CN114553023A - Power conversion system and method of operating the same - Google Patents

Abstract

A power conversion system is in handshake communication with a load to correspondingly convert an input voltage to supply power to the load, and the power conversion system comprises 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 converts an input voltage into a DC voltage, and the DC-DC conversion unit converts the DC voltage into an output voltage. When the request voltage of the load is lower than the threshold voltage, the control unit controls the switch group to lap the direct current-direct current conversion unit so as to provide the output voltage to the output path. When the request voltage is higher than the threshold voltage, the control unit controls the switch group to lap the alternating current-direct current conversion unit so as to provide direct current voltage to the output path.

Description

Power conversion system and method of operating the same

Technical Field

The present invention relates to a power conversion system and an operating method thereof, and more particularly, to a power conversion system with power saving and an operating method thereof.

Background

As more and more electronic products come out nowadays, the power sources usually used by various portable electronic products are different, and it is necessary to use a voltage with a specific potential for power supply (or charging) to enable the electronic products to be used normally. Therefore, in the development of the power supply technology, a power conversion system capable of adjusting the output voltage according to the load requirement is developed. The Power conversion system is mainly suitable for a conversion system under the USB-PD (USB-Power Delivery) specification, and can provide a plurality of groups of voltage supply loads with different potentials. The power conversion system uses the Type-C port to connect a load with the same USB-PD specification, so as to communicate with the load to know the load demand, and then provide power meeting the load demand to enable the load to operate (or charge) normally. The above power conversion system generally includes: a first stage AC-DC conversion unit and a second stage DC-DC conversion unit. The AC-DC conversion unit receives the AC input voltage of the commercial power and converts the input voltage into DC voltage. The DC-DC conversion unit receives the DC voltage and converts the DC voltage into an output voltage.

However, the range of voltage potentials that can be provided by the power conversion system is wide in response to the load requirements, and the power conversion system can usually have multiple voltage outputs within 5V to 20V. And because the power provided by each group of voltages is different under the USB-PD specification, the current provided to the load under each group of voltages is also different. (1) With higher voltage potentials provided, the current that can generally be provided is also relatively high. Thus, the power consumed by the dc-dc conversion unit is greatly increased under the condition of higher voltage potential; (2) if the dc-dc conversion unit outputs a fixed higher dc voltage (e.g., 22V), then when the output voltage of the power conversion system is lower voltage level in the USB-PD specification (e.g., 5V); thus, the dc-dc conversion unit needs to convert the 22V voltage input into the 5V voltage output, which results in poor conversion efficiency of the whole power conversion system. For both of the above reasons, the power consumption loss during the power conversion process is greatly increased, and the energy saving requirement cannot be met.

Therefore, how to design a power conversion system with power consumption saving function and its operation method to save the power consumption of the power conversion system under the condition of higher voltage potential is a major subject to be studied by the present invention.

Disclosure of Invention

In order to solve the above problem, the present invention provides a power conversion system, which converts an input voltage to supply power to a load, and 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 receives an input voltage and converts the input voltage into a DC voltage. The DC-DC conversion unit receives the DC voltage and converts the DC voltage into an output voltage. The control unit is in handshake communication with the load to obtain the requested voltage required by the load. The switch set is coupled to the AC-DC conversion unit and the DC-DC conversion unit, and the output path is coupled to the switch set and the load. When the request voltage is lower than the threshold voltage, the control unit controls the switch group to lap the DC-DC conversion unit and the output path, and controls the DC-DC conversion unit to provide the output voltage which accords with the request voltage to the output path. When the request voltage is higher than the threshold voltage, the control unit controls the switch group to lap the alternating current-direct current conversion unit and the output path, and controls the alternating current-direct current conversion unit to provide direct current voltage which meets the request voltage to the output path.

In order to solve the above problem, the present invention provides a power conversion system, which converts an input voltage to supply power to a load, and includes an ac-dc conversion unit, a dc-dc conversion unit, a control unit, and an output path. The AC-DC conversion unit receives an input voltage and converts the input voltage into a DC voltage. The DC-DC conversion unit receives the DC voltage and converts the DC voltage into an output voltage. The control unit is in handshake communication with the load to obtain a request voltage required by the load, and adjusts the output voltage from the current voltage to the request voltage based on the handshake communication. The output path is coupled with the DC-DC conversion unit group and the load, when the current voltage is less than the request voltage, the control unit firstly increases the output voltage and then increases the DC voltage, and when the current voltage is more than the request voltage, the control unit firstly decreases the output voltage and then decreases the DC voltage.

In order to solve the above problem, the present invention provides an operating method of a power conversion system, which controls the power conversion system to convert an input voltage to supply power to a load, and the power conversion system includes an ac-dc conversion unit, a dc-dc conversion unit, a switch group and an output path. The method of operating a power conversion system includes the steps of: (a) and controlling the alternating current-direct current conversion unit to convert the input voltage into direct current voltage. (b) And controlling the direct current-direct current conversion unit to convert the direct current voltage into the output voltage. (c) And carrying out handshake communication with the load to obtain the required voltage required by the load. (d) When the request voltage is lower than the threshold voltage, the control switch group is used for overlapping the DC-DC conversion unit and the output path, and controlling the DC-DC conversion unit to provide the output voltage which accords with the request voltage to the output path. (e) When the request voltage is higher than the threshold voltage, the control switch group is used for overlapping the alternating current-direct current conversion unit and the output path, and controlling the alternating current-direct current conversion unit to provide direct current voltage which accords with the request voltage to the output path.

In order to solve the above problem, the present invention provides an operating method of a power conversion system, which controls the power conversion system to convert an input voltage to supply power to a load, and 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 comprises the following steps: (a) and controlling the alternating current-direct current conversion unit to convert the input voltage into direct current voltage. (b) And controlling the direct current-direct current conversion unit to convert the direct current voltage into the output voltage. (c) And d, when the output voltage is adjusted from the current voltage to the request voltage and the current voltage is less than the request voltage, the output voltage is firstly increased and then the direct-current voltage is increased. (e) When the output voltage is adjusted from the current voltage to the request voltage and the current voltage is greater than the request voltage, the output voltage is firstly reduced, and then the direct-current voltage is reduced.

The main purpose and effect of the present invention is that when the request voltage is higher, the control unit bypasses the dc-dc conversion unit by controlling the switch set, so as to achieve the effect of saving the power consumption of the power conversion system by providing the dc voltage supply load through the ac-dc conversion unit instead.

The invention is described in detail below with reference to the drawings and specific examples, but the invention is not limited thereto.

Drawings

FIG. 1 is a block diagram of a power conversion system with power consumption saving function according to an embodiment of the present invention;

FIG. 2 is a waveform diagram illustrating DC voltage and output voltage regulation according to an embodiment of the present invention;

FIG. 3A is a block diagram of an alternative embodiment of a power conversion system with power consumption reduction features according to the present invention;

FIG. 3B is a block diagram of another alternative embodiment of the power conversion system with power consumption saving function according to the present invention;

FIG. 4 is a flowchart of a method of operating a power conversion system with power consumption saving features according to the present invention;

FIG. 5A is a detailed flowchart of the first embodiment of step S100;

FIG. 5B is a detailed flowchart of the second embodiment of step S100;

fig. 6A is a detailed flowchart of the first embodiment of step S200; and

fig. 6B is a detailed flowchart of the second embodiment of step S200.

Wherein, the reference numbers:

100. 100', 100 ": power conversion system

1: AC-DC conversion unit

2: DC-DC conversion unit

12. 22: controller

3: control unit

4. 4': switch group

42: first switch unit

44: second switch unit

46: third switch unit

48: path switching node

5: output path

6: discharge circuit

62: resistance (RC)

64: fourth switch unit

GND: grounding point

200: load(s)

Vin: input voltage

Vdc: direct voltage

Vo: output voltage

Vr: request voltage

Vt: threshold voltage

Δ V: voltage difference

And Scom: handshake communication

Sc1, Sc 2: control signal

Detailed Description

The invention will be described in detail with reference to the following drawings, which are provided for illustration purposes and the like:

fig. 1 is a circuit block diagram of a power conversion system with power consumption saving function according to an embodiment of the present invention. The Power conversion system 100 is suitable for a conversion system under the USB-PD (USB-Power Delivery) specification, and can provide a plurality of voltage supply loads 200 with different potentials. The power conversion system 100 is mainly configured to perform handshake communication with the load 200 based on USB-PD related communication protocols to obtain the voltage required by the load 200, and then convert the input voltage Vin via internal power to provide the voltage meeting the requirement of the load 200 to power the load 200. Among them, the conversion system applied under the USB-PD specification can generally 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 an 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 the output voltage Vo. The control unit 3 performs Handshake (Handshake) communication Scom with the load 200 based on the USB-PD related communication protocol to obtain the requested voltage Vr required by the load 200. The dc-dc conversion unit 2 may be, for example but not limited to, a BUCK (BUCK) converter or a BUCK-boost converter, but is not limited thereto. In addition, the ac-dc conversion unit 1 may be preferably an isolated converter (for example, but not limited to, a converter having an isolation transformer in a flyback type, a forward type, etc.).

The switch set 4 is coupled to the output terminal of the ac-dc converting unit 1 and the output terminal of the dc-dc converting unit 2, and the output path 5 is coupled to the switch set 4 and the load 200. The control unit 3 controls the switch set 4 to operate based on the request voltage Vr to control the ac-dc converting unit 1 to provide the dc voltage Vdc to the output path 5, or to control the dc-dc converting unit 2 to provide the output voltage Vo to the output path 5. Specifically, the control unit 3 sets the threshold voltage Vt, and determines whether the request voltage Vr is higher or lower than the threshold voltage Vt after knowing the request voltage Vr through handshake communication Scom. The control unit 3 is also coupled to the feedback terminals of the controllers (12, 22) inside the ac-dc conversion unit 1 and the dc-dc conversion unit 2, respectively, and adjusts the feedback voltages of the feedback terminals of the controllers (12, 22) through the control signals (Sc1, Sc2), so that the controllers (12, 22) control the ac-dc conversion unit 1 and the dc-dc conversion unit 2 to provide the dc voltage Vdc and the output voltage Vo corresponding to the current request voltage Vr accordingly. The control unit 3 may be a PD controller, which is mainly a programmable integrated circuit of a Microprocessor (Microprocessor), but not limited thereto.

Further, there may be different current specifications due to the voltage of different potential under the USB-PD specification. For example, when the request voltage Vr is below 15V, the power conversion system 100 sets the outputtable current to be at most 3A, and the power that can be provided by the power conversion system is usually below 100W (for example, but not limited to, 36W, 60W, etc.). On the contrary, when the request voltage Vr is above 15V, the power conversion system 100 sets the maximum outputtable current to 5A, and the available power is usually 100W. Therefore, when the current is 5A, the power consumed by each power element of the dc-dc conversion unit 2 is large (including the consumption of the inductor, the switch, the internal controller 22, and the like). Therefore, one of the objectives and effects of the present invention is to provide the dc voltage Vdc to the load 200 from the ac-dc conversion unit 1 by bypassing the dc-dc conversion unit 2 when the requested voltage Vr is higher, so as to greatly reduce the power consumption of the power conversion system 100 during the conversion process, and reduce the power loss caused by the 5A current flowing through the switch group 4 from the original more power consumed by the dc-dc conversion unit 2.

Specifically, the control unit 3 controls the switch group 4 to overlap the dc-dc conversion unit 2 and the output path 5 based on the request voltage Vr being lower than the threshold voltage Vt, and controls the dc-dc conversion unit 2 to provide the output voltage Vo according with the request voltage Vr to the output path 5. On the contrary, the control unit 3 controls the switch group 4 to overlap the ac-dc conversion unit 1 and the output path 5 based on the request voltage Vr being higher than the threshold voltage Vt, and controls the ac-dc conversion unit 1 to provide the dc voltage Vdc corresponding to the request voltage Vr to the output path 5.

Referring back to fig. 1, the switch set 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 switching unit 46 is coupled to the path switching node 48 and the output path 5 to selectively provide the output voltage Vo or the dc voltage Vdc to the output path 5 based on states of the first switching unit 42 and the second switching unit 44. Specifically, the control unit 3 controls the second switching unit 44 and the third switching unit 46 to be turned on and the first switching unit 42 to be turned off based on the request voltage Vr being lower than the threshold voltage Vt to supply the output voltage Vo to the output path 5. On the contrary, the control unit 3 controls the first and third switching units 42 and 46 to be turned on and the second switching unit 44 to be turned off based on the request voltage Vr being higher than the threshold voltage Vt to provide the dc voltage Vdc to the output path 5. The third switching unit 46 is mainly applied to a protection mechanism of the power conversion system 100, and is usually kept turned on when the power conversion system 100 operates normally, so that the power conversion system 100 continuously supplies power to the load 200. On the contrary, when an abnormal state (for example, but not limited to, an overcurrent and overvoltage, etc.) occurs in the power conversion system 100, the control unit 3 turns off the third switching unit 46 to protect the power conversion system 100 and the load 200.

The second switching unit 44 may be a diode or a switch. When the second switching unit 44 is a diode, the diode is forward-biased to conduct based on the voltage of the path switching node 48 being lower than the output voltage Vo. This forward-biased on condition occurs when the first switch unit 42 is turned off, which corresponds to a state that the load 200 should be supplied by the output voltage Vo. Conversely, the diode is reverse biased off based on the voltage at the path switching node 48 being higher than the output voltage Vo. Since the dc-dc converting unit 2 may be a buck converter, the output voltage Vo is less than or equal to the dc voltage Vdc, and therefore, the reverse bias cut-off condition occurs when the first switch unit 42 is turned on and the load 200 is powered by the dc voltage Vdc.

On the other hand, the use of a switch as the second switching unit 44 is more suitable for a case where the dc-dc conversion unit 2 is a step-up/step-down converter (the same applies to a step-down converter). The control unit 3 mainly needs to control the second switch unit 44 to be turned on or off within a Hold Time (Hold-Up Time) after the load 200 is powered off, so as to avoid a risk that the power provided by the power conversion system 100 cannot meet the demand of the load 200 in real Time. Specifically, the control unit 3 controls the first switch unit 42 to be turned on during the holding time after the second switch unit 44 is turned off, so that the dc voltage Vdc can be controlled to supply power to the load 200 in real time after the second switch unit 44 is turned off without providing the output voltage Vo. On the contrary, the control unit 3 controls the second switch unit 44 to be turned on within the holding time after the first switch unit 42 is turned off, so that the output voltage Vo can be controlled to supply power to the load 200 in real time after the first switch unit 42 is turned off and the dc voltage Vdc is not provided. Thus, the situation that the first switch unit 42 and the second switch unit 44 are turned on simultaneously to supply the dc voltage Vdc and the output voltage Vo to the load 200 simultaneously can be avoided.

Referring to fig. 1, the power conversion system 100 further includes a discharging circuit 6, and the discharging circuit 6 is coupled to the output path 5 and the ground GND. The discharging circuit 6 mainly turns on the output path 5 and the grounding point GND when the request voltage Vr on the output path 5 needs to be adjusted down, so that the request voltage Vr on the output path 5 can be rapidly discharged through the discharging circuit 6. Specifically, the control unit 3 controls the discharging circuit 6 to turn on the output path 5 and the ground GND when the request voltage Vr is stepped down by the present voltage based on the request voltage Vr, so that the request voltage Vr (here, the output voltage Vo or the dc voltage Vdc) can be rapidly discharged from the present voltage to the request voltage Vr. Then, the control unit 3 controls the discharging circuit 6 to disconnect the output path 5 from the ground GND after the request voltage Vr is reduced to the request voltage Vr to maintain the request voltage Vr.

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 GND, the positions of the resistor 62 and the fourth switching unit 64 can be replaced with each other. When the control unit 3 is turned off from the current voltage based on the request voltage Vr, the fourth switching unit 64 is turned on so that the request voltage Vr may be rapidly discharged from the current voltage to the request voltage Vr. Otherwise, the fourth switching unit 64 is turned off after the current voltage Vr is increased or the requested voltage Vr is decreased to the requested voltage Vr based on the requested voltage Vr. It should be noted that in an embodiment of the present invention, the discharge circuit 6 may be independently disposed outside the control unit 3 (as shown in fig. 1), or may be integrated in the control unit 3, so as to simplify the physical circuit volume.

Fig. 2 is a schematic waveform diagram of dc voltage and output voltage adjustment according to an embodiment of the present invention, and fig. 1 is also included. In the embodiment of fig. 2, when the request voltage Vr is 5V, 9V, 12V and 15V in the USB-PD specification and is smaller than the predetermined threshold voltage Vt (for example, but not limited to 15.5V), the first switch unit 42 is turned off, and the second switch unit 44 is turned on, so that the output voltage Vo supplies power to the load 200. When the request voltage Vr is the highest first-order voltage that can be supplied by the present embodiment, for example, 20V in the USB-PD specification, and is greater than the threshold voltage Vt (for example, but not limited to, 15.5V), the first switch unit 42 is turned on, and the second switch unit 44 is turned off, so that the load 200 is supplied with the dc voltage Vdc. As shown in fig. 2, the control unit 3 can maintain the difference between the dc voltage Vdc and the output voltage Vo within the range of the voltage difference Δ V for voltage adjustment. The main reason for using this adjustment method is that the control unit 3 usually has two protection mechanisms for the power conversion system 100, one of which is latch-off (latched off), and is locked after the power conversion system 100 triggers the protection mechanism, and can resume normal operation after being restarted (for example, but not limited to, power off). Another is auto-recovery (auto-recovery), which is automatically recovered after the power conversion system 100 triggers a protection mechanism by waiting for a short time without restarting. Based on the difference between the two, the protection mechanism for the lock shutdown is usually simple in design, the protection is more extensive and the cost is relatively cheap. The voltage regulation method of fig. 2 is mainly applied to the power conversion system 100 with the protection mechanism being the gate lock off. The reason for this is that the difference between the dc voltage Vdc and the output voltage Vo is changed after the output voltage Vo is adjusted. If the Over Voltage Protection (OVP) and Under Voltage Protection (UVP) Protection points are still set based on the Voltage of 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 may generate an Over Voltage or Under Voltage condition, and enter the gate lock to be turned off and locked, thereby stopping outputting the electric energy to the load 200. As such, the power conversion system 100 must be restarted to resume normal operation.

Therefore, in order to avoid the situation that the difference between the output voltage Vo and the dc voltage Vdc is too large, the control unit 3 maintains the difference between the dc voltage Vdc and the output voltage Vo within the range of the voltage difference Δ V for voltage adjustment. When the control unit 3 adjusts the current voltage to the requested voltage Vr (for example, but not limited to, from 5V to 15V) based on the requested voltage Vr, and the difference between the current voltage and the requested voltage Vr exceeds the range of the voltage difference Δ V (for example, but not limited to, 4.5V), the control unit 3 adjusts the dc voltage Vdc and the output voltage Vo in stages. In fig. 2, after the power conversion system 100 is successfully started, the output voltage Vo is a default voltage of 5V (i.e. the preset value after power-on is 5V), and the dc voltage Vdc is 9.5V based on the default voltage-superposed voltage difference Δ V of 5V (for example, but not limited to, 4.5V).

It is assumed that, when control unit 3 adjusts from current voltage 5V to request voltage Vr of 20V based on request voltage Vr, control unit 3 determines that the current voltage differs from request voltage Vr by more than the range of 4.5V and performs the step of stepwise increasing. Therefore, the control unit 3 first controls the dc-dc converting unit 2 to increase the output voltage Vo to 9V by providing the control signal Sc2, and then controls the ac-dc converting unit 1 to increase the dc voltage Vdc to 13.5V by providing the control signal Sc 1. Thereafter, the output voltage Vo is stepped up by 12V, 15V, 20V in sequence, and the dc voltage Vdc is also stepped up by 16.5V, 19.5V, 20V in sequence based on the step-up of the output voltage.

Since the power conversion system 100 is powered by the ac-dc conversion unit 1 when the request voltage Vr is 15V or more, the dc voltage Vdc adjusted in the last stage is only adjusted from 19.5V to 20V, and the voltage difference Δ V is still within the range of 4.5V. Otherwise, the step of the control unit 3 performing the phased-down operation is similar to the phased-up operation, and will not be described herein again. On the other hand, when the output voltage Vo is 5V, 9V, 12V, 15V, the dc voltage Vdc is different from the output voltage Vo by a fixed voltage difference Δ V (i.e., 4.5V). Therefore, before the output voltage Vo is not adjusted, and the output voltage Vo is within a predetermined voltage range (i.e., within 5V to 15V), the output voltage Vo and the DC voltage Vdc are maintained at a fixed voltage difference Δ V (e.g., 4.5V). Within this range, the dc voltage Vdc will maintain a constant voltage difference Δ V no matter the output voltage Vo is increased or decreased, and thus the voltage difference between the input voltage and the output voltage of the dc-dc conversion unit is kept smaller than the voltage difference Δ V, so that the dc-dc conversion unit can maintain a better conversion efficiency and reduce the power loss during the power conversion process. The predetermined voltage range can be interpreted as a specific range below the threshold voltage Vt, and the size of the predetermined voltage range can be selected according to the actual system design.

Here, the output voltage Vo, the dc voltage Vdc, the request voltage Vr, and the threshold voltage Vt have a corresponding relationship. The request voltage Vr is known by the control unit 3 through the handshake communication Scom with the load 200, and is accordingly known when the demand of the load 200 changes. The control unit 3 can know the current voltage on the output path 5 (or the magnitudes of the output voltage Vo and the dc voltage Vdc) by self-detection of the power conversion system 100. If the present voltage is higher than the threshold voltage Vt set by the control unit 3, the present voltage is referred to as the dc voltage Vdc, otherwise, the present voltage is the output voltage Vo. The control unit 3 controls the switch set 4 based on comparing the output voltage Vo with the threshold voltage Vt. On the other hand, as can be seen from fig. 2, 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 in potential, but the dc-dc converting unit 2 does not supply current (because the second switching unit 44 is turned off at this time), so the power consumption is relatively low.

Fig. 3A is a schematic circuit block diagram of a power conversion system with power consumption saving function according to a modified embodiment of the present invention, and fig. 1-2 are combined. The power conversion system 100' is mainly characterized by including the function of adjusting the dc voltage Vdc and the output voltage Vo in stages as shown in fig. 2. When the current voltage is smaller than the request voltage Vr, the control unit 3 firstly increases the output voltage Vo and then increases the direct current voltage Vdc, otherwise, the control unit 3 firstly decreases the output voltage Vo and then decreases the direct current voltage Vdc. Specifically, before the output voltage Vo is not adjusted and the output voltage Vo is within a predetermined voltage range (such as, but not limited to, 5V to 15V), a voltage difference Δ V (such as, but not limited to, 4.5V) is between the output voltage Vo and the dc voltage Vdc.

When the current voltage is within the predetermined range and is smaller than the request voltage Vr (e.g. 5V is to be increased to 9V), the control unit 3 first increases the output voltage Vo to a second predetermined voltage (from 5V to 4V), and then increases the dc voltage Vdc to the second predetermined voltage (from 9.5V to 4V to 13.5V). Otherwise, the lowering operation of the output voltage Vo is also the same, and will not be described herein again. Thus, when the power conversion system 100 is a latcheted off protection mechanism, the overvoltage or undervoltage protection cannot be triggered due to an excessively large adjustment range during the adjustment of the output voltage Vo and the direct-current voltage Vdc, and the power conversion system 100 is prevented from being failed due to false triggering of the protection when the protection is not really needed. Among them, the third switching unit 46 may be present, so that the power conversion system 100 still has the function of the abnormal protection.

Fig. 3B is a schematic circuit block diagram of another modified embodiment of the power conversion system with power consumption saving function according to the present invention, and fig. 1 to 3A are combined. The power conversion system 100 "is primarily characterized in that the switch set 4' is a three-terminal switch. The control unit 3 controls the switch group 4' to tap the dc-dc converting unit 2 and the output path 5 based on the request voltage Vr being lower than the threshold voltage Vt to provide the output voltage Vo to the output path 5. On the contrary, the control unit 3 controls the switch group 4' to bridge the ac-dc conversion unit 1 and the output path 5 based on the request voltage Vr being higher than the threshold voltage Vt, so as to provide the dc voltage Vdc to the output path 5.

Fig. 4 is a flow chart of an operation method of the power conversion system with the power consumption saving function according to the present invention, and fig. 1 to 3B are combined. The power conversion system 100 includes an ac-dc conversion unit 1, a dc-dc conversion unit 2, a switch set 4 and an output path 5, and the operation method includes an output voltage adjusting stage (S100) and a dc voltage adjusting stage (S200). In step (S100), the output voltage Vo is adjusted based on the request voltage Vr, so that the output voltage Vo approaches toward the request voltage Vr (e.g., is adjusted from 5V to 9V in one step). After the adjustment is completed, the process proceeds to step (S200) to adjust the dc voltage Vdc (e.g., from 9.5V to 13.5V to 9V +4.5V) based on the adjusted output voltage Vo (e.g., 9V). When the output voltage Vo is not adjusted to the requested voltage Vr (for example, the requested voltage Vr is 15V), the process returns to step (S100) to perform the continuous adjustment of the next stage until the output voltage Vo is adjusted to the requested voltage Vr.

Please refer to fig. 5A, which is a detailed flowchart of the first embodiment of step S100, in combination with fig. 1 to 4. The detailed operations of step S100 include:

step S300: whether the request voltage Vr is changed to trigger the trigger output voltage Vo to be adjusted is judged, and the control unit 3 knows whether the output voltage Vo is to be adjusted based on the target value of the request voltage Vr through handshake communication Scom. If the judgment result is yes, the process proceeds to step (S320). When the judgment result is no, the process proceeds to step S200 directly. If the result of the determination is negative, the process proceeds directly to step S200. For example: when the request voltage Vr before and after the adjustment is greater than the threshold voltage Vt (for example, but not limited to, 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, so that it is determined that the output voltage Vo does not need to be adjusted, and the process may directly proceed to step S200.

Step S320: the output voltage Vo of the dc-dc conversion unit 2 is set to be adjusted to the request voltage.

Step S340: it is determined whether the output voltage Vo in step S320 is boosted (S340). If the judgment result is yes, the process proceeds to step (S200). If the judgment result is no, the flow proceeds to step (S360).

Step S360: it is determined whether the state of the first switching unit is correct, and the output path 5 is discharged for a preset discharging period so that the output voltage Vo is lowered to the request voltage Vr. Before the preset discharging period is not finished, the first switch unit 42 is controlled to be turned off, so as to accelerate the reduction of the output voltage Vo and reduce unnecessary power loss. When the discharging period is over, the stepped-down output voltage Vo is smaller than the threshold voltage Vt, so the control unit 3 must control the first switch unit 42 to turn off to avoid the higher dc voltage Vdc being provided to the output path 5.

Step S380: it is confirmed whether the state of the discharge circuit is correct (S380). When the output voltage Vo is to be adjusted down, the control unit 3 must control the discharging circuit 6 to connect the output path 5 and the ground GND to discharge the output voltage Vo for a predetermined discharging period, so that the output voltage Vo can be rapidly discharged from the current voltage to the request voltage Vr. When the preset discharging period is over, the control unit 3 must control the discharging circuit 6 to turn off to isolate the output path 5 from the ground GND, and then proceeds to step (S200).

It should be noted that, in an embodiment of the present invention, the flowchart of fig. 5A is mainly applied to a protection mechanism in which the power conversion system 100 is auto-recovery (auto-recovery). The transient phenomenon during the adjustment of the output voltage Vo occurs when the overvoltage or undervoltage protection is triggered by the direct decrease of the output voltage Vo from the current voltage to the requested voltage Vr (for example, but not limited to, the adjustment from 20V to 5V). When the protection state is automatically recovered for a short time after the protection is triggered, the output voltage Vo is adjusted to the request voltage Vr, and the load 200 can still be normally supplied with power.

Please refer to fig. 5B, which is a detailed flowchart of the second embodiment of step S100, with reference to fig. 1 to 4. The difference between the flowchart of the present embodiment and the flowchart of fig. 5A is that the step (S320) of fig. 5A is replaced by setting the output voltage Vo to be adjusted to the first-order to intermediate voltage in the direction of the request voltage (S320'). The adjustment method mainly applies the step adjustment method shown in fig. 2, and is mainly applied to the power conversion system 100 as a protection mechanism for gate off (latcheted off). In the step of adjusting the output voltage Vo, the output voltage Vo is adjusted only one order at a time, and after the flow of steps (S100) to (S200) of fig. 4 is completed, the output voltage Vo of one order is further adjusted again in the next cycle. Therefore, the condition that the output voltage Vo is directly adjusted to the request voltage Vr (for example, but not limited to, directly adjusted to 20V from 5V or directly adjusted to 5V from 20V) from the current voltage to trigger the over-voltage or under-voltage protection can be avoided, and the transient signal during the adjustment of the output voltage Vo is prevented from triggering the protection mechanism by mistake.

Please refer to fig. 6A, which is a detailed flowchart of the first embodiment of step S200, in combination with fig. 1 to 5B. In fig. 6A, the dc voltage Vdc is mainly adjusted. Since the adjustment of the dc voltage Vdc depends on the adjustment manner of the output voltage Vo, the adjustment manner of the dc voltage Vdc shown in fig. 6A can be adjusted by corresponding fine adjustment (i.e. direct adjustment or step adjustment) based on the spirit of fig. 5A-5B. Specifically, after the output voltage Vo adjustment process ends, the process proceeds to step (S200). Step S200 includes the following steps:

step S300: and judging whether the direct current voltage Vdc needs to be boosted. If yes, the step S420 is entered for adjusting the boost of the dc voltage Vdc; if yes, the process proceeds to step S700, where the dc voltage Vdc is discharged and regulated.

Step S420: it is determined whether (1) the current dc voltage Vdc is below the threshold voltage, and (2) the request voltage Vr is above the threshold voltage. If the results of the determinations (1) and (2) are both yes, the step S440 to 540 is performed, and the power conversion system 100 needs to convert the output voltage Vo into the dc voltage Vdc. In this way, before the load 200 is supplied with the dc voltage Vdc, the dc voltage Vdc needs to be finely adjusted to avoid the situation of the overvoltage protection being erroneously touched when the dc voltage Vdc is adjusted.

Step S440: it is confirmed whether the state of the first switching unit is correct (S440). In the condition that the voltage at the path switching node 48 is lower than the threshold voltage Vt, the load 200 is not powered by the dc voltage Vdc, and the first switching unit 42 needs to be turned off to avoid the dc voltage Vdc being provided to the output path 5. Conversely, in the situation where the voltage at the path switching node 48 is higher than the threshold voltage Vt, the load 200 needs to be powered by the dc voltage Vdc, and the first switch unit 42 needs to be turned on.

Step S460: the dc voltage Vdc is regulated to a threshold voltage (e.g., without limitation, 15.5V). The reason why the dc voltage Vdc is first adjusted to the threshold voltage Vt without continuously adjusting the dc voltage Vdc to the request voltage Vr (for example, but not limited to 20V) higher than the threshold voltage Vt is that the dc voltage Vdc may exceed the limit of the overvoltage protection (OVP) point when the output voltage Vo of the dc-dc converting unit 2 is 20V, and particularly, the transient phenomenon of voltage overshoot may occur during the up-regulation, which may cause the dc-dc converting unit 2 to be in a state of being locked and shut down to stop supplying power to the control unit 3, thereby disabling the control unit 3.

Step S480: the overvoltage protection set point when the output voltage Vo of the dc-dc conversion unit 2 is 20V is additionally superimposed with a first predetermined voltage (for example, but not limited to, 4V to 8V) to avoid the voltage adjustment process from erroneously triggering the overvoltage protection mechanism. During the adjustment of the dc voltage Vdc to the request voltage Vr (for example, but not limited to 20V) higher than the threshold voltage Vt, there is an overshoot (and thus a falling edge) at the rising edge of the voltage adjustment (see fig. 2). However, if the output voltage Vo is 20V (usually designed at a voltage 1.2 times the output voltage Vo), i.e. when the overshoot voltage is higher than 24V, the over-voltage protection mechanism may be triggered. Therefore, the step sets the overvoltage protection to the highest requested voltage (such as, but not limited to, 20V) acceptable by the dc-dc conversion unit 2, superimposed on the first predetermined voltage.

Step S500: the dc voltage Vdc is regulated to between a threshold voltage (e.g., without limitation, 15.5V) and a requested voltage (e.g., without limitation, 20V). The step is mainly to reduce the overshoot amplitude so as to reduce the risk of mistakenly touching the overvoltage protection. Specifically, the higher the amplitude of the dc voltage Vdc rise, the higher the amplitude of the relative overshoot (and thus the output voltage Vo). Therefore, if the request voltage Vr is increased from a current voltage lower than the threshold voltage Vt to a request voltage Vr higher than the threshold voltage Vt, the voltage rising amplitude is usually relatively high. To avoid the overshoot caused by the adjustment, the control unit 3 adjusts the dc voltage Vdc from the current voltage to the relay voltage (for example, but not limited to 17.5V). The relay voltage is mainly between the threshold voltage Vt and the request voltage Vr, and can be reasonably designed according to the level of overshoot in the actual circuit. It should be noted that in an embodiment of the present invention, if the overshoot condition or the overshoot condition is not considered, the step can be omitted.

Step S520: the first switching unit is turned on. When the dc voltage Vdc is increased to the relay voltage, the relay voltage substantially meets the requirement of the load 200, and therefore the first switch unit 42 may be turned on first to provide the dc voltage Vdc to power the load 200. On the other hand, the second switch unit 44 can be controlled accordingly according to its implementation type (diode or switch).

Step S540: the direct current voltage is regulated to the request voltage Vr. After the first switch unit 42 is turned on, the control unit 3 controls the ac-dc converting unit 1 to continue to boost the dc voltage Vdc until the dc voltage Vdc is the requested voltage Vr to meet the requirement of the load 200.

Referring back to fig. 6A, if the determination in step (S400) is negative, the process proceeds to step (S700) to determine whether the state of the first switch unit is correct; if the determination in step (S420) is no, the process proceeds to step (S600) to confirm whether the state of the first switch unit is correct. Steps (S600) and (S700) also confirm that the first switch unit 42 needs to be turned on or off correctly. The concept of controlling the on/off of the first switch unit 42 can be described with reference to the text of fig. 4-6 and the related description of the step (S440), and will not be further described herein.

Step S620: after the completion of the confirmation in the step (S600), the dc voltage is raised to (1) the requested voltage plus the second predetermined voltage or (2) the requested voltage. Referring to fig. 2, the situation (1) indicates that the output voltage Vo is at a voltage level below the threshold voltage Vt before and after the output voltage Vo is adjusted to the voltage level (for example, but not limited to, 9V is adjusted to 12V), but the output voltage Vo is not adjusted to be higher than the threshold voltage Vt, which means that the power conversion system 100 supplies power to the load 200 from the output voltage Vo before and after the output voltage Vo is adjusted to the voltage level. Therefore, the dc voltage Vdc is adjusted to a level of the request 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. For the case (2), when there is more than one set of settable output voltage levels above the threshold voltage Vt, the dc voltage Vdc may be both before and after rising (e.g., without limitation, 18V to 20V). In this way, the power conversion system 100 supplies power to the load 200 from the dc voltage Vdc before and after the boost, and the boost voltage difference is limited. Therefore, in this case, the dc voltage Vdc may be directly increased to the request voltage Vr.

Step S720: after the completion of the confirmation in step (S700), there are three possibilities for the drop of the dc voltage. One is that before and after the adjustment, the DC voltage Vdc is above the threshold voltage Vt; the other is that the direct current voltage Vdc is below the threshold voltage Vt before and after the adjustment; the last is the dc voltage Vdc adjusted from above the threshold voltage Vt to below the threshold voltage Vt. In any of the ramp-down methods, it is necessary to determine whether the state of the discharge circuit is correct. Specifically, in any of the above-mentioned buck modes, the discharging circuit 6 has to turn on the output path 5 and the ground GND, so as to discharge the output path 5 for a predetermined discharging period, so as to lower the voltage at the path switching node 48, such that the dc voltage Vdc can be rapidly discharged from the current voltage to approach the request voltage Vr. After the preset discharging period is over or discharging to the request voltage Vr, the control unit 3 controls the discharging circuit 6 to disconnect the output path 5 from the ground GND.

Step S740: the DC voltage is regulated down to the requested voltage or regulated down to the requested voltage plus a second predetermined voltage. Similar to step (S620), the drop of the dc voltage Vdc is determined based on the drop of the output voltage Vo, and the threshold voltage Vt is used as the partition. When the regulated dc voltage Vdc is below the threshold voltage Vt, the dc voltage Vdc is regulated to the requested voltage Vr plus the second predetermined voltage, otherwise, the dc voltage Vdc is regulated to the requested voltage Vr.

Please refer to fig. 6B, which is a detailed flowchart of the second embodiment of step S200, in combination with fig. 1-5B. The difference between the flowchart of this embodiment and the flowchart of fig. 6A is that:

i. step S620 of fig. 6A is replaced with step S620': the set dc voltage Vdc is stepped up in either (1) the requested voltage plus a second predetermined voltage or (2) the requested voltage by one step to another intermediate voltage.

Step S740 of fig. 6A is replaced with step S740': the set dc voltage Vdc is stepped down one step to another intermediate voltage in the direction of (1) the requested voltage plus a second predetermined voltage or (2) both the requested voltage.

Step S420 of fig. 6A is replaced with step S420': it is determined whether (1) the current dc voltage Vdc is "the highest first order voltage output below a threshold voltage (e.g., without limitation, 15.5V)" (e.g., without limitation, 15V), and (2) the request voltage Vr is above the threshold voltage. If the results of the determinations (1) and (2) are both yes, the steps S440 to 540 are performed, and the power conversion system 100 needs to convert the output voltage Vo into the dc voltage Vdc.

The step adjustment method shown in fig. 2 is mainly applied to this adjustment method, in the step of adjusting the dc voltage Vdc, the dc voltage Vdc is adjusted only one step at a time, and after the flow of steps (S100) to (S200) of fig. 4 is completed, the dc voltage Vdc of one step is further adjusted again in the next cycle. Therefore, the condition that the overvoltage protection or the undervoltage protection is triggered due to the fact that the difference value of the adjustment voltage of the direct current voltage Vdc is too large can be avoided, and the protection mechanism is prevented from being triggered by an instantaneous signal in the adjustment period of the direct current voltage Vdc by mistake.

The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof, and it should be understood that various changes and modifications can be effected therein by one skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.

Claims (25)

1. A power conversion system for converting an input voltage to power a load, the power conversion system comprising:

an AC-DC conversion unit for receiving the input voltage and converting the input voltage into a DC voltage;

a DC-DC conversion unit for receiving the DC voltage and converting the DC voltage into an output voltage;

a control unit, which performs handshake communication with the load to obtain a request voltage required by the load;

a switch set coupled to the AC-DC conversion unit and the DC-DC conversion unit;

an output path coupled to the switch set and the load;

when the request voltage is lower than a threshold voltage, the control unit controls the switch group to lap the DC-DC conversion unit and the output path, and controls the DC-DC conversion unit to provide the output voltage which accords with the request voltage to the output path;

when the request voltage is higher than the threshold voltage, the control unit controls the switch group to lap the AC-DC conversion unit and the output path, and controls the AC-DC conversion unit to provide the DC voltage which accords with the request voltage to the output path.

2. The power conversion system of claim 1, wherein the control unit maintains a difference between the DC voltage and the output voltage within a voltage difference range, and when the control unit adjusts 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 DC voltage and the output voltage in stages.

3. The power conversion system of claim 2, wherein 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 larger than the request voltage, the control unit firstly reduces the output voltage and then reduces the direct current voltage.

4. The power conversion system of claim 1, wherein the switch set comprises:

a first switch unit coupled to the AC-DC conversion unit and a path switching node;

a second switch unit coupled to the DC-DC conversion unit and the path switching node; and

a third switch unit coupled to the path switching node and the output path;

the control unit controls the second switch unit and the third switch unit to be conducted based on the request voltage being lower than the threshold voltage, and controls the first switch unit and the third switch unit to be conducted based on the request voltage being higher than the threshold voltage.

5. The power conversion system of claim 4, wherein when the requested voltage is increased from a current voltage lower than the threshold voltage to a voltage 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.

6. The power conversion system of claim 5, wherein the control unit sets an over-voltage protection threshold of the DC-DC conversion unit to a maximum requested voltage superimposed by a first predetermined voltage, and then adjusts the DC voltage from the current voltage to the intermediate voltage.

7. The power conversion system of claim 4, wherein when the requested voltage is adjusted from a current voltage to a voltage lower than the threshold voltage, the control unit controls the first switch unit to turn off and adjust the output voltage from the current voltage to the requested voltage.

8. The power conversion system of claim 4, wherein the second switch unit is a diode that is forward biased on when the voltage of the path switching node is lower than the output voltage and reverse biased off when the voltage of the path switching node is higher than the output voltage.

9. The power conversion system of claim 4, wherein the control unit controls the second switch unit to be turned off during a holding time before the first switch unit is turned on, and controls the second switch unit to be turned on during the holding time after the first switch unit is turned off.

10. The power conversion system of claim 4, wherein the control unit turns off the third switch unit based on an abnormal state of the power conversion system.

11. The power conversion system of claim 1, further comprising:

a discharge circuit coupled to the output path and a ground point;

the control unit controls the discharge circuit to connect the output path and the grounding point when the current voltage is regulated and reduced based on the request voltage, and controls the discharge circuit to disconnect the output path and the grounding point after the current voltage is regulated and reduced based on the request voltage.

12. The power conversion system of claim 11, wherein the discharge circuit comprises:

a resistor coupled to the output path; and

a fourth switch unit coupled to the resistor and the ground point;

the control unit turns on the fourth switching unit when the current voltage is regulated to be reduced based on the request voltage, and turns off the fourth switching unit after the current voltage is regulated to be reduced based on the request voltage.

13. A power conversion system for converting an input voltage to power a load, the power conversion system comprising:

an AC-DC conversion unit for receiving the input voltage and converting the input voltage into a DC voltage;

a DC-DC conversion unit for receiving the DC voltage and converting the DC voltage into an output voltage;

the control unit is used for carrying out handshake communication with the load so as to obtain a request voltage required by the load, and the control unit adjusts the output voltage from a current voltage to the request voltage based on the handshake communication;

an output path coupled to the DC-DC converting unit and the load;

when the current voltage is smaller than the request voltage, the control unit firstly increases the output voltage and then increases the direct-current voltage; and

when the current voltage is larger than the request voltage, the control unit firstly reduces the output voltage and then reduces the direct current voltage.

14. The power conversion system of claim 13, wherein before the output voltage is unregulated and the output voltage is within a predetermined voltage range, there is a voltage difference between the output voltage and the dc voltage; when the current voltage is lower than the request voltage within the predetermined range, the control unit first increases the output voltage by a second predetermined voltage and then increases the DC voltage by the second predetermined voltage to maintain the voltage difference.

15. The power conversion system of claim 13, wherein before the output voltage is unregulated and the output voltage is within a predetermined voltage range, there is a voltage difference between the output voltage and the dc voltage; when the current voltage is greater than the request voltage within the predetermined range, the control unit first reduces the output voltage to a second predetermined voltage, and then reduces the DC voltage to the second predetermined voltage to maintain the voltage difference.

16. An operation method of a power conversion system, wherein the power conversion system is controlled to convert an input voltage to supply power to a load, and the power conversion system includes an ac-dc conversion unit, a dc-dc conversion unit, a switch set and an output path, the operation method 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 handshake communication with the load to obtain a request voltage required by the load;

when the request voltage is lower than a threshold voltage, controlling the switch group to lap the DC-DC conversion unit and the output path, and controlling the DC-DC conversion unit to provide the output voltage which accords with the request voltage to the output path; and

when the request voltage is higher than the threshold voltage, the switch group is controlled to lap the AC-DC conversion unit and the output path, and the AC-DC conversion unit is controlled to provide the DC voltage which accords with the request voltage to the output path.

17. The method of operation of claim 16, further comprising the steps of:

when the request voltage needs to be adjusted, judging whether the difference between a current voltage of the output path and the request voltage exceeds a voltage difference range; and

when the difference between the current voltage and the requested voltage exceeds the range of the voltage difference, the DC voltage and the output voltage are adjusted in stages.

18. The method of operation of claim 17, further comprising the steps of:

when the current voltage is smaller than the request voltage, firstly increasing the output voltage, and then increasing the direct current voltage; and

when the current voltage is greater than the request voltage, the output voltage is first reduced, and then the DC voltage is reduced.

19. The method of operation of claim 16, further comprising the steps of:

determining whether the requested voltage is increased from a current voltage lower than the threshold voltage to a voltage higher than the threshold voltage;

controlling the AC-DC conversion unit to adjust the DC voltage to the requested voltage based on the requested voltage to be increased from the current voltage to above the threshold voltage; and

and controlling the switch group to lap the AC-DC conversion unit and the output path.

20. The method of operation of claim 19, further comprising the steps of:

setting an overvoltage protection threshold of the DC-DC conversion unit at a highest request voltage superimposed by a first predetermined voltage based on the request voltage to be increased from the current voltage;

adjusting the DC voltage from the current voltage to a relay voltage;

controlling the switch group to lap the AC-DC conversion unit and the output path; and

and adjusting the direct current voltage from the relay voltage to the request voltage.

21. The method of operation of claim 16, further comprising the steps of:

judging whether the request voltage is reduced from a current voltage to be lower than the threshold voltage or not;

controlling the switch set to disconnect the AC-DC conversion unit and the output path based on the request voltage to be reduced from the current voltage to be lower than the threshold voltage;

and controlling the DC-DC conversion unit to adjust the output voltage to the request voltage.

22. The method of operation of claim 21, further comprising the steps of:

and controlling the switch group to lap the DC-DC conversion unit and the output path.

23. The method of operation of claim 16, further comprising the steps of:

controlling a discharging circuit to connect the output path and a grounding point when the current voltage is regulated and reduced based on the request voltage; and

and controlling the discharge circuit to disconnect the output path and the grounding point after the voltage regulation is reduced based on the request voltage.

24. An operation method of a power conversion system, wherein the power conversion system is controlled to convert an input voltage to supply power to a load, and the power conversion system includes an ac-dc conversion unit, a dc-dc conversion unit, a switch set and an output path, the operation method 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 handshake communication with the load to obtain a request voltage required 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 smaller than the request voltage, firstly increasing the output voltage and then increasing the direct current 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, the output voltage is firstly adjusted down, and then the direct current voltage is adjusted down.

25. The method of claim 24, wherein a voltage difference exists between the output voltage and the dc voltage when the output voltage is not adjusted and the output voltage is within a predetermined voltage range, and the method further comprises:

when the current voltage is smaller than the request voltage, firstly increasing the output voltage by a second preset voltage, and then increasing the direct current voltage by the second preset voltage to maintain the voltage difference; and

when the current voltage is greater than the request voltage, the output voltage is first reduced to the second predetermined voltage, and then the DC voltage is reduced to the second predetermined voltage to maintain the voltage difference.

Images