CN114597950A

CN114597950A - DFIG adaptive control strategy and coordination method compatible with feeder automation

Info

Publication number: CN114597950A
Application number: CN202210353492.7A
Authority: CN
Inventors: 田鹏; 李浪; 沈仕巡; 刘赟; 黄薇; 周克; 冯华仲; 潘峰
Original assignee: Moutai University
Current assignee: Moutai University
Priority date: 2022-04-06
Filing date: 2022-04-06
Publication date: 2022-06-07
Also published as: ZA202209109B

Abstract

The invention discloses a DFIG adaptive control strategy compatible with feeder automation and a coordination method, wherein the method comprises the following steps: firstly, a double-fed fan self-adaptive control method which can seamlessly switch a double-fed fan grid-connected/isolated island control mode and create synchronous conditions at any remote interconnection switch is set based on a virtual synchronous machine control technology; and secondly, under the condition of no network-source communication, setting a coordination method for safely connecting the double-fed fan island controlled by the ACS to the network through any connection switch. The ACS and coordination technology disclosed by the invention enable the double-fed fan and the FA to be compatible with each other without splitting and restarting the double-fed fan, the purposes of running without stopping and continuously supplying power to the network side are realized, the utilization rate of the double-fed fan can be improved, the maintenance cost is reduced, the power supply reliability of a power distribution network can be improved, and the elasticity of the power distribution network is enhanced.

Description

DFIG adaptive control strategy and coordination method compatible with feeder automation

Technical Field

The invention relates to a DFIG self-adaptive control strategy and a DFIG self-adaptive control coordination method compatible with feeder automation, and belongs to the technical field of active power distribution networks.

Background

Modern power distribution networks require flexible and reliable operation, and usually adopt a closed-loop design and an open-loop operation mode. Thus, the active power distribution network system to which the present invention is directed is shown in fig. 1. A primary system of the transformer substation is of a ring network structure, B1, B2, B3 and B4 are substation outgoing line switches on two sides respectively, three feeders are led out through B1, B2 and B3 and are mutually connected through a Ring Main Unit (RMU), RMU outgoing and outgoing line switches are all circuit breakers, contact switches L41 and L62 are in a normally open state, a contact line 1 is in contact with a feeder line 1 and a feeder line 3, a contact line 2 is in contact with a feeder line 2 and a feeder line 3, the feeder lines are underground cables, and the voltage level is 10 kV. 5 megawatt double-fed fans (indicated by DFIGx) are respectively connected to the power distribution network through RMUs at different positions. The secondary system is configured as a typical intelligent distributed FA which does not depend on the global information of a main station or a sub-station and exchanges fault information through peer-to-peer communication between intelligent terminals (STUs) to realize rapid isolation of feeder faults and power supply recovery. The communication network is an optical fiber Ethernet ring network structure supporting IEC 61850, and a GOOSE fast message communication mechanism is adopted between the substation outgoing switch and the STUs configured by the ring main units.

In fig. 1, F1, F2, and F3 represent 3 feeder faults. When a fault occurs at a certain part of the power distribution network, the FA exchanges fault information through GOOSE peer-to-peer communication to position the fault and controls circuit breakers at two sides of a fault feeder line to trip to isolate the fault; sending a GOOSE message (SFI) of successful fault isolation after fault isolation; and after receiving the SFI message, the corresponding tie switch is switched on immediately if the fault is judged not to be on the corresponding tie line, and the power supply of the downstream non-fault feeder line section with the fault is recovered. The corresponding relationship between the feeder line and the interconnection switch is as follows: feeder 1 corresponds to tie switch L41; feed 3 corresponds to tie switch L62. Therefore, when a fault occurs on the feeder line 1, after the FA processes the fault isolation, the interconnection switch L41 is switched on; when a fault occurs on the feeder line 3, the connection switch L62 is switched on after the FA processes the fault isolation.

Traditionally, P/Q control is adopted when DFIG is connected to the grid, and V/F control is adopted when DFIG is isolated from the island. In the case of multiple DFIG islands, an operation mode of master-slave control, peer-to-peer control or hierarchical control is required. Therefore, DFIGs currently operate primarily in a continuous grid-connected mode or a pure island mode without switching between the two, and few DFIGs have dual-mode operation capability, or dual-mode seamless switching capability. Because different control strategies and operation modes are needed in different operation modes, the DFIG needs to be configured with an island detection technology to realize grid-connected-island mode switching. The island detection technology mainly comprises three types: communication-based, active and passive technologies. Establishing communication between the DFIG and the power distribution network adds cost and complicates access by the DFIG. And the distribution network and the DFIG generally belong to different owners, so that no secondary cable connection exists between the DFIG and the distribution network in practical engineering. While active and passive island detection techniques are not reliable enough and island detection requires a certain amount of time. In addition, the cable distance between the DFIG and the power distribution network is generally far (1km-2km), and the position of a tie switch is flexibly configured, so that the grid connection of the DFIG island through the tie switch is a remote synchronous grid connection process, which is fundamentally different from the traditional DFIG local synchronous grid connection technology. Moreover, the essence of the existing GOOSE fast communication mechanism is to repeatedly send displacement state messages, which cannot realize real-time transmission of distant sine alternating current, and the sampling value messages (SV) are uneconomical and unreliable for being used in the power distribution network.

Therefore, when the DFIG is connected to a power distribution network (as shown in fig. 1), if the DFIG needs to supply power for local partial loads uninterruptedly in case of a feeder fault and match with a tie switch for synchronous safe closing, two problems exist between the FA and the DFIG. The first problem is that: a series of switch displacement information determined by FA can not timely inform DFIG, and the DFIG can not adapt to the topological change of a power grid; the DFIG does not have dual-mode operation capability, cannot adjust a control mode in time, cannot realize seamless switching between grid connection and an island, and particularly suffers from the problem of multi-machine unplanned island. The second problem is that: the remote detection synchronization function required by the conversion from off-grid to grid connection of the DFIG cannot be supported by the information channel and the message specification of the power distribution network. The two problems cause that the existing FA technology is incompatible with DFIG and mutually exclusive, and the upgrading from an active power distribution network to an intelligent power distribution network is hindered.

Disclosure of Invention

The technical problem to be solved by the invention is as follows: the DFIG adaptive control strategy and the DFIG adaptive control coordination method compatible with feeder automation are provided to solve the problems in the prior art.

The technical scheme adopted by the invention is as follows: a DFIG adaptive control strategy and a coordination method compatible with feeder automation are disclosed, the method comprises the following steps: firstly, setting an adaptive control method (ACS) of the double-fed fan, which can seamlessly switch a grid-connected/isolated island control mode of the double-fed fan and create synchronous conditions at any remote interconnection switch, based on a virtual synchronous machine control technology; secondly, under the condition of no network-source communication, a coordination method for safely connecting a double-fed fan island controlled by the ACS to the network through any contact switch is set, and based on the coordination method, after an isolation switch (breaker) trips to isolate faults, the double-fed fan can seamlessly enter an island mode and stably run, and meanwhile, synchronous closing conditions at any remote contact switch are created; and then the remote interconnection switch is synchronously switched on to enable the double-fed fan island to be connected to the grid again, and the double-fed fan is recovered to a stable state before the fault or enters a new stable state under the support of the grid voltage.

The wind turbine control part of the self-adaptive control method of the double-fed wind turbine still adopts a basic control structure of a GE double-fed wind turbine, the GSC adopts a vector control strategy based on PLL synchronization to maintain the voltage stability of a direct current bus, aiming at RSC control of the control method, a group of DFIG novel virtual synchronous machine control structures (NVSG) are arranged, the power control structures comprise power control, damping control, droop control, voltage control and current inner rings, the power control simulates the inertial response characteristic of a synchronous generator, and 1/(2H) is set_As) is a power control inertia element and K_AFor controlling the power of the scaling factor, wherein H_AControlling a virtual inertial time constant for the power; introduction of a proportion systemNumber K_AThe purpose of (1) is to appropriately accelerate the dynamic response performance of power control. When the actual electromagnetic power output P_eAnd mechanical power P_mWhen unbalance occurs, the angular frequency omega of the potential in the stator is adjusted through an inertia link and a proportion link_si(ii) a Angular frequency omega of stator internal potential_siObtaining the control phase theta of the potential in the stator through an integral link_si，ω_bAt the fundamental angular frequency (omega)_b100 pi); rotor excitation current phase θ_IrThe phase theta is controlled directly by the potential in the stator_siMinus rotor position angle theta_mObtain (theta)_m＝∫ω_mdt)，ω_mIs the rotor electrical angular velocity and thus does not rely on PLL technology. The power control algorithm is as follows:

the damping control simulates the mechanical damping of the synchronous generator and the action of a damping winding, and the internal frequency omega caused by the disturbance to the power grid during grid connection_siThe oscillation and the power oscillation are suppressed to improve the stability of a control system, and the off-grid process is equivalent to the direct tracking control of the island frequency; damping power P_DFrom angular frequency ω of potential in stator_siWith reference angular frequency of the grid

Obtained by a damping step after the difference is made, D_AFor the virtual damping coefficient, the damping control algorithm is as follows:

droop control simulates the droop characteristic of active power and frequency of the synchronous motor, and m is set as a droop coefficient omega_gFor feeding back angular frequency (external frequency) to the stator sideRate), power is given a reference value

The wind turbine torque is controlled to generate delta P, and the delta P is an Automatic Frequency Regulator (AFR); when in grid connection, because

Droop control is not active; when off-grid, ω_g＝ω_siThe droop control and the damping control function as a frequency regulator; the droop control algorithm is as follows:

the voltage control simulates the excitation principle of a synchronous generator, which is equivalent to an Automatic Voltage Regulator (AVR) and is based on a stator voltage amplitude reference value

With actual stator voltage amplitude U_sObtaining a reactive reference value through a typical PI controller after difference making

And a reactive feedback value Q_eAfter comparison, a rotor exciting current amplitude reference value is obtained through a PI controller

Let P_usaAnd I_usaProportional and integral coefficients, P, of voltage control, respectively_QAnd I_QRespectively, proportional and integral coefficients of reactive power control, when in grid connection,

therefore, only the reactive control part in the voltage control is in effect; when the system is off-grid, voltage control maintains voltage stability by adjusting reactive output; the voltage control algorithm is as follows:

the current inner ring is designed in a mode that three-phase instantaneous phase currents are independently controlled respectively, wherein the upper mark of r represents the quantity under a rotor reference system, and the upper mark of ref represents a reference value; rotor excitation current space vector reference value

The phase and amplitude synthesis obtained by power control, damping control, droop control and voltage control will be

Converting to an abc three-phase static coordinate system to obtain a three-phase rotor excitation phase current reference value

The three-phase rotor excitation current reference values are respectively corresponding to the three-phase actual feedback rotor excitation phase currents

Run the posterior meridian G_QPR(s) obtaining corresponding three-phase rotor excitation phase voltage in the control link

G_QPR(s) denotes a quasi-proportional resonant controller (QPR), G compared to a PI controller_QPR(s) is more suitable for precise control of the amount of ac signals (higher gain at a particular frequency), with a transfer function expressed as:

in the formula, P_QPRIs the QPR proportionality coefficient, K_QPRIs the QPR resonance coefficient, ω_iFor QPR resonance term bandwidth, ω_rFor the slip angular frequency, the current inner loop control algorithm is accordingly expressed as:

in the formula, phi represents three phases of a, b and c.

The network-source communication-free coordination method comprises the following steps: firstly, the double-fed fan is controlled by ACS; second, the STU configures a synchronization device at the tie switch (which synchronization device is integrated into the STU); then, the closing condition of the interconnection switch is set as: in the process of automatically creating a remote synchronous condition for a double-fed fan island under ACS control, after an STU at a contact switch confirms that an SFI message is received and a fault is judged to be not on a contact line, the STU immediately controls the contact switch to be switched on by detecting synchronous switching-on conditions (including frequency difference, amplitude difference and phase difference) through a synchronous detection device, synchronous grid connection of the fan island is realized, at the moment, the phase difference in the switching-on conditions of the contact switch is set to be zero, the double-fed fan controlled by the ACS has grid-connected/island double-mode operation capacity, the double-fed fan automatically adapts to island → grid-connected change after the contact switch is switched on, and grid-connected operation is recovered.

The invention has the beneficial effects that: compared with the prior art, the invention can realize seamless grid-connection/island mode conversion of non-grid-source communication under the ACS control after the FA isolation feeder line fails, and continuously supply power to local partial loads, and the interconnection switch can close the switch through local detection and synchronous conditions after the FA isolation failure, so that the double-fed fan under the ACS control can realize safe grid connection without establishing an additional communication system with a power distribution network. In addition, the doubly-fed wind turbine under the ACS control experiences a short-time island during the coordination with the FA, which on one hand is beneficial to solving the problem of electric energy quality of the long-time island of the traditional doubly-fed wind turbine, and on the other hand, the traditional unidirectional power supply recovery mechanism from the feeder to the load is upgraded to a bidirectional power supply recovery mechanism from the DG and the feeder to the load respectively. Therefore, the ACS and coordination technology disclosed by the invention enables the double-fed fan and the FA to be compatible with each other without splitting and restarting the double-fed fan, achieves the purposes of running without stopping and continuously supplying power to the network side, can improve the utilization rate of the double-fed fan, reduce the maintenance cost, improve the power supply reliability of a power distribution network and enhance the elasticity of the power distribution network, and provides a new scheme for the development of an intelligent power grid.

Drawings

FIG. 1 is a schematic diagram of an active power distribution system;

FIG. 2 is a diagram of a network-source compatible solution;

FIG. 3 is a diagram of a primary control architecture of a wind turbine;

FIG. 4 is a GSC DC bus voltage control block diagram;

FIG. 5 is a diagram of a DFIG novel virtual synchronous machine control structure (NVSG);

FIG. 6 is a coordination technical diagram of double-fed wind turbine-feeder automation without communication;

fig. 7 is a graph showing changes in the electrical quantities prevailing on the grid side after the occurrence of the fault at F1;

FIG. 8 is a graph showing changes in the main electrical and mechanical quantities on the side of the fan after a failure at F1;

FIG. 9 is a graph showing the change in the electrical quantities prevailing on the grid side after the occurrence of the fault at F2

FIG. 10 is a graph of the change in the electrical and mechanical quantities prevailing on the side of the fan following a failure at F2;

FIG. 11 is a graph showing changes in the electrical quantities prevailing on the grid side after the occurrence of the fault at F3

Fig. 12 is a diagram showing changes in the main electrical quantities and mechanical quantities on the side of the fan after the failure at F3 occurs.

Detailed Description

The invention is further described with reference to the accompanying drawings and specific embodiments.

Example 1: as shown in fig. 2 to 12, in order to fully and flexibly utilize a doubly-fed wind turbine to enhance the distribution network elasticity under the condition of no network-source communication, a technical solution of the present invention is as shown in fig. 2, and a DFIG adaptive control strategy and a coordination method compatible with feeder automation, the method includes: firstly, setting an adaptive control method (ACS) of the double-fed fan, which can seamlessly switch a grid-connected/isolated island control mode of the double-fed fan and create synchronous conditions at any remote interconnection switch, based on a virtual synchronous machine control technology; secondly, under the condition of no network-source communication, a coordination method for safely connecting a double-fed fan island controlled by the ACS to the network through any contact switch is set, and based on the coordination method, after an isolation switch (breaker) trips to isolate faults, the double-fed fan can seamlessly enter an island mode and stably run, and meanwhile, synchronous closing conditions at any remote contact switch are created; and then the remote interconnection switch is synchronously switched on to enable the double-fed fan island to be connected to the grid again, and the double-fed fan is recovered to a stable state before the fault or enters a new stable state under the support of the grid voltage.

For the double-fed wind turbine, the disclosed technical scheme is a continuous seamless switching process of unplanned island stable operation, island remote synchronization and island grid connection. The process is realized by a network-source non-communication compatible strategy which is formed by control and coordination, and the key point is an advanced double-fed fan grid-connected/island double-mode control strategy ACS, and meanwhile, the non-communication coordination of the double-fed fan and network-side protection equipment is needed.

The invention is explained by taking a GE 1.5MW doubly-fed fan power generation system under typical vector control as an example. In the disclosed ACS, the key point is to control the RSC, the wind turbine control part still adopts the basic control structure of the GE doubly-fed wind turbine (as shown in figure 3), and the GSC still adopts a typical vector control strategy based on PLL synchronization to maintain the voltage of a direct-current bus to be stable (as shown in figure 4).

The wind turbine control part of the self-adaptive control method of the double-fed wind turbine still adopts a basic control structure of a GE double-fed wind turbine, the GSC adopts a vector control strategy based on PLL synchronization to maintain the voltage stability of a direct current bus, and in order to meet dual-mode seamless operation, aiming at RSC control of the control method, a group of DFIG novel virtual synchronous machine control structures (NVSG) is arranged, as shown in figure 5, the NVSG mainly comprises five parts of power control, damping control, droop control, voltage control and current inner ring, the power control simulates the inertia response characteristic of a synchronous generator, and 1/(2H) is set_As) is a power control inertia element and K_AFor controlling the power of the scaling factor, wherein H_AControlling a virtual inertial time constant for the power; introduction of a proportionality coefficient K_AThe purpose of (1) is to appropriately accelerate the dynamic response performance of power control. When the actual electromagnetic power output P_eAnd mechanical power P_mWhen unbalance occurs, the angular frequency omega of the potential in the stator is adjusted through an inertia link and a proportion link_si(ii) a Angular frequency omega of stator internal potential_siObtaining the control phase theta of the potential in the stator through an integral link_si，ω_bAt the fundamental angular frequency (omega)_b100 pi); rotor excitation current phase θ_IrThe phase theta is controlled directly by the potential in the stator_siMinus rotor position angle theta_mTo obtain (theta)_m＝∫ω_mdt) and thus does not rely on PLL techniques. The power control algorithm is as follows:

droop control simulates the droop characteristic of active power and frequency of a synchronous motor, and m is a droop coefficient omega_gTo be fixedSub-side feedback angular frequency (outer frequency), power given reference value

Generated by wind turbine torque control (as shown in FIG. 3), Δ P is an Automatic Frequency Regulator (AFR); when in grid connection, because

Let P_usaAnd I_usaProportional and integral coefficients, P, of the voltage control, respectively_QAnd I_QRespectively, proportional and integral coefficients of reactive power control, when in grid connection,

The phase and amplitude synthesis obtained by power control, damping control, droop control and voltage control will

in the formula, phi represents three phases of a, b and c.

It is noted that the NVSG current inner loop controller may not be limited to QPR, but other controller types may be used, such as: PI control, or individual proportional control, etc. When the proportional control is adopted, if the proportional control coefficient is 1, the virtual resistance is introduced. According to the invention, in order to obtain larger control freedom degree and better control performance of the NVSG, the QPR is selected as the current inner loop controller. In addition, a reactive power control link in voltage control can be omitted for further simplifying the control structure.

As shown in fig. 6, under the condition of no network-source communication, the present invention discloses an automatic coordination method for a doubly-fed wind turbine-feeder, which comprises: firstly, the double-fed fan is controlled by ACS; second, the STU configures a synchronization device at the tie switch (which synchronization device is integrated into the STU); then, the closing condition of the interconnection switch is set as: in the process of automatically creating a remote synchronous condition for a double-fed fan island under ACS control, after an STU at a contact switch confirms that an SFI message is received and a fault is judged to be not on a contact line, the STU immediately controls the contact switch to be switched on by detecting synchronous switching-on conditions (including frequency difference, amplitude difference and phase difference) through a synchronous detection device, synchronous grid connection of the fan island is realized, at the moment, the phase difference in the switching-on conditions of the contact switch is set to be zero, the double-fed fan controlled by the ACS has grid-connected/island double-mode operation capacity, the double-fed fan automatically adapts to island → grid-connected change after the contact switch is switched on, and grid-connected operation is recovered.

To illustrate the effects of the present invention, the following simulation test was performed:

and (3) building a detailed simulation model of the multi-machine active power distribution network system shown in the figure 1 in a MATLAB/Simulink environment. The model parameters, ACS control parameters and power distribution network parameters of the doubly-fed wind turbine are as follows:

the wind turbine mathematical model is as follows:

wherein, ω is_trans＝0.75，C_p-max＝0.5，v_w-cpmax＝11m/s，λ_cp-max＝9.9495，Ω_rated＝1.2pu，c₁＝0.645，c₂＝0.00912，c₃＝5，c₄＝0.4，c₅＝2.5，c₆＝116，c₇＝21，c₈＝0.08，c₉＝0.035，v_wIs the real name value of wind speed, omega_mIs the per unit value of speed, λ represents the tip speed ratio, P_wtThe rated power is 1.5MW (wind turbine reference power) which is the mechanical power captured by the wind turbine under the per unit value.

Mechanical system shafting model (single mass block):

T_wt-T_e＝2H_ms*ω_m (A-5)

wherein, T_wtFor mechanical torque, T_eThe intrinsic inertia time constant H of the mechanical system of the fan is the electromagnetic torque_m＝5s。

Mechanical system shafting model (dual mass block):

in the formula, H_wAnd H_gIs the time constant (H) of inertia of the wind turbine and DFIG, respectively_w＝4.32s，H_g＝0.68s)；ω_wAnd ω_gAngular velocities of the wind turbine and the DFIG, respectively; theta_tsIs the shafting torsion angle; k is a radical of_sAnd D_mRespectively, the stiffness coefficient and the damping coefficient (k)_s＝1.11，D_m＝1.5)；T_wAnd T_eRespectively representing the mechanical torque of the wind turbine and the electromagnetic torque of the DFIG; omega_baseIs the basic speed (omega)_base＝104.67)。

Wind turbine control parameters:

pitch angle control: p_pit＝150，I_pit＝20；

Pitch angle compensation control: p_com＝3，I_com＝30；

And (3) torque control: p_v＝3，I_v＝0.6；

Other parameters: t is_ω＝5，T_β＝0.01，T_Pe＝0.05，β_max＝27°，β_min＝0，dβ_max/dt_max＝10°，dβ_min/dt_min＝-10°，P_emax＝1.12pu，P_emin＝0.04pu，dP_emax/dt_max＝0.45pu，dP_emin/dt_min＝-0.45pu。

The maximum allowable rotating speed of the fan is 1.3pu, and the rated angular speed of the fan is 1.2 pu. When the power is below 0.75pu, the speed reference equation (MPPT) is:

GSC control parameters:

controlling the voltage of the direct current bus: p_dc＝8，I_dc＝400；

Reactive power control: p_gQ＝8，I_gQ＝400；

Current inner loop control: p_gd＝0.83，I_gd＝5，P_gq＝0.83，I_gq＝5。

RSC control Parameter (PQ):

active control: p_P＝0.05，I_P＝20；

Reactive power control: p_Q＝0.05，I_Q＝20；

Current inner loop control: p_Ird＝0.6，I_Ird＝8，P_Irq＝0.6，I_Irq＝8。

RSC control parameter (IAS):

voltage outer loop control: p_usd＝0.1，I_usd＝60，P_usq＝0.1，I_usq＝60；

RSC control parameter (ACS):

and (3) power control: k_A＝0.1，H_A＝5；

Damping control: d_A＝150；

And (3) droop control: m is 0.02;

voltage control: p_usa＝0.5，I_usa＝10，P_Q＝2，I_Q＝50；

Current inner loop control: p_PR＝20，K_PR＝33，ω_i＝π。

1.5MW DFIG parameters:

the rated power is 1.67MW (generator reference power), the maximum active power is 1.5MW, the minimum active power is 0.07MW, the maximum reactive power is 0.736MVAr, the minimum reactive power is-0.736 MVAr, the stator terminal voltage is 690V, the dc bus voltage is 1150V, the number of pole pairs is 3, the rated speed is 1.2pu, the dc capacitor is 15000uF, the rated frequency is 50Hz, the stator resistance is 0.023pu, the rotor resistance is 0.016pu, the stator inductance is 3.08pu, the rotor inductance is 3.06pu, and the mutual inductance is 2.9 pu.

1.5MW SG parameters:

the rated power is 1.67MW, the maximum active power is 1.5MW, the minimum active power is 0.07MW, the maximum reactive power is 0.736MVAr, the minimum reactive power is-0.736 MVAr, the stator terminal voltage is 690V, the rated frequency is 50Hz, the d-axis synchronous reactance is 1.56pu, the d-axis transient reactance is 0.296pu, the d-axis sub-transient reactance is 0.177pu, the q-axis synchronous reactance is 1.06pu, the q-axis sub-transient reactance is 0.177pu, the stator resistance is 0.0036pu, the d-axis transient short-circuit time constant is 3.7s, the d-axis sub-transient short-circuit time constant is 0.05s, the q-axis transient open-circuit time constant is 0.05s, the inertia time constant is 5s, and the pole pair number is 3.

Parameters of the power distribution network:

rated voltage 10kV, rated frequency 50Hz, cable line resistance 0.01273 Ω/km, and cable line inductance 0.9337 × 10^-3H/km, cable line capacitance 12.74 × 10^-9F/km。

3 cable feeder permanent fault scenes (F1, F2 and F3) are set in the power distribution network shown in the figure 1, and the self-adaption and coordination processes of different numbers of doubly-fed wind turbine unplanned islands and the power distribution network FA under different wind speed conditions are simulated. Neglecting the effect of the fault and assuming that the FA is able to isolate the fault instantaneously. Assuming that the maximum frequency of the distribution network for a brief tolerance is 51 Hz; the initial phase error of the voltage across the tie switch is 180. Meanwhile, according to the voltage class of a 10kV power distribution network and the characteristics of a network-source compatible strategy disclosed in this chapter, the simultaneous closing conditions of the interconnection switches are assumed as follows: the phase angle difference is 0 degrees, the amplitude difference is not more than 5 percent, and the frequency difference is not more than 0.5 Hz.

Scene 1, accessing a passive feeder line to a single unplanned island: the F1 fault is set to occur on the feeder 3, the wind speed at the DFIG4 is 15m/s, the FA controls the circuit breakers L42 and L51 to trip to isolate the fault in 30s, the island load is 1.12MW, and the interconnection switch L62 carries out closing by detecting the synchronous closing condition after the F1 fault occurs. Fig. 7 and 8 show the electrical and mechanical quantities prevailing on the network side and the fan side, respectively, after an F1 fault.

Grid connection-island conversion: after 30s of loss of the feeder 3 power supply, the DFIG4, the RMU4, the tie line 2 and the load form a single machine island. DFIG4 automatically enters island mode under ACS control, tie-line 2 voltage u_T2-abcAmplitude jitter of about two cycles of 1.1pu occurs, and no phase jump occurs(ii) a But mainly due to sudden changes in electromagnetic power (from 1.5MW to 1.12MW), the frequency f of the tie-line 2 voltage_T2A 50.6Hz spike occurred; DFIG4 rotor speed ω_m-DFIG4Fluctuation occurs up and down, but the amplitude is not high; rotor current amplitude I of DFIG4_r-DFIG4The voltage is rapidly changed from 0.83pu to about 0.65pu, and the overcurrent phenomenon does not occur; DFIG4 electromagnetic power P_e-DFIG4And also quickly adapts to 1.12MW island load. It can be seen that DFIG4 under ACS control seamlessly enters standalone island mode.

Remote synchronization process: after DFIG4 enters an island mode with unbalanced power, u_T2-abcThe amplitude of the signal is kept relatively stable; omega_m-DFIG4Low-frequency fluctuation with the frequency of 1.5Hz exists and the fluctuation has the attenuation tendency; i is_r-DFIG4No runaway occurs; p_e-DFIG4Matched with island load of 1.12MW, basically has no large-amplitude fluctuation; and f_T2Then the low frequency fluctuates around 50.1Hz so that the voltage phase error Δ θ across the tie switch L62_L62Gradually approaching 0 from 180 deg.. It is clear that DFIG4 under ACS control automatically creates distant contemporaneous conditions while ensuring island stability.

Island grid connection process: the STU at the interconnection switch L62 immediately receives the SFI message after the circuit breakers L42 and L51 trip, and judges that the fault does not occur on the interconnection line 2 through peer-to-peer communication with the adjacent STU; delta theta_L62At 34.9s, it becomes 0 ° and at L62 the STU detects in situ the contemporaneous closing condition (Δ θ) by the detection contemporaneous device _L410 degrees, amplitude difference not more than 5 percent and frequency difference not more than 0.5Hz) are switched on immediately. After the L62 is switched on to the passive feeder 2, the DFIG4 becomes a grid-connected state, I_r-DFIG4And P_e-DFIG4Gradually rising, and no violent fluctuation exists in the rising process; omega_m-DFIG4The fluctuation was suppressed and the steady state before the failure was recovered for about 18 seconds. At the same time u_T2-abcAnd f_T2After the grid connection, the voltage is clamped by the voltage of the feeder 2 and is kept constant; keeping as follows; the current amplitude at the interconnection switch L62 gradually rises from 0pu after closing, no inrush current occurs, and the steady state is entered after about 18 s. Obviously, the ACS controlled DFIG4 island is matched with the interconnection switch L62 to be synchronously switched on and then safely recovered to a grid-connected state.

Scene 2, accessing a passive feeder line by a multi-machine unplanned island: the method comprises the steps that a feeder 3 is set to have a fault at F2, the wind speed at DFIG4 is 10m/s, the wind speed at DFIG5 is 15m/s, the FA controls circuit breakers L52 and B3 to trip to isolate the fault at 30s, the total load of an island is 2MW, and a tie switch L62 is switched on through a detection synchronization condition after the fault of F2 occurs. Fig. 9 and 10 show the electrical and mechanical quantities prevailing on the grid side and the fan side, respectively, after an F2 fault.

Grid connection-island conversion: after L52 and B3 trip, DFIG4, DFIG5, RMU4, RMU5, tie-line 2 and the load constitute a dual island. DFIG4 and DFIG5 automatically enter an island mode respectively under ACS control, and tie line 2 voltage u_T2-abcSlight amplitude jitter occurred, but the waveform was continuous; but mainly due to sudden changes in electromagnetic power (from 2.3MW to 2MW), the frequency f of the tie-line 2 voltage_T2A 50.26Hz spike occurred; DFIG4 and DFIG5 rotor speed (ω)_m-DFIG4And ω_m-DFIG5) Fluctuation occurs up and down, but the amplitude is not high; rotor current amplitude (I) of DFIG4 and DFIG5_r-DFIG4And I_r-DFIG5) All change instantly, but no overcurrent appears; total electromagnetic Power (P) of DFIG4 and DFIG5_C＝P_e-DFIG4+P_e-DFIG5) And 2MW island load is quickly adapted. It can be seen that DFIG4 and DFIG5 under ACS control enter into multi-island mode seamlessly, respectively.

Remote synchronization process: after DFIG4 and DFIG5 enter an island mode with unbalanced power, u_T2-abcThe amplitude of (2) is relatively stable; omega_m-DFIG4And ω_m-DFIG5The low-frequency small-amplitude fluctuation characteristic is kept, and the fluctuation is gradually weakened; i is_r-DFIG4And I_r-DFIG5Shows a trend towards; respectively and automatically allocating P according to respective real-time capacity by DFIG4 and DFIG5_e-DFIG4And P_e-DFIG5Let P stand_C2MW held constant; but f_T2There is low frequency ripple which gradually decreases and remains around 50.05Hz, which causes the voltage phase error Delta theta to be different across the interconnection switch L62_L62Gradually approaching 0 deg.. It is clear that DFIG4 and DFIG5 dual island under ACS control are automatically creating remote synchronization.

Island grid connection process: the STU at the interconnection switch L62 receives the SFI message after tripping L52 and B3, judges that the fault does not occur on the interconnection line 2 through peer-to-peer communication with the adjacent STU, and detects delta theta at 39.6s_L62Becomes 0 deg. and the amplitude and frequency also correspond to the contemporaneous closing regulation, thus immediately controlling the closing of the tie switch L62. After the interconnection switch L62 is switched on to the passive feeder 2, the DFIG4 and the DFIG5 are in a grid-connected state, omega_m-DFIG4And ω_m-DFIG5The volatility of (2) is effectively suppressed; i is_r-DFIG4And I_r-DFIG5Gradually rising; p is_e-DFIG4And P_e-DFIG5And after closing for about 15s, the state is respectively recovered to a stable state (1.5MW and 0.8MW) before the fault. At the same time u_T2-abcAnd f_T2The voltage of the feeder line 2 is clamped and kept constant; delta theta_L62Held at 0 °; the current amplitude I at the interconnection switch L62_L62Quickly rises after closing, but does not generate an impact current phenomenon, and passes through about 15s, I_L62A relatively steady state is entered. Obviously, after the DFIG4 and the DFIG5 controlled by the ACS are synchronously switched on in cooperation with the L62, the two-machine island controlled by the ACS are safely recovered to a grid-connected state.

Scene 3, accessing an active feeder line by a multi-machine unplanned island: the method comprises the steps that F3 fault occurs in a feeder line 1, the wind speed at a DFIG1 position is 15m/s, the wind speed at a DFIG2 position is 11.8m/s, the wind speed at a DFIG3 position is 11.1m/s, the wind speed at a DFIG4 position is 12.1m/s, the wind speed at a DFIG5 position is 11.4m/s, a circuit breaker B1 and an L11 are controlled to trip by FA in 50s, the island total load is 3MW, and a contact switch L41 conducts closing through detecting a synchronous closing condition after the F3 fault occurs. Fig. 11 and 12 show changes in the electrical quantities prevailing on the grid side and the fan side, respectively, after an F1 fault has occurred.

Grid-connected island conversion: after 50s of bus power loss, the DFIG1, DFIG2, DFIG3, RMU1, RMU2, RMU3 tie line 1 and the load form a three-machine island. DFIG1, DFIG2 and DFIG3 automatically enter an island mode respectively under ACS control, and tie line 1 voltage u_T1-abcAmplitude fluctuation of about 12% of maximum two half-cycles occurs, and the waveform transition is stable; frequency f of the voltage of the tie line 1_T1A 50.48Hz spike occurred; DFIG1, DFIG2, and DFIG3 rotor speed (ω [. omega. ])_m-DFIG1、ω_m-DFIG2And ω_m-DFIG3) All appear low frequency fluctuationThe fluctuation range is not high; rotor current amplitude (I) for DFIG1, DFIG2, and DFIG3_r-DFIG1，I_r-DFIG2And I_r-DFIG3) All change immediately, no overcurrent occurs; electromagnetic power (P) of each of DFIG1, DFIG2, and DFIG3_e-DFIG1，P_e-DFIG2And P_e-DFIG3) All change rapidly, and the total electromagnetic power (P) of the three fans_C＝P_e-DFIG1+P_e-DFIG2+P_e-DFIG3) Quickly matched with 3MW island load. It can be seen that DFIG1, DFIG2 and DFIG3 under ACS control enter a multi-island mode seamlessly respectively.

Remote synchronization process: after the DFIG1, the DFIG2 and the DFIG3 enter the island mode with unbalanced power, u_T1-abcThe amplitude of the signal is kept stable; omega_m-DFIG1、ω_m-DFIG2And omega_m-DFIG3The volatility is weakened; i is_r-DFIG1，I_r-DFIG2And I_r-DFIG3Shows a trend towards unity; the DFIG1, the DFIG2 and the DFIG3 automatically distribute P according to the total load of the 3MW island_e-DFIG1，P_e-DFIG2And P_e-DFIG3；P_CA relatively stable state is always maintained. And f_T1Kept fluctuating around 50.1Hz, so that the voltage across the interconnection switch L41 has a phase error Δ θ_L41Gradually approaching 0. It is clear that DFIG1, DFIG2, and DFIG3 tri-island under ACS control are automatically creating remote contemporaneous conditions.

Island grid connection process: the STU at the interconnection switch L41 receives the SFI message immediately after the tripping of the B1 and the L11, judges that the fault does not occur on the interconnection line 1 through peer-to-peer communication with the adjacent STU, and then immediately controls the interconnection switch L41 to be switched on when detecting a synchronization condition at 54.7 s. When the interconnection switch L41 is switched on to the active feeder line 3 to which the DFIG4 and the DFIG5 are connected, the DFIG1, the DFIG2, and the DFIG3 are immediately brought into a grid-connected state, ω is_m-DFIG1、ω_m-DFIG2And ω_m-DFIG3The wave property is effectively suppressed, omega_m-DFIG4And ω_m-DFIG5Is slightly impacted; i is_r-DFIG1，I_r-DFIG2And I_r-DFIG3Recovery with uniform fluctuation, especially I_r-DFIG2And I_r-DFIG3Large amplitude fluctuations occur during the recovery process; i is_r-DFIG4And I_r-DFIG5Then a brief surge (about 5s) occurs after L41 is switched on, followed by a subsequent recovery of stability; p_e-DFIG1，P_e-DFIG2And P_e-DFIG3Exhibit a similar trend of variation, P, to the corresponding rotor current_e-DFIG2And P_e-DFIG3The volatility in the grid connection recovery process is more than P_e-DFIG1；P_e-DFIG4And P_e-DFIG5After L41 was switched on, it received a certain shock, but it also recovered its stability within 5 s. Approximately 25 seconds after L41 closes, DFIG1, DFIG2, and DFIG3 all enter a steady state. At the same time u_T1-abcAnd f_T1The voltage of the feeder line 3 is clamped and kept constant; delta theta_L41Keeping a 0-degree state; the current amplitude I at the interconnection switch L41_L41Rises rapidly, experiences slight fluctuations before reaching steady state, and does not experience current surges. Obviously, after the three-machine island controlled by the ACS, namely DFIG1, DFIG2 and DFIG3, is synchronously closed with L41, the three-machine island is safely recovered to a grid-connected state, and after the three-machine island is subjected to short and limited impact, DFIG4 and DFIG5 are rapidly recovered to a stable state.

Simulation experiment results show that: after the FA isolation feeder fails, the single or multiple double-fed fans under different wind speed conditions can realize seamless grid connection/island mode conversion under ACS control, and continuously supply power to local partial loads; in the island process, the ACS performs poor frequency control and power imbalance so that synchronous conditions at a remote interconnection switch are automatically met; the interconnection switch is switched on by detecting the synchronous condition on site after the FA isolation fault, so that the double-fed fan under the ACS control can realize safe grid connection without establishing an additional communication system with a power distribution network, and the double-fed fan in the active feeder line is not seriously impacted after the double-fed fan under the ACS control is connected with the power distribution network in an isolated island mode. In addition, the doubly-fed wind turbine under the ACS control experiences a short-time island during the coordination with the FA, which on one hand is beneficial to solving the problem of the power quality of the long-time island of the doubly-fed wind turbine, and on the other hand, the traditional unidirectional power supply recovery mechanism from the feeder to the load is upgraded to a bidirectional power supply recovery mechanism from the DG and the feeder to the load respectively. Therefore, the ACS and the coordination technology disclosed by the invention enable the double-fed fan and the FA to be compatible with each other without splitting and restarting the double-fed fan.

The above description is only an embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive of changes or substitutions within the technical scope of the present invention, and therefore, the scope of the present invention should be determined by the scope of the claims.

Claims

1. A DFIG adaptive control strategy and a coordination method compatible with feeder automation are characterized in that: the method comprises the following steps: firstly, a double-fed fan self-adaptive control method which can seamlessly switch a double-fed fan grid-connected/isolated island control mode and create synchronous conditions at any remote interconnection switch is set based on a virtual synchronous machine control technology; secondly, under the condition of non-network-source communication, a coordination method for safely connecting a double-fed fan island controlled by ACS to the grid through any contact switch is set, and based on the coordination method, after the isolation switch trips to isolate faults, the double-fed fan can seamlessly enter an island mode and stably run, and meanwhile, synchronous closing conditions at any remote contact switch are created; and then the remote interconnection switch is synchronously switched on to enable the double-fed fan island to be connected to the grid again, and the double-fed fan is recovered to a stable state before the fault or enters a new stable state under the support of the grid voltage.

2. The feeder automation compatible DFIG adaptive control strategy and coordination method according to claim 1, wherein: the wind turbine control part of the self-adaptive control method of the double-fed wind turbine still adopts a basic control structure of a GE double-fed wind turbine, the GSC adopts a vector control strategy based on PLL synchronization to maintain the voltage stability of a direct current bus, aiming at RSC control of the control method, a group of DFIG novel virtual synchronous machine control structures are arranged, the DFIG novel virtual synchronous machine control structures comprise power control, damping control, droop control, voltage control and a current inner ring, the power control simulates the inertial response characteristic of a synchronous generator, and 1/(2H) is set_As) is a power control inertia element and K_AFor controlling the power of the scaling factor, wherein H_AControlling a virtual inertial time constant for the power; when the actual electromagnetic power output P_eWith mechanical workRate P_mWhen unbalance occurs, the angular frequency omega of the potential in the stator is adjusted through an inertia link and a proportion link_si(ii) a Angular frequency omega of potential in stator_siObtaining the control phase theta of the potential in the stator through an integral link_si，ω_bAt the fundamental angular frequency, ω_b100 pi; rotor excitation current phase θ_IrThe phase theta is controlled directly by the potential in the stator_siMinus rotor position angle theta_mObtained of θ_m＝∫ω_mdt，ω_mFor rotor electrical angular velocity, the power control algorithm is as follows:

the damping control simulates the mechanical damping of the synchronous generator and the action of a damping winding, and the internal frequency omega caused by the disturbance to the power grid during grid connection_siThe oscillation and the power oscillation are suppressed, and the off-grid process is equivalent to the direct tracking control of the island frequency; damping power P_DFrom angular frequency ω of potential in stator_siWith reference angular frequency of the grid

droop control simulates the droop characteristic of active power and frequency of a synchronous motor, and m is a droop coefficient omega_gFor feeding back the angular frequency on the stator side, the power is given a reference value

The torque is controlled and generated by a wind turbine, and delta P is an automatic frequency regulator; when in grid connection, because

the voltage control simulates the excitation principle of a synchronous generator, which is equivalent to an automatic voltage regulator and is based on a stator voltage amplitude reference value

G_QPR(s) represents a quasi-proportional resonant controller whose transfer function is expressed as:

in the formula, φ represents a three-phase a, b, c.

3. The DFIG adaptive control strategy and coordination method compatible with feeder automation of claim 1, wherein: the network-source communication-free coordination method comprises the following steps: firstly, the double-fed fan is controlled by ACS; secondly, the STU configuration checks the synchronization device at the tie switch then, the closing condition of the tie switch is set to: in the process of automatically creating a remote synchronous condition for a double-fed fan island under ACS control, after an STU at a contact switch confirms that an SFI message is received and a fault is judged not to be on a contact line, the contact switch is immediately controlled to be switched on by detecting the synchronous switching-on condition through a synchronous detection device, synchronous grid connection of the fan island is realized, at the moment, a phase difference in the switching-on condition of the contact switch is set to be zero, the double-fed fan controlled by the ACS has grid-connected/island double-mode operation capacity, the double-fed fan automatically adapts to island → grid-connected change after the contact switch is switched on, and grid-connected operation is recovered.