A control method and system of a grid-side converter of a doubly-fed asynchronous motor propulsion system

Abstract

The application discloses a kind of doubly-fed asynchronous motor propulsion system grid-side converter control method and system, method includes: the actual value of DC bus voltage is collected and compared with reference value to obtain voltage error, based on error and its change rate construct discrete sliding surface, generate with the active power reference value matched with voltage stability demand;Based on the discrete prediction model of active and reactive power of grid-side converter mathematical model, construct the cost function with the power reference value as the target to track and realize unit power factor, determine the optimal switching state of grid-side converter in each control cycle by rolling optimization;The optimal switching state is converted into driving signal and directly acts on converter power switch device.The application replaces traditional PI control and SPWM modulation, significantly improves the dynamic response speed of system, anti-interference ability and parameter adaptability, effectively guarantees the stable and efficient operation of electric propulsion system under complex working conditions.

Description

A control method and system for the grid-side converter of a doubly-fed asynchronous motor propulsion system Technical Field

[0001] This invention relates to the field of marine electric propulsion technology, and in particular to a control method and system for a grid-side converter in a doubly fed asynchronous motor propulsion system. Background Technology

[0002] In modern shipbuilding, electric propulsion systems have become a core propulsion technology for green ships, ocean-going cargo ships, LNG carriers, and various special-purpose vessels due to their significant advantages such as high energy efficiency, low operating noise, flexible torque control, and high degree of freedom in engine room layout. Doubly fed asynchronous motors (DFAMs), as key actuators in this system, are widely used in marine electric propulsion because of their wide speed range, ability to cover all operating conditions from berthing to cruising, and the fact that the rotor-side converter capacity only needs to match 30%-50% of the motor's rated capacity, effectively reducing system costs. The electrical energy of the DFAM propulsion system is provided by the ship's power grid. First, it is rectified into DC by the grid-side converter and transmitted through the DC bus. Then, it is inverted into AC by the rotor-side converter to drive the DFAM, ultimately converting electrical energy into mechanical energy to propel the propeller. In this energy chain, the grid-side converter plays a crucial role in maintaining system power balance, stabilizing the DC bus voltage, achieving unity power factor operation on the grid side, and suppressing grid harmonic injection. Its control performance directly determines the smoothness of the propulsion torque and the safety of ship navigation.

[0003] Currently, the industry commonly uses a traditional architecture combining a power outer loop based on proportional-integral (PI) control, a current inner loop based on PI control, and sinusoidal pulse width modulation (PWM) for controlling the grid-side converter in ship doubly-fed asynchronous motor propulsion systems. However, this architecture reveals significant limitations in the complex dynamic scenarios of actual ship operation. First, ships are inevitably affected by both propeller load disturbances and grid voltage fluctuations during navigation, resulting in frequent changes in system power demand. The traditional PI power outer loop relies on fixed parameter tuning, lacking sufficient dynamic adaptive capability, leading to lag in response to such disturbances. This causes DC bus voltage fluctuations, resulting in unstable motor torque output and affecting the ship's heading maintenance and low-speed maneuvering accuracy. Second, the motor speed in the electric propulsion system needs to be adjusted according to operating conditions, and the operating environment easily causes the system's equivalent parameters to drift. The traditional PI current inner loop uses fixed parameters, making it difficult to adapt to the time-varying characteristics of these parameters. In addition, the inherent delay of the PWM loop itself leads to increased current tracking error and grid-side power fluctuations. This may not only cause grid harmonics to exceed limits but also pose a risk of interfering with sensitive shipboard equipment or triggering malfunctions in protection systems. Therefore, developing an advanced control strategy with fast dynamic response, strong anti-interference ability, and the ability to adapt to changes in system parameters to replace the existing traditional architecture has become an urgent technical requirement for improving the overall performance and reliability of ship electric propulsion systems. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the problems of the grid-side converter controller in the prior art, which uses a power outer loop and a current inner loop based on a proportional-integral controller and combined with sinusoidal pulse width modulation, resulting in lag response and weak anti-interference ability under ship dynamic disturbances, and the inability to adapt to system changes due to fixed parameters, thus leading to DC bus voltage fluctuations and insufficient current tracking accuracy.

[0005] To solve the above-mentioned technical problems, the present invention provides a control method for the grid-side converter of a doubly-fed asynchronous motor propulsion system, comprising the following steps:

[0006] S1: Collect the actual value of the DC bus voltage, compare the actual value of the DC bus voltage with a preset reference value to obtain the DC bus voltage error; calculate the error change rate based on the DC bus voltage error; construct a discrete sliding surface based on the DC bus voltage error and the error change rate; obtain an active power reference value that matches the DC bus voltage stability requirements based on the discrete sliding surface;

[0007] S2: Based on the mathematical model of the grid-side converter, establish a discrete prediction model for predicting the active and reactive power of the grid side at the next moment; construct a cost function with the goal of tracking the active power reference value and achieving unity power factor operation; within each control cycle, determine the optimal switching state of the grid-side converter within the current control cycle based on the discrete prediction model and the cost function;

[0008] S3: Convert the optimal switching state into a corresponding drive signal and input it to the power switching device of the grid-side converter to control the grid-side converter.

[0009] In one embodiment of the present invention, in step S2, the method for determining the optimal switching state of the grid-side converter in each control cycle based on the discrete prediction model and the cost function is as follows:

[0010] Iterate through all possible switching states of the grid-side converter; for each switching state, call the discrete prediction model to calculate the predicted active power and reactive power values ​​for the next time step.

[0011] Substitute the predicted active power value and the predicted reactive power value into the cost function to calculate the cost value corresponding to the current switching state.

[0012] Compare the cost values ​​corresponding to all switching states, and determine the switching state with the lowest cost value as the optimal switching state.

[0013] In one embodiment of the present invention, in step S2, the discrete prediction model expression for predicting the active and reactive power on the grid side at the next moment is:

[0014] ,

[0015] in, and These are the predicted active power and reactive power for the next moment, respectively. and The active and reactive power at the current moment; The sampling period; and These are the grid-side filter inductor and resistor, respectively. This refers to the voltage amplitude of the power grid. and For the converter output voltage at Components in the coordinate system; and For the grid voltage at Components in the coordinate system; This is the angular frequency of the power grid.

[0016] In one embodiment of the present invention, in step S2, the cost function The expression is:

[0017] ,

[0018] in, The active power reference value is... For reactive power reference command, when At that time, it achieves unity power factor operation; and These are the predicted active power and reactive power for the next moment, respectively.

[0019] In one embodiment of the present invention, in step S1, the method for obtaining an active power reference value that matches the DC bus voltage stability requirement based on the discrete sliding surface is as follows: according to the discrete sliding surface, an intermediate control quantity is calculated by using a sliding mode control law that combines proportional control and boundary layer saturation function; the intermediate control quantity is discretely integrated to generate a current adjustment command; the current adjustment command is multiplied by the actual value of the DC bus voltage at the current moment to obtain the active power reference value.

[0020] In one embodiment of the present invention, in step S1, the discrete sliding surface The expression is:

[0021] ,

[0022] in, for DC bus voltage error at time t. and For design parameters, This is the sampling period of the control system.

[0023] In one embodiment of the present invention, in step S1, the method for obtaining the active power reference value that matches the DC bus voltage stability requirement based on the discrete sliding surface is as follows: Based on the discrete sliding surface, an intermediate control quantity is calculated using a sliding control law combining proportional control and boundary layer saturation function. For the intermediate control quantity Perform discrete-time integration to generate current regulation commands. Its expression is:

[0024] ,

[0025] in, The sampling period is defined as follows: the current adjustment command is compared with the actual value of the DC bus voltage at the current moment. Multiply by the product to obtain the active power reference value. The expression is:

[0026] .

[0027] In one embodiment of the present invention, the intermediate control quantity The expression is:

[0028] ,

[0029] in, The discrete sliding surface, This is the proportionality coefficient. For interference immunity gain, For boundary layer thickness, It is a saturation function.

[0030] The present invention also provides a grid-side converter control system for a doubly-fed asynchronous motor propulsion system, comprising:

[0031] The voltage outer loop control unit is used to collect the actual value of the DC bus voltage, compare the actual value of the DC bus voltage with a preset reference value to obtain the DC bus voltage error; calculate the error change rate based on the DC bus voltage error; construct a discrete sliding surface based on the DC bus voltage error and the error change rate; and obtain an active power reference value that matches the DC bus voltage stability requirements based on the discrete sliding surface.

[0032] The power inner loop control unit is used to establish a discrete prediction model based on the mathematical model of the grid-side converter to predict the active and reactive power of the grid side at the next moment; to construct a cost function with the goal of tracking the active power reference value and achieving unity power factor operation; and to determine the optimal switching state of the grid-side converter in each control cycle based on the discrete prediction model and the cost function.

[0033] The drive execution unit is used to convert the optimal switching state into a corresponding drive signal and input it to the power switching device of the grid-side converter to control the grid-side converter.

[0034] The present invention also provides a marine electric propulsion device, including a grid-side converter control system for the doubly fed asynchronous motor propulsion system, for controlling the grid-side converter.

[0035] The technical solution of the present invention has the following advantages compared with the prior art:

[0036] This invention constructs a novel dual-closed-loop control architecture by integrating discrete sliding mode control and finite control set model predictive control. This effectively overcomes the shortcomings of traditional proportional-integral control combined with sinusoidal pulse width modulation (PWM), such as slow response, poor disturbance rejection, and inability to adapt to parameter changes. The discrete sliding mode outer loop can quickly and robustly stabilize the DC bus voltage, while the model predictive inner loop can directly and accurately track power commands. This significantly improves the system's dynamic response speed, disturbance rejection capability, and parameter adaptability, thereby ensuring the stable, efficient, and reliable operation of the ship's electric propulsion system under complex operating conditions. Attached Figure Description

[0037] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0038] Figure 1 is a flowchart illustrating the grid-side converter control method for a doubly fed asynchronous motor propulsion system in an embodiment of the present invention.

[0039] Figure 2 is a schematic diagram of the architecture of the ship's doubly fed asynchronous motor electric propulsion system in an embodiment of the present invention;

[0040] Figure 3 is a schematic diagram of the SMC-MPC control framework on the network side in an embodiment of the present invention. Detailed Implementation

[0041] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0042] Example 1:

[0043] As shown in Figure 1, the present invention provides a control method for the grid-side converter of a doubly-fed asynchronous motor propulsion system, comprising the following steps:

[0044] S1: Collect the actual value of the DC bus voltage, compare the actual value of the DC bus voltage with a preset reference value to obtain the DC bus voltage error; calculate the error change rate based on the DC bus voltage error; construct a discrete sliding surface based on the DC bus voltage error and the error change rate; obtain an active power reference value that matches the DC bus voltage stability requirements based on the discrete sliding surface;

[0045] S2: Based on the mathematical model of the grid-side converter, establish a discrete prediction model for predicting the active and reactive power of the grid side at the next moment; construct a cost function with the goal of tracking the active power reference value and achieving unity power factor operation; within each control cycle, determine the optimal switching state of the grid-side converter within the current control cycle based on the discrete prediction model and the cost function;

[0046] S3: Convert the optimal switching state into a corresponding drive signal and input it to the power switching device of the grid-side converter to control the grid-side converter.

[0047] This invention provides a control method for the grid-side converter of a doubly-fed asynchronous motor propulsion system. The method acquires the DC bus voltage in the outer voltage loop and compares it with a reference value to obtain the error. Based on this error and its rate of change, a discrete sliding mode surface is constructed to generate an active power reference value that precisely matches the voltage stability requirements. In the inner power loop, an instantaneous power prediction model is established based on the mathematical model of the grid-side converter, and a cost function is designed to track this power reference value and achieve unity power factor. Then, in each control cycle, the optimal switching state is directly determined through rolling optimization. Finally, this optimal switching state is converted into a drive signal and directly applied to the power switching devices of the grid-side converter. This scheme, through the synergy of the discrete sliding mode outer loop and the model prediction inner loop, achieves fast, accurate, and robust control of active power, effectively overcoming the shortcomings of traditional PI (Proportional-Integral) control, such as slow response, poor disturbance rejection, and insufficient parameter adaptability. It significantly improves the stability and power quality of the doubly-fed asynchronous motor propulsion system under dynamic disturbances and time-varying parameter conditions.

[0048] As shown in Figure 2, the method of this invention is applied to a ship's double-fed induction motor (DFIM) electric propulsion system. This system employs a typical back-to-back converter topology, with the energy flow path as follows: three-phase AC power supplied by the ship's electrical grid passes sequentially through a grid-side converter (GSC, acting as the rectifier), a DC bus, and a rotor-side converter (RSC, acting as the inverter), ultimately driving the DFIM to propel the propeller. The grid-side converter uses a filter inductor (equivalent parameters are...) and () is connected to the power grid, and its three-phase AC voltage and current are denoted as follows: and The core innovation of this invention focuses on optimizing and improving the control algorithm of the grid-side converter.

[0049] As shown in Figure 3, the dual-loop structure of the outer loop of Discrete Sliding Mode Control (SMC) and the inner loop of Finite Control Set Model Predictive Control (FCS-MPC) has the following overall logic: the system samples the grid voltage in real time. Grid-side current And the DC bus voltage, and based on these quantities, the active power at the current moment is calculated. and reactive power The outer loop controller generates a reference command for active power based on the stability requirements of the DC bus voltage using a sliding mode control (SMC) algorithm. At the same time, set the reactive power reference command. To achieve unity power factor operation. The inner loop controller then receives... and Within an extremely short control cycle, a predictive control algorithm based on a finite control set model is used to process all possible switching states (corresponding to switching functions). The system performs evaluation and rolling optimization to predict the power value at the next time step. and And finally select the switch combination that optimizes the control objective, and generate the corresponding drive signal. To control the power switching devices (such as insulated gate bipolar transistors, IGBTs) of the grid-side converter, thereby generating the required converter output voltage. The core of this invention for the dual closed-loop control strategy is the generation of the voltage outer loop SMC. and power inner loop FCS-MPC tracking A detailed design was carried out.

[0050] Specifically, in step S1, the core objective of the voltage outer loop control is to generate an active power reference value that precisely matches the DC bus voltage stability requirements. .

[0051] Real-time acquisition of actual DC bus voltage values ,in Represents the current discrete control moment. The actual value of the DC bus voltage. Compared with the preset DC bus voltage reference value By comparison, the DC bus voltage error is obtained. Defined as: .

[0052] DC bus voltage error It directly reflects the degree to which the DC voltage deviates from the expected value. To construct a controller with good dynamic performance, it is necessary to further consider the trend of error change, usually by using the error from the previous moment. and the system's sampling period To calculate the rate of change of error.

[0053] Based on voltage error And its error change rate, construct discrete sliding surface The expression is:

[0054] ,

[0055] in and These are adjustable design parameters used to balance the system's convergence speed and stability. For the sampling period of the control system (e.g.) To meet the real-time computing requirements of digital signal processors (DSPs), the above-mentioned sliding surface design incorporates current error and error change information, aiming to force the system state (voltage error) to converge to zero along a preset path, thereby laying the foundation for robust control.

[0056] Based on the constructed discrete sliding surface A sliding mode control law combining proportional control and disturbance rejection saturation function is used to calculate the intermediate control quantity. Its specific expression is:

[0057] .

[0058] In this sliding mode control law This is a proportional coefficient used to improve steady-state tracking accuracy; The disturbance rejection gain is designed to compensate for the maximum disturbance the system may encounter. Boundary layer thickness; The saturation function is used. This design balances the system's dynamic disturbance rejection requirements with effective suppression of sliding mode chattering. The calculated... It is a transition signal that integrates the requirements of steady-state tracking and dynamic disturbance rejection.

[0059] To eliminate steady-state error and obtain a smooth control command, the intermediate control quantity is discrete-time integrated to generate a current control command. The integral formula is:

[0060] .

[0061] This current regulation command serves as the direct control output of the sliding mode control outer loop, adapting to the tracking requirements of the subsequent power inner loop. This is in contrast to directly outputting the active power reference value. It is easier to match the current control characteristics of the converter, which is beneficial to improving the dynamic response speed of the system.

[0062] Adjust the current at this moment Compared with the actual value of the DC bus voltage obtained from the current sampling Multiplying them together yields the active power reference value, expressed as:

[0063] .

[0064] Active power reference value This accurately characterizes the amount of active power that the grid-side converter needs to absorb or supply from the grid to maintain DC bus voltage stability, thus providing a clear command target for precise power tracking in the inner loop. The entire outer voltage loop, through the forced convergence characteristics of the discrete sliding mode surface and the disturbance rejection design of saturation switching control, enables the system to quickly and smoothly adjust power commands when facing dynamic disturbances such as load changes and grid voltage fluctuations, significantly improving the response speed and robustness of DC bus voltage control.

[0065] Furthermore, in step S2, in the power inner loop control section, finite control set model predictive control is adopted as the core tracking strategy, aiming to achieve a reference value for the active power generated by the voltage outer loop. This method enables rapid and precise tracking while simultaneously ensuring the grid-side converter operates at unity power factor. The inner-loop control method is based on the grid-side converter's... A mathematical model in a stationary coordinate system is used to construct a discrete prediction model for predicting active and reactive power at the next moment. By designing a suitable cost function, rolling optimization is performed in each control cycle, and the optimal switching state is directly selected to act on the converter, thereby eliminating the traditional sinusoidal pulse width modulation stage and improving the dynamic response speed and tracking accuracy of the system.

[0066] Based on the circuit structure and energy relationship of the grid-side converter, an instantaneous power prediction model is established. In a coordinate system, the mathematical model of a grid-side converter can be expressed as the dynamic relationship between voltage and current, from which the active power can be derived. and reactive power The discrete forward prediction formula is given. This model fully considers the grid-side filter inductance. and resistance Grid voltage amplitude Grid angular frequency and the converter output voltage component , Influenced by factors such as... Specifically, at each control moment... Based on the currently sampled grid voltage components , Current power value , and the converter output voltage determined by the current switching state. , It can predict the next moment. active power and reactive power The prediction model expression is as follows: ,

[0067] in, The system sampling period is typically a small value (e.g., ...). s) to match the real-time computing capabilities of the digital controller; This refers to the phase voltage amplitude of the power grid. The angular frequency of the power grid; and These are the inductance and equivalent resistance of the grid-side filter inductor, respectively. , For the converter output voltage at The values ​​of the components in the coordinate system are uniquely determined by the current switching state of the converter; , The voltage components of the grid are shown in the same coordinate system. This prediction model can accurately reflect the changing trends of the system's active and reactive power at the next moment under a given switching state, providing a theoretical basis for subsequent optimization.

[0068] In order to evaluate the control effect of each possible switching state and guide the system toward the desired goal, a suitable cost function needs to be constructed.

[0069] In this embodiment, the control objective includes two aspects: first, to ensure that the predicted active power... As close as possible to the active power reference value given by the outer ring. This is to achieve accurate power tracking and stable DC bus voltage; secondly, to ensure accurate prediction of reactive power. Approaching zero, thus achieving unity power factor operation on the grid side, reducing reactive power impact and harmonic pollution on the power grid.

[0070] Based on the above control objectives, the designed cost function Using the squared error form, the specific expression is as follows:

[0071] ,

[0072] in, The active power reference value is... This is a reactive power reference command. and These are the predicted active power and reactive power for the next time step, respectively; when When unity power factor operation is achieved, the cost function is... The expression is:

[0073] .

[0074] Cost function Taking into account both active power tracking accuracy and reactive power suppression effect, the smaller the value, the better the control performance of the corresponding switching state.

[0075] The aforementioned cost function is a simplified design suitable for ship electric propulsion scenarios with low requirements for switching losses. Depending on actual needs, a constraint term for the change in switching state can be added to the cost function to suppress frequent switching and reduce losses.

[0076] Within each control cycle, the controller executes a rolling optimization process to determine the optimal switching state at the current moment. The specific steps are: traversing all possible switching states of the three-phase voltage source converter (a total of 8 states, including 6 active vectors and 2 zero vectors); for each switching state, based on its corresponding output voltage component... , By calling the discrete prediction model described above, the corresponding predicted active power value for the next time step is calculated. and reactive power prediction values Then, these predicted values ​​are substituted into the cost function. The cost value of the switching state is calculated. After traversing all states and calculating the costs, the cost values ​​are compared, and the switching state that minimizes the cost function is selected as the optimal switching state for the current control cycle.

[0077] The optimal switching state directly determines the on and off modes of each phase arm of the converter, thereby generating corresponding pulse drive signals that directly act on the power switching devices (such as IGBTs) of the grid-side converter, achieving instantaneous control of their output voltage. Through this online rolling optimization mechanism of prediction, evaluation, and selection, the FCS-MPC inner loop can adjust the switching action in real time during each sampling cycle. This not only significantly improves the tracking speed and accuracy of current and power but also naturally adapts to changes in system parameters (such as equivalent parameter drift caused by changes in motor speed). It effectively overcomes the response delay and steady-state error problems caused by the fixed parameters of the traditional PI current loop and its reliance on modulation links, thus ensuring efficient, stable, and high-quality power conversion of the electric propulsion system under dynamic operating conditions.

[0078] In this embodiment of the invention, the cost function can be flexibly adjusted according to the engineering scenario. The core is to achieve power point tracking and unity power factor through PQ bi-objective optimization. The switching constraint term is an optional extension and does not affect the core control logic.

[0079] Furthermore, in step S3, based on the optimal switching state determined in step S2, a corresponding drive signal is generated and directly applied to the power switching devices of the grid-side converter to achieve final control of the converter.

[0080] Specifically, when the finite control set model predictive control algorithm of the power inner loop completes the traversal, prediction, cost evaluation and comparison of all 8 possible switching states, and selects the one that minimizes the cost function... After finding the minimum optimal switch combination, this switch combination corresponds to a set of defined three-phase switch functions. , , Each phase switching function is typically a binary logic (e.g., 1 for upper bridge arm on and 0 for lower bridge arm off; otherwise, 0). This logic combination directly defines the ideal on-state of each phase bridge arm of the grid-side converter within the current control cycle.

[0081] The control system's drive execution unit converts this set of discrete optimal switching logic into pulse-width modulation (PWM) signals or gate drive signals for the actual driveable power switching devices. In actual hardware implementation, this conversion process is typically performed in a digital signal processor (DSP) or field-programmable gate array (FPGA). The controller generates the corresponding PWM duty cycle signal or direct gate switching command based on the optimal switching state, and amplifies and electrically isolates the signal through an isolation drive circuit, ultimately applying it to the gates of the IGBTs or other fully controllable power switching devices in each phase arm of the grid-side converter. These drive signals control the on and off states of each IGBT, thereby generating an output voltage on the AC side of the converter corresponding to the optimal switching state. , , (exist (in the coordinate system), that is, the physical reproduction of the voltage components used in the prediction model in step S2 is achieved.

[0082] By directly outputting the optimal switching state, this invention completely eliminates the sinusoidal pulse width modulation (SPWM) or space vector pulse width modulation (SVPWM) stages indispensable in traditional control architectures. This eliminates the inherent delays introduced by modulation wave generation, carrier comparison, and dead time, allowing control commands to act on the main circuit with near-zero latency. This not only significantly improves the system's dynamic response speed but also, because the switching state is directly selected based on real-time prediction and multi-objective optimization, the system can more accurately track the active power reference value. Simultaneously, it strictly constrains reactive power to approach zero, thereby ensuring a high sinusoidal waveform and a power factor close to 1 for the grid-side current, and effectively suppressing harmonic content injected into the grid. Finally, by repeatedly executing the closed-loop process of steps S1 to S3 in each extremely short control cycle, the control method proposed in this invention enables the grid-side converter to respond quickly, smoothly, and adaptively to DC bus voltage commands and changes in grid operating conditions, providing stable, efficient, and high-quality power conversion and power regulation functions for the entire ship electric propulsion system.

[0083] Example 2:

[0084] Based on the same inventive concept as Embodiment 1, the present invention also provides a grid-side converter control system for a doubly-fed asynchronous motor propulsion system, used to implement the steps of the grid-side converter control method for a doubly-fed asynchronous motor propulsion system described in Embodiment 1, including the following modules:

[0085] The voltage outer loop control unit is used to collect the actual value of the DC bus voltage, compare the actual value of the DC bus voltage with a preset reference value to obtain the DC bus voltage error; calculate the error change rate based on the DC bus voltage error; construct a discrete sliding surface based on the DC bus voltage error and the error change rate; and obtain an active power reference value that matches the DC bus voltage stability requirements based on the discrete sliding surface.

[0086] The power inner loop control unit is used to establish a discrete prediction model based on the mathematical model of the grid-side converter to predict the active and reactive power of the grid side at the next moment; to construct a cost function with the goal of tracking the active power reference value and achieving unity power factor operation; and to determine the optimal switching state of the grid-side converter in each control cycle based on the discrete prediction model and the cost function.

[0087] The drive execution unit is used to convert the optimal switching state into a corresponding drive signal and input it to the power switching device of the grid-side converter to control the grid-side converter.

[0088] The voltage outer loop control unit, power inner loop control unit, and drive execution unit of the grid-side converter control system for the doubly fed asynchronous motor propulsion system proposed in this embodiment are respectively used to implement steps S1, S2, and S3 in the grid-side converter control method for the doubly fed asynchronous motor propulsion system in Embodiment 1. To avoid redundancy, they will not be described again here.

[0089] Example 3:

[0090] The present invention also provides a ship electric propulsion device, which includes a ship power grid, a three-phase voltage-type PWM grid-side converter, a DC bus, a rotor-side converter, a doubly-fed asynchronous motor, and a propeller connected in sequence. The control terminal of the grid-side converter is connected to the grid-side converter control system of the doubly-fed asynchronous motor propulsion system as described in Embodiment 2, for controlling the rectification operation of the grid-side converter and maintaining the DC bus voltage stability.

[0091] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0092] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in one or more blocks of the flowchart illustrations and / or one or more blocks of the block diagrams.

[0093] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means that implement the functions specified in one or more flowcharts and / or one or more block diagrams.

[0094] These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process, such that the instructions, which execute on the computer or other programmable apparatus, provide steps for implementing the functions specified in one or more flowcharts and / or one or more block diagrams.

[0095] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A control method for the grid-side converter of a doubly-fed asynchronous motor propulsion system, characterized in that, Includes the following steps: S1: Acquire the actual value of the DC bus voltage, compare the actual value of the DC bus voltage with a preset reference value to obtain the DC bus voltage error; calculate the error change rate based on the DC bus voltage error; construct a discrete sliding surface based on the DC bus voltage error and the error change rate; and calculate the intermediate control quantity based on the discrete sliding surface using a sliding mode control law combining proportional control and boundary layer saturation function. For the intermediate control quantity Perform discrete-time integration to generate current regulation commands. Its expression is: ,in, The sampling period is defined as follows: the current adjustment command is compared with the actual value of the DC bus voltage at the current moment. Multiplying these values ​​yields a reference value for active power that matches the DC bus voltage stability requirements. The expression is: S2: Based on the mathematical model of the grid-side converter, a discrete prediction model is established to predict the active and reactive power of the grid side at the next moment; the expression of the discrete prediction model for predicting the active and reactive power of the grid side at the next moment is: ,in, and These are the predicted active power and reactive power for the next moment, respectively. and The active and reactive power at the current moment; The sampling period; and These are the grid-side filter inductor and resistor, respectively. This refers to the voltage amplitude of the power grid. and For the converter output voltage at Components in the coordinate system; and For the grid voltage at Components in the coordinate system; S1: The grid angular frequency is used as the reference value for active power. A cost function is constructed with the goal of tracking the active power reference value and achieving unity power factor operation. In each control cycle, based on the discrete prediction model and the cost function, the optimal switching state of the grid-side converter in the current control cycle is determined. S2: The optimal switching state is converted into a corresponding drive signal and input to the power switching device of the grid-side converter to control the grid-side converter.

2. The control method for the grid-side converter of the doubly-fed asynchronous motor propulsion system according to claim 1, characterized in that: In step S2, the method for determining the optimal switching state of the grid-side converter within each control cycle based on the discrete prediction model and the cost function is as follows: traverse all possible switching states of the grid-side converter; for each switching state, call the discrete prediction model to calculate the predicted active power and reactive power values ​​for the next moment. Substitute the predicted active power value and the predicted reactive power value into the cost function to calculate the cost value corresponding to the current switching state. Compare the cost values ​​corresponding to all switching states, and determine the switching state with the lowest cost value as the optimal switching state.

3. The control method for the grid-side converter of the doubly-fed asynchronous motor propulsion system according to claim 1, characterized in that: In step S2, the cost function The expression is: ,in, The active power reference value is... For reactive power reference command, when At that time, it achieves unity power factor operation; and These are the predicted active power and reactive power for the next moment, respectively.

4. The control method for the grid-side converter of the doubly-fed asynchronous motor propulsion system according to claim 1, characterized in that: In step S1, the method for obtaining the active power reference value that matches the DC bus voltage stability requirement based on the discrete sliding surface is as follows: according to the discrete sliding surface, an intermediate control quantity is calculated by using a sliding mode control law that combines proportional control and boundary layer saturation function; the intermediate control quantity is discretely integrated to generate a current adjustment command; the current adjustment command is multiplied by the actual value of the DC bus voltage at the current moment to obtain the active power reference value.

5. The control method for the grid-side converter of a doubly-fed asynchronous motor propulsion system according to claim 1 or 4, characterized in that: In step S1, the discrete sliding surface The expression is: ,in, for DC bus voltage error at time t. and For design parameters, This is the sampling period of the control system.

6. The control method for the grid-side converter of the doubly-fed asynchronous motor propulsion system according to claim 1, characterized in that: The intermediate control quantity The expression is: ,in, The discrete sliding surface, This is the proportionality coefficient. For interference immunity gain, Boundary layer thickness, It is a saturation function.

7. A grid-side converter control system for a doubly-fed asynchronous motor propulsion system, characterized in that, include: The voltage outer loop control unit is used to acquire the actual value of the DC bus voltage, compare the actual value of the DC bus voltage with a preset reference value to obtain the DC bus voltage error, calculate the error change rate based on the DC bus voltage error, construct a discrete sliding surface based on the DC bus voltage error and the error change rate, and calculate the intermediate control quantity based on the discrete sliding surface using a sliding mode control law combining proportional control and boundary layer saturation function. For the intermediate control quantity Perform discrete-time integration to generate current regulation commands. Its expression is: ,in, The sampling period is defined as follows: the current adjustment command is compared with the actual value of the DC bus voltage at the current moment. Multiplying these values ​​yields a reference value for active power that matches the DC bus voltage stability requirements. The expression is: The power inner loop control unit is used to establish a discrete prediction model for predicting the active and reactive power of the grid side at the next moment, based on the mathematical model of the grid-side converter. The expression of the discrete prediction model for predicting the active and reactive power of the grid side at the next moment is as follows: ,in, and These are the predicted active power and reactive power for the next moment, respectively. and The active and reactive power at the current moment; The sampling period; and These are the grid-side filter inductor and resistor, respectively. This refers to the voltage amplitude of the power grid. and For the converter output voltage at Components in the coordinate system; and For the grid voltage at Components in the coordinate system; The grid angular frequency is defined; a cost function is constructed with the goal of tracking the active power reference value and achieving unity power factor operation; within each control cycle, based on the discrete prediction model and the cost function, the optimal switching state of the grid-side converter within the current control cycle is determined; a drive execution unit is used to convert the optimal switching state into a corresponding drive signal, which is input to the power switching device of the grid-side converter to control the grid-side converter.

8. A ship electric propulsion device, characterized in that, include: The ship's electrical grid, a three-phase voltage-type pulse width modulation grid-side converter, a DC bus, a rotor-side converter, a doubly-fed asynchronous motor, and a propeller are connected in sequence. The control terminal of the grid-side converter is connected to the grid-side converter control system of the doubly-fed asynchronous motor propulsion system as described in claim 7, and is used to control the rectification operation of the grid-side converter and maintain the stability of the DC bus voltage.

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