A multi-port modular multilevel DC / DC converter with fault isolation function and a regulation method thereof

Abstract

The application relates to the technical field of high-voltage direct-current power grids, and discloses a multi-port modular multi-level DC / DC converter with a fault isolation function and a regulation and control method thereof. The converter comprises a power main circuit and a controller for regulating and controlling the power main circuit; the power main circuit comprises one basic power conversion module and n extension power conversion modules, each basic power conversion module is composed of a high-voltage bridge arm, a multiplex bridge arm, a low-voltage bridge arm and a corresponding bridge arm inductor. The high-voltage bridge arms of different power conversion modules are connected to the same high-voltage port, and the low-voltage bridge arms of different power conversion modules are connected to different low-voltage ports; the controller is composed of a sampling isolation unit, a port direct-current regulation and control unit, a bridge arm alternating-current regulation and control unit and a sub-module capacitor voltage regulation and control unit. The application can realize the functions of voltage matching, power flow regulation, fault blocking and open-phase operation of a multi-terminal direct-current interconnection system, and has important application value in the field of high-voltage direct-current power grids.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high-voltage direct-current power grids, and particularly relates to a multi-port modular multi-level DC / DC converter with a fault isolation function and a regulation method thereof. BACKGROUND

[0002] A high-voltage direct-current power grid is one of the preferred solutions for long-distance power transmission, reliable access to large-scale renewable energy, and cross-regional interconnection of traditional energy, and is also an important direction for supporting the future development of a smart grid. At present, mainstream voltage levels of a direct-current power grid include ±160 kV, ±320 kV, and ±800 kV, and there is no unified voltage standard, which poses new conversion requirements and technical challenges for flexible interconnection of a direct-current power grid. A high-voltage and large-capacity DC / DC converter is a key device for flexible networking and controllable interconnection of a direct-current power grid, and is a crucial link in the development of a new power system. The high-voltage and large-capacity DC / DC converter is a step-up sending conversion link for realizing energy transmission in a large-scale new energy sending system, and is a tidal controller between direct-current power grids and a flexible interconnection device between alternating-current power grids. With the large-scale access of new energy and the continuous rise of power consumption load, the voltage level and power capacity of the DC / DC converter are further improved, and not only must match different voltage levels on the input and output sides, but also shoulder the function of flexible interconnection of bidirectional controllable energy transmission. Therefore, efficient and reliable operation of a multi-port DC / DC converter with a capacity of hundreds of kilovolts and megawatts is an important guarantee for realizing the complementary advantages of multi-energy, long-distance and wide-area interconnection of a direct-current power grid.

[0003] Currently, some scholars have proposed face-to-face isolation type high-voltage DC / DC converter, that is, two modular multilevel converters are used for AC / DC conversion, and DC voltage is realized through AC coupling. Some scholars have transformed the traditional modular multilevel converter topology, and constructed a self-coupling type topology by connecting the DC sides in series. A small part of power is directly transmitted between high and low voltages, thereby improving the conversion efficiency and reducing the transformer capacity requirement. On the basis of the two traditional high-voltage and large-capacity DC / DC converter topologies, a multi-low-voltage port DC / DC converter topology can be constructed by reusing some components. The topology based on face-to-face modular multilevel converter can realize the transformation of double low-voltage ports by interlinking three DC / AC circuits, and using two AC transformers or a three-winding transformer to couple the AC link. By using three self-coupling type topology sub-circuits in series connection, a double low-voltage port self-coupling type topology can be obtained. The AC links of the three sub-circuits are connected through an AC transformer or by injecting AC voltage and current to maintain the power balance of each sub-circuit. By increasing the number of series sub-circuits, more input ports can be theoretically expanded. However, the voltage level of each DC port of the self-coupling type topology is sequentially increased, and it is not suitable for the collection and step-up of multiple same voltage levels. At the same time, the above-mentioned topology scheme needs three-level power conversion of “AC-AC-AC / DC”, although the efficiency of each level can reach more than 99% in engineering practice, the overall efficiency is still difficult to break through 98%, and the capacity and voltage level are severely limited by the insulation, cooling design and other problems of the heavy isolation transformer, which is difficult to meet the actual application requirements of future engineering. Therefore, a new type of high-efficiency multi-port DC / DC converter is urgently needed. SUMMARY

[0004] To solve the problems in the prior art, the present application provides a multi-port modular multilevel DC / DC converter with fault isolation function and its control method, which can realize voltage matching, power flow regulation, fault blocking, open-phase operation and other functions of multi-port DC / DC converter.

[0005] The application first provides a multi-port modular multi-level DC / DC converter with fault isolation function, which comprises a power main circuit and a controller for regulating the power main circuit; the power main circuit comprises one basic power conversion module and n extended power conversion modules, each basic power conversion module is composed of a high-voltage bridge arm, a multiplex bridge arm, a low-voltage bridge arm and a corresponding bridge arm inductor, the output end of the high-voltage bridge arm, the input end of the multiplex bridge arm and the input end of the low-voltage bridge arm are connected in common, and the output end of the multiplex bridge arm is connected with a ground signal; the input ends of the high-voltage bridge arms of different power conversion modules are connected and connected to a high-voltage DC bus, and together with the ground signal, they constitute a high-voltage port of the multi-port converter; the output ends of the low-voltage bridge arms of different power conversion modules are respectively connected to different low-voltage DC buses, and together with the ground signal, they constitute a plurality of low-voltage ports of the multi-port converter; the high-voltage bridge arm, the multiplex bridge arm and the low-voltage bridge arm are all composed of a plurality of sub-modules in a cascaded manner; wherein n≥1.

[0006] The controller comprises a sampling isolation unit, a port DC regulation unit, a bridge arm AC regulation unit and a sub-module capacitor voltage regulation unit; the sampling isolation unit is used for detecting the electrical signals of the common high-voltage port of the converter, the electrical signals of each low-voltage port, the electrical signals of the three bridge arms in each power conversion module and the electrical signals of the capacitors in each bridge arm; the port DC regulation unit is used for realizing voltage matching and power transmission between high-voltage and low-voltage ports; the bridge arm AC regulation unit is used for realizing energy balance of the high-voltage bridge arm, the low-voltage bridge arm and the multiplex bridge arm in each power conversion module; and the sub-module capacitor voltage regulation unit is used for controlling voltage balance of the capacitors in each bridge arm.

[0007] Further, the high-voltage bridge arm and the multiplex bridge arm of the basic power conversion module are composed of a plurality of half-bridge sub-modules in a cascaded manner, the low-voltage bridge arm is composed of a plurality of full-bridge sub-modules in a cascaded manner, the high-voltage bridge arms of the n extended power conversion modules are composed of a plurality of half-bridge sub-modules and a plurality of full-bridge sub-modules in a cascaded manner, the multiplex bridge arms are composed of a plurality of half-bridge sub-modules in a cascaded manner, and the low-voltage bridge arms are composed of a plurality of full-bridge sub-modules in a cascaded manner; wherein n≥1.

[0008] Further, the high-voltage bridge arm, the multiplex bridge arm and the low-voltage bridge arm are also configured with bridge arm reactors according to power capacity, the bridge arm reactors are connected in series in the circuit of each bridge arm, and the bridge arm reactors are used for assisting commutation and energy transmission between different bridge arms.

[0009] Further, the full-bridge sub-module comprises four power devices and one energy storage capacitor, the half-bridge sub-module comprises two power devices and one energy storage capacitor, and the power devices are all fully controlled devices, which can be IGBT, MOSFET, IGCT, etc.

[0010] The present invention also provides an AC / DC decoupling control method using the aforementioned multi-port modular multilevel DC / DC converter with fault isolation function, comprising the following steps:

[0011] S1. Let the AC voltage amplitude reference of the basic power conversion module be V. 0_base The transmission power is P L_base The corresponding low-voltage port voltage is V. L_base The AC voltage amplitude reference V0′ of any power conversion module in the extended power conversion module is obtained by the following formula;

[0012] S2, The sampling isolation unit inputs electrical signals X from different low-voltage ports to the port DC control unit. L The electrical signals X of the different low-voltage ports L The voltage V at the low-voltage port L Or the current I at the low-voltage port L The DC control unit at the port operates based on the electrical signal X at the low-voltage port. L The corresponding reference value X of the electrical signal at the set output port ref The error signal X of the electrical signal at the output port is obtained. ref -X L The error signal X ref -X L The power P transmitted from each low-voltage port to the high-voltage port is obtained through calculation by the PI controller in the DC control unit. L ;

[0013] S3, the transmission power P of the different low-voltage ports L The AC control unit of each bridge arm in each power conversion module is fed into the AC control unit. Combined with the high-voltage port voltage, the corresponding low-voltage port voltage, the corresponding AC voltage amplitude reference, the corresponding AC frequency, and the corresponding phase information, the current reference value i for each bridge arm in each power conversion module is obtained. arm_ref and the theoretical reference value of voltage v arm_ref The current reference value i arm_ref The measured values ​​of the current in each bridge arm fed into the sampling isolation unit i arm The error signal i of the current of each bridge arm in each power conversion module is obtained by subtraction. arm_ref -i arm The current error signal i arm_ref -i arm The reference value Δv of the voltage increment of each bridge arm is obtained by the PI controller in the bridge arm AC control unit. arm_ref ;

[0014] S4. Convert the theoretical reference voltage v of each bridge arm in each power conversion module. arm_ref and voltage increment reference value Δv arm_refThe voltage actual reference values of the bridge arms in each power conversion module are obtained by addition, and the voltages of the capacitors of the sub-modules of each bridge arm are sorted from high to low, and the sub-modules of each bridge arm in each power conversion module are switched in combination with the voltage actual reference values of the bridge arms in each power conversion module and the sorting results of the capacitor voltages of the sub-modules of each bridge arm;

[0015] S5, the amplitudes and phases of the voltages and currents of the bridge arms are controlled by controlling the switching of the sub-modules of the bridge arms in the basic power conversion module and the extended power conversion module, the high-voltage port current of the converter is obtained by adding the high-voltage bridge arm currents of the basic power conversion module and the extended power conversion module, and the low-voltage bridge arm currents of the basic power conversion module and the extended power conversion module correspond to different low-voltage port currents, so as to realize voltage matching and power flow regulation between the high-voltage port and the multiple low-voltage ports.

[0016] Compared with the prior art, the application has the beneficial effects of:

[0017] 1) The single-stage topology scheme is adopted, the multiple losses caused by the heavy AC isolation transformer and the "quadrature-interchange-interchange-interchange direct" three-stage power conversion in the existing face-to-face scheme are avoided, the insulation and cooling design problems of the high-voltage large-capacity AC isolation transformer are avoided, and the overall efficiency of the system is improved;

[0018] 2) The sub-module cascading technology is adopted to avoid the technical challenge of device series connection, and the voltage stress bearing demand of a single device is reduced; meanwhile, the multiplexing topology construction technology is adopted to optimize the problem of a large number of bridges in the existing face-to-face topology, the number of required power devices is greatly reduced, and the system construction cost is effectively reduced.

[0019] 3) The multi-port AC / DC decoupling regulation method is simple to control, the different low-voltage ports correspond to independent conversion modules, the port can be further increased and the conversion capacity can be further improved, and the method has the functions of voltage matching, power flow regulation, fault blocking, open-phase operation and the like, and the engineering feasibility is greatly improved; BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 A topology architecture diagram of a multi-port modular multilevel DC / DC converter with a fault isolation function is provided for the embodiments of the application;

[0021] Figure 2 A topology architecture diagram of a power main circuit of a multi-port modular multilevel DC / DC converter with a fault isolation function is provided for the embodiments of the application;

[0022] Figure 3 Half-bridge sub-module and full-bridge sub-module topology architecture diagrams are provided for the embodiments of the application;

[0023] Figure 4 The topological architecture diagram of the power main circuit of an embodiment of the present application, which contains three voltage transformation units, connects one high-voltage port and three low-voltage ports;

[0024] Figure 5 The schematic diagram of the control method of the multi-port modular multilevel DC / DC converter with fault isolation function provided by the embodiment of the present application;

[0025] Figure 6 The waveform of the fault current blocked when the high-voltage port short-circuit fault is encountered in the normal operation process of the topology provided by the embodiment of the present application;

[0026] Figure 7 The waveform of the fault current blocked when the low-voltage port short-circuit fault is encountered in the normal operation process of the topology provided by the embodiment of the present application. DETAILED DESCRIPTION

[0027] The present application will be further described and illustrated in conjunction with the specific embodiments. The embodiments are only exemplary and do not define the limit of the present disclosure. The technical features of each embodiment of the present application can be combined accordingly without conflict.

[0028] The multi-port modular multilevel DC / DC converter with fault isolation function provided by the present application, as shown in Figure 1 contains a power main circuit and a controller for controlling the power main circuit, wherein the controller is used to control the operation state of each bridge arm of the power main circuit, containing a sampling isolation unit, a port DC control unit, a bridge arm AC control unit and a sub-module capacitor voltage control unit. The sampling isolation unit is used to detect the electrical signals of the common high-voltage port of the converter, the electrical signals of different low-voltage ports, the electrical signals of three bridge arms in each power conversion module and the electrical signals of the capacitors of the sub-modules in each bridge arm. The port DC control unit is used to realize the voltage matching and power transmission between the high-voltage port and the low-voltage port. The bridge arm AC control unit is used to realize the energy balance of the high-voltage bridge arm, the low-voltage bridge arm and the multiplex bridge arm in each power conversion module. The sub-module capacitor voltage control unit is used to control the voltage balance of the capacitors of the sub-modules in each bridge arm.

[0029] As shown in Figure 2As shown, the power main circuit comprises one basic power conversion module and n extended power conversion modules, each power conversion module is composed of a high-voltage bridge arm, a multiplex bridge arm, a low-voltage bridge arm and a corresponding bridge arm inductor, the output end of the high-voltage bridge arm is connected with the input end of the multiplex bridge arm and the input end of the low-voltage bridge arm respectively, the input end of the multiplex bridge arm is connected with the input end of the low-voltage bridge arm, and the output end of the multiplex bridge arm is connected with the ground signal; the input ends of the high-voltage bridge arms of different power conversion modules are connected and connected to a high-voltage DC bus, and together with the ground signal, the high-voltage port of the multi-port converter is formed, and the output ends of the low-voltage bridge arms of different power conversion modules are connected to different low-voltage DC buses respectively, and together with the ground signal, a plurality of low-voltage ports of the multi-port converter are formed.

[0030] The input port bridge arm, the multiplex bridge arm and the output port bridge arm are all composed of a plurality of sub-modules in a cascaded manner; in a specific embodiment of the application, the high-voltage bridge arm and the multiplex bridge arm of the basic power conversion module are composed of a plurality of half-bridge sub-modules in cascade, and the low-voltage bridge arm is composed of a plurality of full-bridge sub-modules in cascade. The high-voltage bridge arm of the extended power conversion module is composed of a plurality of half-bridge sub-modules and a plurality of full-bridge sub-modules in cascade, the multiplex bridge arm is composed of a plurality of half-bridge sub-modules in cascade, and the low-voltage bridge arm is composed of a plurality of full-bridge sub-modules in cascade.

[0031] As shown in (a) of FIG. 1, Figure 3 The half-bridge sub-module is composed of two switch tubes in a half-bridge structure, and an external sub-module capacitor is connected; as shown in (b) of FIG. 1, Figure 3 The full-bridge sub-module is composed of four switch tubes in an H-bridge structure, and an external sub-module capacitor is connected.

[0032] Specifically, Figure 3 In (a) of FIG. 2, the two switch tube driving signals of the half-bridge sub-module are complementary, and both the normal mode and the latching mode can output two levels of “0” and “1” to the outside; Figure 3 In (b) of FIG. 2, the switch tube T1 and T2 driving signals of the full-bridge sub-module are complementary, the switch tube T3 and T4 driving signals are complementary, the normal mode can output three levels of “0”, “1” and “-1” to the outside, and the latching mode can output two levels of “1” and “-1” to the outside.

[0033] The embodiment provides an AC / DC decoupling control method using the modular multi-level DC / DC converter described above, as shown in FIG. 3, Figure 5 The control method comprises the following steps:

[0034] S101, AC voltage amplitude reference selection: set the AC voltage amplitude reference of the basic power conversion module as V 0_base , the transmission power is P L_base , and the corresponding low-voltage port voltage is V L_base, the AC voltage amplitude reference of any power conversion module in the n extended power conversion modules can be obtained by the following formula:

[0035]

[0036] wherein V L and P L are the voltage and transmission power of the corresponding low-voltage port of the extended power conversion module, respectively.

[0037] In S102, the voltage V L (or current I L ) of different low-voltage ports is obtained by a sampling isolation unit; and an error signal V L_ref -V L (or I L_ref -I L ) of the electrical quantity of the output port is obtained according to the corresponding reference value V L_ref (or I L_ref ) of the electrical quantity of the output port set by the user; the error signal V L_ref -V L (or I L_ref -I L ) is subjected to PI controller operation in a port DC regulation unit to obtain the transmission power P L of each low-voltage port to the high-voltage port.

[0038] In S103, the transmission power P L of the different low-voltage ports is sent to the bridge arm AC regulation unit of each power conversion module, and the current reference value i armi_ref and voltage reference value v armi_ref of each bridge arm in each power conversion module are obtained in combination with the high-voltage port voltage, the corresponding low-voltage port voltage, the corresponding AC voltage amplitude reference, the corresponding AC frequency and the corresponding phase information. The current reference value i armi_ref is subtracted from the actual measured value i armi of each bridge arm current sent by the sampling isolation unit to obtain the error signal i armi_ref -i armi of the current of each bridge arm in each power conversion module, and the current error signal i armi_ref -i armi is further subjected to PI controller operation in the bridge arm AC regulation unit to obtain the voltage increment reference value Δv armi_ref of each bridge arm; wherein i = 1, 2, 3, respectively corresponding to the low-voltage bridge arm, the multiplexing bridge arm and the high-voltage bridge arm.

[0039] In this embodiment, the current reference value i armi_ref and voltage reference value v armi_ref of each bridge arm in each power conversion module are obtained by the following steps:

[0040] a. For low-voltage bridge arms, the bridge arm current reference value i arm1_ref and the voltage reference value v arm1_ref may be obtained as follows:

[0041]

[0042] where P L , V L , ω, and V0 are the transmission power, low-voltage port voltage, AC frequency, phase information and AC voltage amplitude reference corresponding to each power conversion module, respectively.

[0043] b. For multiplex bridge arms, the bridge arm current reference value i arm2_ref and the voltage reference value v arm3_ref may be obtained as follows:

[0044]

[0045] where P L , V H , V L , ω, and V0 are the transmission power, high-voltage port voltage, low-voltage port voltage, AC frequency, phase information and AC voltage amplitude reference corresponding to each power conversion module, respectively.

[0046] c. For high-voltage bridge arms, the bridge arm current reference value i arm3_ref and the voltage reference value v arm3_ref may be obtained as follows:

[0047]

[0048] where P L , V H , V L , ω, and V0 are the transmission power, high-voltage port voltage, low-voltage port voltage, AC frequency, phase information and AC voltage amplitude reference corresponding to each power conversion module, respectively.

[0049] In the above formulas, for basic power conversion modules, P L , V L and V0 are P L_base , V L_base and V 0_base , respectively, and for extended power conversion modules, P L , V L and V0 are P L ', V L ' and V0', respectively.

[0050] S104, submodule capacitor voltage regulation: adding the voltage theoretical reference value v arm_ref and the voltage increment reference value Δv arm_ref to obtain the voltage actual reference value of each bridge arm in each power conversion module, and the capacitor voltage of each submodule of each bridge arm is sorted from high to low, and further combining the voltage actual reference value of each bridge arm in each power conversion module and the sorting result of the capacitor voltage of each submodule of each bridge arm to switch each submodule of each bridge arm in each power conversion module; when the submodule is put in, the submodule with low capacitor voltage is put in first, and when the submodule is cut off, the submodule with high capacitor voltage is cut off first;

[0051] S105, power module interleaved parallel: by controlling the input and output of each bridge arm submodule in the basic power conversion module and the extended power conversion module, the amplitude and phase of the voltage and current of each bridge arm are controlled, and in a control cycle of the regulation method, the AC voltage components of the bridge arms at the same position in different power conversion modules are 360 / (n+1) degrees apart in phase, and the AC current components are 360 / (n+1) degrees apart in phase; the high-voltage bridge arm current of the basic power conversion module and the extended power conversion module is added to obtain the high-voltage port current of the converter, and the low-voltage bridge arm current of the basic power conversion module and the extended power conversion module corresponds to different low-voltage port currents respectively, so as to realize the voltage matching and power flow regulation between the high-voltage port and the multiple low-voltage ports.

[0052] The simulation verification results provided by the embodiments of the application are introduced below. In one possible embodiment, three voltage transformation units are included, connecting one high-voltage port and three low-voltage ports, as shown in Figure 4 , wherein the basic power conversion module connects the low-voltage port 1, and the extended power conversion module connects the low-voltage ports 2 and 3 respectively. Simulation verification is performed by PLECS, and the effectiveness of the multi-port modular multilevel DC / DC converter with fault isolation function and the regulation method thereof proposed by the application is verified under the operating conditions of high-voltage port voltage 320kV, low-voltage port 1 voltage 100kV, low-voltage port 2 voltage 150kV, low-voltage port 3 voltage 120kV, total transmission power 1GW, and AC frequency 200Hz.

[0053] Specifically, as Figure 6As shown, the high and low voltage port voltage and current waveforms, low voltage bridge arm voltage and current waveforms, multiplex bridge arm voltage and current waveforms, high voltage bridge arm voltage and current waveforms, and each bridge arm submodule capacitor voltage waveform are given, wherein the high voltage port is short-circuited at 25 ms. As can be seen from the figure, before the fault occurs, the converter can stably operate, and there is no obvious ripple in any port voltage and current waveform, and the waveform quality is good. After the high voltage port short-circuit fault occurs, the half-bridge submodule of each bridge arm in each power conversion module is quickly cut off, the full-bridge submodule is negatively put into operation, the fault current is quickly blocked, the low voltage port voltage is supported, and there is no obvious voltage and current overshoot in the converter, and there is no risk of equipment damage.

[0054] As shown, the high and low voltage port voltage and current waveforms, low voltage bridge arm voltage and current waveforms, multiplex bridge arm voltage and current waveforms, high voltage bridge arm voltage and current waveforms, and each bridge arm submodule capacitor voltage waveform are given, wherein the high voltage port is short-circuited at 25 ms. As can be seen from the figure, before the fault occurs, the converter can stably operate, and there is no obvious ripple in any port voltage and current waveform, and the waveform quality is good. After the high voltage port short-circuit fault occurs, the half-bridge submodule of each bridge arm in each power conversion module is quickly cut off, the full-bridge submodule is negatively put into operation, the fault current is quickly blocked, the low voltage port voltage is supported, and there is no obvious voltage and current overshoot in the converter, and there is no risk of equipment damage. Figure 7 As can be seen from the above embodiments, the proposed modular multilevel DC / DC converter and its control method can effectively realize voltage matching, power flow regulation, fault blocking, and open-phase operation of a multi-terminal DC interconnection system without an AC isolation transformer, and has important application value in the field of high-voltage DC power grids.

[0055] The above-described embodiments are merely preferred embodiments of the present application, and do not limit the scope of the present application. Various modifications and improvements made by those skilled in the art to the technical solutions of the present application without departing from the design spirit of the present application shall fall within the protection scope of the claims of the present application.

[0056] The units described above as separate components can or can not be physically separate, and the components shown as units can or can not be physical units, i.e., can be located in one place or distributed on multiple network units. Part or all of the units can be selected to achieve the purpose of the embodiments of the present application according to actual needs.

[0057]

[0058] ​In addition, each function unit in each embodiment of the present application can be integrated in one processing unit, or each unit can exist physically separately, or two or more units can be integrated in one unit. The integrated unit can be realized in the form of hardware or in the form of a software function unit.

[0059] When the integrated unit is realized in the form of a software function unit and sold or used as an independent product, it can be stored in a computer readable storage medium. Based on such understanding, the technical solutions of the present application essentially or the part that contributes to the prior art, or the whole or part of the technical solutions can be embodied in the form of a software product. The computer software product is stored in a storage medium, and includes a number of instructions for causing a computer device (which can be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the above-mentioned methods of the embodiments of the present application. The foregoing storage medium includes: a U disk, a mobile hard disk, a read-only memory (ROM, Read-Only Memory), a random access memory (RAM, Random Access Memory), a magnetic disk or an optical disk, and various program code storage media.

[0060] The above-described embodiments only express several implementation manners of the present application, and the description is relatively specific and detailed, but it should not be understood as a limitation on the patent scope of the present application. For those skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are all within the protection scope of the present application.

Claims

1. A method for controlling a multi-port modular multilevel DC-DC converter with fault isolation function, characterized in that, The converter includes a main power circuit and a controller for regulating the main power circuit. The main power circuit includes one basic power conversion module and n extended power conversion modules. Each power conversion module consists of a high-voltage bridge arm, a multiplexed bridge arm, a low-voltage bridge arm, and corresponding bridge arm inductors. The output terminals of the high-voltage bridge arm, the input terminals of the multiplexed bridge arm, and the input terminals of the low-voltage bridge arm are connected together. The output terminal of the multiplexed bridge arm is connected to the ground signal. The input terminals of the high-voltage bridge arms of different power conversion modules are connected to the high-voltage DC bus, and together with the ground signal, they constitute the high-voltage port of the multi-port converter. The output terminals of the low-voltage bridge arms of different power conversion modules are respectively connected to different low-voltage DC buses, and together with the ground signal, they constitute multiple low-voltage ports of the multi-port converter. The high-voltage bridge arm, the multiplexed bridge arm, and the low-voltage bridge arm are all composed of several sub-modules cascaded together. Wherein, n≥1. The controller includes a sampling isolation unit, a port DC control unit, a bridge arm AC control unit, and a submodule capacitor voltage control unit. The sampling isolation unit is used to detect the electrical signal of the common high-voltage port of the converter, the electrical signals of each low-voltage port, the electrical signals of the three bridge arms in each power conversion module, and the electrical signals of the capacitors of the submodules in each bridge arm. The port DC control unit is used to achieve voltage matching and power transmission between the high-voltage and low-voltage ports. The bridge arm AC control unit is used to achieve energy balance of the high-voltage bridge arm, low-voltage bridge arm, and multiplexed bridge arm in each power conversion module. The submodule capacitor voltage control unit is used to control the voltage balance of the capacitors of the submodules in each bridge arm. The method includes the following steps: S1. Let the AC voltage amplitude reference of the basic power conversion module be V. 0_base The transmission power is P L_base The corresponding low-voltage port voltage is V. L_base The AC voltage amplitude reference of any power conversion module in the extended power conversion module is obtained. ; S2, The sampling isolation unit inputs electrical signals X from different low-voltage ports to the port DC control unit. L The electrical signals X of the different low-voltage ports L The voltage V at the low-voltage port L Or the current I at the low-voltage port L The DC control unit at the port operates based on the electrical signal X at the low-voltage port. L The corresponding reference value X of the electrical signal at the set output port ref The error signal of the electrical signal at the output port is obtained. The error signal The power P transmitted from each low-voltage port to the high-voltage port is obtained through calculation by the PI controller in the DC control unit. L ; S3, the transmission power P of the different low-voltage ports L The AC control unit of each bridge arm in the power conversion module is fed into the AC control unit. By combining the high-voltage port voltage, the corresponding low-voltage port voltage, the corresponding AC voltage amplitude reference, the corresponding AC frequency, and the corresponding phase information, the current reference value of each bridge arm in each power conversion module is obtained. and the theoretical reference value of voltage v arm_ref The current reference value The measured values ​​of the current in each bridge arm fed into the sampling isolation unit i arm The error signal of the current of each bridge arm in each power conversion module is obtained by subtraction. The current error signal The reference value Δv of the voltage increment of each bridge arm is obtained by the PI controller in the bridge arm AC control unit. arm_ref ; S4. Convert the theoretical reference voltage v of each bridge arm in each power conversion module. arm_ref and voltage increment reference value Δv arm_ref The actual reference values ​​of the voltage of each bridge arm in each power conversion module are obtained by summing them, and the voltage of the capacitors of the sub-modules of each bridge arm is sorted from high to low. Then, the sub-modules of each bridge arm in each power conversion module are switched by combining the actual reference values ​​of the voltage of each bridge arm in each power conversion module and the sorting results of the capacitor voltage of the sub-modules of each bridge arm. S5. By controlling the input and output of sub-modules of each bridge arm in the basic power conversion module and the extended power conversion module, the amplitude and phase of the voltage and current of each bridge arm are controlled. The high-voltage bridge arm currents of the basic power conversion module and the extended power conversion module are added together to obtain the high-voltage port current of the converter. The low-voltage bridge arm currents of the basic power conversion module and the extended power conversion module correspond to different low-voltage port currents, thereby realizing voltage matching and power flow regulation between the high-voltage port and multiple low-voltage ports.

2. The method for controlling a multi-port modular multilevel DC-DC converter with fault isolation function according to claim 1, characterized in that, The high-voltage bridge arm and multiplexed bridge arm of the basic power conversion module are composed of multiple cascaded half-bridge sub-modules, and the low-voltage bridge arm is composed of multiple cascaded full-bridge sub-modules. The high-voltage bridge arm of the n extended power conversion modules is composed of multiple cascaded half-bridge sub-modules and multiple full-bridge sub-modules, the multiplexed bridge arm is composed of multiple cascaded half-bridge sub-modules, and the low-voltage bridge arm is composed of multiple cascaded full-bridge sub-modules; where n≥1.

3. The method for controlling a multi-port modular multilevel DC-DC converter with fault isolation function according to claim 1, characterized in that, The high-voltage bridge arm, multiplex bridge arm, and low-voltage bridge arm are also configured with bridge arm inductors according to their power capacity. The bridge arm inductors are connected in series in the circuit of each bridge arm and are used to assist in commutation and energy transfer between different bridge arms.

4. The method for controlling a multi-port modular multilevel DC-DC converter with fault isolation function according to claim 2, characterized in that, The full-bridge submodule includes four power devices and one energy storage capacitor, and the half-bridge submodule consists of two power devices and one energy storage capacitor. All power devices are fully controllable devices, namely IGBTs, MOSFETs, or IGCTs.

5. The method for controlling a multi-port modular multilevel DC-DC converter with fault isolation function according to claim 1, characterized in that, In S1, the AC voltage amplitude reference of any power conversion module in the extended power conversion module is... Obtain by the following formula: ； In the formula V L 'and P L These represent the voltage and transmission power of the low-voltage port corresponding to the extended power conversion module. This is the high-voltage port voltage.

6. The method for controlling a multi-port modular multilevel DC-DC converter with fault isolation function according to claim 1, characterized in that, In S4, when adding a submodule, the submodule with the lower capacitor voltage is added first; when removing a submodule, the submodule with the higher capacitor voltage is removed first.

7. The method for controlling a multi-port modular multilevel DC-DC converter with fault isolation function according to claim 1, characterized in that, Within one control cycle of the aforementioned control method, the AC voltage components and AC current components of the bridge arms at the same location in different power conversion modules are phase-differentiated by 360 / (n+1) degrees.

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