A virtual synchronous generator inertia control system for direct-drive wind turbines

Abstract

The present invention discloses a quasi-virtual synchronous generator inertia control system for a direct-drive wind turbine generator set, comprising: a DC microgrid subsystem for simulating the working environment of the direct-drive wind turbine generator set in the DC microgrid; a data acquisition subsystem for acquiring system parameters of the DC microgrid system; an inertia control subsystem for realizing inertial support for the DC voltage by constructing a virtual inertia control model; an inertia support capability evaluation subsystem for evaluating the inertia support capability of the direct-drive wind turbine generator set under different operating conditions, and obtaining a voltage drop inertia support coefficient and a voltage rise inertia support coefficient; and an adaptive virtual inertia coefficient control subsystem for generating an adaptive virtual inertia coefficient of the direct-drive wind turbine generator set by obtaining a virtual inertia coefficient reference value. The present invention uses adaptive virtual inertia coefficient control to enable wind turbine generator sets under different operating conditions to provide appropriate inertia support for the system, thereby enhancing system stability.

Description

Technical Field

[0001] The present invention relates to the technical field of power supply control, and in particular to a quasi-virtual synchronous generator inertia control system for a direct-drive wind turbine generator set. Background Art

[0002] As an effective approach to expanding distributed power generation technology, DC microgrids offer significant advantages in improving energy utilization and providing flexible control, attracting extensive research. However, due to the isolation provided by power electronic converters, DC microgrids exhibit a "low inertia" characteristic, making the grid extremely sensitive to frequent load switching and sudden changes in renewable energy output power, severely impacting system stability.

[0003] Wind turbines, connected to a DC microgrid via a converter and operating in Maximum Power Point Tracking (MPPT) mode, cannot provide inertial support for the system. Wind turbine speeds vary widely, and their rotors store a significant amount of kinetic energy. By changing the control strategy of the wind turbine-side converter during dynamic operation, the generator rotor releases or stores kinetic energy, providing inertial support for the DC voltage and improving its dynamic stability.

[0004] Virtual synchronous generator (VSG) technology involves introducing the electromechanical transient equations of synchronous machines into converters to simulate their inertia and damping characteristics. Its application in AC microgrids is relatively mature. Existing technologies for DC microgrids include virtual inertia control strategies based on analogous virtual synchronous generators (AVSGs). For example, a virtual inertia control strategy for bidirectional grid-connected converters in DC microgrids is described in the Proceedings of the Chinese Society for Electrical Engineering. A DC-DC converter control strategy based on virtual synchronous generators is described in Automation of Power Systems. However, research on applying this strategy to wind turbine-side converters in DC microgrids is limited, and current research lacks an assessment of the inertial support capacity of wind turbines under different operating conditions. Other control strategies also present various problems. For example, the frequency regulation characteristics analysis of variable-speed wind turbines and the wind farm timing coordinated control strategy described in Automation of Power Systems prioritize wind turbines according to wind speed to quantify their frequency regulation capabilities, but this control strategy is complex. As well as the wind farm virtual inertia multi-machine collaborative control strategy that considers frequency regulation capability as recorded in power grid technology, although it avoids complex timing arrangements, it does not consider the inertial support capability at all wind speeds.

[0005] Therefore, in order to solve the "low inertia" problem of DC microgrids, there is an urgent need for a virtual synchronous generator inertia control system for direct-drive wind turbines. It can evaluate the inertial support capability of wind turbines under different operating conditions, which has certain practical value. Summary of the Invention

[0006] In order to solve the above technical problems, the purpose of the present invention is to provide a virtual synchronous generator inertia control system for a direct-drive wind turbine. By changing the control strategy of the wind turbine-side converter, the wind turbine can respond to system changes and provide inertial support for the DC voltage.

[0007] In order to achieve the above technical objectives, the present invention provides a quasi-virtual synchronous generator inertia control system for a direct-drive wind turbine generator system, comprising:

[0008] The DC microgrid subsystem is used to simulate the working environment of direct-drive wind turbines in a DC microgrid;

[0009] Data acquisition subsystem, used to collect system parameters of the DC microgrid system;

[0010] The inertial control subsystem is used to achieve inertial support for DC voltage by establishing a virtual inertial control model of a virtual synchronous generator of a direct-drive wind turbine;

[0011] The inertial support capacity evaluation subsystem is used to evaluate the inertial support capacity of direct-drive wind turbines under different operating conditions and obtain the voltage drop inertial support coefficient k1 and the voltage rise inertial support coefficient k2;

[0012] The adaptive virtual inertia coefficient control subsystem is used to generate the adaptive virtual inertia coefficient of the direct-drive wind turbine generator set by obtaining the virtual inertia coefficient reference value according to the voltage drop inertia support coefficient k1 and the voltage rise inertia support coefficient k2.

[0013] Preferably, the DC microgrid subsystem consists of a DC bus, a direct-drive wind turbine set, an AC / DC load, an AC-DC converter, a DC-DC converter, a grid-connected converter, an AC power grid, an AC measuring element, a DC measuring element, a filter and a control system, wherein the direct-drive wind turbine set and the AC / DC load are connected to the DC bus through a DC-DC converter or an AC-DC converter, and connected to the AC power grid via a grid-connected converter and a filter device, the input end of the control system is connected to the output end of the DC measuring element and the AC measuring element respectively, and the output end of the control system is connected to the input end of the wind power side converter.

[0014] Preferably, the wind power side converter consists of an IGBT three-phase bridge circuit, a DC side energy storage capacitor C, and an AC side filter inductor L.

[0015] Preferably, the data acquisition subsystem includes:

[0016] Voltage sensor, used to obtain DC bus voltage;

[0017] Current sensor, used to obtain the DC side current and DC side output current of the bridge arm of the wind power side converter;

[0018] The data acquisition module is used to obtain the current speed value of the direct-drive wind turbine and the droop coefficient of the grid-connected converter.

[0019] Preferably, the inertial control subsystem includes:

[0020] The AVSG control module is used to establish the rotor motion equation of the virtual synchronous generator and generate the DC bus voltage AVSG control equation based on the comparability between the variables of the AC grid and the DC grid. The DC bus voltage AVSG control equation is used to adjust the electromagnetic power generated by changing the output current value to achieve inertial support for the DC bus voltage.

[0021] The speed protection module is used to ensure that the current speed value is higher than the minimum speed of the direct-drive wind turbine, where the minimum speed is 0.6pu;

[0022] The speed recovery module is used to restore the fan speed to the speed value when the MPPT is running according to the set speed recovery function.

[0023] Preferably, the DC bus voltage AVSG control equation is expressed as:

[0024]

[0025] Among them, i set The output current is given, i o is the DC side output current, u * dc is the AVSG DC voltage reference value, u dcn is the DC voltage rating, C vir is the virtual inertia time constant, k D is the voltage damping coefficient.

[0026] Preferably, the expression of the speed recovery function is:

[0027]

[0028] Among them, t rec is the starting time of speed recovery control, T rec is the duration of the speed recovery process.

[0029] Preferably, the inertial support capability evaluation subsystem is used to evaluate the inertial support capability of the direct-drive wind turbine in high wind speed areas and low / medium wind speed areas, wherein the inertial support capability evaluation process is as follows:

[0030] Get the deceleration factor k of the wind turbine rotor J1 , the increased capacity factor k of the generator-side converter w1 in,

[0031]

[0032]

[0033] Where, E ωr 、E ωrmin 、E ω2 They are respectively PMSG at the current speed value ω r , minimum rotor speed value ω rmin , rotor kinetic energy at the maximum allowable speed ω2; P ωr 、P ωrmin 、P ω2 are the current speed values ​​ω r , minimum rotor speed value ω rmin , the active power corresponding to the maximum allowable speed ω2;

[0034] According to the current speed value ω of the direct-drive wind turbine r When rotating, it has rotor kinetic energy and active power, of which,

[0035]

[0036]

[0037] Where, J w is the moment of inertia of the wind turbine, ω0 is the cut-in speed, ω1 is the cut-in speed in the constant speed zone, and ω2 is the maximum allowable speed; P max is the upper limit of output active power, k opt is the maximum power tracking curve coefficient, ω1 is 1.1pu, ω2 is 1.12pu;

[0038] Conduct an assessment of inertial support capabilities.

[0039] Preferably, the inertial support capability evaluation subsystem is further configured to obtain a voltage drop inertial support coefficient k1, wherein the voltage drop inertial support coefficient k1 is expressed as:

[0040]

[0041] In the formula, the denominator represents ω r From ω rminThe maximum value of the numerator is reached when the value changes to ω2.

[0042] Preferably, the inertial support capability evaluation subsystem is further configured to obtain the acceleration factor k of the wind turbine rotor. J2 , the down-regulation capacity factor k of the generator-side converter w2 , generate the voltage rise inertia support coefficient k2, where the expression of the voltage rise inertia support coefficient k2 is:

[0043]

[0044]

[0045]

[0046] The present invention discloses the following technical effects:

[0047] 1. It solves the problem that wind turbines cannot respond to system changes, enhances the inertia of DC microgrids, and has a relatively simple control structure and is easy to implement.

[0048] 2. Through adaptive virtual inertia coefficient control, wind turbines under different operating conditions can provide appropriate inertial support for the system, enhancing system stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0050] Figure 1 is a flow chart of the present invention;

[0051] Figure 2 Schematic diagram of the DC microgrid structure in the present invention;

[0052] Figure 3 This is a block diagram of the control principle of the wind turbine side converter based on quasi-virtual generator control in the present invention;

[0053] Figure 4 It is the power tracking curve and operating area of ​​the wind turbine generator set in the present invention;

[0054] Figure 5 is a curve diagram of the inertial support coefficient of the wind turbine generator set in the present invention;

[0055] Figure 6 This is a block diagram of the adaptive virtual inertia coefficient control in the present invention;

[0056] Figure 7 1 is a speed variation curve of a wind turbine with different wind speeds using (a) a fixed Cvir value and (b) an adaptive Cvir value.

[0057] Figure 8 This is the dynamic response of the DC bus voltage of wind turbines with different wind speeds using fixed / adaptive Cvir values ​​in the present invention.

[0058] Figure 9 This is a system simulation diagram when the load fluctuates randomly in the present invention, where (a) represents the random fluctuation of the load in a short period of time, (b) represents the dynamic response of the DC bus voltage, (c) represents the speed change curve of the fan, and (d) represents the output power of the fan. DETAILED DESCRIPTION

[0059] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The components of the embodiments of the present application generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the application for protection, but merely represents the selected embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of this application.

[0060] like Figure 1-9 As shown, the present invention provides a virtual synchronous generator inertia control system for a direct-drive wind turbine generator system, comprising:

[0061] The DC microgrid subsystem is used to simulate the working environment of direct-drive wind turbines in a DC microgrid;

[0062] Data acquisition subsystem, used to collect system parameters of the DC microgrid system;

[0063] The inertial control subsystem is used to achieve inertial support for DC voltage by establishing a virtual inertial control model of a virtual synchronous generator of a direct-drive wind turbine;

[0064] The inertial support capacity evaluation subsystem is used to evaluate the inertial support capacity of direct-drive wind turbines under different operating conditions and obtain the voltage drop inertial support coefficient k1 and the voltage rise inertial support coefficient k2;

[0065] The adaptive virtual inertia coefficient control subsystem is used to generate the adaptive virtual inertia coefficient of the direct-drive wind turbine generator set by obtaining the virtual inertia coefficient reference value according to the voltage drop inertia support coefficient k1 and the voltage rise inertia support coefficient k2.

[0066] Further preferably, the DC microgrid subsystem consists of a DC bus, a direct-drive wind turbine set, an AC / DC load, an AC-DC converter, a DC-DC converter, a grid-connected converter, an AC power grid, an AC measuring element, a DC measuring element, a filter and a control system, wherein the direct-drive wind turbine set and the AC / DC load are connected to the DC bus through a DC-DC converter or an AC-DC converter, and are connected to the AC power grid via a grid-connected converter and a filter device, the input end of the control system is connected to the output end of the DC measuring element and the AC measuring element respectively, and the output end of the control system is connected to the input end of the wind power side converter.

[0067] Further preferably, the wind power side converter is composed of an IGBT three-phase bridge circuit, a DC side energy storage capacitor C, and an AC side filter inductor L.

[0068] Further preferably, the data acquisition subsystem includes:

[0069] Voltage sensor, used to obtain DC bus voltage;

[0070] Current sensor, used to obtain the DC side current and DC side output current of the bridge arm of the wind power side converter;

[0071] The data acquisition module is used to obtain the current speed value of the direct-drive wind turbine and the droop coefficient of the grid-connected converter.

[0072] Further preferably, the inertial control subsystem includes:

[0073] The AVSG control module is used to establish the rotor motion equation of the virtual synchronous generator and generate the DC bus voltage AVSG control equation based on the comparability between the variables of the AC grid and the DC grid. The DC bus voltage AVSG control equation is used to adjust the electromagnetic power generated by changing the output current value to achieve inertial support for the DC bus voltage.

[0074] The speed protection module is used to ensure that the current speed value is higher than the minimum speed of the direct-drive wind turbine, where the minimum speed is 0.6pu;

[0075] The speed recovery module is used to restore the fan speed to the speed value when the MPPT is running according to the set speed recovery function.

[0076] Further preferably, the DC bus voltage AVSG control equation is expressed as:

[0077]

[0078] Among them, i set The output current is given, i o is the DC side output current, u * dc is the AVSG DC voltage reference value, u dcn is the DC voltage rating, C vir is the virtual inertia time constant, k D is the voltage damping coefficient.

[0079] Further preferably, the expression of the speed recovery function is:

[0080]

[0081] Among them, t rec is the starting time of speed recovery control, T rec is the duration of the speed recovery process.

[0082] Further preferably, the inertial support capability evaluation subsystem is used to evaluate the inertial support capability of the direct-drive wind turbine in high wind speed areas and low / medium wind speed areas, wherein the inertial support capability evaluation process is:

[0083] Get the deceleration factor k of the wind turbine rotor J1 , the increased capacity factor k of the generator-side converter w1 in,

[0084]

[0085]

[0086] Where, E ωr 、E ωrmin 、E ω2 They are respectively PMSG at the current speed value ω r , minimum rotor speed value ω rmin , rotor kinetic energy at the maximum allowable speed ω2; P ωr 、P ωrmin 、P ω2 are the current speed values ​​ω r , minimum rotor speed value ω rmin , the active power corresponding to the maximum allowable speed ω2;

[0087] According to the current speed value ω of the direct-drive wind turbine r When rotating, it has rotor kinetic energy and active power, of which,

[0088]

[0089]

[0090] Where, J w is the moment of inertia of the wind turbine, ω0 is the cut-in speed, ω1 is the cut-in speed in the constant speed zone, and ω2 is the maximum allowable speed; P max is the upper limit of output active power, k opt is the maximum power tracking curve coefficient, ω1 is 1.1pu, ω2 is 1.12pu;

[0091] Conduct an assessment of inertial support capabilities.

[0092] Further preferably, the inertial support capability evaluation subsystem is further configured to obtain a voltage drop inertial support coefficient k1, wherein the voltage drop inertial support coefficient k1 is expressed as:

[0093]

[0094] In the formula, the denominator represents ω r From ω rmin The maximum value of the numerator is reached when the value changes to ω2.

[0095] Further preferably, the inertial support capability evaluation subsystem is further configured to obtain the acceleration factor k of the wind turbine rotor by J2 , the down-regulation capacity factor k of the generator-side converter w2 , generate the voltage rise inertia support coefficient k2, where the expression of the voltage rise inertia support coefficient k2 is:

[0096]

[0097]

[0098]

[0099] This example uses a direct-drive wind turbine. The DC voltage reference is typically set to the rated DC link voltage; in this example, it is set to 500V. The grid-connected converter uses droop control to maintain active power balance within the system and ensure DC bus voltage stability. The load is connected to the DC bus via a DC / AC converter or a DC / DC converter, providing a constant power load.

[0100] like Figure 1 As shown, a virtual synchronous generator inertia control system for a direct-drive wind turbine generator system includes the following contents:

[0101] Step 1: Establish a simplified DC microgrid model containing direct-drive wind turbines: Figure 2 As shown in the figure, it mainly consists of a direct-drive wind turbine, AC / DC loads, and corresponding power electronic converters. The wind turbine side converter includes an IGBT three-phase bridge circuit, a DC side energy storage capacitor C, and an AC side filter inductor L.dc is the DC bus voltage; i dc is the DC side current of the bridge arm, i o is the DC side output current of W-VSC.

[0102] Step 2: Signal measurement: Measure the DC bus voltage u using a voltage sensor dc , the DC side current i of the bridge arm of W-VSC is measured by the current sensor dc , DC side output current i o , collect the current speed value ω of the wind turbine r and local information such as the G-VSC droop coefficient.

[0103] Step 3: Establish a virtual inertia control model of a virtual synchronous generator of a direct-drive wind turbine, such as Figure 3 As shown in Figure 2. Equations (1)-(3) are the expressions of the AVSG control module.

[0104]

[0105]

[0106]

[0107] Where: is the inner loop reference value of the wind turbine side converter, and the current reference value given by the maximum power tracking control and the current value obtained by the virtual synchronous generator control Composition; i set The output current is given, i o is the DC side output current, u dc * is the AVSG DC voltage reference value, u dcn is the DC voltage rating, C vir is the virtual inertia time constant, k D is the voltage damping coefficient.

[0108] Formula (4) is the expression of the speed protection module PRO:

[0109]

[0110] Where: ω rmin is the minimum speed of the fan, the present invention takes ω rmin It is 0.6pu.

[0111] Formula (5) is the expression of the speed recovery module f(t):

[0112]

[0113] Where: trec is the starting time of speed recovery control, T rec The present invention assumes that the speed recovery starts 2 seconds after the AVSG control action, and the duration of the speed recovery is 8 seconds.

[0114] Step 4: Evaluate the inertial support capacity of the wind turbine under different operating conditions. The power tracking curve of the wind turbine and the operating area are as follows: Figure 4 As shown in the figure, wind turbines can generally be divided into four zones depending on wind speed: the start-up zone, the maximum power tracking zone (low wind speed zone), the constant speed zone (medium wind speed zone), and the constant power zone (high wind speed zone). In the low and medium wind speed zones, wind turbines implement maximum wind power tracking control or speed control; in the high wind speed zone, wind turbines maintain constant power by adjusting the pitch angle.

[0115] When operating in high wind speeds, the wind turbine's active power reaches its upper limit. When the DC voltage decreases, the generator's output cannot exceed the rated value, rendering it unable to provide inertial support. When the DC voltage increases, the generator's speed cannot continue to increase to store kinetic energy, and therefore, lacks inertial support capability.

[0116] When operating in the low / medium wind speed zone, the DC voltage decreases, the active power output by the generator increases, and the speed decreases to release kinetic energy; if the DC voltage increases, the active power output by the generator decreases, and the speed increases to store kinetic energy.

[0117] In order to evaluate the inertial support capacity of the PMSG wind turbine when the DC voltage decreases, the deceleration factor k of the wind turbine rotor is defined as J1 , the increased capacity factor k of the generator-side converter w1 , The voltage drop inertia support coefficient k1 of the wind turbine is:

[0118]

[0119]

[0120]

[0121] Similarly, to evaluate the inertial support capability of PMSG when DC voltage increases, the acceleration factor k of the wind turbine rotor is defined as J2 , the down-regulation capacity factor k of the generator-side converter w2 , The voltage rise inertia support coefficient k2 of the wind turbine is:

[0122]

[0123]

[0124]

[0125] like Figure 5 The figure shows the inertial support coefficient curve of the wind turbine. The black solid line and dotted line in the figure represent k1 and k2 respectively. The speed range of 0.6-1.1pu is the low wind speed range, and the speed range of 1.1-1.12pu is the medium wind speed range. The inertial support coefficient depends on the speed of the generator and the adjustable capacity of the machine-side converter. Taking the voltage rise inertial support coefficient k2 as an example, when the speed is low, the generator speed has a large room for increase. The k expressed by formula (10) J2 Large; However, the wind turbine itself has a small output and limited adjustable power, that is, k expressed by formula (11) w2 Smaller; therefore affected by k w2 Limit, k2 is small at low wind speed, increases with the increase of speed, and after reaching the maximum value, k2 is limited by k J2 Similarly, k1 is limited by the kinetic energy k that can be released by the rotor in the low wind speed area. J1 After reaching the maximum value, it is limited by the adjustable capacity k of the converter. w1 restrictions.

[0126] Step 5: Adaptive virtual inertia coefficient control. To fully utilize the inertial support capability of the wind turbine, the present invention defines the adaptive virtual inertia coefficient as:

[0127] C vir =k i C vir0 (i=1, 2) (13)

[0128] Where: C vir0 is the virtual inertia coefficient reference value; k i is the inertial support coefficient of the wind turbine when the voltage drops and rises, which is obtained from equations (8) and (12).

[0129] The AVSG control strategy of the direct-drive wind turbine proposed in this invention couples the DC voltage fluctuation with the rotor speed change, so that when the DC bus voltage fluctuates, the kinetic energy stored in the rotor provides inertial support for the wind turbine.

[0130]

[0131] Among them: H w is the inertia time constant of the wind turbine, which is defined as the ratio of the kinetic energy stored when the rotor rotates at the rated speed to the rated capacity of the generator set.

[0132] Integrating both sides of equation (14) simultaneously, we can get

[0133]

[0134] Where: r1 、ωr2 are the per-unit values ​​of the electrical angular velocity before and after the wind turbine speed changes; u dc1 、u dc2 They are the per-unit values ​​of the DC bus voltage before and after the wind turbine speed changes.

[0135] When the load of the DC microgrid system changes, the G-VSC will follow the droop coefficient k G For DC voltage regulation, u dc1 It can be expressed as:

[0136] u dc2 =u dc1 -ΔP L / (k G ·S GN ) (16)

[0137] Where ΔP L is the change in system load, S GN is the rated capacity of G-VSC.

[0138] When the load suddenly increases (decreases) and the voltage decreases (increases), the wind turbine increases (decreases) the active power and the speed decreases (increases) to provide inertial support for the system. The minimum speed can be reduced to 0.6 pu and the maximum speed can be increased to 1.12 pu. The virtual inertia coefficient C is vir The value of should satisfy:

[0139]

[0140] From formula (17), we can see that the virtual inertia coefficient C vir The value of is related to the inertia time constant Hw of the wind turbine and the load change ΔP L Related, C vir The larger the value is, the wider the range of speed change is and the greater the inertia provided is. Figure 5 It can be seen that when the rotation speed is 0.989pu, the inertial support coefficient is the largest, so we take ω r1 is 0.989pu. When the load suddenly increases or decreases by 10kW, C can be calculated by formula (17): vir0 The maximum values ​​can be about 93.15s and 41.64s respectively. The main parameters of the system used in the present invention are shown in Table 1.

[0141] Table 1

[0142] parameter Value and unit parameter Value and unit <![CDATA[W-VSC capacity S WN > 20kW DC link capacitor C 20μF <![CDATA[Rotational speed reference value ω rn > 7.85rad / s <![CDATA[Voltage outer loop k pv 、k iv > 2、100 <![CDATA[Inertia time constant H w 1.0014s <![CDATA[Inner current loop k pi 、k ii > 0.4、20 <![CDATA[Minimum rotational speed ω rmin > 0.6pu <![CDATA[Voltage damping coefficient k D > 2 <![CDATA[Cut-in speed ω1 in the constant speed region]]> 1.1pu <![CDATA[G-VSC Capacity S GN > 30kW <![CDATA[Maximum allowable rotational speed ω2]]> 1.12pu <![CDATA[Drooping coefficient k G > 1 / 0.02 <![CDATA[Maximum power tracking curve coefficient k opt > <![CDATA[0.5 / 1.1 3 pu]]> <![CDATA[Rated DC bus voltage u dcn > 500V <![CDATA[Synchronous inductance L sd , L sq > 0.0021H <![CDATA[Switching frequency f s > 7.65kHz

[0143] like Figure 6The figure shows the block diagram of the adaptive virtual inertia coefficient control. The inertial support capability assessment subsystem obtains the wind turbine rotor speed through the data acquisition module and the DC bus voltage through the voltage sensor. Since the differential link is very sensitive to high-frequency interference mixed in the input signal, in order to avoid signal drowning, a first-order inertia link is introduced to obtain the DC bus voltage change rate. The rotor speed and DC bus voltage change rate are input into the following equation: Figure 5 From the inertia support coefficient curve shown in Figure 1, the inertia support coefficient corresponding to the wind turbine under the current operating conditions can be obtained (when the DC voltage change rate is less than 0, the corresponding voltage drop inertia support coefficient k1; when the DC voltage change rate is greater than 0, the corresponding voltage rise inertia support coefficient k2); the input quantities of the adaptive virtual inertia coefficient control subsystem are the DC bus voltage, the DC bus voltage change rate, the wind turbine inertia time constant, the load change, the G-VSC droop coefficient, and the G-VSC capacity. The virtual inertia coefficient obtained by formula (17) can take the maximum value. In order to avoid a large overshoot of the DC voltage due to a large virtual inertia coefficient, the output virtual inertia coefficient baseline value is 70% of the maximum value, and then multiplied by the inertia support coefficient to obtain the adaptive virtual inertia coefficient of the direct-drive wind turbine. It is input as follows: Figure 3 In the inertial control subsystem shown, by controlling the wind turbine-side converter, changing the q-axis inner loop reference current value, and adjusting the electromagnetic power output by the wind turbine, the generator rotor speed changes to release or store kinetic energy and provide inertial support for the DC voltage.

[0144] like Figure 7 The following table shows the fixed / adaptive C vir Speed ​​variation curve of the value. Figure 8 The following table shows the fixed / adaptive C vir The dynamic response of the DC bus voltage to the specified value was investigated. Three typical wind speeds of 6 m / s, 8.1 m / s, and 9 m / s were selected, with rotor speed per unit values ​​of 0.731 pu, 0.989 pu, and 1.098 pu, respectively. The initial load was 7 kW. The large grid maintained power balance through G-VSC droop control, absorbing approximately 3 kW of power. At t = 15 seconds, the load suddenly increased by 10 kW.

[0145] At different wind speeds, C vir When the fixed value is 35s, the speed of the wind turbine changes as follows: Figure 7 (a) is shown. Figure 7 (a) It can be seen that when the wind speed is 6m / s, the generator speed is low. Without the speed protection module, the generator speed will drop to below the minimum speed of 0.6pu. With the speed protection module, when the speed drops to 0.6pu, the inertial support is exited and the speed is restored, ensuring the stable operation of the wind turbine. Figure 5It can be seen that when the speed is 0.989pu, the inertial support capacity of the unit is the strongest, but when the C is fixed vir When the wind speed is 8.1m / s and 9m / s, the inertia provided by the wind turbine is the same, and the inertial support capacity of the turbine is not fully utilized.

[0146] When the wind speed is 6m / s, 8.1m / s, and 9m / s, according to formulas (6)-(8), the corresponding voltage drop inertia support coefficient k1 can be calculated to be approximately 0.28, 1, and 0.79 respectively. C is calculated from formula (17): vir0 The maximum value is 93.15s. vir When the value is too large, the wind turbine provides a larger inertia for the system, but it will also cause obvious voltage overshoot. Therefore, the present invention takes C vir0 The maximum value is 70%, which is about 65s. The corresponding adaptive virtual inertia coefficients are about 18s, 65s, and 51s. The speed change curves of wind turbines using the above adaptive virtual inertia coefficients at different wind speeds are as follows: Figure 7 (b) shown.

[0147] By comparison Figure 7 As shown in Figures (a) and (b), the wind turbine can provide different inertial supports based on its operating state when using an adaptive virtual inertia coefficient. At a wind speed of 8.1 m / s, the turbine releases the most kinetic energy; at a wind speed of 6 m / s, the turbine releases the least kinetic energy, and the speed protection is not triggered.

[0148] Figure 8 The dynamic response of the DC bus when the wind turbine adopts fixed and adaptive virtual inertia coefficients at different wind speeds is given. Figure 8 It can be seen that when the adaptive virtual inertia coefficient is used, the DC bus voltage of the wind turbine with a wind speed of 6 m / s changes more smoothly, avoiding the voltage drop caused by the speed protection action, while the DC bus voltage of the wind turbine with wind speeds of 8.1 m / s and 9 m / s drops more slowly, indicating that the wind turbine provides greater inertial support for the system; but at a wind speed of 8.1 m / s, due to the excessive release of kinetic energy, the voltage shows obvious overregulation.

[0149] Figure 9 The system simulation diagram when the load fluctuates randomly is given. The wind speed is 9m / s and the load fluctuates randomly between 10kW and 25kW. Figure 9 It can be seen from the figure that when the load fluctuates randomly, the DC bus voltage fluctuation is smaller when AVSG control is used, which improves the voltage quality of the DC microgrid; when MPPT control is used, the speed of the wind turbine does not respond to system changes, and the output power of the wind turbine remains basically unchanged. However, when AVSG control is used, the rotor speed and the output power of the wind turbine change with the load fluctuation, providing inertia support for the system and reducing the fluctuation of the DC voltage.

[0150] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0151] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0152] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowcharts and / or block diagrams, as well as combinations of processes and / or blocks in the flowcharts and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowcharts and / or block diagrams. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

Claims

1. A virtual synchronous generator inertia control system for a direct-drive wind turbine generator system, characterized in that: include: The DC microgrid subsystem is used to simulate the working environment of direct-drive wind turbines in a DC microgrid; Data acquisition subsystem, used to collect system parameters of the DC microgrid subsystem; An inertial control subsystem, configured to achieve inertial support for DC voltage by establishing a virtual inertial control model of a virtual synchronous generator of the direct-drive wind turbine generator set; An inertial support capability evaluation subsystem is used to evaluate the inertial support capability of the direct-drive wind turbine generator set under different operating conditions, and obtain the voltage drop inertial support coefficient k1 and the voltage rise inertial support coefficient k2; An adaptive virtual inertia coefficient control subsystem is used to generate an adaptive virtual inertia coefficient of the direct-drive wind turbine generator set by obtaining a virtual inertia coefficient reference value according to a voltage drop inertia support coefficient k1 and a voltage rise inertia support coefficient k2; The DC microgrid subsystem consists of a DC bus, a direct-drive wind turbine, an AC / DC load, an AC-DC converter, a DC-DC converter, a grid-connected converter, an AC power grid, an AC measuring element, a DC measuring element, a filtering device, and a control system. The direct-drive wind turbine and the AC / DC load are connected to the DC bus through the DC-DC converter or the AC-DC converter, and are connected to the AC power grid via the grid-connected converter and the filtering device. The input end of the control system is connected to the output end of the DC measuring element and the output end of the AC measuring element, respectively, and the output end of the control system is connected to the input end of the wind power side converter. The wind power side converter consists of an IGBT three-phase bridge circuit, a DC side energy storage capacitor C, and an AC side filter inductor L; The data acquisition subsystem includes: Voltage sensor, used to obtain DC bus voltage; A current sensor is used to obtain the DC side current and DC side output current of the bridge arm of the wind power side converter; A data acquisition module, configured to obtain the current speed value of the direct-drive wind turbine generator set and the droop coefficient of the grid-connected converter; The inertial control subsystem includes: An AVSG control module is configured to generate an AVSG control equation for the DC bus voltage by establishing a rotor motion equation for the virtual synchronous generator based on the comparability of variables between the AC and DC grids. The AVSG control equation for the DC bus voltage is configured to adjust the emitted electromagnetic power by varying the output current value to achieve inertial support for the DC bus voltage. A speed protection module, configured to ensure that the current speed value is higher than the minimum speed of the direct-drive wind turbine generator set, wherein the minimum speed is 0.6 pu; The speed recovery module is used to restore the fan speed to the speed value when the MPPT is running according to the set speed recovery function; The DC bus voltage AVSG control equation is expressed as: Among them, i set The output current is given, i o is the DC side output current, u * dc is the AVSG DC voltage reference value, u dcn is the DC voltage rating, C vir is the virtual inertia time constant, k D is the voltage damping coefficient; The expression of the speed recovery function is: Among them, t rec is the starting time of speed recovery control, T rec is the duration of the speed recovery process; The inertial support capability evaluation subsystem is used to evaluate the inertial support capability of the direct-drive wind turbine in high wind speed areas and low / medium wind speed areas. The evaluation process of the inertial support capability is as follows: Get the deceleration factor k of the wind turbine rotor J1 , the increased capacity factor k of the generator-side converter w1 in, Where, E ωr 、E ωrmin 、E ω2 They are respectively PMSG at the current speed value ω r , minimum rotor speed value ω rmin , rotor kinetic energy at the maximum allowable speed ω2; P ωr 、P ωrmin 、P ω2 are the current speed values ​​ω r , minimum rotor speed value ω rmin , the active power corresponding to the maximum allowable speed ω2; According to the current speed value ω of the direct-drive wind turbine group r When rotating, it has rotor kinetic energy and active power, of which, Where, J w is the moment of inertia of the wind turbine, ω0 is the cut-in speed, ω1 is the cut-in speed in the constant speed zone, and ω2 is the maximum allowable speed; P max is the upper limit of output active power, k opt is the maximum power tracking curve coefficient, ω1 is 1.1pu, ω2 is 1.12pu; performing an assessment of the inertial support capability; The inertial support capability evaluation subsystem is further used to obtain the voltage drop inertial support coefficient k1, wherein the expression of the voltage drop inertial support coefficient k1 is: In the formula, the denominator represents ω r From ω rmin The maximum value of the numerator when it changes to ω2; The inertial support capability evaluation subsystem is also used to obtain the acceleration factor k of the wind turbine rotor J2 , the down-regulation capacity factor k of the generator-side converter w2 , generating the voltage rising inertia support coefficient k2, wherein the expression of the voltage rising inertia support coefficient k2 is: Adaptive virtual inertia coefficient control, in order to fully utilize the inertial support capacity of the wind turbine, defines the adaptive virtual inertia coefficient as: C vir =k i C vir0 (i=1,2); Where C vir0 is the virtual inertia coefficient reference value; k i It is the inertial support coefficient of the wind turbine when the voltage drops and rises.

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