Three-level converter, its controller circuit and control method, and electronic equipment using the same

Abstract

To provide a novel switched capacitor converter and a controller for the same.SOLUTION: A controller IC 200 can switch its state to first to fourth states φ1 to φ4. In the first state φ1, a first switch SW1 and a second switch SW2 are ON. In the second state φ2, the first switch SW1 and a third switch SW3 are ON. In the third state φ3, the third switch SW3 and a fourth switch SW4 are ON. In the fourth state φ4, the second switch SW2 and the fourth switch SW4 are ON. The controller IC 200 repeats in an order of the first state φ1, the second state φ2, the third state φ3, the first state φ1, the fourth state φ4, and the third state φ3.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a resonant switched capacitor converter.

Background Art

[0002] To generate a voltage higher or lower than the power supply voltage, a DC / DC converter or a charge pump is used. A DC / DC converter that uses an inductor as an energy storage element can control the output voltage by the inductor, but has a problem that the efficiency decreases due to the switching operation.

[0003] In applications that require high efficiency, a switched capacitor converter (charge pump) that does not require an inductor as an energy storage element is used. As one of these switched capacitor converters, one that adds an inductor for resonance in series with a flying capacitor and operates in resonance is known (referred to as a resonant switched capacitor converter). According to the resonant switched capacitor converter, zero current switching (soft switching) is possible, so high-efficiency operation is possible.

[0004] Also, a hybrid DC / DC converter, a three-level converter, a series capacitor DC / DC converter, etc. have been proposed. While a general DC / DC converter generates a switching signal having an amplitude corresponding to the input voltage V IN and stores energy in the inductor, a hybrid DC / DC converter, a three-level converter, and a series capacitor DC / DC converter use a capacitor to generate a switching signal having an amplitude of 1 / 2 of the input voltage V IN of V IN / 2 and store energy in the inductor. Thereby, the efficiency can be improved.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] This disclosure has been made in such a situation, and one of its exemplary purposes is to provide a novel switched capacitor converter and its controller.

Means for Solving the Problems

[0007] One aspect of this disclosure relates to a controller circuit of a three-level converter. The three-level converter includes a first switch, a second switch, a third switch, and a fourth switch connected in series between an input line and a ground line, a capacitor connected between both ends of the second switch and the third switch, and an inductor connected between a connection node of the second switch and the third switch and an output line. The controller circuit can be switched between a first state in which the first switch and the second switch are on, a second state in which the first switch and the third switch are on, a third state in which the third switch and the fourth switch are on, and a fourth state in which the second switch and the fourth switch are on, and repeats in the order of the first state, the second state, the third state, the first state, the fourth state, and the third state.

[0008] In addition, combinations of the above components arbitrarily, and components and expressions mutually replaced between methods, apparatuses, systems, etc. are also effective as aspects of the present invention.

Effects of the Invention

[0009] According to one aspect of this disclosure, the three-level converter can be operated in a zero-voltage switching mode, and the efficiency can be improved.

Brief Description of the Drawings

[0010]

Figure 1

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DETAILED DESCRIPTION OF THE INVENTION

[0011] (Overview of the Embodiment) An overview of some exemplary embodiments of the present disclosure will be described. This overview simplifies and describes some concepts of one or more embodiments for the purpose of providing a basic understanding of the embodiments as a prelude to the detailed description below, and does not limit the scope of the invention or disclosure. This overview is not an all-inclusive overview of all possible embodiments, nor is it intended to identify important elements of all embodiments or to delineate the scope of some or all aspects. For convenience, "an embodiment" may be used to refer to one embodiment (example or variant) or a plurality of embodiments (examples or variants) disclosed herein.

[0012] A controller circuit according to an embodiment controls a three-level converter. The three-level converter to be controlled includes a first switch, a second switch, a third switch, and a fourth switch connected in series between an input line and a ground line, a capacitor connected between both ends of the second switch and the third switch, and an inductor connected between a connection node of the second switch and the third switch and an output line. The controller circuit can switch between a first state in which the first switch and the second switch are on, a second state in which the first switch and the third switch are on, a third state in which the third switch and the fourth switch are on, and a fourth state in which the second switch and the fourth switch are on, and repeats in the order of the first state, the second state, the third state, the first state, the fourth state, and the third state.

[0013] This control sequence enables zero-voltage switching and can improve efficiency.

[0014] In one embodiment, the time of the first state and the time of the third state may be equal, and the time of the second state and the time of the fourth state may be equal. This simplifies the control and can also simplify the configuration of the controller circuit.

[0015] In one embodiment, the controller circuit may be able to control the time of the first state and the time of the third state according to the state of the load. By controlling the lengths of the first state and the third state, the average value of the coil current flowing through the inductor can be controlled.

[0016] In one embodiment, the controller circuit may include a feedback controller that performs feedback control on at least the lengths of the first state and the third state so that the error between the output voltage generated on the output line and the target level becomes small. Thereby, the output voltage can be stabilized at the target level.

[0017] In one embodiment, the feedback controller may include an error amplifier that amplifies the error between the output voltage generated on the output line and the target level, a pulse modulator that generates a pulse signal according to the output of the error amplifier, and a state control unit that switches from the first state to the fourth state according to the pulse signal.

[0018] In one embodiment, the controller circuit may be integrally integrated on a single semiconductor substrate. "Integral integration" includes cases where all of the circuit components are formed on the semiconductor substrate and cases where the main components of the circuit are integrally integrated, and some resistors, capacitors, etc. may be provided outside the semiconductor substrate for adjusting circuit constants. By integrating the circuit on one chip, the circuit area can be reduced and the characteristics of the circuit elements can be kept uniform.

[0019] (Embodiment) Hereinafter, the present invention will be described based on preferred embodiments with reference to the drawings. The same or equivalent components, members, and processes shown in each drawing are denoted by the same reference numerals, and repeated descriptions will be omitted as appropriate. Also, the embodiments are illustrative and not restrictive of the invention, and all features and combinations thereof described in the embodiments are not necessarily essential to the invention.

[0020] In this specification, the phrase "member A is in a connected state with member B" includes not only the case where member A and member B are physically directly connected, but also the case where member A and member B are indirectly connected via other members that do not substantially affect their electrical connection state or impair the functions and effects achieved by their connection.

[0021] Similarly, the phrase "member C is provided between member A and member B" includes not only the case where member A and member C, or member B and member C are directly connected, but also the case where they are indirectly connected via other members that do not substantially affect their electrical connection state or impair the functions and effects achieved by their connection.

[0022] Also, "signal A (voltage, current) is responsive to signal B (voltage, current)" means that signal A has a correlation with signal B. Specifically, it means (i) when signal A is signal B, (ii) when signal A is proportional to signal B, (iii) when signal A is obtained by level-shifting signal B, (iv) when signal A is obtained by amplifying signal B, (v) when signal A is obtained by inverting signal B, or (vi) any combination thereof, etc. It is understood by those skilled in the art that the scope of "responsive to" is determined according to the types and uses of signals A and B.

[0023] The vertical and horizontal axes of the waveform diagrams and time charts referred to in this specification are appropriately enlarged or reduced for ease of understanding, and each waveform shown is also simplified, exaggerated, or emphasized for ease of understanding.

[0024] (Embodiment) FIG. 1 is a circuit diagram of a resonant switched capacitor converter 100 according to an embodiment. The resonant switched capacitor converter 100 is a three-level converter and includes a controller IC (Integrated Circuit) 200 and its peripheral circuit 110. The resonant switched capacitor converter 100 receives an input voltage V supplied to an input line 102 INStep down the voltage and output the output voltage V to the output line 104 OUT Generate it.

[0025] Specifically, the peripheral circuit 110 includes the first switch SW1 to the fourth switch SW4, and the capacitors C1, C2, and the inductor L1. The first switch SW1 to the fourth switch SW4 are connected in series between the input line 102 and the ground line 106. One end of the capacitor C1 is connected to the first switching node n1, and the other end of the capacitor C1 is connected to the third switching node n3. In other words, the capacitor C1 is connected between both ends of the second switch SW2 and the third switch SW3.

[0026] The inductor L1 is connected between the connection node (the second switching node) n2 of the second switch SW2 and the third switch SW3 and the output line 104. The output capacitor C2 is connected to the output line 104. In this embodiment, the first switch SW1 to the fourth switch SW4 are N-channel MOSFETs, but this is not the only case, and some of them may be replaced with P-channels. Also, instead of MOSFETs, bipolar transistors or IGBTs (Insulated Gate Bipolar Transistors) may be used.

[0027] The controller IC200 drives the plurality of switches SW1 to SW4. The controller IC200 includes a drive circuit 210 and a state control unit 220, and is a functional IC integrated on one semiconductor chip. Note that the first switch SW1 to the fourth switch SW4 may be integrated into the controller IC200.

[0028] The controller IC200 is configured to be able to switch between four states φ1 to φ4. · The first state φ1 The first switch SW1 and the second switch SW2: ON The third switch SW3 and the fourth switch SW4: OFF · The second state φ2 The first switch SW1 and the third switch SW3: ON Second switch SW2 and fourth switch SW4: OFF · Third state φ3 Third switch SW3 and fourth switch SW4: ON First switch SW1 and second switch SW2: OFF · Fourth state φ4 Second switch SW2 and fourth switch SW4: ON First switch SW1 and third switch SW3: OFF

[0029] The controller IC200 repeats in the order of the first state φ1, the second state φ2, the third state φ3, the first state φ1, the fourth state φ4, and the third state φ3. The state transition is controlled by the state control unit 220. In the state transition, it is assumed that the switching from the ON state to the OFF state of each switch is performed first, and then the switching from the OFF state to the ON state is performed subsequently.

[0030] The state control unit 220 generates control signals S1 to S4 for instructing ON and OFF of the switches SW1 to SW4 in each of the states φ1 to φ4. The drive circuit 210 drives the corresponding switches SW1 to SW4 based on the control signals S1 to S4.

[0031] The above is the configuration of the resonant switched capacitor converter 100 and the controller IC200. Subsequently, its operation will be described.

[0032] FIG. 2 is an equivalent circuit diagram of the first state φ1 of the resonant switched capacitor converter 100 of FIG. 1. In the first state φ1, the first switch SW1 and the second switch SW2 are turned on. V n1 =V n2 =V IN Therefore, the voltage across both ends of the inductor L1 is V IN -V OUT And in the first state φ1, the coil current I of the inductor L1 L increases with a slope of (V IN -V OUT ) / L.

[0033] FIG. 3 is an equivalent circuit diagram of the second state φ2 of the resonant switched capacitor converter 100 of FIG. 1. In the second state φ2, the first switch SW1 and the third switch SW3 are turned on. Assuming the voltage across the capacitor C1 is Vc, in the second state φ2, V n3 =V n2 =V IN -Vc. At this time, the voltage across the inductor L1 is V n2 -V OUT =(V IN -Vc)-V OUT , and in the second state φ2, the coil current I L of the inductor L1 changes with a slope of (V IN -Vc-V OUT ) / L. In the steady state, since Vc≒V IN / 2, the coil current I L is substantially constant.

[0034] FIG. 4 is an equivalent circuit diagram of the third state φ3 of the resonant switched capacitor converter 100 of FIG. 1. In the third state φ3, the third switch SW3 and the fourth switch SW4 are turned on. The voltage across the inductor L1 is -V OUT , and in the third state φ3, the coil current I L of the inductor L1 increases (decreases with a slope of -V OUT / L) with a slope of -V OUT / L.

[0035] FIG. 5 is an equivalent circuit diagram of the fourth state φ4 of the resonant switched capacitor converter 100 of FIG. 1. In the fourth state φ4, the second switch SW2 and the fourth switch SW4 are turned on. Assuming the voltage across the capacitor C1 is Vc, in the fourth state φ4, V n2 =Vc. At this time, the voltage across the inductor L1 is V n2 -V OUT =Vc-V OUT , and in the fourth state φ4, the coil current I L of the inductor L1 changes with a slope of (Vc-V OUT ) / L. In the steady state, since Vc≒V IN / 2, the coil current IL It becomes substantially a fixed amount.

[0036] FIG. 6 is a waveform diagram for explaining the operation of the resonant switched capacitor converter 100. In FIG. 6, the coil current I flowing through the inductor L1 L is shown. When the time length of the first state φ1 is t on1 and the time length of the third state φ3 is t on3 , the change amount ΔI L of the coil current I L1 in the first state φ1 L and the change amount ΔI L3 of the coil current I ΔI L1 = (V IN - V OUT ) / L × t on1 ΔI L3 = -V OUT / L × t on3 becomes. In the steady state, when the coil current I L is stabilized, the absolute values of ΔI L1 and ΔI L3 are equal. (V IN - V OUT ) / L × t on1 = V OUT / L × t on3 t on1 = t on3 is imposed as a constraint condition, (V IN - V OUT ) = V OUT is obtained. That is, in the steady state, V OUT = V IN / 2 can be obtained.

[0037] According to this resonant switched capacitor converter 100, zero voltage switching becomes possible, and thereby low-loss and high-efficiency operation can be realized. The reason will be explained.

[0038] · Transition from the first state φ1 to the second state φ2 In the steady state, Vc = V IN / 2, V OUT = V IN / 2 holds. In the first state φ1, V n1 = V n2 = V IN , V n3 = V IN / 2. When the second switch SW2 turns off during the transition from the first state φ1 to the second state φ2, the current flows through the body diode of the MOSFET which is the third switch SW3, resulting in the same current path as the second state. The switching voltage V n2 decreases to V IN / 2, and the drain-source voltage of the MOSFET which is the third switch SW3 becomes zero. When the third switch SW3 turns on in this state, zero-voltage switching occurs and no loss is generated.

[0039] · Transition from the second state φ2 to the third state φ3 In the second state φ2, V n1 = V IN , V n2 = V n3 = V IN / 2. When the first switch SW1 turns off during the transition from the second state φ2 to the third state φ3, the current flows through the body diode of the MOSFET which is the fourth switch SW4, resulting in the same current path as the third state φ3. The switching voltage V n3 decreases to 0V, and the drain-source voltage of the MOSFET which is the fourth switch SW4 becomes zero. When the fourth switch SW4 turns on in this state, zero-voltage switching occurs and no loss is generated.

[0040] · Transition from the third state φ3 to the first state φ1 In the third state φ3, V n1 = V n2 = V IN / 2, V n3 = 0V (GND). In the third state φ3, as shown in Figure 6, the coil current I Ldecreases and becomes a negative current (reverse current). When the third switch SW3 and the fourth switch SW4 turn off during the transition from the third state φ3 to the first state φ1, the current flows into the input line 102 via the body currents of the MOSFETs that are the first switch SW1 and the second switch SW2, resulting in the same current path as in the first state φ1. At this time, since the voltage V n1 of the first switching node n1 is equal to the input voltage V IN , the drain-source voltages of the MOSFETs that are the first switch SW1 and the second switch SW2 become zero. When the first switch SW1 and the second switch SW2 turn on in this state, zero-voltage switching occurs and no loss is generated.

[0041] The above is the reason for zero-voltage switching. The advantages of the resonant switch capacitor converter 100 become clear by comparison with comparative technologies.

[0042] In the comparative technology, assume that a three-level converter is switched among the following three states. · State I The first switch SW1, the third switch SW3; ON The second switch SW2, the fourth switch SW4; OFF

[0043] · State II The third switch SW3, the fourth switch SW4; ON The first switch SW1, the second switch SW2; OFF

[0044] · State III The second switch SW2, the fourth switch SW4; ON The first switch SW1, the third switch SW3; OFF

[0045] States I to III respectively correspond to states φ2, φ3, and φ4 in the embodiment. In the comparative technology, states I, II, III, and II are taken as one cycle and this is repeated. In state I, the capacitor C1 is charged, and in state III, the energy stored in the capacitor C1 is supplied to the inductor L1.

[0046] Figure 7 is a diagram for explaining the operation of a three-level converter according to the comparative technique. Coil current I is shown in Figure 7. In state I, the voltage across both ends of inductor L1 is (V L -Vc)-V IN -Vc)-V OUT and coil current I L changes with a slope of {(V IN -Vc)-V OUT} / L. In state II, the voltage across both ends of inductor L1 is -V OUT and coil current I L changes with a slope of -V OUT / L.

[0047] In state III, the voltage across both ends of inductor L1 is Vc-V OUT and coil current I L changes with a slope of {Vc-V OUT} / L.

[0048] Assuming the time of state I and state III is t on and the time of state II is t off , the change amounts ΔI L ~ΔI L1 ~ΔI L3 of coil current I ΔI L1 ={(V IN -Vc)-V OUT} / L×t on …(1) ΔI L2 =-V OUT / L×t off …(2) ΔI L3 ={Vc-V OUT} / L×t on …(3) In the steady state, when the average value of coil current I L is constant, ΔI L1 =|ΔI L2 |=ΔI L3 holds. Since equations (1) and (3) are equal, Vc=V IN / 2 to obtain this. Substituting this into Equation (1) gives ΔI L1 =(V IN / 2 - V OUT ) / L×t on …(1’) to obtain this. Since the absolute values of Equation (1’) and Equation (2) are equal, Equation (4) is obtained. V OUT =V IN / 2×t on / (t on +t off ) = V IN / 2×d …(4) where d = t on / (t on +t off ) and represents the duty cycle. When d = 0.5, V OUT =V IN / 4.

[0049] The above is the operation of the three - level converter according to the comparative technique. In the comparative technique, when transitioning from state II to III, first switch SW3 turns off. After switch SW3 turns off, since the current flows through the body diode of switch SW3, the current path remains in state II. At this time, since the drain - source voltage of the second switch SW2 is non - zero, turning on the second switch SW2 in this state results in hard switching and power loss occurs.

[0050] When transitioning from state II to I, first switch SW4 turns off. After switch SW4 turns off, since the current flows through the body diode of switch SW4, the current path remains in state II. At this time, since the drain - source voltage of the first switch SW1 is non - zero, turning on the first switch SW1 in this state results in hard switching and power loss occurs.

[0051] Thus, hard switching occurs in the comparative technique.

[0052] On the other hand, according to the controller IC200 according to the embodiment, soft switching can be realized, so that the efficiency can be improved.

[0053] When the controller IC200 according to the embodiment operates in an open loop, it operates as a converter with a gain of 1 / 2 times. However, by incorporating feedback control, the gain, that is, the output voltage V OUT can be set.

[0054] FIG. 8 is a circuit diagram of a resonant switched capacitor converter 100A including a controller IC200A with a feedback function. The controller IC200A can control the lengths of the first state φ1 and the third state φ3 according to the state of the load. The control method may be PWM (pulse width modulation) or PFM (pulse frequency modulation). In the case of PWM, when the lengths of the first state φ1 and the third state φ3 are t on and the pulse period is Tp, the lengths t off of the second state φ2 and the fourth state φ4 are Tp - t on . In the case of PFM control, the lengths t off of the second state φ2 and the fourth state φ4 may be constant.

[0055] The controller IC200A includes a feedback controller 230 in addition to the drive circuit 210 and the state control unit 220. A feedback signal V OUT corresponding to the output voltage V FB generated on the output line 104 is input to the feedback pin FB of the controller IC200A. The feedback signal V FB may be a voltage obtained by dividing the output voltage V OUT by resistors R11 and R12, or may be the output voltage V OUT itself.

[0056] The feedback controller 230 makes the error between the feedback signal V FB and the reference voltage V REF zero. In other words, the output voltage V OUT and the target level V OUT(REF)At least the lengths t of the first state and the third state are feedback-controlled so that the error becomes small. on Perform feedback control.

[0057] The feedback controller 230 can be configured in the same manner as the modulator used in the DC / DC converter.

[0058] FIG. 9 is a circuit diagram showing a configuration example of the feedback controller 230 and the state control unit 220. The feedback controller 230 includes an error amplifier 232 and a pulse modulator 234. The error amplifier 232 amplifies the error between the feedback signal V FB and the reference voltage V REF to generate an error signal V ERR . The pulse modulator 234 generates a pulse signal Sp according to the error signal V ERR . In this example, the pulse modulator 234 is a pulse width modulator and generates the pulse signal Sp in synchronization with the oscillator 236. The pulse width of the pulse signal Sp is controlled according to the error signal V ERR .

[0059] The state control unit 220 receives the pulse signal Sp and the clock CLK generated by the oscillator 236. The state control unit 220 sequentially switches between the first state φ1, the second state φ2, the third state φ3, the first state φ1, the fourth state φ4, and the third state φ3 according to the pulse signal Sp and the clock CLK. The lengths of the first state φ1 and the third state φ3 change according to the pulse width of the pulse signal Sp.

[0060] (Modification example) It is understood by those skilled in the art that the above-described embodiments are examples, and various modifications are possible for the combination of each of these components and each processing process. Hereinafter, such modification examples will be described.

[0061] In FIG. 9, the case where the feedback controller 230 is configured by an analog circuit has been described, but it may also be configured by a digital circuit. In this case, the error amplifier 232 is replaced by a subtractor and a compensator (controller). As the compensator, a PID (Proportional Integral Derivative) compensator or a PI (Proportional Integral) compensator can be used.

[0062] Also, in FIG. 8, the controller IC200A for a constant current output that stabilizes the output voltage V OUT has been described, but the present invention is also applicable to a converter with a constant current output. In this case, as the feedback signal V FB , a signal indicating the output current I OUT may be used.

[0063] (Application) FIG. 10 is a diagram showing an example of an electronic device 700 including a resonant switched capacitor converter 100. A preferred example of the electronic device 700 is a server. Originally, since a 12V power line was drawn into the server, the internal circuit 710 was designed to operate at 12V. The internal circuit 710 may include a CPU (Central Processing Unit), a memory, an interface circuit for a LAN (Local Area Network), and a DC / DC converter that steps down the 12V voltage.

[0064] In recent years, in order to reduce the current flowing through the electric wire, a movement to replace the bus voltage from 12V to 48V has been promoted. In this case, a power supply circuit 720 that steps down the 48V power supply voltage to 12V or 24V is required. The resonant switched capacitor converter 100 can be suitably used for such a power supply circuit 720.

[0065] The electronic device 700 is not limited to a server and may be an in-vehicle device. Conventional automotive batteries are mainly 12V or 24V, but in hybrid vehicles, a 48V system may be adopted. In this case as well, a power supply circuit for converting the 48V battery voltage to 12V or 24V is required. In such a case, the 1 / 2 - fold resonant switched capacitor converter 100 can be suitably used.

[0066] In addition, the electronic device 700 may be an industrial device, an OA device, or a consumer device such as an audio device.

[0067] The embodiments are illustrative, and those skilled in the art will understand that there are various variations in the combination of each component and each processing process, and such variations are also included in the present disclosure and can constitute the scope of the present invention.

Explanation of Reference Numerals

[0068] 100 Resonant switched capacitor converter 102 Input line 104 Output line 106 Ground line 110 Peripheral circuit SW1 First switch SW2 Second switch SW3 Third switch SW4 Fourth switch C1 Capacitor L1 Inductor C2 Capacitor 200 Controller IC 210 Drive circuit 220 State control unit 230 Feedback controller 232 Error amplifier 234 Pulse modulator 236 Oscillator

Claims

1. A controller circuit for a three-level converter, wherein the three-level converter comprises a first switch, a second switch, a third switch, and a fourth switch connected in series between an input line and a ground line; a capacitor connected between both ends of the second switch and the third switch; an inductor connected between a connection node of the second switch and the third switch and an output line; and the controller circuit repeats, in the order of the first state in which the first switch and the second switch are on, the second state in which the first switch and the third switch are on, the third state in which the third switch and the fourth switch are on, the fourth state in which the second switch and the fourth switch are on, the first state, the second state, the third state, the first state, the fourth state, and the third state. A controller circuit.

2. The controller circuit according to claim 1, wherein the time of the first state is equal to the time of the third state, and the time of the second state is equal to the time of the fourth state.

3. The controller circuit according to claim 1 or 2, wherein the controller circuit can control the lengths of the first state and the third state according to the state of the load.

4. The controller circuit comprises a feedback controller that performs feedback control on at least the lengths of the first state and the third state so that the error between the output voltage generated on the output line and the target level is reduced. The controller circuit according to any one of claims 1 to 3.

5. The feedback controller comprises an error amplifier that amplifies the error between the output voltage generated on the output line and the target level; a pulse modulator that generates a pulse signal according to the output of the error amplifier; and a state control unit that switches from the first state to the fourth state according to the pulse signal. The controller circuit according to claim 4.

6. The controller circuit according to any one of claims 1 to 5, which is integrally integrated on a single semiconductor substrate.

7. A three-level converter comprising the controller circuit according to any one of claims 1 to 6.

8. An electronic device comprising the three-level converter according to claim 7.

9. A control method for a three-level converter, wherein the three-level converter A first switch, a second switch, a third switch, and a fourth switch connected in series between an input line and a ground line; A capacitor connected between both ends of the second switch and the third switch; An inductor connected between a connection node of the second switch and the third switch and an output line; Comprising; The control method is as follows: A first state in which the first switch and the second switch are on; A second state in which the first switch and the third switch are on; A third state in which the third switch and the fourth switch are on; The first state; A fourth state in which the second switch and the fourth switch are on; The third state; A control method that repeats them in order.

10. The control method according to claim 9, further comprising a step of feedback controlling at least the lengths of the first state and the third state so that an error between an output voltage generated on the output line and a target level becomes small.

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