JP7535477B2 - DC/DC converter and power supply device - Google Patents

Description

The present invention relates to a DC/DC converter and a power supply device.

In recent years, the number of high-capacity quick chargers for electric vehicles, exceeding 100 kW, has been increasing in line with the increase in battery capacity of electric vehicles. This has made it increasingly important to make the power supply devices used in quick chargers smaller, more efficient, and less expensive.

The power supply device of a quick charger is equipped with an AC/DC power supply unit and a DC/DC power supply unit. Conventionally, a voltage-current type DC/DC converter was used as the DC/DC power supply unit, but in recent years, in light of the above background, current-resonant type DC/DC converters such as the LLC type and CLLC type that utilize current-resonant technology are beginning to be used.

The CHAdeMO charging standard stipulates that a diode must be installed at the output of the power supply unit of a quick charger. Therefore, when the output of the power supply unit is connected to the electric vehicle's battery, the electric vehicle's battery voltage is not applied to the output terminal of the DC/DC converter, so the output voltage of the DC/DC converter is 0 V.

Therefore, DC/DC converters must start up from a state where the output voltage is 0 [V], and startup control is required to gradually increase the output voltage while controlling the current so that excessive inrush current does not flow to the output capacitor at startup.

Patent Document 1 describes a power supply device that includes a current resonant converter (current resonant DC/DC converter) and a boost DC/DC converter. The power supply device described in Patent Document 1 operates the boost DC/DC converter before starting the switching operation of the current resonant converter, and controls the voltage of the smoothing capacitor of the current resonant converter to a predetermined voltage higher than the voltage of the storage battery to which the boost DC/DC converter is output. This control makes it possible to prevent excessive current from flowing at startup. However, in the power supply device described in Patent Document 1, the inclusion of the boost DC/DC converter hinders the miniaturization and cost reduction of the power supply device.

Patent Document 2 also describes a power supply device that includes an isolated resonant converter (current resonant DC/DC converter) and a DC converter. The power supply device described in Patent Document 2 switches the first and second switching elements of the isolated resonant converter at startup to perform startup processing, and starts tracking control of the output voltage to a target value after the startup processing has started. This enables a soft start that suppresses the occurrence of inrush current and voltage surges at startup. However, the power supply device described in Patent Document 2 includes a DC converter and controls the switching elements of the DC converter to adjust the first DC voltage (input voltage of the isolated resonant converter) over a wide range, which hinders the miniaturization, high efficiency, and low cost of the power supply device.

WO2017/022477 publication Patent No. 6021972

The present invention was made in consideration of the above circumstances, and its objective is to provide a DC/DC converter and power supply device that can prevent excessive current from flowing during startup without impeding miniaturization, high efficiency, and low cost.

In order to solve the above problems, a DC/DC converter according to the present invention comprises:
an isolation transformer including a primary coil and a secondary coil;
A primary circuit connected to the primary coil;
A secondary circuit connected to the secondary coil;
A control circuit for controlling the primary side circuit;
A current resonance type DC/DC converter comprising:
The primary side circuit includes:
a full bridge circuit in which a first leg consisting of a first arm and a second arm and a second leg consisting of a third arm and a fourth arm are connected in parallel, a resonant coil, and a resonant capacitor;
the resonant coil, the resonant capacitor, and the primary coil are connected in series between a first connection point of the first arm and the second arm and a second connection point of the third arm and the fourth arm,
Each of the first arm, the second arm, the third arm, and the fourth arm is
A switching element that is turned on/off under the control of the control circuit;
a diode connected in parallel in a reverse direction to the switching element;
a capacitor connected in parallel to the switching element,
The control circuit includes:
during a startup period from startup until an output voltage of the secondary side circuit reaches a first target value, a drive frequency of the full bridge circuit is set to a first drive frequency higher than a resonant frequency determined by the resonant coil and the resonant capacitor, and a frequency control is started;
The phase shift control is started by setting a predetermined first phase shift amount between the first leg and the second leg, and the phase shift amount is reduced to a second phase shift amount smaller than the first phase shift amount by the end of the startup period.

With this configuration, by performing frequency control and phase shift control during the startup period, it is possible to prevent excessive current from flowing during startup without using additional components such as a DC/DC converter for boosting or a DC/DC converter for lowering the input voltage. Moreover, since the first drive frequency is set higher than the resonant frequency, it is possible to avoid the occurrence of through current in the switching element due to phase shift control.

In the DC/DC converter,
The control circuit includes:
The drive frequency may be reduced to a second drive frequency that is equal to or lower than the resonant frequency by the end of the start-up period.

In the DC/DC converter,
The control circuit includes:
During the startup period, in a first period in which the phase shift amount is reduced from the first phase shift amount to a third phase shift amount between the first phase shift amount and the second phase shift amount, the drive frequency may be controlled so that the drive frequency is always greater than the resonant frequency.

In the DC/DC converter,
The control circuit includes:
During the startup period, the target value of the output voltage may be set to zero or a second target value smaller than the first target value to start the frequency control and the phase shift control, and the target value may be increased to the first target value over time.

In order to solve the above problems, a power supply device according to the present invention comprises:
an AC/DC power supply unit that converts an AC input voltage into a DC output voltage;
a DC/DC power supply unit including any one of the DC/DC converters and receiving the DC output voltage;
A control unit that controls the AC/DC power supply unit and the DC/DC power supply unit;
A power supply device comprising:
The control unit is
starting the AC/DC power supply unit and then starting the DC/DC power supply unit;
The present invention is characterized in that, during a start-up period of the DC/DC power supply unit, the AC/DC power supply unit is controlled so that the DC output voltage of the AC/DC power supply unit becomes the minimum voltage that the AC/DC power supply unit can output and that the DC/DC power supply unit can perform power conversion operation.

The present invention provides a DC/DC converter and a power supply device that can prevent excessive current from flowing during startup without impeding miniaturization, high efficiency, and low cost.

1 is a circuit diagram of a DC/DC converter according to the present invention; 10A and 10B are diagrams relating to a comparative example, in which FIG. 10A shows a change in drive frequency during a startup period, and FIG. 10B shows a change in output voltage and a change in current of a switching element during the startup period. 1A and 1B are diagrams showing the amount of phase shift in a DC/DC converter according to the present invention, where FIG. 1A is a diagram showing the amount of phase shift at the start of a start-up period, and FIG. 1A is a diagram showing a change in the amount of phase shift during the startup period; FIG. 1B is a diagram showing a change in the drive frequency during the startup period; and FIG. 1C is a diagram showing a change in the output voltage and a change in the current of the switching element during the startup period. 1 is a block diagram of a power supply device according to the present invention. 1A is a circuit diagram of a DC/DC converter according to a first modified example, and FIG. 1B is a circuit diagram of a DC/DC converter according to a second modified example.

Below, we will explain the embodiments of the DC/DC converter and power supply device according to the present invention with reference to the attached drawings.

[DC/DC converter]
1 shows a DC/DC converter 10A according to one embodiment of the present invention. The DC/DC converter 10A is a current resonance type converter including an insulating transformer Tr, a primary circuit 11, a secondary circuit 12, a control circuit 13, and various detection circuits (not shown).

The isolation transformer Tr is a high-frequency isolation transformer that includes a primary coil consisting of an n1 winding and a secondary coil consisting of n2 windings and n3 windings connected in series via a center tap. The isolation transformer Tr may be configured with one or more units depending on the capacity.

The primary circuit 11 includes input terminals T1 and T2, a full bridge circuit, a resonant capacitor Cr, a resonant coil Lr, and an exciting coil Lm. The resonant coil Lr can be partially or entirely composed of the leakage inductance of the insulating transformer Tr, and the exciting coil Lm can be composed of the exciting inductance of the insulating transformer Tr.

The full bridge circuit comprises a first leg consisting of a first arm and a second arm connected in series, and a second leg consisting of a third arm and a fourth arm connected in series. The first leg and the second leg are connected in parallel. The first arm comprises a switching element Q1, a diode D1, and a capacitor C1. The second arm comprises a switching element Q2, a diode D2, and a capacitor C2. The third arm comprises a switching element Q3, a diode D3, and a capacitor C3. The fourth arm comprises a switching element Q4, a diode D4, and a capacitor C4.

A switching element capable of switching at high frequencies is used for switching element Q1. For example, it is a power semiconductor switching element such as an IGBT (insulated gate bipolar transistor), MOSFET (metal oxide semiconductor field effect transistor), SiC (silicon carbide)-MOSFET, or GaN (gallium nitride)-MOSFET. The same applies to switching elements Q2 to Q4.

Diode D1 is connected in parallel in the reverse direction to the current path of switching element Q1. Diode D1 may be a parasitic diode of switching element Q1, or may be an individual diode independent of switching element Q1. The same applies to diodes D2 to D4.

Capacitor C1 is connected in parallel to the current path of switching element Q1 and diode D1. Capacitor C1 may be a parasitic capacitor of switching element Q1, or may be an individual capacitor independent of switching element Q1. The same applies to capacitors C2 to C4.

The first connection point X1 of the switching element Q1 and the switching element Q2 and the second connection point X2 of the switching element Q3 and the switching element Q4 are connected in series to the n1 winding via the resonant capacitor Cr and the resonant coil Lr. The excitation coil Lm is connected in parallel to the n1 winding.

In FIG. 1, the resonant coil Lr and the excitation coil Lm are shown separately from the n1 winding of the insulating transformer Tr, but the resonant coil Lr and the excitation coil Lm may be included in the n1 winding. Furthermore, in FIG. 1, the resonant capacitor Cr and the resonant coil Lr are provided between the first connection point X1 and the n1 winding, but the resonant capacitor Cr and the resonant coil Lr may be provided between the n1 winding and the second connection point X2. Alternatively, one of the resonant capacitor Cr and the resonant coil Lr may be provided between the first connection point X1 and the n1 winding, and the other may be provided between the n1 winding and the second connection point X2. Alternatively, the constants of the resonant capacitor Cr and the resonant coil Lr may be divided and provided on both sides of the n1 winding.

The secondary circuit 12 includes a rectifier circuit consisting of diodes D5 and D6, a capacitor Co, and output terminals T3 and T4. The secondary circuit 12 rectifies the induced voltage of the n2 winding and the n3 winding with the rectifier circuit consisting of diodes D5 and D6, smoothes it with the capacitor Co, and converts it into a DC voltage (output voltage Vo) for output.

The control circuit 13 includes drive circuits for the switching elements Q1 to Q4 for turning the switching elements Q1 to Q4 on and off, and a control signal generation circuit for sending control signals to each drive circuit. The control circuit 13 may be configured as an analog control circuit, a digital control circuit using a microcontroller or the like, or a circuit that combines an analog control circuit and a digital control circuit.

The control circuit 13 starts up when the power supply voltage is supplied, executes startup control during a predetermined startup period, and executes normal control during a normal period after the startup period ends. The startup period is, for example, the period from startup to when the output voltage Vo reaches a first target value (for example, 400 [V]).

During the startup period, the control circuit 13 sets the target value of the output voltage Vo to zero or a second target value smaller than the first target value, starts output control (phase shift control and frequency control, described below), and increases the target value to the first target value at a predetermined voltage step or voltage change rate as time passes. The value of the voltage step or voltage change rate can be set appropriately. During the startup period, power is not supplied to the load connected to the output terminals T3 and T4, and power supply to the load is started at the start of the normal period.

In the current resonant DC/DC converter 10A, when the switching elements Q1 to Q4 are turned on/off at a drive frequency higher than the first resonant frequency (corresponding to the "resonant frequency" of the present invention) determined by the resonant capacitor Cr and the resonant coil Lr, the output gain falls below 1. However, the rate at which the output gain falls with respect to changes in drive frequency is small, and controllability is poor. For this reason, during normal control, the control circuit 13 sets the drive frequency of the switching elements Q1 to Q4 to a value within a frequency range that is lower than the first resonant frequency at which the output gain is 1 and higher than the second resonant frequency determined including the excitation coil Lm, and controls the output voltage Vo or output current.

If the control circuit 13 executes normal control during the startup period when no charge is stored in the capacitor Co, an overcurrent will flow through the capacitor Co, causing an overcurrent to flow through the switching elements Q1 to Q4 and generating an overvoltage in the resonant capacitor Cr. One possible solution to this problem is to make the drive frequency of the switching elements Q1 to Q4 higher than the first resonant frequency during the startup period, but in that case, it is necessary to limit the overcurrent separately from controlling the drive frequency. Furthermore, if the drive frequency is made too high above the first resonant frequency, the switching loss of the switching elements Q1 to Q4 will increase and the power consumption of each drive circuit for the switching elements Q1 to Q4 will also increase, so the drive frequency cannot be increased unnecessarily.

As a comparative example, Figure 2 shows the changes in drive frequency, output voltage Vo, and current of switching element Q1 when control circuit 13 simply controls the drive frequency. In the figure, 0 to 95 ms is the startup period, and 95 ms onwards is the normal period. The resonant frequency determined by resonant capacitor Cr and resonant coil Lr is 128 kHz.

As shown in FIG. 2(A), the control circuit 13 starts frequency control by setting the drive frequency of the switching elements Q1 to Q4 to a first drive frequency f1 (f1 = 150 kHz) that is greater than the resonant frequency at the start of the startup period, and reduces the drive frequency to a second drive frequency f2 (f2 = 103 kHz) that is less than the resonant frequency at the end of the startup period (95 ms). Note that at the 100 ms point in the normal period, the drive frequency is 100 kHz.

If the control circuit 13 simply controls the drive frequency, as shown in FIG. 2(B), the output voltage Vo rises from 0 [V] to 400 [V], but at the start of the startup period, an overcurrent of approximately 200 [A] flows through the switching element Q1.

Therefore, in this embodiment, phase shift control is executed together with frequency control as startup control. Specifically, the control circuit 13 starts phase shift control by setting the phase shift amount between the first leg (switching elements Q1, Q2) and the second leg (switching elements Q3, Q4) to a predetermined first phase shift amount during the startup period, and reduces the phase shift amount until it becomes a second phase shift amount that is smaller than the first phase shift amount by the end of the startup period.

Figure 3 (A) shows the on/off timing of the switching elements Q1 to Q4 when phase shift control is performed with a first phase shift amount θ1. The first phase shift amount θ1 is an angle of 180 degrees or close to 180 degrees (e.g., an angle of 150 degrees or more). Figure 3 (B) shows the on/off timing of the switching elements Q1 to Q4 when phase shift control is performed with a second phase shift amount θ2. The second phase shift amount θ2 is an angle of 0 degrees or close to 0 degrees (e.g., an angle of 30 degrees or less). During the startup period, the control circuit 13 reduces the phase shift amount by a fixed amount or continuously at regular intervals so that the phase shift amount becomes the second phase shift amount θ2 from the first phase shift amount θ1.

Figure 4 shows the changes in the phase shift amount, drive frequency, output voltage Vo, and current of switching element Q1 when control circuit 13 executes startup control (phase shift control and frequency control). The period from 0 to 95 ms in the figure is the startup period, and the period from 95 ms onwards is the normal period. The resonant frequency determined by resonant capacitor Cr and resonant coil Lr is 128 kHz.

As shown in FIG. 4(A), the control circuit 13 starts phase shift control by setting the phase shift amount to the first phase shift amount θ1 (θ1 = 160 degrees) at the start of the startup period, and gradually reduces the phase shift amount until it becomes the second phase shift amount θ2 (θ2 = 6 degrees) at the end of the startup period (95 ms).

Also, as shown in FIG. 4B, the control circuit 13 starts frequency control by setting the drive frequency of the switching elements Q1 to Q4 to a first drive frequency f1 (f1 = 150 kHz) that is greater than the resonant frequency at the start of the startup period, and reduces the drive frequency to a second drive frequency f2 (f2 = 103 kHz) that is less than the resonant frequency at the end of the startup period (95 ms). Note that at the 100 ms point in the normal period, the phase shift amount is 0 degrees and the drive frequency is 100 kHz.

When the control circuit 13 executes phase shift control and frequency control, the output voltage Vo rises from 0 [V] to 400 [V], as shown in FIG. 4(C). Compared with FIG. 2(B), it can be seen that the overcurrent at the start of the startup period is significantly suppressed in FIG. 4(C). In this way, by setting the first drive frequency f1 to a frequency higher than the resonant frequency (within a range in which the switching losses of the switching elements Q1 to Q4 can be tolerated) and setting the first phase shift amount θ1 to an angle close to 180 degrees, the overcurrent at startup can be significantly suppressed.

In FIG. 4, the first drive frequency f1 is set to 150 kHz and the first phase shift amount θ1 is set to 160 degrees, but the first drive frequency f1 can be selected according to the constants of the LLC resonant circuit, and the first phase shift amount θ1 can be selected arbitrarily as long as the current flowing through the switching elements Q1 to Q4 and the voltage generated in the resonant capacitor Cr in combination with the drive frequency are within the allowable range.

The second phase shift amount θ2 can be selected based on the value of the output voltage Vo at the end of the startup period, which is determined by the second drive frequency f2 and the phase shift period. For example, when a lithium-ion battery of an electric vehicle is connected to the output terminals T3 and T4 after the startup period ends, it is preferable that the voltage (output voltage Vo) at the output terminals T3 and T4 be lower than the battery voltage of the lithium-ion battery. Therefore, the second phase shift amount θ2 is selected so that the output voltage Vo at the end of the startup period is lower than the battery voltage.

In conclusion, the DC/DC converter 10A according to this embodiment can prevent excessive current from flowing at startup without using additional components such as a DC/DC converter for boosting the voltage or a DC/DC converter for lowering the input voltage.

In addition, in the DC/DC converter 10A according to this embodiment, even if the phase shift amount in the phase shift control is a large angle (180 degrees or an angle close to 180 degrees), the drive frequency is set higher than the resonant frequency, so the excitation current is reduced, and even in the case of a large phase shift amount, the direction reversal of the excitation current is unlikely to occur. This makes it possible to avoid the occurrence of through current in the switching elements Q1 to Q4, and thus allows startup control to be executed safely.

[Power supply]
5 shows a power supply device 1A according to one embodiment of the present invention. The power supply device 1A includes AC terminals T5 and T6, an AC/DC power supply unit 20, a DC/DC power supply unit 10, and a control unit 30.

The AC/DC power supply unit 20 performs an AC/DC conversion operation to convert the AC input voltage Vac input to the AC terminals T5 and T6 into a DC voltage Vi and output it to the DC/DC power supply unit 10. The AC/DC power supply unit 20 includes an AC/DC inverter composed of multiple switching elements.

The DC/DC power supply unit 10 includes a DC/DC converter 10A. Specifically, the DC/DC power supply unit 10 includes an insulating transformer Tr, a primary circuit 11, and a secondary circuit 12 that constitute the DC/DC converter 10A.

The control unit 30 controls the AC/DC power supply unit 20 and the DC/DC power supply unit 10. The control unit 30 includes, for example, a control circuit that controls the AC/DC power supply unit 20 and a control circuit (control circuit 13 of the DC/DC converter 10A) that controls the DC/DC power supply unit 10.

The control unit 30 starts up when the power supply voltage is supplied, and starts up the AC/DC power supply unit 20 first, and then the DC/DC power supply unit 10. When starting up the DC/DC power supply unit 10, the control unit 30 controls the AC/DC power supply unit 20 so that the DC voltage Vi of the AC/DC power supply unit 20 becomes the minimum voltage that the AC/DC power supply unit 20 can output and that the DC/DC power supply unit 10 can perform power conversion operations. Then, the control unit 30 executes startup control of the DC/DC power supply unit 10 (DC/DC converter 10A) when the DC voltage Vi is at the minimum voltage.

Even if the drive frequency of the full bridge circuit (switching elements Q1 to Q4) included in the primary circuit 11 of the DC/DC power supply unit 10 is constant, if the DC voltage Vi is small, the output voltage Vo of the DC/DC power supply unit 10 also becomes small, and the overcurrent flowing through the capacitor Co is relatively suppressed. Therefore, by setting the DC voltage Vi to the minimum voltage and starting the startup control of the DC/DC power supply unit 10, it becomes possible to select a combination of smaller values for the first drive frequency f1 and the first phase shift amount θ1, and the overcurrent suppression effect at startup is increased.

In addition, in the DC/DC power supply unit 10, the excitation current also decreases as the DC voltage Vi decreases, so that even in the case of a large phase shift, the direction of the excitation current is unlikely to reverse, and the occurrence of through current in the switching elements Q1 to Q4 can be avoided, allowing startup control to be performed safely.

The above describes the embodiments of the DC/DC converter and power supply device according to the present invention, but the present invention is not limited to the above embodiments.

[First Modification]
6A shows a DC/DC converter 10B according to a first modified example. The DC/DC converter 10B has the same configuration as the DC/DC converter 10A according to the above embodiment, except for the configuration of the secondary coil of the insulating transformer Tr′ and the secondary circuit 12′.

The insulating transformer Tr' is a high-frequency insulating transformer that includes a primary coil and a secondary coil that does not have a center tap. The insulating transformer Tr' may be configured with one or more transformers depending on the capacity.

The secondary circuit 12' includes full-bridge-connected diodes D5 to D8, a capacitor Co, and output terminals T3 and T4. The secondary circuit 12' rectifies the induced voltage of the secondary coil of the isolation transformer Tr' using a rectifier circuit made up of diodes D5 to D8, smoothes it using the capacitor Co, and converts it into a DC voltage (output voltage Vo) for output.

DC/DC converter 10B has the same effects as DC/DC converter 10A. Furthermore, DC/DC converter 10B has a circuit configuration designed for higher power compared to DC/DC converter 10A.

[Second Modification]
6B shows a DC/DC converter 10C according to a second modification. The DC/DC converter 10C is the same as the first modification, except for the configuration of a secondary side circuit 12″ and the fact that a control circuit 13′ performs synchronous rectification control on the secondary side circuit 12″.

The secondary circuit 12'' includes a full bridge circuit, a capacitor Co, and output terminals T3 and T4. The full bridge circuit is composed of a fifth arm to an eighth arm that are fully bridge connected. The fifth arm to the eighth arm have the same configuration as the first arm to the fourth arm of the DC/DC converter 10A according to the above embodiment.

The control circuit 13' performs synchronous rectification control on the secondary circuit 12". During synchronous rectification control, the control circuit 13' turns on and off the switching operations of the fifth arm to the eighth arm in synchronization with the direction of the secondary resonant current. For example, the control circuit 13' detects the direction (polarity) of the current in the secondary coil of the insulating transformer Tr', turns on the switching element Q5 of the fifth arm and the switching element Q8 of the eighth arm when the current direction becomes positive, and turns off the switching element Q5 of the fifth arm and the switching element Q8 of the eighth arm when the current becomes zero. Similarly, the control circuit 13' detects the direction of the current in the secondary coil of the insulating transformer Tr', turns on the switching element Q6 of the sixth arm and the switching element Q7 of the seventh arm when the current direction becomes negative, and turns off the switching element Q6 of the sixth arm and the switching element Q7 of the seventh arm when the current becomes zero.

DC/DC converter 10C has the same effects as DC/DC converter 10B. Furthermore, compared to DC/DC converter 10B, DC/DC converter 10C has a reduced on-resistance of secondary circuit 12'', which improves power conversion efficiency.

[Other Modifications]
The control circuit of the present invention can be configured to set the drive frequency of the full-bridge circuit to a first drive frequency higher than the resonant frequency determined by the resonant coil and the resonant capacitor during the startup period, start frequency control, and perform phase shift control while maintaining the drive frequency at the first drive frequency. For example, the control circuit may perform phase shift control by setting the first drive frequency f1 to 150 kHz, the first phase shift amount θ1 to 160 degrees, and the second phase shift amount θ2 to 0 degrees or a value close to 0 degrees.

In the above embodiment, the drive frequency and phase shift amount of the full bridge circuit are changed linearly at the same time, but a third phase shift amount θ3 may be provided such that the first phase shift amount θ1 > the third phase shift amount θ3 > the second phase shift amount θ2. In this case, during the first period in which the phase shift amount is reduced from the first phase shift amount θ1 to the third phase shift amount θ3, startup control may be performed so that the drive frequency becomes a frequency higher than the resonant frequency, and during the second period in which the phase shift amount is reduced from the third phase shift amount θ3 to the second phase shift amount θ2, startup control may be performed so that the drive frequency becomes equal to or lower than the resonant frequency.

As described above, in the first period, the drive frequency is greater than the resonant frequency, so the excitation current decreases, and even in the case of a large phase shift, the direction of the excitation current is reversed, preventing a through current from occurring in the full bridge circuit.

The method of simultaneously changing the drive frequency and phase shift amount during startup control reduces the drive frequency gradually compared to the method of changing the phase shift amount while keeping the drive frequency constant, so the effect of suppressing overcurrent at the start of startup control is the same, but the increase in current thereafter is greater, so the target voltage at the end of the startup period can be reached in a short time.

The DC/DC converter of the present invention is not limited to the LLC type, and can also adopt the CLLC type, CLLLC type, etc., as long as it is a current resonance type.

In the above embodiment, a DC/DC converter 10A and a power supply unit 1A that perform unidirectional operation are described, but the present invention can also be applied to a DC/DC converter and a power supply unit that perform bidirectional operation, and can prevent excessive current from flowing at startup without using additional components.

1A Power supply device 10 DC/DC power supply units 10A to 10C DC/DC converter 11 Primary side circuits 12, 12', 12'' Secondary side circuits 13, 13' Control circuit 20 AC/DC power supply unit 30 Control unit

Claims (5)

an isolation transformer including a primary coil and a secondary coil;
A primary circuit connected to the primary coil;
A secondary circuit connected to the secondary coil;
A control circuit for controlling the primary side circuit;
A current resonance type DC/DC converter comprising:
The primary side circuit includes:
a full bridge circuit in which a first leg consisting of a first arm and a second arm and a second leg consisting of a third arm and a fourth arm are connected in parallel, a resonant coil, and a resonant capacitor;
the resonant coil, the resonant capacitor, and the primary coil are connected in series between a first connection point of the first arm and the second arm and a second connection point of the third arm and the fourth arm,
Each of the first arm, the second arm, the third arm, and the fourth arm is
A switching element that is turned on/off under the control of the control circuit;
a diode connected in parallel in a reverse direction to the switching element;
a capacitor connected in parallel to the switching element,
The control circuit includes:
during a startup period from startup until an output voltage of the secondary side circuit reaches a first target value, a drive frequency of the full bridge circuit is set to a first drive frequency higher than a resonant frequency determined by the resonant coil and the resonant capacitor, and a frequency control is started;
a phase shift amount between the first leg and the second leg is set to a predetermined first phase shift amount to start phase shift control, and the phase shift amount is reduced to a second phase shift amount smaller than the first phase shift amount by the end of the startup period. The control circuit includes:
2. The DC/DC converter according to claim 1, wherein the drive frequency is reduced to a second drive frequency that is equal to or lower than the resonance frequency by the end of the start-up period. The control circuit includes:
3. The DC/DC converter according to claim 1, wherein, during a first period of the startup period, the phase shift amount is reduced from the first phase shift amount to a third phase shift amount between the first phase shift amount and the second phase shift amount, the drive frequency is controlled so that the drive frequency is always higher than the resonant frequency. The control circuit includes:
4. The DC/DC converter according to claim 1, wherein, during the start-up period, a target value of the output voltage is set to zero or a second target value smaller than the first target value, and the frequency control and the phase shift control are started, and the target value is increased to the first target value over time. an AC/DC power supply unit that converts an AC input voltage into a DC output voltage;
a DC/DC power supply unit including the DC/DC converter according to any one of claims 1 to 4 and receiving the DC output voltage;
A control unit that controls the AC/DC power supply unit and the DC/DC power supply unit;
A power supply device comprising:
The control unit is
starting the AC/DC power supply unit and then starting the DC/DC power supply unit;
A power supply device characterized by controlling the AC/DC power supply unit so that, during a startup period of the DC/DC power supply unit, the DC output voltage of the AC/DC power supply unit becomes the minimum voltage that the AC/DC power supply unit can output and that the DC/DC power supply unit can perform power conversion operation.

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