Vienna rectifier type ec fan control method and system under power grid unbalanced condition

Abstract

The application discloses a Vienna rectifier type EC fan control method and system under power grid unbalanced conditions, three-phase power grid voltage, alternating current side current, DC side filter capacitor voltage and load current are collected first, a phase angle of the power grid is extracted through a phase-locked loop, and abc to dq coordinate transformation is completed. An outer ring voltage sliding mode controller generates an active current instruction according to a DC side voltage error, an ADRC current loop dynamically tracks active and reactive current components, and control output is sent into SVPWM to generate a switching signal through inverse transformation. At the same time, a midpoint voltage balance control is introduced to suppress the asymmetric problem of the DC side capacitor voltage. The system effectively solves the voltage and current control problem under the power grid imbalance, improves the bus stability and power quality, is suitable for the complex working condition operation of the Vienna rectifier, and has strong robustness and control precision.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, specifically to a control method and system for Vienna rectifier EC wind turbines under grid imbalance conditions. Background Technology

[0002] EC (Electrically Commutated) fans are widely used in communications, data centers, energy storage, and industrial manufacturing due to their high efficiency, energy saving, stability, reliability, and ease of maintenance. To meet the stability requirements of EC fans in industrial applications, Vienna rectifiers, with their high power factor, low harmonics, and high efficiency, have become one of the commonly used rectifier topologies in EC fan systems.

[0003] In existing technologies, Vienna rectifiers typically employ a PI control strategy to construct a dual-closed-loop control system, which has advantages such as simple structure and convenient implementation, and has been widely adopted in engineering applications. However, in actual operation, grid imbalance often exists, leading to distortion of the input voltage waveform. Under traditional PI control, the controller struggles to effectively cope with disturbances caused by grid imbalance, affecting the stability of EC wind turbine operation. Summary of the Invention

[0004] The technical problem this invention aims to solve is to provide a control method and system for Vienna rectifier EC wind turbines under grid imbalance conditions. The voltage loop employs a power-approach sliding mode control method, and the current loop employs an active disturbance rejection control (ADRC) method. This control method can achieve rapid recovery and stable output of the DC-side voltage under grid voltage imbalance or fluctuations, thereby improving the stability of the EC wind turbine.

[0005] To address the aforementioned problems, this invention proposes a control method for Vienna rectifier EC wind turbines under grid imbalance conditions, comprising the following steps:

[0006] Step S1: Real-time acquisition of three-phase grid voltage, three-phase AC side current, voltage of the two DC side filter capacitors, and load current;

[0007] Step S2: Based on the three-phase grid voltage collected in step S1, perform phase detection and extract the grid phase angle;

[0008] Step S3: Using the grid phase angle extracted in step S2, the three-phase grid voltage and three-phase AC current collected in step S1 are transformed from the stationary coordinate system to the synchronous rotating coordinate system to obtain the corresponding voltage and current components.

[0009] Step S4: Based on the error between the expected and actual DC side voltage values, and based on the current components in the synchronous rotating coordinate system obtained in step S3, power-approach sliding mode control is used to generate active current commands.

[0010] Step S5: Using the active current command generated in step S4 and the preset reactive current command as targets, active disturbance rejection control is used to dynamically track and control the actual current in the synchronous rotating coordinate system obtained in step S3, and outputs the rectifier control voltage in the synchronous rotating coordinate system.

[0011] Step S6: Transform the control voltage in the synchronous rotating coordinate system output in step S5 to the stationary coordinate system to obtain the three-phase control voltage.

[0012] Step S7: Input the three-phase control voltage obtained in step S6 into the space vector pulse width modulation module to generate a switching signal suitable for the three-level structure of the Vienna rectifier.

[0013] Step S8: Real-time detection of the voltage deviation between the two filter capacitors on the DC side, and compensation for the voltage deviation by adjusting the duty cycle of the switching function in step S7.

[0014] This invention also proposes a Vienna rectifier EC wind turbine control system under grid imbalance conditions, comprising:

[0015] The main circuit module is used to collect the three-phase grid voltage, three-phase AC side current, voltage of the two DC side filter capacitors, and load current in real time.

[0016] The extraction module is used to perform phase detection based on the collected three-phase grid voltage and extract the grid phase angle;

[0017] The rotating module is used to transform the collected three-phase grid voltage and three-phase AC side current from the stationary coordinate system to the synchronous rotating coordinate system using the extracted grid phase angle, so as to obtain the corresponding voltage components and current components.

[0018] The generation module is used to generate active current commands based on the error between the expected and actual DC side voltage values ​​and the current components in the obtained synchronous rotating coordinate system, using power-approach sliding mode control.

[0019] The control module is used to dynamically track and control the actual current in the obtained synchronous rotating coordinate system using active current command and preset reactive current command as targets, and output the rectifier control voltage in the synchronous rotating coordinate system; the control voltage in the synchronous rotating coordinate system is inversely transformed to the stationary coordinate system to obtain the three-phase control voltage; the three-phase control voltage is input to the space vector pulse width modulation module to generate a switching signal suitable for the three-level structure of the Vienna rectifier; the voltage deviation of the two filter capacitors on the DC side is detected in real time, and the voltage deviation is compensated by adjusting the duty cycle of the switching function.

[0020] The beneficial effects of the above-mentioned technical solution of the present invention are as follows:

[0021] The nonlinear dual-loop control system constructed in this invention, under grid imbalance conditions, features a voltage outer loop sliding mode control that rapidly responds to voltage errors and accurately generates active current commands; an ADRC current loop that dynamically tracks current components and, with its strong robustness, suppresses disturbances to ensure unity power factor operation; and a midpoint voltage balance control that effectively avoids capacitor voltage asymmetry and stabilizes the bus voltage. The system overcomes grid imbalance interference, achieving rapid recovery and stable output of the DC-side voltage, thereby improving the stability of the EC wind turbine. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the overall framework of the EC fan control system based on the Vienna rectifier.

[0023] Figure 2 This is a diagram of the main circuit topology of the Vienna rectifier.

[0024] Figure 3 Block diagram of a nonlinear dual-loop control structure for Vienna rectifier using sliding mode control and active disturbance rejection control;

[0025] Figure 4 This is a block diagram of the d-axis current loop controller based on ADRC.

[0026] Figure 5 This is a block diagram of the q-axis current loop controller based on ADRC.

[0027] Figure 6 This is a flowchart of the EC fan control method based on Vienna rectifier. Detailed Implementation

[0028] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments.

[0029] Combination Figure 6As shown, this invention proposes a control method for Vienna rectifier EC wind turbines under grid imbalance conditions, comprising the following steps:

[0030] Step S1 involves real-time acquisition of three-phase grid voltage, three-phase AC current, voltage of the two DC-side filter capacitors, and load current; specifically, this may include:

[0031] Data acquisition steps: Real-time acquisition of three-phase power grid voltage 、 , Three-phase AC side current 、 , and the voltage of the two filter capacitors on the DC side. , and load current ;like Figure 1 The diagram shown is an overall framework diagram of the EC wind turbine control system based on the Vienna rectifier. Figure 2 This is a diagram of the main circuit topology of the Vienna rectifier. The voltage and current on the AC side are represented; L and R are the AC side filter inductance and equivalent input resistance, respectively; the bidirectional switch for each phase consists of two switching devices connected in reverse series. Sx 1 and Sx 2. Composition; DC side passes through two filter capacitors. and Voltage stabilization R L is the DC-side load, and the voltage across it is the DC output voltage. .

[0032] Step S2 involves performing phase detection based on the three-phase grid voltage acquired in step S1 to extract the grid phase angle; specifically, this may include:

[0033] The power grid phase acquisition step involves performing phase detection on the collected three-phase power grid voltage using a phase-locked loop (PLL) to extract the power grid phase angle. .

[0034] Step S3: Using the grid phase angle extracted in step S2, transform the three-phase grid voltage and three-phase AC current collected in step S1 from the stationary coordinate system to the synchronous rotating coordinate system to obtain the corresponding voltage and current components; specifically, this may include:

[0035] The coordinate transformation step is based on the obtained power grid phase angle. The three-phase AC side voltage and the three-phase grid voltage will be converted. 、 , and current 、 , Transforming from the abc stationary coordinate system to the dq synchronous rotating coordinate system, we obtain the d-axis voltage. q-axis voltage d-axis current q-axis current .

[0036] Step S4: Based on the error between the expected and actual DC-side voltage values, and using the current components in the synchronous rotating coordinate system obtained in step S3, power-law approach sliding mode control is employed to generate an active current command; specifically, this may include:

[0037] The voltage loop control steps employ power-law approach sliding mode control to construct the outer voltage loop, based on the desired DC-side voltage value. Compared with actual value Error generates d-axis active current command .

[0038] Step S5, using the active current command generated in step S4 and the preset reactive current command as targets, employs active disturbance rejection control to dynamically track and control the actual current in the synchronous rotating coordinate system obtained in step S3, and outputs the rectifier control voltage in the synchronous rotating coordinate system; specifically, it may include:

[0039] The current loop control procedure employs active disturbance rejection control to construct the inner current loop, using d-axis current commands. and q-axis current command With 0 as the target, the actual current in the dq coordinate system is respectively... , Perform dynamic tracking control and output the rectifier control voltage in the dq coordinate system. , .

[0040] Step S6 involves inversely transforming the control voltage output in the synchronous rotating coordinate system from step S5 to the stationary coordinate system to obtain the three-phase control voltage; specifically, this may include:

[0041] The control voltage in the dq coordinate system , Inverse transformation to the abc coordinate system yields the three-phase control voltage. 、 , .

[0042] Step S7 involves inputting the three-phase control voltage obtained in step S6 into the space vector pulse width modulation module to generate a switching signal suitable for the three-level structure of the Vienna rectifier; specifically, this may include:

[0043] In the switching signal generation step, the three-phase control voltage is sent to the space vector pulse width modulation module to generate a switching signal adapted to the three-level structure of the Vienna rectifier, which drives the rectifier switching device to operate.

[0044] Step S8 involves real-time detection of the voltage deviation between the two filter capacitors on the DC side, and compensation for the voltage deviation by adjusting the duty cycle of the switching function in step S7; specifically, this may include:

[0045] The midpoint voltage balance control procedure involves real-time detection of the voltage deviation between the two filter capacitors on the DC side. By adjusting the duty cycle of the switching function, voltage deviation is compensated, and capacitor voltage asymmetry is suppressed.

[0046] In this embodiment, by real-time acquisition of three-phase grid voltage and precise extraction of phase angle, combined with coordinate system transformation (stationary → synchronous rotation), the positive and negative sequence components under grid imbalance can be effectively separated, avoiding the current distortion and power fluctuation problems that occur in traditional control when the grid is unbalanced. This ensures that the EC wind turbine can still operate stably in complex grid environments such as voltage asymmetry and harmonic interference. The active current command generation stage adopts power-law approach sliding mode control. Compared with traditional sliding mode control, it has a faster approach speed and less chattering, which can quickly suppress DC side voltage deviation and ensure DC side voltage stability (reducing filter capacitor voltage fluctuation). The current tracking stage introduces active disturbance rejection control, which can actively offset uncertainties such as grid disturbances and load changes (such as load changes caused by EC wind turbine wind speed regulation), achieving precise tracking of active / reactive current commands, reducing AC side current distortion rate, improving the energy conversion efficiency of Vienna rectifier, and reducing energy consumption. By real-time detection of the two DC side filter capacitors, the system can effectively separate the positive and negative sequence components under grid imbalance. The voltage deviation of the capacitor is compensated by dynamically adjusting the duty cycle of the switching function, which avoids problems such as uneven stress on the rectifier switching tube and accelerated capacitor aging caused by capacitor voltage imbalance. This improves the hardware reliability of the Vienna rectifier's three-level structure and extends the overall service life of the EC fan. Finally, the switching signal adapted to the Vienna rectifier's three-level structure is generated through space vector pulse width modulation (SVPWM). Compared with two-level modulation, this reduces the voltage stress on the switching tube, reduces switching losses, and improves the output voltage quality, further adapting to the EC fan's requirements for power supply stability and low-noise operation.

[0047] like Figure 3As shown, this control system addresses the operational requirements of the Vienna rectifier under grid imbalance conditions, constructing a nonlinear dual-loop control structure centered on sliding mode control and ADRC. The system first acquires the three-phase grid voltage, three-phase AC current, and the voltage and load current of the two DC-side filter capacitors. Then, it extracts the grid phase angle in real time through a phase-locked loop (PLL), followed by an abc to dq coordinate transformation. The outer voltage loop employs a sliding mode controller, specifically a power-approach sliding mode control, to generate active current commands based on the DC-side voltage error. And through the ADRC current loop respectively and Dynamic tracking control is performed, in which The ADRC control output is sent to the SVPWM module after inverse coordinate transformation to generate a switching signal suitable for Vienna's three-level structure. The system also introduces midpoint voltage balance control to effectively suppress DC-side capacitor voltage asymmetry and improve bus stability.

[0048] In a preferred embodiment of the present invention, the execution of voltage loop control and current loop control in steps S4 and S5 is based on a dynamic mathematical model established in a dq synchronous rotating coordinate system; the dynamic mathematical model is constructed in the following manner:

[0049] Based on the voltage and current components in the synchronous rotating coordinate system obtained in step S3, the d-axis current dynamic characteristics are constructed. These characteristics are defined as the functional relationship between the d-axis current change rate and the d-axis grid voltage, the d-axis rectifier output voltage, the voltage drop across the loop resistance, and the rotating electromotive force coupling term. Specifically, they are expressed as follows: ;

[0050] Based on the d-axis current dynamic characteristics, the q-axis current dynamic characteristics are constructed. These characteristics are defined as the functional relationship between the q-axis current change rate and the q-axis grid voltage, the q-axis rectifier output voltage, the voltage drop across the loop resistance, and the rotating electromotive force coupling term. Specifically, they are expressed as follows: ;

[0051] Based on the coupling relationship described by the d-axis and q-axis current dynamic characteristics, the DC-side voltage dynamic characteristics are constructed. These characteristics are defined as the functional relationship between the DC-side voltage change rate and the interaction terms between the rectifier switching state and the AC-side current, as well as the load current influence term. Specifically, they are expressed as follows: .

[0052] In the formula, , , , These represent the components of the grid-side voltage and current in the dq coordinate system, respectively. , These are the equivalent components of the switching functions of each phase in the dq coordinate system; , To represent the output voltage components of the rectifier in the dq coordinate system, the following relationship must be satisfied: .

[0053] In a preferred embodiment of the present invention, the generation of active current command using power-approach sliding mode control in step S4 is implemented in the following manner:

[0054] Based on the current components and actual DC-side voltage values ​​obtained in step S3 under the synchronous rotating coordinate system, the deviation between the expected value and the actual output voltage of the DC-side output voltage is defined as the voltage tracking error, expressed as:

[0055] ;

[0056] in, and These represent the expected and actual values ​​of the DC-side output voltage, respectively.

[0057] Based on the voltage tracking error and its rate of change, a sliding mode surface is constructed, and the design is as follows:

[0058] ;

[0059] In the formula, The time constant coefficient, This represents the rate of change of the DC-side output voltage tracking error.

[0060] Under the condition of operating in sliding mode and with a unity power factor, i.e., when the system is in sliding mode, the rate of change of the current component is zero. Meanwhile, in order to ensure that the system operates under unity power factor conditions, the following settings are made: , Based on the sliding surface and these assumptions, the above conditions are substituted into the dynamic mathematical model under the dq synchronous rotating coordinate system:

[0061] ;

[0062] The mathematical relationship between the switching function components and the parameters can be derived to obtain the expression for the dynamic characteristics of the DC-side voltage:

[0063] ;

[0064] Based on the expression for the dynamic characteristics of the DC-side voltage, the sliding mode control law is divided into two parts: an equivalent control term and a nonlinear control term, namely:

[0065] ;

[0066] in, This represents the equivalent control item. This represents discontinuous terms (nonlinear control terms).

[0067] Define constant term Where C is the equivalent value of the filter capacitor. (where the load resistance is on the DC side), then the d-axis current can be obtained. The equivalent control term is represented as:

[0068] ;

[0069] The nonlinear control term is designed based on a power-law reaching law. Its construction includes a function of the sliding surface and its sign function, and incorporates an adjustable gain coefficient and an exponential parameter. Using a power-law reaching law to construct the reaching term of the sliding mode controller, the corresponding nonlinear control term design is as follows:

[0070] ;

[0071] in, , and It is a constant. , .

[0072] The equivalent control term is added to the nonlinear control term to synthesize a complete sliding mode control law:

[0073] ;

[0074] The d-axis active current command value is generated based on the complete sliding mode control law, that is, the d-axis active current command is output according to the sliding mode control law. .

[0075] In a preferred embodiment of the present invention, the dynamic tracking control using active disturbance rejection control in step S5 is achieved by mutually independent d-axis current active disturbance rejection controllers and q-axis current active disturbance rejection controllers.

[0076] The d-axis current active disturbance rejection controller and the q-axis current active disturbance rejection controller are determined based on the actual current in the synchronous rotating coordinate system obtained in step S3, and the controller for each axis consists of an extended state observer and a nonlinear state error feedback control law; wherein, the extended state observer is used to observe the current and total disturbance of the corresponding axis in real time, and the nonlinear state error feedback control law generates the final control voltage based on the active current command or preset reactive current command generated in step S4 and the observation results of the extended state observer.

[0077] In this embodiment, the current loop adopts ADRC, and sig is a nonlinear error feedback function. The specific expression of sig() is shown in the following formula:

[0078] ;

[0079] In the formula, x represents the input error. Nonlinear adjustment parameter , The sign function is used to maintain the consistency of the feedback direction. The current loop active disturbance rejection control includes d-axis current active disturbance rejection control and q-axis current active disturbance rejection control. Each axis active disturbance rejection controller consists of an extended state observer and a nonlinear state error feedback control law.

[0080] In a preferred embodiment of the present invention, the d-axis current active disturbance rejection controller is executed according to the following steps:

[0081] Based on the actual d-axis current obtained in step S3 and the grid phase angle extracted in step S2, the d-axis current equation is transformed into a standard form d-axis current equation that includes the control gain coefficient, total disturbance term, and the dynamic characteristics of the current itself. The original form of the d-axis current equation is:

[0082] ;

[0083] In the formula, For coupling terms, This represents the disturbance of the current by the d-axis voltage. The disturbance is caused by the current itself.

[0084] Transform the above equation into its standard form:

[0085] ;

[0086] In the formula, To control the gain coefficient; The total disturbance term in the current loop is defined as follows: ;function The dynamic characteristics generated by the d-axis current itself are defined as follows: .

[0087] Based on the standard form of the d-axis current equation, a d-axis extended state observer (ESO) is determined for real-time observation of the d-axis current value and its total disturbance. The design of the d-axis extended state observer includes: updating the current observation value using a nonlinear function and sampling time based on the deviation between the actual and observed d-axis current values; and updating the disturbance observation value based on this deviation and the nonlinear function. The specific design of the d-axis current ESO is as follows:

[0088] ;

[0089] In the formula, The observation error of the d-axis output current; These are the observed values ​​of the d-axis current; The observed values ​​represent the unknown perturbation along the d-axis; , Let be the gain coefficient of the nonlinear function in the d-axis current loop ESO. The sampling time of the system.

[0090] Using the d-axis active current command value generated in step S4 as the target, and based on the current observations and disturbance observations obtained from the d-axis extended state observer, the d-axis nonlinear state error feedback control law (NLSEF) is determined. The determination of the d-axis nonlinear state error feedback control law includes: constructing a nonlinear error function based on the error between the d-axis current command value and the observed value to generate the initial control quantity; then, combining the disturbance observations and the current's own dynamic characteristic term, and adjusting the control gain coefficient, the final d-axis control voltage is obtained. The d-axis current loop NLSEF is designed as follows:

[0091] ;

[0092] The determination process of the q-axis current active disturbance rejection controller is the same as that of the d-axis current active disturbance rejection controller, and the preset q-axis reactive current command value is used as the control target.

[0093] like Figure 5 As shown, the q-axis current active disturbance rejection controller is determined according to the following steps:

[0094] The standard form transformation of the q-axis current equation, based on the actual q-axis current and the grid phase angle, converts the q-axis current dynamic characteristic equation into a standard form that includes the control gain coefficient, total disturbance term, and the current's own dynamic characteristics; the original form of the q-axis current equation is:

[0095] ;

[0096] In the formula, This is the coupling term between the d and q axes (generated by the rotational characteristics of the synchronous rotating coordinate system). This is the q-axis term representing the disturbance of current by the grid voltage. This is the self-perturbation term generated by the q-axis current flowing through the AC side resistor.

[0097] The original equation above is rearranged into its standard form:

[0098] ;

[0099] In the formula, This is the q-axis control gain coefficient, whose value is determined by the circuit parameters (corresponding to the original equation). item); The total disturbance term in the q-axis current loop, taking into account both coupling disturbances and voltage disturbances, is defined as follows: ;function The dynamic characteristics generated by the q-axis current itself are only related to the current itself and the resistance parameters, and are defined as follows: .

[0100] Based on the standard form of the q-axis current equation obtained by transformation, a q-axis extended state observer is determined to perform real-time observation of the q-axis current value and its total disturbance. The determination of the q-axis extended state observer includes: updating the current observation value through a nonlinear function (sig function) and the system sampling time according to the deviation between the actual value and the observed value of the q-axis current, and updating the disturbance observation value based on the deviation and the nonlinear function.

[0101] The specific expression for the design of the q-axis current ESO is as follows:

[0102] ;

[0103] In the formula, The observation error of the q-axis output current at time k is equal to the observed value of the q-axis current. Compared with actual value The difference; Let k be the observed value of the q-axis current at time k. The observed value of the unknown perturbation on the q-axis at time k; , This is the gain coefficient of the nonlinear function in the q-axis current loop ESO, used to adjust the observer's response speed and observation accuracy; The sampling time of the system determines the update frequency of the observer; This is a nonlinear error feedback function used to enhance the observer's ability to suppress nonlinear errors.

[0104] The preset q-axis reactive current command value (usually set to) With the goal of achieving unity power factor operation, and based on current observations obtained from the q-axis extended state observer... and disturbance observations Determine the q-axis nonlinear state error feedback control law.

[0105] The determination of the q-axis nonlinear state error feedback control law includes: constructing a nonlinear error function based on the error between the q-axis current command value and the observed value to generate the initial control quantity; then, combining the disturbance observation value and the current's own dynamic characteristic term, and adjusting the control gain coefficient, the final q-axis control voltage is obtained. .

[0106] The specific expression for the q-axis current loop NLSEF design is as follows:

[0107] ;

[0108] In the formula: The tracking error of the q-axis current command at time k is equal to the q-axis reactive current command value. Compared with current observations The difference; The initial control input at time k is determined by the control gain. With nonlinear error function Multiplying them together, we get The nonlinear adjustment parameter for the q-axis NLSEF (satisfying 0 < <1); The final output q-axis control voltage at time k is used to actively cancel out disturbances through the form of "initial control quantity - disturbance compensation term + self-dynamic characteristic compensation term". For disturbance compensation, This is a compensation term for the dynamic characteristics of the current itself.

[0109] In this embodiment, the transformation from the stationary coordinate system to the synchronously rotating coordinate system in step S3 is achieved through two coordinate transformations:

[0110] Three-phase to two-phase stationary coordinate transformation (Clark transformation), based on the three-phase grid voltage collected in step S1 ( ) and three-phase AC side current ( The Clark transformation converts the voltage signal from the three-phase abc stationary coordinate system to the two-phase αβ stationary coordinate system. ) and current signal ( The core of this transformation is to convert three-phase unbalanced or balanced AC quantities into two-phase orthogonal stationary coordinate system quantities, reducing the dimensionality of variables while retaining the amplitude and phase information of the original electrical quantities, thus laying the foundation for further transformations.

[0111] Two-phase stationary-synchronous rotating coordinate transformation (Park transformation), using the grid phase angle extracted in step S2 The voltage signal in the αβ stationary coordinate system is transformed by the Park transform. ) and current signal ( This is converted into a signal in the dq synchronous rotating coordinate system. The final d-axis voltage is then obtained. q-axis voltage and d-axis current q-axis current This enables the conversion of AC to DC, facilitating independent and precise control of the active and reactive components.

[0112] In step S8, "compensating for voltage deviation by adjusting the duty cycle of the switching function in step S7" specifically involves dynamically adjusting the duty cycle of the switching function of each phase of the Vienna rectifier to compensate for the voltage deviation of the two filter capacitors on the DC side. The compensation process for voltage deviation is as follows:

[0113] First, based on the switching signal generated in step S7, the actual voltage of the two filter capacitors on the DC side is detected in real time. ), and calculate the voltage deviation between the two. ;

[0114] Secondly, differentiated control logic is executed based on the positive or negative direction of the voltage deviation value:

[0115] when (Right now Higher than When this is done, the switching devices on the upper bridge arm of each phase of the rectifier are increased through control logic. The conduction time is reduced, and the switching devices in the lower bridge arm are reduced accordingly. The on-time. This operation can increase the conduction time of lower voltages. Reduce charging time and reduce higher voltage The charging time, thus rise, Decrease, reducing the deviation between the two;

[0116] when (Right now Below When this is done, the switching devices of the lower bridge arm of each phase of the rectifier are increased through control logic. Reduce the conduction time and correspondingly reduce the switching devices in the upper bridge arm. The conduction time, this operation can increase the voltage at lower voltages. Reduce charging time and reduce higher voltage The charging time prompts rise, The voltage is reduced to balance the voltage; finally, the voltage deviation is reduced by periodically adjusting the duty cycle of each phase's switching function. The voltage is kept stable within the preset allowable threshold range, ultimately achieving dynamic balance of the DC side midpoint potential.

[0117] This invention simplifies the complex three-phase AC control problem into a DC control problem in the dq coordinate system through a two-step transformation of "Clark transformation + Park transformation," achieving decoupling of the active component (d-axis) and reactive component (q-axis). This decoupling characteristic makes the control logic of the subsequent voltage and current loops simpler, enabling precise and independent adjustment of active and reactive power, avoiding mutual interference between components, and significantly improving control stability under grid imbalance conditions. By adjusting the switch duty cycle in real time to compensate for capacitor voltage deviation, it effectively avoids the problems caused by capacitor voltage imbalance in the three-level structure of the Vienna rectifier—preventing damage to the switching transistors due to uneven voltage stress and slowing down the aging of capacitors due to excessive voltage deviation, greatly improving the hardware reliability of the rectifier, indirectly extending the overall service life of the EC wind turbine, and ensuring the stability of the DC-side output voltage, providing high-quality power supply for the EC wind turbine.

[0118] This invention also proposes a Vienna rectifier EC wind turbine control system under grid imbalance conditions, comprising:

[0119] The main circuit module is used to collect the three-phase grid voltage, three-phase AC side current, voltage of the two DC side filter capacitors, and load current in real time.

[0120] The extraction module is used to perform phase detection based on the collected three-phase grid voltage and extract the grid phase angle;

[0121] The rotating module is used to transform the collected three-phase grid voltage and three-phase AC side current from the stationary coordinate system to the synchronous rotating coordinate system using the extracted grid phase angle, so as to obtain the corresponding voltage components and current components.

[0122] The generation module is used to generate active current commands based on the error between the expected and actual DC side voltage values ​​and the current components in the obtained synchronous rotating coordinate system, using power-approach sliding mode control.

[0123] The control module is used to dynamically track and control the actual current in the obtained synchronous rotating coordinate system using active current command and preset reactive current command as targets, and output the rectifier control voltage in the synchronous rotating coordinate system; the control voltage in the synchronous rotating coordinate system is inversely transformed to the stationary coordinate system to obtain the three-phase control voltage; the three-phase control voltage is input to the space vector pulse width modulation module to generate a switching signal suitable for the three-level structure of the Vienna rectifier; the voltage deviation of the two filter capacitors on the DC side is detected in real time, and the voltage deviation is compensated by adjusting the duty cycle of the switching function.

[0124] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A control method for Vienna rectifier EC wind turbines under grid imbalance conditions, characterized in that, Includes the following steps: Step S1: Real-time acquisition of three-phase grid voltage, three-phase AC side current, voltage of the two DC side filter capacitors, and load current; Step S2: Based on the three-phase grid voltage collected in step S1, perform phase detection and extract the grid phase angle; Step S3: Using the grid phase angle extracted in step S2, transform the three-phase grid voltage and three-phase AC current collected in step S1 from the stationary coordinate system to the synchronous rotating coordinate system to obtain the corresponding voltage and current components. Step S4: Based on the error between the expected and actual DC-side voltage values, and using the current components in the synchronous rotating coordinate system obtained in step S3, a power-approaching sliding mode control is employed to generate an active current command, specifically: Based on the current component and actual DC-side voltage value obtained in the synchronous rotating coordinate system in step S3, the deviation between the expected value and the actual output voltage of the DC-side output voltage is defined as the voltage tracking error. A sliding mode surface is constructed based on the voltage tracking error and its rate of change. Under the conditions of operating in sliding mode and with a set unity power factor, based on the assumptions of the sliding surface, zero rate of change of current, and zero q-axis current, the mathematical relationship between the switching function components and parameters is derived to obtain the expression for the dynamic characteristics of the DC side voltage. Based on the expression of the dynamic characteristics of the DC side voltage, the sliding mode control law is divided into two parts: equivalent control term and nonlinear control term. The equivalent control term is constructed based on the parameters and the actual value of the DC side voltage, while the nonlinear control term is designed based on the power-law approach. Its construction includes the function of the sliding surface and its sign function, and integrates the adjustable gain coefficient and the exponential parameter. The equivalent control term and the nonlinear control term are added together to synthesize a complete sliding mode control law; Generate d-axis active current command values ​​based on the complete sliding mode control law; Step S5: Using the active current command generated in step S4 and the preset reactive current command as targets, active disturbance rejection control is used to dynamically track and control the actual current in the synchronous rotating coordinate system obtained in step S3, and outputs the rectifier control voltage in the synchronous rotating coordinate system. Step S6: Transform the control voltage in the synchronous rotating coordinate system output in step S5 to the stationary coordinate system to obtain the three-phase control voltage. Step S7: Input the three-phase control voltage obtained in step S6 into the space vector pulse width modulation module to generate a switching signal suitable for the three-level structure of the Vienna rectifier. Step S8: Real-time detection of the voltage deviation between the two filter capacitors on the DC side, and compensation for the voltage deviation by adjusting the duty cycle of the switching function in step S7.

2. The Vienna rectifier EC wind turbine control method under grid imbalance conditions according to claim 1, characterized in that, The execution of voltage loop control and current loop control in steps S4 and S5 is based on a dynamic mathematical model established in the dq synchronous rotating coordinate system; the dynamic mathematical model is constructed in the following way: Based on the voltage and current components in the synchronous rotating coordinate system obtained in step S3, the d-axis current dynamic characteristics are constructed. The d-axis current dynamic characteristics are defined as the functional relationship between the d-axis current change rate and the d-axis grid voltage, the d-axis rectifier output voltage, the voltage drop across the loop resistance, and the rotating electromotive force coupling term. Based on the dynamic characteristics of the d-axis current, the dynamic characteristics of the q-axis current are constructed. The dynamic characteristics of the q-axis current are defined as the functional relationship between the rate of change of the q-axis current and the q-axis grid voltage, the q-axis rectifier output voltage, the voltage drop across the loop resistance, and the rotating electromotive force coupling term. Based on the coupling relationship described by the d-axis current dynamic characteristics and the q-axis current dynamic characteristics, the DC-side voltage dynamic characteristics are constructed. The DC-side voltage dynamic characteristics are defined as the functional relationship between the DC-side voltage change rate and the interaction terms of the rectifier switching state and the AC-side current, as well as the load current influence terms.

3. The Vienna rectifier EC wind turbine control method under grid imbalance conditions according to claim 1, characterized in that, In step S5, active disturbance rejection control is used for dynamic tracking control, which is achieved through independent d-axis current active disturbance rejection controllers and q-axis current active disturbance rejection controllers. The d-axis current active disturbance rejection controller and the q-axis current active disturbance rejection controller are determined based on the actual current in the synchronous rotating coordinate system obtained in step S3, and the controller for each axis consists of an extended state observer and a nonlinear state error feedback control law. The extended state observer is used to observe the current and total disturbance of the corresponding axis in real time, and the nonlinear state error feedback control law generates the final control voltage based on the active current command or preset reactive current command generated in step S4 and the observation results of the extended state observer.

4. The Vienna rectifier EC wind turbine control method under grid imbalance conditions according to claim 3, characterized in that, The d-axis current active disturbance rejection controller is executed according to the following steps: Based on the actual d-axis current obtained in step S3 and the grid phase angle extracted in step S2, the d-axis current equation is transformed into a standard form d-axis current equation that includes the control gain coefficient, the total disturbance term, and the dynamic characteristics of the current itself. Specifically, ； In the formula, This represents the rate of change of current along the d-axis. To control the gain coefficient; The control voltage for the d-axis rectifier; This represents the total disturbance term in the current loop; Let be the dynamic characteristic function of the d-axis current itself; where, Defined as , Defined as , This represents the actual current along the d-axis. This represents the actual q-axis current. The angular frequency of the power grid. Forming coupling terms, d is the grid voltage, L is the AC side filter inductance, and R is the AC side equivalent input resistance; Based on the standard form of the d-axis current equation, a d-axis extended state observer is determined to perform real-time observation of the d-axis current value and its total disturbance. The design of the d-axis extended state observer includes: updating the current observation value through a nonlinear function and sampling time according to the deviation between the actual and observed d-axis current values, and updating the disturbance observation value based on the deviation and the nonlinear function. Using the d-axis active current command value generated in step S4 as the target, and based on the current observation value and disturbance observation value obtained from the d-axis extended state observer, the d-axis nonlinear state error feedback control law is determined. The determination of the d-axis nonlinear state error feedback control law includes: constructing a nonlinear error function based on the error between the d-axis current command value and the observation value to generate the initial control quantity, and then combining the disturbance observation value and the current's own dynamic characteristic term, and after adjusting the control gain coefficient, the final d-axis control voltage is obtained. The determination process for the q-axis current active disturbance rejection controller is the same as that for the d-axis current active disturbance rejection controller, with the preset q-axis reactive current command value as the control target.

5. The Vienna rectifier EC wind turbine control method under grid imbalance conditions according to claim 3, characterized in that, The q-axis current active disturbance rejection controller is determined according to the following steps: Based on the actual q-axis current and the grid phase angle, the dynamic characteristic equation of the q-axis current is transformed into a standard form that includes the control gain coefficient, the total disturbance term, and the dynamic characteristics of the current itself, as follows: ; In the formula, This represents the rate of change of current along the q-axis. This is the q-axis control gain coefficient; This is the control voltage for the q-axis rectifier; This represents the total disturbance term in the q-axis current loop; Let be the dynamic characteristic function of the q-axis current itself; where, Defined as , Defined as , This represents the actual current along the d-axis. This represents the actual q-axis current. The angular frequency of the power grid. Forming coupling terms, R is the q-axis grid voltage, L is the AC side filter inductance, and R is the AC side equivalent input resistance. Based on the standard form of the q-axis current equation obtained by transformation, a q-axis extended state observer is determined to perform real-time observation of the q-axis current value and its total disturbance. The determination of the q-axis extended state observer includes: updating the current observation value through a nonlinear function and sampling time according to the deviation between the actual value and the observed value of the q-axis current, and updating the disturbance observation value based on the deviation and the nonlinear function. With a preset q-axis reactive current command value as the target, and based on the current observation value and disturbance observation value obtained from the q-axis extended state observer, the q-axis nonlinear state error feedback control law is determined. The determination of the q-axis nonlinear state error feedback control law includes: constructing a nonlinear error function based on the error between the q-axis current command value and the observed value to generate the initial control quantity, and then combining the disturbance observation value and the current's own dynamic characteristic term, and after adjusting the control gain coefficient, the final q-axis control voltage is obtained.

6. The Vienna rectifier EC wind turbine control method under grid imbalance conditions according to claim 1, characterized in that, In step S3, the transformation from the stationary coordinate system to the synchronous rotating coordinate system is achieved through two coordinate transformations: Based on the three-phase grid voltage and three-phase AC side current collected in step S1, the signals are converted from the abc three-phase stationary coordinate system to the two-phase αβ stationary coordinate system using Clark transformation. Using the grid phase angle extracted in step S2, the signal in the αβ stationary coordinate system is converted into the signal in the dq synchronous rotating coordinate system through Park transformation, so as to obtain the voltage and current components of the d-axis and q-axis.

7. The Vienna rectifier EC wind turbine control method under grid imbalance conditions according to claim 1, characterized in that, In step S8, voltage deviation is compensated by adjusting the duty cycle of the switching function in step S7. This is achieved by adjusting the duty cycle of the switching function of each phase of the Vienna rectifier to compensate for the voltage deviation of the two filter capacitors on the DC side. Specifically, this includes: Based on the switching signal generated in step S7, the voltage deviation values ​​of the two filter capacitors on the DC side are detected and calculated in real time. Determine the positive or negative direction of the voltage deviation value; when the voltage deviation value is greater than zero, increase the conduction time of the upper bridge arm switching device of the rectifier through the control logic, and at the same time reduce the conduction time of the lower bridge arm switching device accordingly, so that the capacitor voltage on the lower voltage side rises and the capacitor voltage on the higher voltage side falls. When the voltage deviation is less than zero, the control logic increases the conduction time of the lower bridge arm switching device of the rectifier and correspondingly reduces the conduction time of the upper bridge arm switching device, so that the capacitor voltage on the lower voltage side rises and the capacitor voltage on the higher voltage side falls. By repeatedly adjusting the duty cycle of each phase switching function, the voltage deviation is suppressed within the preset allowable threshold range, thereby achieving a balance of the DC side midpoint potential.

8. A system for implementing the Vienna rectifier EC wind turbine control method under grid imbalance conditions as described in any one of claims 1-7, characterized in that, include: The main circuit module is used to collect the three-phase grid voltage, three-phase AC side current, voltage of the two DC side filter capacitors, and load current in real time. The extraction module is used to perform phase detection based on the collected three-phase grid voltage and extract the grid phase angle; The rotating module is used to transform the collected three-phase grid voltage and three-phase AC current from the stationary coordinate system to the synchronous rotating coordinate system using the extracted grid phase angle, so as to obtain the corresponding voltage and current components. The generation module is used to generate active current commands based on the error between the expected and actual DC side voltage values ​​and the current components in the obtained synchronous rotating coordinate system, using power-approach sliding mode control. The control module is used to dynamically track and control the actual current in the obtained synchronous rotating coordinate system using active current command and preset reactive current command as targets, and outputs the rectifier control voltage in the synchronous rotating coordinate system. The control voltage in the synchronous rotating coordinate system is inversely transformed to the stationary coordinate system to obtain the three-phase control voltage. The three-phase control voltage is input to the space vector pulse width modulation module to generate switching signals suitable for the three-level structure of Vienna rectifier. The voltage deviation of the two filter capacitors on the DC side is detected in real time, and the voltage deviation is compensated by adjusting the duty cycle of the switching function.

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