23 are commonly connected to terminal S3. More specifically, the other end of coil 22 is connected to node n2 provided in the middle of the wiring connecting one end of coil 23 and terminal S3. Hereinafter, the current flowing from the other end of coil 22 into node n2 is referred to as i2, and the current flowing from the other end of coil 23 into node n2 is referred to as i3.

[0022] Capacitors C1 and C2 are provided to block the inflow of the ripple current (DC component) of the overcurrent that may occur during the startup or transient state of switching power supply 1 into ripple current cancellation device 2. Capacitor C2 is for blocking the inflow of the overcurrent from the secondary side of magnetic coupling section L C and is also used in the ripple current cancellation circuit according to the background art shown in FIG. 4 (capacitor C2). On the other hand, capacitor C1 is for blocking the inflow of the overcurrent from the primary side of magnetic coupling section L C and is a characteristic configuration of ripple current cancellation device 2 according to the present embodiment. That is, in ripple current cancellation device 2 according to the present embodiment, although inductance L L and magnetic coupling section L C are electrically connected but separated as coils, depending on the balance between inductance L L and exciting inductance L m , there is a possibility that overcurrent flows into ripple current cancellation device 2 not only from the secondary side but also from the primary side of magnetic coupling section L C . Therefore, in ripple current cancellation device 2 according to the present embodiment, it is necessary to provide capacitor C1 on the primary side of magnetic coupling section L C .

[0023] An auxiliary inductance L S is inserted between one end of coil 23 and terminal S3 (more specifically, between one end of coil 23 and node n2). This auxiliary inductance L S is typically magnetic coupling section LC is the leakage inductance. However, the auxiliary inductance L can also be realized by implementing an inductor as an element. S The specific value of the auxiliary inductance L S is determined based on the exciting inductance L m , the inductance L L , and the turns ratio of the magnetic coupling part L C . This will be described in detail below.

[0024] The condition for the ripple current in the output voltage of the switching power supply 1 to become zero is expressed as the following equation (1) using the above-described currents i1 to i3.

[0025]

Equation

[0026] Also, the AC component v C of the primary-side voltage of the magnetic coupling part L p is equal to the AC component v L of the voltage across the output reactor L L , and thus is expressed as the following equation (2). However, the L p on the right side of equation (2) is the combined inductance expressed by equation (3).

[0027]

Equation

[0028] The AC component v C of the primary-side voltage of the magnetic coupling part L p can also be represented by the AC component v C of the secondary-side voltage of the magnetic coupling part L s , and is expressed as the following equation (4). However, N in equation (4) is the turns ratio of the magnetic coupling part L C , and is the value obtained by dividing the number of turns n p of coil 22 by the number of turns n s of coil 23, i.e., n p / n sIt becomes

Number

[0029] From Equation (2) and Equation (4), the following Equation (5) is obtained.

Number

[0030] Furthermore, current i2 and current i3 satisfy the following Equation (6).

[0031]

Number

[0032] Substituting Equation (5) and Equation (6) into Equation (1) gives Equation (7), and by transforming this Equation (7), the auxiliary inductance L S can be expressed as in Equation (8). By determining the auxiliary inductance L S to satisfy Equation (8), it becomes possible to suitably reduce the ripple current of the switching power supply 1.

[0033]

Number

[0034] Figure 3 is a diagram showing the simulation results of currents i1 to i3 and current i L The simulation in this figure was performed using the auxiliary inductance L S determined to satisfy Equation (8). The figure also shows the current i2 + i3 obtained by adding currents i2 and i3.

[0035] As shown in Figure 3, a triangular ripple current with an amplitude of approximately 10 A peak-to-peak is superimposed on current i1, but current i LIn this case, this ripple current is significantly reduced, leaving only a small ripple current. Looking at the current i2 + i3 shown in FIG. 3, it can be understood that such a reduction in the ripple current is achieved because the current i2 + i3 is out of phase with the ripple current of the current i1 and has an amplitude of approximately 10 A peak-to-peak. From this simulation result, it can be said that by using the ripple current canceling device 2 according to the present embodiment, the ripple current of the switching power supply 1 can be significantly reduced.

[0036] As described above, the ripple current canceling device 2 according to the present embodiment can be retrofitted to the switching power supply 1 by connecting the terminals S1, S2, and S3 to the terminals T5, T6, and T4 of the switching power supply 1, respectively. And according to the ripple current canceling device 2 according to the present embodiment, the auxiliary inductance L S is determined based on the exciting inductance L C of the magnetic coupling part L m , the inductance L L of the output reactor L L , and the turn ratio N of the magnetic coupling part L C , the ripple current of the switching power supply 1 can be significantly reduced. Therefore, it can be said that according to the ripple current canceling device 2 according to the present embodiment, it is possible to provide a ripple current canceling device that can be retrofitted to the switching power supply 1.

[0037] As described above, the preferred embodiments of the present invention have been described, but the present invention is not limited to such embodiments at all, and it goes without saying that the present invention can be implemented in various modes without departing from the gist thereof.

[0038] For example, in the above embodiment, an example of using the ripple current canceling device 2 according to the present invention by connecting it to the switching power supply 1 has been described, but the ripple current canceling device according to the present invention can be used by connecting it to any DC / DC converter (power conversion device) including the switching power supply 1.

Explanation of Reference Numerals

[0039] 1 Switching power supply 2 Ripple current cancellation device 3 DC power supply 4 Load 10 Full-bridge circuit 11, 21 Core 12, 22, 23 Coil C1, C2 Capacitor C out Output capacitor L C Magnetic coupling part L S Auxiliary inductance L L Output reactor L m Excitation inductance N Turns ratio S1~S3 Terminals S1A, S2A, S1B, S2B Switches T1~T6 Terminals

Claims

1. A first coil and a second coil constituting a magnetic coupling part, A first terminal connected to one end of the first coil via a first capacitor, A second terminal connected to the other end of the second coil via a second capacitor, A third terminal commonly connected to the other end of the first coil and one end of the second coil, An auxiliary inductance inserted between one end of the second coil and the third terminal, A ripple current canceling device including the above.

2. The first terminal is connected to the input end of the output reactor of the DC / DC converter, The third terminal is connected to the output end of the output reactor of the DC / DC converter, The second terminal is connected to the low-side output end of the DC / DC converter, The ripple current canceling device according to Claim 1.

3. The first coil and the second coil are wound around a core that does not constitute the magnetic core of the output reactor, The ripple current canceling device according to Claim 2.

4. The auxiliary inductance L Ｓ is expressed by Equation (1) using the exciting inductance L ｍ of the magnetic coupling section, the inductance L L of the output reactor, and the turns ratio N of the magnetic coupling section obtained by dividing the number of turns of the first coil by the number of turns of the second coil The ripple current canceling device according to Claim 2 or 3.

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