A direct current transformer and a control method thereof

Abstract

This disclosure relates to a DC transformer and its control method. The control method includes: acquiring first AC voltage information of the primary and secondary sides, and acquiring an initial control command; establishing reactive power equations and active power equations of the DC transformer based on the first AC voltage information and the initial control command; and determining a first target control command for the DC transformer based on the reactive power equations and the active power equations, provided that the reactive power equations satisfy a decoupling condition; wherein the decoupling condition is that the reactive power in the reactive power equations is 0. This disclosure enables complete decoupling of the active and reactive power of the DC transformer, so that all the current of the DC transformer is used to transmit active power, thereby eliminating ineffective circulating current and improving the DC transmission efficiency of the entire system.

Description

Technical Field

[0001] This disclosure relates to the field of power electronics technology, and in particular to a DC transformer and its control method. Background Technology

[0002] High-power DC / DC isolation transformers (DCTs), as core equipment connecting DC systems of different voltage levels and providing electrical isolation and fault interruption capabilities, have become a research hotspot in the field of power electronics. However, the complex coupling relationships between the power at each port of a DC transformer lead to significant design challenges for controllers and make it difficult to guarantee dynamic performance.

[0003] In related technologies, decoupling control of DC transformers mostly adopts single-phase-shift control. Although the control logic of single-phase-shift control is simple, using only a single phase shift angle as the control degree of freedom still leads to an inherent strong coupling between the active and reactive power of the system. If the phase shift angle is adjusted to meet the active power transmission demand under voltage mismatch or light load conditions, uncontrollable reactive circulating current will inevitably be introduced, making it difficult to transmit power efficiently, significantly aggravating conduction losses, and reducing the efficiency of the DC transmission system. Therefore, how to provide a control method that can completely decouple active and reactive power has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0004] To solve the above-mentioned technical problems, or at least partially solve them, this disclosure provides a DC transformer and its control method, which can completely decouple the active power and reactive power of the DC transformer, so that all the current of the DC transformer is used to transmit active power, thereby eliminating ineffective circulating current and improving the DC transmission efficiency of the entire system.

[0005] This disclosure provides a control method for a DC transformer, the DC transformer including a DC input circuit, a DC output circuit, and a transformer; The DC side of the DC input circuit is connected to the voltage input circuit, the primary side of the transformer is connected to the AC side of the DC input circuit, the secondary side of the transformer is connected to the AC side of the DC output circuit, and the DC side of the DC output circuit is connected to the voltage output circuit. Control methods include: Obtain the first AC voltage information of the primary and secondary sides, and obtain the initial control command; Based on the first AC voltage information and the initial control command, the reactive power equation and active power equation of the DC transformer are established. Under the condition that the reactive power equation satisfies the decoupling condition, the first target control command of the DC transformer is determined based on the reactive power equation and the active power equation. The decoupling condition is that the reactive power in the reactive power equation is 0. The first target control command is used to control the operation of the DC input circuit and the DC output circuit.

[0006] Optionally, the first AC voltage information includes: the primary AC voltage of the primary side and the secondary AC voltage of the secondary side; The initial control commands include the initial phase shift angle and the initial duty cycle; Based on the first AC voltage information and the initial control command, the reactive power equation and active power equation of the DC transformer are established, including: Based on the primary-side AC voltage and the secondary-side AC voltage, the first fundamental peak value of the primary-side AC voltage and the second fundamental peak value of the secondary-side AC voltage are obtained. Based on the first fundamental peak value, the second fundamental peak value, the initial phase shift angle, and the initial duty cycle, the reactive power equation and the active power equation are established.

[0007] Alternatively, the active power equation is:

[0008] The reactive power equation is:

[0009] Where P is the calculated active power, Q is the reactive power, and V is the reactive power. p V is the first fundamental peak value. s The second fundamental peak value is given by δ, the initial phase shift angle is given by D, the initial duty cycle is given by ω, and the intermediate frequency (IF) is given by L. S This is the equivalent leakage inductance of the transformer.

[0010] Optionally, the first target control command includes the target phase shift angle and the target peak value of the second fundamental peak value; Under the condition that the reactive power equation satisfies the decoupling condition, the first target control command for the DC transformer is determined based on the reactive power equation and the active power equation, including: When the reactive power in the reactive power equation is 0, the target peak value is determined based on the reactive power equation. The target phase shift angle is determined based on the target peak value and the active power equation.

[0011] Optionally, the method also includes: Acquire the second AC voltage information of the DC input circuit and DC output circuit under the current control cycle; The current active power and current reactive power of the DC transformer are calculated based on the second AC voltage information. Based on the first target control command, the current active power, and the current reactive power, obtain the feedback correction command for the DC transformer; Based on the feedback correction instruction and the first target control instruction, the second target control instruction of the DC transformer in the current control cycle is obtained.

[0012] Optionally, based on the first target control command, the current active power, and the current reactive power, a feedback correction command for the DC transformer is obtained, including: The Jacobian matrix is ​​established using partial derivative operations based on the first target control command, and the decoupling matrix is ​​obtained based on the Jacobian matrix; wherein, the decoupling matrix is ​​the inverse of the Jacobian matrix; Obtain active power reference values ​​and reactive power reference values; Based on the current active power, current reactive power, active power reference value, and reactive power reference value, calculate the active power error and reactive power error of the DC transformer. Based on the decoupling matrix, active power error, reactive power error, current active power, and current reactive power, feedback correction instructions are obtained.

[0013] Optionally, based on the decoupling matrix, active power error, reactive power error, current active power, and current reactive power, feedback correction instructions are obtained, including: Based on active power error and reactive power error, a proportional-integral controller is used to generate a virtual control vector. Based on the virtual control vector, a linear transformation using the decoupling matrix is ​​employed to obtain the feedback correction command. Optionally, the decoupling matrix is ​​obtained based on the Jacobian matrix, including: The decoupling matrix is ​​calculated based on the Jacobian matrix using the Tikhonov regularized pseudo-inverse algorithm. The decoupling matrix is:

[0014] Where M is the decoupling matrix and J is the Jacobian matrix. Here, I is the regularization parameter, and I is the identity matrix.

[0015] This disclosure also provides a DC transformer that can be applied to any of the control methods described above. The DC input circuit includes a first full-bridge module; the DC output circuit includes two second full-bridge modules; the transformer includes a first transformer unit and a second transformer unit. The first terminal of the first transformer unit and the second terminal of the second transformer unit are connected to the AC side of the first full-bridge module, the second terminal of the first transformer unit is connected to the first terminal of the second transformer unit, and the DC side of the first full-bridge module is connected to the voltage input circuit. The third and fourth terminals of the first transformer unit are connected to the AC side of the corresponding second full-bridge module. The third and fourth terminals of the second transformer unit are connected to the AC side of the corresponding second full-bridge module. The DC side of the second full-bridge module is connected to the voltage output circuit.

[0016] Optionally, the first full-bridge module includes four first bridge arms; The first bridge arm includes multiple first switching units; Multiple first switching units are connected in series and / or in parallel. The first end of the first bridge arm is connected to the DC side of the first full-bridge module, and the second end of the first bridge arm is connected to the AC side of the first full-bridge module.

[0017] Optionally, the first switching unit includes a first IGBT, a second IGBT, and a first capacitor; The first terminal of the first IGBT is connected to the first terminal of the first capacitor, the second terminal of the first IGBT is connected to the first terminal of the first switching unit, and the second terminal of the second IGBT is connected to the second terminal of the first capacitor. The first end of the second IGBT is used to connect to the second end of the adjacent first switching unit or the DC side of the first full-bridge module; The second end of the second IGBT is used to connect to the first end of the adjacent first switching unit or the AC side of the first full-bridge module.

[0018] Optionally, the second full-bridge module includes four second bridge arms; The second bridge arm includes multiple second switching units; Multiple second switching units are connected in series and / or in parallel. The first end of the second bridge arm is connected to the DC side of the second full-bridge module, and the second end of the second bridge arm is connected to the AC side of the second full-bridge module.

[0019] Optionally, the second switching unit includes a first IGCT transistor, a second IGCT transistor, and a second capacitor; The first end of the first IGCT transistor is connected to the first end of the second capacitor, the second end of the first IGCT transistor and the first end of the second IGCT transistor are connected to the first end of the second switching unit, and the second end of the second IGCT transistor and the second end of the second capacitor are connected to the second end of the second switching unit. The first end of the second IGCT tube is used to connect to the second end of the adjacent second switching unit or the DC side of the second full-bridge module; The second end of the second IGCT tube is used to connect to the first end of the adjacent second switching unit or the AC side of the second full-bridge module.

[0020] This disclosure provides a DC transformer and its control method. The DC transformer includes a DC input circuit, a DC output circuit, and a transformer. The DC side of the DC input circuit is connected to a voltage input circuit, the primary side of the transformer is connected to the AC side of the DC input circuit, the secondary side of the transformer is connected to the AC side of the DC output circuit, and the DC side of the DC output circuit is connected to the voltage output circuit. The control method includes: acquiring first AC voltage information of the primary and secondary sides, and acquiring an initial control command; establishing reactive power equations and active power equations of the DC transformer based on the first AC voltage information and the initial control command; and determining a first target control command of the DC transformer based on the reactive power equations and the active power equations, provided that the reactive power equations satisfy the decoupling condition; wherein the decoupling condition is that the reactive power in the reactive power equations is 0. This disclosure establishes the reactive power equations and active power equations of the DC transformer based on the first AC voltage information of the primary and secondary sides and the initial control command. Furthermore, when the reactive power in the reactive power equation is 0, based on the reactive power equation and the active power equation, a first target control command is determined that enables the DC transformer to achieve 0 reactive power while still outputting active power normally. This achieves the acquisition of the first target control command that satisfies the decoupling condition of reactive and active power in the DC transformer. Therefore, the control method provided in this disclosure completely decouples the active and reactive power of the DC transformer, enabling the DC transformer to operate in a state where reactive power is 0 when entering steady state. At this time, all current is used to transmit active power, thereby eliminating ineffective circulating current and improving the DC transmission efficiency of the entire system. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application 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.

[0022] Figure 1 This is a schematic diagram of the structure of a DC transformer provided in an embodiment of this disclosure.

[0023] Figure 2 This is a flowchart illustrating a control method for a DC transformer provided in an embodiment of this disclosure.

[0024] Figure 3 This is a flowchart illustrating another control method for a DC transformer provided in an embodiment of this disclosure.

[0025] Figure 4 This is a comparison diagram between the simulation effect of the control method of this disclosure embodiment and the simulation effect of related technologies.

[0026] Figure 5 This is a schematic diagram of another DC transformer provided in an embodiment of the present disclosure. Detailed Implementation

[0027] The features and exemplary embodiments of various aspects of this application will now be described in detail. Numerous specific details are set forth in the following detailed description in order to provide a comprehensive understanding of this application. However, it will be apparent to those skilled in the art that this application can be implemented without some of these specific details. The following description of embodiments is merely intended to provide a better understanding of this application by illustrating examples thereof.

[0028] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The embodiments will now be described in detail with reference to the accompanying drawings.

[0029] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus that includes said element.

[0030] It should be understood that when describing the structure of a component, when referring to a layer or region as being "above" or "on top of" another layer or region, it can mean that it is directly above the other layer or region, or that it contains other layers or regions between it and the other layer or region. Furthermore, if the component is flipped over, that layer or region will be located "below" or "under" the other layer or region.

[0031] It should be understood that the term "and / or" used in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.

[0032] In the embodiments of this application, the term "electrical connection" can refer to a direct electrical connection between two components, or it can refer to an electrical connection between two components via one or more other components.

[0033] In the embodiments of this application, the first node, the second node, and the third node are defined only for the convenience of describing the circuit structure, and the first node, the second node, and the third node are not actual circuit units.

[0034] Various modifications and variations can be made to this application without departing from its spirit or scope, which will be apparent to those skilled in the art. Therefore, this application is intended to cover modifications and variations falling within the scope of the corresponding claims (the claimed technical solutions) and their equivalents. It should be noted that the embodiments provided in this application can be combined with each other without contradiction.

[0035] High-power DC / DC isolation transformers (DCTs), as core equipment connecting DC systems of different voltage levels and providing electrical isolation and fault interruption capabilities, have become a research hotspot in the field of power electronics. However, the complex coupling relationships between the power at each port of a DC transformer lead to significant design challenges for controllers and make it difficult to guarantee dynamic performance.

[0036] In related technologies, decoupling control of DC transformers mostly adopts single-phase-shift control. Although the control logic of single-phase-shift control is simple, using only a single phase shift angle as the control degree of freedom still leads to an inherent strong coupling between the active and reactive power of the system. If the phase shift angle is adjusted to meet the active power transmission demand under voltage mismatch or light load conditions, uncontrollable reactive circulating current will inevitably be introduced, making it difficult to transmit power efficiently, significantly aggravating conduction losses, and reducing the efficiency of the DC transmission system. Therefore, how to provide a control method that can completely decouple active and reactive power has become a technical problem that urgently needs to be solved by those skilled in the art.

[0037] Therefore, this disclosure provides a DC transformer and its control method. Based on the first AC voltage information of the primary and secondary sides and the initial control command, the reactive power equation and active power equation of the DC transformer are established. Furthermore, when the reactive power in the reactive power equation is 0, based on the reactive power equation and the active power equation, a first target control command is determined that enables the DC transformer to achieve 0 reactive power and normal active power output. This achieves the acquisition of the first target control command that satisfies the decoupling condition of reactive power and active power in the DC transformer. Therefore, the control method provided by this disclosure completely decouples the active power and reactive power of the DC transformer, enabling the DC transformer to operate in a state where reactive power is 0 when entering steady state. At this time, all current is used to transmit active power, thereby eliminating ineffective circulating current and improving the DC transmission efficiency of the entire system.

[0038] The embodiments will now be described in detail with reference to the accompanying drawings.

[0039] Figure 1 This is a schematic diagram of the structure of a DC transformer provided in an embodiment of the present disclosure, as shown below. Figure 1 As shown, the DC transformer includes a DC input circuit 10, a DC output circuit 20, and a transformer 30.

[0040] The DC side of the DC input circuit 10 is connected to the voltage input circuit 41, the primary side of the transformer 30 is connected to the AC side of the DC input circuit 10, the secondary side of the transformer 30 is connected to the AC side of the DC output circuit 20, and the DC side of the DC output circuit 20 is connected to the voltage output circuit 42.

[0041] For example, the DC transformer may be a split DC transformer. Both the DC input circuit 10 and the DC output circuit 20 are full-bridge modules. The voltage input circuit 41 provides a first DC voltage to the DC transformer, and the voltage output circuit 42 provides a second DC voltage to an external module, where the first voltage is greater than the second voltage.

[0042] Figure 2 This is a flowchart illustrating a control method for a DC transformer provided in an embodiment of the present disclosure, as shown below. Figure 2 As shown, the control methods include: S110-S130.

[0043] S110: Obtain the first AC voltage information of the primary and secondary sides, and obtain the initial control command.

[0044] For example, the first AC voltage information includes AC voltage information corresponding to the primary side and AC voltage information corresponding to the secondary side. A voltage acquisition sensor acquires the first AC voltage waveform output from the AC side of the DC input circuit 10 on the primary side of the transformer 30, and acquires the second AC voltage waveform after voltage transformation by the transformer 30 on the secondary side of the transformer 30. The generation of the second AC voltage waveform is also affected by the modulation parameters of the DC output circuit 20. The AC voltage information corresponding to the primary side is obtained by analyzing the first AC voltage waveform, and the AC voltage information corresponding to the secondary side is obtained by analyzing the second AC voltage waveform.

[0045] S120. Based on the first AC voltage information and the initial control command, establish the reactive power equation and active power equation of the DC transformer.

[0046] For example, the initial control command is provided by the external control module to the DC input circuit 10 and the DC output circuit 20, initiating the AC-DC conversion between them. Based on the initial control command, the AC voltage information corresponding to the primary side, and the AC voltage information corresponding to the secondary side, the reactive power equation and the active power equation of the DC transformer are established. Since both the reactive power equation and the active power equation are functions based on the AC voltage information corresponding to the primary side and the AC voltage information corresponding to the secondary side, they both carry relevant parameter information related to the AC voltage information corresponding to the primary side and the AC voltage information corresponding to the secondary side. This allows the reactive power equation and the active power equation to reflect the coupling relationship between reactive power and active power.

[0047] S130. Under the condition that the reactive power equation satisfies the decoupling condition, determine the first target control command of the DC transformer based on the reactive power equation and the active power equation.

[0048] The decoupling condition is that the reactive power in the reactive power equation is 0. The first target control command is used to control the operation of the DC input circuit 10 and the DC output circuit 20.

[0049] For example, since both the active power equation and the reactive power equation are functions established based on the AC voltage information corresponding to the primary and secondary sides, when the reactive power equation satisfies the decoupling condition, calculations are performed using both the reactive power equation and the active power equation. This allows us to obtain the specific values ​​of the parameters corresponding to the first target control command that satisfy the decoupling condition in the active power equation and the reactive power equation when the reactive power is 0. The external control module then uses the first target control command to control the DC transformer, thereby enabling the DC input circuit 10 and the DC output circuit 20 to operate under the condition of reactive power and active power decoupling.

[0050] This disclosure establishes the reactive power equation and active power equation of the DC transformer based on the first AC voltage information of the primary and secondary sides and the initial control command. Furthermore, when the reactive power in the reactive power equation is 0, based on the reactive power equation and the active power equation, a first target control command is determined that enables the DC transformer to achieve 0 reactive power and normal active power output. This achieves the acquisition of the first target control command that satisfies the decoupling condition of reactive and active power in the DC transformer. Therefore, the control method provided by this disclosure completely decouples the active and reactive power of the DC transformer, enabling the DC transformer to operate in a state with 0 reactive power when entering steady state. At this time, all current is used to transmit active power, thereby eliminating ineffective circulating current and improving the DC transmission efficiency of the entire system.

[0051] In some embodiments, the first AC voltage information includes: the primary AC voltage of the primary side and the secondary AC voltage of the secondary side; the initial control command includes the initial phase shift angle and the initial duty cycle.

[0052] For example, a voltage acquisition sensor acquires the first AC voltage waveform of the primary AC voltage output from the AC side of the DC input circuit 10 on the primary side of the transformer 30, and acquires the second AC voltage waveform of the secondary AC voltage after the transformer 30 transforms the first AC voltage waveform on the secondary side. Furthermore, the DC input circuit 10 and DC output circuit 20 in the DC transformer control the conduction state of their respective internal switching devices according to the initial phase shift angle and initial duty cycle, thereby realizing AC / DC voltage conversion. Therefore, the initial control command is the input initial phase shift angle and initial duty cycle.

[0053] S120 includes: obtaining the first fundamental peak value of the primary AC voltage and the second fundamental peak value of the secondary AC voltage based on the primary AC voltage and the secondary AC voltage.

[0054] For example, based on the primary AC voltage, the peak value of the fundamental peak voltage of the corresponding first AC voltage waveform is obtained, and based on the secondary AC voltage, the peak value of the fundamental peak voltage of the corresponding second AC voltage waveform is obtained, also based on the primary AC voltage. Furthermore, the phase of the secondary AC voltage lags behind the phase of the primary AC voltage by an initial phase shift angle.

[0055] Based on the first fundamental peak value, the second fundamental peak value, the initial phase shift angle, and the initial duty cycle, the reactive power equation and the active power equation are established.

[0056] For example, after obtaining the first fundamental peak value, the second fundamental peak value, the initial phase shift angle, and the initial duty cycle, it is also necessary to obtain the intermediate frequency angular frequency of the DC transformer and the equivalent leakage inductance of the transformer 30. The intermediate frequency angular frequency is the switching angular frequency of the DC input circuit, which can be directly acquired. The equivalent leakage inductance of the transformer 30 can be directly measured by appropriate instruments when the DC transformer is de-energized.

[0057] Based on the first fundamental peak value, the second fundamental peak value, the initial phase shift angle, the initial duty cycle, the intermediate frequency angular frequency of the DC transformer, and the equivalent leakage inductance of transformer 30, the reactive power equation and the active power equation of the DC transformer in the steady-state power transmission relationship are established as a steady-state model.

[0058] The active power equation is:

[0059] The reactive power equation is:

[0060] Where P is the calculated active power, Q is the reactive power, and V is the reactive power. p V is the first fundamental peak value. s The second fundamental peak value is given by δ, the initial phase shift angle is given by D, the initial duty cycle is given by ω, and the intermediate frequency (IF) is given by L. S This is the equivalent leakage inductance of the transformer.

[0061] In some embodiments, the first target control command includes a target phase shift angle and a target peak value of a second fundamental peak value.

[0062] For example, the external control module can use the first target control command obtained under decoupling conditions to control the DC transformer, thereby realizing the operation of the DC input circuit 10 and the DC output circuit 20 under the condition of decoupling of reactive power and active power by using the first target control command.

[0063] S130 includes: determining the target peak value based on the reactive power equation when the reactive power in the reactive power equation is 0.

[0064] The target phase shift angle is determined based on the target peak value and the active power equation.

[0065] For example, since the second fundamental peak of the secondary AC voltage is determined by the duty cycle of the DC transformer, the target peak value of the second fundamental peak can be calculated when the reactive power is 0. This allows the determination of the target duty cycle for controlling the operation of the DC input circuit 10 and the DC output circuit 20. The external controller can perform nonlinear inversion operation on given active and reactive power reference values ​​based on the reactive power equation and the active power equation, thereby obtaining the target control vector.

[0066] The target control vector is:

[0067] Among them, P ref Q is the active power reference value. ref This is a reference value for reactive power. For the target phase shift angle, V s0 The target peak value.

[0068] Therefore, when the reactive power reference value in the reactive power equation is 0, the target peak value is determined based on the reactive power equation. Substituting the target peak value into the active power equation, the target phase shift angle between the phase of the secondary AC voltage and the phase of the primary AC voltage can be obtained when the reactive power is 0.

[0069] The target phase shift angle is:

[0070] The target peak value is:

[0071] The target phase shift angle and the target peak value are feedforward solutions for the optimal operating point of the DC transformer under zero reactive power.

[0072] Therefore, this disclosure can calculate the first target control command for controlling the operation of DC input circuit 10 and DC output circuit 20 when the reactive power is 0 by using the reactive power equation and the active power equation, thereby realizing the decoupling of reactive power and active power when the DC input circuit 10 and DC output circuit 20 are controlled by the first target control command.

[0073] In some embodiments, Figure 3 A flowchart illustrating another control method for a DC transformer provided in this disclosure is shown below. Figure 3 As shown, the control method also includes: S140-S170.

[0074] S140: Obtain the second AC voltage information of the DC input circuit and DC output circuit in the current control cycle.

[0075] S150. Calculate the current active power and current reactive power of the DC transformer based on the second AC voltage information.

[0076] For example, the second AC voltage information includes the primary AC voltage, the primary AC current, the secondary AC voltage, and the secondary AC current.

[0077] A primary AC voltage acquisition unit and a primary AC current acquisition unit are provided on the primary side of transformer 30, which can acquire the primary AC voltage and primary AC current of the DC input circuit. A secondary AC voltage acquisition unit and a secondary AC current acquisition unit are provided on the secondary side of transformer 30, which can acquire the secondary AC voltage and secondary AC current of the DC output circuit.

[0078] Wherein, the primary AC voltage is v p (t), the primary side alternating current is i p (t), the secondary AC voltage is v s (t), the secondary side AC current is i s (t).

[0079] Let the AC component of the voltage on the secondary side be... and The AC component of the secondary current is and .

[0080] Therefore, the current active power and current reactive power of the DC transformer can be obtained.

[0081] The current active power is:

[0082] The current reactive power is:

[0083] Where ps(t) is the current active power and qs(t) is the current reactive power.

[0084] S160. Based on the first target control command, the current active power, and the current reactive power, obtain the feedback correction command for the DC transformer.

[0085] S170. Based on the feedback correction instruction and the first target control instruction, obtain the second target control instruction for the DC transformer in the current control cycle.

[0086] For example, the first target control instruction is the target control instruction obtained by the DC transformer in the previous control cycle, used to control the operation of the DC transformer in the current cycle. The second target control instruction is the target control instruction obtained by modifying the first target control instruction based on the feedback correction instruction obtained in the previous control cycle, used to control the operation of the DC transformer in the next control cycle.

[0087] This disclosure acquires the second AC voltage information of the DC input circuit and DC output circuit during the current control cycle, thereby calculating the current active power and reactive power of the DC transformer during the current control cycle. The current active power and reactive power are then processed by low-pass filtering, moving average, or synchronous periodic averaging to obtain a feedback correction command for the DC transformer. This feedback correction command can be used to correct the first target control command, thereby modifying it into a second target control command. This second target control command then controls the operation of the DC transformer in the next control cycle. Therefore, this disclosure enables closed-loop control of the DC transformer, compensating for errors in the DC transformer through the feedback correction command and suppressing disturbances within the DC transformer, thus improving the stability of the entire DC transformer system.

[0088] In some embodiments, S160 includes: establishing a Jacobian matrix based on a first target control command using partial derivative operations, and obtaining a decoupling matrix based on the Jacobian matrix; wherein the decoupling matrix is ​​the inverse moment of the Jacobian matrix.

[0089] For example, by applying partial derivatives to the first target control command, a Jacobian matrix can be established.

[0090] The Jacobian matrix is:

[0091] The elements within the Jacobian matrix can be specifically represented as follows:

[0092]

[0093]

[0094]

[0095] The decoupling matrix is ​​obtained based on the Jacobian matrix, including: The decoupling matrix is ​​calculated based on the Jacobian matrix using the Tikhonov regularized pseudo-inverse algorithm. The decoupling matrix is:

[0096] Where M is the decoupling matrix and J is the Jacobian matrix. Here, I is the regularization parameter, and I is the identity matrix.

[0097] Obtain active power reference values ​​and reactive power reference values.

[0098] Based on the current active power, current reactive power, active power reference value, and reactive power reference value, calculate the active power error and reactive power error of the DC transformer.

[0099] For example, after filtering based on the current active power and the current reactive power, the active power feedback quantity and the reactive power feedback quantity can be obtained.

[0100] The active power feedback quantity is:

[0101] The reactive power feedback quantity is:

[0102] Among them, P fb Q is the active power feedback quantity. fb G is the reactive power feedback quantity. f (s) is the power filtering expression.

[0103] The active power error is calculated based on the active power feedback and the active power reference value. The reactive power error is calculated based on the reactive power feedback and the reactive power reference value.

[0104] The active power error is:

[0105] The active power error is:

[0106] Among them, e P For active power error, e Q For reactive power error, P ref Q is the active power reference value. ref This is the reactive power reference value. The active power reference value and reactive power reference value are the theoretical values ​​of active power and reactive power obtained after the DC transformer operates based on the target control command provided in the previous control cycle.

[0107] Based on the decoupling matrix, active power error, reactive power error, current active power, and current reactive power, feedback correction instructions are obtained.

[0108] For example, based on the decoupling matrix, active power error, reactive power error, current active power, and current reactive power, a feedback correction command can be obtained. This feedback correction command can be used to correct the first target control command, thereby modifying the first target control command into a second target control command. The second target control command is then used to control the operation of the DC transformer in the next control cycle. Therefore, this disclosure can achieve closed-loop control of the DC transformer, compensate for errors in the DC transformer through the feedback correction command, and suppress disturbances within the DC transformer, thereby improving the stability of the entire DC transformer system.

[0109] In some embodiments, feedback correction instructions are obtained based on the decoupling matrix, active power error, reactive power error, current active power, and current reactive power, including: Based on active power error and reactive power error, a proportional-integral controller is used to generate a virtual control vector.

[0110] For example, based on active power error and reactive power error, the virtual control vector generated by the proportional-integral controller is as follows:

[0111] in, , G P (s) represents the parameters corresponding to the active power channel of the proportional-integral controller, G Q (s) represents the parameters corresponding to the reactive power channel of the proportional-integral controller.

[0112] Based on the virtual control vector, a linear transformation using a decoupling matrix is ​​employed to obtain feedback correction commands.

[0113] For example, based on the virtual control vector, a linear transformation is performed using the decoupling matrix to obtain the feedback correction instruction, which is:

[0114] Therefore, based on the feedback correction instruction and the first target control instruction, this disclosure obtains the second target control instruction for the DC transformer in the current control cycle as follows:

[0115] Where u0 is the target control vector corresponding to the first target control command, u f This is the second target control command.

[0116] The control method provided in this disclosure acquires the corresponding first target control command when the reactive power is 0, and then generates the final second target control command through feedback adjustment. This ensures that the reactive power of the DC transformer is always precisely suppressed to near zero, successfully achieving complete decoupling of active and reactive power. Furthermore, this disclosure can also achieve closed-loop control of the DC transformer, compensating for errors in the DC transformer through feedback correction commands and suppressing disturbances within the DC transformer, thereby improving the stability of the entire DC transformer system.

[0117] Figure 4 This is a comparison diagram between the simulation effect of the control method of this disclosure embodiment and the simulation effect of related technologies, such as... Figure 4 As shown, in terms of dynamic response and accuracy, when the power command steps at t=0.05s, the active power response obtained by the embodiment of this disclosure is fast, smooth, and without overshoot, converging precisely to the reference value within 5ms, demonstrating power tracking capability. In contrast, the phase-shift control in related technologies exhibits severe power oscillations and significant steady-state errors, completely failing to effectively track the command, proving its control failure when facing system nonlinearity. Secondly, in terms of power decoupling and efficiency improvement, the embodiment of this disclosure accurately suppresses reactive power to near zero, successfully achieving complete decoupling of active and reactive power. In contrast, the phase-shift control in related technologies generates reactive circulating current while regulating active power, severely impacting the DC transformer system, resulting in additional conduction losses and significantly reducing operating efficiency. Finally, in terms of control stability and smoothness, the phase-shift angle and the second fundamental peak value corresponding to the secondary AC voltage in the control method provided by the embodiment of this disclosure are smooth, stable, and converge rapidly throughout the entire adjustment process. In contrast, the phase-shift angle in related technologies exhibits severe, saturated oscillations, revealing the instability of its closed-loop system. Therefore, this disclosure can eliminate the coupling between active and reactive power and achieve fast, accurate, stable and efficient power control.

[0118] This disclosure also provides a DC transformer, which is applied to the control method corresponding to any of the above embodiments.

[0119] Figure 5 This is a schematic diagram of the structure of another DC transformer provided in an embodiment of the present disclosure, as shown below. Figure 5 As shown, the DC input circuit includes a first full-bridge module 100; the DC output circuit includes two second full-bridge modules 200; and the transformer includes a first transformer unit 310 and a second transformer unit 320.

[0120] The first end of the first transformer unit 310 and the second end of the second transformer unit 320 are connected to the AC side of the first full-bridge module 100, the second end of the first transformer unit 310 is connected to the first end of the second transformer unit 320, and the DC side of the first full-bridge module 100 is connected to the voltage input circuit 41.

[0121] The third and fourth terminals of the first transformer unit 310 are connected to the AC side of the corresponding second full-bridge module 200. The third and fourth terminals of the second transformer unit 320 are also connected to the AC side of the corresponding second full-bridge module 200. The DC sides of both second full-bridge modules 200 are connected to the voltage output circuit 42.

[0122] For example, the DC transformer provided in this embodiment is a two-split DC transformer. Using a two-split DC transformer in the control method corresponding to any of the above embodiments can make it easier to achieve independent power regulation, circulating current suppression, voltage and current equalization and fault isolation of the two second full-bridge modules 200, and can also improve the system controllability.

[0123] It is understood that the DC transformer provided in this embodiment can achieve the corresponding beneficial effects of the control method provided in the above embodiments, which will not be elaborated here.

[0124] In some embodiments, see continue to see Figure 5 The first full-bridge module 100 includes four first bridge arms 101.

[0125] The first bridge arm 101 includes multiple first switching units 1010.

[0126] Multiple first switching units 1010 are connected in series and / or in parallel. The first end of the first bridge arm 101 is connected to the DC side of the first full-bridge module 100, and the second end of the first bridge arm 101 is connected to the AC side of the first full-bridge module 100 through the bridge arm inductor L.

[0127] For example, multiple first switching units 1010 connected in series can improve the high voltage withstand capability of each first bridge arm 101. Multiple first switching units 1010 connected in parallel can improve the current carrying capacity of each first bridge arm 101. The multiple first switching units 1010 include both multiple first switching units 1010 connected in series and multiple first switching units 1010 connected in parallel, thus improving both the high voltage withstand capability and the current carrying capacity of each first bridge arm 101.

[0128] It should be noted that, Figure 5The diagram only illustrates the interconnection of multiple first switch units 1010. The specific connection between the multiple first switch units 1010 needs to be determined according to actual requirements, and no specific limitation is made here.

[0129] In some embodiments, see continue to see Figure 5 The first switching unit 1010 includes a first IGBT Q1, a second IGBT Q2, and a first capacitor C1.

[0130] The first terminal of the first IGBT Q1 is connected to the first terminal of the first capacitor C1. The second terminal of the first IGBT Q1 and the first terminal of the second IGBT Q2 are connected to the first terminal of the first switching unit 1010. The second terminal of the second IGBT Q2 and the second terminal of the first capacitor C1 are connected to the second terminal of the first switching unit 1010.

[0131] The first end of the second IGBT Q2 is used to connect to the second end of the adjacent first switching unit 1010 or the DC side of the first full-bridge module 100.

[0132] The second end of the second IGBT Q2 is used to connect to the first end of the adjacent first switching unit 1010 or the AC side of the first full-bridge module 100.

[0133] For example, the first IGBT Q1 and the second IGBT Q2 in the plurality of first switching units 1010 are used to alternately turn on or off according to the second target control command, thereby converting the DC voltage received on the DC side of the first full-bridge module 100 into AC voltage.

[0134] In some embodiments, see continue to see Figure 5 The second full-bridge module 200 includes four second bridge arms 201.

[0135] The second bridge arm 201 includes multiple second switching units 2010.

[0136] Multiple second switching units 2010 are connected in series and / or in parallel. The first end of the second bridge arm 201 is connected to the DC side of the second full-bridge module 200, and the second end of the second bridge arm 201 is connected to the AC side of the second full-bridge module 200 through the bridge arm inductor L.

[0137] For example, multiple second switching units 2010 connected in series can improve the high voltage withstand capability of each second bridge arm 201. Multiple second switching units 2010 connected in parallel can improve the current carrying capacity of each second bridge arm 201. The multiple second switching units 2010 include both multiple second switching units 2010 connected in series and multiple second switching units 2010 connected in parallel, thus improving both the high voltage withstand capability and the current carrying capacity of each second bridge arm 201.

[0138] It should be noted that, Figure 5 The diagram only illustrates the interconnection of multiple second switch units 2010. The specific connection between the multiple second switch units 2010 needs to be determined according to actual requirements, and no specific limitation is made here.

[0139] In some embodiments, see continue to see Figure 5 The second switching unit 2010 includes a first IGCT transistor Q3, a second IGCT transistor Q4, and a second capacitor C2.

[0140] The first terminal of the first IGCT transistor Q3 is connected to the first terminal of the second capacitor C2. The second terminal of the first IGCT transistor Q3 and the first terminal of the second IGCT transistor Q4 are connected to the first terminal of the second switching unit 2010. The second terminal of the second IGCT transistor Q4 and the second terminal of the second capacitor C2 are connected to the second terminal of the second switching unit 2010.

[0141] The first end of the second IGCT tube Q4 is used to connect to the second end of the adjacent second switching unit 2010 or the DC side of the second full-bridge module 200.

[0142] The second end of the second IGCT tube Q4 is used to connect to the first end of the adjacent second switching unit 2010 or the AC side of the second full-bridge module 200.

[0143] For example, the first IGCT transistor Q3 and the second IGCT transistor Q4 in the plurality of second switching units 2010 are used to alternately turn on or off according to the second target control command, thereby converting the AC voltage received on the AC side of the second full-bridge module 200 into DC voltage.

[0144] The above are merely specific embodiments of this disclosure, enabling those skilled in the art to understand or implement this disclosure. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this disclosure. Therefore, this disclosure is not to be limited to these embodiments, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A control method for a DC transformer, characterized in that, The DC transformer includes a DC input circuit, a DC output circuit, and a transformer. The DC side of the DC input circuit is connected to the voltage input circuit, the primary side of the transformer is connected to the AC side of the DC input circuit, the secondary side of the transformer is connected to the AC side of the DC output circuit, and the DC side of the DC output circuit is connected to the voltage output circuit. The control method includes: Obtain the first AC voltage information of the primary side and the secondary side, and obtain the initial control command; Based on the first AC voltage information and the initial control command, the reactive power equation and active power equation of the DC transformer are established. If the reactive power equation satisfies the decoupling condition, the first target control command for the DC transformer is determined based on the reactive power equation and the active power equation. The decoupling condition is that the reactive power in the reactive power equation is 0. The first target control command is used to control the operation of the DC input circuit and the DC output circuit.

2. The control method according to claim 1, characterized in that, The first AC voltage information includes: the primary AC voltage of the primary side and the secondary AC voltage of the secondary side; The initial control command includes the initial phase shift angle and the initial duty cycle; The step of establishing the reactive power equation and active power equation of the DC transformer based on the first AC voltage information and the initial control command includes: Based on the primary-side AC voltage and the secondary-side AC voltage, the first fundamental peak value of the primary-side AC voltage and the second fundamental peak value of the secondary-side AC voltage are obtained; Based on the first fundamental peak value, the second fundamental peak value, the initial phase shift angle, and the initial duty cycle, the reactive power equation and the active power equation are established.

3. The control method according to claim 2, characterized in that, The active power equation is as follows: The reactive power equation is: Where P is the calculated active power, Q is the reactive power, and V is the reactive power. p V is the peak value of the first fundamental frequency. s The second fundamental peak value is given by δ, the initial phase shift angle is given by D, the initial duty cycle is given by ω, and the intermediate frequency (IF) is given by L. S The equivalent leakage inductance of the transformer is given.

4. The control method according to claim 3, characterized in that, The first target control command includes the target phase shift angle and the target peak value of the second fundamental frequency peak value; The step of determining the first target control command for the DC transformer based on the reactive power equation and the active power equation, when the reactive power equation satisfies the decoupling condition, includes: When the reactive power in the reactive power equation is 0, the target peak value is determined based on the reactive power equation. The target phase shift angle is determined based on the target peak value and the active power equation.

5. The control method according to claim 1, characterized in that, The method further includes: Obtain the second AC voltage information of the DC input circuit and the DC output circuit under the current control cycle; The current active power and current reactive power of the DC transformer are calculated based on the second AC voltage information. Based on the first target control command, the current active power, and the current reactive power, obtain the feedback correction command for the DC transformer; Based on the feedback correction instruction and the first target control instruction, the second target control instruction for the DC transformer in the current control cycle is obtained.

6. The control method according to claim 5, characterized in that, The step of obtaining the feedback correction command for the DC transformer based on the first target control command, the current active power, and the current reactive power includes: A Jacobian matrix is ​​established based on the first target control command using partial derivative operations, and a decoupling matrix is ​​obtained based on the Jacobian matrix; wherein, the decoupling matrix is ​​the inverse of the Jacobian matrix; Obtain active power reference values ​​and reactive power reference values; Based on the current active power, the current reactive power, the active power reference value, and the reactive power reference value, calculate the active power error and reactive power error of the DC transformer; The feedback correction instruction is obtained based on the decoupling matrix, the active power error, the reactive power error, the current active power, and the current reactive power.

7. The control method according to claim 6, characterized in that, The step of obtaining the feedback correction instruction based on the decoupling matrix, the active power error, the reactive power error, the current active power, and the current reactive power includes: Based on the active power error and the reactive power error, a virtual control vector is generated using a proportional-integral controller. Based on the virtual control vector, the feedback correction command is obtained by performing a linear transformation using the decoupling matrix.

8. The control method according to claim 6, characterized in that, The process of obtaining the decoupling matrix based on the Jacobian matrix includes: The decoupling matrix is ​​calculated based on the Jacobian matrix using the Tikhonov regularized pseudo-inverse algorithm. The decoupling matrix is: Where M is the decoupling matrix and J is the Jacobian matrix. Here, I is the regularization parameter, and I is the identity matrix.

9. A DC transformer, characterized in that, Applied to the control method as described in any one of claims 1-8; The DC input circuit includes a first full-bridge module; the DC output circuit includes two second full-bridge modules; the transformer includes a first transformer unit and a second transformer unit. The first end of the first transformer unit and the second end of the second transformer unit are connected to the AC side of the first full-bridge module, the second end of the first transformer unit is connected to the first end of the second transformer unit, and the DC side of the first full-bridge module is connected to the voltage input circuit. The third and fourth terminals of the first transformer unit are connected to the AC side of the corresponding second full-bridge module, and the DC side of the second full-bridge module is connected to the voltage output circuit.

10. The DC transformer according to claim 9, characterized in that, The first full-bridge module includes four first bridge arms; The first bridge arm includes a plurality of first switching units; Multiple first switching units are connected in series and / or in parallel; The first end of the first bridge arm is connected to the DC side of the first full-bridge module, and the second end of the first bridge arm is connected to the AC side of the first full-bridge module.

11. The DC transformer according to claim 10, characterized in that, The first switching unit includes a first IGBT, a second IGBT, and a first capacitor; The first end of the first IGBT is connected to the first end of the first capacitor, the second end of the first IGBT is connected to the first end of the first switching unit, and the second end of the second IGBT is connected to the second end of the first capacitor. The first end of the second IGBT is used to connect to the second end of the adjacent first switching unit or the DC side of the first full-bridge module; The second end of the second IGBT is used to connect to the first end of the adjacent first switching unit or the AC side of the first full-bridge module.

12. The DC transformer according to claim 9, characterized in that, The second full-bridge module includes four second bridge arms; The second bridge arm includes multiple second switching units; Multiple second switching units are connected in series and / or in parallel; The first end of the second bridge arm is connected to the DC side of the second full-bridge module, and the second end of the second bridge arm is connected to the AC side of the second full-bridge module.

13. The DC transformer according to claim 12, characterized in that, The second switching unit includes a first IGCT transistor, a second IGCT transistor, and a second capacitor; The first end of the first IGCT transistor is connected to the first end of the second capacitor, the second end of the first IGCT transistor and the first end of the second IGCT transistor are connected to the first end of the second switching unit, and the second end of the second IGCT transistor and the second end of the second capacitor are connected to the second end of the second switching unit. The first end of the second IGCT tube is used to connect to the second end of the adjacent second switching unit or the DC side of the second full-bridge module; The second end of the second IGCT tube is used to connect to the first end of the adjacent second switching unit or the AC side of the second full-bridge module.

Images