CN112909940A - AC/DC power supply system and switch switching method based on AC/DC power supply system - Google Patents
AC/DC power supply system and switch switching method based on AC/DC power supply system Download PDFInfo
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- CN112909940A CN112909940A CN202110289492.0A CN202110289492A CN112909940A CN 112909940 A CN112909940 A CN 112909940A CN 202110289492 A CN202110289492 A CN 202110289492A CN 112909940 A CN112909940 A CN 112909940A
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- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
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Abstract
The application discloses alternating current-direct current power supply system and a switch switching method based on the alternating current-direct current power supply system, and the switch switching method based on the alternating current-direct current power supply system comprises the following steps: when the voltage on the load side meets the preset voltage, the alternating current power supply is directly carried out through an alternating current transmission line; when the voltage of the load side does not meet the preset voltage, firstly rectifying the alternating current into direct current through the transmitting end converter for direct current power supply, and then reversely inverting the direct current into the alternating current through the receiving end converter for transmitting to the load side. By the mode, alternating current power supply is adopted to improve the power supply efficiency when the tail end voltage is qualified; when the voltage of the tail end is low, the direct current power supply is switched to improve the voltage qualification rate of a user at the tail end, and finally, the high-efficiency and high-quality power supply is realized.
Description
Technical Field
The application relates to the technical field of power distribution, in particular to an alternating current and direct current power supply system and a switch switching method based on the alternating current and direct current power supply system.
Background
At the initial stage of power grid construction, remote end users are limited by living standards, the power consumption is low, and the power consumption quality requirements are not high, so that the power consumption voltage drop of the users is not obvious, and the power consumption requirements are not strict. However, as the living standard of people is increased, household loads are diversified, refined and large in capacity, so that the centralized starting of high-power loads causes obvious voltage drop of a remote distribution line and the problem of voltage drop of a terminal user is obvious. In addition, the starting of various high-power electric loads is often periodic, so that the problem of low terminal voltage occurs periodically, and the problem is remarkably aggravated due to the time concentration, and the daily life and the production and the electricity utilization of residents are influenced.
In order to solve the problem of low voltage at the end, the existing solutions mainly comprise: (1) and a 10kV line and a transformer are added, line transformation is carried out simultaneously, and the power supply radius is shortened. The mode has huge investment, and the line spans the mountain area, the green vegetation of the mountain grows rapidly, the ground short circuit fault is easy to cause, and great difficulty is brought to the later operation and maintenance work; (2) the photovoltaic power generation device and the energy storage device are arranged at the tail end of the user, namely, a new power supply is arranged on the side of the user to improve the voltage of the user, the power is prevented from being transmitted for a long distance through the original power transmission line, and the voltage drop can be reduced. However, the photovoltaic energy storage device has high cost and long investment return period, and the rural area faces the land acquisition problem. (3) Reactive compensation and voltage regulation devices are installed, voltage regulators are connected in series on a line with an overlong power supply radius, and a centralized automatic reactive compensation station is built in an inductive load dense area. Although the voltage can be raised by about 20%, the voltage is still not qualified, and the problem cannot be solved fundamentally.
The inventor researches and discovers that the voltage drop and the loss of the traditional alternating current transmission mode are both increased remarkably with the increase of the transmission distance, and the terminal voltage is probably not satisfied. The direct current transmission mode can meet the voltage quality requirement, but in the direct current transmission mode, 6% -8% of switching loss, conduction loss and the like of a converter switching tube can be caused besides line loss. Moreover, the scheme for determining the switching logic time sequence based on the communication of the remote communication line has more defects, needs to be additionally provided with a communication line and has high manufacturing cost; the communication line is easy to damage and has low reliability; the information transmission speed is slow, and the rapid switching of the alternating current and direct current transmission modes cannot be ensured.
There is currently no suitable way to achieve efficient, high quality end user power.
Disclosure of Invention
The application provides an alternating current-direct current power supply system and a switch switching method based on the alternating current-direct current power supply system, and aims to solve the problem that high-efficiency and high-quality power supply of a terminal user cannot be realized in the prior art.
In order to solve the above technical problem, the present application provides an ac/dc power supply system, including: the power transmission line is used for connecting the power grid side and the load side; the transmitting end converter is connected between the power grid side and the power transmission line; the receiving end converter is connected between the load side and the power transmission line; the switch switching assembly comprises a plurality of switches and is used for carrying out alternating current power supply directly through the power transmission line when the voltage on the load side meets the preset voltage; when the voltage of the load side does not meet the preset voltage, alternating current is rectified into direct current through the transmitting end converter for direct current power supply, and the direct current is inverted into the alternating current through the receiving end converter and is transmitted to the load side.
Optionally, when the load side is overloaded or unloaded, the voltage of the load side does not meet the preset voltage, and the switch switching component switches the alternating current/direct current power supply system into a direct current power supply mode; when the load side is lightly loaded, the voltage of the load side meets the preset voltage, and the switch switching component switches the alternating current and direct current power supply system into an alternating current power supply mode; wherein, the load side current is light load when the current is less than 50% of the rated value; the load side current is a heavy load with a rated value of 50% -100%.
Optionally, the switch switching assembly comprises: the first switch is arranged between the output end of the sending end converter and the power transmission line; the second switch is arranged between the output end of the receiving end converter and the power transmission line; the third switch is arranged between the input end of the receiving end converter and the power transmission line; the fourth switch is arranged in the power transmission line between the input end and the output end of the sending end converter; and the fifth switch is arranged in the power transmission line between the input end and the output end of the receiving end converter.
Optionally, when the load-side voltage does not meet the preset voltage, the fifth switch and the fourth switch are turned off, the first switch, the second switch and the third switch are turned on, and the direct-current power supply mode is switched.
Optionally, the fifth switch is turned off when detecting that the current of the power transmission line is greater than a first preset value and zero or the right side thereof detects a direct-current voltage; the third switch is closed through same-side communication when detecting that the load is not supported by voltage; the fourth switch is disconnected when the current of the power transmission line is detected to be zero; the first switch is closed through same-side communication when the intermediate transmission line is free of voltage support; the second switch is closed when the voltage of the transmission line is direct current.
Optionally, when the load-side voltage meets the preset voltage, the fifth switch and the fourth switch are turned on, and the first switch, the second switch and the third switch are turned off, so that the alternating-current power supply mode is switched.
Optionally, the first switch is turned off when the current of the power transmission line is less than or equal to a first preset value; the second switch is switched off when the inflow current is suddenly changed to zero; the fourth switch is closed when no voltage is supported on the right side of the fourth switch; the fifth switch is closed when the voltage on the left side of the fifth switch is changed from direct current to alternating current; the third switch is disconnected during the same-side communication.
Optionally, the rated value of the dc bus voltage of the sending-end converter is 750V, and the transmission line is a three-phase four-wire transmission line.
In order to solve the above technical problem, the present application further provides a switch switching method based on an ac/dc power supply system, including: when the voltage on the load side meets the preset voltage, the alternating current power supply is directly carried out through the power transmission line; when the voltage of the load side does not meet the preset voltage, alternating current is rectified into direct current through the transmitting end converter for direct current power supply, and the direct current is inverted into the alternating current through the receiving end converter and is transmitted to the load side.
Optionally, when the load side is overloaded or unloaded, the voltage of the load side does not meet the preset voltage, and the direct current power supply mode is switched to; when the load side is lightly loaded, the voltage of the load side meets the preset voltage, and the load side is switched to an alternating current power supply mode; wherein, the load side current is light load when the current is less than 50% of the rated value; the load side current is a heavy load with a rated value of 50% -100%.
The application provides an alternating current-direct current power supply system and a switch switching method based on the alternating current-direct current power supply system, and the switch switching method based on the alternating current-direct current power supply system comprises the following steps: when the voltage on the load side meets the preset voltage, the alternating current power supply is directly carried out through an alternating current transmission line; when the voltage of the load side does not meet the preset voltage, firstly rectifying the alternating current into direct current through the transmitting end converter for direct current power supply, and then reversely inverting the direct current into the alternating current through the receiving end converter for transmitting to the load side. By the mode, alternating current power supply is adopted to improve the power supply efficiency when the tail end voltage is qualified; when the voltage of the tail end is low, the direct current power supply is switched to improve the voltage qualification rate of a user at the tail end, and finally, the high-efficiency and high-quality power supply is realized; moreover, a communication line is not required to be additionally arranged to control the switching of the switch, so that the cost performance is high; the reliability is high, and transmission speed is fast, can also ensure the accurate fast switch-over of switch.
Drawings
In order to more clearly illustrate the technical solution of the present application, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.
FIG. 1 is a schematic structural diagram of an embodiment of an AC/DC power supply system according to the present application;
FIG. 2 is an equivalent circuit diagram of one embodiment of power distribution transmission;
FIG. 3 is a graph of voltage drop and loss as a function of transmission distance;
FIG. 4 is a graph showing the relationship between loss and transmission power in an AC/DC power transmission mode;
FIG. 5(a) is a waveform of the load-side voltage current as a whole according to an embodiment;
FIG. 5(b) is a partial enlarged waveform of the load side voltage current according to an embodiment;
fig. 5(c) is an overall waveform diagram of voltage and current at the power transmission line 1 according to an embodiment;
fig. 5(d) is a partial enlarged waveform diagram of voltage and current at the power transmission line 1 according to an embodiment;
fig. 5(e) is an overall waveform diagram of voltage and current at the power transmission line 2 according to an embodiment;
fig. 5(f) is a partial enlarged waveform diagram of voltage and current at the power transmission line 2 according to an embodiment;
FIG. 5(g) is a DC side voltage waveform diagram of an embodiment;
FIG. 6(a) is a waveform of the entire load-side voltage current of another embodiment;
FIG. 6(b) is a partial enlarged waveform diagram of the load side voltage current of another embodiment;
fig. 6(c) is an overall waveform diagram of voltage and current on the left side of the transmission line according to another embodiment;
FIG. 6(d) is a partial enlarged waveform diagram of voltage and current on the left side of the transmission line according to another embodiment;
fig. 6(e) is a voltage and current integral waveform diagram on the left side of the transmission line of yet another embodiment;
FIG. 6(f) is a partial enlarged waveform diagram of voltage and current on the left side of the transmission line according to still another embodiment;
fig. 7 is a schematic flowchart of an embodiment of a switching method based on an ac/dc power supply system according to the present application.
Detailed Description
In order to make those skilled in the art better understand the technical solution of the present application, the ac/dc power supply system and the switching method based on the ac/dc power supply system provided in the present application are further described in detail below with reference to the accompanying drawings and the detailed description.
Referring to fig. 1, fig. 1 is a schematic structural diagram of an embodiment of an ac/dc power supply system according to the present application. In this embodiment, the ac/dc power supply system 100 may include a power transmission line 110, a transmitting-end converter 120, a receiving-end converter 130, and a switch switching component.
The transmission line 110 may be used to connect the grid side and the load side. In this embodiment, the power transmission line 110 may be a three-phase four-wire line.
The transmitting converter 120 may be connected between the grid side and the transmission line 110. Alternatively, the dc bus voltage rating of the sending end converter 120 may be 750V.
The receiving-side converter 130 may be connected between the load side and the transmission line 110. The receiving-side converter 130 may be the same as the transmitting-side converter 120.
The switch switching component may include a plurality of switches, and is configured to perform ac power supply directly through the power transmission line 110 when the load side voltage satisfies a preset voltage; when the load side voltage does not meet the preset voltage, the transmitting-end converter 120 rectifies the alternating current into direct current for direct current power supply, and the receiving-end converter 130 inverts the direct current into the alternating current for transmission to the load side.
Optionally, when the load side is overloaded or unloaded, the voltage of the load side does not meet the preset voltage, and the switch switching component can be switched to the direct-current power supply mode; when the load side is lightly loaded, the voltage of the load side meets the preset voltage, and the switch switching component can be switched to an alternating current power supply mode; wherein, the load side current is light load when the current is less than 50% of the rated value; the load side current is a heavy load with a rated value of 50% -100%.
Wherein the preset voltage can be set to 198V, because the national standard electricity requirement is 198V-231V.
The inventor researches and discovers that the voltage drop and the loss of the traditional alternating current transmission mode are both increased remarkably with the increase of the transmission distance, and the terminal voltage is probably not satisfied. The direct current transmission mode can meet the voltage quality requirement, but in the direct current transmission mode, 6% -8% of switching loss, conduction loss and the like of a converter switching tube can be caused besides line loss.
Furthermore, in order to determine which power transmission mode is used under which working condition, respective advantages of the ac-dc conversion system need to be analyzed first. Taking a 380V system, analysis with a distance of 3km between the substation and the load side as an example, the substation is transmitted to the user side (five or six families) through a transmission line (BLV model), and an equivalent circuit of the substation is shown in fig. 2.
The voltage drop and the active loss ratio obtained by the relevant knowledge of the power system are as follows:
wherein, U is 380V, and S is three-phase apparent power. The transmission line uses BLV wire with radius of 4mm, the parameters are R/km 0.5 and X/km 0.3, and the graph of voltage drop and loss with the change of transmission distance is shown in fig. 3.
As can be seen from the figure, in the conventional ac transmission system, the voltage drop and the loss are both significantly increased with the increase in the transmission distance, and the terminal voltage is likely to be unsatisfactory. The direct current transmission can meet the voltage quality requirement, the 380V-level alternating current and direct current change technology is mature, and the cost is low. The line loss calculation formula under direct current transmission is as follows:
fig. 4 is a graph showing a relationship between loss and transmission power in the ac/dc power transmission mode. In the direct current transmission mode, 6% -8% of the switching loss and the conduction loss of a converter switching tube can be caused besides the line loss. The inventor invents the AC/DC power supply system of the application in consideration of two aspects of transmission efficiency and voltage quality: when the light load and the tail end voltage are qualified, alternating current power supply is adopted to improve the power supply efficiency; when the load is heavy and the end voltage is low, the direct current power supply is switched to improve the end user voltage qualified rate.
The switching of alternating current-direct current transmission needs to confirm the switching logic of the switch switching component, because the power grid side and the load side are far away from each other, the method belongs to long-distance distribution, and the scheme that the switching logic time sequence is determined by adopting communication of different-place communication lines has more defects: 1) a communication line needs to be additionally arranged, so that the manufacturing cost is high; 2) the communication line is easy to damage and has low reliability; 3) the information transmission speed is slow and fast handover cannot be ensured. Therefore, in order to ensure the rapidity and reliability of switching, the embodiment also proposes a scheme for determining the two-side switching logic sequence by detecting the change situation of the two-side voltage and current.
Specifically, the switch switching component may control the power transmission line 110 to perform ac power supply or dc power supply through the closing of the switch. The switch switching assembly may include first to fifth switches S1 to S5.
The first switch S1 may be disposed between the output of the sending-end converter 120 and the transmission line 110; the second switch S2 may be disposed between the output terminal of the receiving-side converter 130 and the transmission line 110; the third switch S3 may be disposed between the input terminal of the receiving-side converter 130 and the transmission line 110; the fourth switch S4 may be disposed in the power transmission line 110 between the input and output of the sending-end converter 120; the fifth switch S5 may be disposed in the power transmission line 110 between the input and output terminals of the receiving-side converter 130.
Since the transmission line 110 is a three-phase four-wire transmission line, the first switch S1 to the fifth switch S5 do not mean a single switch, but mean a group of switches.
As shown in fig. 1, the transmitting-side converter 120 includes an input terminal a, an input terminal B, an input terminal C, a + output terminal, an-output terminal, and an N terminal. The input end a, the input end B, the input end C, and the N end are correspondingly connected to the a-phase line, the B-phase line, the C-phase line, and the N line in the power transmission line 110, and the + output end and the-output end are connected to two lines that are not adjacent to each other through the first switch S1, that is, the + output end and the-output end of the sending-end converter 120 can be connected to any two-phase line in the power transmission line 110: AB. AC or BC. The receiving-side converter 130 is almost the same as the transmitting-side converter 120 except that the input terminal of the receiving-side converter 130 needs to be connected to the transmission line 110 through the third switch S3. And will not be described in detail herein.
In addition, the power transmission line 110 may further include other components to ensure the safety of the power transmission line 110, such as resistance, inductance, and the like.
1) Switching from AC mode to DC mode
Under heavy load, if alternating current transmission is adopted, the terminal voltage is low due to large line loss, so that alternating current transmission needs to be switched to direct current transmission. Since the load side may be unloaded at midnight, when the line current is also zero, the fourth switch S4 will detect and activate. Therefore, the AC mode is switched to the DC mode under the condition of heavy load or no load.
Therefore, when the load-side voltage does not satisfy the preset voltage, the fifth switch S5 and the fourth switch S4 may be opened, the first switch S1, the second switch S2, and the third switch S3 may be closed, the transmitting-side converter 120 may rectify the ac power received from the grid-side into the dc power, switch to the dc power supply mode, and invert the dc power into the ac power through the receiving-side converter 130, and finally deliver the ac power to the load-side.
The fifth switch S5 may be turned off when the current of the power transmission line 110 is detected to be greater than the first preset value, zero, or the direct-current voltage is detected on the right side thereof; the third switch S3 may be closed by ipsilateral communication upon detection of no voltage support to the load; the fourth switch S4 may be opened when it is detected that the current of the transmission line 110 is zero; the first switch S1 may be closed by ipsilateral communication when the intermediate transmission line 110 is voltage free; the second switch S2 may be closed when the transmission line 110 voltage becomes dc. As shown in table 1 below:
TABLE 1 simulation logic time sequence table for switching AC to DC
Here, the operation time is assumed by the simulation software and is not the time of actual switching. For example, the whole AC/DC power supply system is set to run time of 1 second in simulation software. Therefore, in the simulation, the fifth switch S5 operates when 0.55S is set, the third switch S3 operates when 0.555S is set, the fourth switch S4 operates when 0.56S is set, the first switch S1 operates when 0.563S is set, and the second switch S2 operates when 0.565S is set, and data of the simulation result is obtained.
Referring to fig. 5(a) - (g), fig. 5(a) - (g) are waveform diagrams of simulation of switching from the ac mode to the dc mode, respectively. As can be seen from fig. 5(a) and (b), after the ac mode is switched to the dc mode, the load side voltage rises from 269.5V to 310.86V, and the load side voltage THD in the dc mode is 0.84%, which satisfies the requirement.
In fig. 5(e) and (f), when t is 0.55s, voltage surge occurs because zero voltage turn-off is not performed and the inductive energy in the power transmission line 110 cannot be released. In order to prevent the situation where the fourth switch S4 is first actuated in the no-load condition and the fifth switch S5 is not actuated to cause the dc voltage to be transmitted to the load side through the fifth switch S5, the fifth switch S5 should be provided with a function of detecting the automatic disconnection of the dc voltage.
As can be seen from fig. 5(g), the dc-side voltage is stabilized around 700V during the switching process, which explains the reliability of the control strategy of the transmitting-side converter 120.
Where 1 and 2 are shown in figure 1, respectively.
2) Switching from DC mode to AC mode
Under the condition of light load, extra converter loss is caused if direct current transmission is adopted, the electric energy transmission efficiency is low, and the voltage at the end of the alternating current transmission can reach the standard, so that the direct current transmission is switched to the alternating current transmission under the condition of light load.
Therefore, when the load side voltage meets the preset voltage, the fifth switch S5 and the fourth switch S4 may be closed, the first switch S1, the second switch S2 and the third switch S3 may be opened, and the ac power supply mode is switched to the ac power supply mode, and the ac power received by the grid side may be directly transmitted to the load side through the power transmission line 110 without passing through the receiving-side converter 130 and the transmitting-side converter 120.
The first switch S1 may be turned off when the opposite-side communication detects that the current of the power transmission line 110 is less than or equal to the first preset value; the second switch S2 may be opened when the inflow current is abruptly changed to zero; the fourth switch S4 may be closed when it is detected that its right side has no voltage support; the fifth switch S5 may be closed when the voltage on its left side changes from dc to ac; the third switch S3 may be opened when closing of the fifth switch S5 is detected by the ipsilateral communication. As shown in table 2:
TABLE 2 simulation logic time sequence table for switching DC to AC
Referring to fig. 6(a) - (f), fig. 6(a) - (f) are waveform diagrams showing simulation of switching from the dc mode to the ac mode. As can be seen from fig. 6(a) and (b), after the dc mode is switched to the ac mode, the amplitude of the voltage on the load side does not change much, but the phases of the dc power supply and the ac power supply are not consistent, and the switching time easily causes the impact at t-0.663 in fig. 6(e) and (f), so the amplitude and phase characteristics of the ac power supply need to be detected by the receiving-end converter 130 before switching, so as to achieve pre-synchronization.
In fig. 6(c) and (d), the voltage surge when t is 0.65s is due to the dc switch being off, and the energy in the inductor is not released. The direct current does not have a zero crossing point, arc extinction is more difficult than the alternating current, and a related direct current breaker needs to be selected for arc extinction.
In summary, the switching logic of each switch is shown in table 3:
TABLE 3 switch switching logic table
The application provides an alternating current-direct current power supply system includes: the power transmission line is used for connecting the power grid side and the load side; the transmitting end converter is connected between the power grid side and the power transmission line; the receiving end converter is connected between the load side and the power transmission line; the switch switching assembly comprises a plurality of switches and is used for carrying out alternating current power supply directly through the power transmission line when the voltage on the load side meets the preset voltage; when the voltage of the load side does not meet the preset voltage, alternating current is rectified into direct current through the transmitting end converter for direct current power supply, and the direct current is inverted into the alternating current through the receiving end converter and is transmitted to the load side. By the mode, alternating current power supply is adopted to improve the power supply efficiency when the tail end voltage is qualified; when the voltage of the tail end is low, the direct current power supply is switched to improve the voltage qualification rate of a user at the tail end, and finally, the high-efficiency and high-quality power supply is realized; moreover, a communication line is not required to be additionally arranged to control the switching of the switch, so that the cost performance is high; the reliability is high, and transmission speed is fast, can also ensure the accurate fast switch-over of switch.
Referring to fig. 7, fig. 7 is a schematic flowchart of an embodiment of a switching method based on an ac/dc power supply system according to the present application, where the ac/dc power supply system is the above-described ac/dc power supply system and is not described herein again.
The switch switching method specifically comprises the following steps:
s110: when the voltage on the load side meets the preset voltage, the alternating current power supply is directly carried out through the power transmission line; when the voltage of the load side does not meet the preset voltage, alternating current is rectified into direct current through the transmitting end converter for direct current power supply, and the direct current is inverted into the alternating current through the receiving end converter and is transmitted to the load side.
Optionally, when the load side is overloaded or unloaded, the voltage of the load side does not meet the preset voltage, and the direct current power supply mode can be switched to; when the load side is lightly loaded, the voltage of the load side meets the preset voltage and can be switched into an alternating current power supply mode; wherein, the load side current is light load when the current is less than 50% of the rated value; the load side current is a heavy load with a rated value of 50% -100%.
It is to be understood that the specific embodiments described herein are merely illustrative of the application and are not limiting of the application. In addition, for convenience of description, only a part of structures related to the present application, not all of the structures, are shown in the drawings. The step numbers used herein are also for convenience of description only and are not intended as limitations on the order in which the steps are performed. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.
The terms "first", "second", etc. in this application are used to distinguish between different objects and not to describe a particular order. Furthermore, the terms "include" and "have," as well as any variations thereof, are intended to cover non-exclusive inclusions. For example, a process, method, system, article, or apparatus that comprises a list of steps or elements is not limited to only those steps or elements listed, but may alternatively include other steps or elements not listed, or inherent to such process, method, article, or apparatus.
Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearances of the phrase in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. It is explicitly and implicitly understood by one skilled in the art that the embodiments described herein can be combined with other embodiments.
The above description is only for the purpose of illustrating embodiments of the present application and is not intended to limit the scope of the present application, and all modifications of equivalent structures and equivalent processes, which are made by the contents of the specification and the drawings of the present application or are directly or indirectly applied to other related technical fields, are also included in the scope of the present application.
Claims (10)
1. A switch switching method based on an alternating current-direct current power supply system is characterized by comprising the following steps:
when the voltage on the load side meets the preset voltage, the alternating current power supply is directly carried out through an alternating current transmission line; when the voltage of the load side does not meet the preset voltage, firstly rectifying the alternating current into direct current through the transmitting end converter for direct current power supply, and then reversely inverting the direct current into the alternating current through the receiving end converter for transmitting to the load side.
2. The switch-switching method according to claim 1, further comprising:
when the load side is overloaded or unloaded, the voltage of the load side does not meet the preset voltage, and the direct current power supply mode is switched to; when the load side is lightly loaded, the voltage of the load side meets the preset voltage, and the load side is switched to an alternating current power supply mode;
wherein, the load side current is light load when the current is less than 50% of the rated value; the load side current is a heavy load with a rated value of 50% -100%.
3. An ac-dc power supply system, comprising:
the power transmission line is used for connecting the power grid side and the load side;
a sending end converter connected between the power grid side and the power transmission line;
a receiving end converter connected between the load side and the transmission line;
the switch switching component comprises a plurality of switches and is used for carrying out alternating current power supply directly through the power transmission line when the voltage on the load side meets the preset voltage; when the voltage of the load side does not meet the preset voltage, the alternating current is rectified into direct current through the transmitting end converter for direct current power supply, and the direct current is inverted into the alternating current through the receiving end converter and is transmitted to the load side.
4. The AC/DC power supply system according to claim 3,
when the load side is in heavy load or no load, the voltage of the load side does not meet the preset voltage, and the switch switching component switches the alternating current-direct current power supply system into a direct current power supply mode; when the load side is lightly loaded, the voltage of the load side meets the preset voltage, and the switch switching component switches the alternating current and direct current power supply system into an alternating current power supply mode;
wherein, the load side current is light load when the current is less than 50% of the rated value; the load side current is a heavy load with a rated value of 50% -100%.
5. The AC-DC power supply system according to claim 3, wherein said switch switching assembly comprises:
the first switch is arranged between the output end of the sending end converter and the power transmission line;
the second switch is arranged between the output end of the receiving end converter and the power transmission line;
the third switch is arranged between the input end of the receiving end converter and the power transmission line;
the fourth switch is arranged in the power transmission line between the input end and the output end of the sending end converter;
and the fifth switch is arranged in the power transmission line between the input end and the output end of the receiving end converter.
6. The AC/DC power supply system according to claim 5,
when the voltage on the load side does not meet the preset voltage, the fifth switch and the fourth switch are turned off, the first switch, the second switch and the third switch are turned on, and the direct-current power supply mode is switched.
7. The AC/DC power supply system according to claim 6,
the fifth switch is disconnected when the fifth switch detects that the current of the power transmission line is larger than a first preset value and is zero or the right side of the fifth switch detects direct-current voltage; the third switch is closed through same-side communication when detecting that the load is free of voltage support; the fourth switch is disconnected when the current of the power transmission line is detected to be zero; the first switch is closed through same-side communication when the intermediate transmission line is free of voltage support; the second switch is closed when the voltage of the power transmission line is direct current.
8. The AC/DC power supply system according to claim 5,
when the voltage at the load side meets the preset voltage, the fifth switch and the fourth switch are switched on, and the first switch, the second switch and the third switch are switched off to be switched into an alternating current power supply mode.
9. The AC/DC power supply system according to claim 8,
the first switch is switched off when the current of the power transmission line is smaller than or equal to a first preset value; the second switch is switched off when the inflow current is suddenly changed to zero; the fourth switch is closed when no voltage is supported on the right side of the fourth switch; the fifth switch is closed when the voltage on the left side of the fifth switch is changed from direct current to alternating current; and the third switch is disconnected during communication on the same side.
10. The AC/DC power supply system according to claim 3,
the rated value of the voltage of a direct current bus of the sending end converter is 750V, and the power transmission line is a three-phase four-wire power transmission line.
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