Symmetrical capacitor sub-module multilevel converter active power decoupling control method

Abstract

The application discloses a kind of symmetric capacitor submodule multi-level converter active power decoupling control methods, belong to multi-level converter technical field, this method includes constructing the symmetric capacitor decoupling submodule topology of multi-level converter;According to symmetric capacitor decoupling submodule topology, establish inductance current model and capacitor voltage model;According to inductance current model and capacitor voltage model, voltage and current double closed loop control is carried out, and active power decoupling control of multi-level converter is completed.The application solves the problem that traditional MMC submodule capacitor voltage will have fundamental frequency and double-frequency ripple when power exchange of modular multi-level converter dc-ac side.

Description

Technical Field

[0001] This invention belongs to the field of multilevel converter technology, and particularly relates to an active power decoupling control method for a symmetrical capacitor submodule multilevel converter. Background Technology

[0002] Multilevel technology utilizes low-voltage, low-current power devices to form novel topologies for medium- and high-voltage, high-power applications. It offers advantages such as a high number of output levels, low output voltage harmonics, low switching frequency, and low voltage stress on power switching devices, making it increasingly popular and widely researched in medium- and high-voltage, high-power applications. Commonly used multilevel topologies include: Neutral Point Clamped Converter (NPC), Cascaded H-Bridge Converter (CHB), and Modular Multilevel Converter (MMC).

[0003] Due to its highly modular design, easily expandable voltage and power capacity, redundant control, and high output quality, this converter is widely used in high-voltage flexible DC transmission and medium-voltage power distribution. Each submodule of this converter has a DC-side capacitor, which acts as a DC source to provide the voltage level for MMC operation. However, during DC-AC power exchange, the submodule capacitor voltage exhibits fundamental and second-harmonic ripple. Excessive ripple can affect device stress and output characteristics. In engineering applications, larger capacitors are generally used to suppress voltage ripple; however, larger capacitors significantly increase system hardware cost and size.

[0004] One existing technical approach proposes an active power decoupling scheme based on a symmetrical half-bridge structure of a rectifier single-phase converter. This technique transfers ripple of a specific frequency to energy storage elements by controlling the switching of power devices. The filter decoupling circuit stores energy through the two capacitors of the symmetrical half-bridge, ensuring that the ripple voltages of the two capacitors are equal in magnitude and opposite in direction. The sum of the DC components of the voltages equals the rectified output voltage, while ensuring that the power ripple of the symmetrical capacitors remains the same after active power decoupling, thus guaranteeing stable converter operation. However, the rectifier single-phase converter system has a simple structure, and the active power decoupling technique can only handle the inherent second harmonic component of the capacitor voltage ripple. Furthermore, the system's operational model is simple, and the active decoupling control algorithm is rudimentary, employing only a voltage loop control method with a directly given capacitor voltage. Due to the simplistic control scheme, the system stability is poor. When there are sudden load changes or external interference, the amplitude of the rectified output DC voltage fluctuates significantly and takes a long time to stabilize, resulting in a slow dynamic response. Summary of the Invention

[0005] To address the aforementioned shortcomings in the existing technology, the present invention provides an active power decoupling control method for a symmetrical capacitor submodule multilevel converter, which solves the problem that the capacitor voltage of the traditional MMC submodule has fundamental frequency and second harmonic ripple during the DC-AC power exchange of the modular multilevel converter.

[0006] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows: an active power decoupling control method for a symmetrical capacitor submodule multilevel converter, comprising the following steps:

[0007] S1. Construct the topology of the symmetrical capacitor decoupling submodule of the multilevel converter;

[0008] S2. Based on the topology of the symmetrical capacitor decoupling submodule, establish the inductor current model and the capacitor voltage model;

[0009] S3. Based on the inductor current model and capacitor voltage model, perform voltage and current dual closed-loop control to complete the active power decoupling control of the multilevel converter.

[0010] The beneficial effects of this invention are as follows: by controlling the voltage of the symmetrical capacitor decoupling submodule to be DC through the inductor current model and the capacitor voltage model, the problem of the traditional MMC submodule capacitor voltage having fundamental frequency and second harmonic ripple during DC-AC power exchange in modular multilevel converters is solved.

[0011] Furthermore, the topology of the symmetrical capacitor decoupling submodule in step S1 includes switch S1, switch S2, switch S3, switch S4, and inductor L. f Capacitors C1 and C2; one end of the switching transistor S1 is connected to one end of the switching transistor S2 and is connected to an external current; the other end of the switching transistor S1 is connected to one end of the switching transistor S3 and one end of the capacitor C1; the other end of the switching transistor S2 is connected to one end of the switching transistor S4 and one end of the capacitor C2; the other end of the switching transistor S3 is connected to the other end of the switching transistor S4 and the inductor L. f One end is connected; inductor L f The other end is connected to the other end of capacitor C1 and the other end of capacitor C2, respectively.

[0012] The beneficial effects of the above-mentioned further scheme are as follows: two capacitors with different parameters cooperate to charge and discharge, with the large-capacitance capacitor playing the main energy storage role and the small-capacitance capacitor playing the secondary energy storage role, which solves the problem that the capacitor voltage of the traditional MMC submodule has fundamental frequency and second harmonic ripple; the inductor does not store energy, but only serves as a medium for energy exchange between the two capacitors.

[0013] Further, step S2 specifically includes:

[0014] S201. Obtain the ideal voltage of capacitor C1 and the ideal voltage of capacitor C2:

[0015]

[0016]

[0017] Among them, u c1The ideal voltage of capacitor C1; u c2 U is the ideal voltage across capacitor C2; c1 U is the DC voltage across capacitor C1; c2 The DC voltage across capacitor C2; The AC voltage across capacitor C1; The AC voltage of capacitor C2;

[0018] S202. Based on the ideal voltages of capacitor C1 and C2, the inductance L is obtained using the state-space averaging equation. f Voltage across terminals:

[0019]

[0020] in, For inductor L f The voltage across the terminals; d2 is the duty cycle of switch S3; d'2 is the duty cycle of switch S4; i L For inductor L f The current; d is the differential symbol; t is the time.

[0021] S203. Based on the ideal voltage of capacitor C1 and the ideal voltage of capacitor C2, obtain the current in capacitor C1 and the current in capacitor C2:

[0022]

[0023]

[0024]

[0025] Among them, i c1 i represents the current in capacitor C1; c2 The current in capacitor C2 is C; c1 The capacitance of capacitor C1; C c2 The capacitance of capacitor C2; The AC current of capacitor C2; The AC current of capacitor C2;

[0026] S204, based on inductance L f Using Kirchhoff's current law, the voltage across the capacitors, the current in capacitor C1, and the current in capacitor C2, the inductance L can be obtained. f The current relationship between capacitors C1 and C2:

[0027]

[0028] Where R(i) represents the current relationship;

[0029] S205, based on inductance L fFrom the current relationship between capacitors C1 and C2, we can obtain the relationship between inductor current and voltage across capacitor C1, as well as the inductor-capacitor equations:

[0030]

[0031]

[0032] Where R(i) L ) represents the relationship between inductor current and capacitor C1 voltage; P represents the inductor-capacitor equations;

[0033] S206. Perform a Laplace transform on the relationship between the inductor current and the voltage across capacitor C1 to obtain the duty cycle AC component – ​​the inductor current transfer function, thus completing the construction of the inductor current model:

[0034]

[0035] in, Let be the duty cycle AC component-inductor current transfer function, and be the objective function of the inductor current model; s is the frequency domain factor; i L (s) represents the frequency domain inductor current; L represents the frequency domain AC duty cycle of switch S3. f For inductor L f Inductance; U sm The voltage of the symmetrical capacitor decoupling submodule is used;

[0036] S207. Perform a Laplace transform on the inductor-capacitor equations to obtain the AC component transfer function set, thus completing the construction of the capacitor voltage model:

[0037]

[0038] Where P' is the set of AC component transfer functions; The transfer function of the AC component of inductor current-capacitor C1 voltage; The transfer function of the AC component of inductor current-capacitor C2 voltage; This represents the frequency domain AC component of the voltage across capacitor C1. This represents the frequency domain AC component of the voltage across capacitor C2.

[0039] The beneficial effects of the above-mentioned further scheme are: simplifying the topology of the symmetrical capacitor decoupling submodule, establishing a linear model, and providing a theoretical basis and calculation model for the subsequent active power decoupling control scheme of multilevel converter.

[0040] Further, step S3 specifically includes:

[0041] S301. Obtain the switching transistor control scheme data of a traditional single-phase multilevel converter;

[0042] S302, control switch S1 and switch S2 operate according to the switch control scheme data to obtain the initial model of voltage and current dual closed-loop control;

[0043] S303. Obtain the voltage feedback value of the symmetrical capacitor decoupling submodule, and perform voltage outer loop calculation based on the initial model of voltage and current dual closed loop control to obtain the inductor current reference value.

[0044] S304. Obtain the inductor current feedback value, and based on the inductor current feedback value and the inductor current reference value, perform the current inner loop calculation based on the voltage and current dual closed-loop control initial model to obtain the AC modulation data signal of switch S3 and the AC modulation data signal of switch S4.

[0045] S305. Obtain the original parameters of the traditional single-phase multilevel converter, and calculate the DC modulation data signal of switch S3 and switch S4 respectively based on the original parameters of the traditional single-phase multilevel converter.

[0046] S306. Based on the DC modulation data signal and the AC modulation data signal of the switching transistor S3, obtain the modulation data signal of the switching transistor S3.

[0047] S307. Based on the DC modulation data signal and the AC modulation data signal of the switching transistor S4, obtain the modulation data signal of the switching transistor S4.

[0048] S308: Based on the modulation data signals of switch S3 and switch S4, the voltage of the symmetrical capacitor decoupling submodule is controlled to be DC through modulation techniques sequentially through the inductor current model and the capacitor voltage model, thus completing the active power decoupling control of the multilevel converter.

[0049] The beneficial effects of the above-mentioned further scheme are as follows: the voltage and current dual closed-loop control scheme results in a stable control system, rapid response, outstanding dynamic tracking performance, and AC / DC decoupled active power control.

[0050] Further, step S303 specifically includes:

[0051] S3031. Based on the initial model of voltage and current dual closed-loop control and the capacitor voltage model, obtain the voltage feedback value of the symmetrical capacitor decoupling submodule.

[0052] S3032. Obtain the voltage reference value of the symmetrical capacitor decoupling submodule, and calculate the difference between the voltage reference value and the voltage feedback value of the symmetrical capacitor decoupling submodule to obtain the voltage difference;

[0053] S3033. Based on the voltage difference, the quasi-resonant control technology is used to obtain the reference value of the AC voltage of capacitor C2;

[0054] S3034. Perform differential control and proportional calculation on the AC voltage reference value of capacitor C2 to obtain the inductor current reference value.

[0055] The beneficial effects of the above-mentioned further scheme are as follows: the voltage outer loop operation can obtain the ideal inductor current reference value from the voltage feedback value of the symmetrical capacitor decoupling submodule through a series of technical control methods, thus preparing for the current inner loop operation.

[0056] Further, step S304 specifically includes:

[0057] S3041. Obtain the inductor current feedback value based on the initial model of voltage and current dual closed-loop control and the inductor current model.

[0058] S3042. Subtract the inductor current feedback value from the inductor current reference value to obtain the current difference value;

[0059] S3043. Perform a sampling ratio calculation on the current difference to obtain the first data;

[0060] S3044. The first data and the AC voltage reference value of capacitor C2 are linearly superimposed, and the ratio is normalized to obtain the AC modulation data signal of switch S3 and the AC modulation data signal of switch S4.

[0061] The beneficial effects of the above-mentioned further scheme are as follows: the current inner loop operation obtains the AC modulation signal of the switching transistors S3 and S4 from the difference between the reference value and the feedback value of the inductor current through control means. The DC modulation signal can be calculated and directly given according to the inherent parameters of the system, thus realizing AC-DC decoupling and simplifying the control process. Attached Figure Description

[0062] Figure 1 This is a flowchart of the method of the present invention.

[0063] Figure 2 This is a topology diagram of the symmetrical capacitor decoupling submodule in this invention.

[0064] Figure 3 This is a schematic diagram of the AC / DC decoupling model of the symmetrical capacitor submodule topology in this invention. Detailed Implementation

[0065] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0066] like Figure 1As shown, in one embodiment of the present invention, an active power decoupling control method for a symmetrical capacitor submodule multilevel converter includes the following steps:

[0067] S1. Construct the topology of the symmetrical capacitor decoupling submodule of the multilevel converter;

[0068] S2. Based on the topology of the symmetrical capacitor decoupling submodule, establish the inductor current model and the capacitor voltage model;

[0069] S3. Based on the inductor current model and capacitor voltage model, perform voltage and current dual closed-loop control to complete the active power decoupling control of the multilevel converter.

[0070] In this embodiment, the output voltage and current of the single-phase MMC (multilevel converter) topology are known:

[0071]

[0072] The voltages of the upper and lower bridge arms are:

[0073]

[0074] The upper arm current and the lower arm current are:

[0075]

[0076] In the above formula, I dc This indicates that the MMC circulating current contains only a DC component, and the bridge arm power can be expressed as the product of the bridge arm voltage and current:

[0077]

[0078] Under normal system operation, the bridge arm power is a completely AC component, with low-frequency components mainly consisting of fundamental and second harmonic ripple. The AC bridge arm power causes a certain amount of ripple in the MMC submodule capacitor voltage. When the ripple is too large, it will affect the stress on the system switching devices, circulating current, and the output characteristics of the AC and DC ports.

[0079] like Figure 2 As shown, the topology of the symmetrical capacitor decoupling submodule in step S1 includes switch S1, switch S2, switch S3, switch S4, and inductor L. f Capacitors C1 and C2; one end of the switching transistor S1 is connected to one end of the switching transistor S2 and is connected to an external current; the other end of the switching transistor S1 is connected to one end of the switching transistor S3 and one end of the capacitor C1; the other end of the switching transistor S2 is connected to one end of the switching transistor S4 and one end of the capacitor C2; the other end of the switching transistor S3 is connected to the other end of the switching transistor S4 and the inductor L. f One end is connected; inductor Lf The other end is connected to the other end of capacitor C1 and the other end of capacitor C2, respectively.

[0080] Step S2 specifically involves:

[0081] S201. Obtain the ideal voltage of capacitor C1 and the ideal voltage of capacitor C2:

[0082]

[0083]

[0084] Among them, u c1 The ideal voltage of capacitor C1; u c2 U is the ideal voltage across capacitor C2; c1 U is the DC voltage across capacitor C1; c2 The DC voltage across capacitor C2; The AC voltage across capacitor C1; The AC voltage of capacitor C2;

[0085] S202. Based on the ideal voltages of capacitor C1 and C2, the inductance L is obtained using the state-space averaging equation. f Voltage across terminals:

[0086]

[0087] in, For inductor L f The voltage across the terminals; d2 is the duty cycle of switch S3; d'2 is the duty cycle of switch S4; i L For inductor L f The current; d is the differential symbol; t is the time.

[0088] S203. Based on the ideal voltage of capacitor C1 and the ideal voltage of capacitor C2, obtain the current in capacitor C1 and the current in capacitor C2:

[0089]

[0090]

[0091]

[0092] Among them, i c1 i represents the current in capacitor C1; c2 The current in capacitor C2 is C; c1 The capacitance of capacitor C1; C c2 The capacitance of capacitor C2; The AC current of capacitor C2; The AC current of capacitor C2;

[0093] S204, based on inductance L f Using Kirchhoff's current law, the voltage across the capacitors, the current in capacitor C1, and the current in capacitor C2, the inductance L can be obtained. f The current relationship between capacitors C1 and C2:

[0094]

[0095] Where R(i) represents the current relationship;

[0096] S205, based on inductance L f From the current relationship between capacitors C1 and C2, we can obtain the relationship between inductor current and voltage across capacitor C1, as well as the inductor-capacitor equations:

[0097]

[0098]

[0099] Where R(i) L ) represents the relationship between inductor current and capacitor C1 voltage; P represents the inductor-capacitor equations;

[0100] S206. Perform a Laplace transform on the relationship between the inductor current and the voltage across capacitor C1 to obtain the duty cycle AC component – ​​the inductor current transfer function, thus completing the construction of the inductor current model:

[0101]

[0102] in, Let be the duty cycle AC component-inductor current transfer function, and be the objective function of the inductor current model; s is the frequency domain factor; i L (s) represents the frequency domain inductor current; L represents the frequency domain AC duty cycle of switch S3. f For inductor L f Inductance; U sm The voltage of the symmetrical capacitor decoupling submodule is used;

[0103] S207. Perform a Laplace transform on the inductor-capacitor equations to obtain the AC component transfer function set, thus completing the construction of the capacitor voltage model:

[0104]

[0105] Where P' is the set of AC component transfer functions; The transfer function of the AC component of inductor current-capacitor C1 voltage; The transfer function of the AC component of inductor current-capacitor C2 voltage; This represents the frequency domain AC component of the voltage across capacitor C1. This represents the frequency domain AC component of the voltage across capacitor C2.

[0106] In this embodiment, for Figure 2 The symmetrical capacitor decoupling submodule topology shown, to ensure its normal operation like a traditional MMC submodule topology, requires that the submodule voltage be U. SM =U dc / N, and the sum of the power of the two capacitors equals the original power of the bridge arm. Since the energy storage capacity of inductors is much weaker than that of capacitors, the power of inductors is ignored. Furthermore, assuming that the power of the bridge arm is uniformly distributed across N submodules, the following expression applies to the bridge arm analysis above:

[0107]

[0108] The ideal voltage expressions for capacitors C1 and C2 are obtained as follows:

[0109]

[0110] Where b is a DC constant, used to ensure that the value under the square root is always greater than 0. From the above equation, it can be seen that the capacitor voltage is the superposition of DC and AC quantities, which can be expressed as follows:

[0111]

[0112] Two of the AC components are equal in magnitude and opposite in direction. And the sum of the DC components is U SM , that is U c1 +U c2 =U SM Therefore, the working principle of this topology is as follows: through active power decoupling technology, the sum of the AC components of the two capacitor voltages is controlled to be zero, eliminating fundamental frequency and second harmonic ripple, while ensuring that the sum of the DC components is equal to the submodule capacitor voltage U. SM This ensures the necessary bridge arm power for normal MMC operation while minimizing voltage fluctuations in the submodule capacitors, providing DC U... SM .

[0113] The voltage across the inductor can be obtained using the state-space averaging equation:

[0114]

[0115] Where d2 represents the duty cycle of switch S3 and d'2 represents the duty cycle of switch S4. Since the signals of switches S3 and S4 are complementary, then d2 + d'2 = 1. AC / DC decoupling, i L Includes direct current I L and communication volume u c1 Includes direct current U c1 and communication volume u c2 Includes direct current U c2 and communication volume d2 includes DC current D2 and AC current. The formula can then be rewritten as follows:

[0116]

[0117] In the formula, D2 + D2' = 1.

[0118] We can obtain the corresponding DC and AC components as follows:

[0119]

[0120] In a decoupled topology, if a DC component exists in the inductor voltage during steady-state operation of an MMC system, the inductor current will increase linearly, causing system instability. Therefore, in steady state, there is no DC component in the inductor voltage, i.e.:

[0121]

[0122] When the submodule voltage is controlled to be constant DC, there is U c1 +U c2 =U SM We can obtain the following formula:

[0123]

[0124] The above equation shows that the DC component of the capacitive voltage is only proportional to the DC component of the duty cycle. Furthermore, the AC part of the formula can be rewritten as:

[0125]

[0126] It can be seen that in the process of achieving decoupling control, the control objective is only related to the ripple voltage in the two capacitors, and is not related to the DC bias of the voltage.

[0127] In summary, we obtain:

[0128]

[0129] Analyze the current and C of two symmetrical capacitor structures. c1 C c2 The relationship between them can be derived from the relationship between capacitor voltage and current:

[0130]

[0131] because We can obtain:

[0132]

[0133] As can be seen from the above formula, the current flowing through the capacitor has only an AC component and no DC component, and the current flowing through the two capacitors is distributed proportionally according to their respective capacitance values.

[0134] According to Kirchhoff's current law, the inductor current i can be obtained. L Relationship with the current of capacitors C1 and C2:

[0135]

[0136] Right now:

[0137]

[0138] The inductor current i can be obtained. L and capacitor voltage u c1 relation:

[0139]

[0140] Taking the Laplace transform of the above equation, we can obtain the frequency domain expression:

[0141]

[0142] Simplifying the above equation further, we can obtain the duty cycle AC component—the inductor current transfer function:

[0143]

[0144] Combining the above equations, we can obtain the AC / DC decoupling model of the symmetrical capacitor submodule topology, such as... Figure 3 As shown.

[0145] The following expression can be obtained:

[0146]

[0147] Taking the Laplace transform of the above equation, we can obtain the frequency domain expression:

[0148]

[0149] Then the transfer functions of the AC components of inductor current-capacitor C1 voltage and inductor current-capacitor C2 voltage can be obtained respectively:

[0150]

[0151] Step S3 specifically involves:

[0152] S301. Obtain the switching transistor control scheme data of a traditional single-phase multilevel converter;

[0153] S302, control switch S1 and switch S2 operate according to the switch control scheme data to obtain the initial model of voltage and current dual closed-loop control;

[0154] S303. Obtain the voltage feedback value of the symmetrical capacitor decoupling submodule, and perform voltage outer loop calculation based on the initial model of voltage and current dual closed loop control to obtain the inductor current reference value.

[0155] S304. Obtain the inductor current feedback value, and based on the inductor current feedback value and the inductor current reference value, perform the current inner loop calculation based on the voltage and current dual closed-loop control initial model to obtain the AC modulation data signal of switch S3 and the AC modulation data signal of switch S4.

[0156] S305. Obtain the original parameters of the traditional single-phase multilevel converter, and calculate the DC modulation data signal of switch S3 and switch S4 respectively based on the original parameters of the traditional single-phase multilevel converter.

[0157] S306. Based on the DC modulation data signal and the AC modulation data signal of the switching transistor S3, obtain the modulation data signal of the switching transistor S3.

[0158] S307. Based on the DC modulation data signal and the AC modulation data signal of the switching transistor S4, obtain the modulation data signal of the switching transistor S4.

[0159] S308: Based on the modulation data signals of switch S3 and switch S4, the voltage of the symmetrical capacitor decoupling submodule is controlled to be DC through modulation techniques sequentially through the inductor current model and the capacitor voltage model, thus completing the active power decoupling control of the multilevel converter.

[0160] In this embodiment, since the AC components (fundamental frequency and second harmonic frequency) of the two capacitor voltages cannot be perfectly equal in amplitude and opposite in direction in actual control, the submodule terminal voltage contains a low-frequency AC component with a very small amplitude. The submodule terminal voltage setpoint is subtracted from the feedback value, and this subtracted from the feedback value is amplified by a quasi-resonant controller (QPR) to obtain the AC component reference value of the capacitor C1 voltage. Differentiating this value yields the current flowing through capacitor C2, which is then proportionally proportional to obtain the inductor current reference value. The inductor current reference value is subtracted from the feedback value, and this subtracted from the feedback value is proportionally proportional to obtain the inductor voltage. Since the AC components of the two capacitor voltages are equal in magnitude and opposite in direction, subtracting the AC component of the inductor voltage from the AC component of capacitor C1 is equivalent to adding the AC component of the inductor voltage from the AC component of capacitor C2. This is then normalized to obtain the AC component of the switch duty cycle.

[0161] Step S303 specifically involves:

[0162] S3031. Based on the initial model of voltage and current dual closed-loop control and the capacitor voltage model, obtain the voltage feedback value of the symmetrical capacitor decoupling submodule.

[0163] S3032. Obtain the voltage reference value of the symmetrical capacitor decoupling submodule, and calculate the difference between the voltage reference value and the voltage feedback value of the symmetrical capacitor decoupling submodule to obtain the voltage difference;

[0164] S3033. Based on the voltage difference, the quasi-resonant control technology is used to obtain the reference value of the AC voltage of capacitor C2;

[0165] S3034. Perform differential control and proportional calculation on the AC voltage reference value of capacitor C2 to obtain the inductor current reference value.

[0166] Step S304 specifically involves:

[0167] S3041. Obtain the inductor current feedback value based on the initial model of voltage and current dual closed-loop control and the inductor current model.

[0168] S3042. Subtract the inductor current feedback value from the inductor current reference value to obtain the current difference value;

[0169] S3043. Perform a sampling ratio calculation on the current difference to obtain the first data;

[0170] S3044. The first data and the AC voltage reference value of capacitor C2 are linearly superimposed, and the ratio is normalized to obtain the AC modulation data signal of switch S3 and the AC modulation data signal of switch S4.

Claims

1. A method for active power decoupling control of a symmetrical capacitor submodule multilevel converter, characterized in that, Includes the following steps: S1. Construct the topology of the symmetrical capacitor decoupling submodule of the multilevel converter; S2. Based on the topology of the symmetrical capacitor decoupling submodule, establish the inductor current model and the capacitor voltage model; step S2 specifically involves: S201, Obtain the capacitor Ideal voltage and capacitance Ideal voltage: in, For capacitor The ideal voltage; For capacitor The ideal voltage; For capacitor DC voltage; For capacitor DC voltage; For capacitor AC voltage; For capacitor AC voltage; S202, According to the capacitor Ideal voltage and capacitance Given an ideal voltage, the inductance can be obtained using the state-space averaging equation. Voltage across terminals: in, For inductance Voltage at both ends; For switching transistors Duty cycle; For switching transistors Duty cycle; For inductance The current; The differential symbol; For a specific moment; S203, According to the capacitor Ideal voltage and capacitance The ideal voltage is used to obtain the capacitance. Current and capacitance Current: in, For capacitor The current; For capacitor The current; For capacitor The capacitance; For capacitor The capacitance; For capacitor Alternating current; For capacitor Alternating current; S204, based on inductance Voltage at both ends, capacitance Current and capacitance The current is used to obtain the inductance using Kirchhoff's current law. ,capacitance and capacitor Current relationship: in, It relates to the current. S205, based on inductance ,capacitance and capacitor From the current relationship, we can obtain the inductor current and the capacitance. The relationship between voltage and the inductor-capacitor equations: in, For inductor current and capacitance The relationship of voltage; P This is the inductor-capacitor equation set; S206, Regarding inductor current and capacitance The voltage relationship is subjected to a Laplace transform to obtain the duty cycle AC component-inductor current transfer function, thus completing the construction of the inductor current model: in, Let be the duty cycle AC component-inductor current transfer function, and let be the objective function of the inductor current model. Frequency domain factor; This refers to the frequency domain inductor current. For switching transistors Frequency domain AC duty cycle; For inductance Inductance; The voltage of the symmetrical capacitor decoupling submodule is used; S207. Perform a Laplace transform on the inductor-capacitor equations to obtain the AC component transfer function set, thus completing the construction of the capacitor voltage model: in, For AC component transfer function group; Inductor current - capacitor Voltage AC component transfer function; Inductor current - capacitor Voltage AC component transfer function; For capacitor The frequency domain AC component of voltage; For capacitor The frequency domain AC component of voltage; S3. Based on the inductor current model and capacitor voltage model, perform voltage and current dual closed-loop control to complete the active power decoupling control of the multilevel converter.

2. The active power decoupling control method for a symmetrical capacitor submodule multilevel converter according to claim 1, characterized in that, The symmetrical capacitor decoupling submodule topology in step S1 includes a switching transistor. Switching transistor Switching transistor Switching transistor ,inductance ,capacitance and capacitor The switching transistor One end is connected to the switching transistor One end is connected and an external current is applied; the switching transistor The other end is connected to the switching transistor. one end and capacitor One end is connected; switching transistor The other end is connected to the switching transistor. one end and capacitor One end is connected; switching transistor The other end is connected to the switching transistor. The other end and the inductor One end is connected; inductor The other end is connected to the capacitor. The other end and capacitor The other end is connected.

3. The active power decoupling control method for a symmetrical capacitor submodule multilevel converter according to claim 1, characterized in that, Step S3 specifically involves: S301. Obtain the switching transistor control scheme data of a traditional single-phase multilevel converter; S302, control switch transistor and switching transistor Based on the switching transistor control scheme data, an initial model for voltage and current dual closed-loop control is obtained. S303. Obtain the voltage feedback value of the symmetrical capacitor decoupling submodule, and perform voltage outer loop calculation based on the initial model of voltage and current dual closed loop control to obtain the inductor current reference value. S304. Obtain the inductor current feedback value, and based on the inductor current feedback value and the inductor current reference value, perform current inner loop calculation based on the voltage and current dual closed-loop control initial model to obtain the switching transistor value. AC modulated data signals and switching transistors AC modulated data signals; S305. Obtain the original parameters of the traditional single-phase multilevel converter, and calculate the switching transistors based on the original parameters of the traditional single-phase multilevel converter. DC modulation data signal and switching transistor DC modulated data signal; S306, according to the switching transistor DC modulation data signal and switching transistor AC modulated data signal, to obtain switching transistor Modulated data signal; S307, according to the switching transistor DC modulation data signal and switching transistor AC modulated data signal, to obtain switching transistor Modulated data signal; S308, according to the switching transistor Modulated data signal and switching transistor The modulated data signal is passed sequentially through the inductor current model and the capacitor voltage model using modulation techniques. This controls the voltage of the symmetrical capacitor decoupling submodule to be DC, thus completing the active power decoupling control of the multilevel converter.

4. The active power decoupling control method for a symmetrical capacitor submodule multilevel converter according to claim 3, characterized in that, Step S303 specifically involves: S3031. Based on the initial model of voltage and current dual closed-loop control and the capacitor voltage model, obtain the voltage feedback value of the symmetrical capacitor decoupling submodule. S3032. Obtain the voltage reference value of the symmetrical capacitor decoupling submodule, and calculate the difference between the voltage reference value and the voltage feedback value of the symmetrical capacitor decoupling submodule to obtain the voltage difference; S3033. Based on the voltage difference, the quasi-resonant control technique is used to obtain the capacitance. AC voltage reference value; S3034, Capacitor The AC voltage reference value is used for differential control and proportional calculation to obtain the inductor current reference value.

5. The active power decoupling control method for a symmetrical capacitor submodule multilevel converter according to claim 4, characterized in that, Step S304 specifically involves: S3041. Obtain the inductor current feedback value based on the initial model of voltage and current dual closed-loop control and the inductor current model. S3042. Subtract the inductor current feedback value from the inductor current reference value to obtain the current difference value; S3043. Perform a sampling ratio calculation on the current difference to obtain the first data; S3044, Combine the first data and capacitor The AC voltage reference values ​​are linearly superimposed and then normalized proportionally to obtain the switching transistor. AC modulated data signals and switching transistors AC modulated data signal.

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