Regulation inertia type grid-connected device for reducing motor voltage to ground and control method

Abstract

This invention discloses an inertia-adjustable grid-connected device and control method for reducing motor-to-ground voltage. The device comprises an even number of motor grid-connected interface devices connected in series between the positive and negative buses of a bipolar DC-DC converter. The intermediate node of each even number of motor grid-connected interface devices is grounded to reduce the motor-to-ground voltage. Each motor grid-connected interface device includes a doubly-fed induction generator (DFIG), a first DC / AC converter, a permanent magnet synchronous motor (PMSM), and a second DC / AC converter. The positive terminal of each motor grid-connected interface device is connected to the positive DC side of both the first and second DC / AC converters, and the negative terminal is connected to the negative DC side of both the first and second DC / AC converters. This invention aims to reduce the ground voltage of both the DFIG and PMSM, lower insulation requirements, extend insulation life, and improve the stability and reliability of the electrical system.

Description

Technical Field

[0001] This invention belongs to the field of grid connection technology for new energy power plants, specifically relating to a grid-connected device and control method for adjusting inertia that can reduce the voltage of a motor to ground. Background Technology

[0002] In recent years, my country's renewable energy power generation scale has grown rapidly, and building a new power system based on microgrids of new energy sources is an inevitable trend in the current power system development. Currently, microgrids using new energy power generation are mainly connected to the grid via power electronic converters, which convert the electricity generated by the microgrid into alternating current before feeding it into the grid. However, with the increasing penetration rate of new energy sources, the overall inertia of the power system is relatively insufficient, and the frequency and voltage characteristics of the entire grid are deteriorating. Although existing technologies use synchronous condensers to increase the rotational inertia of the system and also serve as reactive power compensation devices to provide voltage support for new energy systems, traditional synchronous condensers have limitations. Firstly, their inertia constant is small, and inertia release cannot be actively controlled. Secondly, they mainly provide reactive power support to the grid and can only provide short-term frequency support, resulting in limited support capabilities. Based on this, existing technologies use electric motors as grid-connected devices. However, these devices often have high voltages to ground, such as 20kV, posing safety risks like electric shock and fire. Furthermore, they can damage the motor itself: the motor's insulation material ages and deteriorates faster under high voltage. Breakdown of the insulation can lead to short circuits or grounding faults in the motor's windings, damaging key components like the windings and core. High voltage to ground can create a current path through the motor's bearings, causing electro-corrosion. This corrosion creates tiny sparks on the bearing surface, resulting in pitting and other damage, increasing wear and ultimately damaging the bearing and affecting the motor's normal operation. In addition, high voltage to ground can cause abnormal operating parameters, such as increased current and decreased power factor. This reduces motor efficiency, increases energy consumption, and shortens its lifespan. Excessive voltage to ground can also be conducted to other electrical equipment through the grounding system, interfering with their normal operation. For example, it may cause signal distortion in the control system, malfunction of electronic equipment, etc., affecting the stability and reliability of the entire electrical system. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a grid-connected device and control method for adjusting inertia that can reduce the voltage to ground of a motor, in view of the above-mentioned problems of the prior art. The present invention aims to reduce the voltage to ground of doubly fed motors and permanent magnet synchronous motors, reduce insulation requirements, extend insulation life, and improve the stability and reliability of electrical systems.

[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0005] An inertia-adjustable grid-connected device for reducing motor-to-ground voltage includes an even number of motor grid-connected interface devices connected in series between the positive and negative busbars of a bipolar DC-DC collector circuit. The intermediate nodes of these even number of motor grid-connected interface devices are grounded to reduce the motor-to-ground voltage of the motor grid-connected interface devices. Each motor grid-connected interface device includes a doubly-fed motor, a first DC / AC converter, a permanent magnet motor, and a second DC / AC converter. The positive terminal of each motor grid-connected interface device is connected to the positive DC side of both the first and second DC / AC converters, and the negative terminal is connected to the negative DC side of both the first and second DC / AC converters. The AC side of the first DC / AC converter is connected to the doubly-fed motor, and the AC side of the second DC / AC converter is connected to the permanent magnet motor. The output shaft of the permanent magnet motor is connected to the output shaft of the doubly-fed motor via a coaxial cable.

[0006] Optionally, the even number of motor grid connection interface devices refers to two motor grid connection interface devices, such that the motor-to-ground voltage of the doubly fed motor and the permanent magnet motor in the motor grid connection interface device is half the voltage between the positive and negative busbars.

[0007] Optionally, the voltage between the positive and negative buses of the bipolar DC collection circuit is 20kV, and the motor-to-ground voltage of the doubly fed motor and permanent magnet motor in the motor grid connection interface device is 10kV.

[0008] Furthermore, the present invention also provides a control method for the adjustable inertia grid-connected device that can reduce the voltage of the motor to ground, comprising a dual-loop control method consisting of an outer loop control and an inner loop control to control the first DC / AC converter of the doubly-fed motor to control the grid-connected output power of the doubly-fed motor, wherein the outer loop control is to adjust the grid-side frequency... and power frequency The deviation multiplied by the proportionality coefficient To obtain speed deviation , will speed deviation and initial rotational speed The reference speed is obtained by subtraction. , reference speed and current speed The deviation is used for PI control to obtain the q-axis reference current of the doubly-fed motor control winding. and the d-axis reference current with a value of 0. Combined with the obtained doubly-fed motor control winding dq-axis reference current The inner loop control uses the dq-axis reference current of the doubly-fed motor control winding. , control the dq axis current of the winding dq axis current of power winding This is used as the input to the preset first closed-loop controller to obtain the dq-axis reference voltage of the doubly-fed motor control winding. A first DC / AC converter for controlling a doubly-fed motor.

[0009] Optionally, the preset first closed-loop controller is a model-free predictive current controller based on an extended state observer, and the discrete-form functional expression of the model-free predictive current controller is:

[0010] ;

[0011] ;

[0012] in, and The reference voltages of the doubly fed motor control windings along the dq axis at time k are respectively. The dq axis components in and These represent the dq-axis input gains of the doubly-fed motor control windings. and Reference current for the dq axis of the doubly fed motor control winding The dq axis components in and The control winding dq-axis currents at time k are respectively The dq axis components in To control the cycle, and These are the dq-axis disturbance components of the doubly fed motor control winding at time k, as observed by the extended state observer.

[0013] Optionally, the extended state observer is a cascaded noise-suppressed extended state observer, which includes a cascaded first-level extended state observer and a second-level extended state observer:

[0014] ;

[0015] ;

[0016] in, This represents a first-order extended state observer. The auxiliary integral variable error of the doubly fed motor control winding for the first-stage extended state observer. Auxiliary integral variables of the doubly-fed motor control windings estimated by the first-stage extended state observer. For the auxiliary integral variable of the control winding of the doubly-fed motor, At the initial moment, For the current moment, For the control winding current of a doubly fed motor, for The first-order differential, The doubly fed motor control winding current is used for the first-stage extended state observer. , and For the parameters of the extended state observer, for The first-order differential, The doubly fed motor control winding current estimated by the first-stage extended state observer. Lumped disturbances in the hyperlocal equations of the doubly-fed motor control windings estimated by a first-order extended state observer. To control the input gain of the winding hyperlocal model, To control the winding voltage, for The first differential; It is a second-level extended state observer. The auxiliary integral variable error of the doubly-fed motor control winding for the second-level extended state observer. Auxiliary integral variables of the doubly-fed motor control winding estimated by the second-level extended state observer. for The first-order differential, The doubly-fed motor control winding current estimated by the second-level extended state observer. for The first-order differential, Lumped disturbances in the hyperlocal equations of the doubly-fed motor control windings estimated by a second-order extended state observer. for The first derivative; and the functional expression of the d-axis component or q-axis component in the doubly fed motor control winding dq-axis disturbance term obtained by the cascaded noise suppression expansion state observer is:

[0017] ,

[0018] in, This refers to the d-axis component or q-axis component in the dq-axis disturbance term of the doubly fed motor control winding.

[0019] Optionally, the perturbation estimation error and the transfer function of the perturbation estimation of the cascaded noise suppression extended state observer are expressed as follows:

[0020] ;

[0021] ;

[0022] in, Let be the transfer function of the perturbation estimation error. For complex variables, The cutoff frequency, The transfer function is used for perturbation estimation.

[0023] Optionally, a dual-loop control method consisting of an outer loop control and an inner loop control is used to control the second DC / AC converter of the permanent magnet motor to control the mechanical axis output power of the permanent magnet motor. The outer loop control involves using PI control to obtain the q-axis reference current of the permanent magnet motor by measuring the deviation between the DC-side voltage of the second DC / AC converter and a reference voltage, and comparing this with the d-axis reference current of the permanent magnet motor, which is set to 0. Combined, the reference current of the dq axis of the permanent magnet motor is obtained. The inner loop control uses the dq-axis reference current of the permanent magnet motor as the reference. dq axis current of permanent magnet motor This serves as the input to the preset second closed-loop controller to obtain the reference voltage for the dq axis of the permanent magnet motor. A second DC / AC converter for controlling a permanent magnet motor.

[0024] Optionally, the preset second closed-loop controller is an adaptive model-free predictive current controller based on an extended state observer, and the discrete-form functional expression of the adaptive model-free predictive current controller is:

[0025] ;

[0026] ;

[0027] In the formula, and The reference voltages of the permanent magnet motor dq axis at time k are respectively. The dq axis components in and This is the input gain for the dq axis of the permanent magnet motor. and Reference current for the dq axis of the permanent magnet motor The dq axis components in and The dq-axis currents of the permanent magnet motor at time k are respectively The dq axis components in To control the cycle, and These are the dq-axis disturbance components of the permanent magnet motor at time k, as observed by the extended state observer.

[0028] Optionally, the extended state observer in the adaptive model-free predictive current controller based on the extended state observer is a cascaded noise-suppressed extended state observer. The cascaded noise-suppressed extended state observer includes a cascaded first-level extended state observer and a second-level extended state observer, wherein the functional expressions of the first-level and second-level extended state observers are:

[0029] ;

[0030] ;

[0031] in, This represents a first-order extended state observer. For the permanent magnet synchronous motor auxiliary integral variable error of the first-stage extended state observer, Auxiliary integral variables of the permanent magnet synchronous motor estimated by a first-stage extended state observer. For the auxiliary integral variable of the permanent magnet synchronous motor, At the initial moment, For the current moment, This refers to the stator current of a permanent magnet synchronous motor. for The first-order differential, Stator current of permanent magnet synchronous motor estimated by a first-stage extended state observer. , and For the parameters of the extended state observer, for The first-order differential, for The estimated value, Lumped disturbances in the hyperlocal equations of a permanent magnet synchronous motor estimated by a first-order extended state observer. This represents the input gain in the hyperlocal equations of a permanent magnet synchronous motor. This refers to the stator voltage of the permanent magnet synchronous motor. The imaginary unit, This refers to the angular velocity of the permanent magnet synchronous motor. for The first differential; It is a second-level extended state observer. For the permanent magnet synchronous motor auxiliary integral variable error of the second-level extended state observer, Auxiliary integral variables of permanent magnet synchronous motor estimated by a second-level extended state observer. for The first-order differential, The stator current of the permanent magnet synchronous motor estimated by the second-level extended state observer. for The first-order differential, Lumped disturbances in the hyperlocal equations of a permanent magnet synchronous motor estimated by a second-order extended state observer. for The first derivative; and the functional expression of the d-axis component or q-axis component in the permanent magnet motor dq-axis disturbance term at time k obtained by the cascaded noise suppression extended state observer is:

[0032] ;

[0033] in, To obtain the d-axis component or q-axis component of the permanent magnet motor dq-axis disturbance term at time k using a cascaded noise suppression extended state observer, we have:

[0034] ;

[0035] in, for The first-order differential, This is an estimate of the input gain. To vary the step size, Let be the objective function. For gradient operators, and To adjust the parameters of the adaptive iteration step size, and satisfy:

[0036] , ;

[0037] in, For time.

[0038] Compared with the prior art, the present invention can mainly achieve the following beneficial effects:

[0039] 1. The present invention provides an inertia-based grid-connected device for reducing motor-to-ground voltage. This device comprises an even number of motor grid-connected interface devices connected in series between the positive and negative buses of a bipolar DC collector circuit. The intermediate nodes of these even number of motor grid-connected interface devices are grounded to reduce the motor-to-ground voltage of the motor grid-connected interface devices. The ground voltage of both the doubly-fed induction generator (DFIG) and the permanent magnet synchronous motor (PMSM) is half the DC bus voltage. This reduces the ground voltage of the DFIG and PMSM, lowers insulation requirements, extends insulation life, and prevents excessively high ground voltage from interfering with normal equipment operation, leading to signal distortion in the control system and malfunctions in electronic equipment. This improves the stability and reliability of the entire electrical system.

[0040] 2. The motor grid-connection interface device of the present invention, which is a type of grid-connected device for reducing motor-to-ground voltage, includes a doubly-fed motor, a first DC / AC converter, a permanent magnet motor, and a second DC / AC converter. The positive terminal of the motor grid-connection interface device is connected to the positive DC side of the first DC / AC converter and the second DC / AC converter, respectively. The negative terminal of the motor grid-connection interface device is connected to the negative DC side of the first DC / AC converter and the second DC / AC converter, respectively. The AC side of the first DC / AC converter is connected to the doubly-fed motor, and the AC side of the second DC / AC converter is connected to the permanent magnet motor. The output shaft of the permanent magnet motor is connected to the output shaft of the doubly-fed motor through a coaxial cable. This device can significantly increase the rotational inertia of the system and, as a reactive power compensation device, can provide voltage support for the new energy system, thus providing good reactive power support for the power grid. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the structure of the grid-connected device with adjustable inertia in an embodiment of the present invention.

[0042] Figure 2 This is a schematic diagram of the control principle of the doubly fed motor in an embodiment of the present invention.

[0043] Figure 3 The following is a Bode plot of the transfer function of the cascaded noise suppression extended state observer in an embodiment of the present invention, where (a) is the Bode plot of the transfer function of the perturbation estimation error; and (b) is the Bode plot of the transfer function of the perturbation estimation.

[0044] Figure 4 This is a schematic diagram of the control principle of the permanent magnet motor in an embodiment of the present invention.

[0045] Figure 5 This is a diagram showing the adaptive identification result of the input gain of the permanent magnet motor in an embodiment of the present invention.

[0046] Figure 6 dq-axis current of a permanent magnet motor under conventional model-free predictive control , As a result, and the phase a current result.

[0047] Figure 7 The dq-axis current of the permanent magnet motor in the adaptive model-free predictive control of the cascaded noise suppression extended state observer in this embodiment of the invention. , As a result, and the phase a current result. Detailed Implementation

[0048] To enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be further described in detail below with reference to the accompanying drawings in the embodiments of the present invention.

[0049] like Figure 1 As shown, this embodiment of the adjustable inertia grid-connected device for reducing motor-to-ground voltage includes an even number of motor grid-connected interface devices connected in series between the positive and negative busbars of a bipolar DC collector circuit. The intermediate node of the even number of motor grid-connected interface devices is grounded to reduce the motor-to-ground voltage of the motor grid-connected interface devices. The motor grid-connected interface device includes a doubly fed motor (which can be brushless or brushed), a first DC / AC converter, a permanent magnet motor, and a second DC / AC converter. The positive terminal of the motor grid-connected interface device is connected to the positive DC side of the first DC / AC converter and the second DC / AC converter, respectively. The negative terminal of the motor grid-connected interface device is connected to the negative DC side of the first DC / AC converter and the second DC / AC converter, respectively. The AC side of the first DC / AC converter is connected to the doubly fed motor, and the AC side of the second DC / AC converter is connected to the permanent magnet motor. The output shaft of the permanent magnet motor is connected to the output shaft of the doubly fed motor through a coaxial cable.

[0050] In this embodiment, an even number of motor grid-connected interface devices refers to two motor grid-connected interface devices, such that the motor-to-ground voltage of the doubly-fed motor and permanent magnet motor in the motor grid-connected interface device is half the voltage between the positive and negative busbars. For example, in a specific implementation, the voltage between the positive and negative busbars of the bipolar DC collector circuit in this embodiment is 20kV, and the motor-to-ground voltage of the doubly-fed motor and permanent magnet motor in the motor grid-connected interface device is 10kV, effectively reducing the motor's voltage to ground.

[0051] To maintain voltage stability while achieving rapid frequency response of the system, this embodiment also provides a control method for a grid-connected device with adjustable inertia that reduces the motor-to-ground voltage. This embodiment further provides separate control schemes for doubly-fed induction generators (DFIGs) and permanent magnet synchronous motors (PMSMs) to maintain voltage stability while regulating the inertia of the grid-connected device. The outer loop of the DFIG uses a PI controller to control the speed of the grid-connected device, enabling it to respond quickly to frequency changes. The outer loop of the PMSM uses a PI controller to control the DC bus voltage from the ground point to the negative terminal interface of the converter. Thus, the DC bus voltage at the DFIG port is simultaneously and stably controlled. The inner loop control of both the DFIG and PMSMs employs a model-free predictive control strategy based on a cascaded noise extended state observer to significantly improve the noise suppression capability and parameter robustness of the DFIG and PMSM control systems.

[0052] like Figure 2As shown, the control method for the adjustable inertia grid-connected device that can reduce the voltage of the motor to ground in this embodiment includes a dual-loop control method consisting of an outer loop control and an inner loop control to control the first DC / AC converter of the doubly-fed motor to control the grid-connected output power of the doubly-fed motor. The outer loop control involves adjusting the grid-side frequency... and power frequency The deviation multiplied by the proportionality coefficient To obtain speed deviation , will speed deviation and initial rotational speed The reference speed is obtained by subtraction. , reference speed and current speed The deviation is used for PI control to obtain the q-axis reference current of the doubly-fed motor control winding. and the d-axis reference current with a value of 0. Combined with the obtained doubly-fed motor control winding dq-axis reference current The inner loop control uses the dq-axis reference current of the doubly-fed motor control winding. , control the dq axis current of the winding dq axis current of power winding This is used as the input to the preset first closed-loop controller to obtain the dq-axis reference voltage of the doubly-fed motor control winding. A first DC / AC converter used to control a doubly-fed motor. See also Figure 2 It can be seen that in order to control the speed of the doubly fed motor, a speed loop is designed in the outer loop and a grid frequency feedback loop is added to improve the system response speed, while the current inner loop adopts predictive control.

[0053] It should be noted that the preset first closed-loop controller can adopt the required closed-loop control algorithm as needed. For example, as an optional implementation, this embodiment also provides control schemes for doubly-fed motors and permanent magnet synchronous motors respectively, in which the inner loop adopts a model-free control strategy and they all have the same mathematical model:

[0054] ;

[0055] In the formula, y and u These represent the system's output and input signals, respectively. Indicates input gain. F This represents the lumped disturbance of the system. The key is to estimate the lumped disturbance. for y The first derivative. Specifically, in this embodiment, the preset first closed-loop controller is a model-free predictive current controller based on an extended state observer, and the discrete form of the model-free predictive current controller is expressed as:

[0056] ;

[0057] ;

[0058] in, and The reference voltages of the doubly fed motor control windings along the dq axis at time k are respectively. The dq axis components in and These represent the dq-axis input gains of the doubly-fed motor control windings. and Reference current for the dq axis of the doubly fed motor control winding The dq axis components in and The control winding dq-axis currents at time k are respectively The dq axis components in To control the cycle, and Let be the dq-axis disturbance components of the doubly-fed motor control winding at time k, as observed by the extended state observer. Their continuous form can be expressed as:

[0059] ;

[0060] in, The resistance of the stator winding; and These are the inductances of the control winding and the stator winding, respectively; For magnetizing inductance; and These represent the dq-axis currents of the control windings, The electric angular velocity of the power winding, The rotor's electric angular velocity, and These are the dq-axis currents of the stator windings, respectively. and Let p and p represent the dq-axis voltages of the stator windings, respectively. The mathematical model of the doubly-fed induction generator in the dq coordinate system is as follows:

[0061] ,

[0062] ,

[0063] ,

[0064] ,

[0065] ,

[0066] ,

[0067] ,

[0068] ,

[0069] ,

[0070] In the above formulas, and These represent the dq-axis voltages of the control winding (indicated by the subscript c). and These are the dq-axis voltages of the stator windings (indicated by the subscript p); and These are the dq-axis currents of the control winding, respectively. and These are the dq-axis currents of the stator windings, respectively. and These are the dq-axis flux linkages of the control winding, respectively. and These are the dq axis flux linkages of the stator windings, respectively. and These are the resistances of the control winding and the stator winding, respectively; and These are the inductances of the control winding and the stator winding, respectively; For magnetizing inductance; The electric angular velocity of the power winding is equal to the synchronous electric angular velocity on the grid side; The rotor's electric angular velocity, It is electromagnetic torque.

[0071] Substituting the flux linkage equation into the voltage equation, and rearranging the current components of the stator and rotor of the doubly-fed motor, we get:

[0072] ;

[0073] ;

[0074] Therefore, the hyperlocal model of the control winding can be described as:

[0075] ;

[0076] In the above formula, and These are the input dq axis coefficients. and The dq axis perturbation can be described as follows:

[0077] .

[0078] In reality, and This can be obtained from a disturbance observer. As an optional implementation, to further suppress parameter disturbances and noise disturbances, a model-free predictive current control based on a cascaded noise-suppressed extended state observer is designed. In this embodiment, the extended state observer is a cascaded noise-suppressed extended state observer, which includes a cascaded first-stage extended state observer and a second-stage extended state observer:

[0079] ;

[0080] ;

[0081] in, This represents a first-order extended state observer. The auxiliary integral variable error of the doubly fed motor control winding for the first-stage extended state observer. Auxiliary integral variables of the doubly-fed motor control windings estimated by the first-stage extended state observer. For the auxiliary integral variable of the control winding of the doubly-fed motor, At the initial moment, For the current moment, For the control winding current of a doubly fed motor, for The first-order differential, The doubly fed motor control winding current is used for the first-stage extended state observer. , and For the parameters of the extended state observer, for The first-order differential, The doubly fed motor control winding current estimated by the first-stage extended state observer. Lumped disturbances in the hyperlocal equations of the doubly-fed motor control windings estimated by a first-order extended state observer. To control the input gain of the winding hyperlocal model, To control the winding voltage, for The first differential; It is a second-level extended state observer. The auxiliary integral variable error of the doubly-fed motor control winding for the second-level extended state observer. Auxiliary integral variables of the doubly-fed motor control winding estimated by the second-level extended state observer. for The first-order differential, The doubly-fed motor control winding current estimated by the second-level extended state observer. for The first-order differential, Lumped disturbances in the hyperlocal equations of the doubly-fed motor control windings estimated by a second-order extended state observer. for The first derivative; and the functional expression of the d-axis component or q-axis component in the doubly fed motor control winding dq-axis disturbance term obtained by the cascaded noise suppression expansion state observer is:

[0082] ,

[0083] in, This refers to the d-axis component or q-axis component in the dq-axis disturbance term of the doubly fed motor control winding.

[0084] In this embodiment, the perturbation estimation error and the transfer function of the perturbation estimation of the cascaded noise suppression extended state observer are expressed as follows:

[0085] ;

[0086] ;

[0087] in, Let be the transfer function of the perturbation estimation error. For complex variables, The cutoff frequency, The transfer function is used for perturbation estimation.

[0088] To analyze the advanced perturbation estimation and noise immunity capabilities of the Cascaded Noise Suppression Extended State Observer (CNS-ESO) in this embodiment, this embodiment compares and analyzes the perturbation estimation error and transfer function of the Cascaded Noise Suppression Extended State Observer (CNS-ESO) with those of other existing observers (including ESO, CESO, and NS-ESO). The perturbation estimation error and transfer function of other existing observers are shown in Table 1.

[0089] Table 1: Transfer Functions of Existing Observers

[0090]

[0091] in, .

[0092] To ensure fairness, this embodiment sets the bandwidth of all four perturbation observers—ESO, CESO, NS-ESO, and CNS-ESO—to 500 rad / s. The final results are as follows. Figure 3 As shown. According to Figure 3It can be seen that in the low-frequency and mid-frequency regions, the amplitudes of the perturbation estimation error transfer functions of CESO and the Cascaded Noise Suppression Extended State Observer (CNS-ESO) in this embodiment are significantly lower than those of ESO and NS-ESO. This indicates that introducing a cascaded structure can significantly improve the perturbation estimation accuracy of the observer. However, in the high-frequency band, CESO has the highest perturbation estimation transfer function amplitude, and the amplitude of the perturbation estimation transfer function of the Cascaded Noise Suppression Extended State Observer (CNS-ESO) in this embodiment is also slightly higher than that of NS-ESO. This indicates that introducing a cascaded structure increases noise sensitivity. However, because NS-ESO has the best noise suppression capability, even with the introduction of a cascaded structure, the Cascaded Noise Suppression Extended State Observer (CNS-ESO) in this embodiment still shows a significant advantage in noise suppression capability compared to ESO and CESO. CESO claims a significant advantage in noise suppression capability, based on the principle of reducing bandwidth settings; it only requires designing a smaller bandwidth to achieve better estimation accuracy than ESO. In contrast, the cascaded noise suppression extended state observer (CNS-ESO) in this embodiment, being composed of two cascaded NS-ESOs, possesses both the excellent noise immunity and superior disturbance estimation capabilities of NS-ESOs.

[0093] like Figure 4 As shown, this embodiment also includes a dual-loop control method consisting of outer-loop control and inner-loop control to control the second DC / AC converter of the permanent magnet motor to control the mechanical axis output power of the permanent magnet motor. The outer-loop control involves using PI control to obtain the q-axis reference current of the permanent magnet motor by comparing the deviation between the DC-side voltage of the second DC / AC converter and the reference voltage, and then comparing this with the d-axis reference current of the permanent magnet motor, which is set to 0. Combined, the reference current of the dq axis of the permanent magnet motor is obtained. The inner loop control uses the dq-axis reference current of the permanent magnet motor as the reference. dq axis current of permanent magnet motor This serves as the input to the preset second closed-loop controller to obtain the reference voltage for the dq axis of the permanent magnet motor. A second DC / AC converter for controlling a permanent magnet motor.

[0094] Similarly, permanent magnet motors also use CNS-ESO to estimate lumped disturbances. However, their stability is easily affected by inductor mismatch, so the gradient descent method is used to identify the inductor parameters. Considering the measurement noise in the current mathematical model, the electric angular velocity term is extracted, and the hyperlocal current model of the permanent magnet motor is as follows:

[0095] ;

[0096] in, For permanent magnet synchronous motors, the current includes medium-strate noise. For aggregated disturbance The derivative of is usually a bounded real number. To measure noise, For the measurement noise of the dq axis, For the stator current of a permanent magnet synchronous motor, For the lumped disturbance of the permanent magnet motor, For input gain, This refers to the stator voltage of a permanent magnet synchronous motor. This refers to the angular velocity of the permanent magnet synchronous motor. For the disturbance of the dq axis of the permanent magnet motor, we have:

[0097] ;

[0098] in, This refers to the flux linkage size of the permanent magnet motor.

[0099] In this embodiment, the preset second closed-loop controller is an adaptive model-free predictive current controller based on an extended state observer. The discrete form function expression of the adaptive model-free predictive current controller is as follows:

[0100] ,

[0101] ,

[0102] In the formula, and The reference voltages of the permanent magnet motor dq axis at time k are respectively. The dq axis components in and This is the input gain for the dq axis of the permanent magnet motor. and Reference current for the dq axis of the permanent magnet motor The dq axis components in and The dq-axis currents of the permanent magnet motor at time k are respectively The dq axis components in To control the cycle, and These are the dq-axis disturbance components of the permanent magnet motor at time k, as observed by the extended state observer.

[0103] Similar to the doubly-fed induction generator (DFIG) motor control, the extended state observer in the adaptive model-free predictive current controller based on the extended state observer used in this embodiment is a cascaded noise-suppressed extended state observer. This cascaded noise-suppressed extended state observer includes a cascaded first-level extended state observer and a second-level extended state observer, wherein the function expressions for the first-level and second-level extended state observers are:

[0104] ;

[0105] ;

[0106] in, This represents a first-order extended state observer. For the permanent magnet synchronous motor auxiliary integral variable error of the first-stage extended state observer, Auxiliary integral variables of the permanent magnet synchronous motor estimated by a first-stage extended state observer. For the auxiliary integral variable of the permanent magnet synchronous motor, At the initial moment, For the current moment, This refers to the stator current of a permanent magnet synchronous motor. for The first-order differential, Stator current of permanent magnet synchronous motor estimated by a first-stage extended state observer. , and For the parameters of the extended state observer, for The first-order differential, for The estimated value, Lumped disturbances in the hyperlocal equations of a permanent magnet synchronous motor estimated by a first-order extended state observer. This represents the input gain in the hyperlocal equations of a permanent magnet synchronous motor. This refers to the stator voltage of the permanent magnet synchronous motor. The imaginary unit, This refers to the angular velocity of the permanent magnet synchronous motor. for The first differential; It is a second-level extended state observer. For the permanent magnet synchronous motor auxiliary integral variable error of the second-level extended state observer, Auxiliary integral variables of permanent magnet synchronous motor estimated by a second-level extended state observer. for The first-order differential, The stator current of the permanent magnet synchronous motor estimated by the second-level extended state observer. for The first-order differential, Lumped disturbances in the hyperlocal equations of a permanent magnet synchronous motor estimated by a second-order extended state observer. for The first derivative; and the functional expression of the d-axis component or q-axis component in the permanent magnet motor dq-axis disturbance term at time k obtained by the cascaded noise suppression extended state observer is:

[0107] ;

[0108] in, To obtain the d-axis component or q-axis component of the permanent magnet motor dq-axis disturbance term at time k using a cascaded noise suppression extended state observer, we have:

[0109] ;

[0110] in, for The first-order differential, This is an estimate of the input gain. To vary the step size, Let be the objective function. For gradient operators, and To adjust the parameters of the adaptive iteration step size, and satisfy:

[0111] , ;

[0112] in, For time. In model-free control of permanent magnet motors, the input gain of the hyperlocal model is designed as the inductance nameplate value. reciprocal When the model parameters match the motor parameters (i.e., The lumped disturbance contains only the DC component, and according to Under control, the lumped disturbance will satisfy the following equation:

[0113] ;

[0114] However, when the inductor parameters are mismatched, a voltage term is introduced, which contains high-frequency harmonic disturbances. Due to the low-pass filter structure of the ESO, it attenuates high-frequency harmonic disturbances; therefore, the high-frequency harmonic disturbances cannot be accurately estimated, and the estimation error will degrade the steady-state performance of the system. Therefore, it is essential to accurately estimate the input gain. The finite-time gradient method (FGM) is used to update the input gain coefficient in real time. The control method, the expression for the lumped disturbance on the d-axis is:

[0115] ;

[0116] It is obvious that if the lumped perturbation of the d-axis is... If it converges to 0, then the input gain... It will converge to Therefore, the objective function is designed as follows:

[0117] ;

[0118] Further derivation of the gradient of the objective function is as follows:

[0119] ;

[0120] Therefore, the input gain can be obtained as follows:

[0121] ,

[0122] in, for The first-order differential, This is an estimate of the input gain. To vary the step size, Let be the objective function. For gradient operators, and To adjust the parameters of the adaptive iteration step size, and satisfy:

[0123] , ,

[0124] in, For time.

[0125] Figure 5 This is a diagram showing the adaptive identification result of the input gain of the permanent magnet motor obtained using the control method of the adjustable inertia grid-connected device that reduces the motor-to-ground voltage in this embodiment. Figure 5 The results show that the control method of the adjustable inertia grid-connected device that reduces the voltage of the motor to ground in this embodiment can accurately estimate the input gain. . Figure 6 This describes the dq-axis current of a conventional model-free predictive controller under input gain mismatch and input noise interference. , As a result, and the phase a current Results: The peak-to-peak ripple of the q-axis current was 0.26 A, and the peak-to-peak ripple of the d-axis current was 0.38 A, resulting in a significant total harmonic distortion (THD) of 5.99% in the a-phase current. Figure 7This paper describes the dq-axis current of a cascaded noise suppression extended state observer and an improved model-free predictive controller for input gain identification in a control method for a grid-connected device with adjustable inertia that reduces motor-to-ground voltage under interference from input gain mismatch and input noise, based on this embodiment. , As a result, and the phase a current Results: The peak-to-peak ripple of the q-axis current was 0.23A, and the peak-to-peak ripple of the d-axis current was 0.24A, resulting in a significant total harmonic distortion (THD) of 4.38% in the a-phase current. The results indicate that the control method for the regulating inertia-type grid-connected device that reduces motor-to-ground voltage in this embodiment effectively suppresses high-frequency harmonic disturbances through a cascaded noise suppression extended state observer and input gain identification.

[0126] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A control method for a grid-connected device with adjustable inertia that can reduce motor-to-ground voltage, the grid-connected device comprising an even number of motor grid-connection interface devices connected in series between the positive and negative buses of a bipolar DC-DC collector circuit, wherein the intermediate node of the even number of motor grid-connection interface devices is grounded to reduce the motor-to-ground voltage of the motor grid-connection interface devices, the motor grid-connection interface device comprising a doubly-fed induction generator (DFIG), a first DC / AC converter, a permanent magnet motor, and a second DC / AC converter, wherein the positive terminal of the motor grid-connection interface device is connected to the positive DC side of the first DC / AC converter and the second DC / AC converter respectively, and the negative terminal of the motor grid-connection interface device is connected to the positive DC side of the first DC / AC converter respectively. The DC side of the first DC / AC converter is connected to the negative terminal of the second DC / AC converter. The AC side of the first DC / AC converter is connected to the doubly-fed motor, and the AC side of the second DC / AC converter is connected to the permanent magnet motor. The output shaft of the permanent magnet motor is connected to the output shaft of the doubly-fed motor via a coaxial cable. The even number of motor grid-connected interface devices refers to two motor grid-connected interface devices, such that the motor-to-ground voltage of the doubly-fed motor and the permanent magnet motor in the motor grid-connected interface device is half the voltage between the positive and negative busbars. The control method includes a dual-loop control method consisting of an outer loop control and an inner loop control to control the first DC / AC converter of the doubly-fed motor to control the grid-connected output power of the doubly-fed motor. The outer loop control is to set the grid-side frequency... and power frequency The deviation multiplied by the proportionality coefficient To obtain speed deviation , will speed deviation and initial rotational speed The reference speed is obtained by subtraction. , reference speed and current speed The deviation is used for PI control to obtain the q-axis reference current of the doubly-fed motor control winding. and the d-axis reference current with a value of 0. Combined with the obtained doubly-fed motor control winding dq-axis reference current The inner loop control uses the dq-axis reference current of the doubly-fed motor control winding. , control the dq axis current of the winding dq axis current of power winding This is used as the input to the preset first closed-loop controller to obtain the dq-axis reference voltage of the doubly-fed motor control winding. A first DC / AC converter for controlling a doubly-fed motor.

2. The control method for the adjustable inertia grid-connected device that can reduce the voltage to ground of the motor according to claim 1, characterized in that, The voltage between the positive and negative buses of the bipolar DC collector circuit is 20kV, and the motor-to-ground voltage of the doubly fed motor and permanent magnet motor in the motor grid connection interface device is 10kV.

3. The control method for the adjustable inertia grid-connected device that can reduce the voltage to ground of the motor according to claim 1, characterized in that, The preset first closed-loop controller is a model-free predictive current controller based on an extended state observer. The discrete form of the model-free predictive current controller is expressed as follows: ； ； in, and The reference voltages of the doubly fed motor control windings along the dq axis at time k are respectively. The dq axis components in and These represent the dq-axis input gains of the doubly-fed motor control windings, respectively. and Reference current for the dq axis of the doubly fed motor control winding The dq axis components in and The control winding dq-axis currents at time k are respectively The dq axis components in To control the cycle, and These are the dq-axis disturbance components of the doubly fed motor control winding at time k, as observed by the extended state observer.

4. The control method for the adjustable inertia grid-connected device that can reduce the voltage to ground of the motor according to claim 3, characterized in that, The extended state observer is a cascaded noise-suppressed extended state observer, which includes a cascaded first-level extended state observer and a second-level extended state observer: ； ； in, This represents a first-order extended state observer. The auxiliary integral variable error of the doubly fed motor control winding for the first-stage extended state observer. Auxiliary integral variables of the doubly-fed motor control windings estimated by the first-stage extended state observer. For the auxiliary integral variable of the control winding of the doubly-fed motor, At the initial moment, For the current moment, For the control winding current of a doubly fed motor, for The first-order differential, The doubly fed motor control winding current is used for the first-stage extended state observer. , and For the parameters of the extended state observer, for The first-order differential, The doubly fed motor control winding current estimated by the first-stage extended state observer. Lumped disturbances in the hyperlocal equations of the doubly-fed motor control windings estimated by a first-order extended state observer. To control the input gain of the winding hyperlocal model, To control the winding voltage, for The first derivative; It is a second-level extended state observer. The auxiliary integral variable error of the doubly-fed motor control winding for the second-level extended state observer. Auxiliary integral variables of the doubly-fed motor control winding estimated by the second-level extended state observer. for The first-order differential, The doubly-fed motor control winding current estimated by the second-level extended state observer. for The first-order differential, Lumped disturbances in the hyperlocal equations of the doubly-fed motor control windings estimated by a second-order extended state observer. for The first derivative; and the functional expression of the d-axis component or q-axis component in the doubly fed motor control winding dq-axis disturbance term obtained by the cascaded noise suppression expansion state observer is: ， in, This refers to the d-axis component or q-axis component in the dq-axis disturbance term of the doubly fed motor control winding.

5. The control method for the adjustable inertia grid-connected device that can reduce motor-to-ground voltage according to claim 4, characterized in that, The perturbation estimation error and the perturbation estimation transfer function of the cascaded noise suppression extended state observer are expressed as follows: ； ； in, Let be the transfer function of the perturbation estimation error. For complex variables, The cutoff frequency, The transfer function is used for perturbation estimation.

6. The control method for the adjustable inertia grid-connected device that can reduce motor-to-ground voltage according to claim 3, characterized in that, This includes a dual-loop control method consisting of an outer loop control and an inner loop control to control the second DC / AC converter of the permanent magnet motor, thereby controlling the mechanical axis output power of the permanent magnet motor. The outer loop control involves using PI control to obtain the q-axis reference current of the permanent magnet motor by measuring the deviation between the DC-side voltage of the second DC / AC converter and a reference voltage, and comparing this with the d-axis reference current of the permanent magnet motor, which is set to 0. Combined, the reference current of the dq axis of the permanent magnet motor is obtained. The inner loop control uses the dq-axis reference current of the permanent magnet motor as the reference. dq axis current of permanent magnet motor This serves as the input to the preset second closed-loop controller to obtain the reference voltage for the dq axis of the permanent magnet motor. A second DC / AC converter for controlling a permanent magnet motor.

7. The control method for the adjustable inertia grid-connected device that can reduce motor-to-ground voltage according to claim 6, characterized in that, The preset second closed-loop controller is an adaptive model-free predictive current controller based on an extended state observer. The discrete form of the adaptive model-free predictive current controller is expressed as follows: ； ； In the formula, and The reference voltages of the permanent magnet motor dq axis at time k are respectively. The dq axis components in and This is the input gain for the dq axis of the permanent magnet motor. and Reference current for the dq axis of the permanent magnet motor The dq axis components in and The dq-axis currents of the permanent magnet motor at time k are respectively The dq axis components in To control the cycle, and These are the dq-axis disturbance components of the permanent magnet motor at time k, as observed by the extended state observer.

8. The control method for the adjustable inertia grid-connected device that can reduce the voltage to ground of the motor according to claim 3, characterized in that, The extended state observer in the adaptive model-free predictive current controller based on the extended state observer is a cascaded noise-suppressed extended state observer, which includes a cascaded first-level extended state observer and a second-level extended state observer, wherein the functional expressions of the first-level extended state observer and the second-level extended state observer are: ； ； in, This represents a first-order extended state observer. For the permanent magnet synchronous motor auxiliary integral variable error of the first-stage extended state observer, Auxiliary integral variables of the permanent magnet synchronous motor estimated by a first-stage extended state observer. For the auxiliary integral variable of the permanent magnet synchronous motor, At the initial moment, For the current moment, This refers to the stator current of a permanent magnet synchronous motor. for The first-order differential, Stator current of permanent magnet synchronous motor estimated by a first-stage extended state observer. , and For the parameters of the extended state observer, for The first-order differential, for The estimated value, Lumped disturbances in the hyperlocal equations of a permanent magnet synchronous motor estimated by a first-order extended state observer. This represents the input gain in the hyperlocal equations of a permanent magnet synchronous motor. This refers to the stator voltage of the permanent magnet synchronous motor. The imaginary unit, This refers to the angular velocity of the permanent magnet synchronous motor. for The first derivative; It is a second-level extended state observer. For the permanent magnet synchronous motor auxiliary integral variable error of the second-level extended state observer, Auxiliary integral variables of permanent magnet synchronous motor estimated by a second-level extended state observer. for The first-order differential, The stator current of the permanent magnet synchronous motor estimated by the second-level extended state observer. for The first-order differential, Lumped disturbances in the hyperlocal equations of a permanent magnet synchronous motor estimated by a second-order extended state observer. for The first derivative; and the functional expression of the d-axis component or q-axis component in the permanent magnet motor dq-axis disturbance term at time k obtained by the cascaded noise suppression extended state observer is: ； in, To obtain the d-axis component or q-axis component of the permanent magnet motor dq-axis disturbance term at time k using a cascaded noise suppression extended state observer, we have: ； in, for The first-order differential, This is an estimate of the input gain. To vary the step size, Let be the objective function. For gradient operators, and To adjust the parameters of the adaptive iteration step size, and satisfy: ， ； in, For time.

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