Active power calculation method and system for direct-drive wind turbine based on fault ride-through process

Abstract

The present application relates to a kind of active power calculation method and system of direct-drive wind turbine based on fault ride-through process, belong to power system fault analysis technical field, solve the problem that the active power in the fault ride-through process obtained is not accurate in the prior art, direct-drive wind turbine fault current ignores the influence of wind turbine terminal voltage phase angle jump.Forget after the occurrence of symmetrical fault, obtain fault network voltage, direct-drive wind turbine output current, DC voltage, fault point voltage, voltage drop rate and voltage phase angle jump angle, and the active power and direct-drive wind turbine output current before fault;According to the information obtained, obtain the voltage jump angle in the fault ride-through process, direct-drive wind turbine output current reference value and network-side converter output voltage expected value, and then obtain the direct-drive wind turbine output current in the fault ride-through process;Based on the active power of direct-drive wind turbine in the fault ride-through process, network-side converter output voltage expected value and the DC voltage collected, obtain.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power system fault analysis, and particularly relates to a method and system for calculating active power of direct-drive wind turbine based on fault ride-through process. BACKGROUND

[0002] In recent years, the single-machine capacity of grid-connected wind turbine is increasing, and the low voltage ride-through capability of wind turbine is a necessary condition to ensure its safe operation after fault. Direct-drive wind turbine has low sensitivity to grid fluctuation because of the isolation between grid side and stator side, so it is one of the key points in the development of wind turbine technology.

[0003] However, the existing research on fault current of permanent magnet direct-drive wind turbine mostly ignores the phase angle jump of wind turbine terminal voltage, and does not consider the low penetration standard and requirement, and the analytical expression of short-circuit current is not clear, so the transient characteristics of direct-drive wind turbine obtained by solving is not accurate, which is not consistent with the engineering practice, thereby making the subsequent research and discussion based thereon have greater error. SUMMARY

[0004] In view of the above analysis, the embodiments of the present application aim to provide a method and system for calculating active power of direct-drive wind turbine based on fault ride-through process, to solve the problem that the existing fault current of direct-drive wind turbine ignores the influence of phase angle jump of wind turbine terminal voltage, and the active power obtained in the fault ride-through process is not accurate.

[0005] In one aspect, the embodiments of the present application provide a method for calculating active power of direct-drive wind turbine based on fault ride-through process, comprising the following steps:

[0006] When it is monitored that the direct-drive wind turbine occurs symmetrical fault, the grid-side voltage after fault, the output current of direct-drive wind turbine, the DC voltage, the voltage at fault point, the voltage drop rate and the voltage phase angle jump angle, and the output current and active power of direct-drive wind turbine before fault are obtained;

[0007] According to the obtained information, the voltage jump angle in the fault ride-through process, the output current reference value of direct-drive wind turbine and the expected output voltage of grid-side converter are obtained;

[0008] Based on the voltage jump angle in the fault ride-through process and the output current reference value of direct-drive wind turbine, the output current of direct-drive wind turbine in the fault ride-through process is obtained;

[0009] Based on the output current of direct-drive wind turbine in the fault ride-through process, the expected output voltage of grid-side converter and the collected DC voltage, the active power of direct-drive wind turbine in the fault ride-through process is obtained.

[0010] Further, the output current of direct-drive wind turbine in the fault ride-through process is obtained by executing the following steps:

[0011] Based on the obtained information and the phase-locked loop control, a voltage jump angle after the fault is obtained, and then a direct-drive wind turbine mathematical model is established based on engine convention;

[0012] Based on the direct-drive wind turbine mathematical model, voltage outer loop and current inner loop control equations of the grid-side converter are obtained, and then a direct-drive wind turbine output current reference value in the fault ride-through process is obtained.

[0013] Based on the voltage outer loop and current inner loop control equations of the grid-side converter and the direct-drive wind turbine output current reference value in the fault ride-through process, a direct-drive wind turbine output current in the fault ride-through process is obtained.

[0014] Further, any time before the fault occurs is taken as an initial time, the fault occurs at t1, and the direct-drive wind turbine is in the fault ride-through process at the t time, wherein t≥t1; the active power P s (t) output by the direct-drive wind turbine at the t time is represented as:

[0015]

[0016] In the formula, u g2 (t) represents the expected value of the grid-side converter output voltage in the fault ride-through process at the t time, represents the conjugate vector of the direct-drive wind turbine output current i g (t) at the t time, u dc (t) represents the real-time value of the DC voltage in the fault ride-through process at the t time, and C represents the DC bus capacitor.

[0017] Further, the expected value of the grid-side converter output voltage u g2 (t) at the t time in the fault ride-through process is represented as:

[0018]

[0019] In the formula,

[0020] e gd =ke g ,

[0021] In the formula, e g represents the instantaneous value of the grid-side voltage at the fault occurrence time, e gd represents the instantaneous value of the d-axis voltage of the grid-side voltage at the fault occurrence time, ω1 represents the synchronous angular velocity before the fault, k represents the voltage amplitude drop rate at the fault occurrence time, represents the voltage phase angle jump angle after the fault.

[0022] Further, the direct-drive wind turbine output current i g (t) at the t time in the fault ride-through process is represented as:

[0023]

[0024] wherein,

[0025]

[0026]

[0027]

[0028]

[0029]

[0030] wherein, i g_ref (t) represents the direct-drive wind turbine output current reference value in the fault ride-through process at the tth moment, L and R represent the stator inductance and resistance of the wind turbine respectively; k pu , k iu respectively represent the proportional and integral coefficients of the voltage outer loop PI controller, Δθ(t) represents the voltage jump angle at the tth moment, i_ref(0) represents the direct-drive wind turbine output current reference value in the steady state operation.

[0031] Further, the direct-drive wind turbine output current reference value i g_ref (t) in the fault ride-through process at the tth moment is represented as:

[0032] i g_ref (t) = i gd_ref2 (t) + ji gq_ref2

[0033] wherein,

[0034] i gq_ref2 = 1.5*(0.9-U T )I N ,

[0035]

[0036]

[0037]

[0038]

[0039]

[0040]

[0041] wherein, U Trepresents the voltage base value of the wind farm grid-connected point, I N represents the current base value of the wind farm; P s represents the active power output by the direct-drive wind turbine during stable operation; i gd_ref(0) represents the d-axis reference value of the output current of the direct-drive wind turbine at the time of fault occurrence, represents the reference value of the DC voltage.

[0042] Further, the voltage jump angle Δθ(t) at the tth moment is represented as:

[0043]

[0044] wherein,

[0045]

[0046]

[0047] wherein, U m represents the voltage amplitude at the fault point, k ppll , k ipll respectively represent the proportional and integral constants of the phase-locked loop PI controller, Δθ (0) represents the phase angle jump value of the terminal voltage at the time of fault occurrence.

[0048] On the other hand, the embodiment of the present application provides a system for calculating the active power of a direct-drive wind turbine based on a fault ride-through process, comprising the following steps:

[0049] a data acquisition module, configured to acquire the post-fault grid-side voltage, the output current of the direct-drive wind turbine, the DC voltage, the voltage at the fault point, the voltage drop rate, the voltage phase angle jump angle, and the pre-fault output current and active power of the direct-drive wind turbine when it is monitored that the direct-drive wind turbine has occurred a symmetrical fault;

[0050] a voltage and current obtaining module, configured to obtain the voltage jump angle during the fault ride-through process, the reference value of the output current of the direct-drive wind turbine, and the expected value of the output voltage of the grid-side converter based on the acquired information, and to obtain the output current of the direct-drive wind turbine during the fault ride-through process based on the voltage jump angle during the fault ride-through process and the reference value of the output current of the direct-drive wind turbine;

[0051] an active power calculation module, configured to obtain the active power of the direct-drive wind turbine during the fault ride-through process based on the output current of the direct-drive wind turbine during the fault ride-through process, the expected value of the output voltage of the grid-side converter, and the collected DC voltage.

[0052] Further, the voltage and current obtaining module obtains the output current of the direct-drive wind turbine during the fault ride-through process by performing the following steps:

[0053] Based on the obtained information and the phase-locked loop control, a voltage jump angle after the fault is obtained, and then a direct-drive wind turbine mathematical model is established based on engine convention;

[0054] Based on the direct-drive wind turbine mathematical model, voltage outer loop and current inner loop control equations of the grid-side converter are obtained, and then a direct-drive wind turbine output current reference value in the fault ride-through process is obtained.

[0055] Based on the voltage outer loop and current inner loop control equations of the grid-side converter and the direct-drive wind turbine output current reference value in the fault ride-through process, the direct-drive wind turbine output current in the fault ride-through process is obtained.

[0056] Further, any time before the fault occurs is taken as an initial time, the fault occurs at t1, and the direct-drive wind turbine is in the fault ride-through process at the t time, wherein t≥t1;The active power P s (t) output by the direct-drive wind turbine at the t time is represented as:

[0057]

[0058] In the formula, u g2 (t) represents the expected value of the grid-side converter output voltage in the fault ride-through process at the t time, represents the conjugate vector of the direct-drive wind turbine output current i g (t) at the t time, u dc (t) represents the real-time value of the DC voltage in the fault ride-through process at the t time, and C represents the DC bus capacitor.

[0059] Compared with the prior art, the present application can achieve the following beneficial effects:

[0060] The active power calculation method and system for the direct-drive wind turbine based on the fault ride-through process provided in the present application add a typical phase-locked vector control strategy in the analysis process, analyze the jump angle through the control link, and then deduce the direct-drive single-machine short-circuit current considering the voltage phase angle jump influence in the fault ride-through process. In combination with the internal energy flow of the direct-drive wind turbine and the energy flow and structure of the wind turbine structure, the transient active power output by the direct-drive wind turbine in the fault ride-through process is obtained, which is closer to the transient characteristics of the direct-drive wind turbine and also conforms to the engineering practice.

[0061] The above technical solutions can be combined with each other in the present application to realize more preferred combination solutions. Other features and advantages of the present application will be described in the subsequent specification, and some advantages will become apparent from the specification, or will be understood by implementing the present application. The purpose and other advantages of the present application can be realized and obtained from the contents specifically pointed out in the specification and the drawings. BRIEF DESCRIPTION OF DRAWINGS

[0062] The accompanying drawings are included to provide a further understanding of the application and are incorporated in and constitute a part of this specification, illustrate embodiments of the application and are not intended to limit the scope of the application, and together with the description serve to explain the principles of the application.

[0063] Figure 1 A flowchart of the active power calculation method of the direct-drive wind turbine based on the fault ride-through process provided for Embodiment 1 of the application;

[0064] Figure 2 A schematic diagram of the working principle of the phase-locked loop provided for Embodiment 1 of the application;

[0065] Figure 3 A diagram of the energy flow near the direct-current side of the direct-drive wind turbine provided for Embodiment 1 of the application;

[0066] Figure 4 A schematic diagram of the power grid structure of the direct-drive wind turbine provided for Embodiment 3 of the application;

[0067] Figure 5 The fault A-phase current when the terminal voltage of the direct-drive wind turbine drops to 40% provided for Embodiment 3 of the application;

[0068] Figure 6 The fault A-phase current when the terminal voltage of the direct-drive wind turbine drops to 60% provided for Embodiment 3 of the application;

[0069] Figure 7 The fault A-phase current when the terminal voltage of the direct-drive wind turbine drops to 80% provided for Embodiment 3 of the application;

[0070] Figure 8 The active power output when the terminal voltage of the direct-drive wind turbine drops to 40% provided for Embodiment 3 of the application;

[0071] Figure 9 The active power output when the terminal voltage of the direct-drive wind turbine drops to 60% provided for Embodiment 3 of the application;

[0072] Figure 10 The active power output when the terminal voltage of the direct-drive wind turbine drops to 80% provided for Embodiment 3 of the application. DETAILED DESCRIPTION

[0073] The preferred embodiments of the application will be described in detail with reference to the drawings, wherein:

[0074] Embodiment 1

[0075] In one specific embodiment of the application, an active power calculation method of a direct-drive wind turbine based on a fault ride-through process is disclosed, as shown in Figure 1 the following steps are included:

[0076] S1, when monitoring that the direct drive wind turbine occurs symmetrical fault, obtaining the post-fault grid voltage, direct drive wind turbine output current, DC voltage, fault point voltage, voltage drop rate and voltage phase angle jump angle, and, the pre-fault direct drive wind turbine output current and active power.

[0077] In implementation, the present embodiment takes any time before the fault occurrence time as the initial time, and the fault occurrence time is t1, the direct drive wind turbine is in the fault ride-through process at the t time, wherein t≥t1, the present embodiment is based on this setting to derive and calculate the active power.

[0078] S2, according to the obtained information, the voltage jump angle in the fault ride-through process, the direct drive wind turbine output current reference value and the grid-side converter output voltage expected value are obtained; based on the voltage jump angle in the fault ride-through process, the direct drive wind turbine output current reference value, the direct drive wind turbine output current in the fault ride-through process is obtained.

[0079] In implementation, in step S2, the direct drive wind turbine output current in the fault ride-through process is obtained by executing the following mode:

[0080] S21, based on the obtained information and the phase-locked loop control, the post-fault voltage jump angle is obtained, and then the direct drive wind turbine mathematical model is established based on the engine convention.

[0081] When the fault point of the direct drive wind turbine occurs symmetrical fault, let the voltage jump angle be Δθ(t), and the pre-fault phase angle be θ1, then the post-fault angle θ(t)=Δθ(t)+θ1, the working principle of the phase-locked loop is as shown in Figure 2 , and the control link is represented as:

[0082]

[0083] In the formula, Δω(t) represents the angular velocity difference generated by the voltage jump angle at the t time, u sq (t) represents the q-axis component of the wind turbine stator voltage.

[0084] By simultaneous and Taylor expansion, the second-order differential equation about the jump angle is obtained as:

[0085]

[0086] Therefore, in implementation, the voltage jump angle of the voltage jump angle Δθ(t) at the t time is represented as:

[0087]

[0088] Among them,

[0089]

[0090]

[0091] In the formula, U m represents the fault point voltage amplitude, k ppll , k ipll respectively represent the proportional and integral constants of the phase-locked loop PI controller, Δθ (0) represents the machine terminal voltage phase angle jump value at the fault occurrence time.

[0092] In this embodiment, the direct drive wind turbine is a permanent magnet direct drive wind turbine. The grid-side converter of the direct drive wind turbine is oriented to the grid voltage vector in the synchronous rotating coordinate system, and the d-axis direction is aligned with the grid voltage vector e g , so that e gd = |e g |, e gq = 0, wherein e gd , e gq respectively represent the instantaneous values of the d-axis and q-axis of the grid voltage at the fault occurrence time.

[0093] Based on the generator convention and considering the influence of the phase-locked loop, the mathematical model of the direct drive wind turbine in the fault ride-through process is obtained, which is represented as:

[0094]

[0095] wherein,

[0096] In the formula, u gd (t), u gq (t) respectively represent the d-axis and q-axis expected values of the grid-side converter output voltage in the fault ride-through process at the tth time, i gd (t), i gq (t) respectively represent the d-axis and q-axis components of the direct drive wind turbine output current in the fault ride-through process at the tth time, e g represents the instantaneous value of the grid voltage at the fault occurrence time, L and R respectively represent the stator inductance and resistance of the wind turbine, ω1 represents the synchronous angular velocity before the fault, and Δθ(t) represents the voltage jump angle at the tth time.

[0097] S22, based on the mathematical model of the direct drive wind turbine, the voltage outer loop and current inner loop control equations of the grid-side converter are obtained, and then the direct drive wind turbine output current reference value in the fault ride-through process is obtained.

[0098] In the implementation, in step S22, the direct drive wind turbine output current reference value in the fault ride-through process is obtained based on the following derivation steps:

[0099] When the power grid is in normal operation, the reactive power reference value is generally set to 0, so as to ensure that the wind turbine is operated in a unit power factor. The control system of the grid-side converter generally adopts a control mode of a voltage outer loop and a current inner loop. Based on the established mathematical model, the voltage outer loop control equation is represented as:

[0100]

[0101] In the formula, i gd_ref (t) and i gq_ref (t) respectively represent the d-axis and q-axis reference values of the output current of the direct-drive wind turbine in a fault ride-through process at the tth moment, k pu and k iu respectively represent the proportional and integral coefficients of the voltage outer loop PI controller, k pq and k iq respectively represent the proportional and integral coefficients of the power outer loop PI controller, u dc (t) represents the real-time value of the DC voltage at the tth moment, represents the reference value of the DC voltage, Q g represents the real-time value of the grid-side reactive power at the tth moment, represents the reference value of the grid-side reactive power, represents an integral operator.

[0102] Based on the established mathematical model, the control equation of the current inner loop is represented as:

[0103]

[0104] In the formula, k pgc and k igc respectively represent the proportional and integral coefficients of the current inner loop PI controller, and L g represents the grid-side line filter inductance.

[0105] The energy flow of the permanent magnet direct-drive wind power generator is shown in FIG. 1. Figure 3 Under normal working conditions, when the system is operated to a steady state, there is power conservation: the instantaneous active power output by the direct-drive wind turbine = the instantaneous active power output by the grid-side converter on the AC side, i.e., P s = P g At this time, the DC bus voltage is constant.

[0106] When the power grid is in a fault state, the grid-side voltage drops. Because the full-power converter has an isolation function, P s only depends on the change of the wind speed and does not change with the change of P g . If the output power P s of the direct-drive wind turbine is constant, in order to ensure the power balance relationship, the grid-side converter must increase the output current, so as to ensure that the output active power P gInvariable, thus, the active power output by the direct-drive wind turbine is expressed as:

[0107]

[0108] where P c represents the capacitive energy storage power, and C represents the DC bus capacitor.

[0109] When the grid-side voltage slightly drops (e gd = 1 ~ 0.9.pu), the output value of the outer loop controller is the inner loop reference value, and a second-order differential equation about the d-axis reference value of the direct-drive wind turbine output current i

[0110]

[0111] where i gd_ref1 represents the d-axis reference value of the direct-drive wind turbine output current when the grid-side voltage slightly drops, and P s ' represents the active power output by the direct-drive wind turbine when the system is stable.

[0112] According to equation (8), the d-axis reference value of the direct-drive wind turbine output current when the grid-side voltage slightly drops at time t is obtained as:

[0113]

[0114] where,

[0115]

[0116]

[0117]

[0118]

[0119] where i gd_ref(0) represents the d-axis reference value of the direct-drive wind turbine output current at the time of the fault occurrence.

[0120] Based on this, when the grid-side voltage severely drops (e gd drops to below 0.9p.u.), that is, in the fault ride-through process, the outer loop controller does not act, and the wind turbine needs to provide reactive current to the grid for voltage support, and the inner loop reference current value is a specified value:

[0121] i gq_ref2 = 1.5*(0.9-U T )I N (10)

[0122]

[0123] wherein i gq_ref2 , i gd_ref2 (t) respectively represent the d-axis and q-axis reference values of the direct-drive wind turbine output current during the fault ride-through process at the tth moment, U T represents the per-unit value of the wind farm grid-connected point voltage, I N represents the per-unit value of the wind farm rated current.

[0124] Thus, in the implementation, the reference value i g_ref (t) of the direct-drive wind turbine output current during the fault ride-through process at the tth moment is represented as:

[0125] i g_ref (t) = i gd_ref2 (t) + ji gq_ref2 (12)

[0126] S23, based on the voltage outer loop and current inner loop control equations of the grid-side converter and the reference value of the direct-drive wind turbine output current during the fault ride-through process, obtaining the direct-drive wind turbine output current during the fault ride-through process.

[0127] In the implementation, in step S23, the direct-drive wind turbine output current during the fault ride-through process is obtained based on the following analysis steps:

[0128] By simultaneously solving equation (4), equation (5) and equation (6), a second-order differential equation about the direct-drive wind turbine output current is obtained:

[0129]

[0130] Equation (13) is represented as a complex vector:

[0131]

[0132] wherein i g represents the direct-drive wind turbine output current.

[0133] It can be seen that equation (14) is a variable coefficient second-order differential equation, so in order to solve the equation, the time-varying parameters are split into constant parameters, i.e. the fault duration [t1, t'] is split into several equal parts [t1, t'0], [t'0, t'1], …; in each time period, the current reference value output by the outer loop and the phase-locked loop output angle are equal to the values at the initial moment of the time period:

[0134]

[0135]

[0136]

[0137] …

[0138] Thus, the second-order differential equation of the direct-drive wind turbine output current is obtained, expressed as:

[0139]

[0140] Solving equation (15), the direct-drive wind turbine output current i g (t) in the fault ride-through process at the t-th moment in the specific implementation is obtained, expressed as:

[0141]

[0142] wherein,

[0143]

[0144]

[0145]

[0146]

[0147]

[0148] In the formula, i g_ref (t) represents the direct-drive wind turbine output current reference value in the fault ride-through process at the t-th moment, L and R represent the stator inductance and resistance of the wind turbine respectively; Δθ(t) represents the voltage jump angle at the t-th moment, and i_ref(0) represents the direct-drive wind turbine output current reference value in the steady-state operation.

[0149] The calculation is converted to the stator three-phase stationary coordinate system, and the short-circuit current instantaneous expression is obtained as:

[0150]

[0151] In the formula, is the coordinate transformation matrix from two-phase rotation to three-phase stationary, is the angle of the d-axis leading the a-axis; i sA , i sB , i sC respectively represent the three-phase grid-side currents after the fault in the three-phase stationary coordinate system, Re() represents the real part of a complex number, and Im() represents the imaginary part of a complex number.

[0152] In the implementation, in step S2, the grid-side converter output voltage expectation value in the fault ride-through process is obtained through the following derivation:

[0153] When the power grid is in the steady-state operation, the grid-side voltage amplitude is e gd , at the t1 moment, a symmetrical short-circuit fault occurs, the voltage amplitude drop rate at the fault occurrence moment is k, and the voltage phase angle jump angle after the fault is And in the process of falling, the rotor speed is constant.

[0154] Thus, in the specific implementation, the expected value u g2 (t) of the output voltage of the grid-side converter in the fault ride-through process at the t-th moment is represented as:

[0155]

[0156] wherein,

[0157] e gd = ke g ,

[0158] In the formula, e g (t) represents the instantaneous value of the grid-side voltage at the moment of fault occurrence, e gd represents the instantaneous value of the d-axis voltage of the grid-side at the moment of fault occurrence, ω1 represents the synchronous rotational speed before the fault, and k represents the voltage amplitude drop rate at the moment of fault occurrence. represents the voltage phase angle jump angle after the fault.

[0159] S3, based on the output current of the direct-driven wind turbine, the expected value of the output voltage of the grid-side converter, and the collected DC voltage, the active power of the direct-driven wind turbine in the fault ride-through process is obtained.

[0160] In the implementation, according to the formula (7), formula (16) and formula (18), the active power P s (t) output by the direct-driven wind turbine at the t-th moment is obtained, which is represented as:

[0161]

[0162] In the formula, u g2 (t) represents the expected value of the output voltage of the grid-side converter in the fault ride-through process at the t-th moment, represents the conjugate vector of the output current i g (t) of the direct-driven wind turbine in the fault ride-through process at the t-th moment, u dc (t) represents the real-time value of the DC voltage in the fault ride-through process at the t-th moment, and C represents the DC bus capacitor. It should be noted that the positive sign in the coefficient is because the stator winding adopts the generator convention to define the flow direction of power, because the amplitude constant principle is adopted in the coordinate transformation.

[0163] Compared with the prior art, the embodiment provides an active power calculation method of a direct-drive wind turbine based on a fault ride-through process, a typical phase-locked vector control strategy is added in the analysis process, a jump angle is analyzed through the control link, and then a direct-drive single-machine short-circuit current considering the influence of voltage phase angle jump in the fault ride-through condition is derived, and then the transient active power output by the direct-drive wind turbine in the fault ride-through process is obtained by combining the internal energy flow of the direct-drive wind turbine and the energy flow and structure of the wind turbine structure, which is closer to the transient characteristics of the direct-drive wind turbine and is more in line with engineering practice.

[0164] Embodiment 2

[0165] In one specific embodiment 2 of the present application, an active power calculation system of a direct-drive wind turbine based on a fault ride-through process is provided, comprising the following steps:

[0166] A data acquisition module is configured to acquire the post-fault grid-side voltage, the direct-drive wind turbine output current, the DC voltage, the fault point voltage, the voltage drop rate and the voltage phase angle jump angle when monitoring that the direct-drive wind turbine occurs a symmetrical fault, and the pre-fault direct-drive wind turbine output current and the active power.

[0167] A voltage and current obtaining module is configured to obtain the voltage jump angle in the fault ride-through process, the direct-drive wind turbine output current reference value and the grid-side converter output voltage expected value according to the acquired information, and obtain the direct-drive wind turbine output current in the fault ride-through process based on the voltage jump angle in the fault ride-through process and the direct-drive wind turbine output current reference value.

[0168] An active power calculation module is configured to obtain the active power of the direct-drive wind turbine in the fault ride-through process based on the direct-drive wind turbine output current in the fault ride-through process, the grid-side converter output voltage expected value and the collected DC voltage.

[0169] In implementation, the voltage and current obtaining module obtains the direct-drive wind turbine output current in the fault ride-through process by executing the following mode:

[0170] Based on the acquired information and the phase-locked loop control, the voltage jump angle after the fault is obtained, and then a direct-drive wind turbine mathematical model is established based on the engine convention;

[0171] Based on the direct-drive wind turbine mathematical model, the voltage outer loop and current inner loop control equations of the grid-side converter are obtained, and then the direct-drive wind turbine output current reference value in the fault ride-through process is obtained.

[0172] Based on the voltage outer loop and current inner loop control equations of the grid-side converter and the direct-drive wind turbine output current reference value in the fault ride-through process, the direct-drive wind turbine output current in the fault ride-through process is obtained.

[0173] In a specific implementation, any time before the fault occurrence time is taken as an initial time, the fault occurrence time is t1, the direct-drive wind turbine is in a fault ride-through process at the tth time, wherein t≥t1; the active power P s (t) is expressed as:

[0174]

[0175] In the formula, u g2 (t) represents an expected value of the grid-side converter output voltage in the fault ride-through process at the tth time, represents an output current i g (t) of the direct-drive wind turbine in the fault ride-through process at the tth time, u dc (t) represents a real-time value of the DC voltage in the fault ride-through process at the tth time, and C represents a DC bus capacitor.

[0176] The specific implementation process of the embodiment of the application can be referred to the method embodiment described above, and the embodiment will not be described here.

[0177] Since the embodiment has the same principle as the method embodiment described above, the system also has the corresponding technical effects of the method embodiment.

[0178] Embodiment 3

[0179] To verify the correctness of the embodiments 1 and 2 of the application, the scheme in the above embodiments is tested and verified in this embodiment, the main parameters of the wind turbine are shown in Table 1, and the grid structure diagram of the direct-drive wind turbine is shown in Figure 4 .

[0180] Table 1 Main parameters of the direct-drive wind turbine

[0181]

[0182] Suppose that 2s before the fault occurrence time is taken as the initial time, at the t=2s time, a three-phase symmetrical short-circuit fault occurs at the outlet of the PMSG, the PMSG terminal voltage respectively drops to 40%, 60% and 80%, and the comparison graphs of the calculated value and the simulation value are shown in Figure 5 , Figure 6 , Figure 7 . As shown in the graphs, the calculated value and the simulation value of the wind turbine short-circuit current are basically consistent in size and change trend, and thus meet the short-circuit current transient characteristics of the direct-drive wind turbine after the fault.

[0183] Suppose that 2s before the fault occurrence time is taken as the initial time, at the t=2s time, a three-phase symmetrical short-circuit fault occurs at the outlet of the PMSG, the PMSG terminal voltage respectively drops to 40%, 60% and 80%, and the comparison graphs of the calculated value and the simulation value are shown in Figure 8、 Figure 9 、 Figure 10 The calculation results of the output active power after the symmetrical fault at the outlet of the fan are basically consistent with the simulation results in terms of trend and value, and can reflect the transient characteristics of the active power during the fault.

[0184] Those skilled in the art can understand that all or part of the processes of the above-mentioned embodiment methods can be completed by a computer program instructing related hardware, and the program can be stored in a computer readable storage medium. The computer readable storage medium is a disk, an optical disk, a read-only memory, a random access memory, etc.

[0185] The above is only a preferred specific embodiment of the present application, but the protection scope of the present application is not limited to this. Any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. A method for calculating the active power of a direct-drive wind turbine based on fault ride-through process, characterized in that, Includes the following steps: When a symmetrical fault is detected in a direct-drive wind turbine, the grid-side voltage, direct-drive wind turbine output current, DC voltage, fault point voltage, voltage drop rate, and voltage phase angle jump angle after the fault are obtained, as well as the direct-drive wind turbine output current and active power before the fault. Based on the information obtained, the voltage jump angle, the reference value of the direct-drive wind turbine output current, and the expected value of the grid-side converter output voltage during fault ride-through are obtained. Based on the voltage jump angle and the reference value of the direct drive fan output current during fault ride-through, the output current of the direct drive fan during fault ride-through is obtained. Based on the output current of the direct-drive wind turbine, the expected output voltage of the grid-side converter, and the collected DC voltage during fault ride-through, the active power of the direct-drive wind turbine during fault ride-through is obtained.

2. The method for calculating the active power of a direct-drive wind turbine based on fault ride-through process according to claim 1, characterized in that, The output current of the direct-drive fan during fault ride-through is obtained by performing the following steps: Based on the acquired information and phase-locked loop control, the voltage jump angle after the fault is obtained, and then a mathematical model of the direct-drive fan is established based on engine conventions. Based on the mathematical model of the direct-drive wind turbine, the voltage outer loop and current inner loop control equations of the grid-side converter are obtained, and then the reference value of the output current of the direct-drive wind turbine during fault ride-through is obtained. Based on the voltage outer loop and current inner loop control equations of the grid-side converter and the reference value of the direct-drive wind turbine output current during fault ride-through, the output current of the direct-drive wind turbine during fault ride-through is obtained.

3. The method for calculating the active power of a direct-drive wind turbine based on fault ride-through process according to claim 2, characterized in that, Taking any time before the fault occurrence as the initial time, the fault occurrence time is t1. At time t, the direct-drive fan is in the fault ride-through process, where t ≥ t1; the active power P output by the direct-drive fan at time t. s (t), represented as: In the formula, u g2 (t) represents the expected output voltage of the grid-side converter during fault ride-through at time t. Indicates the output current i of the direct-drive fan during fault ride-through at time t. g The conjugate vector of (t), u dc (t) represents the real-time value of the DC voltage during fault ride-through at time t, and C represents the DC bus capacitance.

4. The method for calculating the active power of a direct-drive wind turbine based on fault ride-through process according to claim 3, characterized in that, The expected output voltage u of the grid-side converter during fault ride-through at time t g2 (t), represented as: in, yes gd =I am g , In the formula, e g e represents the instantaneous value of the grid-side voltage at the moment the fault occurs. gd ω1 represents the instantaneous d-axis value of the grid-side voltage at the moment the fault occurs, ω1 represents the synchronous rotational angular velocity before the fault, and k represents the voltage amplitude drop rate at the moment the fault occurs. This indicates the voltage phase angle jump angle after a fault.

5. The method for calculating the active power of a direct-drive wind turbine based on fault ride-through process according to claim 4, characterized in that, During the fault ride-through at time t, the direct-drive fan output current i g (t), represented as: in, In the formula, i g_ref (t) represents the reference value of the direct-drive fan output current during fault ride-through at time t, where L and R represent the stator inductance and resistance of the fan, respectively; k pu k iu represents the proportional and integral coefficients of the voltage outer loop PI controller, respectively; Δθ(t) represents the voltage jump angle at time t; and i_ref(0) represents the reference value of the direct drive fan output current during steady-state operation.

6. The method for calculating the active power of a direct-drive wind turbine based on fault ride-through process according to claim 5, characterized in that, Reference value of direct-drive fan output current i during fault ride-through at time t g_ref (t), represented as: i g_ref (t)=i gd_ref2 (t)+ji gq_ref2 in, i gq_ref2 =1.5*(0.9-U T )I N , In the formula, U T I represents the per-unit voltage at the grid connection point of the wind farm. N P represents the per-unit value of the rated current of a wind farm. s ′ represents the active power output of the direct-drive fan during stable operation; i gd_ref(0) The d-axis reference value represents the output current of the direct-drive fan at the moment the fault occurred. This indicates a reference value for DC voltage.

7. The method for calculating the active power of a direct-drive wind turbine based on fault ride-through process according to claim 6, characterized in that, The voltage jump angle Δθ(t) at time t is expressed as: in, In the formula, U m k represents the voltage amplitude at the fault point. ppll k ipll These represent the proportional and integral constants of the phase-locked loop PI controller, respectively, and Δθ (0) This indicates the phase angle jump value of the terminal voltage at the moment the fault occurs.

8. A system for calculating the active power of a direct-drive wind turbine based on fault ride-through process, characterized in that, Includes the following steps: The data acquisition module is used to acquire the grid-side voltage, direct-drive wind turbine output current, DC voltage, fault point voltage, voltage drop rate and voltage phase angle jump angle after a symmetrical fault is detected in the direct-drive wind turbine, as well as the direct-drive wind turbine output current and active power before the fault. The voltage and current acquisition module is used to obtain the voltage jump angle, the reference value of the direct-drive wind turbine output current, and the expected value of the grid-side converter output voltage during fault ride-through based on the acquired information. Based on the voltage jump angle and the reference value of the direct drive fan output current during fault ride-through, the output current of the direct drive fan during fault ride-through is obtained. The active power calculation module is used to obtain the active power of the direct-drive wind turbine during fault ride-through based on the output current of the direct-drive wind turbine, the expected value of the output voltage of the grid-side converter, and the collected DC voltage.

9. The active power calculation system for a direct-drive wind turbine based on fault ride-through process according to claim 8, characterized in that, The voltage and current acquisition module obtains the output current of the direct-drive fan during fault ride-through by performing the following steps: Based on the acquired information and phase-locked loop control, the voltage jump angle after the fault is obtained, and then a mathematical model of the direct-drive fan is established based on engine conventions. Based on the mathematical model of the direct-drive wind turbine, the voltage outer loop and current inner loop control equations of the grid-side converter are obtained, and then the reference value of the output current of the direct-drive wind turbine during fault ride-through is obtained. Based on the voltage outer loop and current inner loop control equations of the grid-side converter and the reference value of the direct-drive wind turbine output current during fault ride-through, the output current of the direct-drive wind turbine during fault ride-through is obtained.

10. The active power calculation system for a direct-drive wind turbine based on fault ride-through process according to claim 9, characterized in that, Taking any time before the fault occurrence as the initial time, the fault occurrence time is t1. At time t, the direct-drive fan is in the fault ride-through process, where t ≥ t1; the active power P output by the direct-drive fan at time t. s (t), represented as: In the formula, u g2 (t) represents the expected output voltage of the grid-side converter during fault ride-through at time t. Indicates the output current i of the direct-drive fan during fault ride-through at time t. g The conjugate vector of (t), u dc (t) represents the real-time value of the DC voltage during fault ride-through at time t, and C represents the DC bus capacitance.

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