Chopper circuit

Abstract

This invention provides a chopper circuit that can reduce circuit losses. [Solution] The chopper circuit comprises a switching element and a reactor. Both the low-load current flowing through the reactor and the high-load current, which has a current value higher than the low-load current, have a section in which they flow in the negative direction within one cycle. The switching element performs soft switching at both the low-load current and high-load current. Ripple current Δi at low-load current L The ripple current Δi at the high load current H Control it so that it becomes smaller than that.

Description

[Technical Field]

[0001] This invention relates to a chopper circuit that performs soft switching. [Background technology]

[0002] A known type of circuit is the chopper circuit, which converts current and voltage into different magnitudes by switching them ON and OFF. A reactor is implemented in this chopper circuit. Generally, it is said that maintaining a high inductance value for the reactor, not only at low load currents but also at high load currents where the average current is greater than the average current at low loads, can suppress ripple current. In other words, a technique is employed to maintain a constant high inductance value from low load currents to high load currents (see Figure 4).

[0003] Furthermore, switching methods for turning switching elements ON and OFF are known, such as the soft switching method. When soft switching is performed at both low and high load currents, it is necessary to ensure that a negative current flows from the low load current to the high load current. In order to ensure that a negative current flows from the low load current to the high load current, the inductance value of the reactor is kept constant at a low value (see Figure 6). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2016-67187 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, if the inductance value is kept constant, the ripple current in the low-load current region and the high-load current region will be approximately the same. In other words, if the inductance value of the reactor is kept constant at a low value, the current waveform at low load currents will shift too far to the negative side, resulting in a large ripple current at low load currents. A large ripple current leads to increased circuit losses.

[0006] The present invention was made to solve the above problems, and its objective is to provide a chopper circuit that can reduce circuit losses. [Means for solving the problem]

[0007] The chopper circuit of the present invention comprises a switching element and a reactor, wherein both the low-load current flowing through the reactor and the high-load current, whose average value is higher than the average value of the low-load current, have a section in one cycle in which they flow in the negative direction, and the switching element performs soft switching at both the low-load current and high-load current levels, controlling the ripple current at the low-load current level to be smaller than the ripple current at the high-load current level. [Effects of the Invention]

[0008] According to the present invention, a chopper circuit that can reduce circuit losses can be obtained. [Brief explanation of the drawing]

[0009] [Figure 1] This is a circuit diagram of the soft-switching chopper circuit of this embodiment. [Figure 2] This graph shows the current waveforms of the reactor under low and high load currents. [Figure 3] This graph shows the inductance value when the reactors are superimposed. [Figure 4] This graph shows the superposition characteristics of a typical reactor. [Figure 5]This graph shows the current waveform of a reactor that maintains high inductance superposition characteristics from low load current to high load current. [Figure 6] This graph shows the superposition characteristics of a conventional reactor that performs soft switching from low load current to high load current. [Figure 7] This graph shows the current waveform of a reactor that maintains low inductance superposition characteristics from low load current to high load current. [Modes for carrying out the invention]

[0010] [Embodiment] The chopper circuit in this embodiment will be described with reference to the drawings. Figure 1 is a circuit diagram of the soft-switching chopper circuit of this embodiment.

[0011] A chopper circuit 10 is a circuit that converts current and voltage into other magnitudes by switching them ON and OFF. One example of the conversion method used by the chopper circuit 10 is a soft-switching method. The chopper circuit 10 includes a DC power supply 1, a switching element 2, a reactor 3, a diode 4, and a capacitor 5.

[0012] DC power supply 1 is a component that supplies a stable DC voltage and current. The positive terminal of DC power supply 1 is connected in series with reactor 3. The negative terminal of DC power supply 1 is connected to the negative terminals of switching element 2 and capacitor 5.

[0013] Switching element 2 is a semiconductor element that switches the current flowing through the circuit ON or OFF. Switching element 2 is connected to the anodes of reactor 3 and diode 4. Switching element 2 performs the ON and OFF of the switching element. Switching element 2 performs soft switching.

[0014] The switching element 2 performs soft switching for both a low load current and a high load current whose average current value is higher than the average value of the low load current. The low load current and the high load current can be defined as follows. In the inductance value during the superimposition characteristic of the reactor 3 described later (see FIG. 3), the maximum inductance value at which the inductance value is maximum is designated as L MAX , and when an arbitrary inductance value is designated as L, L / L MAX The current at which the value becomes 0.1 is defined as the maximum average current. The maximum average current indicates a current at which the inductance approaches saturation. A current having an average current value less than half of the maximum average current is referred to as a low load current, and a current having an average current value equal to or more than half of the maximum average current is referred to as a high load current. Note that the average current and the average value of the current refer to a current obtained by averaging the current over one cycle in the current waveform.

[0015] Further, unlike the definition based on the maximum average current described above, the boundary between the low load current and the high load current may be based on 4A as the average current value. That is, it is preferable that the average value of the low load current is a current less than 4A, and the average value of the high load current is a current of 4A or more. In the following description, the low load current is described as a current having an average value of less than 4A, and the high load current is described as a current having an average value of 4A or more, but the boundary between the low load current and the high load current is not limited to 4A.

[0016] The reactor 3 is an electromagnetic component that converts electric energy into magnetic energy to store and release the magnetic energy. More specifically, the reactor 3 repeats storage and release of the magnetic energy converted from the electric energy in accordance with ON and OFF of the switching element 2, whereby the chopper circuit 10 can perform voltage step-up and voltage step-down. The reactor 3 is connected to the positive electrodes of the DC power supply 1 and the capacitor 5. The reactor 3 includes a core and a coil.

[0017] The core is made of a magnetic material. A coil is attached to the core. Lead wires are drawn out from the coil, and the lead wires are electrically connected to an external device including a circuit board. Power is supplied from the external device to the coil, and the coil generates magnetic flux. The core serves as a closed magnetic path through which the magnetic flux generated by the coil passes.

[0018] Figure 2 is a graph showing current waveforms of the reactor 3 at the time of low load current and at the time of high load current. As shown in Figure 2, the reactor 3 has a region where the current falls below 0A at the time of low load current and at the time of high load current.

[0019] Further, the reactor 3 is adjusted such that the ripple current Δi at the time of low load current L is smaller than the ripple current Δi at the time of high load current H . In the present embodiment, by adjusting the inductance value of the reactor 3 in the superimposed characteristic state, the ripple current Δi at the time of low load current L is made smaller than the ripple current Δi at the time of high load current H .

[0020] Figure 3 is a graph showing the inductance value of the reactor 3 in the superimposed characteristic state. As shown in Figure 3, the inductance value of the reactor 3 is not constant, and draws a curve that drops sharply at the time of high load current. More specifically, in the low load current region where the average current value is less than 4A, the high inductance value is maintained, while in the high load current region where the average current value is 4A or more, the inductance value is sharply decreased.

[0021] As the sharp reduction rate of the inductance value, it is preferable that the reduction rate of the inductance value L at the maximum average current is 50% or less compared to the inductance value L at half of the maximum average current. That is, it is preferable that (the inductance value at the maximum average current) / (the inductance value at half of the maximum average current) is 0.5 or less. By setting the reduction rate to 50% or less, a negative current can flow even under a high load current, soft switching can be performed, and the ripple current at the time of low load current can be reduced. Note that the reduction rate is preferably 5% or more. If the inductance drops more sharply than 5%, the ripple current becomes unnecessarily large, and the loss of the chopper circuit 10 increases.

[0022] Furthermore, it is preferable that the inductance value at a current twice the maximum average current is reduced by 50% or less compared to the inductance value at the maximum average current. Looking at the graph in Figure 2, the current waveform at high load current shows a steep slope from around 10A. For example, if the inductance value is sharply reduced at 5A, immediately after entering the high load current region, the slope of the low load current region above 5A will also become steep, as shown in Figure 2, and the ripple current Δi at low load current will decrease. L It will get bigger.

[0023] Diode 4 is a semiconductor element that allows current to flow in a specific direction. The anode of diode 4 is connected to the switching element 2 and the reactor 3, and the cathode of diode 4 is connected to the positive terminal of capacitor 5.

[0024] Capacitor 5 is an electronic component that stores and releases electricity. The positive terminal of capacitor 5 is connected to the cathode of diode 4, and the negative terminal of capacitor 5 is connected to the DC power supply 1 and the switching element 2.

[0025] [Effects and Effects] This section will explain in detail the relationship between the superposition characteristics of the inductance of reactor 3 and the current waveform of reactor 3. Figure 4 is a graph showing the superposition characteristics of a typical reactor. As shown in Figure 4, generally, a reactor is considered good if it maintains a high value at a constant level from low load current to high load current. In other words, a reactor whose inductance value drops quickly when the current is increased is considered to have poor magnetic properties.

[0026] FIG. 5 is a graph showing current waveforms of a reactor that maintains high inductance superimposition characteristics from a low load current time to a high load current time. In FIG. 5, the solid line represents the waveform at the time of low load current with an average value of 1A (black circle mark in FIG. 4), and the dotted line represents the waveform at the time of high load current with an average value of 5A (black triangle mark in FIG. 4). As shown in FIG. 5, at the time of low load current, there is a region that reaches a position below 0A, but at the time of high load current, there is no region that reaches a position below 0A. Therefore, this reactor cannot perform soft switching at the time of high load current.

[0027] In order to pass a current below 0A at the time of high load current, it is necessary to lower the inductance value during the superimposition characteristic. FIG. 6 is a graph showing the superimposition characteristics of a conventional reactor that performs soft switching from a low load current time to a high load current time. As shown in FIG. 6, the conventional reactor keeps the inductance value during the superimposition characteristic constant at a low value.

[0028] FIG. 7 is a graph showing current waveforms of a reactor that maintains low inductance superimposition characteristics from a low load current time to a high load current time. The solid line and the dotted line in FIG. 7 are the same as those in FIG. 5, the solid line represents the waveform at the time of low load current, and the dotted line represents the waveform at the time of high load current. As shown in FIG. 7, a current below 0A is generated even at the time of high load current, and soft switching can be performed not only at the time of low load current but also at the time of high load current. However, the negative current flowing at the time of low load current also increases. Therefore, the ripple current Δi2 at the time of low load current is larger than the ripple current Δi1 at the time of low load current shown in FIG. 5. As a result, the loss of the chopper circuit increases.

[0029] Accordingly, as shown in FIG. 2, in the chopper circuit of the present invention, the ripple current Δi at the time of low load current L is the ripple current Δi at the time of high load current HThe reactor 3 is controlled to be smaller than the specified value. This suppresses the increase in ripple current at low load currents, allows switching to occur from low load currents to high load currents, and reduces losses in the chopper circuit 10.

[0030] In particular, in this embodiment, as shown in Figure 3, the inductance value of the reactor 3 during superposition characteristics is controlled to maintain a high value at low load currents and to decrease at high load currents. This allows for soft switching at both low and high load currents while suppressing ripple current without the use of auxiliary circuits, reducing the number of components and lowering manufacturing costs and the size of the chopper circuit 10.

[0031] (Other embodiments) While embodiments of the present invention have been described herein, these embodiments are presented as examples and are not intended to limit the scope of the invention. The above embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the scope of the invention. Embodiments and their variations are included in the scope and essence of the invention, as well as in the claims and their equivalents.

[0032] In the above embodiment, the chopper circuit 10 was a boost type, but the chopper circuit 10 is not limited to this. The chopper circuit 10 may be a buck type or a buck-boost type. [Explanation of Symbols]

[0033] 10. Chopper Circuit 1 DC power supply 2 Switching elements 3 Reactor 4 diodes 5 Capacitors

Claims

1. Equipped with a switching element and a reactor, The low-load current flowing through the reactor and the high-load current, whose average value is higher than the average value of the low-load current, both have a section in which they flow in the negative direction within one cycle. The switching element performs soft switching at both the low load current and the high load current. Controlling the ripple current at low load current to be smaller than the ripple current at high load current, A chopper circuit characterized by the following.

2. By adjusting the inductance value in the superposition characteristics of the reactor, the ripple current at low load current is controlled to be smaller than the ripple current at high load current. A chopper circuit according to claim 1, characterized by the following:

3. The inductance value at high load current is lower than the inductance value at low load current. The chopper circuit according to claim 2, characterized by the above.

4. In the inductance value when the reactor has superimposed characteristics, the maximum inductance value that results in the maximum inductance value is L ＭＡＸ If we assume that L is an arbitrary inductance value, then L / L ＭＡＸ The current at which this becomes 0.1 is defined as the maximum average current, the current with an average value of less than half of the maximum average current is the low-load current, and the current with an average value of more than half of the maximum average current is the high-load current. A chopper circuit according to any one of claims 1 to 3, characterized by the following:

5. The average value of the aforementioned low-load current is less than 4A. The average value of the aforementioned high load current is 4A or more. A chopper circuit according to any one of claims 1 to 3, characterized by the following:

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