An energy balance control method, device and equipment of a modular DC transformer

Abstract

This application relates to an energy balancing control method, apparatus, and device for a modular DC transformer. The energy balancing control method uses a pulse phase-shifting sequence to control the corresponding sub-modules to absorb energy sequentially according to the order of capacitor voltage sets, thereby adjusting the capacitor voltage balance of each sub-module. The pulse phase shifting can change the duty cycle of the secondary voltage of the intermediate frequency transformer, thus ensuring energy balance of the MMDC sub-module capacitors in the modular DC transformer and enabling normal operation across the entire range. This solves the technical problem that instability or imbalance of energy in any sub-module or bridge arm unit within the existing modular multilevel DC converter (MMDC) will affect the normal operation of the converter.

Description

Technical Field

[0001] This application relates to the field of DC power transmission technology, and in particular to an energy balance control method, device and equipment for a modular DC transformer. Background Technology

[0002] Unlike conventional DC-DC converters, modular multilevel DC-DC converters (MMDCs) are not only structurally complex but also incorporate a large number of submodule capacitors as voltage support and energy buffer units. The extensive energy buffer units involved in energy transfer result in a complex internal power flow within the MMDC. Since the submodule capacitors support voltage in series, any instability or imbalance in the energy of any submodule or bridge arm unit within the MMDC will affect its normal operation. A crucial control aspect of MMDCs is the equalization of submodule capacitor voltages. This equalization is essential for ensuring stable operation of the MMDC and represents a significant control problem that needs to be addressed.

[0003] Because the primary power supply of the MMDC converter may fluctuate, or the load may be unstable, the power of the DC transformer may change, resulting in voltage fluctuations or voltage mismatches on the primary side of the MMDC converter. Therefore, when a simple sorting algorithm is used to balance the voltage fluctuations or voltage mismatches on the primary side of the MMDC converter, the energy of the sub-modules of the MMDC converter cannot be balanced. Summary of the Invention

[0004] This application provides an energy balancing control method, apparatus, and device for a modular DC transformer, which addresses the technical problem that instability or imbalance of energy in any sub-module or bridge arm unit within an existing modular multilevel DC converter (MMDC) can affect the normal operation of the converter.

[0005] To achieve the above objectives, the embodiments of this application provide the following technical solutions:

[0006] On the one hand, an energy balance control method for a modular DC transformer is provided, including the following steps:

[0007] The capacitor voltage and pulse phase shift of each sub-module of the bridge arm in the modular DC transformer are obtained at any time period, and the capacitor voltage of each sub-module is determined to be balanced based on the capacitor voltage of each sub-module.

[0008] If at least one of the submodules has an unbalanced capacitor voltage, the pulse phase shift sequence of the bridge arm is obtained by sorting all the pulse phase shifts in ascending order; the set of capacitor voltages of the bridge arm is obtained by sorting all the capacitor voltages in ascending order.

[0009] Obtain the parameter data of each sub-module of the bridge arm in the modular DC transformer during the time period, and calculate the absorbed energy of the corresponding sub-module during the time period based on the parameter data of each sub-module.

[0010] According to the pulse phase shift sequence, the corresponding sub-modules are controlled to absorb the corresponding absorbed energy in sequence according to the order of the capacitor voltage set, so as to adjust the capacitor voltage balance of each sub-module.

[0011] Preferably, the parameter data of the submodule includes pulse phase shift and the duration of half a switching cycle of the submodule. Calculating the absorbed energy of the corresponding submodule within this time period based on the parameter data of each submodule includes:

[0012] Obtain the bridge arm current corresponding to the submodule during the time period, as well as the start and end times of the time period;

[0013] The absorbed energy of the corresponding submodule during this time period is calculated using the formula for the absorbed charge based on the pulse phase shift, the duration of half a switching cycle, the bridge arm current, the initial time, and the end time.

[0014] The formula for the amount of absorbed charge is as follows:

[0015]

[0016] In the formula, Q i For the energy absorbed by the i-th submodule, t end Let t be the end time of time interval t. start Let d be the initial time of time interval t. i For the pulse phase shift of the i-th submodule, T h For half a switching cycle duration, i al (t) represents the bridge arm current during time interval t.

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

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

[0019] The common-mode current corresponding to the bridge arm is calculated based on the transmission power and the input voltage.

[0020] The bridge arm current for the corresponding bridge arm in the time period is obtained by using the bridge arm current formula based on the common mode current and the differential mode current components.

[0021] The formula for the bridge arm current is: i al =I dc1 / 2-i / 2, I dc1 =P / V dc1 In the formula, i al For the bridge arm current, I dc1 V 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 This refers to the input voltage of the modular DC transformer.

[0022] Preferably, obtaining the transmission power of the intermediate frequency transformer includes:

[0023] The operating modes of each sub-module of the bridge arm in the modular DC transformer are determined based on this time period. The operating modes include a first operating mode, a second operating mode, and / or a third operating mode.

[0024] The electrical parameters of the modular DC transformer are obtained, and the total energy absorbed by the primary side of the intermediate frequency transformer on the AC side is calculated based on the operating mode and the electrical parameters. The electrical parameters include the equivalent voltage of the primary AC side, the maximum pulse phase shift, the input voltage, the output voltage, the duration of half a switching cycle, the equivalent inductance of the primary side, and the transformation ratio.

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

[0026] Preferably, if the operating mode includes an operating mode, obtaining the total energy absorbed by the primary side of the intermediate frequency transformer on the AC side includes: calculating the primary AC side voltage and primary AC side current of the intermediate frequency transformer based on the electrical quantity parameters corresponding to the operating mode; calculating the primary side energy absorbed by the intermediate frequency transformer in the operating mode based on the primary AC side voltage and primary AC side current, and using the primary side energy absorbed as the total primary side energy absorbed by the intermediate frequency transformer on the AC side.

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

[0028] The primary AC voltage and primary AC current of the transformer under each operating mode are calculated based on the electrical quantity parameters corresponding to each operating mode.

[0029] The primary-side AC voltage and the primary-side AC current are used to calculate the primary-side absorbed energy of the intermediate frequency transformer under the corresponding operating mode.

[0030] The sum of the primary-side absorbed energy under all the aforementioned operating modes is taken as the total primary-side absorbed energy of the AC side of the intermediate frequency transformer.

[0031] On the other hand, a modular DC transformer energy balancing control device is provided, including a data acquisition and judgment module, a data sorting module, a calculation module and a balance adjustment module;

[0032] The data acquisition and judgment module is used to acquire the capacitor voltage and pulse phase shift of each sub-module of the bridge arm in the modular DC transformer at any time period, and to determine whether the capacitor voltage of each sub-module is balanced based on the capacitor voltage of each sub-module.

[0033] The data sorting module is used to obtain the pulse phase shift sequence of the bridge arm by sorting all the pulse phase shifts in ascending order based on the capacitor voltage imbalance of at least one of the sub-modules; and to obtain the sorted capacitor voltage set of the bridge arm by sorting all the capacitor voltages in ascending order.

[0034] The calculation module is used to obtain the parameter data of each sub-module of the bridge arm in the modular DC transformer during the time period, and calculate the absorbed energy of the corresponding sub-module during the time period based on the parameter data of each sub-module.

[0035] The balance adjustment module is used to control the corresponding sub-modules to absorb the corresponding absorbed energy in sequence according to the pulse phase shift sequence and the order of the capacitor voltage set, so as to adjust the capacitor voltage balance of each sub-module.

[0036] Preferably, the parameter data of the submodule includes pulse phase shift and the duration of half a switching cycle of the submodule, and the calculation module includes a parameter acquisition submodule and a calculation submodule;

[0037] The parameter acquisition submodule is used to acquire the bridge arm current corresponding to the submodule during the time period, as well as the initial and end times of the time period.

[0038] The calculation submodule is used to calculate the energy absorbed by the corresponding submodule within the time period based on the pulse phase shift, the duration of half a switching cycle, the bridge arm current, the initial time, and the end time using the formula for the amount of absorbed charge.

[0039] The formula for the amount of absorbed charge is as follows:

[0040]

[0041] In the formula, Q i For the energy absorbed by the i-th submodule, t end Let t be the end time of time interval t.start Let d be the initial time of time interval t. i For the pulse phase shift of the i-th submodule, T h For half a switching cycle duration, i al (t) represents the bridge arm current during time interval t.

[0042] Preferably, the parameter acquisition submodule is further configured to acquire the input voltage of the modular DC transformer during the time period, the differential-mode current component of its bridge arm, and the transmission power of its intermediate frequency transformer; calculate the common-mode current of the corresponding bridge arm based on the transmission power and the input voltage; and calculate the bridge arm current of the corresponding bridge arm during the time period using the bridge arm current formula based on the common-mode current and the differential-mode current component; wherein, the bridge arm current formula is: i al =I dc1 / 2-i / 2, I dc1 =P / V dc1 In the formula, i al For the bridge arm current, I dc1 V 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 This refers to the input voltage of the modular DC transformer.

[0043] On the other hand, a terminal device is provided, including a processor and a memory;

[0044] The memory is used to store program code and transmit the program code to the processor;

[0045] The processor is used to execute the energy equalization control method for the modular DC transformer described above, according to the instructions in the program code.

[0046] This invention discloses an energy balancing control method, apparatus, and equipment for a modular DC transformer. The method includes: acquiring the capacitor voltage and pulse phase shift of each submodule in the bridge arm of the modular DC transformer at any given time period; determining whether the capacitor voltages of each submodule are balanced based on their respective capacitor voltages; if at least one submodule has an unbalanced capacitor voltage, obtaining the pulse phase shift sequence of the bridge arm by sorting all pulse phase shifts from smallest to largest; obtaining the sorted set of capacitor voltages for the bridge arm by sorting all capacitor voltages from smallest to largest; acquiring the parameter data of each submodule in the bridge arm of the modular DC transformer within that time period; calculating the absorbed energy of the corresponding submodule within that time period based on the parameter data of each submodule; and controlling the corresponding submodule to absorb the corresponding absorbed energy sequentially according to the pulse phase shift sequence and the sorting of the capacitor voltage sets, thereby adjusting the capacitor voltage balance of each submodule. As can be seen from the above technical solutions, the embodiments of this application have the following advantages: The energy balancing control method of the modular DC transformer controls the corresponding sub-modules to absorb the corresponding absorbed energy in sequence according to the order of the capacitor voltage set by the pulse phase shift sequence, so as to adjust the capacitor voltage balance of each sub-module; the duty cycle of the secondary voltage of the intermediate frequency transformer can be changed by the pulse phase shift, thereby making the capacitor energy of the MMDC sub-modules in the modular DC transformer balanced and operating normally in the full range; it solves the technical problem that the instability or imbalance of energy of any sub-module or bridge arm unit inside the existing modular multilevel DC converter MMDC will affect the normal operation of the converter. Attached Figure Description

[0047] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0048] Figure 1 This is a diagram of the MMDC topology of the modular DC transformer energy equalization control method described in the embodiments of this application.

[0049] Figure 2 This is a diagram of the half-bridge sub-module structure of the MMDC in the energy equalization control method for modular DC transformers described in this application embodiment.

[0050] Figure 3 This is a structural diagram of a single sub-module of the energy equalization control method for modular DC transformers described in the embodiments of this application;

[0051] Figure 4 This is a structural diagram of the MMDC series submodule of the energy equalization control method for the modular DC transformer described in the embodiments of this application;

[0052] Figure 5 This is a waveform diagram of the equivalent voltage across the two ends of the modular DC transformer described in the embodiments of this application;

[0053] Figure 6 This is a flowchart illustrating the steps of the energy equalization control method for a modular DC transformer described in an embodiment of this application.

[0054] Figure 7 This is a flowchart illustrating the energy balance sorting process in the energy balance control method for modular DC transformers described in this application embodiment.

[0055] Figure 8 This is a diagram showing the operating range of the energy balance sorting in the energy balance control method for the modular DC transformer described in this application embodiment;

[0056] Figure 9 This is a diagram showing the operating range of the MMDC in the energy equalization control method for modular DC transformers described in the embodiments of this application.

[0057] Figure 10 This is a simulation diagram of Case 1 of the modular DC transformer energy balance control method described in the embodiments of this application;

[0058] Figure 11 This is a simulation diagram of Case 2 of the modular DC transformer energy balance control method described in the embodiments of this application;

[0059] Figure 12 This is a simulation diagram of Case 3 of the modular DC transformer energy balance control method described in the embodiments of this application;

[0060] Figure 13 This is a simulation diagram of Case 4 of the modular DC transformer energy balance control method described in the embodiments of this application;

[0061] Figure 14 This is a schematic diagram of the energy balancing control device for the modular DC transformer described in the embodiments of this application;

[0062] Figure 15 This is a schematic diagram of the terminal device described in an embodiment of this application. Detailed Implementation

[0063] To make the inventive objectives, features, and advantages of this application more apparent and understandable, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0064] In the description of the embodiments of this application, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0065] In the embodiments of this application, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0066] With the increasing penetration of renewable energy resources (RES), DC distribution systems are performing better and better in terms of efficiency, scalability, and stability, making them the preferred transmission system for power grids. Most renewable energy sources, such as solar panels and fuel cells, and energy storage systems (ESS), such as batteries, are essential DC sources. Using DC power grids eliminates the need for DC-AC conversion stages, reducing power losses and component costs. Even for wind or gas turbines, a single-stage AC-DC conversion is more efficient than a two-stage AC-DC-AC conversion. The same principle can be applied to electronic loads such as personal computers and variable-speed appliances.

[0067] With fewer rectifiers and power factor correctors, DC power distribution systems can save approximately 25% of components and 8% of power losses. Furthermore, connecting RES and ESS to a DC power distribution system that only considers amplitude is simpler when frequency and phase synchronization issues are not present. The effectiveness of DC power distribution systems has been proven in several industrial applications, such as telecommunications systems, aircraft, and ships.

[0068] The DC power distribution system was proposed by Thomas Edison over 100 years ago. In the competition between DC and AC systems, AC systems won because DC voltage could not be transmitted as easily. However, with advancements in power electronic devices, magnetic materials, and microprocessors, this technological barrier has been overcome. Now, DC voltage can be transformed to different levels using a DC transformer, essentially a high-voltage bidirectional DC-DC converter with thermocouple isolation. The DC voltage is inverted to an intermediate-frequency AC voltage, which is then stepped up or stepped down using an intermediate-frequency transformer, and finally rectified back to DC voltage.

[0069] There are existing DC transformers that use a single MF transformer with a Modular Multilevel DC Converter (MMDC). Figure 1 This is a schematic diagram of a single-phase MMDC (Multi-Level Converter). The MMDC is derived from the Dual Active Bridge (DAB) and Modular Multilevel Converter (MMDC), inheriting the excellent characteristics of both topologies. Like other MMDCs, the MMDC internally uses series submodules (SMs) to support high voltages. A crucial control aspect of the MMDC is the equalization of the submodule capacitor voltages, which is essential for ensuring stable operation and represents a significant control problem that needs to be addressed.

[0070] This application provides an energy balancing control method, apparatus, and device for a modular DC transformer, which solves the technical problem that instability or imbalance of energy in any sub-module or bridge arm unit within an existing modular multilevel DC converter (MMDC) will affect the normal operation of the converter.

[0071] In the embodiments of this application, such as Figure 1 As shown, the MMDC topology includes a sequentially connected MMDC full-bridge submodule structure, an intermediate frequency transformer, and a full-bridge structure. The MMDC full-bridge submodule structure is composed of submodules connected in series. The intermediate frequency transformer is used for electrical isolation. The full-bridge structure consists of IGBT switching transistors. The MMDC full-bridge submodule structure includes at least two phase units. Each phase unit consists of an upper bridge arm and a lower bridge arm. The positive terminal of the DC side is connected to the positive terminal of the upper bridge arm of each phase unit, and the negative terminal of the DC side is connected to the negative terminal of the lower bridge arm. In each bridge arm, n submodules (represented by SM1 to SMn) with identical circuit parameters are connected in series, along with a bridge arm inductor Lp connected in series within the bridge arm. The negative terminal of the upper bridge arm and the positive terminal of the lower bridge arm are each connected in series with the bridge arm inductor Lp and then led out to form the AC output side of each phase unit.

[0072] It should be noted that the MMDC full-bridge submodule structure includes full-bridge, half-bridge, and other submodules. Each submodule consists of IGBTs and capacitors, such as... Figure 2 The working principle of the half-bridge submodule is illustrated using the half-bridge structure shown as an example. In this embodiment, the working principle of the half-bridge submodule includes controlling, for example... Figure 3 The different on or off states of the switching devices T1 and T2 shown can switch between the three operating states of the half-bridge submodule.

[0073] In this embodiment, the three operating states of the half-bridge submodule are: active operating state, deactivated operating state, and latched operating state. The active operating state includes: when switching device T1 is turned on and switching device T2 is turned off, the half-bridge submodule is in the active operating state; when the half-bridge submodule is in the active operating state, the freewheeling diode D2 is subjected to the submodule capacitor voltage v. c And reverse cutoff. When the current i flowing into the submodule arm When the current is greater than 0, the submodule current flows through the freewheeling diode D1 and the submodule capacitor C. sm A current path is formed, and electrical energy is fed into capacitor C from both ends of the submodule. sm Submodule capacitor C sm Charging. When the current i flowing into the submodule arm When <0, the submodule current i arm Through switching device T1, submodule capacitor C sm A current path is formed, and the submodule absorbs electrical energy from the capacitor side at both ends. The submodule capacitor C sm Discharge. Regardless of the direction of the current flowing into the submodule, the voltage u across the submodule remains constant. SM Both are related to the submodule capacitor voltage v c Equal. The content of the disconnected operating state includes: when switching device T1 is off and switching device T2 is on, the half-bridge submodule is in the disconnected operating state; when the half-bridge submodule is in the disconnected operating state, the freewheeling diode D1 is subjected to the submodule capacitor voltage v. c And reverse cutoff. When the current i flowing into the submodule arm When the current is greater than 0, the submodule current forms a current path through the switching device T2. When the current i flowing into the submodule... arm When <0, the submodule current i arm A current path is formed through the freewheeling diode D2. Regardless of the direction of the current flowing into the submodule, the submodule capacitance C... sm All are bypassed and not connected to the current path; the voltage u across the submodule is... SMThe value is 0. The latching operation state includes: when both switching devices T1 and T2 are off, the half-bridge submodule is in a latched operation state; when the half-bridge submodule is in a latched operation state, current cannot flow through switching device T1 (off) or switching device T2, and must flow through freewheeling diode D1 or freewheeling diode D2 to form a path. When the current i flowing into the submodule... arm When the current is greater than 0, the submodule current flows through the freewheeling diode D1 and the submodule capacitor C. sm A current path is formed, and electrical energy is fed into capacitor C from both ends of the submodule. sm Submodule capacitor C sm Charging, voltage u at both ends of the submodule SM Both are related to the submodule capacitor voltage v c Equal. When the current i flowing into the submodule arm When <0, the submodule current i arm A 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 across the submodule is... SM The value is 0. During the steady-state normal operation of the MMDC topology transmission system, the submodules of the MMDC topology only use two operating states: connected and disconnected. The interlocked operating state is not used; it is only used during the startup or fault period of the MMDC topology transmission system.

[0074] In this embodiment of the application, the working principle of the MMDC full-bridge submodule structure includes:

[0075] When switching device T1 or freewheeling diode D1 is turned on, the submodule is engaged, and the bridge arm current i arm The capacitor C flowing through the submodule sm Submodule output voltage v sm =v c ;

[0076] When switching device T2 or freewheeling diode D2 is turned on, the submodule is disconnected, and the output voltage v sm =0.

[0077] It should be noted that the output voltage v of the entire bridge arm arm Let V be the sum of the output voltages of each submodule, and the average capacitor voltage of each submodule be V. c The sum of the average voltages of all capacitors within the bridge arm, V arm =nV c (n is the number of submodules in the bridge arm). Ignore submodule capacitor voltage ripple, S sm S is the switch function for the submodule. sm =1 corresponds to the submodule being put into operation; S sm =0 corresponds to the cut-off state of the submodule. T sThe switching period is denoted by Ds, where S is the switching period. sm Duty cycle. Bridge arm switching function S sm This is the sum of the switching functions of each submodule. The input voltage v of the submodule chain. arm The sum of the voltages applied to each submodule. From Figure 5 As can be seen, in the quasi-two-level modulation mode, except for the stepped wave voltage edge, the control process and voltage and current waveforms of the bridge arms of the MMDC full-bridge submodule structure are basically the same as those of a single submodule. Ignoring the transient transition process of the bridge arm voltage between zero and high levels, and treating the quasi-two-level voltage as a two-level voltage, the bridge arm of the MMDC full-bridge submodule structure can be considered as a single large submodule with a capacitor voltage of NVc. Figure 4 As shown.

[0078] In this embodiment of the application, the submodule switching function S sm The expression is:

[0079]

[0080] In the formula, t0 is the starting point of the switching cycle, t is the independent variable time, and D s The on-time of the switch within one switching cycle. The output voltage v of the submodule. sm It can be written as a switching function S sm and sub-module capacitor voltage v c The product of, i.e., v sm =v c S sm In quasi-two-level modulation mode, ignoring capacitor voltage ripple and transient transitions in bridge arm voltages, the entire submodule chain can be equivalent to a single submodule with capacitor voltage multiplied by N. At this point, the sum of the bridge arm capacitor voltages, V... arm for:

[0081]

[0082] In the formula, v c,i Let be the capacitor voltage of the i-th submodule in the submodule chain. A quasi-two-level modulation of the isolated MMDC is achieved using control pulse phase shifting. The equivalent voltage waveform across the modular DC transformer in quasi-two-level modulation mode is shown below. Figure 5 As shown.

[0083] In this embodiment, based on the principle of having an area equal to that enclosed by the time axis, the primary voltage v of the intermediate frequency voltage transformer in the modular DC transformer is... po The rising and falling phases of a stepped wave can be equivalent to a wave with a slope of 2V. dc1 / d N A first-order curve, d N V represents the maximum phase shift within half a cycle of the submodule. dc1This refers to the input voltage of the modular DC transformer. For example... Figure 1 and Figure 5 As shown, the steady-state operation of the isolated MMDC is decomposed by combining the equivalent voltage transformation process of the primary and secondary sides. Since the AC voltage and current waveforms are symmetrical in the first and second halves of the operating cycle, the operating mode of the isolated MMDC in the first half of the cycle is analyzed as an example. Before time t0, all sub-modules of the lower arm of phase A on the primary side of the modular DC transformer are disconnected, and all sub-modules of the upper arm are engaged; all sub-modules of the lower arm of phase B on the primary side of the modular DC transformer are engaged, and all sub-modules of the upper arm are disconnected; the upper arm switch of phase A on the secondary side of the modular DC transformer is open, and the lower arm switch is closed; the upper arm switch of phase B on the secondary side of the modular DC transformer is closed, and the lower arm switch is open. At this time, the voltage and current of the intermediate frequency transformer can be expressed by the first formula. The first formula is:

[0084]

[0085] In the formula, V dc2 V is the output voltage of the modular DC transformer. po (t) represents the primary AC voltage of the intermediate frequency transformer, nV so (t) represents the equivalent voltage on the primary AC side of the intermediate frequency transformer, i p (t) represents the primary AC current of the intermediate frequency transformer.

[0086] Example 1:

[0087] Figure 6 This is a flowchart illustrating the steps of the energy balance control method for a modular DC transformer described in this application. Figure 7 This is a flowchart illustrating the energy balance sorting process in the energy balance control method for modular DC transformers described in this application.

[0088] like Figure 6 and Figure 7 As shown in the figure, this application provides an energy equalization control method for a modular DC transformer, including the following steps:

[0089] S1. Obtain the capacitor voltage and pulse phase shift of each submodule of the bridge arm in the modular DC transformer at any time period, and determine whether the capacitor voltages of each submodule are balanced based on the capacitor voltages of each submodule.

[0090] It should be noted that in step S1, the capacitor voltage and phase shift pulse of each sub-module of the bridge arm in the modular DC transformer are obtained at any time period, and then it is determined whether the capacitor voltage of the collected sub-module is unbalanced.

[0091] In this embodiment, the rule for determining whether the capacitor voltage of the submodule is unbalanced is: if the capacitor voltage of the submodule is within the set voltage range, then 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, then the capacitor voltage of the submodule is in an unbalanced state.

[0092] It should be noted that in other embodiments, determining whether the capacitor voltage of a submodule is unbalanced can also be done by comparing the difference in capacitor voltage between two adjacent moments with a set threshold. Whether the difference in capacitor voltage falls within the set threshold range indicates whether the capacitor voltage of the submodule is in a balanced state. For example, if the difference in capacitor voltage of the submodule is within the set threshold range, then the capacitor voltage of the submodule is in a balanced state; if the difference in capacitor voltage of the submodule is not within the set threshold range, then the capacitor voltage of the submodule is in an unbalanced state. The set voltage and set threshold can be set according to requirements and are not specifically limited here.

[0093] S2. If at least one submodule has an unbalanced capacitor voltage, sort all pulse phase shifts in ascending order to obtain the pulse phase shift sequence of the bridge arm; sort all capacitor voltages in ascending order to obtain the sorted set of capacitor voltages of the bridge arm.

[0094] 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 capacitor voltages and pulse phase shifts collected in step S1 are sorted from smallest to largest to obtain the corresponding capacitor voltage set and pulse phase shift sequence. In this embodiment, the voltage shift ratio D of the primary and secondary sides of the intermediate frequency transformer of the modular DC transformer is affected by the operating conditions of the intermediate frequency converter and changes with the transmission power. During the change of D, the maximum pulse phase shift d of the submodule is calculated. N This leads to the determination of an incremental pulse phase-shifting sequence. To eliminate higher harmonics in the AC link voltage, a centrally symmetrical pulse phase-shifting sequence can be used. The maximum pulse phase shift d... N It is determined based on the phase shift time Δt of each submodule and the number of submodules n in the bridge arm, d N =Δt×n.

[0095] S3. Obtain the parameter data of each sub-module of the bridge arm in the modular DC transformer during the time period, and calculate the absorbed energy of the corresponding sub-module during the time period based on the parameter data of each sub-module.

[0096] It should be noted that in step S3, based on the premise of judging the capacitor voltage imbalance of the sub-module in step S1, the parameter data of each sub-module in the time period corresponding to step S1 is obtained, and then the absorbed energy of each sub-module in the time period is calculated based on the obtained parameter data.

[0097] S4. Based on the pulse phase shift sequence and the order of the capacitor voltage sets, control the corresponding sub-modules to absorb the corresponding absorbed energy in sequence, so as to adjust the capacitor voltage balance of each sub-module.

[0098] It should be noted that in step S4, based on the pulse phase shift sequence and capacitor voltage set obtained in step S2 and the energy absorbed by each submodule obtained in step S3, the submodule with the smaller pulse phase shift and higher energy allocation is controlled to absorb energy first, thereby achieving the balance of capacitor voltages among the submodules. This modular DC transformer energy balancing control method implements a submodule pulse regulation and allocation mechanism. It requires sampling and sorting the capacitor voltages of the submodules in each bridge arm. In the next switching cycle, the drive signal with the smaller pulse phase shift (i.e., higher energy allocation) controls the submodule with the lower capacitor voltage, and the drive signal with the larger pulse phase shift (i.e., lower energy allocation) controls the submodule with the higher capacitor voltage. Figure 7 As shown, the sorted pulse phase shift sequence d1-d k -d N The corresponding submodule's switch signals S1-S N The energy levels decrease from top to bottom. The capacitor voltages of the submodules are sorted, and the submodule with the lower capacitor voltage is controlled by the drive signal with the smaller pulse shift ratio (i.e., the one allocated more energy); and vice versa.

[0099] In this embodiment, the energy balancing control method for the modular DC transformer changes the duty cycle of the secondary voltage of the intermediate frequency transformer by pulse phase shifting, thereby altering the secondary voltage and the current waveform. The energy absorbed by the capacitor of a sub-module within one switching cycle is related to the current flowing through the bridge arm; therefore, the energy absorbed by the capacitor of the sub-module corresponding to the phase shift of the control pulse will also change within one cycle. This solves the problem of energy imbalance in the sub-module capacitors of the modular DC transformer caused by fluctuations in the primary side voltage and overall power of the transformer.

[0100] Figure 8 This is a diagram showing the operating range of energy balance sorting in the energy balance control method for modular DC transformers described in this application.

[0101] It should be noted that in traditional submodule energy balance sorting control algorithms, such as Figure 7 and Figure 8 As shown, when S k+1 The submodule controlled by (the (k+1)th pulse) absorbs less than S charge in one switching cycle. k The charge absorbed by the submodule controlled by (the k-th pulse), Q k For the independent variable d kThe decreasing sequence. This means that using a larger pulse phase shift to drive the submodule actually results in the corresponding submodule gaining relatively less energy in one switching cycle. Therefore, the energy absorbed by each submodule in one switching cycle is related to the pulse phase shift d between submodules. k The decreasing function, d k Submodules driven by larger control pulses absorb less energy. The pulses between submodules are phase-shifted by d. k If an increasing sequence is selected, then the corresponding signal sequence S driving each submodule is... k The energy allocated to submodules exhibits a decreasing characteristic.

[0102] This application provides an energy balancing control method for a modular DC transformer. The method includes: acquiring the capacitor voltage and pulse phase shift of each submodule in the bridge arm of the modular DC transformer at any given time period; determining whether the capacitor voltages of each submodule are balanced based on their respective capacitor voltages; if at least one submodule has an unbalanced capacitor voltage, obtaining the pulse phase shift sequence of the bridge arm by sorting all pulse phase shifts from smallest to largest; obtaining the sorted set of capacitor voltages for the bridge arm by sorting all capacitor voltages from smallest to largest; acquiring the parameter data of each submodule in the bridge arm of the modular DC transformer during that time period; calculating the absorbed energy of the corresponding submodule during that time period based on the parameter data of each submodule; and controlling the corresponding submodule to absorb the corresponding absorbed energy sequentially according to the pulse phase shift sequence and the sorting of the capacitor voltage sets, thereby adjusting the capacitor voltage balance of each submodule. This modular DC transformer energy balancing control method uses a pulse phase-shifting sequence to control the corresponding sub-modules to absorb the corresponding energy in sequence according to the order of the capacitor voltage set, thereby adjusting the capacitor voltage balance of each sub-module. The pulse phase shifting can change the duty cycle of the secondary voltage of the intermediate frequency transformer, thereby making the capacitor energy of the MMDC sub-modules in the modular DC transformer balanced and operating normally across the entire range. It solves the technical problem that the instability or imbalance of energy in any sub-module or bridge arm unit within the existing modular multilevel DC converter (MMDC) will affect the normal operation of the converter.

[0103] In one embodiment of this application, the parameter data of the submodule includes pulse phase shift and the duration of half a switching cycle of the submodule. Calculating the absorbed energy of the corresponding submodule within this time period based on the parameter data of each submodule includes:

[0104] Obtain the bridge arm current corresponding to the submodule during the time period, as well as the start and end times of the time period;

[0105] The energy absorbed by the corresponding submodule during this time period is calculated using the formula for absorbed charge based on pulse phase shift, half-switching cycle duration, bridge arm current, initial time, and end time.

[0106] The formula for the amount of absorbed charge is:

[0107]

[0108] In the formula, Q i For the energy absorbed by the i-th submodule, t end Let t be the end time of time interval t. start Let d be the initial time of time interval t. i For the pulse phase shift of the i-th submodule, T h For half a switching cycle duration, i al (t) represents the bridge arm current during time interval t.

[0109] It should be noted that the energy balance control method of this modular DC transformer is based on the amount of charge absorbed by the submodule in each switching cycle as the bridge arm current i. al The integral over the module input interval is equal to i al The area enclosed by the time axis within the corresponding time period. For example, the pulse S within one switching cycle. k The charge Q absorbed by the exchange control submodule in a switch k Then Q k for

[0110]

[0111] In the formula, such as Figure 5 As shown, t0 is the start time of a switching cycle, and t3 is the end time of a switching cycle.

[0112] In one embodiment of this application, obtaining the bridge arm current corresponding to the submodule during the time period includes:

[0113] Obtain the input voltage of the modular DC transformer, the differential mode current component of its bridge arm, and the transmission power of its intermediate frequency transformer during the specified time period.

[0114] The common-mode current of the corresponding bridge arm is calculated based on the transmission power and input voltage.

[0115] The bridge arm current during this time period is obtained by using the bridge arm current formula based on the common-mode current and differential-mode current components.

[0116] The formula for the bridge arm current is: i al =I dc1 / 2-i / 2, I dc1 =P / V dc1 In the formula, i al For the bridge arm current, I dc1 V 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 dc1This refers to the input voltage of the modular DC transformer.

[0117] It should be noted that the bridge arm current of the MMDC full-bridge submodule structure is the difference between the common-mode current and the differential-mode current of the bridge arm.

[0118] In one embodiment of this application, obtaining the transmission power of the intermediate frequency transformer includes:

[0119] The operating modes of each sub-module of the bridge arm in the modular DC transformer are determined based on this time period. The operating modes include the first operating mode, the second operating mode, and / or the third operating mode.

[0120] Obtain the electrical parameters of the modular DC transformer, and calculate the total energy absorbed by the primary side of the AC side of the intermediate frequency transformer based on the operating mode and electrical parameters. The electrical parameters include the equivalent voltage of the primary AC side, the maximum pulse phase shift, the input voltage, the output voltage, the duration of half a switching cycle, the equivalent inductance of the primary side, and the transformation ratio.

[0121] The transmission power of the intermediate frequency transformer is calculated based on the total energy absorbed by the primary side and the duration of half a switching cycle.

[0122] It should be noted that calculating the transmission power of the intermediate frequency transformer requires determining the operating mode of each sub-module during that time period. Based on the operating mode, the total energy absorbed by the primary side of the intermediate frequency transformer is calculated, and the transmission power of the intermediate frequency transformer is obtained by dividing the total energy absorbed by the primary side by half the switching cycle duration.

[0123] In one embodiment of this application, if the operating mode includes one operating mode, obtaining the total energy absorbed by the primary side of the intermediate frequency transformer on the AC side includes: calculating the primary AC side voltage and primary AC side current of the intermediate frequency transformer based on the electrical quantity parameters corresponding to the operating mode; calculating the primary side energy absorbed by the intermediate frequency transformer in that operating mode based on the primary AC side voltage and primary AC side current, and using the primary side absorbed energy as the total primary side energy absorbed by the intermediate frequency transformer on the AC side. If the operating mode includes at least two operating modes, obtaining the total primary side energy absorbed by the intermediate frequency transformer on the AC side includes:

[0124] Based on the electrical parameters corresponding to each operating mode, the primary AC voltage and primary AC current of the transformer under the corresponding operating mode are calculated.

[0125] The primary-side AC voltage and primary-side AC current are used to calculate the primary-side energy absorbed by the intermediate frequency transformer under the corresponding operating mode.

[0126] The sum of the primary-side absorbed energy under all operating modes is taken as the total primary-side absorbed energy of the AC side of the intermediate frequency transformer.

[0127] It should be noted that if each submodule of the bridge arm in the modular DC transformer is in the first operating mode, the time period of the first operating mode is... Figure 5 As shown in the time interval t0-t1, during this period, the lower bridge arm submodules of phase A on the primary side of the modular DC transformer are sequentially engaged according to a pulse phase-shifting sequence, while the upper bridge arm submodules are sequentially disengaged; similarly, the lower bridge arm submodules of phase B on the modular DC transformer are sequentially disengaged according to a pulse phase-shifting sequence, while the upper bridge arm submodules are sequentially engaged. Under this first operating mode, the primary voltage v of the intermediate frequency transformer... po The voltage increases linearly. The upper arm switch of phase A on the secondary side of the intermediate frequency transformer is open, and the lower arm switch of phase A on the secondary side of the intermediate frequency transformer is closed. The upper arm switch of phase B on the secondary side of the intermediate frequency transformer is closed, and the lower arm switch of phase B on the secondary side of the intermediate frequency transformer is open. Voltage nV so -nV dc2 nV dc2 This is the voltage equivalent to the primary side of the secondary side of the intermediate frequency transformer. Based on the operating mode (first operating mode) and electrical parameters, the energy absorbed by the primary side of the AC side of the intermediate frequency transformer is calculated using the first energy calculation formula:

[0128]

[0129]

[0130] In the formula, d N For maximum pulse phase shift, L ac T is the primary-side equivalent inductance. h E1 represents half a switching cycle duration and is the primary-side energy absorbed in the first operating mode.

[0131] In the embodiments of this application, if each sub-module of the bridge arm in the modular DC transformer is in the second operating mode, the time period of the second operating mode is... Figure 5 As shown in the time interval t1-t2, during this interval, the lower bridge arm submodules of phase A on the primary side of the modular DC transformer are sequentially engaged according to a pulse phase-shifting sequence, while the upper bridge arm submodules are sequentially disengaged; similarly, the lower bridge arm submodules of phase B on the modular DC transformer are sequentially disengaged according to a pulse phase-shifting sequence, while the upper bridge arm submodules are sequentially engaged. Under this second operating mode, the primary voltage v of the intermediate frequency transformer... po The voltage rises linearly. The upper arm switch of phase A on the secondary side of the intermediate frequency transformer closes, and the lower arm switch of phase A on the secondary side of the intermediate frequency transformer opens. The upper arm switch of phase B on the secondary side of the intermediate frequency transformer opens, and the lower arm switch of phase B on the secondary side of the intermediate frequency transformer closes. The secondary voltage of the intermediate frequency transformer is nV. so For nV dc2 nV dc2This is the voltage equivalent to the primary side of the secondary side of the intermediate frequency transformer; the primary voltage of the intermediate frequency transformer is at a high level and equal to the input constant voltage V. dc1 Based on the second operating mode and electrical parameters, the energy absorbed by the primary side of the AC side of the intermediate frequency transformer is calculated using the second energy calculation formula. The second energy calculation formula is as follows:

[0132]

[0133]

[0134] In the formula, E2 is the primary-side absorbed energy of the second working mode.

[0135] In the embodiments of this application, if each sub-module of the bridge arm in the modular DC transformer is in the third operating mode, the time period of the third operating mode is... Figure 5 As shown in the time interval t2-t3, during this period, all the lower bridge arm submodules of phase A on the primary side of the modular DC transformer are engaged, and all the upper bridge arm submodules are disengaged; all the lower bridge arm submodules of phase B on the modular DC transformer are disengaged, and all the upper bridge arm submodules are engaged. The upper bridge arm switch of phase A on the secondary side of the intermediate frequency transformer is closed, and the lower bridge arm switch of phase A on the secondary side of the intermediate frequency transformer is open. The upper bridge arm switch of phase B on the secondary side of the intermediate frequency transformer is open, and the lower bridge arm switch of phase B on the secondary side of the intermediate frequency transformer is closed. The secondary voltage nV of the intermediate frequency transformer... so Maintain at nV dc2 nV dc2 This is the voltage equivalent to the primary side of the secondary side of the intermediate frequency transformer. Based on the third operating mode and electrical parameters, the energy absorbed by the primary side of the AC side of the intermediate frequency transformer is calculated using the third energy calculation formula:

[0136]

[0137]

[0138] In the formula, E3 is the primary-side absorbed energy of the third working mode.

[0139] Figure 9 This is a diagram showing the operating range of the MMDC in the energy equalization control method for the modular DC transformer described in the embodiments of this application.

[0140] In the embodiments of this application, the energy equalization control method for the modular DC transformer is illustrated as Case 1, with a secondary duty cycle of 0.4 and a primary-secondary shift ratio of 0.055 for half a cycle. The operating mode within half a cycle of Case 1 includes: based on the principle of equal area enclosed by the time axis, the primary voltage v of the intermediate frequency transformer... po The rising and falling phases of a stepped wave can be equivalent to a wave with a slope of 2V.dc1 / d N A curve of the first degree, where v po The waveform can be simplified to a trapezoidal wave. Before time t0, all lower bridge arm submodules of phase A on the primary side are disconnected, and all upper bridge arm submodules are engaged; all lower bridge arm submodules of phase B on the primary side are engaged, and all upper bridge arm submodules are disconnected; all secondary-side switches of the transformer are closed. The upper bridge arm switch of phase A on the secondary side of the intermediate frequency transformer is open, and the lower bridge arm switch is closed. The upper bridge arm switch of phase B on the secondary side of the intermediate frequency transformer is closed, and the lower bridge arm switch is open. At this time, the transformer voltage and current can be expressed as...

[0141]

[0142] Mode 1 (t0-t1): Within the interval t0-t1, the primary side A-phase lower arm submodule follows the delayed pulse phase shift sequence d1-d... k -d N One by one, the upper bridge arm submodules are deployed and then disconnected one by one; the lower bridge arm submodules of phase B are deployed according to the delayed pulse phase shift sequence d1-d k -d N The upper bridge arm submodules are disconnected one by one, and then connected one by one. In this mode, the primary-side voltage Vpo rises linearly. On the secondary side, the upper bridge arm switch of phase A is open, and the lower bridge arm switch is closed. On the secondary side, the upper bridge arm switch of phase B is closed, and the lower bridge arm switch is open. Voltage nV so -nV dc2 The transformer voltage and current can be expressed as:

[0143]

[0144] Mode 2 (t1-t2): Under this condition, all lower bridge arm submodules of the original A phase are engaged, and all upper bridge arm submodules are disengaged; all lower bridge arm submodules of the original B phase are disengaged, and all upper bridge arm submodules are engaged. All secondary-side switches are closed. Secondary-side voltage nV. so When the value is 0, the primary voltage is at a high level and equal to V. dc1 In this mode, the transformer voltage and current are:

[0145]

[0146] By integrating the product of the primary voltage and current of the transformer over the interval t1-t2, we can obtain the energy absorbed by the AC side from the primary MMDC converter under this operating mode:

[0147]

[0148] Mode 3 (t2-t3): Under this condition, all lower bridge arm submodules of the primary A phase are engaged, and all upper bridge arm submodules are disengaged; all lower bridge arm submodules of the primary B phase are disengaged, and all upper bridge arm submodules are engaged. The upper bridge arm switch of the secondary A phase is closed, and the lower bridge arm switch is open. The upper bridge arm switch of the secondary B phase is open, and the lower bridge arm switch is closed. The transformer voltage and current at this time can be expressed as:

[0149]

[0150] By integrating the product of the primary voltage and current of the transformer over the interval t2-t3, we can obtain the energy absorbed by the AC side from the primary MMDC converter under this operating mode:

[0151]

[0152] Mode 3 (t3-t4): Under this condition, all lower bridge arm submodules of the original A phase are engaged, and all upper bridge arm submodules are disengaged; all lower bridge arm submodules of the original B phase are disengaged, and all upper bridge arm submodules are engaged. All secondary-side switching transistors of the transformer are closed. The transformer voltage and current at this time can be expressed as follows:

[0153]

[0154] By integrating the product of the primary voltage and current of the transformer over the interval (t3-t4), we can obtain the energy absorbed by the AC side from the primary MMDC converter under this operating mode.

[0155]

[0156] The transmission power of the intermediate frequency transformer is:

[0157]

[0158] In the formula, P is the transmission power of the intermediate frequency transformer.

[0159] The bridge arm current is i al =I dc1 / 2-i / 2. The amount of charge absorbed by the submodule in each switching cycle is the lower bridge arm current i. al The integral over the module input interval is equal to i al The area enclosed by the time axis within the corresponding time period. For example, the amount of charge absorbed by the submodule controlled by pulse Sk during one switching cycle in one switching cycle is...

[0160]

[0161] If the transmission power of the modular DC transformer is: pu=f(D,d,v) po ,nv soIn the formula, pu is the per-unit value of the rated power, D is the duty cycle of the secondary square wave voltage, d is the shift ratio between the primary and secondary sides of the transformer, and v po The primary voltage of the transformer is nV. so Let be the voltage equivalent to the primary side of the transformer secondary. Then the current ial flowing through the lower arm of phase A of submodule A is i. al =f(D,d,vpo,nvso). By analyzing the energy absorbed by the submodule capacitor controlled by each pulse within one switching cycle, it is found that the energy absorbed by the submodule capacitor within each bridge arm is monotonic within the range shown in the shaded area below. Figure 9 It is known that, under the same power, by reducing the duty cycle of the secondary-side square wave voltage, the energy absorbed by each submodule in one switching cycle can be made a decreasing function of the pulse phase shift between submodules, thus enabling the use of the energy balance control method for this modular DC transformer. After the control cycle begins, the capacitor voltage of the bridge arm submodule is first detected. If the submodule capacitor voltage is already balanced, the existing sorting algorithm continues to control it. If the submodule capacitor voltage is unbalanced, the current phase shift, power, and duty cycle are detected, and the energy balance control method for this modular DC transformer is applied. Figure 9 The duty cycle of the submodule is adjusted according to its operating range. When the duty cycle is adjusted to its operating range, the energy absorbed by each submodule in one switching cycle is a monotonic function of the pulse phase shift between submodules, and then a sorting algorithm is applied to them.

[0162] Figure 10 This is a simulation diagram of Case 1 of the modular DC transformer energy balance control method described in this application. Figure 11 This is a simulation diagram of Case 2 of the modular DC transformer energy balance control method described in the embodiments of this application. Figure 12 This is a simulation diagram of Case 3 of the modular DC transformer energy balance control method described in the embodiments of this application. Figure 13 This is a simulation diagram of Case 4 of the modular DC transformer energy balance control method described in the embodiments of this application.

[0163] In the embodiments of this application, the energy balance control method of the modular DC transformer is simulated through Case 1, Case 2, Case 3, and Case 4. According to... Figure 1 The modular DC transformer shown is constructed using MATLAB / Simulink software. Figure 1 The modular DC transformer structure shown is used for simulation verification of this topology. The simulation parameters are shown in Table 1 below. Figure 10As shown, after steady state, the four sub-modules are in energy balance. However, in some cases, the energy absorbed by each sub-module in one switching cycle is not a decreasing function of the pulse phase shift between sub-modules, thus making the sorting algorithm unusable. Under otherwise unchanged conditions, when the primary voltage is 20kV, the voltage of the sub-modules using the sorting algorithm is as follows: Figure 11 As shown. The energy absorbed by each submodule in one switching cycle is not a decreasing function of the pulse phase shift between submodules, resulting in the energy corresponding to each submodule pulse being non-monotonic, thus causing the submodule capacitor voltage to diverge. It is well known that the transmission power must remain constant during converter operation. Under the same transmission power of 0.1 pu, when the duty cycle is 50%, combined with... Figure 11 and Figure 12 If the capacitor voltage in the submodule cannot be balanced and becomes unbalanced, it can lead to overcharging and damage to the device. Under the above conditions, adjusting the duty cycle to 45% while keeping other conditions unchanged, simulations show... Figure 13 As verified by theory, the voltage of the submodule capacitors is now balanced.

[0164] Table 1 shows the simulation parameters.

[0165] Switching frequency 1kHz Transmission power 1MW AC side equivalent inductance 0.0375H Capacitance value of submodule capacitor 2.2mF Number of bridge arm sub-modules 4 primary voltage 18kV Secondary voltage 750V Phase shifting between each submodule 5us

[0166] It should be noted that the parameters for Case 1 are a primary voltage of 18kV and a duty cycle of 50% for the modular DC transformer. The parameters for Case 2 are a primary voltage of 20kV and a duty cycle of 50% for the modular DC transformer. The parameters for Case 3 are a primary voltage of 18kV, a duty cycle of 40%, and a power of 0.1pu for the modular DC transformer. The parameters for Case 4 are a primary voltage of 20kV, a duty cycle of 45%, and a power of 0.1pu for the modular DC transformer.

[0167] Example 2:

[0168] Figure 14 This is a schematic diagram of the energy balancing control device for the modular DC transformer described in this application embodiment.

[0169] like Figure 14 As shown, this application embodiment provides an energy balancing 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;

[0170] The data acquisition and judgment module 10 is used to acquire the capacitor voltage and pulse phase shift of each sub-module of the bridge arm in the modular DC transformer at any time period, and to judge whether the capacitor voltage of each sub-module is balanced based on the capacitor voltage of each sub-module.

[0171] The data sorting module 20 is used to sort all pulse phase shifts in ascending order based on the capacitor voltage imbalance of at least one submodule to obtain the pulse phase shift sequence of the bridge arm; and to sort all capacitor voltages in ascending order to obtain the sorted capacitor voltage set of the bridge arm.

[0172] The calculation module 30 is used to obtain the parameter data of each sub-module of the bridge arm in the modular DC transformer during the time period, and calculate the absorbed energy of the corresponding sub-module during the time period based on the parameter data of each sub-module.

[0173] The balance adjustment module 40 is used to control the corresponding sub-modules to absorb the corresponding energy in sequence according to the pulse phase shift sequence and the order of the capacitor voltage set, so as to adjust the capacitor voltage balance of each sub-module.

[0174] In this embodiment, the parameter data of the submodule includes pulse phase shift and half a switching cycle duration of the submodule, and the calculation module 30 includes a parameter acquisition submodule and a calculation submodule;

[0175] The parameter acquisition submodule is used to acquire the bridge arm current corresponding to the submodule during the time period, as well as the start and end times of the time period.

[0176] The calculation submodule is used to calculate the energy absorbed by the corresponding submodule during the time period based on the pulse phase shift, half-switching cycle duration, bridge arm current, initial time, and end time using the formula for absorbed charge.

[0177] The formula for the amount of absorbed charge is:

[0178]

[0179] In the formula, Q i For the energy absorbed by the i-th submodule, t end Let t be the end time of time interval t. start Let d be the initial time of time interval t. i For the pulse phase shift of the i-th submodule, T h For half a switching cycle duration, i al (t) represents the bridge arm current during time interval t.

[0180] In this embodiment, the parameter acquisition submodule is further configured to acquire the input voltage of the modular DC transformer during the specified time period, the differential-mode current component of its bridge arm, and the transmission power of its intermediate frequency transformer; calculate the common-mode current of the corresponding bridge arm based on the transmission power and input voltage; and calculate the bridge arm current of the corresponding bridge arm during the specified time period using the bridge arm current formula based on the common-mode current and differential-mode current components; wherein, the bridge arm current formula is: i al =I dc1 / 2-i / 2, Idc1 =P / V dc1 In the formula, i al For the bridge arm current, I dc1 V 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 This refers to the input voltage of the modular DC transformer.

[0181] It should be noted that the modules in the device of Embodiment 2 correspond to the steps of the method in Embodiment 1. The energy equalization control method for this modular DC transformer has already been described in Embodiment 1, and the steps of the energy equalization control method for this modular DC transformer will not be described in detail in this embodiment.

[0182] Example 3:

[0183] Figure 15 This is a schematic diagram of the terminal device described in an embodiment of this application.

[0184] like Figure 15 As shown, this application provides a terminal device, including a processor and a memory;

[0185] Memory is used to store program code and transfer the program code to the processor;

[0186] The processor is used to execute the energy equalization control method of the modular DC transformer described above according to the instructions in the program code.

[0187] It should be noted that the processor is used to execute the steps in the above-described embodiment of the energy balancing control method for a modular DC transformer according to the instructions in the program code. Alternatively, when the processor executes the computer program, it implements the functions of each module / unit in the above-described system / device embodiments.

[0188] For example, a computer program can be divided into one or more modules / units, one or more of which are stored in memory and executed by a processor to complete this application. One or more modules / units can be a series of computer program instruction segments capable of performing a specific function, which describe the execution process of the computer program in a terminal device.

[0189] Terminal devices can be computing devices such as desktop computers, laptops, handheld computers, and cloud servers. Terminal devices may include, but are not limited to, processors and memory. Those skilled in the art will understand that this does not constitute a limitation on the terminal device, which may include more or fewer components than illustrated, or combinations of certain components, or different components. For example, a terminal device may also include input / output devices, network access devices, buses, etc.

[0190] The processor referred to can be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor can be a microprocessor or any conventional processor.

[0191] Memory can be an internal storage unit of a terminal device, such as a hard drive or RAM. Memory can also be an external storage device, such as a plug-in hard drive, Smart Memory Card (SMC), Secure Digital Card (SD), or Flash Memory Card. Furthermore, memory can include both internal and external storage units. Memory is used to store computer programs and other programs and data required by the terminal device. Memory can also be used for temporary storage of data that has been output or will be output.

[0192] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0193] In the several embodiments provided in this application, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be an indirect coupling or communication connection between apparatuses or units through some interfaces, and may be electrical, mechanical, or other forms.

[0194] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0195] Furthermore, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0196] If the integrated unit is implemented as 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 this application, in essence, 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. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RDM), magnetic disks, or optical disks.

[0197] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. An energy balance control method for a modular DC transformer, characterized in that, Includes the following steps: The capacitor voltage and pulse phase shift of each sub-module of the bridge arm in the modular DC transformer are obtained at any time period, and the capacitor voltage of each sub-module is determined to be balanced based on the capacitor voltage of each sub-module. If at least one of the submodules has an unbalanced capacitor voltage, the pulse phase shift sequence of the bridge arm is obtained by sorting all the pulse phase shifts in ascending order; the set of capacitor voltages of the bridge arm is obtained by sorting all the capacitor voltages in ascending order. Obtain the parameter data of each sub-module of the bridge arm in the modular DC transformer during the time period, and calculate the absorbed energy of the corresponding sub-module during the time period based on the parameter data of each sub-module. According to the pulse phase shift sequence, the corresponding sub-modules are controlled to absorb the corresponding absorbed energy in sequence according to the order of the capacitor voltage set, so as to adjust the capacitor voltage balance of each sub-module.

2. The energy balance control method for a modular DC transformer according to claim 1, characterized in that, The parameter data of the submodule includes pulse phase shift and the duration of half a switching cycle of the submodule. The energy absorbed by the corresponding submodule within this time period is calculated based on the parameter data of each submodule, including: Obtain the bridge arm current corresponding to the submodule during the time period, as well as the start and end times of the time period; The absorbed energy of the corresponding submodule during this time period is calculated using the formula for the absorbed charge based on the pulse phase shift, the duration of half a switching cycle, the bridge arm current, the initial time, and the end time. The formula for the amount of absorbed charge is as follows: In the formula, Q i For the energy absorbed by the i-th submodule, t end Let t be the end time of time interval t. start Let d be the initial time of time interval t. i For the pulse phase shift of the i-th submodule, T h For half a switching cycle duration, i al (t) represents the bridge arm current during time interval t.

3. The energy equalization control method of the modular DC transformer according to claim 2, characterized in that, Obtaining the bridge arm current corresponding to the submodule during this time period includes: Obtain the input voltage of the modular DC transformer, the differential mode current component of its bridge arm, and the transmission power of its intermediate frequency transformer during the specified time period. The common-mode current corresponding to the bridge arm is calculated based on the transmission power and the input voltage. The bridge arm current for the corresponding bridge arm in the time period is obtained by using the bridge arm current formula based on the common mode current and the differential mode current components. The formula for the bridge arm current is: i al =I dc1 / 2-i / 2, I dc1 =P / V dc1 In the formula, i al For the bridge arm current, I dc1 V 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 This refers to the input voltage of the modular DC transformer.

4. The energy equalization control method of a modular DC transformer according to claim 3, characterized by, The information obtained regarding the transmission power of the intermediate frequency transformer includes: The operating modes of each sub-module of the bridge arm in the modular DC transformer are determined based on this time period. The operating modes include a first operating mode, a second operating mode, and / or a third operating mode. The electrical parameters of the modular DC transformer are obtained, and the total energy absorbed by the primary side of the intermediate frequency transformer on the AC side is calculated based on the operating mode and the electrical parameters. The electrical parameters include the equivalent voltage of the primary AC side, the maximum pulse phase shift, the input voltage, the output voltage, the duration of half a switching cycle, the equivalent inductance of the primary side, and the transformation ratio. The transmission power of the intermediate frequency transformer is calculated based on the total energy absorbed by the primary side and the duration of half a switching cycle.

5. The energy equalization control method of the modular DC transformer according to claim 4, characterized in that, If the operating mode includes an operating mode, obtaining the total energy absorbed by the primary side of the intermediate frequency transformer on the AC side includes: calculating the primary AC side voltage and primary AC side current of the intermediate frequency transformer based on the electrical quantity parameters corresponding to the operating mode; calculating the primary side energy absorbed by the intermediate frequency transformer in the operating mode based on the primary AC side voltage and primary AC side current, and using the primary side absorbed energy as the total primary side energy absorbed by the intermediate frequency transformer on the AC side.

6. The energy equalization control method of a modular DC transformer according to claim 4, characterized by, If the operating mode includes at least two operating modes, the total energy absorbed by the primary side of the AC side of the intermediate frequency transformer includes: The primary AC voltage and primary AC current of the transformer under each operating mode are calculated based on the electrical quantity parameters corresponding to each operating mode. The primary-side AC voltage and the primary-side AC current are used to calculate the primary-side absorbed energy of the intermediate frequency transformer under the corresponding operating mode. The sum of the primary-side absorbed energy under all the aforementioned operating modes is taken as the total primary-side absorbed energy of the AC side of the intermediate frequency transformer.

7. An energy equalization control device for a modular DC transformer, characterized by, It includes a data acquisition and judgment module, a data sorting module, a calculation module, and a balance adjustment module; The data acquisition and judgment module is used to acquire the capacitor voltage and pulse phase shift of each sub-module of the bridge arm in the modular DC transformer at any time period, and to determine whether the capacitor voltage of each sub-module is balanced based on the capacitor voltage of each sub-module. The data sorting module is used to obtain the pulse phase shift sequence of the bridge arm by sorting all the pulse phase shifts in ascending order based on the capacitor voltage imbalance of at least one of the sub-modules; and to obtain the sorted capacitor voltage set of the bridge arm by sorting all the capacitor voltages in ascending order. The calculation module is used to obtain the parameter data of each sub-module of the bridge arm in the modular DC transformer during the time period, and calculate the absorbed energy of the corresponding sub-module during the time period based on the parameter data of each sub-module. The balance adjustment module is used to control the corresponding sub-modules to absorb the corresponding absorbed energy in sequence according to the pulse phase shift sequence and the order of the capacitor voltage set, so as to adjust the capacitor voltage balance of each sub-module.

8. The energy balancing control device for a modular DC transformer according to claim 7, characterized in that, The parameter data of the submodule includes pulse phase shift and half a switching cycle duration of the submodule; the calculation module includes a parameter acquisition submodule and a calculation submodule. The parameter acquisition submodule is used to acquire the bridge arm current corresponding to the submodule during the time period, as well as the initial and end times of the time period. The calculation submodule is used to calculate the energy absorbed by the corresponding submodule within the time period based on the pulse phase shift, the duration of half a switching cycle, the bridge arm current, the initial time, and the end time using the formula for the amount of absorbed charge. The formula for the amount of absorbed charge is as follows: In the formula, Q i For the energy absorbed by the i-th submodule, t end Let t be the end time of time interval t. start Let d be the initial time of time interval t. i For the pulse phase shift of the i-th submodule, T h For half a switching cycle duration, i al (t) represents the bridge arm current during time interval t.

9. The energy equalization control device of the modular DC transformer according to claim 8, characterized in that, The parameter acquisition submodule is also used to acquire the input voltage of the modular DC transformer during the time period, the differential-mode current component of its bridge arm, and the transmission power of its intermediate frequency transformer; calculate the common-mode current of the corresponding bridge arm based on the transmission power and the input voltage; and calculate the bridge arm current of the corresponding bridge arm during the time period using the bridge arm current formula based on the common-mode current and the differential-mode current component; wherein, the bridge arm current formula is: i al =I dc1 / 2-i / 2, I dc1 =P / V dc1 In the formula, i al For the bridge arm current, I dc1 V 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 This refers to the input voltage of the modular DC transformer.

10. A terminal device, comprising: Including the processor and memory; The memory is used to store program code and transmit the program code to the processor; The processor is configured to execute the energy equalization control method of the modular DC transformer according to the instructions in the program code.

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