Decoupling control method and device for current inner loop of modular multilevel converter of network construction type

Abstract

This invention discloses a current inner-loop decoupling control method and apparatus for a grid-connected modular multilevel converter. The method includes: acquiring the three-phase AC voltage and current, output active power, and reactive power at the point of common coupling (PCC); obtaining the output AC voltage and phase angle reference values ​​of the converter based on the output active and reactive power; acquiring the dq-axis voltage and current components at PCC based on the three-phase AC voltage and current and phase angle reference values; obtaining a first reference value for the dq-axis current through integral control; obtaining a second reference current for the dq-axis based on the first reference value through a decoupling stage; obtaining dq-axis control signals based on the dq-axis current components and the second reference current; and obtaining control signals based on the dq-axis control signals to control the switching on or off of the converter. This invention can reduce the coupling problem between the output active and reactive power of the converter when using grid-connected control, thereby improving its dynamic control performance.

Description

Technical Field

[0001] This invention relates to the field of power grid technology, and in particular to a method and apparatus for decoupling the inner current loop of a grid-type modular multilevel converter. Background Technology

[0002] Unlike grid-following control based on grid-connection point voltage phase detection, grid-connected control actively establishes the frequency and phase of the converter, manifesting as a controlled voltage source to the grid. Grid-connected control of converters originated in microgrids without or with weak synchronous power sources to address the off-grid operation of inverters in microgrids. With the rapid increase in the proportion of renewable energy, the problem of low-inertia, weak grids has become more prominent, and research on grid-connected control has gradually expanded to grid-connected converters such as wind power converters, photovoltaic inverters, and energy storage inverters, with some initial demonstration applications.

[0003] For grid-connected converters under grid-connected control, current limiting is a major technical challenge. Existing current limiting schemes include the virtual impedance method and the inner current loop method. The former limits the output current by adding an adjustable virtual impedance to the control loop; however, its current limiting effect is affected by the location of grid faults, resulting in poor current limiting accuracy. The latter achieves current limiting by establishing a three-loop structure: an active power synchronization outer loop, an AC voltage middle loop, and an AC current inner loop. However, this control structure is typically based on a two-level topology converter design, using its AC-side filter capacitor as the AC voltage reference point to achieve decoupling of active and reactive power control. However, modular multilevel topology converters lack filter capacitors on the AC side, making it difficult to provide this voltage reference point, leading to degraded control performance and coupling between the active and reactive power control loops. Summary of the Invention

[0004] To overcome the shortcomings of the existing technology, the present invention aims to provide a current inner loop decoupling control method and device for a grid-type modular multilevel converter, so as to reduce the coupling between active and reactive power control loops and improve the control performance of the multilevel converter when there is no filter capacitor on the AC side.

[0005] To achieve the above objectives, the present invention provides a current inner loop decoupling control method for a grid-type modular multilevel converter, comprising the following steps:

[0006] Obtain the three-phase AC voltage, three-phase AC current, output active power, and reactive power at the point of common coupling;

[0007] Based on the obtained output active power and reactive power, the reference values ​​of the output AC voltage and output phase angle of the grid-type modular multilevel converter are calculated.

[0008] The d-axis voltage component and q-axis voltage component of the common coupling point are obtained based on the three-phase AC voltage and the output phase angle reference value. The d-axis current component and q-axis current component of the common coupling point are obtained based on the three-phase AC current and the output phase angle reference value.

[0009] Based on the difference between the d-axis voltage component and the reference value of the output AC voltage of the grid-type modular multilevel converter, and the q-axis voltage component, the first reference values ​​of the d-axis current and the q-axis current are obtained through integral control.

[0010] The first reference value of the d-axis current and the first reference value of the q-axis current are decoupled to obtain the second reference current of the d-axis and the second reference current of the q-axis, respectively.

[0011] The d-axis control signal is obtained based on the d-axis current component and the second reference current of the d-axis, and the q-axis control signal is obtained based on the q-axis current component and the second reference current of the q-axis;

[0012] The final control signal is obtained based on the d-axis control signal and the q-axis control signal to control the activation or deactivation of the grid-type modular multilevel converter.

[0013] Optionally, in the step of calculating the output AC voltage reference value and output phase angle reference value of the grid-type modular multilevel converter based on the obtained output active power and reactive power, the difference between the output reactive power at the common coupling point and the set reactive power reference value is obtained, multiplied by a preset droop coefficient, and then added to the rated voltage to obtain the output AC voltage reference value of the grid-type modular multilevel converter.

[0014] Optionally, in the step of calculating the output AC voltage reference value and output phase angle reference value of the grid-type modular multilevel converter based on the obtained output active power and reactive power, the difference between the output active power at the common coupling point and the set active power reference value is obtained, multiplied by a preset droop coefficient, and then added to the rated frequency to obtain the reference value of the output frequency of the grid-type modular multilevel converter. Finally, the reference value of the output frequency is integrated to obtain the output phase angle reference value.

[0015] Optionally, the step of obtaining the d-axis voltage component and q-axis voltage component of the common connection point based on the three-phase AC voltage and phase reference value further includes: performing a park change on the three-phase AC voltage under the output phase angle reference value to obtain the d-axis voltage component and q-axis voltage component.

[0016] Optionally, obtaining the d-axis current component and q-axis current component of the common connection point based on the three-phase AC current and the output phase angle reference value includes: performing a park change on the three-phase AC current under the output phase angle reference value to obtain the d-axis current component and q-axis current component.

[0017] Optionally, in the step of obtaining the first reference values ​​of the d-axis current and q-axis current through integral transformation based on the difference between the d-axis voltage component and the output AC voltage reference value of the grid-type modular multilevel converter, and the q-axis voltage component, the first reference values ​​of the d-axis current and q-axis current are obtained through an integral controller and a proportional-integral control based on the difference between the d-axis voltage component and the output AC voltage reference value of the grid-type modular multilevel converter, and the q-axis voltage component.

[0018] Optionally, the step of obtaining the second reference current of the d-axis and the second reference current of the q-axis respectively through a decoupling process after decoupling the first reference value of the d-axis current and the first reference value of the q-axis current further includes:

[0019] The first reference value of the d-axis current and the first reference value of the q-axis current are combined to form a column vector I. rec1 Then, it is decoupled using a decoupling matrix to obtain the decoupled column vector I. rec2 ;

[0020] Based on the decoupled column vector I rec2 The second reference current along the d-axis and the second reference current along the q-axis are obtained.

[0021] Optionally, the decoupling matrix is ​​in the form of:

[0022]

[0023] In the formula, s is the Laplace operator, ω MMC This is a reference value for the output frequency of the grid-type modular multilevel converter.

[0024] Optionally, the step of obtaining the d-axis control signal based on the d-axis current component and the second d-axis reference current, and obtaining the q-axis control signal based on the q-axis current component and the second q-axis reference current, further includes:

[0025] The d-axis current component and the second d-axis reference current are passed through a proportional-integral controller to obtain the d-axis control signal.

[0026] The q-axis current component and the second q-axis reference current are passed through a proportional-integral controller to obtain the q-axis control signal.

[0027] To achieve the above objectives, the present invention also provides a current inner loop decoupling control device for a grid-type modular multilevel converter, comprising:

[0028] The parameter acquisition unit is used to acquire the three-phase AC voltage, three-phase AC current, output active power and reactive power at the point of common coupling.

[0029] The output AC voltage and phase angle reference value calculation unit is used to calculate the output AC voltage reference value and output phase angle reference value of the grid-type modular multilevel converter based on the obtained output active power and reactive power.

[0030] The d-axis and q-axis voltage and current component acquisition unit is used to acquire the d-axis voltage component and q-axis voltage component of the common coupling point based on the three-phase AC voltage and the output phase angle reference value, and to acquire the d-axis current component and q-axis current component of the common coupling point based on the three-phase AC current and the output phase angle reference value.

[0031] An integrator unit is used to obtain first reference values ​​of the d-axis current and q-axis current through integral control based on the difference between the d-axis voltage component and the output AC voltage reference value of the grid-type modular multilevel converter, as well as the q-axis voltage component.

[0032] A decoupling unit is used to obtain a second reference current on the d-axis and a second reference current on the q-axis by decoupling the first reference value of the d-axis current and the first reference value of the q-axis current, respectively.

[0033] The dq-axis control signal acquisition unit is used to obtain the d-axis control signal based on the d-axis current component and the second reference current of the d-axis, and to obtain the q-axis control signal based on the q-axis current component and the second reference current of the q-axis.

[0034] The control unit is used to obtain the final control signal based on the d-axis control signal and the q-axis control signal to control the activation or deactivation of the grid-type modular multilevel converter.

[0035] Compared with the prior art, the present invention provides a current inner loop decoupling control method and device for a grid-type modular multilevel converter. By adding an integral element and a decoupling element, the modular multilevel converter under grid-type control can reduce the coupling between the active and reactive power control loops and improve the control performance of the converter when there is no filter capacitor on the AC side.

[0036] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0037] The above and other objects, features, and advantages of the present invention will become more apparent from the more detailed description of the embodiments of the invention in conjunction with the accompanying drawings. The drawings are provided to further illustrate the embodiments of the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings, the same reference numerals generally represent the same parts or steps.

[0038] Figure 1 This is a system architecture diagram of the flexible DC grid-connected system used in the embodiments of the present invention;

[0039] Figure 2 This is a flowchart illustrating an exemplary embodiment of the present invention for a current inner loop decoupling control method for a grid-type modular multilevel converter.

[0040] Figure 3 This is a graph showing the reactive power variation of the grid-type modular multilevel converter in this embodiment;

[0041] Figure 4 This is a graph showing the change in active power output of the grid-type modular multilevel converter in this embodiment;

[0042] Figure 5 This is a structural block diagram of a grid-type modular multilevel converter current inner loop decoupling control device provided in an exemplary embodiment of the present invention. Detailed Implementation

[0043] The implementation methods of the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings and descriptions. The described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort should fall within the scope of protection of the present invention.

[0044] In the following text, the terms “first,” “second,” etc., are used to distinguish between similar elements and are not necessarily used to describe a specific order or chronological sequence. It should be understood that these terms, as used herein, may be replaced where appropriate. Similarly, if the methods described herein comprise a series of steps, and the order of these steps presented herein is not necessarily the only possible order in which they can be performed, and some described steps may be omitted and / or other steps not described herein may be added to the method.

[0045] Figure 1This is a system architecture diagram of the flexible DC grid-connected system used in an embodiment of the present invention. The flexible DC grid-connected system includes: a grid-type modular multilevel converter 110, a transformer 120, and an AC system 140. The grid-type modular multilevel converter 110 inverts DC to AC, which then reaches the AC system 140 via the connecting transformer 120. A control signal is calculated from the voltage at the common connection point 130 after the grid-type modular multilevel converter 110 and the connecting transformer 120.

[0046] Exemplary methods

[0047] Figure 2 This is a flowchart illustrating a current inner-loop decoupling control method for a grid-type modular multilevel converter, provided by an exemplary embodiment of the present invention. Figure 2 As shown, the present invention provides a current inner loop decoupling control method for a grid-type modular multilevel converter, comprising the following steps:

[0048] Step S1: Obtain the three-phase AC voltage, three-phase AC current, output active power, and reactive power at the point of common coupling.

[0049] Step S2: Calculate the reference values ​​of the output AC voltage and the output phase angle of the grid-type modular multilevel converter based on the obtained output active power and reactive power.

[0050] In this embodiment, the method for calculating the reference value of the output AC voltage of the grid-type modular multilevel converter includes: subtracting the output reactive power of the point of common coupling obtained in step S1 from the set reactive power reference value, multiplying by a set droop coefficient, and then adding it to the rated voltage to obtain the reference value of the converter output voltage. The specific calculation formula is as follows:

[0051] E ref =k E (Q ref -Q)+E nom ;

[0052] Where, k E E is the droop factor for AC voltage control. ref E is the reference value for the converter output voltage. nom Q is the rated value of the output AC voltage, and Q is the actual reactive power output of the converter. ref This is a reference value for the reactive power output of the converter.

[0053] The method for calculating the output phase angle reference value of the grid-type modular multilevel converter includes:

[0054] The difference between the output active power at the point of common coupling obtained in step S1 and the set active power reference value is multiplied by the set droop coefficient, and then added to the rated frequency to obtain the reference value of the converter output frequency. The output phase angle reference value is then obtained by integrating the reference value of the output frequency. In this embodiment, the rated frequency of the sending-end converter is 50Hz. The specific calculation formula is as follows:

[0055]

[0056] Where, θ MMC Here, ω represents the converter output phase angle reference value, s is the Laplace operator, and ω is the phase angle reference value. MMC ω is the reference value for the converter output frequency. nom For the rated frequency, P ref P represents the actual active power output of the converter. ref This is a reference value for the active power output of the converter.

[0057] Step S3: Obtain the d-axis voltage component and q-axis voltage component of the common coupling point based on the three-phase AC voltage and the output phase angle reference value; obtain the d-axis current component and q-axis current component of the common coupling point based on the three-phase AC current and the output phase angle reference value.

[0058] Specifically, the step of obtaining the d-axis voltage component and q-axis voltage component of the common coupling point based on the three-phase AC voltage and the output phase angle reference value further includes:

[0059] The three-phase AC voltage is park-transformed under the output phase angle reference value to obtain the d-axis voltage component and the q-axis voltage component.

[0060] Specifically, the park change is expressed using the following formula:

[0061]

[0062] Among them, u d u q For the voltage components along the d-axis and q-axis, u a u b and u c For three-phase AC voltage, θ MMC To output the phase angle reference value, u0 is generally zero in the case of three-phase symmetry.

[0063] Similarly, the method for obtaining the d-axis current component and q-axis current component of the point of common coupling based on the three-phase AC current and phase angle reference value includes:

[0064] The three-phase AC current is park-transformed under the output phase angle reference value to obtain the d-axis current component and the q-axis current component.

[0065]

[0066] Among them, i d i q i represents the current components along the d-axis and q-axis. a i b and i c For three-phase AC voltage, θ MMC It is the output phase angle reference value. In the case of three-phase symmetry, i0 is generally zero.

[0067] It should be noted that the methods for obtaining three-phase AC voltage and three-phase AC current are existing technologies and will not be elaborated here. The methods for obtaining the d-axis and q-axis voltage components are also existing technologies and will not be elaborated here.

[0068] Step S4: Based on the difference between the d-axis voltage component and the reference value of the output AC voltage of the grid-type modular multilevel converter, as well as the q-axis voltage component, the first reference values ​​of the d-axis current and q-axis current are obtained through an integral controller and a proportional-integral controller.

[0069] In step S4, based on the difference between the d-axis voltage component and the output AC voltage reference value, and the difference between the q-axis voltage component and 0, the first reference values ​​of the d-axis current and q-axis current are obtained through an integral controller and a proportional-integral controller. The specific calculation formula is as follows:

[0070]

[0071] Among them, E ref u is the reference value for the converter output voltage. d For the d-axis voltage component, u q Let be the q-axis voltage component, and s be the Laplace operator. and For the integral controller, k i1d and k i1q These are the control parameters for the integral controller. and For the proportional-integral controller, k p2d k p2q k i2d and k i2q For the control parameters of the proportional-integral controller, i dref1 and i qref1 These are the first reference currents along the d-axis and the first reference currents along the q-axis, respectively.

[0072] Step S5: The first reference value of the d-axis current and the first reference value of the q-axis current are decoupled to obtain the second reference current of the d-axis and the second reference current of the q-axis respectively.

[0073] Specifically, step S5 further includes:

[0074] Step S500: Combine the first reference value of the d-axis current and the first reference value of the q-axis current into a column vector I. rec1 It is then decoupled using a decoupling matrix D to obtain the decoupled column vector I. rec2 .

[0075] Specifically, the first reference value of the d-axis current and the first reference value of the q-axis current are combined to form a column vector I. rec1 :

[0076]

[0077] Among them, i dref1 i is the first reference value for the d-axis current. qref1 This is the first reference value for the q-axis current. Then, a decoupling matrix D is left-multiplied by this column vector to obtain the decoupled column vector I. rec2 :

[0078] I rec2 =D×I rec1

[0079] Step S501, based on the decoupled column vector I rec2 The second reference current along the d-axis and the second reference current along the q-axis are obtained.

[0080] With the decoupled column vector I rec2 The first term serves as the second reference value for the d-axis current, expressed in column vector I. rec2 The second term serves as the second reference value for the q-axis current.

[0081] Preferably, the decoupling matrix D is in the form of:

[0082]

[0083] In the formula, s is the Laplace operator, ω MMC This is a reference value for the converter output frequency.

[0084] Step S6: Obtain the d-axis control signal based on the d-axis current component and the second reference current of the d-axis, and obtain the q-axis control signal based on the q-axis current component and the second reference current of the q-axis.

[0085] Specifically, step S6 further includes:

[0086] Step S600: The d-axis current component and the second reference current of the d-axis are passed through a proportional-integral controller to obtain the d-axis control signal;

[0087] Step S601: Pass the q-axis current component and the second q-axis reference current through a proportional-integral controller to obtain the q-axis control signal.

[0088] Step S7: Obtain control signals based on the d-axis control signal and the q-axis control signal to control the activation or deactivation of the grid-type modular multilevel converter.

[0089] In this embodiment, a control signal is obtained by inverse park change based on the d-axis control signal and the q-axis control signal, and the grid-type modular multilevel converter is put into or taken out of control through the control signal.

[0090] Specifically, the inverse Park change is expressed using the following formula:

[0091]

[0092] Among them, u d u q For the d-axis and q-axis control signals, u a u b and u c For three-phase AC voltage, θ MMC This is to output the phase angle reference value.

[0093] Meanwhile, this invention verified the above method through simulation. This invention utilizes PSCAD / EMTDC software, and this paper uses PSCAD / EMTDC software based on... Figure 1 A simulation model of the modular multilevel converter with a grid structure was constructed, and simulation results were obtained. Figure 3 and Figure 4 The simulation system parameters are shown in Table 1, which contains parameters for the grid-type modular multilevel converter.

[0094] Table 1

[0095]

[0096] Assuming the initial active power of a grid-type modular multilevel converter is 50MW and the initial reactive power is 0Mvar, the output reactive power is modified to 50Mvar at t=0.5s, and the output active power is modified to 0Mvar at t=1.5s. The reactive power changes throughout the process are as follows: Figure 3 Changes in active power, such as Figure 4 ,from Figure 3 and Figure 4As can be seen from the embodiments of the present invention, after adopting the decoupling control method, when the reactive power setpoint is modified, the converter can quickly control its output reactive power to the setpoint, while the change in active power is very small. When the active power setpoint is modified, the converter can quickly control its output active power to the setpoint, while the change in reactive power is very small. Therefore, the decoupling control method of the embodiments of the present invention can effectively solve the problem of active and reactive power control coupling in grid-type modular multilevel converters.

[0097] Exemplary device

[0098] Figure 5 This is a schematic diagram of the current inner loop decoupling control device for a grid-type modular multilevel converter, provided as an exemplary embodiment of the present invention. Figure 5 As shown, the present invention provides a current inner loop decoupling control device for a grid-type modular multilevel converter, comprising:

[0099] The parameter acquisition unit 501 is used to acquire the three-phase AC voltage, three-phase AC current, output active power and reactive power at the point of common coupling.

[0100] The output AC voltage and phase angle reference value calculation unit 502 is used to calculate the output AC voltage reference value and output phase angle reference value of the grid-type modular multilevel converter based on the acquired output active power and reactive power.

[0101] In this embodiment, the output AC voltage and phase angle reference value calculation unit 502 calculates the difference between the output reactive power at the common coupling point obtained by the parameter acquisition unit 501 and the set reactive power reference value, multiplies it by a set droop coefficient, and then adds it to the rated voltage to obtain the reference value of the converter output voltage. The specific calculation formula is as follows:

[0102] E ref =k E (Q ref -Q)+E nom ;

[0103] Where, k E E is the droop factor for AC voltage control. ref E is the reference value for the converter output voltage. nom Q is the rated value of the output AC voltage, and Q is the actual reactive power output of the converter. ref This is a reference value for the reactive power output of the converter.

[0104] The output AC voltage and phase angle reference value calculation unit 502 calculates the difference between the output active power at the common coupling point obtained by the parameter acquisition unit 501 and the set active power reference value, multiplies it by a set droop coefficient, and then adds it to the rated frequency to obtain the reference value of the converter output frequency. The output phase angle reference value is then obtained by integrating the reference value of the output frequency. In this embodiment, the rated frequency of the sending-end converter is 50Hz. The specific calculation formula is as follows:

[0105]

[0106] Where, θ MMC Here, ω represents the converter output phase angle reference value, s is the Laplace operator, and ω is the phase angle reference value. MMC ω is the reference value for the converter output frequency. nom For the rated frequency, P ref P represents the actual active power output of the converter. ref This is a reference value for the active power output of the converter.

[0107] The d-axis and q-axis voltage and current component acquisition unit 503 is used to acquire the d-axis voltage component and q-axis voltage component of the common coupling point based on the three-phase AC voltage and the output phase angle reference value, and to acquire the d-axis current component and q-axis current component of the common coupling point based on the three-phase AC current and the phase angle reference value.

[0108] Specifically, the d-axis and q-axis voltage and current component acquisition unit 503 performs park-like changes on the three-phase AC voltage under the output phase angle reference value to obtain the d-axis voltage component and the q-axis voltage component.

[0109] Similarly, the d-axis and q-axis voltage and current component acquisition unit 503 performs park changes on the three-phase AC current under the output phase angle reference value to obtain the d-axis current component and the q-axis current component.

[0110] The integrator unit 504 is used to obtain the first reference values ​​of the d-axis current and the q-axis current through an integral controller and a proportional-integral control based on the difference between the d-axis voltage component and the output AC voltage reference value of the grid-type modular multilevel converter and the q-axis voltage component.

[0111] In this embodiment, the integrator 504 obtains the first reference values ​​of the d-axis current and q-axis current based on the difference between the d-axis voltage component and the output AC voltage reference value, and the difference between the q-axis voltage component and 0, through an integral controller and a proportional-integral controller. The specific calculation formula is as follows:

[0112]

[0113] Among them, E ref u is the reference value for the converter output voltage.d For the d-axis voltage component, u q Let be the q-axis voltage component, and s be the Laplace operator. and For the integral controller, k i1d and k i1q These are the control parameters for the integral controller. and For the proportional-integral controller, k p2d k p2q k i2d and k i2q For the control parameters of the proportional-integral controller, i dref1 and i qref1 These are the first reference currents along the d-axis and the first reference currents along the q-axis, respectively.

[0114] The decoupling unit 505 is used to obtain the second reference current of the d-axis and the second reference current of the q-axis by passing the first reference value of the d-axis current and the first reference value of the q-axis current through a decoupling link.

[0115] Specifically, the decoupling unit 505 further includes:

[0116] The first reference value of the d-axis current and the first reference value of the q-axis current are combined to form a column vector I. rec1 It is then decoupled using a decoupling matrix D to obtain the decoupled column vector I. rec2 .

[0117] Specifically, the first reference value of the d-axis current and the first reference value of the q-axis current are combined to form a column vector I. rec1 :

[0118]

[0119] Among them, i dref1 i is the first reference value for the d-axis current. qref1 This is the first reference value for the q-axis current. Then, a decoupling matrix D is left-multiplied by this column vector to obtain the decoupled column vector I. rec2 :

[0120] I rec2 =D×I rec1

[0121] The second reference current along the d-axis and the second reference current along the q-axis are obtained from the decoupled column vectors.

[0122] With the decoupled column vector I rec2 The first term serves as the second reference value for the d-axis current, expressed in column vector I. rec2 The second term serves as the second reference value for the q-axis current.

[0123] Preferably, the decoupling matrix D is in the form of:

[0124]

[0125] In the formula, s is the Laplace operator, ω MMC This is a reference value for the converter output frequency.

[0126] The dq-axis control signal acquisition unit 506 is used to obtain the d-axis control signal based on the d-axis current component and the second reference current of the d-axis, and to obtain the q-axis control signal based on the q-axis current component and the second reference current of the q-axis.

[0127] Specifically, the dq-axis control signal is obtained by passing the d-axis current component and the second reference current of the d-axis through a proportional-integral controller to obtain the d-axis control signal, and the q-axis control signal is obtained by passing the q-axis current component and the second reference current of the q-axis through a proportional-integral controller to obtain the q-axis control signal.

[0128] Control unit 507 is used to obtain control signals based on d-axis control signals and q-axis control signals to control the activation or deactivation of the grid-type modular multilevel converter.

[0129] In this embodiment, the control unit 507 obtains a control signal through inverse park change based on the d-axis control signal and the q-axis control signal, and controls the connection or disconnection of the grid-type modular multilevel converter through the control signal.

[0130] The basic principles of this disclosure have been described above with reference to specific embodiments. However, it should be noted that the advantages, benefits, and effects mentioned in this disclosure are merely examples and not limitations, and should not be considered as essential features of each embodiment of this disclosure. Furthermore, the specific details disclosed above are for illustrative and facilitative purposes only, and are not limitations. These details do not limit the scope of this disclosure to the necessity of employing the aforementioned specific details for implementation.

[0131] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For system embodiments, since they largely correspond to method embodiments, the description is relatively simple; relevant parts can be referred to the descriptions in the method embodiments.

[0132] The block diagrams of devices, apparatuses, devices, and systems disclosed herein are merely illustrative examples and are not intended to require or imply that they must be connected, arranged, or configured in the manner shown in the block diagrams. As those skilled in the art will recognize, these devices, apparatuses, devices, and systems can be connected, arranged, and configured in any manner. Words such as “comprising,” “including,” “having,” etc., are open-ended terms meaning “including but not limited to,” and are used interchangeably with them. The terms “or” and “and” as used herein refer to the terms “and / or,” and are used interchangeably with them unless the context clearly indicates otherwise. The term “such as” as used herein refers to the phrase “such as but not limited to,” and is used interchangeably with it.

[0133] The methods and apparatus of this disclosure may be implemented in many ways. For example, they may be implemented by software, hardware, firmware, or any combination of software, hardware, and firmware. The above-described order of steps for the methods is for illustrative purposes only, and the steps of the methods of this disclosure are not limited to the order specifically described above unless otherwise specifically stated. Furthermore, in some embodiments, this disclosure may also be implemented as a program recorded on a recording medium, the program including machine-readable instructions for implementing the methods according to this disclosure. Thus, this disclosure also covers recording media storing programs for performing the methods according to this disclosure.

[0134] It should also be noted that in the apparatus, devices, and methods of this disclosure, the components or steps are decomposable and / or recombinable. Such decomposition and / or recombination should be considered equivalent to the present disclosure. The above description of the disclosed aspects is provided to enable any person skilled in the art to make or use this disclosure. Various modifications to these aspects will be readily apparent to those skilled in the art, and the general principles defined herein can be applied to other aspects without departing from the scope of this disclosure. Therefore, this disclosure is not intended to be limited to the aspects shown herein, but rather to be carried out within the widest scope consistent with the principles and novel features disclosed herein.

[0135] The above description has been given for purposes of illustration and description. Furthermore, this description is not intended to limit the embodiments of this disclosure to the forms disclosed herein. Although numerous exemplary aspects and embodiments have been discussed above, those skilled in the art will recognize certain variations, modifications, alterations, additions, and sub-combinations therein.

Claims

1. A current inner loop decoupling control method for a grid-type modular multilevel converter, comprising the following steps: Obtain the three-phase AC voltage, three-phase AC current, output active power, and reactive power at the point of common coupling; Based on the obtained output active power and reactive power, the reference values ​​of the output AC voltage and output phase angle of the grid-type modular multilevel converter are calculated. The d-axis voltage component and q-axis voltage component of the point of common coupling are obtained based on the three-phase AC voltage and the output phase angle reference value; the d-axis current component and q-axis current component of the point of common coupling are obtained based on the three-phase AC current and the output phase angle reference value. Based on the difference between the d-axis voltage component and the output AC voltage reference value of the grid-type modular multilevel converter, and the q-axis voltage component, first reference values ​​for the d-axis current and q-axis current are obtained through an integral controller and a proportional-integral controller. The first reference values ​​for the d-axis current and q-axis current are then decoupled to obtain second reference currents for the d-axis and q-axis currents, respectively. The step of obtaining the second reference currents for the d-axis current and q-axis current through decoupling further includes: forming a column vector I from the first reference values ​​for the d-axis current and the first reference values ​​for the q-axis current. rec1 Then, it is decoupled using a decoupling matrix to obtain the decoupled column vector I. rec2 Based on the decoupled column vector I rec2 The second reference current along the d-axis and the second reference current along the q-axis are obtained; the decoupling matrix is ​​in the form of: In the formula, s is the Laplace operator. This is a reference value for the output frequency of the grid-type modular multilevel converter; The d-axis control signal is obtained based on the d-axis current component and the second reference current of the d-axis, and the q-axis control signal is obtained based on the q-axis current component and the second reference current of the q-axis; The final control signal is obtained based on the d-axis control signal and the q-axis control signal to control the activation or deactivation of the grid-type modular multilevel converter.

2. The current inner loop decoupling control method for a grid-type modular multilevel converter as described in claim 1, characterized in that, In the step of calculating the output AC voltage reference value and output phase angle reference value of the grid-type modular multilevel converter based on the obtained output active power and reactive power, the difference between the output reactive power at the common connection point and the set reactive power reference value is obtained, multiplied by the preset droop coefficient, and then added to the rated voltage to obtain the output AC voltage reference value of the grid-type modular multilevel converter.

3. The current inner loop decoupling control method for a grid-type modular multilevel converter as described in claim 2, characterized in that, In the step of calculating the reference value of the output AC voltage and the reference value of the output phase angle of the grid-type modular multilevel converter based on the obtained output active power and reactive power, the difference between the output active power at the common coupling point and the set active power reference value is obtained, multiplied by a preset droop coefficient, and then added to the rated frequency to obtain the reference value of the output frequency of the grid-type modular multilevel converter. Finally, the reference value of the output frequency is integrated to obtain the reference value of the output phase angle.

4. The current inner loop decoupling control method for a grid-type modular multilevel converter as described in claim 3, characterized in that, The step of obtaining the d-axis voltage component and q-axis voltage component of the common connection point based on the three-phase AC voltage and the output phase reference value further includes: performing a park change on the three-phase AC voltage under the output phase angle reference value to obtain the d-axis voltage component and q-axis voltage component.

5. The current inner loop decoupling control method for a grid-type modular multilevel converter as described in claim 4, characterized in that, The step of obtaining the d-axis current component and q-axis current component of the common connection point based on the three-phase AC current and the output phase angle reference value includes: performing a park change on the three-phase AC current under the output phase angle reference value to obtain the d-axis current component and q-axis current component.

6. The current inner loop decoupling control method for a grid-type modular multilevel converter as described in claim 1, characterized in that, The step of obtaining the d-axis control signal based on the d-axis current component and the second d-axis reference current, and obtaining the q-axis control signal based on the q-axis current component and the second q-axis reference current, further includes: The d-axis current component and the second d-axis reference current are passed through a proportional-integral controller to obtain the d-axis control signal. The q-axis current component and the second q-axis reference current are passed through a proportional-integral controller to obtain the q-axis control signal.

7. A current inner loop decoupling control device for a grid-type modular multilevel converter, comprising: The parameter acquisition unit is used to acquire the three-phase AC voltage, three-phase AC current, output active power and reactive power at the point of common coupling. The output AC voltage and phase angle reference value calculation unit is used to calculate the output AC voltage reference value and output phase angle reference value of the grid-type modular multilevel converter based on the obtained output active power and reactive power. The d-axis and q-axis voltage and current component acquisition unit is used to acquire the d-axis voltage component and q-axis voltage component of the common coupling point based on the three-phase AC voltage and the output phase angle reference value, and to acquire the d-axis current component and q-axis current component of the common coupling point based on the three-phase AC current and the output phase angle reference value. An integral unit is used to obtain first reference values ​​of d-axis current and q-axis current based on the difference between the d-axis voltage component and the output AC voltage reference value of the grid-type modular multilevel converter, and the q-axis voltage component, through an integral controller and a proportional-integral control. A decoupling unit is used to obtain a second reference current on the d-axis and a second reference current on the q-axis respectively by decoupling the first reference value of the d-axis current and the first reference value of the q-axis current. The step of obtaining the second reference current on the d-axis and the second reference current on the q-axis respectively by decoupling the first reference value of the d-axis current and the first reference value of the q-axis current further includes: forming a column vector I from the first reference value of the d-axis current and the first reference value of the q-axis current. rec1 Then, it is decoupled using a decoupling matrix to obtain the decoupled column vector I. rec2 Based on the decoupled column vector I rec2 The second reference current along the d-axis and the second reference current along the q-axis are obtained; the decoupling matrix is ​​in the form of: In the formula, s is the Laplace operator. This is a reference value for the output frequency of the grid-type modular multilevel converter; The dq-axis control signal acquisition unit is used to obtain the d-axis control signal based on the d-axis current component and the second reference current of the d-axis, and to obtain the q-axis control signal based on the q-axis current component and the second reference current of the q-axis; The control unit is used to obtain the final control signal based on the d-axis control signal and the q-axis control signal to control the activation or deactivation of the grid-type modular multilevel converter.

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