A linear active disturbance rejection and quasi-proportional-resonant-based MMC shore power grid-connected control method

Abstract

This invention relates to the field of ship power systems and power electronic control technology. A shore power grid-connected control method for MMC based on linear active disturbance rejection and quasi-proportional resonance is disclosed, characterized by the following steps: Step 1: Constructing a power outer loop based on linear active disturbance rejection control to obtain a reference current command including disturbance compensation; Step 2: Constructing a current inner loop based on quasi-proportional resonance (QPR) to generate a base modulation voltage; Step 3: Extracting the differential-mode circulating current within the MMC and constructing a multi-band QPR circulating current suppressor; Step 4: Generating a flexible converter trigger pulse based on the nearest-level approximation and voltage equalization sorting strategy. This invention exhibits strong dynamic disturbance rejection capability and significantly improved dynamic response speed; it completely eliminates control chattering, effectively extending equipment lifespan; it has excellent frequency adaptability, and multi-harmonic circulating current suppression is more reliable; it has good decoupling effect and is of great engineering practicality and promotional value.

Description

Technical Field

[0001] This invention relates to the field of ship power systems and power electronic control technology, specifically to a grid-connected control method for a modular multilevel converter (MMC) in a high-voltage shore power system. Background Technology

[0002] With increasingly stringent requirements for energy conservation and emission reduction in the global shipping industry, using shore power to replace ship auxiliary generators during berthing has become a core means of reducing port air pollution and creating "green ports." Among various power electronic converters, modular multilevel converters (MMCs) are gradually becoming key equipment for grid connection of high-voltage, high-capacity shore power systems due to their significant advantages such as high withstand voltage levels, good output waveform quality, low switching frequency, and ease of modular expansion. However, high-voltage shore power systems face extremely complex operating challenges in actual operation when connected to ship power systems.

[0003] Shipboard electrical systems are essentially isolated microgrids with relatively low system inertia and complex load characteristics. After a ship connects to a shore power network, frequent starts and stops of heavy inductive loads such as large cargo pumps, thrusters, and refrigerated containers, or transient faults on the shore power grid side, can cause drastic changes in active and reactive power at the point of connection (PCC). These extreme transient impacts can easily disrupt the power supply-demand balance, causing sudden drops in system voltage and severe fluctuations in grid frequency, seriously affecting the safety of sensitive shipboard electrical equipment and even triggering protective devices that lead to grid interruption.

[0004] To address the aforementioned dynamic disturbances, existing shore power grid-connected control strategies typically employ Virtual Synchronous Generator (VSG) technology, supplemented by nonlinear algorithms such as Sliding Mode Control (SMC) for optimization. While VSG technology can provide crucial virtual inertia and frequency support for ship microgrids by simulating the rotor motion equations of traditional synchronous motors, its inherent power outer-loop regulation mechanism suffers from inherent response lag. To compensate for this slow response, researchers introduced sliding mode control. Although sliding mode control effectively improves the transient convergence speed of the system in the face of sudden load changes, its discontinuous switching characteristics based on sign functions inevitably introduce high-frequency chattering into the control output. This high-frequency chattering not only imposes significant control stress and additional switching losses on the insulated-gate bipolar transistors (IGBTs) inside the converter, but also easily generates high-frequency harmonics that are difficult to filter out in the grid-side output, thereby shortening the lifespan of shore power hardware.

[0005] On the other hand, from the perspective of the internal operating mechanism of the converter, the special bridge arm topology of the MMC determines that during the AC / DC power conversion process, internal differential mode circulating currents, mainly composed of second and fourth harmonics, will inevitably be generated between phases. These circulating currents not only increase the effective value of the bridge arm current, leading to unnecessary power loss, but also cause drastic fluctuations in the voltage of the submodule capacitors, seriously threatening the internal voltage equalization stability of the system. Currently, proportional-integral resonant (PIR) controllers are commonly used in engineering practice and academia to achieve zero steady-state error suppression of multi-harmonic circulating currents. However, the ideal resonant peak bandwidth of traditional PIR controllers is extremely narrow. When ship microgrids experience large load changes, their fundamental frequency often cannot be strictly maintained at the rated value, but will experience a certain range of transient deviation. Once the actual operating frequency deviates from the set center frequency of the controller, the gain of the traditional PIR controller in the corresponding frequency band will drop sharply, causing its ability to suppress circulating currents to decrease significantly or even fail completely, which may ultimately lead to voltage divergence and collapse of the entire converter system.

[0006] In summary, existing high-voltage shore power MMC grid-connected control methods still have significant limitations in terms of resisting strong external load disturbances, eliminating high-frequency chattering, and adapting to transient frequency deviations in the grid. Therefore, there is an urgent need in this field for a novel grid-connected control strategy that does not rely on precise mathematical modeling of the system, can actively observe and feedforward compensate for complex disturbances, and has strong adaptive capabilities to microgrid frequency deviations, in order to effectively ensure the high reliability and high power quality of shore power systems under extreme operating conditions. Summary of the Invention

[0007] To address the shortcomings of existing high-voltage shore power grid connection control technologies, such as slow dynamic response, high-frequency chattering caused by sliding mode control, and poor adaptability of traditional proportional-integral resonant (PIR) controllers to grid frequency deviation, the present invention aims to provide a linear active disturbance rejection and quasi-proportional resonant control (LADRC-QPR) method for MMC shore power grid connection control.

[0008] To achieve the above objectives, the technical solution adopted by this invention is a method for grid-connected MMC shore power control based on linear active disturbance rejection and quasi-proportional resonance, characterized by comprising the following steps: Step 1: Construct a power outer loop based on Linear Active Disturbance Rejection Control (LADRC) to obtain a reference current command that includes disturbance compensation; (1) Real-time acquisition of three-phase voltage and three-phase current at the shore power grid connection point (PCC), and calculation of the actual active power output of the shore power system after coordinate transformation. and reactive power ; (2) Establish linear extended state observers (LESO) for active power and reactive power respectively; taking the active power channel as an example, define the sudden change in ship load, unmodeled dynamics within the system and parameter perturbations as the total disturbance variable. ; Real-time tracking of actual power output via LESO, outputting power state observations. and total disturbance observations ; (3) The given reference active power With power state observations The deviation is input into the linear state error feedback (LSEF) stage, while the observed total disturbance variable is also introduced. Perform division or subtraction feedforward compensation to directly calculate and output the grid-connected reference current component (or d / q axis reference current component) in the stationary coordinate system. Step 2: Construct a current inner loop based on quasi-proportional resonance (QPR) to generate the basic modulation voltage; (1) Convert the actual grid-connected three-phase current collected to a static state. Coordinate system, to obtain the actual current and ; (2) Calculate the reference current and the actual current output in step one. Tracking error; (3) The tracking error is input to the fundamental frequency quasi-proportional resonance (QPR) controller; the transfer function of the controller includes the input from the cutoff frequency. The determined damping term is such that it is at the fundamental angular frequency. A high-gain region with a certain bandwidth is formed nearby; after the QPR controller performs zero steady-state error adjustment, it outputs the basic modulation voltage command in the stationary coordinate system. and And inversely transform it to the three-phase coordinate system to obtain ; Step 3: Extract the differential mode circulating current inside the MMC and construct a multi-band QPR circulating current suppressor; (1) Real-time acquisition of the current of each phase upper and lower bridge arm of the MMC, and extraction of the actual value of the differential mode circulating current inside each phase using the formula. ; (2) Set the circulation reference value to zero. Compare the zero reference value with the actual value. The deviation is input to the multi-band QPR circulating current controller; (3) The multi-band QPR circulating current controller consists of a proportional element and a second harmonic element. QPR resonant circuit and a fourth harmonic (QPR resonant circuit and a fourth harmonic) The QPR resonant elements are connected in parallel. Even if the grid-side frequency changes at the moment of grid connection... Despite the offset, the wideband characteristics of each resonant element can still output an accurate circulating current compensation voltage. ; Step 4: Generate flexible converter trigger pulses based on the nearest level approximation and voltage equalization sorting strategy; (1) The basic modulation voltage obtained in step two The circulating current compensation voltage obtained in step three By performing algebraic superposition, the final combined command voltage of the upper and lower arms of each phase of the MMC is obtained; (2) Input the comprehensive command voltage to the nearest level approximation modulation (NLM) algorithm module to calculate the total number of sub-modules that need to be put into operation at each bridge arm at the current moment; (3) Real-time detection of the capacitor voltage of all sub-modules in the bridge arm and bubble sorting, combined with the charging and discharging direction of the bridge arm current, select the sub-module with the optimal capacitor voltage in sequence for connection or disconnection, and finally output the IGBT switching pulse signal to drive the converter to complete the closed-loop grid connection control of the high-voltage shore power system.

[0009] The beneficial effects of this invention are: Compared with existing technologies, the MMC shore power grid-connected control method based on linear active disturbance rejection and quasi-proportional resonance provided by this invention has the following significant advantages: 1. Strong active anti-interference capability and significantly improved dynamic response speed. Existing virtual synchronous generator (VSG) technology relies primarily on virtual inertia for passive buffering when dealing with sudden switching of heavy inductive loads on ships, resulting in significant response lag. This invention employs Linear Active Disturbance Rejection Control (LADRC) to construct the power outer loop, independent of precise mathematical models of shore power systems and ship microgrids. Through a Linear Extended State Observer (LESO), internal parameter perturbations and external load surges are treated as a unified "total disturbance" for real-time and accurate estimation, with feedforward compensation in the control law. This enables the system to proactively adjust under extreme conditions, effectively curbing large drops in power and frequency, significantly shortening grid connection transient recovery time, and improving system robustness.

[0010] 2. Completely eliminates control vibration, effectively extending equipment lifespan. While existing sliding mode control (SMC) can accelerate response speed, its sign-function-based switching logic inevitably leads to high-frequency chattering, causing significant switching stress and heat loss to core components such as insulated-gate bipolar transistors (IGBTs) within the converter. This invention directly replaces SMC with a smooth and continuous LADRC control law, fundamentally eliminating the chattering risk. This not only further reduces the total harmonic distortion (THD) of the grid-side output current but also significantly reduces the operating load on hardware equipment, ensuring the long-term safety and service life of high-voltage, high-capacity shore power facilities.

[0011] 3. Excellent frequency adaptability, and more reliable suppression of multi-harmonic circulating current. In complex berthing and grid-connected environments, shipboard electrical networks are prone to frequency shifts of 0.2% to 1%. Traditional proportional-integral (PIR) controllers have extremely narrow resonant peaks, and once the frequency deviates from the center point, their ability to suppress second and fourth harmonic differential mode circulating currents within the MMC (Multi-mode Controller) decreases sharply or even fails. The current inner loop and multi-band circulating current suppressor of this invention both employ quasi-proportional resonant (QPR) control, effectively widening the resonant bandwidth by utilizing the cutoff frequency damping term in the transfer function. Even if the actual operating frequency experiences transient drift, the system can still maintain extremely high control gain, perfectly achieving zero steady-state error suppression of multiple harmonic circulating currents and maintaining the balanced and stable voltage of the submodule capacitors.

[0012] 4. It has a good decoupling effect and is of great practical engineering and promotional value. Existing multi-loop nonlinear joint control systems often face the challenges of severe parameter cross-coupling and extremely cumbersome engineering tuning. This invention centrally handles both internal and external disturbances of the system, and the physical meaning of the LADRC parameter design is clear. This simplified control architecture greatly reduces the system's design complexity and the difficulty of on-site commissioning, making it highly suitable for large-scale implementation and application in high-voltage shore power MMC industrial equipment. Attached Figure Description

[0013] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0014] Figure 1 This is the overall flowchart of the MMC shore power grid connection control method of the present invention.

[0015] Figure 2 This is a block diagram of the overall control architecture of the present invention based on LADRC and QPR.

[0016] Figure 3This is a comparison curve of the dynamic response of active power in this invention.

[0017] Figure 4 This is a comparison diagram of the steady-state waveform of the grid-connected current in this invention.

[0018] Figure 5 This is a comparison chart of the circulating current suppression effect under the frequency offset condition of the present invention.

[0019] Figure 6 This is a comparison chart of the core performance of the three shore power grid connection control strategies of this invention. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Part One: This invention describes the complete steps of a method for grid-connected MMC shore power control based on linear active disturbance rejection and quasi-proportional resonance, specifically including the following steps: S001 Shore Power Grid Connection Point Electrical Quantity Acquisition and Instantaneous Power Calculation The system controller uses high-precision voltage and current sensors to collect the three-phase AC voltage at the shore power grid connection point (PCC) in real time. and three-phase alternating current Using a synchronous rotating coordinate system ( The Park transformation matrix in a coordinate system converts stationary three-phase AC quantities into DC quantities that rotate with the fundamental frequency of the power grid: in, Representing voltage or current ; The phase angle of the grid voltage obtained through a phase-locked loop (PLL) For synchronous rotating coordinate system Axial (direct axis) components, For synchronous rotating coordinate system Axial (intersecting axis) components, For zero-order components, For the A-phase component in a three-phase stationary coordinate system, The B-phase component is shown in a three-phase stationary coordinate system. The C-phase component is defined in a three-phase stationary coordinate system.

[0022] Furthermore, a grid voltage-oriented vector control strategy is adopted, allowing... The axis coincides with the grid voltage vector, that is... Based on this, calculate the actual active power output of the system at the current moment. With reactive power : in, This is the grid voltage. for shaft current, for Shaft current; as can be seen from the above decoupling formula, under the grid voltage Under stable conditions, active power and reactive power can be adjusted separately. shaft current and shaft current Exercise independent control.

[0023] S002 Total Disturbance Estimation and Power Outer Loop Adjustment Based on Linear Active Disturbance Rejection (LADRC) This step aims to eliminate the inertial response of traditional PI regulators or virtual synchronous generators (VSGs) and actively observe grid-connected disturbances using linear active disturbance rejection technology. Taking the active power control channel as an example (the reactive power channel is similar): First, establish the state-space expression for the first-order active power system, which includes external load mutations and internal parameter perturbations: in, This is the derivative of the actual output active power with respect to time. This represents the actual output active power. The input is an unknown external load disturbance suffered by the system. This represents the sum of unmodeled dynamics and unknown external disturbances in the system; This is the nominal value of the system control gain; For controller output Shaft reference current.

[0024] Define the total disturbance as a new extended state variable. and order , The system's fundamental state variables represent active power. To represent the extended state variables of the total system disturbance, a second-order linear extended state observer (LESO) is constructed: in, Let be the derivative of the active power state observation with respect to time. The derivative of the total disturbance observations with respect to time. This is the nominal value of the system control gain. For controller output Shaft reference current, Actual active power Observed values; For total disturbance Observed values; and The observer gain matrix parameters are... This represents the actual output active power. According to the pole placement method, the observer poles are uniformly placed at... Place, then , ,in This represents the observer bandwidth.

[0025] Obtain total disturbance observations Then, it is introduced into the Linear State Error Feedback (LSEF) stage for feedforward compensation, generating a disturbance rejection characteristic. Shaft reference current : in, For controller output Shaft reference current, The target active power command value set for the shore power system; This is the gain of the proportional controller. Using this formula, when the system encounters a sudden load change, It can instantly sense and generate a reverse compensation current in this formula, thus achieving advanced disturbance rejection.

[0026] S003: Inner-loop tracking of grid-connected current based on quasi-proportional resonance (QPR) in stationary coordinate system To accommodate the potential 0.2% to 1% fundamental frequency shift in the ship's microgrid, the inner loop control is kept stationary. A quasi-proportional resonance (QPR) controller is used in the coordinate system.

[0027] Using the inverse Park transformation, the command current generated in S002 is... Reference current converted to stationary coordinate system Then the current tracking error was calculated: in, In a stationary coordinate system Shaft current tracking error, In a stationary coordinate system Shaft current tracking error, The actual coordinate system in the stationary coordinate system shaft current, The actual coordinate system in the stationary coordinate system The shaft current inputs the tracking error to the QPR controller. Taking the axis as an example, the controller is in The transfer function and control law of the domain are expressed as follows: in, For inner loop output Shaft base modulation voltage; This is the proportional gain, used to improve the dynamic response speed of the system; This is the resonant gain, used to eliminate steady-state errors; The cutoff frequency (damping term) determines the bandwidth of the resonant peak, effectively preventing the frequency from deviating from the rated fundamental angular frequency due to the power grid frequency. This leads to control failure. Similarly, we can derive... Shaft modulation voltage , For the Laplace operator, In a stationary coordinate system Current tracking error of the shaft.

[0028] Finally, through Clark inverse transform, and Transform back to the three-phase coordinate system to obtain the basic modulation voltage. , .

[0029] S004: Differential Mode Circulating Current Suppression in Converters Based on Multi-Band QPR Extract each phase of MMC (in terms of...) For example, The actual differential mode circulation inside : in, and They are respectively The actual current of the upper and lower bridge arms; This represents the total input current on the DC side.

[0030] Due to the nonlinear characteristics of voltage fluctuations within the MMC, the circulating current is mainly composed of second harmonics (...). ) and fourth harmonic ( Harmonic components constitute the current. The circulating current command reference value is set to 0, and the circulating current error... , For circulation error, This is the actual differential mode circulation.

[0031] The circulating current error is fed into a multi-band QPR circulating current suppressor composed of a fundamental frequency proportional control and a multi-order frequency resonant control connected in parallel, generating a circulating current compensation voltage command. : in, This is the command for the j-phase circulating current compensation voltage. For circulating proportional gain, This represents the resonant gain of the h-th harmonic resonant controller (i.e., when h=2 it represents the second harmonic resonant gain, and when h=4 it represents the fourth harmonic resonant gain). The cutoff frequency, For the Laplace operator, This refers to the differential mode circulating current error within phase j; This represents the harmonic order (2 and 4 here). This structure can accurately track multiple high-frequency harmonics and also... To ensure its robustness under frequency shift, This is the fundamental angular frequency of the power grid.

[0032] S005: Integrated command modulation and submodule switching signal generation based on voltage equalization sorting According to Kirchhoff's Voltage Law (KVL), the fundamental modulation voltage generated by S003 and the circulating current compensation voltage generated by S004 are algebraically synthesized to obtain the final command voltages for the upper and lower arms of the MMC: in, This refers to the DC bus voltage of the shore power supply. and These are the reference voltages required for the upper and lower bridge arms, respectively. The j-phase base modulation voltage, This is the command for the j-phase circulating current compensation voltage.

[0033] The nearest level approximation modulation (NLM) algorithm is used to calculate the current control cycle. The total number of sub-modules required for the upper and lower bridge arms and : in, The rated voltage of a single submodule capacitor; The nearest integer function.

[0034] Finally, we proceed to the capacitor voltage equalization sorting algorithm submodule. Real-time reading... The current capacitor voltage of all submodules within the phase is then sorted using a fast sorting mechanism. 1) If the bridge arm current direction is to charge the submodule capacitor: prioritize the capacitor with the lowest voltage. (or Sub-modules.

[0035] 2) If the bridge arm current direction is to discharge the submodule capacitor: prioritize connecting the capacitor with the highest voltage. (or (Number of submodules)

[0036] 3) Generate the final IGBT gate drive switching signal and send it to the hardware execution end to complete a complete control cycle of shore power grid connection regulation.

[0037] Part Two: The inventive point of this invention: 1. Introducing LADRC for proactive disturbance rejection: Replacing the traditional virtual synchronous generator (VSG) with linear active disturbance rejection control. It can directly calculate and compensate for external influences such as load changes as total disturbances, transforming the system from passive response to active defense, resulting in faster response speed.

[0038] 2. Eliminating chattering by using continuous control law: The smooth control signal of LADRC completely replaces sliding mode control (SMC), directly eliminating the root cause of high-frequency chattering caused by SMC, greatly reducing the physical losses of the converter switching devices (IGBTs), and extending the equipment life.

[0039] 3. Improve frequency adaptability by applying QPR: The inner current loop is replaced with a quasi-proportional resonant (QPR) controller. Compared with traditional control methods, QPR has a wider operating bandwidth. Even if the frequency of the ship's microgrid deviates slightly, it can still achieve steady-state error-free tracking and will not fail due to frequency fluctuations.

[0040] 4. Multi-band targeted suppression of internal circulating current: Multiple QPR parallel suppression channels are specifically designed to suppress the core second and fourth harmonic differential mode circulating currents within the MMC. Even under complex grid frequency disturbance conditions, harmonics can be accurately eliminated, ensuring the stability of capacitor voltages in each submodule.

[0041] The various embodiments in this specification are described in a related manner. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, the system embodiments are basically similar to the method embodiments, so the description is relatively simple; relevant parts can be referred to the descriptions of the method embodiments.

[0042] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. A method for grid-connected control of shore power based on linear active disturbance rejection and quasi-proportional resonance (MMC), characterized in that, Includes the following steps: Step 1: Construct a power outer loop based on linear active disturbance rejection control and obtain a reference current command that includes disturbance compensation; (1) Real-time acquisition of three-phase voltage and three-phase current at the shore power grid connection point, and calculation of the actual active power output of the shore power system after coordinate transformation. and reactive power ; (2) Establish linear extended state observers for active power and reactive power respectively; taking the active power channel as an example, define the sudden change in ship load, unmodeled dynamics within the system and parameter perturbations as the total disturbance variable. ; Real-time tracking of actual power output via LESO, outputting power state observation values. and total disturbance observations ; (3) The given reference active power With power state observations The deviation is input to the linear state error feedback law, and the observed total disturbance variable is also introduced. Perform division or subtraction feedforward compensation to directly calculate and output the grid-connected reference current component or d / q-axis reference current component in the stationary coordinate system. Step 2: Construct a current inner loop based on quasi-proportional resonance to generate the basic modulation voltage; (1) Convert the actual grid-connected three-phase current collected to a static state. Coordinate system, to obtain the actual current and ; (2) Calculate the reference current and the actual current output in step one. Tracking error; (3) The tracking error is input to the fundamental frequency quasi-proportional resonant controller; the transfer function of the controller includes the input from the cutoff frequency. The determined damping term is such that it is at the fundamental angular frequency. A high-gain region with a certain bandwidth is formed nearby; after the QPR controller performs zero steady-state error adjustment, it outputs the basic modulation voltage command in the stationary coordinate system. and And inversely transform it to the three-phase coordinate system to obtain ; Step 3: Extract the differential mode circulating current inside the MMC and construct a multi-band QPR circulating current suppressor; (1) Real-time acquisition of the current of each phase upper and lower bridge arm of the MMC, and extraction of the actual value of the differential mode circulating current inside each phase using the formula. ; (2) Set the circulation reference value to zero; compare the zero reference value with the actual value. The deviation is input to the multi-band QPR circulating current controller; (3) The multi-band QPR circulating current controller is composed of a proportional element, a second harmonic QPR resonant element, and a fourth harmonic QPR resonant element connected in parallel; even if the grid-side frequency changes at the moment of grid connection. Despite the offset, the wideband characteristics of each resonant element can still output an accurate circulating current compensation voltage. ; Step 4: Generate flexible converter trigger pulses based on the nearest level approximation and voltage equalization sorting strategy; (1) The basic modulation voltage obtained in step two The circulating current compensation voltage obtained in step three By performing algebraic superposition, the final combined command voltage of the upper and lower arms of each phase of the MMC is obtained; (2) Input the comprehensive command voltage to the nearest level approximation modulation algorithm module to calculate the total number of sub-modules that need to be put into operation at the current moment for each bridge arm; (3) Real-time detection of the capacitor voltage of all sub-modules in the bridge arm and bubble sorting, combined with the charging and discharging direction of the bridge arm current, select the sub-module with the optimal capacitor voltage in sequence for connection or disconnection, and finally output the IGBT switching pulse signal to drive the converter to complete the closed-loop grid connection control of the high-voltage shore power system.

2. The MMC shore power grid-connected control method based on linear active disturbance rejection and quasi-proportional resonance according to claim 1, characterized in that... Specifically, it includes the following steps: S001 Shore power grid connection point electrical quantity acquisition and instantaneous power calculation: The system controller uses high-precision voltage and current sensors to collect the three-phase AC voltage at the shore power grid connection point in real time. and three-phase alternating current ; Using the Park transformation matrix in a synchronous rotating coordinate system, the stationary three-phase AC quantities are converted into DC quantities that rotate with the fundamental frequency of the power grid: in, Representing voltage or current ; The phase angle of the grid voltage obtained through a phase-locked loop. For synchronous rotating coordinate system Axial components, For synchronous rotating coordinate system Axial components, For zero-order components, For the A-phase component in a three-phase stationary coordinate system, The B-phase component is shown in a three-phase stationary coordinate system. The C-phase component is defined in a three-phase stationary coordinate system. S002 Total Disturbance Estimation and Power Outer Loop Adjustment Based on Linear Active Disturbance Rejection: This step aims to abandon the inertial response of traditional PI regulators or virtual synchronous generators and adopt linear active disturbance rejection technology to actively observe grid-connected disturbances; taking the active power control channel as an example: First, establish the state-space expression for the first-order active power system, which includes external load mutations and internal parameter perturbations: in, This is the derivative of the actual output active power with respect to time. This represents the actual output active power. The input is an unknown external load disturbance suffered by the system. This represents the sum of unmodeled dynamics and unknown external disturbances in the system; This is the nominal value of the system control gain; For controller output Shaft reference current; Define the total disturbance as an expanded new state variable. and order , The system's fundamental state variables represent active power. To represent the extended state variables of the total system disturbance, a second-order linear extended state observer is constructed: in, Let be the derivative of the active power state observation with respect to time. The derivative of the total disturbance observations with respect to time. This is the nominal value of the system control gain. For controller output Shaft reference current, Actual active power Observed values; Total disturbance Observed values; and The observer gain matrix parameters are... This represents the actual output active power; according to the pole placement method, the observer poles are uniformly placed at... Place, then , ,in For observer bandwidth; Obtain total disturbance observations Then, it is introduced into the linear state error feedback loop for feedforward compensation, generating a system with disturbance rejection characteristics. Shaft reference current : in, For controller output Shaft reference current, The target active power command value set for the shore power system; This is the gain of the proportional controller; using this formula, when the system encounters a sudden load change, It can instantly sense and generate a reverse compensation current in this formula to achieve advanced disturbance rejection; S003: Inner loop tracking of grid-connected current based on quasi-proportional resonance in stationary coordinate system: To accommodate the potential 0.2% to 1% fundamental frequency shift in the ship's microgrid, the inner loop control is kept stationary. A quasi-proportional resonant controller is used in the coordinate system; Using the inverse Park transformation, the command current generated in S002 is... Reference current converted to stationary coordinate system Then the current tracking error was calculated: in, In a stationary coordinate system Current tracking error of the shaft, In a stationary coordinate system Current tracking error of the shaft, The actual coordinate system in the stationary coordinate system shaft current, The actual coordinate system in the stationary coordinate system The shaft current inputs the tracking error to the QPR controller. Taking the axis as an example, the controller is in The transfer function and control law of the domain are expressed as follows: in, For inner loop output Shaft base modulation voltage; This is the proportional gain, used to improve the dynamic response speed of the system; This is the resonant gain, used to eliminate steady-state errors; The cutoff frequency determines the bandwidth of the resonant peak, effectively preventing the resonant peak from deviating from the rated fundamental angular frequency due to the power grid frequency. This leads to control failure; similarly, we can obtain... Shaft modulation voltage , For the Laplace operator, In a stationary coordinate system Current tracking error of the shaft; Finally, through Clark inverse transform, and Transform back to the three-phase coordinate system to obtain the basic modulation voltage. , ; S004: Differential Mode Circulating Current Suppression in Converters Based on Multi-Band QPR Extract the actual differential mode circulation current within each phase of the MMC. : in, and They are respectively The actual current of the upper and lower bridge arms; This is the total input current on the DC side; Due to the nonlinear characteristics of voltage fluctuations within the MMC, the circulating current mainly consists of second and fourth harmonic components; the circulating current command reference value is set to 0, and the circulating current error... , For circulation error, This is the actual differential mode circulation; The circulating current error is fed into a multi-band QPR circulating current suppressor composed of a fundamental frequency proportional control and a multi-order frequency resonant control connected in parallel, generating a circulating current compensation voltage command. : in, This is the command for the j-phase circulating current compensation voltage. For circulating proportional gain, This represents the resonant gain of the h-th harmonic resonant controller (i.e., when h=2 it represents the second harmonic resonant gain, and when h=4 it represents the fourth harmonic resonant gain). The cutoff frequency, For the Laplace operator, This refers to the differential mode circulating current error within phase j. Represents the harmonic order; this structure can accurately track multiple high-frequency harmonics and can also... To ensure its robustness under frequency shift, The fundamental angular frequency of the power grid; S005: Generation of submodule switching signals based on integrated command modulation and voltage equalization sorting: According to Kirchhoff's voltage law, the fundamental modulation voltage generated by S003 and the circulating current compensation voltage generated by S004 are algebraically synthesized to obtain the final command voltages for the upper and lower arms of the MMC: in, This refers to the DC bus voltage of the shore power supply. and These are the reference voltages required for the upper and lower bridge arms, respectively. The j-phase base modulation voltage, This is the command for the j-phase circulating current compensation voltage. The nearest-level approximation modulation algorithm is used to calculate the current control cycle. The total number of sub-modules required for the upper and lower bridge arms and : in, The rated voltage of a single submodule capacitor; The nearest integer function; Finally, we proceed to the capacitor voltage equalization sorting algorithm submodule; real-time reading. The current capacitor voltage of all submodules within the phase is then sorted using a fast sorting mechanism. 1) If the bridge arm current direction is to charge the submodule capacitor: prioritize the capacitor with the lowest voltage. or Each submodule; 2) If the bridge arm current direction is to discharge the submodule capacitor: prioritize connecting the capacitor with the highest voltage. or Each submodule; 3) Generate the final IGBT gate drive switching signal and send it to the hardware execution end to complete a complete control cycle of shore power grid connection regulation.

3. The MMC shore power grid-connected control method based on linear active disturbance rejection and quasi-proportional resonance according to claim 1, characterized in that... In step S001, a grid voltage-oriented vector control strategy is adopted, making... The axis coincides with the grid voltage vector, that is... Based on this, calculate the actual active power output of the system at the current moment. With reactive power : in, This is the grid voltage. for shaft current, for Shaft current; as can be seen from the above decoupling formula, under the grid voltage Under stable conditions, active power and reactive power can be adjusted separately. shaft current and shaft current Exercise independent control.

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