Three-phase power supply system and power supply method thereof

Abstract

A three-phase power supply system and a power supply method thereof. The three-phase power supply system comprises: three phase branches, the three phase branches form a triangle connection; each phase branch comprises at least one power conversion unit, the power conversion unit is at least two-stage; the at least one power conversion unit of each phase branch is connected in parallel with the at least one power conversion unit of the remaining two phase branches; when one of the phase branches stops running, the other two phase branches continue to run, and by adjusting the active power and reactive power of the other two phase branches, the current of the three phases of the three-phase power supply system can be balanced. Through the present invention, when one of the phase branches stops running, the other two phase branches continue to run, and the current of the three phases of the three-phase power supply system can be balanced.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronics, and in particular to a three-phase power supply system and a power supply method thereof. Background Art

[0002] As an "energy router" that exchanges active / reactive power with the medium-voltage AC power grid, the reliability of the power electronic transformer (SST) is its key performance indicator. The current means of improving reliability is generally to increase the number of module cascades to achieve N-1 or NM redundancy, or to achieve system-level redundancy through system parallel connection.

[0003] For example, one architecture of SST consists of two-stage isolation modules connected in series and in parallel. The medium-voltage AC side is connected in series through a cascaded H-Bridge (CHB) and connected to the three-phase AC medium-voltage power grid through a delta connection. The low-voltage DC sides of all three-phase modules are connected in parallel to form a low-voltage DC bus to connect to loads / power sources such as inverters and car charging piles. The control objectives of SST mainly include: (1) three-phase current control on the medium-voltage AC side, such as three-phase current balance; (2) equal average bus voltage of each module; (3) low-voltage DC side voltage, current or power control as required; (4) voltage / current sharing control between modules, etc.

[0004] In order to further improve the reliability of SST, the "Open Delta" operation mode can be used to disconnect the faulty phase bridge arm when the SST bridge arm fails, and the remaining two phases provide power while maintaining the three-phase balance of the medium-voltage AC side current. At the same time, for scenarios such as new energy access, the power factor (PF) should still be maintained during "Open Delta" operation to meet relevant standards such as "GBT29321-2012" and "GBT19963-2011".

[0005] Existing literature has discussed how to achieve "open triangle" operation in static var generators (SVG) and solar photovoltaics (PV) based on the CHB architecture. However, due to the limitations of the CHB architecture, when SVG is in the "open triangle" operation mode, in order to maintain the bus voltage balance, it is necessary to inject additional negative sequence current on the medium voltage AC grid side, resulting in unbalanced grid current; when solar photovoltaic is in the "open triangle" operation mode, in order to maintain the bus voltage balance, it is necessary to inject additional reactive current on the medium voltage AC grid side, resulting in the system being unable to operate at the specified power factor.

[0006] In addition, the busbar of the CHB architecture is in a suspended state, so the "open triangle" operation scheme based on the CHB architecture does not support arbitrary power factor operation, that is, it does not support four-quadrant operation.

[0007] However, the difference between the SST architecture and the CHB architecture is that the SST architecture provides a common DC bus on the low-voltage DC side, so there is an opportunity to adjust the active and reactive power of the non-fault bridge arm during "open triangle" operation, thereby supporting four-quadrant operation while maintaining the three-phase balance of the grid-side current.

[0008] In other words, when the SST architecture operates in an “open triangle”, there is no need to inject additional negative sequence or reactive current on the medium voltage AC grid side. Summary of the invention

[0009] The object of the present invention is to provide a three-phase power supply system and a power supply method thereof, which can ensure that when one phase branch stops running, the other two phase branches continue to run, and can make the current of the three phases of the three-phase power supply system symmetrical.

[0010] In order to achieve the above-mentioned purpose, the present invention provides a three-phase power supply system, which is characterized in that it includes: three phase branches, the three phase branches form a triangle connection; each of the phase branches includes at least one power conversion unit, and the power conversion unit is at least two-stage; the at least one power conversion unit of each phase branch is connected in parallel with the at least one power conversion unit of the remaining two phase branches; when one of the phase branches stops running, the other two phase branches continue to run, and by adjusting the active power and reactive power of the other two phase branches, the current of the three phases of the three-phase power supply system can be balanced.

[0011] In an embodiment of the present invention, each of the power conversion units at least includes a cascaded front-stage converter and a rear-stage converter, and the rear-stage converter has a first end and a second end located on the DC side.

[0012] In one embodiment of the present invention, the AC side of at least one power conversion unit of each of the three phase branches is connected in series and forms a triangle to an AC power grid, the first end of the DC side of all the power conversion units of the three phase branches is connected in parallel to the first bus, and the second end of the DC side of all the power conversion units of the three phase branches is connected in parallel to the second bus.

[0013] In one embodiment of the present invention, the AC side of at least one power conversion unit of each of the three phase branches is connected in series and forms a triangle to an AC power grid, and the DC side of each of the three phase branches has m DC ports, where m≥2, and at least one of the DC ports is connected to the three phase branches at the same time.

[0014] In one embodiment of the present invention, the three-phase power supply system also includes: a main controller, which is communicatively connected to at least one power conversion unit in the three phase branches, and the main controller receives information from the three phase branches and adjusts the three phase branches according to the information.

[0015] In one embodiment of the present invention, the three-phase power supply system also includes: at least three phase controllers, which are respectively communicated with the at least one power conversion unit in each of the phase branches, each of the phase controllers also includes a communication interface and the at least three phase controllers are communicatively connected to each other through the communication interface; wherein the phase controller corresponding to each phase branch receives information sent by the phase controllers corresponding to the other two phase branches through the communication interface to adjust the phase branch.

[0016] In one embodiment of the present invention, the front-stage converter and the rear-stage converter in each of the power conversion units in each of the phase branches are controlled separately, wherein:

[0017] Controlling the average bus voltage output by the front-stage converter of each power conversion unit in the corresponding phase branch, and each phase branch receives active power information of the other two phase branches and reactive power instructions of the receiving system, and generates reactive power adjustment values ​​of each phase branch to control the reactive power of the phase branch;

[0018] Each of the phase branches also controls the DC side active power of the subsequent converter of each of the power conversion units in the corresponding phase branch by receiving the active power adjustment values ​​of the other two phase branches.

[0019] In one embodiment of the present invention, the method further includes controlling the DC side active power of the subsequent converter of each power conversion unit in the corresponding phase branch, which is to control the voltage, current or power on the DC side.

[0020] In one embodiment of the present invention, when the other two phase branches that continue to operate trigger overcurrent protection, the corresponding phase branch that stops operating triggers current limiting operation according to a preset priority to give priority to satisfying active power demand, or to give priority to satisfying reactive power demand, or to give priority to satisfying a fixed power factor requirement.

[0021] In one embodiment of the present invention, the three-phase power supply system operates in four quadrants.

[0022] In order to achieve the above-mentioned object, the present invention further provides a power supply method for a three-phase power supply system, which is characterized in that the three-phase power supply system includes three phase branches, and the three phase branches form a triangle connection; each of the phase branches includes at least one power conversion unit, and the power conversion unit is at least two-stage; the at least one power conversion unit of each phase branch is connected in parallel with the at least one power conversion unit of each of the remaining two phase branches; the power supply method includes:

[0023] When one of the phase branches stops running, the other two phase branches continue to run, and by adjusting the active power and reactive power of the other two phase branches, the current of the three phases of the three-phase power supply system can be balanced.

[0024] In another embodiment of the present invention, each of the power conversion units at least includes a cascaded front-stage converter and a rear-stage converter, and the rear-stage converter has a first end and a second end located on the DC side.

[0025] In another embodiment of the present invention, the AC side of at least one power conversion unit of each of the three phase branches is connected in series and forms a triangle to an AC power grid, the first end of the DC side of all the power conversion units of the three phase branches is connected in parallel to the first bus, and the second end of the DC side of all the power conversion units of the three phase branches is connected in parallel to the second bus.

[0026] In another embodiment of the present invention, the AC side of at least one power conversion unit of each of the three phase branches is connected in series and forms a triangle to an AC power grid, and the DC side of each of the three phase branches has m DC ports, where m≥2, and at least one of the DC ports is connected to the three phase branches at the same time.

[0027] In another embodiment of the present invention, the power supply method further includes: utilizing a main controller to communicate with all power conversion units in the three phase branches, receiving information from the three phase branches through the main controller and adjusting the three phase branches according to the information.

[0028] In another embodiment of the present invention, the power supply method also includes: using at least three phase controllers to communicate with at least one power conversion unit in each phase branch respectively, each phase controller also includes a communication interface and the at least three phase controllers are communicatively connected to each other through the communication interface; wherein the phase controller corresponding to each phase branch receives information sent by the phase controllers corresponding to the other two phase branches through the communication interface to adjust the phase branch.

[0029] In another embodiment of the present invention, the front-stage converter and the rear-stage converter in each of the power conversion units in each of the phase branches are controlled separately, wherein:

[0030] Controlling the average bus voltage output by the front-stage converter of each power conversion unit in the corresponding phase branch, and each phase branch receives active power information of the other two phase branches and reactive power instructions of the receiving system, and generates reactive power adjustment values ​​of each phase branch to control the reactive power of the phase branch;

[0031] Each of the phase branches also controls the DC side active power of the subsequent converter of each of the power conversion units in the corresponding phase branch by receiving the active power adjustment values ​​of the other two phase branches.

[0032] In another embodiment of the present invention, the method further includes controlling the DC side active power of the subsequent converter of each power conversion unit in the corresponding phase branch, which is to control the voltage, current or power on the DC side.

[0033] In another embodiment of the present invention, the power supply method also includes: when the other two phase branches that continue to operate trigger overcurrent protection, the corresponding phase branch that stops operating triggers current limiting operation according to a preset priority by giving priority to satisfying active power demand, or giving priority to satisfying reactive power demand, or giving priority to satisfying a fixed power factor requirement.

[0034] In another embodiment of the present invention, the three-phase power supply system operates in four quadrants.

[0035] By means of the present invention, when one phase branch of a three-phase power supply system stops running, the other two phase branches continue to run, and the currents of the three phases of the three-phase power supply system are balanced.

[0036] Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings.

[0038] Figure 1 A schematic diagram of the circuit structure of a three-phase power supply system according to a first preferred embodiment of the present invention;

[0039] Figure 2 for Figure 1 A schematic diagram of the structure of a power conversion unit in FIG.

[0040] Figure 3 for Figure 1 The schematic diagram of simulation waveform of the three-phase power supply system shown;

[0041] Figure 4 A schematic diagram of the circuit structure of a three-phase power supply system according to a second preferred embodiment of the present invention;

[0042] Figure 5 A schematic diagram of the circuit structure of a three-phase power supply system according to a third preferred embodiment of the present invention;

[0043] Figure 6 A schematic diagram of the circuit structure of a three-phase power supply system according to a fourth preferred embodiment of the present invention;

[0044] Figure 7 Shows Figure 2 The schematic diagram of the front-stage control algorithm of the two-stage power conversion unit shown;

[0045] Figure 8 Shows Figure 2 Schematic diagram of the post-stage control algorithm of the two-stage power conversion unit shown. DETAILED DESCRIPTION

[0046] Example embodiments will now be described more fully with reference to the accompanying drawings. However, example embodiments can be implemented in a variety of forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that the present invention will be comprehensive and complete and fully convey the concepts of the example embodiments to those skilled in the art. The same reference numerals in the figures represent the same or similar structures, and thus their detailed description will be omitted.

[0047] When introducing the elements / components / etc. described and / or illustrated herein, the terms "a", "an", "the", "said", and "at least one" are used to indicate that there are one or more elements / components / etc. The terms "comprising", "including", and "having" are used to indicate an open-ended inclusive meaning and mean that there may be additional elements / components / etc. in addition to the listed elements / components / etc. In addition, the terms "first", "second", etc. in the claims are used only as labels and are not numerical limitations of their objects.

[0048] like Figure 1As shown, the three-phase power supply system 100-1 of the first preferred embodiment of the present invention is a delta-connected SST architecture with a common bus output, which mainly includes three phase branches, for example, an A phase branch 10, a B phase branch 20 and a C phase branch 30, wherein the A phase branch 10, the B phase branch 20 and the C phase branch 30 form a triangle connection. In addition, each phase branch includes a plurality of power conversion units 40, for example, the A phase branch 10 includes n power conversion units Cell A1, Cell A2, ..., Cell An, the B phase branch 20 includes n power conversion units Cell B1, Cell B2, ..., Cell Bn, and the C phase branch 30 includes n power conversion units Cell C1, Cell C2, ..., Cell Cn. These power conversion units 40 can be, for example, at least two stages. The multiple power conversion units in each phase branch are connected in parallel with the multiple power conversion units of the remaining two phase branches. Furthermore, when one of the phase branches stops operating, the other two phase branches continue to operate, and by adjusting the active power and reactive power of the other two phase branches, the current of the three phases of the three-phase power supply system can be balanced.

[0049] exist Figure 1 In the embodiment shown, Figure 2 As shown, each power conversion unit 40 may be, for example, a two-stage isolation structure, and may include, for example, a cascaded front-stage converter 41 and a rear-stage converter 42. The front-stage converter 41 may be, for example, an AC / DC converter and has an AC input terminal AC_in and an AC output terminal AC_out, and the rear-stage converter 42 may be, for example, a DC / DC converter and has a first terminal (e.g., a DC+ terminal) and a second terminal (e.g., a DC- terminal) located on the DC side. Of course, it can be understood that in other embodiments, the power conversion unit 40 may also be an isolation structure with more stages, which is not intended to limit the present invention.

[0050] exist Figure 1 In the illustrated embodiment, the AC side of the power conversion unit of each phase branch of the three-phase power supply system 100-1 of the SST architecture is connected in series and forms a triangle to an AC power grid, such as a medium-voltage AC power grid, and the low-voltage DC side of all the power conversion units of the three-phase branch is connected in parallel to the same bus. For example, the AC side of multiple power conversion units 40 of each phase branch of the A-phase branch 10, the B-phase branch 20, and the C-phase branch 30 is connected in series and forms a triangle to the AC power grid. The first end (e.g., DC+ end) of the DC side of all the power conversion units 40 of the A-phase branch 10, the B-phase branch 20, and the C-phase branch 30 is connected in parallel to the first bus 51, and the second end (e.g., DC- end) of the DC side of all the power conversion units 40 of the A-phase branch 10, the B-phase branch 20, and the C-phase branch 30 is connected in parallel to the second bus 52.

[0051] Figure 1 The three-phase power supply system 100-1 of the delta-connected SST architecture with a common output busbar is shown without loss of generality. Assuming that the CA phase bridge arm (e.g., the C phase branch 30) fails, the system will enter the "open triangle" operation mode. At this time, according to the reactive power demand of the system, the active power of the non-faulty AB phase bridge arm (e.g., the A phase branch 10) and the BC phase bridge arm (e.g., the B phase branch 20) is adjusted, and the reactive power is adjusted accordingly, so that the power demand can be met while maintaining the three-phase balance of the grid current.

[0052] Among them, when the system enters the "open triangle" operation mode, assuming that the system reactive power command is q r , the low voltage DC power is p r , then the active power of the remaining two phases AB and BC should be adjusted to At the same time, the reactive power of phase AB and phase BC should be adjusted to

[0053] It should be pointed out that after the above adjustment, as long as there is no overcurrent in each bridge arm (phase branch), the total active power of the system is still p r , the total reactive power is q r In one embodiment, the reactive power is q r is the reactive power command given by the system.

[0054] In particular, when the system reactive power command q r =0, that is, when the power factor PF = 1, the active power of the remaining two phases AB and BC should be equal, that is, At the same time, the reactive power should be

[0055] Figure 3 The simulation waveform of the three-phase power supply system of the present invention is shown, wherein:

[0056] (1) At time t1, the system starts to operate normally;

[0057] (2) At t2, the bridge arm of phase CA fails and the bridge arm current drops to zero. The system reactive power command q r =0, by adjusting the active power and reactive power of the AB phase bridge arm and the BC phase bridge arm, the grid-side current maintains a three-phase balance, and the grid voltage and current are in phase, that is, PF = 1;

[0058] (3) At time t3, the system reactive power command q r ≠0. At this time, the active power and reactive power of the AB phase bridge arm and the BC phase bridge arm are adjusted so that the grid-side current maintains a three-phase balance. At the same time, the grid voltage and current are no longer in phase, and the reactive power is the command value.

[0059] like Figure 4 As shown, it shows the circuit architecture of the three-phase power supply system 100-2 of the second preferred embodiment of the present invention, which is a multi-port delta-connected SST architecture, wherein the AC side of the n power conversion units 40 of each phase branch of the A phase branch 10, the B phase branch 20 and the C phase branch 30 is connected in series and forms a triangle to an AC power grid, and the DC side of each phase branch of the A phase branch 10, the B phase branch 20 and the C phase branch 30 has m DC ports, namely DC 1, ..., DC m, where m ≥ 2, and at least one of the DC ports is simultaneously connected to the A phase branch 10, the B phase branch 20 and the C phase branch 30. For example, in Figure 4 In the embodiment, the first end and the second end of the DC side of the power conversion unit Cell A1 in the A phase branch 10, the power conversion unit Cell B1 in the B phase branch 20, and the power conversion unit Cell C1 in the C phase branch 30 are respectively connected in parallel to the first bus 51 and the second bus 52 to form a DC port DC 1; the first end and the second end of the DC side of the power conversion units Cell A2 to Cell An in the A phase branch 10, the power conversion units Cell B2 to Cell Bn in the B phase branch 20, and the power conversion units Cell C2 to Cell Cn in the C phase branch 30 are respectively connected in parallel to the third bus 53 and the fourth bus 54 to form a DC port DC m.

[0060] The three-phase power supply system of the present invention is combined with a controller architecture and has several different implementations. Figure 5 As shown, it shows the circuit architecture of the three-phase power supply system 100-3 of the third embodiment of the present invention, wherein the three-phase power supply system 100-3 is an implementation scheme using a centralized controller, which is in the Figure 1 Based on the circuit architecture shown in FIG. 1 , a main controller 60 is further included. The main controller 60 is in communication connection with at least one power conversion unit 40 in the three phase branches 10, 20, and 30. The main controller 60 receives information from the three phase branches 10, 20, and 30 and adjusts the three phase branches 10, 20, and 30 according to the information. For example, the main controller 60 may receive a three-phase grid voltage v gab 、v gbc 、v gca and the three-phase grid current i ga 、i gb 、i gc and other information and make adjustments accordingly. Figure 5 In the three-phase power supply system 100 - 3 shown, when a phase branch fails, combined with the above-mentioned solution, only the phase will stop supplying power, and the system will still maintain partial power supply capacity.

[0061] like Figure 6 FIG. 4 shows a circuit structure of a three-phase power supply system 100-4 according to a fourth embodiment of the present invention, wherein the three-phase power supply system 100-4 is an implementation scheme using a distributed phase controller. Figure 1 On the basis of the circuit architecture shown, it further includes at least three phase controllers 61, 62, 63, which are respectively connected to each phase branch 10, 20, 30 in communication with at least one power conversion unit 40, each of which may also include a communication interface, and the at least three phase controllers 61, 62, 63 are connected to each other in communication via the communication interface. The phase controller corresponding to each phase branch receives information sent by the phase controllers corresponding to the other two phase branches and information of the current phase through the communication interface to adjust the phase branch. For example, the phase controller 61 may receive the grid voltage v gab , grid current i ga and the active power information of the other two phases and adjust the phase branch 10 accordingly. The phase controller 62 can receive the grid voltage v gbc , grid current i gb and the active power information of the other two phases and adjust the phase branch 20 accordingly. The phase controller 63 can receive the grid voltage v gca , grid current i gc And the active power information of the other two phases and other information and adjust the phase branch 30 accordingly. Figure 6 The three-phase power supply system 100 - 4 shown, no matter a phase branch fails or a phase controller fails, only the phase will stop supplying power, thereby eliminating the risk of single point failure caused by a centralized controller failure.

[0062] Figure 7 and Figure 8 They are shown respectively Figure 2 The front-stage control block diagram and the rear-stage control block diagram of the two-stage power conversion unit shown in FIG. Figure 2 The front-stage converter and the rear-stage converter of the power conversion unit shown in FIG. Figure 7 As shown in the front-stage control block diagram, the average bus voltage output by the front-stage converter of each power conversion unit in the corresponding phase branch can be controlled, and each phase branch receives the active power information of the other two phase branches and the reactive power instruction of the receiving system, and generates the reactive power adjustment value of each phase branch to control the reactive power of the phase branch. Figure 8As shown in the back-end control block diagram, each phase branch can control the DC side active power of the back-end converter of each power conversion unit in the corresponding phase branch by receiving the active power adjustment value of the other two phase branches. In one embodiment, it is also necessary to control the voltage, current or power of the DC side.

[0063] like Figure 7 As shown, for the front-stage controller, the front-stage controller of each phase connected in parallel at the same port controls the average bus voltage of each power conversion unit, and at the same time receives the active power information of the other two phases to generate the reactive power adjustment value Δq of each phase. AB , Δq BC and Δq CA ,and where p AB 、p BC 、p CA They are the three-phase active power information respectively.

[0064] At the same time, the front-stage controller of each phase also receives the system reactive power command. The reactive power command of each phase is The reactive power of each phase is adjusted according to the reactive power adjustment value and the reactive power command of each phase.

[0065] like Figure 8 As shown, in addition to controlling the voltage / current or power of the low-voltage DC side as required, the subsequent controller of each phase also needs to introduce an active power adjustment value Δp AB , Δp BC and Δp CA , in order to achieve the distribution of low voltage DC side active power on the three-phase bridge arm. In normal operation, there is Δp AB =Δp BC =Δp CA = 0, so the active power on the DC side is evenly distributed to the three-phase bridge arm. When the "open triangle" operation is in progress, the value is taken according to the above scheme to meet the four-quadrant operation requirements. For example, when the CA phase fails, there is In particular, when the system reactive power command q r =0, the active power on the DC side is evenly distributed to the remaining two non-fault phase bridge arms.

[0066] The above schemes are all situations where the active / reactive power of the non-fault phase bridge arm is adjusted without causing overcurrent in the bridge arm. In fact, when the system load is heavy, the above scheme may cause one or two phases of the remaining non-fault phases to trigger overcurrent protection. Therefore, current limiting operation can be introduced in this situation.

[0067] Before the current limiting operation is triggered, the system can still achieve the aforementioned four-quadrant operation.

[0068] After the current limiting operation is triggered, the system needs to give priority to meeting the active power demand, or give priority to meeting the reactive power demand, or give priority to meeting the fixed power factor requirement, etc. This embodiment takes giving priority to meeting the active power demand as an example.

[0069] Assume that the maximum apparent power of the system is S MAX , system active power before fault

[0070] Then the system active power after the fault is p r_post And reactive power power command q r_post The value range of is:

[0071] when

[0072] The above formula shows that when the system active power before the fault is When the fault occurs, the limit At the same time, the reactive power command q r =0 to prevent the non-fault phase arm power from exceeding the limit, that is, the SST can only operate at PF=1 at this time to meet the active power demand as much as possible.

[0073] when

[0074] The above formula shows that when the system active power before the fault is When the fault occurs, the active power is not affected, and the reactive power instruction q r By selecting the value within the range of the above formula, four-quadrant operation can be achieved while avoiding over-limit of the power of the non-fault phase bridge arm.

[0075] Accordingly, the present invention provides a power supply method for a three-phase power supply system, wherein the three-phase power supply system includes three phase branches, and the three phase branches form a triangle connection; each of the phase branches includes at least one power conversion unit, and the power conversion unit is at least two-stage; the at least one power conversion unit of each phase branch is connected in parallel with the at least one power conversion unit of the remaining two phase branches; the power supply method includes: when one of the phase branches stops running, the other two phase branches continue to run, and by adjusting the active power and reactive power of the other two phase branches, the current of the three phases of the three-phase power supply system can be balanced.

[0076] Preferably, each of the power conversion units at least comprises a cascaded front-stage converter and a rear-stage converter, and the rear-stage converter has a first end and a second end located on the DC side.

[0077] Preferably, the AC side of at least one power conversion unit of each of the three phase branches is connected in series and forms a triangle to an AC power grid, the first end of the DC side of all the power conversion units of the three phase branches is connected in parallel to the first bus, and the second end of the DC side of all the power conversion units of the three phase branches is connected in parallel to the second bus.

[0078] Preferably, the AC side of at least one power conversion unit of each of the three phase branches is connected in series and forms a triangle to an AC power grid, and the DC side of each of the three phase branches has m DC ports, where m≥2, and at least one of the DC ports is connected to the three phase branches at the same time.

[0079] Preferably, the power supply method further comprises: utilizing a main controller to communicate with all power conversion units in the three phase branches, receiving information from the three phase branches through the main controller and adjusting the three phase branches according to the information.

[0080] Preferably, the power supply method also includes: using at least three phase controllers to respectively communicate with the at least one power conversion unit in each phase branch, each phase controller also includes a communication interface and the at least three phase controllers are communicatively connected to each other through the communication interface; wherein the phase controller corresponding to each phase branch receives information sent by the phase controllers corresponding to the other two phase branches through the communication interface to adjust the phase branch.

[0081] Preferably, the front-stage converter and the rear-stage converter in each of the power conversion units in each of the phase branches are controlled separately, wherein the average bus voltage output by the front-stage converter of each of the power conversion units in the corresponding phase branch is controlled, and each of the phase branches receives active power information of the other two phase branches and reactive power instructions of the receiving system, and generates reactive power adjustment values ​​of each of the phase branches to control the reactive power of the phase branch; each of the phase branches also controls the DC side active power of the rear-stage converter of each of the power conversion units in the corresponding phase branch by receiving the active power adjustment values ​​of the remaining two phase branches.

[0082] Preferably, controlling the DC side active power of the subsequent converter of each of the power conversion units in the corresponding phase branch is controlling the voltage, current or power on the DC side.

[0083] Preferably, the power supply method further includes: when the other two phase branches that continue to operate trigger overcurrent protection, the corresponding phase branch that stops operating triggers current limiting operation by giving priority to satisfying active power demand, or giving priority to satisfying reactive power demand, or giving priority to satisfying fixed power factor requirement according to preset priority.

[0084] Preferably, the three-phase power supply system operates in four quadrants.

[0085] By means of the present invention, when one phase branch of a three-phase power supply system stops running, the other two phase branches continue to run, and the currents of the three phases of the three-phase power supply system are balanced.

[0086] Through the present invention, it is also possible to support four-quadrant operation in "open triangle".

[0087] The exemplary embodiments of the present invention are specifically shown and described above. It should be understood that the present invention is not limited to the disclosed embodiments, but rather is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. A three-phase power supply system, It is characterized in that include: three phase branches, the three phase branches forming a triangle connection; Each of the phase branches comprises at least one power conversion unit, each of the power conversion units comprises at least a cascaded front-stage converter and a rear-stage converter, and the rear-stage converter has a first end and a second end located on the DC side; The at least one power conversion unit of each phase branch is connected in parallel with the at least one power conversion unit of each of the remaining two phase branches; When one of the phase branches stops running, the other two phase branches continue to run, and by adjusting the active power and reactive power of the other two phase branches, the current of the three phases of the three-phase power supply system can be balanced. Among them, the front-stage converter and the rear-stage converter in each of the power conversion units in each of the phase branches are controlled separately, including controlling the average bus voltage output by the front-stage converter of each of the power conversion units in the phase branch, and the voltage, current or power on the DC side of the rear-stage converter of each of the power conversion units in the phase branch.

2. The three-phase power supply system according to claim 1, It is characterized in that The AC side of at least one power conversion unit of each of the three phase branches is connected in series and forms a triangle to an AC power grid, the first end of the DC side of all the power conversion units of the three phase branches is connected in parallel to the first bus, and the second end of the DC side of all the power conversion units of the three phase branches is connected in parallel to the second bus.

3. The three-phase power supply system according to claim 1, It is characterized in that The AC side of at least one power conversion unit of each of the three phase branches is connected in series and forms a triangle to an AC power grid, and the DC side of each of the three phase branches has m DC ports, where m≥2, and at least one of the DC ports is connected to the three phase branches at the same time.

4. The three-phase power supply system according to any one of claims 1 to 3, It is characterized in that Also includes: A main controller is communicatively connected with at least one power conversion unit in the three phase branches, and the main controller receives information from the three phase branches and adjusts the three phase branches according to the information.

5. The three-phase power supply system according to any one of claims 1 to 3, It is characterized in that Also includes: At least three phase controllers are respectively connected to the at least one power conversion unit in each phase branch, each phase controller further comprises a communication interface and the at least three phase controllers are connected to each other through the communication interface; The phase controller corresponding to each phase branch receives information sent by the phase controllers corresponding to the other two phase branches through the communication interface to adjust the phase branch.

6. The three-phase power supply system according to any one of claims 1 to 3, It is characterized in that Each of the phase branches receives active power information of the other two phase branches and a reactive power instruction of the receiving system, and generates a reactive power adjustment value of each phase branch to control the reactive power of the phase branch; Each of the phase branches also controls the DC side active power of the subsequent converter of each of the power conversion units in the corresponding phase branch by receiving the active power adjustment values ​​of the other two phase branches.

7. The three-phase power supply system according to any one of claims 1 to 3, It is characterized in that When the other two phase branches that continue to operate trigger overcurrent protection, the corresponding phase branch that stops operating triggers current limiting operation according to preset priorities to give priority to meeting active power requirements, reactive power requirements, or fixed power factor requirements.

8. The three-phase power supply system according to any one of claims 1 to 3, It is characterized in that The three-phase power supply system operates in four quadrants.

9. A power supply method for a three-phase power supply system, It is characterized in that The three-phase power supply system comprises three phase branches, and the three phase branches form a triangle connection; each phase branch comprises at least one power conversion unit, and each power conversion unit comprises at least a cascaded front-stage converter and a rear-stage converter, and the rear-stage converter has a first end and a second end located on the DC side; the at least one power conversion unit of each phase branch is connected in parallel with the at least one power conversion unit of each of the remaining two phase branches; the power supply method comprises: When one of the phase branches stops running, the other two phase branches continue to run, and by adjusting the active power and reactive power of the other two phase branches, the current of the three phases of the three-phase power supply system can be balanced. Among them, the front-stage converter and the rear-stage converter in each of the power conversion units in each of the phase branches are controlled separately, including controlling the average bus voltage output by the front-stage converter of each of the power conversion units in the phase branch, and the voltage, current or power on the DC side of the rear-stage converter of each of the power conversion units in the phase branch.

10. The power supply method according to claim 9, It is characterized in that The AC side of at least one power conversion unit of each of the three phase branches is connected in series and forms a triangle to an AC power grid, the first end of the DC side of all the power conversion units of the three phase branches is connected in parallel to the first bus, and the second end of the DC side of all the power conversion units of the three phase branches is connected in parallel to the second bus.

11. The power supply method according to claim 9, It is characterized in that The AC side of at least one power conversion unit of each of the three phase branches is connected in series and forms a triangle to an AC power grid, and the DC side of each of the three phase branches has m DC ports, where m≥2, and at least one of the DC ports is connected to the three phase branches at the same time.

12. The power supply method according to any one of claims 9 to 11, It is characterized in that Also includes: A main controller is used to communicate with all the power conversion units in the three phase branches, and the main controller receives information from the three phase branches and adjusts the three phase branches according to the information.

13. The power supply method according to any one of claims 9 to 11, It is characterized in that Also includes: Using at least three phase controllers to communicate with at least one power conversion unit in each phase branch, each phase controller further comprises a communication interface and the at least three phase controllers are communicatively connected to each other via the communication interface; The phase controller corresponding to each phase branch receives information sent by the phase controllers corresponding to the other two phase branches through the communication interface to adjust the phase branch.

14. The power supply method according to any one of claims 9 to 11, It is characterized in that Each of the phase branches receives active power information of the other two phase branches and a reactive power instruction of the receiving system, and generates a reactive power adjustment value of each phase branch to control the reactive power of the phase branch; Each of the phase branches also controls the DC side active power of the subsequent converter of each of the power conversion units in the corresponding phase branch by receiving the active power adjustment values ​​of the other two phase branches.

15. The power supply method according to any one of claims 9 to 11, It is characterized in that Also includes: When the other two phase branches that continue to operate trigger overcurrent protection, the corresponding phase branch that stops operating triggers current limiting operation according to preset priorities to give priority to meeting active power requirements, reactive power requirements, or fixed power factor requirements.

16. The power supply method according to any one of claims 9 to 11, It is characterized in that The three-phase power supply system operates in four quadrants.

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