Power supply device

Abstract

When the power consumption of the DCDC converter is less than a first power, the power supply device controls the DCDC converter so that the output voltage of the DCDC converter is greater than a predetermined target voltage. When the power consumption exceeds a second power that is greater than the first power, the power supply device controls the DCDC converter so that the output voltage is less than the target voltage.

Description

Technical Field

[0001] The present invention relates to a power supply device. Background Art

[0002] A DC-DC converter is a circuit that converts a certain DC (direct current) input voltage into a required constant DC output voltage (Patent Document 1). The required output voltage is determined by an inverter connected to the downstream stage of the DC-DC converter.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2013-192383 Summary of the Invention

[0006] Problems to be solved by the invention

[0007] Typically, the output voltage of a DC-DC converter is controlled to a constant value. In addition, the output voltage must be below the input allowable voltage (withstand voltage) of the inverter connected to the subsequent stage. When the load connected to the inverter decreases sharply, the output voltage of the DC-DC converter rises sharply. Taking into account the sharp rise in output voltage, the output voltage of the DC-DC converter must be set lower than the withstand voltage of the inverter. On the other hand, when the load increases sharply, the output voltage of the DC-DC converter drops sharply. Therefore, as a countermeasure for the sharp rise in output voltage, it is preferable that the target value of the output voltage is lower, but as a countermeasure for the sharp drop in output voltage, it is preferable that the target value of the output voltage is higher. That is, the appropriate target voltage varies depending on the load. Therefore, an object of the present invention is to variably control the target voltage according to the load.

[0008] Means for solving problems

[0009] According to the present invention, for example, a power supply device is provided, wherein:

[0010] The power supply device comprises:

[0011] a DCDC converter that converts a first DC voltage supplied from a DC power source to generate a second DC voltage;

[0012] an inverter that is supplied with the second DC voltage from the DCDC converter and outputs an AC current and an AC voltage; and

[0013] a controller that controls the DCDC converter so that the second DC voltage becomes a target voltage,

[0014] The controller includes a power calculation unit for calculating the power consumption of the DCDC converter.

[0015] When the consumed power is less than the first power, the controller controls the DCDC converter so that the second DC voltage outputted from the DCDC converter is greater than the target voltage.

[0016] When the power consumption exceeds a second power greater than the first power, the controller controls the DCDC converter so that the second DC voltage output from the DCDC converter is lower than the target voltage.

[0017] Effects of the Invention

[0018] According to the present invention, the target voltage is variably controlled according to the load.

[0019] Other features and advantages of the present invention will become clear from the following description with reference to the accompanying drawings. In addition, in the accompanying drawings, the same or similar structures are marked with the same reference numerals. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the present invention and, together with the description, serve to explain the principles of the present invention.

[0021] Figure 1 This is a block diagram showing a power supply device.

[0022] Figure 2 This is a block diagram showing the functions implemented by the CPU.

[0023] Figure 3 This is a block diagram showing the functions implemented by the CPU.

[0024] Figure 4 This is a flowchart showing a control method executed by the CPU. DETAILED DESCRIPTION

[0025] The following embodiments are described in detail with reference to the accompanying drawings. The following embodiments do not limit the inventions described herein. Furthermore, not all combinations of features described in the embodiments are essential to the invention. Any combination of two or more of the multiple features described in the embodiments may be used. Identical or similar components are denoted by the same reference numerals, and duplicate descriptions are omitted.

[0026] <Power supply>

[0027] Figure 1Figure 2 shows a power supply device 1. The power supply device 1 includes a DC power supply 10, a DC-DC converter 20, and an inverter 30. The DC power supply 10 is a battery, an engine-driven generator, or the like. Here, a battery-type DC power supply 10 is assumed. The DC-DC converter 20 converts a DC input voltage Vdc_in supplied from the DC power supply 10 into a DC output voltage Vdc_out, and outputs the voltage to the inverter 30. The inverter 30 converts the output voltage Vdc_out supplied from the DC-DC converter 20 into an AC output voltage Vac_out, and supplies the voltage to a load 40.

[0028] DC power supply

[0029] In the DC power supply 10, the battery cells 11 output a battery voltage Vbat. The voltage detection circuit 12 detects the battery voltage Vbat and outputs the detection result to the CPU 18. The current detection circuit 13 detects the battery current Ibat flowing from the battery cells 11 to the DC-DC converter 20 and outputs the detection result to the CPU 18. The CPU 18 is a processor circuit that executes a control program stored in the memory 19. The CPU 18 transmits the detection results of the battery voltage Vbat and the battery current Ibat to the DC-DC converter 20 via the communication circuit 17.

[0030] DC-DC converter

[0031] In the DC-DC converter 20, the current detection circuit 23 is a circuit that detects the input current Idc_in from the DC power supply 10 and outputs the detection result to the AD port of the CPU 28. The AD port is a port that includes an AD converter that converts analog signals into digital signals. The current detection circuit 23 includes, for example, a shunt resistor (a resistor for current detection). The voltage detection circuit 22a is a circuit that detects the input voltage Vdc_in from the DC power supply 10 and outputs the detection result to the CPU 28. The voltage detection circuit 22a includes, for example, a plurality of voltage-dividing resistors that convert the input voltage Vdc_in into a detection voltage proportional to the input voltage Vdc_in. The conversion circuit 25 is a circuit that converts the input voltage Vdc_in into an output voltage Vdc_out. The conversion circuit 25 controls the output voltage Vdc_out to a target voltage Vtar based on the voltage command value Vref output from the CPU 28. Therefore, the voltage command value Vref is a command value representing the target voltage Vtar. Alternatively, the voltage command value Vref may be realized by a PWM wave (a pulsed drive signal) whose pulse width is adjusted according to the target voltage Vtar. Such a drive signal is supplied to each of the four switching elements constituting the switching circuit.

[0032] The conversion circuit 25 may be a switching converter including a switching circuit (eg, a full-bridge circuit based on four field-effect transistors), a transformer, a rectification circuit (eg, a bridge diode), and a smoothing circuit (eg, an electrolytic capacitor).

[0033] CPU 28 executes various processes according to the control program stored in memory 29. For example, CPU 28 may determine the power consumption Pin in DC-DC converter 20 based on the detection results of input voltage Vdc_in and output voltage Vdc_out, and calculate the primary correction value α of target voltage Vtar based on the power consumption Pin. Furthermore, CPU 28 may calculate the overall efficiency based on the detection results of battery voltage Vbat, battery current Ibat, AC output voltage Vac_out sent from inverter 30, and AC output current Iac_out. Overall efficiency refers to the efficiency Ef of the DC power supply 10, DC-DC converter 20, and inverter 30 as a whole.

[0034] Ef=(Vac_out×Iac_out) / (Vbat×Ibat)...(1)

[0035] CPU 28 determines or updates the target voltage Vtar to improve efficiency Ef. Furthermore, CPU 28 receives detection results of the AC output voltage Vac_out and the AC output current Iac_out from inverter 30 via communication circuit 27b. Voltage detection circuit 22b detects output voltage Vdc_out and feeds the result back to conversion circuit 25. This controls output voltage Vdc_out to approach target voltage Vtar corresponding to voltage command value Vref.

[0036] CPU 28, memory 29, and communication circuits 27a and 27b form a controller. An auxiliary power supply that supplies operating voltage to CPU 28, memory 29, and communication circuits 27a and 27b is not shown. This auxiliary power supply converts the input voltage Vdc_in to generate the operating voltage. The auxiliary power supply can also be composed of, for example, a high-voltage regulator, a three-terminal regulator, or an isolated power supply.

[0037] Inverter 30

[0038] In inverter 30, conversion circuit 35 converts the output voltage Vdc_out from DC-DC converter 20 into an AC output voltage Vac_out. Conversion circuit 35 includes, for example, a bridge circuit formed by multiple switching elements. Voltage detection circuit 32 detects output voltage Vac_out and outputs the detection result to CPU 38. Current detection circuit 33 detects output current Iac_out and outputs the detection result to CPU 38. CPU 38 controls inverter 30 according to a control program stored in memory 39. CPU 38 transmits the detection results of AC output voltage Vac_out and AC output current Iac_out to DC-DC converter 20 via communication circuit 37.

[0039] [CPU Function]

[0040] Figure 2 " indicates a function related to determining the voltage command value Vref. The CPU 28 implements the functions described below by executing a control program. Some or all of the functions described below may also be implemented using hardware circuits such as an ASIC (application-specific integrated circuit) or an FPGA (field-programmable gate array). Alternatively, the CPU 28 may be comprised of one or more processor circuits. Thus, each function may be implemented using either logic circuits or program modules.

[0041] The power calculation unit 201 calculates the power consumption Pin of the DC-DC converter 20 based on the input voltage Vdc_in and the input current Idc_in. For example, the power calculation unit 201 calculates the power consumption Pin of the DC-DC converter 20 by multiplying the input voltage Vdc_in by the input current Idc_in (Pin = Vdc_in × Idc_in). The correction value determination unit 202 determines the correction value X of the target voltage Vtar based on the power consumption Pin. Here, the new target voltage Vtar can also be expressed as the sum of the old target voltage Vtar' stored in the memory 29 and the correction value X (Vtar = Vtar' + X).

[0042] For example, if the rated power of the power supply device 1 is 1500W and the power consumption Pin is less than the first power P1 (e.g., P1 = 500W), the load 40 is expected to increase from this point on. This is because, generally, users sometimes use a load 40 with a power consumption close to the rated power. Therefore, if the power consumption Pin is less than the first power P1, the correction value determination unit 202 determines the correction value X (X = +α) so that the output voltage Vdc_out is higher than the current target voltage Vtar by +α. By raising the output voltage Vdc_out in advance, the power supply device 1 can effectively follow a sudden increase in the load 40. For example, if the target voltage Vtar is 180V and α is 20V, the output voltage Vdc_out increases to 200V.

[0043] On the other hand, if the power consumption Pin exceeds the second power P2 (e.g., P2 = 1000 W), the load 40 is expected to decrease rapidly from this point on. If the load 40 decreases rapidly, the output current Idc_out of the DC-DC converter 20 decreases rapidly, and the output voltage Vac_out increases rapidly. If the output voltage Vac_out increases rapidly, there is a possibility that the output voltage Vac_out exceeds the withstand voltage of the inverter 30. Therefore, if the power consumption Pin exceeds the second power P2, the correction value determination unit 202 determines the correction value X (X = -β) so that the output voltage Vdc_out is -β lower than the current target voltage Vtar. By lowering the output voltage Vdc_out in advance, the power supply device 1 can effectively follow the rapid decrease in the load 40. For example, if the target voltage Vtar is 180 V and β is 15 V, the output voltage Vdc_out is reduced to 165 V. By lowering the output voltage Vdc_out in this way, a margin is ensured for the withstand voltage of the inverter 30.

[0044] The command value determination unit 203 reads the target voltage Vtar from the memory 29 , adds the correction value X received from the correction value determination unit 202 to obtain the sum, determines the voltage command value Vref corresponding to the sum, and sets the voltage command value Vref to the conversion circuit 25 .

[0045] Figure 3Indicates a function of improving the overall efficiency of the power supply device 1. As already described, the CPU 28 implements the function described below by executing a control program. After correcting or adjusting the output voltage Vdc_out according to the power consumption Pin, the CPU 28 obtains the detection result of the battery voltage Vbat and the detection result of the battery current Ibat from the DC power supply 10, and obtains the detection result of the output voltage Vac_out and the detection result of the output current Iac_out from the inverter 30, and inputs them to the efficiency calculation unit 211. The efficiency calculation unit 211 calculates the efficiency Ef based on formula (1). Here, the current efficiency Ef is recorded as Ef_new. The last efficiency Ef obtained by the last calculation and stored in the memory 29 is recorded as Ef_old. The efficiency determination unit 212 determines whether the current efficiency Ef_new is greater than the last efficiency Ef_old, and outputs the determination result to the target voltage determination unit 213.

[0046] The target voltage determination unit 213 determines a new target voltage Vtar based on the determination result. For example, if the current efficiency Ef_new is greater than the previous efficiency Ef_old, the target voltage determination unit 213 increases the target voltage Vtar. For example, the target voltage determination unit 213 adds a predetermined value Y to the target voltage Vtar and stores the result in the memory 29. On the other hand, if the current efficiency Ef_new is less than the previous efficiency Ef_old, the target voltage determination unit 213 decreases the target voltage Vtar. For example, the target voltage determination unit 213 subtracts the predetermined value Y from the target voltage Vtar and stores the result in the memory 29. The efficiency update unit 214 then updates the previous efficiency Ef_old stored in the memory 29 by overwriting the previous efficiency Ef_old with the current efficiency Ef_new.

[0047] <Flowchart>

[0048] Figure 4 This shows a series of processes executed by the CPU 28 according to the control program.

[0049] In step S401, the CPU 28 sets the initial value Vtar_ini as the target voltage Vtar. The initial value Vtar_ini is a value determined in the design of the power supply device 1 and is stored in the ROM area of the memory 29. The target voltage Vtar is stored in the RAM area of the memory 29 as a variable.

[0050] In step S402, the CPU 28 sets the initial value Ef_ini for the previous efficiency Ef_old. The initial value Ef_ini is a value determined in the design of the power supply device 1 and is stored in the ROM area of the memory 29. The previous efficiency Ef_old is stored in the RAM area of the memory 29 as a variable.

[0051] In step S403, the CPU 28 determines the voltage command value Vref based on the target voltage Vtar read from the memory 29 and outputs it to the conversion circuit 25. This starts the voltage conversion process in the conversion circuit 25. The conversion circuit 25 controls the output voltage Vdc_out so that the output voltage Vdc_out approaches the target voltage Vtar corresponding to the voltage command value Vref.

[0052] In step S404, CPU 28 determines whether output voltage Vdc_out has reached target voltage Vtar based on the detection result of output voltage Vdc_out. The detection result of output voltage Vdc_out is the voltage (detection voltage) obtained by dividing output voltage Vdc_out by the voltage divider circuit. If output voltage Vdc_out has reached target voltage Vtar, CPU 28 proceeds to step S405.

[0053] In step S405, the CPU 28 calculates the power consumption Pin of the DC-DC converter 20. As described above, the CPU 28 may calculate the power consumption Pin of the DC-DC converter 20 by multiplying the input voltage Vdc_in by the input current Idc_in.

[0054] In step S406, CPU 28 determines whether power consumption Pin is less than a predetermined value P1. In other words, it determines whether power consumption Pin is at a level at which the output voltage Vdc_out is expected to increase sharply. If power consumption Pin is less than predetermined value P1, CPU 28 proceeds to step S407. In step S407, CPU 28 increases output voltage Vdc_out to target voltage Vtar+α by setting correction value X to +α. On the other hand, if power consumption Pin is not less than predetermined value P1, CPU 28 proceeds to step S420. In step S420, CPU 28 determines whether power consumption Pin exceeds predetermined value P2 (P1 < P2). In other words, it determines whether power consumption Pin is at a level at which the output voltage Vdc_out is expected to decrease sharply. If power consumption Pin exceeds predetermined value P2, CPU 28 proceeds to step S421. In step S421, CPU 28 decreases output voltage Vdc_out to target voltage Vtar-β by setting correction value X to -β. On the other hand, when the power consumption Pin does not exceed the predetermined value P2 (P1≤Pin≤P2), the CPU 28 sets the correction value X to zero to maintain the output voltage Vdc_out at the target voltage Vtar.

[0055] In step S408, CPU 28 calculates the overall efficiency Ef. Here, the current efficiency Ef_new is calculated based on the detection results of the battery voltage Vbat, the battery current Ibat, and the AC output voltage Vac_out and AC output current Iac_out transmitted from inverter 30. Equation (1) is merely an example; any of the four variables constituting Equation (1) may be added to or multiplied by a coefficient.

[0056] In step S409, CPU 28 determines whether the current efficiency Ef_new is greater than the previous efficiency Ef_old. The previous efficiency Ef_old is stored in memory 29. If the current efficiency Ef_new is greater than the previous efficiency Ef_old, CPU 28 proceeds to step S410. In step S410, CPU 28 updates the previous efficiency Ef_old by overwriting the current efficiency Ef_new with the previous efficiency Ef_old. In step S411, CPU 28 increases the target voltage Vtar. For example, CPU 28 may add a predetermined value Y to the target voltage Vtar. CPU 28 then returns to step S404.

[0057] On the other hand, if the current efficiency Ef_new is not greater than the previous efficiency Ef_old, the CPU 28 proceeds to step S430. In step S430, the CPU 28 updates the previous efficiency Ef_old by overwriting the current efficiency Ef_new with the previous efficiency Ef_old. In step S431, the CPU 28 decreases the target voltage Vtar. For example, the CPU 28 may subtract a predetermined value Y from the target voltage Vtar. The CPU 28 then returns to step S404.

[0058] Summary

[0059] [Viewpoint 1]

[0060] The DC-DC converter 20 is an example of a DC-DC converter that converts a first DC voltage supplied from a DC power supply to generate a second DC voltage. The inverter 30 is an example of an inverter that receives the second DC voltage from the DC-DC converter and outputs an AC current and an AC voltage. The CPU 28 is an example of a controller that controls the DC-DC converter so that the second DC voltage reaches a target voltage. The CPU 28 may also include a power calculation unit that calculates the power consumption of the DC-DC converter. When the power consumption is less than the first power, the CPU 28 may control the DC-DC converter so that the second DC voltage outputted from the DC-DC converter is greater than the target voltage. When the power consumption (e.g., Pin) exceeds a second power (e.g., P2) that is greater than the first power (e.g., P1), the CPU 28 may control the DC-DC converter so that the second DC voltage outputted from the DC-DC converter is less than the target voltage. Power consumption varies depending on the load. Therefore, in this embodiment, the target voltage is variably controlled according to the load. By controlling the output voltage in accordance with power consumption, the output voltage response can be improved. For example, transient drops and increases in the DC output voltage can be suppressed. As a result, instantaneous fluctuations in the output voltage of the inverter are also suppressed.

[0061] [Viewpoint 2]

[0062] When the power consumption is less than the first power, the CPU 28 may control the DCDC converter so that the second DC voltage output from the DCDC converter is the sum of the target voltage (e.g., Vtar) and a predetermined value (e.g., α). When the power consumption exceeds the second power, the CPU 28 may control the DCDC converter so that the second DC voltage output from the DCDC converter is the difference between the target voltage and a predetermined value (e.g., β). For example, if the power consumption is less than 500W, the target voltage is set to 200V. If the power consumption is greater than 500W and less than 1000W, the target voltage is set to 180V. If the power consumption exceeds 1000W, the target voltage is set to 165V. These values are merely examples. Furthermore, generally, if the load decreases sharply, the output voltage from the DCDC converter rises sharply, so the inverter requires a capacitor with a high withstand voltage. In this embodiment, the target voltage is controlled to be low in advance in a state where the output voltage may rise sharply. Therefore, the input withstand voltage of the inverter can be reduced.

[0063] [Viewpoint 3]

[0064] The voltage detection circuit 22a functions as a voltage detection circuit that detects a first DC voltage (e.g., Vdc_in) input from the DC power supply to the DC-DC converter. The current detection circuit 23 functions as a current detection circuit that detects an input DC current (e.g., Vdc_in) input from the DC power supply to the DC-DC converter. A power calculation unit (e.g., CPU 28) can also calculate the power consumption (e.g., Pin) of the DC-DC converter based on the value of the first DC voltage detected by the voltage detection circuit and the value of the input DC current detected by the current detection circuit.

[0065] [Viewpoint 4, Viewpoint 9]

[0066] The CPU 28 may also include an efficiency calculation unit (e.g., efficiency calculation unit 211) that calculates the overall efficiency (e.g., Ef) of the DC power supply, DCDC converter, and inverter. The CPU 28 may also include a setting unit (e.g., efficiency determination unit 212, target voltage determination unit 213) that sets the target voltage based on the efficiency. Thus, the target voltage is adjusted to improve efficiency. Typically, the target voltage is set to a fixed value, but in this embodiment, the target voltage is variably controlled to improve efficiency. Thus, the overall efficiency of the power supply device including the DC-DC converter and inverter is improved. Thus, when efficiency is improved, the battery included in the DC power supply can supply power for a longer time. Alternatively, the engine-driven generator mounted on the DC power supply can operate for a longer time. If efficiency is improved, the amount of heat dissipated by the power supply device 1 is reduced, so the cooling fan can be omitted, or the cooling performance of the cooling fan can be reduced. Thus, quieting can also be achieved.

[0067] [Viewpoint 5]

[0068] CPU 28 may also obtain the AC current and AC voltage values output by the inverter from the inverter. Furthermore, CPU 28 may also obtain the output voltage and output current values of the DC power supply from the DC power supply. Efficiency calculation unit 211 may also be configured to calculate efficiency based on the AC current, AC voltage, output voltage, and output current values.

[0069] [Viewpoint 6]

[0070] As shown in the formula (1), the efficiency calculation unit 211 may obtain a first product by multiplying the AC current value by the AC voltage value, obtain a second product by multiplying the output voltage value by the output current value, and obtain efficiency by dividing the first product by the second product.

[0071] [Viewpoint 7]

[0072] Memory 29 functions as a storage unit for storing the first efficiency (e.g., Ef_old) calculated by the efficiency calculation unit. CPU 28 may also increase the target voltage if the second efficiency (e.g., Ef_new) calculated by the efficiency calculation unit after calculating the first efficiency is greater than the first efficiency. CPU 28 may also decrease the target voltage if the second efficiency is not greater than the first efficiency. This maintains a high-efficiency operating state.

[0073] [Viewpoint 8]

[0074] The CPU 28 may calculate the efficiency based on the AC current value, AC voltage value, output voltage value, and output current value acquired after executing the control of the second DC voltage based on the power consumption of the DCDC converter.

[0075] The present invention is not limited to the above-described embodiment, and various modifications and changes can be made within the scope of the gist of the present invention.

Claims

1. A power supply device, wherein: The power supply device comprises: a DCDC converter that converts a first DC voltage supplied from a DC power source to generate a second DC voltage; an inverter that is supplied with the second DC voltage from the DCDC converter and outputs an AC current and an AC voltage; as well as a controller that controls the DCDC converter so that the second DC voltage becomes a target voltage, The controller includes a power calculation unit for calculating the power consumption of the DCDC converter. When the consumed power is less than the first power, the controller controls the DCDC converter so that the second DC voltage outputted from the DCDC converter is greater than the target voltage. When the power consumption exceeds a second power greater than the first power, the controller controls the DCDC converter so that the second DC voltage output from the DCDC converter is lower than the target voltage.

2. The power supply device according to claim 1, wherein When the power consumption is less than the first power, the controller controls the DCDC converter so that the second DC voltage output from the DCDC converter becomes the sum of the target voltage and a predetermined value. When the power consumption exceeds the second power, the controller controls the DCDC converter so that the second DC voltage output from the DCDC converter becomes a difference between the target voltage and the predetermined value.

3. The power supply device according to claim 1 or 2, wherein: The power supply device also has: a voltage detection circuit that detects the first DC voltage input from the DC power supply to the DCDC converter; and a current detection circuit for detecting an input DC current input from the DC power supply to the DCDC converter, The power calculation unit calculates the consumed power of the DCDC converter based on the value of the first DC voltage detected by the voltage detection circuit and the value of the input DC current detected by the current detection circuit.

4. The power supply device according to claim 2, wherein: The controller has: an efficiency calculation unit for calculating the overall efficiency of the DC power supply, the DCDC converter, and the inverter; and A setting unit sets the target voltage according to the efficiency.

5. The power supply device according to claim 4, wherein: The efficiency calculation unit is configured to obtain the value of the AC current and the value of the AC voltage output by the inverter from the inverter, obtain the value of the output voltage and the value of the output current of the DC power supply from the DC power supply, and calculate the efficiency based on the value of the AC current, the value of the AC voltage, the value of the output voltage, and the value of the output current.

6. The power supply device according to claim 5, wherein: The efficiency calculation unit multiplies the AC current value and the AC voltage value to obtain a first product, multiplies the output voltage value and the output current value to obtain a second product, and divides the first product by the second product to obtain the efficiency.

7. The power supply device according to claim 5, wherein: The power supply device further includes a storage unit that stores the first efficiency obtained by the efficiency calculation unit. When a second efficiency obtained by the efficiency calculation unit after obtaining the first efficiency is equal to or greater than the first efficiency, the setting unit increases the target voltage. When the second efficiency is not greater than the first efficiency, the setting unit decreases the target voltage. The second efficiency is a calculation result after the output voltage is corrected or adjusted according to the power consumption in the current cycle, and the first efficiency is a calculation result in the previous cycle.

8. The power supply device according to claim 5, wherein: The efficiency calculation unit is configured to calculate the efficiency based on the AC current value, the AC voltage value, the output voltage value, and the output current value acquired after the second DC voltage is controlled based on the power consumption of the DCDC converter.

9. A control method, which is executed by a controller in a power supply device having a DC power supply, a DC-DC converter, an inverter, and a controller, wherein: The control method has the following steps: Calculating the power consumption of the DCDC converter; When the consumed power is less than the first power, controlling the DCDC converter so that an output DC voltage outputted from the DCDC converter is greater than a target voltage preset for the DCDC converter; and When the power consumption exceeds a second power greater than the first power, the DCDC converter is controlled so that the output DC voltage output from the DCDC converter becomes lower than the target voltage.

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