Energy balance control method, system and equipment for modular direct-current transformer and medium

Abstract

The invention relates to an energy balance control method, system and device for a modular direct-current transformer and a medium. The method comprises the steps of obtaining capacitor voltage and pulse phase shift of each sub-module of a bridge arm sub-module in the modular direct-current transformer in any time period; obtaining parameter data of each sub-module of a bridge arm in the modularized direct current transformer in the time period, calculating an energy value of a corresponding pulse phase shift in a period in the time period according to the parameter data of each sub-module, finding out the pulse phase shifts with the maximum and minimum corresponding energy, and placing the pulse phase shifts at the head and the tail of a pulse phase shift set; the other pulse phase shifts are arranged in sequence to form a pulse phase shift set; according to the ascending order arrangement of all the capacitor voltages, obtaining a capacitor voltage set of the bridge arm; and distributing the pulse signals in the pulse phase shift sequence set to the sub-modules corresponding to the capacitor voltage set in sequence so as to realize capacitor voltage balance of each sub-module. Compared with the prior art, the method has the advantage of good balance stability.

Description

Technical Field

[0001] The present invention relates to the technical field of direct current transformers, and in particular to an energy balancing control method, system, device and medium for a modular direct current transformer. Background Art

[0002] Different from conventional DC-DC converters, modular multi-level DC-DC converters are not only complex in structure, but also introduce a large number of sub-module capacitors as voltage support and energy buffer units. A large number of energy buffer units participate in energy transmission, resulting in a complex internal power flow in the modular multi-level DC converter MMDC. The sub-module capacitors support voltage in series. The instability or imbalance of energy in any sub-module or bridge arm unit in the modular multi-level DC converter MMDC will affect the normal operation of the converter. An important control for the modular multi-level DC converter MMDC is the balance of the sub-module capacitor voltage. The balance of the sub-module capacitor voltage is crucial to ensure the stable operation of the modular multi-level DC converter MMDC, and is an important control problem that needs to be solved.

[0003] Since the primary side power supply of the DC converter MMDC may fluctuate to a certain extent, or the instability of the load may also cause the power of the DC transformer to change, resulting in voltage fluctuations or voltage mismatch on the primary side of the DC converter MMDC, when a simple sorting algorithm is used to balance the voltage fluctuations or voltage mismatch on the primary side of the DC converter MMDC, the capacitor voltage of the sub-module of the DC converter MMDC cannot be balanced. Summary of the invention

[0004] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and to provide an energy balancing control method, system, device and medium for modular DC transformers with good balancing stability.

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] According to a first aspect of the present invention, there is provided an energy balancing control method for a modular DC transformer, the method comprising:

[0007] Obtaining the capacitor voltage and pulse phase shift of each submodule of the bridge arm submodule in the modular DC transformer in a set time period;

[0008] Obtain parameter data of each submodule of the bridge arm in the modular DC transformer in the time period, calculate the energy value of the corresponding pulse phase shift in one cycle in the time period according to the parameter data of each submodule, and find the pulse phase shifts with the maximum and minimum corresponding energy and place them at the beginning and end of the pulse phase shift set, and arrange the remaining pulse phase shifts in sequence to form a pulse phase shift set;

[0009] Arrange all the capacitor voltages in ascending order to obtain a capacitor voltage set of the bridge arm;

[0010] The pulse signals in the pulse phase shift sequence set are sequentially distributed to the submodules corresponding to the capacitor voltage set to achieve capacitor voltage balance of each of the submodules.

[0011] Preferably, the parameter data of the submodules include pulse phase shift and half switching cycle duration; and calculating the absorbed energy of the corresponding submodule in the time period according to the parameter data of each submodule includes:

[0012] Acquire the bridge arm current of the bridge arm corresponding to the submodule in the time period and the initial time and the end time of the time period;

[0013] According to the pulse phase shift, half switching cycle length, bridge arm current, initial time and end time, the absorbed charge formula is used to calculate and obtain the absorbed energy of the corresponding submodule in the time period.

[0014] Preferably, the absorbed charge formula is:

[0015]

[0016] In the formula, Q i is the absorbed energy of the ith submodule, t end is the end time of time period t, t start is the initial time of time period t, d i is the pulse phase shift of the ith submodule, T h is the half switching cycle duration, i al (t) is the bridge arm current in time period t.

[0017] Preferably, the obtaining of the bridge arm current of the bridge arm corresponding to the submodule in the time period includes:

[0018] Obtaining the input voltage of the modular DC transformer during the time period, the differential mode current component of the bridge arm, and the transmission power of the intermediate frequency transformer;

[0019] Calculate the common mode current of the corresponding bridge arm according to the transmission power and the input voltage;

[0020] Calculate the bridge arm current corresponding to the bridge arm in the time period by using the bridge arm current formula according to the common mode current and the differential mode current components;

[0021] Wherein, the bridge arm current formula is: al =I dc1 / 2-i / 2,I dc1 =P / V dc1 , where ial is the bridge arm current, I dc1 is the common mode current of the bridge arm, i / 2 is the differential mode current component; P is the transmission power of the intermediate frequency transformer, V dc1 is the input voltage of the modular DC transformer.

[0022] Preferably, the calculation process of the transmission power of the medium frequency transformer includes:

[0023] Determining the working mode of each submodule of the bridge arm in the modular DC transformer according to the time period, wherein the working mode includes a first working mode, a second working mode and / or a third working mode;

[0024] Obtain electrical quantity parameters of the modular DC transformer, and calculate according to the working mode and the electrical quantity parameters to obtain the total energy absorbed by the primary side of the AC side of the intermediate frequency transformer; the electrical quantity parameters include the primary AC side equivalent voltage, the maximum pulse phase shift, the input voltage, the output voltage, the half switching cycle duration, the primary equivalent inductance and the transformation ratio;

[0025] The transmission power of the intermediate frequency transformer is obtained by calculating based on the total energy absorbed by the primary side and the half switching cycle duration.

[0026] Preferably, if the working mode includes a working mode, obtaining the total primary absorbed energy on the AC side of the medium frequency transformer includes: calculating according to the electrical quantity parameters corresponding to the working mode to obtain the primary AC side voltage and the primary AC side current of the medium frequency transformer; calculating according to the primary AC side voltage and the primary AC side current to obtain the primary absorbed energy of the medium frequency transformer in the working mode and using the primary absorbed energy as the total primary absorbed energy on the AC side of the medium frequency transformer.

[0027] Preferably, if the working mode includes at least two working modes, obtaining the total energy absorbed by the primary side of the AC side of the medium frequency transformer includes:

[0028] Calculating according to the electrical quantity parameters corresponding to each of the working modes, obtaining the primary AC side voltage and the primary AC side current of the transformer under the corresponding working mode;

[0029] Calculate the primary side absorbed energy of the intermediate frequency transformer in the corresponding working mode according to the primary side AC side voltage and the primary side AC side current;

[0030] The sum of the primary side absorbed energies under all the working modes is taken as the total primary side absorbed energy on the AC side of the medium frequency transformer.

[0031] According to a second aspect of the present invention, there is provided an energy balancing control device for a modular DC transformer, comprising:

[0032] A data acquisition and judgment module is used to obtain the capacitor voltage and pulse phase shift of each submodule in the bridge arm of the modular DC transformer in any time period, and judge whether the capacitor voltages of each submodule are balanced according to the capacitor voltages of each submodule;

[0033] A data sorting module is used to calculate the energy value corresponding to each pulse phase shift according to the energy calculation method based on the capacitor voltage imbalance of at least one of the submodules, and place the pulses with the largest and smallest energies at the beginning and end of the pulse phase shift set, and arrange the remaining pulse roots in sequence to form a pulse phase shift set. Sorting all the capacitor voltages from small to large to obtain the capacitor voltage set of the bridge arm after sorting;

[0034] A calculation module, used for obtaining parameter data of each submodule of the bridge arm in the modular DC transformer in the time period, and calculating the absorbed energy of the corresponding submodule in the time period according to the parameter data of each submodule;

[0035] The balance adjustment module is used to distribute the pulse signals in the pulse phase shift sequence set to the sub-modules corresponding to the capacitor voltage set in sequence, so as to adjust the capacitor voltage balance of each of the sub-modules.

[0036] According to a third aspect of the present invention, there is provided a terminal device, comprising a memory and a processor, wherein a computer program is stored in the memory, and when the processor executes the program, any one of the methods described above is implemented.

[0037] According to a fourth aspect of the present invention, there is provided a computer-readable storage medium having a computer program stored thereon, wherein when the program is executed by a processor, any one of the methods described above is implemented.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] The energy balancing control method of the modular DC transformer designed in the present invention controls the corresponding sub-modules to absorb the corresponding absorbed energy in sequence according to the order of the capacitor voltage set by reconstructing the pulse phase shift sequence set, so as to adjust the capacitor voltage balance of each sub-module; by reconstructing and distributing the pulse phase shift set, the capacitor energy of the MMDC sub-module in the modular DC transformer can be balanced and operate normally in the full range; the technical problem that the instability or imbalance of the energy of any sub-module or bridge arm unit in the existing modular multi-level DC converter MMDC will affect the normal operation of the converter is solved. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is a MMDC topology diagram of the energy balancing control method of the modular DC transformer described in an embodiment of the present application;

[0041] Figure 2 A submodule half-bridge structure diagram of the MMDC of the energy balancing control method of the modular DC transformer described in an embodiment of the present application;

[0042] Figure 3 A structural diagram of a single submodule of the energy balancing control method of the modular DC transformer described in an embodiment of the present application;

[0043] Figure 4 This is a structural diagram of the MMDC series submodule of the energy balance control method of the modular DC transformer described in an embodiment of the present application;

[0044] Figure 5 This is a waveform diagram of the equivalent voltage at both ends of the modular DC transformer described in the embodiment of the present application;

[0045] Figure 6 This is a flowchart of the steps of the energy balance control method of the modular DC transformer according to an embodiment of the present application;

[0046] Figure 7 This is a simulation diagram of Example 1 of the energy balancing control method for a modular DC transformer according to an embodiment of the present application;

[0047] Figure 8 A schematic diagram of a framework of an energy balancing control device for a modular DC transformer according to an embodiment of the present application;

[0048] Fig. 9 A schematic diagram of a terminal device described in an embodiment of the present application. DETAILED DESCRIPTION

[0049] In order to make the purpose, features, and advantages of the invention of this application more obvious and easy to understand, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the embodiments described below are only part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0050] In the description of the embodiments of the present application, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the embodiments of the present application, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined.

[0051] In the embodiments of the present application, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0052] As the penetration rate of renewable energy resources (RES) continues to increase, DC distribution systems are performing better and better in terms of efficiency, scalability, and stability, becoming the preferred transmission system for power grids. Most renewable energy sources, such as solar panels and fuel cells. Energy storage systems (ESS), such as batteries, are essential DC sources. The use of DC grids in the power transmission system of the power grid can save the DC-AC link, reduce power loss and component costs. Even for wind power or gas units, single-stage AC-DC is more efficient than two-stage AC-DC-AC conversion. The same principle can be applied to electronic loads such as personal computers and variable speed appliances.

[0053] With the reduction of rectifiers and power factor correctors, the DC distribution system can save about 25% of components and 8% of power loss. In addition, it is simpler to connect RES and ESS to the DC distribution system that only considers the amplitude without the problem of frequency and phase synchronization. The effectiveness of the DC distribution system has been proven in some industrial applications, such as in telecommunication systems, aircraft and ships.

[0054] The DC power distribution system was proposed by Thomas Edison more than 100 years ago. In the competition between the DC system and the AC system, the AC system won because the DC voltage could not be increased for transmission. However, with the advancement of power electronic devices, magnetic materials and microprocessors, this technical barrier has been overcome. Now the DC voltage can be transformed to different levels through a DC transformer, which is essentially a high-voltage bidirectional DC-DC converter with galvanic isolation capability. The DC voltage is inverted into an intermediate frequency AC voltage, and the intermediate frequency transformer is used to step up or down the voltage, and then rectified to a DC voltage.

[0055] There is currently a DC transformer using a single MF transformer of a Modular Multilevel DC Converter (MMDC). Figure 1The schematic diagram of a single-phase MMDC is shown in Figure 2. MMDC is derived from the dual active bridge converter (DAB) and the modular multilevel converter (MMDC), and inherits the excellent characteristics of the two topologies. Like MMDC, MMDC uses series submodules (SM) to support high voltage. An important control for MMDC is the balance of the submodule capacitor voltage, which is crucial to ensure stable operation and is an important control problem that needs to be solved.

[0056] The embodiment of the present application provides an energy balancing control method and system for a modular DC transformer, which solves the technical problem that the instability or imbalance of energy of any sub-module or bridge arm unit inside the existing modular multi-level DC converter MMDC will affect the normal operation of the converter.

[0057] In the embodiments of the present application, Figure 1 As shown, the MMDC topology structure includes an MMDC full-bridge submodule structure, an intermediate frequency transformer and a full-bridge structure connected in sequence, an MMDC full-bridge submodule structure composed of submodule strings, an intermediate frequency transformer for electrical isolation, and a full-bridge structure composed of IGBT switch tubes. The MMDC full-bridge submodule structure includes at least two phase units, each phase unit is composed of an upper bridge arm and a lower bridge arm, the positive pole of the DC side is connected to the positive pole of the upper bridge arm of each phase unit, and the negative pole of the DC side is connected to the negative pole of the lower bridge arm. In each bridge arm, n submodules (Submodule, represented by SM1 to SMn, respectively) with the same circuit parameters are connected in series and a bridge arm inductor Lp is connected in series in the bridge arm. The negative pole of the upper bridge arm and the positive pole of the lower bridge arm are connected in series with the bridge arm inductor Lp, and then connected to each other, and are led out as the AC output side of each phase unit.

[0058] It should be noted that the MMDC full-bridge submodule structure includes a full-bridge, a half-bridge and other submodules, and the submodules are composed of IGBTs and capacitors, such as Figure 2 The working principle of the half-bridge submodule is described by taking the half-bridge structure shown in FIG. 1 as an example. In this embodiment, the working principle of the half-bridge submodule includes controlling Figure 3 The different on or off states of the switch device T1 and the switch device T2 shown can switch the half-bridge submodule among three working states.

[0059] In the embodiment of the present application, the three working states of the half-bridge submodule are respectively the put-in working state, the cut-off working state and the locked working state. The put-in working state includes: when the switch device T1 is turned on and the switch device T2 is turned off, the half-bridge submodule is in the put-in working state; when the half-bridge submodule is in the put-in working state, the freewheeling diode D2 is subjected to the submodule capacitor voltage v cWhen the current i flowing into the submodule is arm >0, the submodule current flows through the freewheeling diode D1 and the submodule capacitor C sm A current path is formed, and the electric energy is fed from both ends of the submodule into the capacitor C sm , submodule capacitance C sm Charging. When the current i flowing into the submodule arm <0, the submodule current i arm Through the switch device T1, the submodule capacitor C sm A current path is formed, and both ends of the submodule absorb electric energy from the capacitor side. The submodule capacitor C sm Discharge. Regardless of the direction of the current flowing into the submodule, the voltage u SM Both are related to the submodule capacitor voltage v c The cut-off working state includes: when the switch device T1 is turned off and the switch device T2 is turned on, the half-bridge sub-module is in the cut-off working state; when the half-bridge sub-module is in the cut-off working state, the freewheeling diode D1 is subjected to the sub-module capacitor voltage v c When the current i flowing into the submodule is arm >0, the submodule current forms a current path through the switch device T2. arm <0, the submodule current i arm The current path is formed through the freewheeling diode D2. Regardless of the direction of the current flowing into the submodule, the submodule capacitor C sm All are bypassed and not connected to the current path. The voltage u SM The contents of the locked working state include: when the switch device T1 and the switch device T2 are both turned off, the half-bridge submodule is in the locked working state; when the half-bridge submodule is in the locked working state, the current cannot flow through the switch device T1 turned off or the switch device T2, and must flow through the freewheeling diode D1 or the freewheeling diode D2 to form a path. When the current i flowing into the submodule arm >0, the submodule current flows through the freewheeling diode D1 and the submodule capacitor C sm A current path is formed, and the electric energy is fed from both ends of the submodule into the capacitor C sm , submodule capacitance C sm Charging, voltage across the submodule u SM Both are related to the submodule capacitor voltage v c When the current i flowing into the submodule arm <0, the submodule current i arm The current path is formed through the freewheeling diode D2, and the submodule capacitor C sm All are bypassed and not connected to the current path. The voltage u SM0. Among them, when the transmission system of the MMDC topology structure is in steady-state normal operation, the submodule of the MMDC topology structure only uses the two working states of input and removal, and does not use the blocking working state. The blocking working state is only used during the startup or fault period of the transmission system of the MMDC topology structure.

[0060] In the embodiment of the present application, the working principle of the MMDC full-bridge submodule structure includes:

[0061] When the switch device T1 or the freewheeling diode D1 is turned on, the submodule is put into operation and the bridge arm current i arm Flowing through the submodule capacitor C sm , submodule output voltage v sm =v c ;

[0062] When the switch device T2 or the freewheeling diode D2 is turned on, the submodule is cut off and the output voltage v sm =0.

[0063] It should be noted that the output voltage v of the entire bridge arm arm is the sum of the output voltages of each submodule, and the average value of the capacitor voltage of each submodule is V c , the sum of the average voltages of all capacitors in the bridge arm V arm =nV c (n is the number of submodules in the bridge arm). Ignoring the submodule capacitor voltage ripple, S sm is the submodule switch function, S sm =1 corresponds to the submodule being put into operation; S sm =0 corresponds to the cut-off working state of the submodule. s is the switching cycle, Ds is S sm The bridge arm switching function S sm is the sum of the switching functions of each submodule. The submodule chain input voltage v arm It is the sum of the input voltages of each submodule. Figure 5 It can be seen from the figure that in the quasi-two-level modulation mode, except for the step wave voltage edge, the control process and voltage and current waveforms of the bridge arm of the MMDC full-bridge submodule structure are basically the same as those of a single submodule. Ignoring the transient conversion process of the bridge arm voltage between zero level and high level, the quasi-two-level voltage is regarded as a two-level voltage. The bridge arm of the MMDC full-bridge submodule structure can be regarded as a single large submodule with a capacitor voltage of N Vc, such as Figure 4 shown.

[0064] In the embodiment of the present application, the submodule switch function S sm The expression is:

[0065]

[0066] Where t0 is the starting point of the switching cycle, t is the independent variable time, and D s is the switch conduction time in one switching cycle. The output voltage v sm It can be written as the switching function S sm and the submodule capacitor voltage v c The product of sm =v c S sm In the quasi-two-level modulation mode, ignoring the transient conversion process of capacitor voltage ripple and bridge arm voltage, the entire submodule chain can be equivalent to a single submodule with capacitor voltage enlarged N times. At this time, the sum of the bridge arm capacitor voltage V arm for:

[0067]

[0068] In the formula, v c,i is the capacitor voltage of the ith submodule in the submodule chain. The isolated MMDC quasi-two-level modulation is realized by controlling the pulse phase shift. The equivalent voltage waveform at both ends of the modular DC transformer in the quasi-two-level modulation mode is as follows: Figure 5 shown.

[0069] In the embodiment of the present application, based on the principle that the area enclosed by the time axis is equal, the primary voltage v of the intermediate frequency transformer in the modular DC transformer is po The rising and falling stages of the step wave can be equivalent to a slope of 2V dc1 / d N The first-order curve, d N is the maximum phase shift within half a cycle of the submodule, V dc1 is the input voltage of the modular DC transformer. Figure 1 and Figure 5 As shown, the working mode decomposition of the steady-state operation process of the isolated MMDC is carried out in combination with the equivalent voltage conversion process of the primary and secondary sides. Since the voltage and current waveforms of the AC side in the front and rear half working cycles are symmetrical, the working mode analysis of the isolated MMDC in the first half cycle is used as a case illustration. Before time t0, all the sub-modules of the lower bridge arm of the A phase of the primary side of the modular DC transformer are removed, and all the upper bridge arm sub-modules are put into operation; all the lower bridge arm sub-modules of the B phase of the primary side of the modular DC transformer are put into operation, and all the upper bridge arm sub-modules are removed; the upper bridge arm switch tube of the A phase of the secondary side of the modular DC transformer is disconnected, and the lower bridge arm switch tube is closed; the upper bridge arm switch tube of the B phase of the secondary side of the modular DC transformer is closed, and the lower bridge arm switch tube is disconnected. At this time, the voltage and current of the intermediate frequency transformer can be expressed by the first formula. The first formula is:

[0070]

[0071] Where V dc2is the output voltage of the modular DC transformer, V po (t) is the primary AC voltage of the medium frequency transformer, nv so (t) is the equivalent voltage of the primary AC side of the medium frequency transformer, i p (t) is the primary AC side current of the medium frequency transformer.

[0072] Embodiment 1:

[0073] like Figure 6 As shown, the embodiment of the present application provides an energy balancing control method for a modular DC transformer, comprising the following steps:

[0074] Obtaining the capacitor voltage and pulse phase shift of each submodule of the bridge arm submodule in the modular DC transformer in any time period;

[0075] Obtain parameter data of each submodule of the bridge arm in the modular DC transformer in the time period, calculate the energy value of the corresponding pulse phase shift in one cycle in the time period according to the parameter data of each submodule, and find the pulse phase shifts with the maximum and minimum corresponding energy and place them at the head and tail of the pulse phase shift set, and arrange the remaining pulse phase shifts in sequence to form a pulse phase shift set;

[0076] Sorting all the capacitor voltages from small to large to obtain a capacitor voltage set of the bridge arm after sorting;

[0077] The pulse signals in the pulse phase shift sequence set are sequentially distributed to the submodules corresponding to the capacitor voltage set to achieve capacitor voltage balance of each of the submodules.

[0078] S1. Obtain the capacitor voltage and pulse phase shift of each submodule in the bridge arm of the modular DC transformer in any time period, and determine whether the capacitor voltages of each submodule are balanced according to the capacitor voltages of each submodule.

[0079] It should be noted that in step S1, the capacitor voltage and phase-shift pulse of each submodule of the bridge arm in the modular DC transformer in any time period are obtained, and then it is determined whether the acquired capacitor voltage of the submodule is unbalanced.

[0080] In an embodiment of the present application, the rule for determining whether the capacitor voltage of a submodule is unbalanced is: if the capacitor voltage of the submodule is within a set voltage range, the capacitor voltage of the submodule is in a balanced state; if the capacitor voltage of the submodule is not within the set voltage range, the capacitor voltage of the submodule is in an unbalanced state.

[0081] It should be noted that, in other embodiments, the judgment of whether the capacitor voltage of the submodule is unbalanced can also be based on the comparison of the capacitor voltage difference between two adjacent moments with the set threshold value, and whether the capacitor voltage difference is within the set threshold range to indicate whether the capacitor voltage of the submodule is in a balanced state. For example, if the capacitor voltage difference of the submodule is within the set threshold range, the capacitor voltage of the submodule is in a balanced state; if the capacitor voltage difference of the submodule is not within the set threshold range, the capacitor voltage of the submodule is in an unbalanced state. The set voltage and the set threshold value can be set according to the needs, and are not specifically limited here.

[0082] S2. If the capacitor voltage of at least one submodule is unbalanced, obtain the parameter data of each submodule in the bridge arm of the modular DC transformer in the time period, calculate the energy value of the corresponding pulse phase shift in one cycle in the time period according to the parameter data of each submodule, and find the pulse phase shifts with the maximum and minimum corresponding energies and place them at the beginning and end of the pulse phase shift set, and arrange the remaining pulse phase shifts in sequence to form a pulse phase shift set;

[0083] It should be noted that in step S2, based on the premise of determining the capacitor voltage imbalance of the submodule in step S1, the energy value of the pulse phase shift collected in step S1 is calculated and the pulse phase shift sequence is reconstructed. n The corresponding energy Q n , and find the maximum energy Q max With minimum energy Q min The corresponding pulse phase shift d max d min . And redistribute it to the head and tail of the pulse phase shift set, and the remaining pulse phase shifts are distributed in sequence to form a new pulse phase shift set.

[0084] S3. Sorting all the capacitor voltages from small to large to obtain a capacitor voltage set of the bridge arm after sorting;

[0085] It should be noted that in step S3, based on the premise that the capacitor voltage of the submodule is unbalanced according to step S1, the capacitor voltage number in each submodule in the time period corresponding to step S1 is obtained, and the numbers are sorted from small to large to construct a submodule capacitor voltage set.

[0086] S4. Allocate the pulse signals in the pulse phase shift sequence set to the submodules corresponding to the capacitor voltage set in sequence, so as to achieve capacitor voltage balance of each of the submodules.

[0087] It should be noted that step S4 allocates the new pulse phase shift sequence set obtained in step S2 and the elements in the capacitor voltage set obtained in step S3 in a one-to-one correspondence to adjust the capacitor voltage balance of each submodule. The energy balance control method of the modular DC transformer is to realize the submodule pulse adjustment and allocation mechanism.

[0088] Figure 7 This is a simulation of Example 1 of the energy balancing control method for the modular DC transformer described in an embodiment of the present application.

[0089] In the embodiment of the present application, the energy balance control method of the modular DC transformer is simulated through case 1, case 2, case 3 and case 4. Figure 1 The modular DC transformer shown in the figure is constructed using MATLAB / Simulink software. Figure 1 The modular DC transformer structure shown in the figure is simulated and verified for this topology, and the simulation parameters are shown in Table 1. Figure 7 As shown in the figure, based on the following three working states, the energy balance control strategy of the proposed modular DC transformer is verified in the voltage mismatch scenario. The specific working states are described as follows:

[0090] State 1: During 0-0.5s, the primary voltage of MMDC is V dc1 The secondary voltage V is 20kV and the transmission power is 0.4pu dc2 It is 750V, at which point the primary and secondary voltages match.

[0091] State 2: During 0.5-1.5s, the secondary voltage V dc2 The change from 750V to 800V results in a mismatch between the primary and secondary side voltages of the MMDC.

[0092] State 3: During 1.5-3.5s, the proposed sub-module energy balance control strategy is activated.

[0093] Figure 7 (a) shows that the submodule capacitor voltage is unbalanced in state 2, indicating that the conventional sorting algorithm is not applicable in the case of 0.83 voltage conversion ratio. The proposed scheme can restore the submodule capacitor voltage balance in state 3. The detailed experimental results are shown in Figure 2. Figure 7 As shown in (b)-(d).

[0094] Table 1 shows the simulation parameters.

[0095] variable parameter variable parameter Switching frequency 1kHz Transmission power 1MW AC side equivalent inductance 0.0375H Submodule capacitance value 2.2mF Number of bridge arm submodules 8 Primary voltage 20kV Secondary voltage 750V Phase shift between each submodule 5us

[0096] Embodiment 2:

[0097] Figure 8This is a schematic diagram of the framework of the energy balancing control device of the modular DC transformer described in an embodiment of the present application.

[0098] like Figure 8 As shown, the embodiment of the present application provides an energy balance control device for a modular DC transformer, including a data acquisition and judgment module 10, a data sorting module 20, a calculation module 30 and a balance adjustment module 40;

[0099] The data acquisition and judgment module 10 is used to obtain the capacitor voltage and pulse phase shift of each submodule of the bridge arm submodule in the modular DC transformer in any time period, and judge whether the capacitor voltage of each submodule is balanced according to the capacitor voltage of each submodule;

[0100] A data sorting module 20, for sorting all the capacitor voltages from small to large to obtain a sorted capacitor voltage set of the bridge arm;

[0101] The calculation module 30 obtains the parameter data of each submodule of the bridge arm in the modular DC transformer in the time period, calculates the energy value of the corresponding pulse phase shift in one cycle in the time period according to the parameter data of each submodule, and finds the pulse phase shifts with the maximum and minimum corresponding energies and places them at the head and tail of the pulse phase shift set, and the remaining pulse phase shifts are arranged in sequence to form a pulse phase shift set;

[0102] A balance adjustment module 40 distributes the pulse signals in the pulse phase shift sequence set to the submodules corresponding to the capacitor voltage set in sequence, so as to achieve capacitor voltage balance of each of the submodules;

[0103] In the embodiment of the present application, the parameter data of the submodule includes the pulse phase shift and the half switching cycle duration of the submodule, and the calculation module 30 includes a parameter acquisition submodule and a calculation submodule;

[0104] A parameter acquisition submodule, used to acquire the bridge arm current of the bridge arm corresponding to the submodule in the time period and the initial time and the end time of the time period;

[0105] The calculation submodule is used to calculate the absorbed energy of the corresponding submodule in the time period by using the absorbed charge formula according to the pulse phase shift, half switching cycle length, bridge arm current, initial time and end time;

[0106] The formula for absorbed charge is:

[0107]

[0108] In the formula, Q i is the absorbed energy of the ith submodule, t end is the end time of time period t, t start is the initial time of time period t, di is the pulse phase shift of the ith submodule, T h is the half switching cycle duration, i al (t) is the bridge arm current in time period t.

[0109] In the embodiment of the present application, the parameter acquisition submodule is also used to obtain the input voltage of the modular DC transformer in the time period, the differential mode current component of its bridge arm, and the transmission power of its intermediate frequency transformer; according to the transmission power and the input voltage, the common mode current of the corresponding bridge arm is calculated; according to the common mode current and the differential mode current component, the bridge arm current formula is used to calculate and obtain the bridge arm current of the corresponding bridge arm in the time period; wherein the bridge arm current formula is: i al =I dc1 / 2-i / 2,I dc1 =P / V dc1 , where i al is the bridge arm current, I dc1 is the common mode current of the bridge arm, i / 2 is the differential mode current component; P is the transmission power of the intermediate frequency transformer, V dc1 is the input voltage of the modular DC transformer.

[0110] It should be noted that the content of the module in the device of Example 2 corresponds to the step content of the method in Example 1. The content of the energy balance control method of the modular DC transformer has been described in Example 1, and the step content of the energy balance control method of the modular DC transformer will not be described in detail in this embodiment.

[0111] Embodiment three:

[0112] Fig. 9 A schematic diagram of a terminal device described in an embodiment of the present application.

[0113] like Fig. 9 As shown, an embodiment of the present application provides a terminal device, including a processor and a memory;

[0114] A memory, used for storing program codes and transmitting the program codes to a processor;

[0115] The processor is used to execute the energy balancing control method of the modular DC transformer according to the instructions in the program code.

[0116] It should be noted that the processor is used to execute the steps in the above-mentioned embodiment of the energy balance control method of a modular DC transformer according to the instructions in the program code. Alternatively, the processor implements the functions of each module / unit in the above-mentioned system / device embodiments when executing the computer program.

[0117] Exemplarily, the computer program may be divided into one or more modules / units, one or more modules / units are stored in a memory and executed by a processor to complete the present application. One or more modules / units may be a series of computer program instruction segments capable of completing a specific function, and the instruction segments are used to describe the execution process of the computer program in a terminal device.

[0118] The terminal device may be a computing device such as a desktop computer, a notebook, a PDA, or a cloud server. The terminal device may include, but is not limited to, a processor and a memory. Those skilled in the art will appreciate that this does not constitute a limitation on the terminal device, and may include more or fewer components than shown in the figure, or a combination of certain components, or different components. For example, the terminal device may also include input and output devices, network access devices, buses, etc.

[0119] The processor may be a central processing unit (CPU), other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor may be a microprocessor or any conventional processor, etc.

[0120] The memory may be an internal storage unit of the terminal device, such as a hard disk or memory of the terminal device. The memory may also be an external storage device of the terminal device, such as a plug-in hard disk, a smart memory card (SmartMedia Card, SMC), a secure digital (Secure Digital, SD) card, a flash card (Flash Card), etc. equipped on the terminal device. Furthermore, the memory may also include both an internal storage unit of the terminal device and an external storage device. The memory is used to store computer programs and other programs and data required by the terminal device. The memory may also be used to temporarily store data that has been output or is to be output.

[0121] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working processes of the systems, devices and units described above can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0122] In the several embodiments provided in the present application, it should be understood that the disclosed systems, devices and methods can be implemented in other ways. For example, the device embodiments described above are only schematic. For example, the division of the units is only a logical function division. There may be other division methods in actual implementation, such as 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.

[0123] 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.

[0124] In addition, each functional unit in each embodiment of the present application 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.

[0125] 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 application 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, and the computer software product is stored in a storage medium, including a number of instructions to enable a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present application. The aforementioned storage medium includes: various media that can store program codes, such as a USB flash drive, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a disk or an optical disk.

[0126] As described above, the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. 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 application.

Claims

1. An energy balancing control method for a modular DC transformer, characterized in that: The method includes: Obtaining the capacitor voltage and pulse phase shift of each submodule of the bridge arm submodule in the modular DC transformer in any time period; Obtain parameter data of each submodule of the bridge arm in the modular DC transformer in the time period, calculate the energy value of the corresponding pulse phase shift in one cycle in the time period according to the parameter data of each submodule, and find the pulse phase shifts with the maximum and minimum corresponding energy and place them at the head and tail of the pulse phase shift set, and arrange the remaining pulse phase shifts in sequence to form a pulse phase shift set; Sorting all the capacitor voltages from small to large to obtain a capacitor voltage set of the bridge arm after sorting; The pulse signals in the pulse phase shift sequence set are sequentially distributed to the submodules corresponding to the capacitor voltage set to achieve capacitor voltage balance of each of the submodules.

2. The energy balancing control method for a modular DC transformer according to claim 1, characterized in that: Calculating the absorbed energy of the corresponding submodule in the time period according to the parameter data of each submodule includes: The parameter data of the submodule includes pulse phase shift and half switching cycle duration; Acquire the bridge arm current of the bridge arm corresponding to the submodule in the time period and the initial time and the end time of the time period; According to the pulse phase shift, half switching cycle length, bridge arm current, initial time and end time, the absorbed charge formula is used to calculate and obtain the absorbed energy of the corresponding submodule in the time period.

3. The energy balancing control method for a modular DC transformer according to claim 2, characterized in that: The absorbed charge formula is: In the formula, Q i is the absorbed energy of the ith submodule, t end is the end time of time period t, t start is the initial time of time period t, d i is the pulse phase shift of the ith submodule, T h is the half switching cycle duration, i al (t) is the bridge arm current in time period t.

4. The energy balancing control method for a modular DC transformer according to claim 2, characterized in that: The obtaining of the bridge arm current of the bridge arm corresponding to the submodule in the time period includes: Obtaining the input voltage of the modular DC transformer during the time period, the differential mode current component of the bridge arm, and the transmission power of the intermediate frequency transformer; Calculate the common mode current of the corresponding bridge arm according to the transmission power and the input voltage; Calculate the bridge arm current corresponding to the bridge arm in the time period by using the bridge arm current formula according to the common mode current and the differential mode current components; Wherein, the bridge arm current formula is: al =I dc1 / 2-i / 2,I dc1 =P / V dc1 , where i al is the bridge arm current, I dc1 is the common mode current of the bridge arm, i / 2 is the differential mode current component; P is the transmission power of the intermediate frequency transformer, V dc1 is the input voltage of the modular DC transformer.

5. The energy balancing control method for a modular DC transformer according to claim 4, characterized in that: The transmission power of the intermediate frequency transformer is calculated by: Determining the working mode of each submodule of the bridge arm in the modular DC transformer according to the time period, wherein the working mode includes a first working mode, a second working mode and / or a third working mode; Obtain electrical quantity parameters of the modular DC transformer, and calculate according to the working mode and the electrical quantity parameters to obtain the total energy absorbed by the primary side of the AC side of the intermediate frequency transformer; the electrical quantity parameters include the primary AC side equivalent voltage, the maximum pulse phase shift, the input voltage, the output voltage, the half switching cycle duration, the primary equivalent inductance and the transformation ratio; The transmission power of the intermediate frequency transformer is obtained by calculating based on the total energy absorbed by the primary side and the half switching cycle duration.

6. The energy balancing control method for a modular DC transformer according to claim 5, characterized in that: If the working mode includes a working mode, obtaining the total primary absorbed energy on the AC side of the medium frequency transformer includes: calculating according to the electrical quantity parameters corresponding to the working mode to obtain the primary AC side voltage and the primary AC side current of the medium frequency transformer; calculating according to the primary AC side voltage and the primary AC side current to obtain the primary absorbed energy of the medium frequency transformer in the working mode and using the primary absorbed energy as the total primary absorbed energy on the AC side of the medium frequency transformer.

7. The energy balancing control method for a modular DC transformer according to claim 5, characterized in that: If the working mode includes at least two working modes, the total energy absorbed by the primary side of the AC side of the intermediate frequency transformer includes: Calculating according to the electrical quantity parameters corresponding to each of the working modes, obtaining the primary AC side voltage and the primary AC side current of the transformer under the corresponding working mode; Calculate the primary side absorbed energy of the intermediate frequency transformer in the corresponding working mode according to the primary side AC side voltage and the primary side AC side current; The sum of the primary side absorbed energies under all the working modes is taken as the total primary side absorbed energy on the AC side of the medium frequency transformer.

8. An energy balancing control system for a modular DC transformer, characterized in that: include: A data acquisition and judgment module is used to obtain the capacitor voltage and pulse phase shift of each submodule in the bridge arm of the modular DC transformer in any time period, and judge whether the capacitor voltages of each submodule are balanced according to the capacitor voltages of each submodule; A data sorting module is used to calculate the energy value corresponding to each pulse phase shift according to the energy calculation method based on the capacitor voltage imbalance of at least one of the submodules, and place the pulses with the largest and smallest energies at the beginning and end of the pulse phase shift set, and arrange the remaining pulse roots in sequence to form a pulse phase shift set. Sorting all the capacitor voltages from small to large to obtain the capacitor voltage set of the bridge arm after sorting; A calculation module, used for obtaining parameter data of each submodule of the bridge arm in the modular DC transformer in the time period, and calculating the absorbed energy of the corresponding submodule in the time period according to the parameter data of each submodule; The balance adjustment module is used to distribute the pulse signals in the pulse phase shift sequence set to the sub-modules corresponding to the capacitor voltage set in sequence, so as to adjust the capacitor voltage balance of each of the sub-modules.

9. A terminal device, comprising a memory and a processor, wherein a computer program is stored in the memory, characterized in that: When the processor executes the program, the method according to any one of claims 1 to 7 is implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the method according to any one of claims 1 to 7 is implemented.

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