Coordination control method and system for modular multi-level direct-current transformer

Abstract

The invention relates to the technical field of transformers, and discloses a coordinated control method and system for a modular multi-level direct-current transformer, and the method comprises the steps: carrying out the load voltage control of the low-voltage side load voltage of the modular multi-level direct-current transformer through a reference value of the low-voltage side load voltage; zero static error tracking is carried out on the voltage reference value by the low-voltage side load voltage, and bus capacitor voltage control is carried out on the direct-current power flow controller by using the reference value of the bus capacitor voltage of the direct-current power flow controller, so that the bus capacitor voltage of the direct-current power flow controller tracks the reference value of the bus capacitor voltage; and performing power flow control on the direct-current power flow controller by using the reference value of the direct-current port current of the direct-current power flow controller, so that the direct-current port current of the direct-current power flow controller tracks the reference value of the direct-current port current, thereby performing coordinated control on the modular multi-level direct-current transformer and the direct-current power flow controller.

Description

Technical Field

[0001] The present invention relates to the technical field of transformers, and in particular to a coordinated control method and system for a modular multi-level direct current transformer. Background Art

[0002] In a multi-voltage DC grid, the conversion of DC voltage must be based on power electronics technology and pulse modulation technology, and the voltage change and energy transmission are achieved through power converters. Therefore, the conversion equipment of the multi-voltage DC grid is a DC transformer. With the gradual increase of DC voltage levels, the modular multilevel DC transformer MMDCT (Modular Multilevel DC-DC Transformer) can meet the needs of different voltage levels due to its modularity and scalability. It can be used to connect DC lines of different voltage levels in high-voltage large power grids and is becoming more and more widely used.

[0003] At present, the modulation control strategy of modular multi-level DC transformers focuses on forming different types of modulation waves by controlling the drive signals of sub-modules. For example, the control system performs sampling and control only once in a medium frequency or high frequency cycle. This modulation control method allows the generation of asymmetric step-shaped waves with two rising slopes and falling slopes by controlling the phase shift angle between the drive signals of different half-bridge modules of the half-bridge module valve group, and changes the slope and duty cycle of the modulation wave by detecting the output voltage, thereby adjusting the output voltage of the modular multi-level DC transformer. This method realizes the fixed frequency operation of the resonant circuit, reduces the design difficulty of the magnetic components, and realizes the zero current shutdown of the low-voltage side full-bridge module switch tube, reducing the current stress.

[0004] Modular multilevel DC transformers provide important technical support for the interconnection of future high-voltage DC grids and the consumption of large-scale new energy. However, their existing modulation control strategies mainly follow a single-loop approach, that is, they only consider adjusting and improving the waveform and duty cycle of the modulation wave, thereby changing the transformer output voltage. This makes it difficult to comprehensively coordinate and control the actual operation of modular multilevel DC transformers. Summary of the invention

[0005] In view of this, the present invention provides a coordinated control method and system for a modular multi-level DC transformer, which solves the technical problem that it is difficult to comprehensively coordinate and control the actual operation of the modular multi-level DC transformer.

[0006] A first aspect of the present invention provides a coordinated control method of a modular multilevel DC transformer, which is applied to a modular multilevel DC transformer, wherein the modular multilevel DC transformer has a built-in DC power flow controller; the method comprises:

[0007] Using the reference value of the low-voltage side load voltage to perform load voltage control on the low-voltage side load voltage of the modular multi-level DC transformer, the load voltage control is used to make the low-voltage side load voltage track the voltage reference value with zero static error;

[0008] Using the reference value of the bus capacitor voltage of the DC power flow controller to control the bus capacitor voltage of the DC power flow controller, the bus capacitor voltage control is used to make the bus capacitor voltage of the DC power flow controller track the reference value of the bus capacitor voltage;

[0009] The DC power flow controller is subjected to power flow control using a reference value of the DC port current of the DC power flow controller, wherein the power flow control is used to make the DC port current of the DC power flow controller track the reference value of the DC port current.

[0010] Preferably, the method of using the reference value of the low-voltage side load voltage to perform load voltage control on the low-voltage side load voltage of the modular multi-level DC transformer, wherein the load voltage control is used to make the low-voltage side load voltage track the voltage reference value with zero static error, comprises:

[0011] Performing difference processing on the low-voltage side load voltage of the modular multi-level DC transformer and the reference value of the low-voltage side load voltage to obtain a load voltage difference;

[0012] normalizing the load voltage difference;

[0013] The amplitude of the AC voltage is generated by multiplying the pre-acquired MMDC phase shift duty cycle with the normalized load voltage difference;

[0014] Inputting the amplitude of the AC voltage into a first PI controller to generate an MMDC phase-shift duty cycle, wherein the pre-acquired MMDC phase-shift duty cycle is the MMDC phase-shift duty cycle obtained after power flow adjustment;

[0015] The MMDC phase-shift duty cycle is used to perform phase-shift modulation on the low-voltage side load voltage of the modular multi-level DC transformer.

[0016] Preferably, the transfer function of the first PI controller is:

[0017]

[0018] In the formula, is the transfer function, is the delay time, is the PI controller index, is the amplitude of the AC voltage on the secondary side of the transformer, s is the Laplace operator, is the transformer ratio, is the switching frequency, is the bridge arm capacitance, is the load impedance, , are the control parameters of the first PI controller.

[0019] Preferably, the bus capacitor voltage of the DC power flow controller is controlled by using a reference value of the bus capacitor voltage of the DC power flow controller, and the bus capacitor voltage control is used to make the bus capacitor voltage of the DC power flow controller track the reference value of the bus capacitor voltage, including:

[0020] Performing a difference process on a reference value of the bus capacitor voltage of the DC power flow controller and the bus capacitor voltage to obtain a bus capacitor voltage difference;

[0021] Normalizing the bus capacitor voltage difference;

[0022] Inputting the bus capacitor voltage difference into a second PI controller, and outputting the input-end phase shift duty ratio of the DC power flow controller;

[0023] The bus capacitor voltage of the DC power flow controller is modulated using the input-end phase-shift duty cycle.

[0024] Preferably, the transfer function of the second PI controller is:

[0025]

[0026] In the formula, is the transfer function between the bus voltage and the phase shift duty cycle at the input of the DC power flow controller, is the amplitude of the transformer primary AC voltage, is the bus capacitance of the DC power flow controller, is the equivalent total inductance on the low voltage side of the AC circuit.

[0027] Preferably, the utilizing the reference value of the DC port current of the DC power flow controller to perform power flow control on the DC power flow controller, wherein the power flow control is used to make the DC port current of the DC power flow controller track the reference value of the DC port current, comprises:

[0028] Performing a difference process on a reference value of a DC port current of the DC power flow controller and the DC port current to obtain a DC port current difference;

[0029] Normalizing the DC port current difference;

[0030] Inputting the DC port current difference into a third PI controller, and outputting the output end phase shift duty ratio of the DC power flow controller;

[0031] The DC port current of the DC power flow controller is modulated using the output-end phase-shift duty cycle.

[0032] Preferably, the method further comprises: performing energy balance control on each submodule of the modular multi-level DC transformer;

[0033] The energy balance control of each submodule of the modular multi-level DC transformer includes:

[0034] By compensating the phase shift angle of the voltage and current of each submodule of the modular multi-level DC transformer, the energy between the submodules is balanced.

[0035] In a second aspect, the present invention further provides a coordinated control system of a modular multilevel DC transformer, which is applied to a modular multilevel DC transformer, wherein the modular multilevel DC transformer is embedded with a DC power flow controller; the system comprises:

[0036] A load voltage control module, used for performing load voltage control on the low-voltage side load voltage of the modular multi-level DC transformer using a reference value of the low-voltage side load voltage, wherein the load voltage control is used for making the low-voltage side load voltage perform zero static error tracking on the voltage reference value;

[0037] A bus capacitor voltage control module, used to perform bus capacitor voltage control on the DC power flow controller using a reference value of the bus capacitor voltage of the DC power flow controller, wherein the bus capacitor voltage control is used to make the bus capacitor voltage of the DC power flow controller track the reference value of the bus capacitor voltage;

[0038] The power flow control module is used to perform power flow control on the DC power flow controller using the reference value of the DC port current of the DC power flow controller, wherein the power flow control is used to make the DC port current of the DC power flow controller track the reference value of the DC port current.

[0039] In a third aspect, the present invention further provides an electronic device, wherein the electronic device 10 comprises a memory 20 and a processor 30, wherein a computer program is stored in the memory 20, and when the computer program is executed by the processor 30, the processor 30 executes the steps of the coordinated control method of the modular multi-level DC transformer as described in the first aspect.

[0040] In a fourth aspect, the present invention further provides a computer-readable storage medium having a computer program stored thereon, wherein the computer program, when executed, implements the steps of the coordinated control method of the modular multi-level DC transformer as described in the first aspect.

[0041] It can be seen from the above technical solutions that the present invention uses the reference value of the low-voltage side load voltage to control the load voltage of the low-voltage side of the modular multi-level DC transformer, so that the low-voltage side load voltage tracks the voltage reference value with zero static error, and also uses the reference value of the bus capacitor voltage of the DC power flow controller to control the bus capacitor voltage of the DC power flow controller, so that the bus capacitor voltage of the DC power flow controller tracks the reference value of the bus capacitor voltage, and also uses the reference value of the DC port current of the DC power flow controller to control the DC power flow controller, so that the DC port current of the DC power flow controller tracks the reference value of the DC port current, thereby coordinating the control of the modular multi-level DC transformer and the DC power flow controller to provide comprehensive stability support for the modular multi-level DC transformer and optimize the system stability of the modular multi-level DC transformer. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 An application environment of a coordinated control method for a modular multi-level DC transformer provided in an embodiment of the present invention;

[0043] Figure 2 A flowchart of a coordinated control method of a modular multi-level DC transformer provided by an embodiment of the present invention;

[0044] Figure 3 A schematic diagram of coordinated control logic of a modular multi-level DC transformer provided in an embodiment of the present invention;

[0045] Figure 4 A load voltage control logic diagram provided by an embodiment of the present invention;

[0046] Figure 5 A schematic diagram of bus capacitor voltage control logic provided by an embodiment of the present invention;

[0047] Figure 6 A schematic diagram of power flow control logic provided by an embodiment of the present invention;

[0048] Figure 7 A schematic diagram of the principle of a phase shift angle less than zero in energy balance control provided by an embodiment of the present invention;

[0049] Figure 8 A schematic diagram of the principle of a phase shift angle greater than zero in energy balance control provided by an embodiment of the present invention;

[0050] Fig. 9A schematic diagram of the structure of a coordinated control system of a modular multi-level DC transformer provided by an embodiment of the present invention;

[0051] Fig.10 A schematic diagram of the structure of an electronic device provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0052] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0053] The coordinated control method of the modular multi-level DC transformer provided in the embodiment of the present application can be applied to Figure 1 In the application environment shown. The modular multilevel DC transformer communicates with the server 102 via a network. The data storage system can store data that the server 102 needs to process. The data storage system can be integrated on the server 102, or placed on a cloud or other network server. The server 102 can be an independent physical server, or a server cluster or distributed system composed of multiple physical servers, or a cloud server that provides cloud computing services.

[0054] like Figure 2~3 As shown, the embodiment of the present application provides a coordinated control method for a modular multi-level DC transformer, which is applied to a modular multi-level DC transformer. The modular multi-level DC transformer has a built-in DC power flow controller. The method is applied to Figure 1 The server 102 in the example is used as an example to illustrate, including the following steps S1 to step 3. Among them:

[0055] Step S1, using a reference value of the low-voltage side load voltage to perform load voltage control on the low-voltage side load voltage of the modular multi-level DC transformer, wherein the load voltage control is used to enable the low-voltage side load voltage to track the voltage reference value with zero static error.

[0056] It should be noted that if the operation of the modular multilevel DC transformer is to be kept stable, the actual value of the load voltage on the low voltage side of the modular multilevel DC transformer needs to be kept stable.

[0057] To this end, the embodiment of the present application uses the reference value of the low-voltage side load voltage to perform load voltage control on the low-voltage side load voltage of the modular multi-level DC transformer, so that the low-voltage side load voltage tracks the voltage reference value with zero static error.

[0058] Specifically, if Figure 4 As shown, step S1 includes:

[0059] Step S101: The low-voltage side load voltage V of the modular multi-level DC transformer is dc1 and the reference value of the low voltage side load voltage V dc1-ref Perform difference processing to obtain the load voltage difference;

[0060] Step S102: normalize the load voltage difference.

[0061] in, Figure 4 The K in represents the normalization operation.

[0062] Step S103, performing a product operation using the pre-acquired MMDC phase shift duty cycle and the normalized load voltage difference to generate an AC voltage amplitude;

[0063] Step S104: Input the amplitude of the AC voltage to the first PI controller to generate the MMDC phase shift duty cycle d DAB , wherein the pre-acquired MMDC phase-shift duty cycle is the MMDC phase-shift duty cycle obtained after power flow adjustment.

[0064] Among them, the transfer function of the first PI controller is:

[0065]

[0066] In the formula, is the transfer function, is the delay time, is the PI controller index, is the amplitude of the AC voltage on the secondary side of the transformer, s is the Laplace operator, is the transformer ratio, is the switching frequency, is the bridge arm capacitance, is the load impedance, , are the control parameters of the first PI controller.

[0067] Among them, the PID Tuner design tool in MATLAB can be used to calculate the control parameters of the PI controller.

[0068] like Figure 4 As shown, the MMDC phase shift duty cycle d DAB Flow regulation is performed to obtain 1 / (1±d DAB ), then 1 / (1±d DAB ) is input to the zero-order holder ZOH for adjustment to obtain the pre-acquired MMDC phase-shift duty cycle.

[0069] Step S105: performing phase shift modulation on the low-voltage side load voltage of the modular multi-level DC transformer by using the MMDC phase shift duty cycle.

[0070] It can be understood that in the embodiment of the present application, in the process of modulating the load voltage on the low voltage side of the block multi-level DC transformer, the transfer function of the system is determined according to the small signal model of the system, and the gain of the transfer function is related to the phase shift duty cycle. The load voltage (transmission power) control loop is implemented using a classic PI controller. In order to allow the controller to have good control performance under different working conditions, the signal is processed in the controller to remove the items related to the phase shift duty cycle. By normalizing the error between the given reference value and the actual value, the processed signal is sent to the PI controller to achieve zero static error tracking of the reference value.

[0071] Step S2: Using the reference value of the bus capacitor voltage of the DC power flow controller to control the bus capacitor voltage of the DC power flow controller, the bus capacitor voltage control is used to make the bus capacitor voltage of the DC power flow controller track the reference value of the bus capacitor voltage.

[0072] Among them, Figure 5 As shown, step S2 specifically includes:

[0073] Step S201: a reference value u of the bus capacitor voltage of the DC power flow controller c * and bus capacitor voltage u c Perform difference processing to obtain the bus capacitor voltage difference;

[0074] Step S202, normalizing the bus capacitor voltage difference;

[0075] Step S203, inputting the bus capacitor voltage difference into the second PI controller, and outputting the input-end phase shift duty ratio d-PFC-in of the DC power flow controller;

[0076] Among them, the transfer function of the second PI controller is:

[0077]

[0078] In the formula, is the transfer function between the bus voltage and the phase shift duty cycle at the input of the DC power flow controller, is the amplitude of the transformer primary AC voltage, is the bus capacitance of the DC power flow controller, is the equivalent total inductance on the low voltage side of the AC circuit.

[0079] Step S204: modulate the bus capacitor voltage of the DC power flow controller using the input-end phase shift duty cycle d-PFC-in.

[0080] like Figure 5 As shown in the figure, according to the system transfer function, the bus capacitor voltage balance control loop is designed using a PI controller. The input signal of the regulator is the difference between a given capacitor voltage reference value and an actual capacitor voltage value. The difference between the actual bus capacitor voltage value and the given value is normalized and then the phase shift duty cycle of the PFC input end is obtained through a PI controller. Static error-free tracking is achieved through closed-loop control.

[0081] Step S3: performing power flow control on the DC power flow controller using the reference value of the DC port current of the DC power flow controller, wherein the power flow control is used to make the DC port current of the DC power flow controller track the reference value of the DC port current.

[0082] In some embodiments, Figure 6 As shown in the figure, the two switches and one inductor at the output end of the DC power flow controller can be regarded as a buck converter. By adjusting the duty cycle of the switch at the output end of the DC power flow controller, the output voltage of the buck converter can be adjusted, thereby changing the output current. When the transmission power of the DC transformer remains unchanged, the sum of the currents of each branch should remain unchanged. Therefore, when reducing the current of one line, the current of other lines needs to be increased. Consider the case where there are two output lines, and assume that their output duty cycles are respectively and ,So According to the transfer function expression of the system, it can be found that the gain of the transfer function is proportional to the bus capacitor voltage. In order to make the controller more universal, the transfer function is normalized, that is, the output signal of the PI controller is divided by the last sampled PFC bus capacitor voltage.

[0083] Specifically, step S3 includes:

[0084] Step S301: a reference value I of the DC port current of the DC power flow controller out-ref and DC port current I out Perform difference processing to obtain the DC port current difference;

[0085] Step S302, normalizing the DC port current difference;

[0086] Step S303, inputting the DC port current difference into the third PI controller, and outputting the output-end phase shift duty ratio d-PFC-out of the DC power flow controller;

[0087] Among them, the transfer function of the third PI controller is:

[0088]

[0089] In the formula, is the transfer function of the DC port current and the corresponding half-bridge module duty cycle, is the capacitor voltage, , are the inductance and resistance at the output end of the power flow controller respectively. The PID Tuner design tool in MATLAB can also be used to calculate the control parameters of the PI controller and complete the design of the control loop.

[0090] Step S304: modulate the DC port current of the DC power flow controller using the output-end phase-shift duty cycle d-PFC-out.

[0091] Since the actual size of the capacitor cannot be guaranteed to be exactly the same, this will cause different voltage changes in the capacitors of each sub-module when absorbing or releasing the same energy. For the problem of unbalanced sub-modules, the unbalanced voltages of different sub-modules will further increase the difference in energy absorption or release of the capacitors, causing the sub-module voltages to continue to increase or decrease, which is not conducive to the normal operation of the system.

[0092] The traditional MMC converter submodule energy balance control method is to directly detect the direction of the bridge arm current and determine the submodule switching order based on the current direction to maintain voltage stability. Since MMDC directly performs DC-DC conversion, the switching frequency is high and the working state is quite different from that of traditional MMC, the submodule balance control method is also different.

[0093] To this end, the embodiment of the present application also performs energy balance control on each submodule of the modular multi-level DC transformer, and controls the submodule voltages by introducing a submodule balance control link to maintain the same voltage for each submodule.

[0094] Specifically, if Figure 7-8 As shown, the process of performing energy balance control on each submodule of the modular multilevel DC transformer includes:

[0095] By compensating the phase shift angle of the voltage and current of each submodule of the modular multi-level DC transformer, the energy between the submodules is balanced.

[0096] It can be understood that by adding an additional phase shift angle between submodules, the submodule put into operation later absorbs less energy, releases more energy, and reduces the voltage. Therefore, the control strategy only needs to sample and sort the submodule voltages in each cycle, put the submodule with low voltage into operation first, and the submodule with high voltage into operation later, so as to maintain the energy balance of each submodule.

[0097] For example, assuming that Pp P is the energy of the submodule at the same time when the current and voltage directions are the same; n It is the energy of the submodule at the moment when the current and voltage directions are opposite.

[0098] The total energy of the submodule is P=P p +P n ,like Figure 7 As shown, additional phase shifting by submodules can reduce P p , increase P n , the overall energy control of the sub-module can be achieved.

[0099] It should be noted that the embodiment of the present application uses the reference value of the low-voltage side load voltage to control the load voltage of the low-voltage side of the modular multi-level DC transformer, so that the low-voltage side load voltage tracks the voltage reference value with zero static error, and also uses the reference value of the bus capacitor voltage of the DC power flow controller to control the bus capacitor voltage of the DC power flow controller, so that the bus capacitor voltage of the DC power flow controller tracks the reference value of the bus capacitor voltage, and also uses the reference value of the DC port current of the DC power flow controller to control the DC power flow controller, so that the DC port current of the DC power flow controller tracks the reference value of the DC port current, thereby coordinating the control of the modular multi-level DC transformer and the DC power flow controller to provide comprehensive stability support for the modular multi-level DC transformer and optimize the system stability of the modular multi-level DC transformer.

[0100] Based on the same inventive concept, an embodiment of the present application further provides a coordinated control system of a modular multi-level DC transformer for implementing the coordinated control method of the modular multi-level DC transformer involved above.

[0101] The implementation solution to the problem provided by the system is similar to the implementation solution recorded in the above method. Therefore, the specific limitations in the coordinated control system embodiment of one or more modular multi-level DC transformers provided below can be referred to the limitations on the coordinated control method of modular multi-level DC transformers above, and will not be repeated here.

[0102] like Fig. 9 As shown, the embodiment of the present application also provides a coordinated control system of a modular multi-level DC transformer, which is applied to a modular multi-level DC transformer, and the modular multi-level DC transformer is embedded with a DC power flow controller; the system includes:

[0103] A load voltage control module 100 is used to perform load voltage control on the low-voltage side load voltage of the modular multi-level DC transformer using a reference value of the low-voltage side load voltage, wherein the load voltage control is used to make the low-voltage side load voltage track the voltage reference value with zero static error;

[0104] The bus capacitor voltage control module 200 is used to control the bus capacitor voltage of the DC power flow controller using the reference value of the bus capacitor voltage of the DC power flow controller, and the bus capacitor voltage control is used to make the bus capacitor voltage of the DC power flow controller track the reference value of the bus capacitor voltage;

[0105] The power flow control module 300 is used to perform power flow control on the DC power flow controller using the reference value of the DC port current of the DC power flow controller. The power flow control is used to make the DC port current of the DC power flow controller track the reference value of the DC port current.

[0106] In some embodiments, the load voltage control module 100 is specifically used to perform difference processing on the low-voltage side load voltage of the modular multi-level DC transformer and the reference value of the low-voltage side load voltage to obtain the load voltage difference; normalize the load voltage difference; multiply the normalized load voltage difference by the pre-acquired MMDC phase-shift duty cycle to generate the amplitude of the AC voltage; input the amplitude of the AC voltage to the first PI controller to generate the MMDC phase-shift duty cycle, wherein the pre-acquired MMDC phase-shift duty cycle is the MMDC phase-shift duty cycle obtained after power flow regulation; and use the MMDC phase-shift duty cycle to perform phase-shift modulation on the low-voltage side load voltage of the modular multi-level DC transformer.

[0107] In some embodiments, the transfer function of the first PI controller is:

[0108]

[0109] In the formula, is the transfer function, is the delay time, is the PI controller index, is the amplitude of the AC voltage on the secondary side of the transformer, s is the Laplace operator, is the transformer ratio, is the switching frequency, is the bridge arm capacitance, is the load impedance, , are the control parameters of the first PI controller.

[0110] In some embodiments, the bus capacitor voltage control module 200 is specifically used to perform difference processing on the reference value of the bus capacitor voltage of the DC power flow controller and the bus capacitor voltage to obtain the bus capacitor voltage difference; normalize the bus capacitor voltage difference; input the bus capacitor voltage difference to the second PI controller, and output the input phase shift duty cycle of the DC power flow controller; and modulate the bus capacitor voltage of the DC power flow controller using the input phase shift duty cycle.

[0111] In some embodiments, the transfer function of the second PI controller is:

[0112]

[0113] In the formula, is the transfer function between the bus voltage and the phase shift duty cycle at the input of the DC power flow controller, is the amplitude of the transformer primary AC voltage, is the bus capacitance of the DC power flow controller, is the equivalent total inductance on the low voltage side of the AC circuit.

[0114] In some embodiments, the power flow control module 300 is specifically used to perform difference processing on the reference value of the DC port current of the DC power flow controller and the DC port current to obtain the DC port current difference; normalize the DC port current difference; input the DC port current difference to the third PI controller, and output the output end phase shift duty cycle of the DC power flow controller; and modulate the DC port current of the DC power flow controller using the output end phase shift duty cycle.

[0115] In some embodiments, the system further includes: an energy balancing module, which is used to perform energy balance control on each sub-module of the modular multi-level DC transformer; specifically including: compensating the phase shift angle of the voltage and current of each sub-module of the modular multi-level DC transformer to achieve energy balance between the sub-modules.

[0116] like Fig.10 As shown, an embodiment of the present application also provides an electronic device, the electronic device 10 includes a memory 20 and a processor 30, the memory 20 stores a computer program, and when the computer program is executed by the processor 30, the processor 30 executes the steps of the coordinated control method of the modular multi-level DC transformer in any of the above embodiments.

[0117] An embodiment of the present application further provides a computer-readable storage medium having a computer program stored thereon, and when the computer program is executed, the steps of the coordinated control method of the modular multi-level DC transformer in any of the above embodiments are implemented.

[0118] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working processes of the above-described system, electronic device and computer storage medium can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0119] It should be noted that the terms "including" and "having" and any variations thereof in the specification and claims of the present invention and the above-mentioned drawings are intended to cover non-exclusive inclusions. For example, a process, method, system, product or apparatus comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or apparatus.

[0120] In several embodiments provided by the present invention, it is understood that each box in the flow chart or block diagram can represent a module, a program segment or a part of a code, and a part of a module, a program segment or a code includes one or more executable instructions for realizing the specified logical function. It should also be noted that in some alternative implementations, the functions marked in the box can also occur in a different order from that marked in the accompanying drawings. For example, two consecutive boxes can actually be executed substantially in parallel, and they can sometimes be executed in the opposite order, depending on the functions involved.

[0121] In the several embodiments provided by the present invention, it should be understood that the disclosed systems, electronic devices, computer storage media and methods can be implemented in other ways. For example, the device embodiments described above are only schematic. For example, the division of units is only a logical function division. There may be other division methods in actual implementation. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be an indirect coupling or communication connection through some interfaces, devices or units, which can be electrical, mechanical or other forms.

[0122] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0123] In addition, each functional unit in each embodiment of the present invention may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of software functional units.

[0124] If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention is essentially or the part that contributes to the prior art or all or part of the technical solution can be embodied in the form of a software product. The computer software product is stored in a storage medium, including several instructions for executing all or part of the steps of the method described in each embodiment of the present invention through a computer device (which can be a personal computer, server, or network device, etc.). The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (full name in English: Read-Only Memory, English abbreviation: ROM), random access memory (full name in English: Random Access Memory, English abbreviation: RAM), disk or optical disk and other media that can store program codes.

[0125] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A coordinated control method for a modular multi-level DC transformer, applied to a modular multi-level DC transformer, wherein the modular multi-level DC transformer is embedded with a DC power flow controller; characterized in that: The method comprises: Using the reference value of the low-voltage side load voltage to perform load voltage control on the low-voltage side load voltage of the modular multi-level DC transformer, the load voltage control is used to make the low-voltage side load voltage track the voltage reference value with zero static error; Using the reference value of the bus capacitor voltage of the DC power flow controller to control the bus capacitor voltage of the DC power flow controller, the bus capacitor voltage control is used to make the bus capacitor voltage of the DC power flow controller track the reference value of the bus capacitor voltage; The DC power flow controller is subjected to power flow control using a reference value of the DC port current of the DC power flow controller, wherein the power flow control is used to make the DC port current of the DC power flow controller track the reference value of the DC port current.

2. The coordinated control method of modular multi-level DC transformer according to claim 1, characterized in that: The method of using the reference value of the low-voltage side load voltage to perform load voltage control on the low-voltage side load voltage of the modular multi-level DC transformer, wherein the load voltage control is used to make the low-voltage side load voltage track the voltage reference value with zero static error, comprises: Performing a difference process on the low-voltage side load voltage of the modular multi-level DC transformer and a reference value of the low-voltage side load voltage to obtain a load voltage difference; normalizing the load voltage difference; The amplitude of the AC voltage is generated by multiplying the pre-acquired MMDC phase shift duty cycle with the normalized load voltage difference; Inputting the amplitude of the AC voltage into a first PI controller to generate an MMDC phase-shift duty cycle, wherein the pre-acquired MMDC phase-shift duty cycle is the MMDC phase-shift duty cycle obtained after power flow adjustment; The MMDC phase-shift duty cycle is used to perform phase-shift modulation on the low-voltage side load voltage of the modular multi-level DC transformer.

3. The coordinated control method of modular multi-level DC transformer according to claim 2, characterized in that: The transfer function of the first PI controller is: In the formula, is the transfer function, is the delay time, is the PI controller index, is the amplitude of the AC voltage on the secondary side of the transformer, s is the Laplace operator, is the transformer ratio, is the switching frequency, is the bridge arm capacitance, is the load impedance, , are the control parameters of the first PI controller.

4. The coordinated control method of modular multi-level DC transformer according to claim 1, characterized in that: The bus capacitor voltage of the DC power flow controller is controlled by using the reference value of the bus capacitor voltage of the DC power flow controller, wherein the bus capacitor voltage control is used to make the bus capacitor voltage of the DC power flow controller track the reference value of the bus capacitor voltage, including: Performing a difference process on a reference value of the bus capacitor voltage of the DC power flow controller and the bus capacitor voltage to obtain a bus capacitor voltage difference; Normalizing the bus capacitor voltage difference; Inputting the bus capacitor voltage difference into a second PI controller, and outputting the input-end phase shift duty ratio of the DC power flow controller; The bus capacitor voltage of the DC power flow controller is modulated using the input-end phase-shift duty cycle.

5. The coordinated control method of modular multi-level DC transformer according to claim 4, characterized in that: The transfer function of the second PI controller is: In the formula, is the transfer function between the bus voltage and the phase shift duty cycle at the input of the DC power flow controller, is the amplitude of the transformer primary AC voltage, is the bus capacitance of the DC power flow controller, is the equivalent total inductance on the low voltage side of the AC circuit.

6. The coordinated control method of modular multi-level DC transformer according to claim 1, characterized in that: The utilizing the reference value of the DC port current of the DC power flow controller to perform power flow control on the DC power flow controller, wherein the power flow control is used to make the DC port current of the DC power flow controller track the reference value of the DC port current, comprises: Performing a difference process on a reference value of a DC port current of the DC power flow controller and the DC port current to obtain a DC port current difference; Normalizing the DC port current difference; Inputting the DC port current difference into a third PI controller, and outputting the output end phase shift duty ratio of the DC power flow controller; The DC port current of the DC power flow controller is modulated using the output-end phase-shift duty cycle.

7. The coordinated control method of modular multi-level DC transformer according to claim 1, characterized in that: Also includes: Performing energy balance control on each submodule of the modular multi-level DC transformer; The energy balance control of each submodule of the modular multi-level DC transformer includes: By compensating the phase shift angle of the voltage and current of each submodule of the modular multi-level DC transformer, the energy between the submodules is balanced.

8. A coordinated control system of a modular multi-level DC transformer, applied to a modular multi-level DC transformer, wherein the modular multi-level DC transformer is embedded with a DC power flow controller; characterized in that: The system comprises: A load voltage control module, used for performing load voltage control on the low-voltage side load voltage of the modular multi-level DC transformer using a reference value of the low-voltage side load voltage, wherein the load voltage control is used for making the low-voltage side load voltage perform zero static error tracking on the voltage reference value; A bus capacitor voltage control module, used to perform bus capacitor voltage control on the DC power flow controller using a reference value of the bus capacitor voltage of the DC power flow controller, wherein the bus capacitor voltage control is used to make the bus capacitor voltage of the DC power flow controller track the reference value of the bus capacitor voltage; The power flow control module is used to perform power flow control on the DC power flow controller using the reference value of the DC port current of the DC power flow controller, wherein the power flow control is used to make the DC port current of the DC power flow controller track the reference value of the DC port current.

9. An electronic device, characterized in that: The electronic device includes a memory and a processor, wherein a computer program is stored in the memory, and when the computer program is executed by the processor, the processor executes the steps of the coordinated control method of a modular multi-level DC transformer as described in any one of claims 1 to 7.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed, the steps of the coordinated control method of the modular multi-level DC transformer according to any one of claims 1 to 7 are implemented.

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