Power conversion system and method of operating the same

Abstract

A power conversion system is in handshake communication with a load to convert an input voltage to power the load accordingly, and the power conversion system includes an AC-DC conversion unit, a DC-DC conversion unit, a control unit, a switch set, and an output path. The AC-DC conversion unit converts the input voltage to a DC voltage, and the DC-DC conversion unit converts the DC voltage to an output voltage. When a requested voltage of the load is lower than a threshold voltage, the control unit controls the switch set to be coupled to the DC-DC conversion unit to provide the output voltage to the output path. When the requested voltage is higher than the threshold voltage, the control unit controls the switch set to be coupled to the AC-DC conversion unit to provide the DC voltage to the output path.

Description

Technical Field

[0001] This invention relates to a power conversion system and its operating method, and more particularly to a power conversion system and its operating method with power saving function. Background Technology

[0002] With the increasing prevalence of electronic products, various portable electronic devices typically require different power sources, necessitating specific voltage levels for power supply (or charging) to function properly. Therefore, current power supply technology development has led to the development of power conversion systems that can adjust the output voltage according to load demands. These power conversion systems are primarily applicable to USB-PD (USB-Power Delivery) specifications and can provide multiple voltage levels to loads. The power conversion system uses a Type-C port to connect to loads that also meet the USB-PD standard, communicating with the load to determine its needs and then providing the appropriate power to enable operation (or charging). These power conversion systems generally include: a first-stage AC-DC conversion unit and a second-stage DC-DC conversion unit. The AC-DC conversion unit receives AC mains input voltage and converts it to DC voltage. The DC-DC conversion unit receives DC voltage and converts it to output voltage.

[0003] However, in response to load demands, power conversion systems can provide a wide range of voltage potentials, typically with multiple voltage outputs ranging from 5V to 20V. Also, because the power output corresponding to each voltage is different under the USB-PD specification, the current supplied to the load varies under each voltage. (1) When a higher voltage potential is provided, the current supplied is usually also relatively higher. This results in a significant increase in the power consumed by the DC-DC converter at higher voltage potentials; (2) If the AC-DC converter outputs a fixed higher DC voltage (e.g., 22V), then when the power conversion system outputs a lower voltage potential under the USB-PD specification (e.g., 5V), the DC-DC converter needs to convert the 22V input voltage to a 5V output voltage, resulting in poor overall conversion efficiency of the power conversion system. Both of these reasons significantly increase the energy lost during power conversion, failing to meet energy-saving requirements.

[0004] Therefore, how to design a power conversion system and its operation method with power saving function, so as to save the power consumption of the power conversion system under high voltage potential, is a major research topic of this invention. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a power conversion system that converts input voltage to supply power to a load. The power conversion system includes an AC-DC conversion unit, a DC-DC conversion unit, a control unit, a switch group, and an output path. The AC-DC conversion unit receives the input voltage and converts it into a DC voltage. The DC-DC conversion unit receives the DC voltage and converts it into an output voltage. The control unit communicates with the load to determine the requested voltage. The switch group is coupled to the AC-DC conversion unit and the DC-DC conversion unit, and the output path is coupled to the switch group and the load. When the requested voltage is lower than a threshold voltage, the control unit controls the switch group to connect the DC-DC conversion unit and the output path, and controls the DC-DC conversion unit to provide an output voltage matching the requested voltage to the output path. When the requested voltage is higher than the threshold voltage, the control unit controls the switch group to connect the AC-DC conversion unit and the output path, and controls the AC-DC conversion unit to provide a DC voltage matching the requested voltage to the output path.

[0006] To address the aforementioned problems, this invention provides a power conversion system that converts input voltage to supply power to a load. The power conversion system includes an AC-DC conversion unit, a DC-DC conversion unit, a control unit, and an output path. The AC-DC conversion unit receives the input voltage and converts it into a DC voltage. The DC-DC conversion unit receives the DC voltage and converts it into an output voltage. The control unit communicates with the load to determine the requested voltage. Based on this communication, the control unit adjusts the output voltage from the current voltage to the requested voltage. The output path couples the DC-DC conversion unit group to the load. When the current voltage is less than the requested voltage, the control unit first increases the output voltage and then increases the DC voltage; when the current voltage is greater than the requested voltage, the control unit first decreases the output voltage and then decreases the DC voltage.

[0007] To address the aforementioned problems, this invention provides an operation method for a power conversion system. The power conversion system controls the conversion of input voltage to supply power to a load. The power conversion system includes an AC-DC conversion unit, a DC-DC conversion unit, a switch group, and an output path. The operation method includes the following steps: (a) controlling the AC-DC conversion unit to convert the input voltage to DC voltage. (b) controlling the DC-DC conversion unit to convert the DC voltage to an output voltage. (c) communicating with the load to determine the requested voltage. (d) when the requested voltage is lower than a threshold voltage, controlling the switch group to connect the DC-DC conversion unit and the output path, and controlling the DC-DC conversion unit to provide an output voltage matching the requested voltage to the output path. (e) when the requested voltage is higher than a threshold voltage, controlling the switch group to connect the AC-DC conversion unit and the output path, and controlling the AC-DC conversion unit to provide a DC voltage matching the requested voltage to the output path.

[0008] To address the aforementioned problems, this invention provides an operation method for a power conversion system. The power conversion system controls the conversion of input voltage to supply power to a load. The power conversion system includes an AC-DC conversion unit, a DC-DC conversion unit, a switch group, and an output path. The operation method includes the following steps: (a) controlling the AC-DC conversion unit to convert the input voltage to DC voltage. (b) controlling the DC-DC conversion unit to convert the DC voltage to an output voltage. (c) communicating with the load to determine the requested voltage, and adjusting the output voltage from the current voltage to the requested voltage based on the requested voltage. (d) when the output voltage is adjusted from the current voltage to the requested voltage, and the current voltage is less than the requested voltage, first increasing the output voltage, then increasing the DC voltage. (e) when the output voltage is adjusted from the current voltage to the requested voltage, and the current voltage is greater than the requested voltage, first decreasing the output voltage, then decreasing the DC voltage.

[0009] The main objective and effect of this invention is that, when a higher voltage is required, the control unit bypasses the DC-DC conversion unit by controlling the switch group, so that the AC-DC conversion unit provides DC voltage to the load, thereby saving the power consumption of the power conversion system.

[0010] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments, but this is not intended to limit the present invention. Attached Figure Description

[0011] Figure 1 This is a circuit block diagram of an embodiment of the power conversion system with power saving function of the present invention;

[0012] Figure 2 This is a waveform diagram of an embodiment of the DC voltage and output voltage adjustment of the present invention;

[0013] Figure 3A This is a circuit block diagram of a variant embodiment of the power conversion system with power saving function of the present invention.

[0014] Figure 3B This is a circuit block diagram of another variant embodiment of the power conversion system with power saving function of the present invention;

[0015] Figure 4 This is a flowchart illustrating the operation method of the power conversion system with power saving function of the present invention;

[0016] Figure 5A This is a detailed flowchart of the first embodiment of step S100;

[0017] Figure 5B This is a detailed flowchart of the second embodiment of step S100;

[0018] Figure 6A A detailed flowchart of the first embodiment of step S200; and

[0019] Figure 6B This is a detailed flowchart of the second embodiment of step S200.

[0020] In the attached figures, the following labels are used:

[0021] 100, 100', 100”: Power conversion system

[0022] 1: AC-DC conversion unit

[0023] 2: DC-DC conversion unit

[0024] 12, 22: Controller

[0025] 3: Control Unit

[0026] 4, 4': Switch group

[0027] 42: First Switching Unit

[0028] 44: Second Switching Unit

[0029] 46: Third Switching Unit

[0030] 48: Path switching node

[0031] 5: Output path

[0032] 6: Discharge circuit

[0033] 62: Resistance

[0034] 64: Fourth Switching Unit

[0035] GND: Grounding point

[0036] 200: Load

[0037] Vin: Input voltage

[0038] Vdc: DC voltage

[0039] Vo: Output voltage

[0040] Vr: Requested voltage

[0041] Vt: Threshold voltage

[0042] ΔV: Voltage difference

[0043] Scom: Interlocking Communications

[0044] Sc1, Sc2: Control signals Detailed Implementation

[0045] The structural and working principles of the present invention will be described in detail below with reference to the accompanying drawings:

[0046] Please see Figure 1 This is a circuit block diagram of an embodiment of the power conversion system with power-saving function of the present invention. The power conversion system 100 is a conversion system applicable to the USB-PD (USB-Power Delivery) specification and can provide multiple sets of voltages with different potentials to the load 200. The power conversion system 100 mainly communicates with the load 200 based on the USB-PD related communication protocol to know the voltage required by the load 200, and then provides the voltage that meets the requirements of the load 200 after internal power conversion of the input voltage Vin. Among them, the conversion system applicable to the USB-PD specification can typically provide voltages of 5V, 10V, 12V, 15V, 20V, etc., with different potentials. The power conversion system 100 includes an AC-DC conversion unit 1, a DC-DC conversion unit 2, a control unit 3, a switch group 4, and an output path 5. The AC-DC conversion unit 1 receives the input voltage Vin and converts the input voltage Vin into a DC voltage Vdc. The DC-DC conversion unit 2 receives the DC voltage Vdc and converts the DC voltage Vdc into an output voltage Vo. The control unit 3 communicates with the load 200 via a handshake (Scom) protocol based on the USB-PD protocol to determine the requested voltage Vr of the load 200. The DC-DC conversion unit 2 can be, for example, but not limited to, a buck converter or a buck-boost converter, but is not limited thereto. Furthermore, the AC-DC conversion unit 1 is preferably an isolated converter (for example, but not limited to, a flyback, forward, or other converter with an isolation transformer).

[0047] Switch group 4 is coupled to the output terminal of AC-DC conversion unit 1 and DC-DC conversion unit 2, and output path 5 is coupled to switch group 4 and load 200. Control unit 3 controls the operation of switch group 4 based on the requested voltage Vr, to control AC-DC conversion unit 1 to provide DC voltage Vdc to output path 5, or to control DC-DC conversion unit 2 to provide output voltage Vo to output path 5. Specifically, control unit 3 sets a threshold voltage Vt, and after learning the requested voltage Vr through handshake communication Scom, determines whether the requested voltage Vr is higher or lower than the threshold voltage Vt. Control unit 3 is also coupled to the feedback terminals of the controllers (12, 22) inside AC-DC conversion unit 1 and DC-DC conversion unit 2, respectively, and adjusts the feedback voltage of the controller (12, 22) feedback terminal through control signals (Sc1, Sc2), so that the controller (12, 22) controls AC-DC conversion unit 1 and DC-DC conversion unit 2 to provide DC voltage Vdc and output voltage Vo that conform to the current requested voltage Vr. Among them, the control unit 3 can be a PD controller, which is mainly a programmable integrated circuit of a microprocessor, but is not limited thereto.

[0048] Furthermore, due to the different voltage levels under the USB-PD specification, there are different current specifications. For example, when the requested voltage Vr is below 15V, the maximum current that the power conversion system 100 can output is 3A, and the power it can provide is usually below 100W (e.g., but not limited to, 36W, 60W, etc.). Conversely, when the requested voltage Vr is above 15V, the maximum current that the power conversion system 100 can output is 5A, and the power it can provide is usually 100W. Therefore, when the current is 5A, the power consumed by each power component of the DC-DC conversion unit 2 is relatively large (including the power consumed by inductors, switches, internal controller 22, etc.). Therefore, one of the objectives and effects of the present invention is that when the requested voltage Vr is high, the DC voltage Vdc supplied to the load 200 is provided by the AC-DC conversion unit 1 instead of the DC-DC conversion unit 2. This can significantly reduce the power consumption of the power conversion system 100 during the conversion process, reducing the large amount of power consumed by the DC-DC conversion unit 2 to the power loss caused by the 5A current flowing through the switch group 4.

[0049] Specifically, the control unit 3, based on the requested voltage Vr being lower than the threshold voltage Vt, controls the switch group 4 to connect the DC-DC converter 2 and the output path 5, and controls the DC-DC converter 2 to provide an output voltage Vo that conforms to the requested voltage Vr to the output path 5. Conversely, based on the requested voltage Vr being higher than the threshold voltage Vt, the control unit 3 controls the switch group 4 to connect the AC-DC converter 1 and the output path 5, and controls the AC-DC converter 1 to provide a DC voltage Vdc that conforms to the requested voltage Vr to the output path 5.

[0050] See also Figure 1 The switch group 4 includes a first switch unit 42, a second switch unit 44, and a third switch unit 46. The first switch unit 42 is coupled to the AC-DC conversion unit 1 and the path switching node 48, and the second switch unit 44 is coupled to the DC-DC conversion unit 2 and the path switching node 48. The third switch unit 46 is coupled to the path switching node 48 and the output path 5, selectively providing either an output voltage Vo or a DC voltage Vdc to the output path 5 based on the states of the first switch unit 42 and the second switch unit 44. Specifically, the control unit 3 controls the second switch unit 44 and the third switch unit 46 to be turned on and the first switch unit 42 to be turned off when the requested voltage Vr is lower than the threshold voltage Vt, thereby providing the output voltage Vo to the output path 5. Conversely, the control unit 3 controls the first switch unit 42 and the third switch unit 46 to be turned on and the second switch unit 44 to be turned off when the requested voltage Vr is higher than the threshold voltage Vt, thereby providing the DC voltage Vdc to the output path 5. The third switch unit 46 is mainly used in the protection mechanism of the power conversion system 100. It is usually kept on when the power conversion system 100 is operating normally, so that the power conversion system 100 continuously supplies power to the load 200. Conversely, when the power conversion system 100 experiences an abnormal state (such as, but not limited to, overcurrent and overvoltage), the control unit 3 shuts off the third switch unit 46 to protect the power conversion system 100 and the load 200.

[0051] The second switching unit 44 can be a diode or a switch. When the second switching unit 44 is a diode, the diode is forward-biased and conducts when the voltage at the path switching node 48 is lower than the output voltage Vo. This forward-biased conduction occurs when the first switching unit 42 is turned off, corresponding to the state where the load 200 should be powered by the output voltage Vo. Conversely, the diode is reverse-biased and cut off when the voltage at the path switching node 48 is higher than the output voltage Vo. Since the DC-DC conversion unit 2 can be a buck converter, the output voltage Vo will be less than or equal to the DC voltage Vdc. Therefore, this reverse-biased cutoff occurs when the first switching unit 42 is turned on, and the load 200 is powered by the DC voltage Vdc.

[0052] On the other hand, using a switch as the second switching unit 44 is more suitable for situations where the DC-DC conversion unit 2 is a buck-boost converter (it also applies to buck converters). The control unit 3 mainly needs to control the second switching unit 44 to be turned on or off during the hold-up time after the load 200 is de-energized, to avoid the risk that the power provided by the power conversion system 100 cannot meet the demands of the load 200 in real time. Specifically, the control unit 3 controls the first switching unit 42 to be turned on during the hold-up time after the second switching unit 44 is turned off, so that after the second switching unit 44 is turned off and no longer provides output voltage Vo, the DC voltage Vdc can be controlled in real time to supply power to the load 200. Conversely, the control unit 3 controls the second switching unit 44 to be turned on during the hold-up time after the first switching unit 42 is turned off, so that after the first switching unit 42 is turned off and no longer provides DC voltage Vdc, the output voltage Vo can be controlled in real time to supply power to the load 200. In this way, the situation where the first switching unit 42 and the second switching unit 44 are turned on at the same time, causing the DC voltage Vdc and the output voltage Vo to supply power to the load 200 at the same time, can be avoided.

[0053] See also Figure 1 The power conversion system 100 further includes a discharge circuit 6, which is coupled to the output path 5 and the ground point GND. The discharge circuit 6 is primarily used to connect the output path 5 and the ground point GND when the requested voltage Vr on the output path 5 needs to be reduced, allowing the requested voltage Vr on the output path 5 to discharge rapidly through the discharge circuit 6. Specifically, when the requested voltage Vr is reduced from the current voltage, the control unit 3 controls the discharge circuit 6 to connect the output path 5 and the ground point GND, allowing the requested voltage Vr (here referring to the output voltage Vo or DC voltage Vdc) to be rapidly discharged from the current voltage to the requested voltage Vr. Then, after the requested voltage Vr is reduced to the requested voltage Vr, the control unit 3 controls the discharge circuit 6 to disconnect the output path 5 and the ground point GND to maintain the requested voltage Vr.

[0054] In a preferred embodiment, the discharge circuit 6 includes a resistor 62 and a fourth switching unit 64. The resistor 62 is coupled to the output path 5, and the fourth switching unit 64 is coupled to the resistor 62 and the ground point GND. The positions of the resistor 62 and the fourth switching unit 64 can be interchanged. When the requested voltage Vr decreases from the current voltage, the control unit 3 turns on the fourth switching unit 64, so that the requested voltage Vr can be quickly discharged from the current voltage to the requested voltage Vr. Conversely, when the requested voltage Vr increases from the current voltage or decreases from the requested voltage Vr, the control unit 3 turns off the fourth switching unit 64. It is worth noting that in one embodiment of the present invention, the discharge circuit 6 can be independently disposed outside the control unit 3 (e.g., Figure 1 (As shown), it can also be integrated into the control unit 3 to simplify the physical circuit size.

[0055] Please see Figure 2 This is a waveform diagram of an embodiment of the DC voltage and output voltage adjustment of the present invention, which can be further referenced. Figure 1 .At Figure 2 In this embodiment, when the requested voltage Vr is 5V, 9V, 12V, or 15V as specified in the USB-PD standard, and is less than the preset threshold voltage Vt (e.g., but not limited to 15.5V), the first switching unit 42 is turned off, and the second switching unit 44 is turned on, with the output voltage Vo supplying power to the load 200. When the requested voltage Vr is the highest-order voltage that can be supplied in this embodiment, such as 20V as specified in the USB-PD standard, and is greater than the threshold voltage Vt (e.g., but not limited to 15.5V), the first switching unit 42 is turned on, and the second switching unit 44 is turned off, with the DC voltage Vdc supplying power to the load 200 instead. Figure 2 As shown, control unit 3 can maintain the voltage difference between DC voltage Vdc and output voltage Vo within the range of voltage difference ΔV during voltage adjustment. The main reason for using this adjustment method is that control unit 3 typically has two protection mechanisms for the power conversion system 100. One is latched-off, which locks the system after the protection mechanism is triggered and requires a restart (e.g., but not limited to power outage) to restore normal operation. The other is auto-recovery, which automatically recovers after a short period of time without requiring a restart, once the protection mechanism is triggered. Based on the difference between the two, the latched-off protection mechanism is usually simpler in design, more comprehensive in protection, and relatively cheaper. However,... Figure 2 The voltage adjustment method is mainly applied to power conversion systems 100 with a lockout protection mechanism. This is because adjusting the output voltage Vo changes the difference between the DC voltage Vdc and the output voltage Vo. If the overvoltage protection (OVP) and undervoltage protection (UVP) settings are still based on the output voltage Vo, and the difference between the output voltage Vo and the DC voltage Vdc is too large, the power conversion system 100 will experience overvoltage or undervoltage and enter lockout mode, thus stopping the output power to the load 200. In this case, the power conversion system 100 must be restarted to restore normal operation.

[0056] Therefore, to avoid an excessively large difference between the output voltage Vo and the DC voltage Vdc, the control unit 3 maintains the difference between the DC voltage Vdc and the output voltage Vo within a voltage difference ΔV range during voltage adjustment. When the control unit 3 adjusts the current voltage to a requested voltage Vr (e.g., but not limited to, from 5V to 15V) based on a requested voltage Vr, and the difference between the current voltage and the requested voltage Vr exceeds a voltage difference ΔV (e.g., but not limited to 4.5V), the control unit 3 adjusts the DC voltage Vdc and the output voltage Vo in stages. Figure 2 In the process, after the power conversion system 100 starts up successfully, the output voltage Vo is the default voltage of 5V (that is, the preset value after power-on is 5V), and the DC voltage Vdc is 9.5V based on the default voltage of 5V plus the voltage difference ΔV (for example, but not limited to 4.5V).

[0057] Suppose that when control unit 3 adjusts the requested voltage Vr from the current voltage of 5V to a requested voltage Vr of 20V, control unit 3 determines that the difference between the current voltage and the requested voltage Vr exceeds 4.5V and performs a phased increase step. Therefore, control unit 3 first controls DC-DC converter 2 to increase the output voltage Vo to 9V by providing control signal Sc2, and then controls AC-DC converter 1 to increase the DC voltage Vdc to 13.5V by providing control signal Sc1. Subsequently, the output voltage Vo is sequentially increased step by step to 12V, 15V, and 20V, and the DC voltage Vdc is also sequentially increased step by step to 16.5V, 19.5V, and 20V based on the increase in output voltage.

[0058] Since the power conversion system 100 is powered by the AC-DC conversion unit 1 when the requested voltage Vr is above 15V, the final adjustment of the DC voltage Vdc only changes it from 19.5V to 20V, and the voltage difference ΔV remains within the range of 4.5V. Conversely, the step of the control unit 3 performing the phased reduction is similar to the step of the phased increase, and will not be described in detail here. On the other hand, since the difference between the DC voltage Vdc and the output voltage Vo is a fixed voltage difference ΔV (i.e., 4.5V) when the output voltage Vo is at 5V, 9V, 12V, and 15V, the difference between the output voltage Vo and the DC voltage Vdc is maintained at a fixed voltage difference ΔV (e.g., 4.5V). Therefore, before the output voltage Vo is adjusted, and when the output voltage Vo is within a predetermined voltage range (i.e., 5V to 15V), the output voltage Vo and the DC voltage Vdc maintain a fixed voltage difference ΔV (e.g., 4.5V). Within this range, regardless of whether the output voltage Vo is increased or decreased, the DC voltage Vdc will maintain a fixed voltage difference ΔV. This ensures that the voltage difference between the input and output voltages of the DC-DC converter is less than ΔV, allowing the DC-DC converter to maintain optimal conversion efficiency and reducing energy loss during power conversion. The predetermined voltage range can be interpreted as a specific range below the threshold voltage Vt, and its size can be selected according to the actual system design.

[0059] It should be noted that the output voltage Vo, DC voltage Vdc, requested voltage Vr, and threshold voltage Vt have a corresponding relationship. The requested voltage Vr is obtained by the control unit 3 through handshake communication Scom with the load 200, and is obtained accordingly when the demand of the load 200 changes. The control unit 3 can know the current voltage on the output path 5 (and also the magnitude of the output voltage Vo and DC voltage Vdc) through the self-detection of the power conversion system 100. If the current voltage is higher than the threshold voltage Vt set by the control unit 3, then the current voltage refers to the DC voltage Vdc; otherwise, it is the output voltage Vo. The control unit 3 controls the switch group 4 mainly by comparing the output voltage Vo with the threshold voltage Vt. On the other hand, from Figure 2 It can be seen that when the output voltage Vo is higher than the threshold voltage Vt, the output voltage Vo and the DC voltage Vdc are almost the same potential. However, since the DC-DC conversion unit 2 does not provide current (because the second switching unit 44 is turned off at this time), the power consumption is relatively low.

[0060] Please see Figure 3A This is a circuit block diagram of a variant embodiment of the power conversion system with power saving function of the present invention, and can be further referenced. Figures 1-2 The main features of the 100' power conversion system are that it includes... Figure 2The control unit 3 has a phased adjustment function for the DC voltage Vdc and the output voltage Vo. When the current voltage is lower than the requested voltage Vr, the control unit 3 first increases the output voltage Vo, and then increases the DC voltage Vdc; conversely, the control unit 3 first decreases the output voltage Vo, and then decreases the DC voltage Vdc. Specifically, before the output voltage Vo is adjusted, and when the output voltage Vo is within a predetermined voltage range (e.g., but not limited to 5V to 15V), there is a voltage difference ΔV (e.g., but not limited to 4.5V) between the output voltage Vo and the DC voltage Vdc.

[0061] When the voltage is within a predetermined range and the current voltage is less than the requested voltage Vr (e.g., 5V to be increased to 9V), the control unit 3 first increases the output voltage Vo by a second predetermined voltage (from 5V to 9V by 4V), and then increases the DC voltage Vdc by a second predetermined voltage (from 9.5V to 13.5V by 4V). Conversely, the decrease of the output voltage Vo is performed in the same way, which will not be elaborated further here. Thus, under the latched-off protection mechanism of the power conversion system 100, the overvoltage or undervoltage protection will not be triggered due to excessive adjustment of the output voltage Vo and DC voltage Vdc during the adjustment process, avoiding the situation where the power conversion system 100 erroneously triggers protection and fails when protection is not actually needed. The third switching unit 46 may be present to ensure that the power conversion system 100 still has abnormal protection functionality.

[0062] Please see Figure 3B This is a circuit block diagram of another variant embodiment of the power conversion system with power saving function of the present invention, which can be further referred to in conjunction with the above. Figures 1-3A The main feature of the power conversion system 100 is that the switch group 4' is a three-terminal switch. The control unit 3 controls the switch group 4' to connect the DC-DC conversion unit 2 and the output path 5 when the requested voltage Vr is lower than the threshold voltage Vt, so as to provide the output voltage Vo to the output path 5. Conversely, the control unit 3 controls the switch group 4' to connect the AC-DC conversion unit 1 and the output path 5 when the requested voltage Vr is higher than the threshold voltage Vt, so as to provide the DC voltage Vdc to the output path 5.

[0063] Please see Figure 4 This is a flowchart of the operation method of the power conversion system with power saving function of the present invention, which can be referred to in conjunction with the above. Figures 1-3BThe power conversion system 100 includes an AC-DC conversion unit 1, a DC-DC conversion unit 2, a switch group 4, and an output path 5. The operation method includes an output voltage adjustment stage (S100) and a DC voltage adjustment stage (S200). In step (S100), the output voltage Vo is adjusted based on the requested voltage Vr, bringing the output voltage Vo closer to the requested voltage Vr (e.g., adjusting from 5V to 9V in one step). After this adjustment stage is completed, step (S200) is entered to adjust the DC voltage Vdc based on the adjusted output voltage Vo (e.g., 9V) (e.g., adjusting from 9.5V to 13.5V = 9V + 4.5V). If the output voltage Vo has not yet been adjusted to the requested voltage Vr (e.g., the requested voltage Vr is 15V), the process returns to step (S100) for the next stage of continuous adjustment until the requested voltage Vr is reached.

[0064] Please see Figure 5A This is a detailed flowchart of the first embodiment of step S100, which can be referenced in conjunction with the diagram. Figures 1-4 The detailed actions of step S100 include:

[0065] Step S300: Determine whether the requested voltage Vr has changed, triggering an adjustment of the trigger output voltage Vo. The control unit 3 determines through handshake communication Scom whether the output voltage Vo needs to be adjusted based on the target value of the requested voltage Vr. If the determination result is yes, proceed to step (S320). If the determination result is no, proceed directly to step S200. For example: when the requested voltage Vr before and after the adjustment is greater than the threshold voltage Vt (e.g., but not limited to, adjusting from 25V to 20V), the load 200 is powered by the DC voltage Vdc output by the AC-DC conversion unit 1 before and after the adjustment. In this case, it is determined that there is no need to adjust the output voltage Vo, and the process can proceed directly to step S200.

[0066] Step S320: Set the output voltage Vo of the DC-DC conversion unit 2 to the requested voltage.

[0067] Step S340: Determine whether the output voltage Vo in step S320 has been boosted (S340). If the determination result is yes, proceed to step (S200). If the determination result is no, proceed to step (S360).

[0068] Step S360: Confirm that the state of the first switching unit is correct, and then discharge the output path 5 for a preset discharge period to reduce the output voltage Vo to the requested voltage Vr. Before the preset discharge period ends, control the first switching unit 42 to turn off to accelerate the reduction of the output voltage Vo and reduce unnecessary power loss. When the discharge period ends, the reduced output voltage Vo is less than the threshold voltage Vt, so the control unit 3 must control the first switching unit 42 to turn off to prevent a higher DC voltage Vdc from being supplied to the output path 5.

[0069] Step S380: Confirm the correct status of the discharge circuit (S380). When the output voltage Vo is to be reduced, the control unit 3 must control the discharge circuit 6 to connect the output path 5 and the ground point GND to discharge the output voltage Vo for a preset discharge period, so that the output voltage Vo can be quickly discharged from the current voltage to the requested voltage Vr. After the preset discharge period ends, the control unit 3 must control the discharge circuit 6 to turn off, so that the output path 5 is isolated from the ground point GND, and proceed to step (S200).

[0070] It is worth mentioning that, in one embodiment of the present invention, Figure 5A The flowchart mainly describes the automatic recovery protection mechanism applicable to the power conversion system 100. When the output voltage Vo is directly reduced from the current voltage to the requested voltage Vr (e.g., but not limited to, from 20V to 5V), triggering overvoltage or undervoltage protection, this is a transient phenomenon during the adjustment of the output voltage Vo. After a short period of time following the triggering of the protection, when the system automatically recovers from the protection state, the output voltage Vo has been adjusted to the requested voltage Vr, and can still supply power to the load 200 normally.

[0071] Please see Figure 5B This is a detailed flowchart of the second embodiment of step S100, which can be referred to in conjunction with the above. Figures 1-4 The flowchart in this embodiment is consistent with... Figure 5A The difference in the flowcharts is that, Figure 5A Step (S320) is replaced by setting the output voltage Vo to adjust the relay voltage by one step in the direction of the requested voltage (S320'). This adjustment method is mainly used in application Figure 2 The step adjustment method shown is mainly applicable to the protection mechanism of power conversion systems where the circuit breaker is 100% latched off. In the output voltage Vo adjustment steps, the output voltage Vo is adjusted only one step at a time, until... Figure 4After steps (S100) to (S200) are completed, the output voltage Vo is further adjusted one level in the next cycle. In this way, the overvoltage or undervoltage protection is not triggered when the output voltage Vo is directly adjusted from the current voltage to the requested voltage Vr (e.g., but not limited to: directly adjusted from 5V to 20V, or directly adjusted from 20V to 5V), and the protection mechanism is not mistakenly triggered by the instantaneous signal during the adjustment of the output voltage Vo.

[0072] Please see Figure 6A This is a detailed flowchart of the first embodiment of step S200, which can be referred to in conjunction with the above. Figures 1-5B .in, Figure 6A The main focus is on adjusting the DC voltage Vdc. Because the adjustment of the DC voltage Vdc depends on the adjustment method of the output voltage Vo, therefore... Figure 6A The DC voltage Vdc adjustment method can be based on Figures 5A-5B Following the spirit of this process, make corresponding fine adjustments (i.e., direct adjustment or step adjustment). Specifically, after the output voltage Vo adjustment process is completed, proceed to step (S200). Step S200 includes the following steps:

[0073] Step S300: Determine whether the DC voltage Vdc needs to be boosted. If the determination result is yes, proceed to step S420 DC voltage Vdc boost adjustment step; if the determination result is yes, proceed to step S700 DC voltage Vdc discharge de-voltage adjustment step.

[0074] Step S420: Determine whether (1) the current DC voltage Vdc is lower than the threshold voltage and (2) the requested voltage Vr is higher than the threshold voltage. If both (1) and (2) are true, proceed to steps S440-540 for boosting the voltage and the power conversion system 100 needs to switch from supplying power at the output voltage Vo to supply power at the DC voltage Vdc. Therefore, it is necessary to perform a fine-tuning operation on the DC voltage Vdc before using it to supply power to the load 200, in order to avoid accidentally triggering the overvoltage protection during the adjustment of the DC voltage Vdc.

[0075] Step S440: Confirm the correct state of the first switching unit (S440). When the voltage at path switching node 48 is lower than the threshold voltage Vt, DC voltage Vdc will not be used to power load 200, and the first switching unit 42 needs to be turned off to prevent DC voltage Vdc from being supplied to output path 5. Conversely, when the voltage at path switching node 48 is higher than the threshold voltage Vt, DC voltage Vdc needs to be used to power load 200, and the first switching unit 42 needs to be turned on.

[0076] Step S460: Increase the DC voltage Vdc to the threshold voltage (e.g., but not limited to 15.5V). The reason for adjusting the DC voltage Vdc to the threshold voltage Vt first instead of continuing to increase it is that if the DC voltage Vdc is directly adjusted to a requested voltage Vr (e.g., but not limited to 20V) higher than the threshold voltage Vt, it may exceed the overvoltage protection (OVP) limit when the output voltage Vo of the DC-DC converter unit 2 is 20V. In particular, there will be a momentary phenomenon of voltage overshoot when increasing it, which is very easy to accidentally trigger the overvoltage protection, causing the DC-DC converter unit 2 to be locked off and stop supplying power to the control unit 3, resulting in the control unit 3 becoming inoperable.

[0077] Step S480: An additional first predetermined voltage (e.g., but not limited to 4V to 8V) is added to the overvoltage protection setting point when the output voltage Vo of the DC-DC converter unit 2 is 20V, to prevent the overvoltage protection mechanism from being erroneously triggered during the voltage adjustment process. This is because during the process of adjusting the DC voltage Vdc to the requested voltage Vr (e.g., but not limited to 20V) above the threshold voltage Vt, at the rising edge of the voltage increase (see reference...). Figure 2 This can lead to overshoot (the same applies to the falling edge). However, if the design uses an output voltage Vo of 20V as the overvoltage protection point (typically designed at 1.2 times the output voltage Vo), then when the overshoot voltage exceeds 24V, the overvoltage protection mechanism may be triggered. Therefore, this step sets the overvoltage protection to the highest requested voltage (e.g., but not limited to 20V) acceptable to the DC-DC converter unit 2, plus a first predetermined voltage.

[0078] Step S500: The DC voltage Vdc is increased to between the threshold voltage (e.g., but not limited to 15.5V) and the requested voltage (e.g., but not limited to 20V). This step is mainly to reduce the overshoot amplitude, thereby reducing the risk of accidental overvoltage protection activation. Specifically, the higher the DC voltage Vdc is increased, the higher the relative overshoot amplitude (the same applies to the output voltage Vo). Therefore, if the requested voltage Vr is increased from the current voltage, which is below the threshold voltage Vt, to a requested voltage Vr, which is above the threshold voltage Vt, the voltage increase amplitude is usually relatively high. To avoid excessive overshoot caused by this adjustment, the control unit 3 adjusts the DC voltage Vdc from the current voltage to the relay voltage (e.g., but not limited to 17.5V). The relay voltage is mainly between the threshold voltage Vt and the requested voltage Vr, and can be reasonably designed according to the degree of overshoot in the actual circuit. It is worth mentioning that in one embodiment of the present invention, if the overshoot condition is not considered or the overshoot condition is low, this step can be omitted.

[0079] Step S520: Turn on the first switching unit. After the DC voltage Vdc is increased to the relay voltage, the relay voltage can roughly meet the needs of the load 200. Therefore, the first switching unit 42 can be turned on first to provide DC voltage Vdc to power the load 200. On the other hand, the second switching unit 44 can be controlled according to its implementation type (diode or switch).

[0080] Step S540: Increase the DC voltage to the requested voltage Vr. After the first switching unit 42 is turned on, the control unit 3 controls the AC-DC conversion unit 1 to continue increasing the DC voltage Vdc until the DC voltage Vdc reaches the requested voltage Vr and meets the requirements of the load 200.

[0081] See also Figure 6A If step (S400) determines otherwise, the process proceeds to step (S700) to confirm the correct state of the first switching unit; if step (S420) determines otherwise, the process proceeds to step (S600) to confirm the correct state of the first switching unit. Steps (S600) and (S700) also confirm that the first switching unit 42 must be correctly turned on or off. For the control logic of turning the first switching unit 42 on or off, please refer to [link to relevant documentation]. Figure 4 The details of steps (S440) in section 6 will not be repeated here.

[0082] Step S620: After confirmation in step (S600), the DC voltage is increased to either (1) the requested voltage plus the second predetermined voltage or (2) the requested voltage. For case (1), please refer to [reference needed]. Figure 2 This refers to a situation where the output voltage Vo is below the threshold voltage Vt before and after adjustment (e.g., but not limited to adjusting from 9V to 12V), but not above the threshold voltage Vt. This means that the power conversion system 100 supplies power to the load 200 with the output voltage Vo before and after adjustment. Therefore, the DC voltage Vdc is adjusted to the requested voltage Vr (i.e., the output voltage Vo) plus a second predetermined voltage (e.g., 4.5V) in response to the adjustment of the output voltage Vo. In case (2), when there is more than one set of settable output voltage potentials on the threshold voltage Vt, the DC voltage Vdc may be above the threshold voltage Vt before and after adjustment (e.g., but not limited to adjusting from 18V to 20V). In this case, the power conversion system 100 supplies power to the load 200 with the DC voltage Vdc before and after adjustment, and the adjustment voltage difference is limited. Therefore, in this case, the DC voltage Vdc can be directly adjusted to the requested voltage Vr.

[0083] Step S720: After confirmation in step (S700), there are three possibilities for the DC voltage reduction. One is that the DC voltage Vdc is above the threshold voltage Vt before and after the reduction; another is that the DC voltage Vdc is below the threshold voltage Vt before and after the reduction; and the last is that the DC voltage Vdc is adjusted from above the threshold voltage Vt to below the threshold voltage Vt. Regardless of the reduction method, it is necessary to confirm whether the state of the discharge circuit is correct. Specifically, regardless of the reduction method, the discharge circuit 6 must connect the output path 5 and the ground point GND to discharge the output path 5 for a preset discharge period, so that the voltage of the path switching node 48 decreases, and the DC voltage Vdc can be quickly discharged from the current voltage to approach the requested voltage Vr. After the preset discharge period ends or the requested voltage Vr is discharged, the control unit 3 controls the discharge circuit 6 to disconnect the output path 5 and the ground point GND.

[0084] Step S740: Reduce the DC voltage to the requested voltage or reduce it to the requested voltage plus a second predetermined voltage. Similar to step (S620), the reduction of the DC voltage Vdc is determined based on the reduction of the output voltage Vo, and is separated by a threshold voltage Vt. When the reduced DC voltage Vdc is below the threshold voltage Vt, the DC voltage Vdc will be reduced to the requested voltage Vr plus a second predetermined voltage; otherwise, the DC voltage Vdc will be reduced to the requested voltage Vr.

[0085] Please see Figure 6B This is a detailed flowchart of the second embodiment of step S200, which can be referred to in conjunction with the above. Figures 1-5B The flowchart in this embodiment is consistent with... Figure 6A The differences in the flowcharts are:

[0086] i. Figure 6A Step S620 is replaced by step S620': Set the DC voltage Vdc to be increased one step to another relay voltage in the direction of (1) request voltage plus the second predetermined voltage or (2) request voltage.

[0087] ii. Figure 6A Step S740 is replaced by step S740': Set the DC voltage Vdc to decrease by one order to another relay voltage in the direction of (1) request voltage plus the second predetermined voltage or (2) request voltage.

[0088] iii. Figure 6AStep S420 is replaced by step S420': Determine whether (1) the current DC voltage Vdc is "the highest-order voltage output below the threshold voltage (e.g., but not limited to 15.5V)" (e.g., but not limited to 15V) and (2) the requested voltage Vr is above the threshold voltage. When both (1) and (2) are true, proceed to steps S440-540 for boosting and the power conversion system 100 needs to switch from power supply to DC voltage Vdc.

[0089] This adjustment method is mainly based on the application Figure 2 The step adjustment method shown indicates that in the DC voltage Vdc adjustment steps, the DC voltage Vdc is adjusted only one step at a time. Figure 4 After steps (S100) to (S200) are completed, the DC voltage Vdc is further adjusted in the next cycle. This avoids the situation where the DC voltage Vdc adjustment voltage difference is too large, triggering overvoltage or undervoltage protection, and avoids the protection mechanism being falsely triggered by instantaneous signals during DC voltage Vdc adjustment.

[0090] Of course, the present invention may have other various embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the appended claims.

Claims

1. A power conversion system, characterized by, A power conversion system converts an input voltage to power a load, and the power conversion system includes: an AC-DC conversion unit receiving the input voltage and converting the input voltage to a DC voltage; a DC-DC conversion unit receiving the DC voltage and converting the DC voltage to an output voltage; a control unit communicating with the load to obtain a requested voltage demanded by the load; a switch set coupled between the AC-DC conversion unit and the DC-DC conversion unit; an output path coupled between the switch set and the load; wherein when the requested voltage is lower than a threshold voltage, the control unit controls the switch set to couple the DC-DC conversion unit to the output path and controls the DC-DC conversion unit to provide the output voltage conforming to the requested voltage to the output path; when the requested voltage is higher than the threshold voltage, the control unit controls the switch set to couple the AC-DC conversion unit to the output path and controls the AC-DC conversion unit to provide the DC voltage conforming to the requested voltage to the output path; wherein the control unit maintains a difference between the DC voltage and the output voltage within a voltage difference range, when the control unit adjusts the DC voltage from a current voltage to a requested voltage based on the requested voltage, and the difference between the current voltage and the requested voltage exceeds the voltage difference range, the control unit adjusts the output voltage and the DC voltage by a second predetermined voltage in stages, in each stage, the control unit maintains the difference between the output voltage and the DC voltage less than the voltage difference; and when the current voltage is greater than the requested voltage, the control unit adjusts the output voltage and the DC voltage by the second predetermined voltage in stages, in each stage, the control unit maintains the difference between the output voltage and the DC voltage less than the voltage difference. wherein when the current voltage is less than the requested voltage, the control unit first adjusts the output voltage and then adjusts the DC voltage; when the current voltage is greater than the requested voltage, the control unit first adjusts the DC voltage and then adjusts the output voltage.

2. The power conversion system of claim 1, wherein, wherein the switch set includes:

3. The power conversion system of claim 1, wherein, a first switch unit coupled between the AC-DC conversion unit and a path switching node; a second switch unit coupled between the DC-DC conversion unit and the path switching node; and a third switch unit coupled between the path switching node and the output path; wherein the control unit controls the second switch unit and the third switch unit to be turned on based on the requested voltage being lower than the threshold voltage, and controls the first switch unit and the third switch unit to be turned on based on the requested voltage being higher than the threshold voltage. wherein when the requested voltage is raised from a current voltage lower than the threshold voltage to be higher than the threshold voltage, the control unit controls the first switch unit to be turned on after adjusting the DC voltage from the current voltage to a relay voltage, and adjusts the DC voltage from the relay voltage to the requested voltage after the first switch unit is turned on.

4. The power conversion system of claim 3, wherein, ​ 5. The power conversion system of claim 4, wherein, The control unit sets an overvoltage protection threshold of the DC-DC conversion unit at a highest requested voltage plus a first predetermined voltage, and then adjusts the DC voltage from a current voltage to a relay voltage.

6. The power conversion system of claim 3, wherein, When the requested voltage is adjusted from the current voltage to be lower than the threshold voltage, the control unit controls the first switch unit to be off, and adjusts the output voltage from the current voltage to the requested voltage.

7. The power conversion system of claim 3, wherein, The second switch unit is a diode, which is forward-biased on and reverse-biased off based on the voltage of the path switching node being lower and higher than the output voltage, respectively.

8. The power conversion system of claim 3, wherein, The control unit controls the second switch unit to be off for a maintaining time before the first switch unit is on, and controls the second switch unit to be on for the maintaining time after the first switch unit is off.

9. The power conversion system of claim 3, wherein, The control unit controls the third switch unit to be off based on an abnormal state of the power conversion system.

10. The power conversion system of claim 1, wherein, Further comprising: a discharge circuit coupled between the output path and a ground point; The control unit controls the discharge circuit to be on between the output path and the ground point based on the requested voltage being adjusted from the current voltage, and controls the discharge circuit to be off between the output path and the ground point based on the requested voltage being adjusted.

11. The power conversion system of claim 10, wherein, The discharge circuit comprises: a resistor coupled between the output path; and a fourth switch unit coupled between the resistor and the ground point; The control unit controls the fourth switch unit to be on based on the requested voltage being adjusted from the current voltage, and controls the fourth switch unit to be off based on the requested voltage being adjusted.

12. A power conversion system characterized by, The power conversion system converts an input voltage to supply power to a load, and comprises: an AC-DC conversion unit receiving the input voltage and converting the input voltage to a DC voltage; a DC-DC conversion unit receiving the DC voltage and converting the DC voltage to an output voltage; a control unit performing a handshake communication with the load to obtain a requested voltage required by the load, and adjusting the output voltage from a current voltage to the requested voltage based on the handshake communication; an output path coupled between the DC-DC conversion unit and the load; When the current voltage is less than the requested voltage, the control unit first adjusts the output voltage, and then adjusts the DC voltage; When the current voltage is greater than the requested voltage, the control unit first adjusts the output voltage, and then adjusts the DC voltage; and Before the output voltage is adjusted, and when the output voltage is within a predetermined voltage range, the control unit maintains a difference between the DC voltage and the output voltage within a voltage difference range; When the output voltage is within the predetermined voltage range, and the current voltage is less than the requested voltage, the control unit first adjusts the output voltage by a second predetermined voltage, and then adjusts the DC voltage by the second predetermined voltage, so that the difference between the output voltage and the DC voltage is always less than the voltage difference. When the current voltage is greater than the requested voltage, the control unit first adjusts the output voltage down by the second predetermined voltage, and then adjusts the DC voltage down by the second predetermined voltage, so that the difference between the output voltage and the DC voltage always remains less than the voltage difference.

13. A method of operating a power conversion system, characterized by, The operation method for controlling the power conversion system to convert an input voltage for supplying power to a load includes the following steps: controlling the AC-DC conversion unit to convert the input voltage into a DC voltage; controlling the DC-DC conversion unit to convert the DC voltage into an output voltage; performing a handshake communication with the load to obtain a requested voltage required by the load; when the requested voltage is lower than a threshold voltage, controlling the switch group to connect the DC-DC conversion unit and the output path, and controlling the DC-DC conversion unit to provide the output voltage conforming to the requested voltage to the output path; when the requested voltage is higher than the threshold voltage, controlling the switch group to connect the AC-DC conversion unit and the output path, and controlling the AC-DC conversion unit to provide the DC voltage conforming to the requested voltage to the output path; when the requested voltage needs to be adjusted, determining whether a difference between a current voltage of the output path and the requested voltage exceeds a range of a voltage difference; when the difference between the current voltage and the requested voltage exceeds the range of the voltage difference, adjusting the DC voltage and the output voltage in stages; when the current voltage is less than the requested voltage, adjusting the output voltage and the DC voltage in stages by a second predetermined voltage, so that in each stage, the difference between the output voltage and the DC voltage always remains less than the voltage difference; and when the current voltage is greater than the requested voltage, adjusting the output voltage and the DC voltage in stages by the second predetermined voltage, so that in each stage, the difference between the output voltage and the DC voltage always remains less than the voltage difference. The operation method further includes the following steps:

14. The operating method of claim 13, wherein, when the current voltage is less than the requested voltage, first adjusting the output voltage, and then adjusting the DC voltage; and when the current voltage is greater than the requested voltage, first adjusting the output voltage, and then adjusting the DC voltage. The operation method further includes the following steps:

15. The operating method of claim 13, wherein, determining whether the requested voltage is raised from a current voltage lower than the threshold voltage to be higher than the threshold voltage; based on the requested voltage being raised from the current voltage to be higher than the threshold voltage, controlling the AC-DC conversion unit to adjust the DC voltage to the requested voltage; and controlling the switch group to connect the AC-DC conversion unit and the output path. The operation method further includes the following steps:

16. The operating method of claim 15, wherein, based on the requested voltage being raised from the current voltage, setting a voltage protection threshold of the DC-DC conversion unit at a highest requested voltage plus a first predetermined voltage; adjusting the DC voltage from the current voltage to an intermediate voltage; controlling the switch group to connect the AC-DC conversion unit and the output path; and adjusting the DC voltage from the intermediate voltage to the requested voltage. The operation method further includes the following steps:

17. The operating method of claim 15, wherein, determining whether the requested voltage is lowered from a current voltage to be lower than the threshold voltage; ​ based on the request voltage being reduced from a current voltage below the threshold voltage, controlling the switch set to disconnect the AC-DC conversion unit from the output path; controlling the DC-DC conversion unit to adjust the output voltage to the request voltage.

18. The operating method of claim 17, wherein, further comprising the steps of: controlling the switch set to connect the DC-DC conversion unit to the output path.

19. The operating method of claim 13, wherein, further comprising the steps of: based on the request voltage being reduced from a current voltage, controlling a discharge circuit to connect the output path to a ground; and based on the request voltage being reduced, controlling the discharge circuit to disconnect the output path from the ground.

20. A method of operating a power conversion system, characterized by, controlling the power conversion system to convert an input voltage to power a load, and the power conversion system comprising an AC-DC conversion unit, a DC-DC conversion unit, a switch set, and an output path, the method comprising the steps of: controlling the AC-DC conversion unit to convert the input voltage to a DC voltage; controlling the DC-DC conversion unit to convert the DC voltage to an output voltage; communicating with the load to obtain a request voltage demanded by the load, and adjusting the output voltage from a current voltage to the request voltage based on the request voltage; when the output voltage is adjusted from the current voltage to the request voltage, and the current voltage is less than the request voltage, first increasing the output voltage, and then increasing the DC voltage; and when the output voltage is adjusted from the current voltage to the request voltage, and the current voltage is greater than the request voltage, first decreasing the output voltage, and then decreasing the DC voltage; wherein, before the output voltage is adjusted, and the output voltage is within a predetermined voltage range, there is a voltage difference between the output voltage and the DC voltage, and the method further comprises the steps of: when the current voltage is less than the request voltage, first increasing the output voltage by a second predetermined voltage, and then increasing the DC voltage by the second predetermined voltage, to maintain the voltage difference; and when the current voltage is greater than the request voltage, first decreasing the output voltage by the second predetermined voltage, and then decreasing the DC voltage by the second predetermined voltage, to maintain the voltage difference. ​

Images