Method for starting a wind power plant with a diode-based grid connection based on active power-frequency coupling

Abstract

The application discloses a wind power diode sending-out system starting method based on active power-frequency coupling network construction, only needs to install a small-capacity energy storage device on a wind turbine generator, and through the collaborative control of a receiving end MMC converter and the wind turbine generator, can realize the smooth starting of the offshore wind farm diode sending-out system, and the sending end alternating current power grid can maintain the active power-frequency coupling electrical characteristics, significantly reduces the engineering construction cost, guarantees the operation stability of the system, and has remarkable economic benefits and good application prospect.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of new energy power generation, and particularly relates to a wind power diode sending-out system starting method based on active power-frequency coupling network construction. BACKGROUND

[0002] At present, offshore wind power is developing towards the deep sea, and the flexible direct current transmission technology based on the modular multilevel converter (MMC) topology has the advantages of low manufacturing difficulty, low system loss, high waveform quality, etc., and has a very good application prospect in long-distance power collection and transmission. However, in the large-capacity offshore wind farm flexible direct current transmission system, the offshore converter station adopting the MMC topology structure has a large volume and weight, and its construction and transportation cost is very high, which is not conducive to the on-grid parity of offshore wind power. Compared with the MMC topology structure, the adoption of the diode topology can significantly reduce the volume and weight of the equipment, thereby reducing the construction cost of the offshore converter station. However, the adoption of the diode topology by the sending-end converter station will cause the uncontrollability of the sending-end alternating current power grid and the difficulty in system starting, etc., and the offshore wind turbine needs to adopt a network construction type control strategy.

[0003] Since the voltage of the offshore alternating current power grid and the direct current voltage of the direct current transmission system jointly determine the transmission power of the diode converter, the existing wind turbine network type control method for the diode rectification system generally adopts an active power-voltage coupled network type control strategy, however, this control strategy is significantly different from the active power-frequency coupling characteristics of the traditional synchronous generator set, and the system stability is not clear when multiple machines are running. If the wind turbine adopts an active power-frequency coupled network type control strategy, the system starting process will face the problem of difficult coordination of the power at both ends of the diode converter. Therefore, it is necessary to study the corresponding wind power diode sending-out system starting method for the wind turbine adopting the active power-frequency coupled control network type. SUMMARY

[0004] The purpose of the present application is to overcome the problem of difficult coordination of the power at both ends of the diode converter in the system starting process when the wind turbine adopts the active power-frequency coupled network type control strategy, and to propose a wind power diode sending-out system starting method based on active power-frequency coupling network construction. Only a small-capacity energy storage device needs to be installed on one wind turbine, and through the collaborative control of the receiving-end MMC converter and the wind turbine, the smooth starting of the offshore wind farm diode sending-out system can be realized, and the sending-end alternating current power grid can maintain the active power-frequency coupled electrical characteristics, thereby significantly reducing the engineering construction cost while ensuring the operation stability of the system.

[0005] In order to achieve the above-mentioned application purpose, the method adopts the following technical scheme:

[0006] The application discloses a wind power diode sending-out system starting method based on active-frequency coupling network construction, and has the characteristics that the wind power diode sending-out system based on active-frequency coupling network construction comprises: energy storage batteries, a bidirectional DC / DC converter, a wind power generator, a wind turbine side converter, a wind turbine DC bus, a wind turbine grid-side converter, a wind turbine booster transformer, a wind turbine circuit breaker, a sending terminal coupling transformer, a sending terminal diode converter, a receiving terminal MMC converter, a starting resistor and a receiving terminal coupling transformer.

[0007] The energy storage batteries are connected to the wind turbine DC bus through the bidirectional DC / DC converter, the wind power generator is connected to the wind turbine side converter, the wind turbine DC bus and the wind turbine grid-side converter are connected to the offshore AC power grid, the voltage level of the offshore AC bus is raised through the wind turbine booster transformer, the offshore AC bus is connected through the wind turbine circuit breaker, the voltage level matched with the DC power transmission system is raised through the sending terminal coupling transformer after the offshore AC bus is gathered through a plurality of wind turbine circuit breakers, the DC is rectified through the sending terminal diode converter, the AC is inverted through the receiving terminal MMC converter after the DC is transmitted to the receiving terminal, and the starting resistor and the receiving terminal coupling transformer are connected to the receiving terminal AC power grid.

[0008] The wind turbine grid-side converter adopts the network construction type control strategy based on active-frequency coupling, is responsible for maintaining the stability of the sending terminal AC power grid, the wind turbine side converter adopts the constant DC bus voltage and reactive power control strategy, is responsible for maintaining the stability of the wind turbine DC bus voltage, and the receiving terminal MMC converter adopts the constant DC bus voltage and reactive power control strategy, adjusts the DC bus voltage of the DC power transmission system according to the angle frequency of the sending terminal AC power grid, and maintains the active power balance in the system.

[0009] The wind power diode sending-out system starting method based on active-frequency coupling network construction has the characteristics that:

[0010] The system starting process starts, first, the starting resistor is used to charge the receiving terminal MMC converter;

[0011] The receiving terminal MMC converter is unlocked, and the DC bus voltage of the DC power transmission system is adjusted to the rated value;

[0012] The energy storage batteries and the bidirectional DC / DC converter are started, and the wind turbine DC bus voltage is adjusted to the rated value;

[0013] The wind turbine grid-side converter is started, the offshore AC bus voltage is established through the network construction type control strategy based on active-frequency coupling;

[0014] The offshore AC bus voltage is gradually increased to the rated value, so that the sending terminal diode converter has the conduction condition;

[0015] The sending end AC grid angular frequency is transmitted to the receiving end MMC converter through communication, and the DC bus voltage of the DC power transmission system is adjusted according to the sending end AC grid angular frequency;

[0016] The fan machine side converter and the wind turbine are started, and the output active power of the fan is gradually increased.

[0017] Further, the fan grid side converter adopts a grid-forming control strategy based on active-power-frequency coupling, is responsible for establishing the sending end AC grid voltage, and maintains the stability of the sending end AC grid during operation, and the active power reference value is given according to the maximum power tracking module; the specific implementation mode of the grid-forming control strategy of the fan grid side converter is as follows:

[0018] In the active-power-frequency coupling control module, the reference phase θ g is calculated according to the following method:

[0019] θ g (k+1)=∫ω g (k+1)dt

[0020]

[0021] Wherein, θ g (k+1) is the reference phase of the next sampling period, ω g (k+1) is the angular frequency of the next sampling period, ω g (k) is the angular frequency of the current sampling period, ω n is the rated angular frequency, P gref is the active power reference value, P g (k) is the active power of the current sampling period, J is the virtual rotor moment of inertia, D p is the active damping coefficient.

[0022] In the reactive-power-voltage coupling control module, the d-axis voltage reference value u gdref is calculated according to the following method:

[0023]

[0024] Wherein, u gdref (k+1) is the d-axis voltage reference value of the next sampling period, |U g (k) | is the voltage amplitude of the current sampling period, U ref is the voltage amplitude reference value, Q gref is the reactive power reference value, Q g (k) is the reactive power of the current sampling period, K is the virtual excitation coefficient, D q is the reactive damping coefficient.

[0025] Further, the receiving MMC converter adopts a constant DC bus and reactive power control strategy, and the DC bus voltage reference value U dc2ref According to the sending end AC power grid angular frequency calculation, the specific implementation manner is as follows.

[0026] I dcref = F PI1 (s)(I g -I gref )

[0027]

[0028] U dc2ref = U dc2N -F PI2 (s)(I dcref -I dc )

[0029]

[0030] Wherein, I dcref is a DC current reference value, I dc is a DC current, ω gref is a sending end power grid angular frequency reference value, ω g is a sending end power grid angular frequency, U dc2ref is a DC bus voltage reference value, U dc2N is a DC bus voltage rated value, F PI1 (s) is a transfer function of an angular frequency PI controller, k p1 is a proportional coefficient, k i1 is an integral coefficient, F PI2 (s) is a transfer function of a DC current PI controller, k p2 is a proportional coefficient, and k i2 is an integral coefficient.

[0031] The beneficial effects of the present application are:

[0032] By adopting the technical scheme of the present application, only a small-capacity energy storage device needs to be installed on a wind turbine generator, and through the collaborative control of the receiving MMC converter and the wind turbine generator, the smooth startup of the offshore wind farm through the diode sending-out system can be realized, the sending end AC power grid can maintain the active-frequency coupling electrical characteristics, the engineering construction cost is significantly reduced, the operation stability of the system is ensured, and the present application has significant economic benefits and good application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 The present application is based on the active-frequency coupling network-based wind power diode sending-out system startup method flow chart.

[0034] Figure 2 A typical topology diagram of the wind power generation system based on active-frequency coupling network and sending out through diode according to the present application.

[0035] Figure 3 A specific example system principle diagram of the wind turbine side converter control method according to the present application.

[0036] Figure 4 A specific example system principle diagram of the wind turbine side converter control method according to the present application.

[0037] Figure 5 A specific example system principle diagram of the receiving end MMC converter control method according to the present application. DETAILED DESCRIPTION

[0038] In order to describe the present application more specifically, the technical solutions of the present application are described in detail below in combination with the drawings and specific embodiments.

[0039] In the embodiment of the present application, the wind power generation system based on active-frequency coupling network and sending out through diode is shown in Figure 2 , which comprises an energy storage battery 1, a bidirectional DC / DC converter 2, a wind turbine 3, a wind turbine side converter 4, a wind turbine DC bus 5, a wind turbine grid side converter 6, a wind turbine booster transformer 7, a wind turbine circuit breaker 8, a sending end coupling transformer 9, a sending end diode converter 10, a receiving end MMC converter 11, a starting resistor 12 and a receiving end coupling transformer 13.

[0040] In the embodiment of the present application, the energy storage battery 1 is connected to the wind turbine DC bus 5 through the bidirectional DC / DC converter 2, the wind turbine 3 is connected to the wind turbine DC bus 5 through the wind turbine side converter 4, the wind turbine DC bus 5 and the wind turbine grid side converter 6 are connected to the offshore AC power grid, the voltage level of the offshore AC bus is boosted through the wind turbine booster transformer 7, the offshore AC bus is connected through the wind turbine circuit breaker 8, the offshore AC bus is connected to the sending end coupling transformer 9 through the wind turbine circuit breaker 8, the voltage level is boosted to match the voltage level of the DC power transmission system, the DC is rectified through the sending end diode converter 10, the AC is inverted through the receiving end MMC converter 11, and the receiving end AC power grid is connected through the starting resistor 12 and the receiving end coupling transformer 13.

[0041] In the embodiment of the present application, the specific process of the starting method of the wind power generation system based on active-frequency coupling network and sending out through diode is shown in Figure 1 .

[0042] In the first step, the receiving end MMC converter 11 is charged through the starting resistor 12, and when the receiving end MMC converter 11 has the unlocking condition, the receiving end MMC converter 11 is unlocked, and the DC bus voltage of the DC power transmission system is adjusted to the rated value.

[0043] Second step, start the energy storage battery 1 and the bidirectional DC / DC converter 2, adjust the fan DC bus voltage to the rated value through the control strategy of the bidirectional DC / DC converter; wherein the bidirectional DC / DC converter 2 adopts the constant DC bus voltage control strategy.

[0044] Third step, start the fan grid-side converter 6, close the fan circuit breaker 8, establish the offshore AC grid voltage through the grid-forming control strategy based on active-power-frequency coupling of the fan grid-side converter 6; in the embodiment of the application, the grid-forming control strategy based on active-power-frequency coupling adopted by the fan grid-side converter 6 has a control system as shown in the figure, which includes: a maximum power tracking module 101, an active-power-frequency coupling control module 102, a reactive-power-voltage coupling control module 103, a Park transformation module 104, a voltage outer loop control module 105, a current inner loop control module 106, a Park inverse transformation module 107, and a modulation module 108. Figure 3

[0045] In the active-power-frequency coupling control module 102, the reference phase θ g (k+1) is calculated according to the following method:

[0046] θ g (k+1) = ∫ω g (k+1)dt

[0047]

[0048] wherein θ g (k+1) is the reference phase of the next sampling period, ω g (k+1) is the angular frequency of the next sampling period, ω g (k) is the angular frequency of the current sampling period, ω n is the rated angular frequency, P gref is the active power reference value, P g (k) is the active power of the current sampling period, J is the virtual rotor moment of inertia, and D p is the active damping coefficient.

[0049] In the reactive-power-voltage coupling control module 103, the d-axis voltage reference value u gdref (k+1) is calculated according to the following method:

[0050]

[0051] wherein u gdref (k+1) is the d-axis voltage reference value of the next sampling period, |U g (k)| is the voltage amplitude of the current sampling period, U ref is the voltage amplitude reference value, and Q gref ​Q is a reactive power reference value g (k) is a reactive power in the current sampling period, K is a virtual excitation coefficient, and D q is a reactive power damping coefficient.

[0052] The implementation of the voltage outer loop control module 105 is as follows:

[0053]

[0054] wherein: F PI3 (s) is a transfer function of a PI controller, k p3 is a proportional coefficient, k i3 is an integral coefficient, i gdref , i gqref correspond to d-axis and q-axis components of a current vector I gdqref , u gdref , u gqref correspond to d-axis and q-axis components of a voltage vector reference value U gdqref , u gd , u gq correspond to d-axis and q-axis components of a voltage vector reference value U gdq .

[0055] The implementation of the current inner loop control module 106 is as follows:

[0056]

[0057] wherein: F PI4 (s) is a transfer function of a PI controller, k p4 is a proportional coefficient, k i4 is an integral coefficient, u vdref , u vqref correspond to d-axis and q-axis components of a voltage vector U vdqref , u gd , u gq correspond to d-axis and q-axis components of a voltage vector U gdq , i gd , i gq correspond to d-axis and q-axis components of a current vector I gdq , ω g is an angular frequency of a grid voltage, L g is a filter inductance.

[0058] Step 4: gradually increase the offshore AC grid voltage to the rated value, so that the sending-end diode converter 10 has a conduction condition;

[0059] In the fifth step, the angle frequency of the sending end AC power grid is transmitted to the receiving end MMC converter 11 through communication, and the DC bus voltage of the DC power transmission system is adjusted according to the angle frequency of the sending end AC power grid; in the embodiment of the application, the control system of the receiving end MMC converter 11 is shown in the figure, which comprises a DC current reference value calculation module 301, a DC voltage reference value calculation module 302, a DC bus voltage and reactive power control module 303, a differential mode current control module 304, a Park inverse transformation module 305, a common mode current control module 306, a bridge arm voltage calculation module 307 and a modulation module 308. Figure 5

[0060] The specific implementation of the DC current reference value calculation module 301 is as follows:

[0061] I dcref = F PI1 (s)(ω g -ω gref )

[0062]

[0063] Wherein, I dcref is the DC current reference value, ω gref is the reference value of the angle frequency of the sending end power grid, ω g is the angle frequency of the sending end power grid, F PI1 (s) is the transfer function of the angle frequency PI controller, k p1 is the proportional coefficient, and k i1 is the integral coefficient.

[0064] The specific implementation of the DC voltage reference value calculation module 302 is as follows:

[0065] U dc2ref = U dc2N -F PI2 (s)(I dcref -I dc )

[0066]

[0067] Wherein, I dcref is the DC current reference value, I dc is the DC current, U dc2ref is the DC bus voltage reference value, U dc2N is the rated value of the DC bus voltage, F PI2 (s) is the transfer function of the DC current PI controller, k p2 is the proportional coefficient, and k i2 is the integral coefficient.

[0068] ​Step 6, start the fan side of the converter 4 and wind turbine 3, gradually increase the output active power of the fan. The fan side of the converter 4 adopts the constant DC bus voltage and reactive power control strategy, and its control system is shown in Figure 4 Figure 2, including: rotor position observation module 201, Park transformation module 202, DC bus voltage and reactive power control module 203, current inner loop control module 204, Park inverse transformation module 205, modulation module 206.

[0069] The implementation of the DC bus voltage and reactive power control module 203 is as follows:

[0070]

[0071] Where: F PI5 (s) is the transfer function of the PI controller, k p5 is the proportional coefficient, k i5 is the integral coefficient, i sdref , i sqref correspond to the d-axis and q-axis components of the voltage vector U sdqref , U dcref is the fan DC bus voltage reference value, U dc is the fan DC bus voltage, Q sref is the reactive power reference value, Q s is the reactive power.

[0072] The implementation of the current inner loop control module 204 is as follows:

[0073]

[0074] Where: F PI6 (s) is the transfer function of the PI controller, k p6 is the proportional coefficient, k i6 is the integral coefficient, u sdref , u sqref correspond to the d-axis and q-axis components of the voltage vector U sdqref , i sd , i sq correspond to the d-axis and q-axis components of the current vector I sdq , ω r is the rotor angular frequency, L s is the fan stator inductance, and Ψ is the rotor permanent magnet flux linkage.

[0075] Step 7, at this time, the first fan containing energy storage equipment in the wind farm has completed grid connection, and the subsequent wind turbines in the wind farm continue to be connected to the grid one by one, and the system startup process is completed.

[0076] The above description of the embodiments is to assist those of ordinary skill in the art to understand and apply the present application. Those skilled in the art can easily make various modifications to the above embodiments and apply the general principles described herein to other embodiments without creative labor. Therefore, the present application is not limited to the above embodiments, and improvements and modifications made to the present application by those skilled in the art based on the disclosure of the present application are within the scope of protection of the present application.

Claims

1. A method for starting a wind power diode sending-out system based on active-frequency coupling network construction, characterized in that, The wind power diode sending-out system based on active-frequency coupling network construction comprises: energy storage batteries, a bidirectional DC / DC converter, a wind turbine, a wind turbine side converter, a wind turbine DC bus, a wind turbine grid-side converter, a wind turbine booster transformer, a wind turbine circuit breaker, a sending-end coupling transformer, a sending-end diode converter, a receiving-end MMC converter, a starting resistor and a receiving-end coupling transformer. The energy storage batteries are connected to the wind turbine DC bus through the bidirectional DC / DC converter, the wind turbine is connected to the offshore AC power grid through the wind turbine side converter, the wind turbine DC bus and the wind turbine grid-side converter, and is boosted to the voltage level of the offshore AC bus through the wind turbine booster transformer, and is connected to the offshore AC bus through the wind turbine circuit breaker; after being collected at the offshore AC bus, the multiple wind turbine circuit breakers are boosted to the voltage level matched with the DC power transmission system through the sending-end coupling transformer, and are rectified to DC through the sending-end diode converter, and are converted to AC through the receiving-end MMC converter after being transmitted to the receiving end, and are connected to the receiving-end AC power grid through the starting resistor and the receiving-end coupling transformer. The wind turbine grid-side converter adopts the network construction control strategy based on active-frequency coupling, and is responsible for maintaining the stability of the sending-end AC power grid; the wind turbine side converter adopts the constant DC bus voltage and reactive power control strategy, and is responsible for maintaining the stability of the wind turbine DC bus voltage; and the receiving-end MMC converter adopts the constant DC bus voltage and reactive power control strategy, adjusts the DC bus voltage of the DC power transmission system according to the angle frequency of the sending-end AC power grid, and maintains the active power balance in the system. The wind power diode sending-out system based on active-frequency coupling network construction comprises: energy storage batteries, a bidirectional DC / DC converter, a wind turbine, a wind turbine side converter, a wind turbine DC bus, a wind turbine grid-side converter, a wind turbine booster transformer, a wind turbine circuit breaker, a sending-end coupling transformer, a sending-end diode converter, a receiving-end MMC converter, a starting resistor and a receiving-end coupling transformer. The system starting process is started, the starting resistor is used to charge the receiving-end MMC converter first; The receiving-end MMC converter is unlocked, and the DC bus voltage of the DC power transmission system is adjusted to the rated value; The energy storage batteries and the bidirectional DC / DC converter are started, and the wind turbine DC bus voltage is adjusted to the rated value; The wind turbine grid-side converter is started, the offshore AC grid voltage is established through the network construction control strategy based on active-frequency coupling; The offshore AC grid voltage is gradually increased to the rated value, and the sending-end diode converter has the conduction condition; The angle frequency of the sending-end AC power grid is transmitted to the receiving-end MMC converter through communication, and the DC bus voltage of the DC power transmission system is adjusted according to the angle frequency of the sending-end AC power grid; The wind turbine side converter and the wind turbine are started, and the output active power of the wind turbine is gradually increased. The receiving MMC converter adopts a fixed DC bus and reactive power control strategy, and the DC bus voltage reference value U dc2ref According to the sending end AC power grid angular frequency calculation, the specific implementation manner is as follows: I dcref = F PI1 (s)(ω g - ω gref ) U dc2ref = U dc2N - F PI2 (s) (I dcref - I dc ) wherein: I dcref is the DC current reference value, I dc is the DC current, ω gref is the sending end power grid angular frequency reference value, ω g is the sending end power grid angular frequency, U dc2ref is the DC bus voltage reference value, U dc2N is the DC bus voltage rated value, F PI1 (s) is the transfer function of the angular frequency PI controller, k p1 is the proportional coefficient, k i1 is the integral coefficient, F PI2 (s) is the transfer function of the DC current PI controller, k p2 is the proportional coefficient, k i2 is the integral coefficient.

2. The wind power diode sending-out system based on active-frequency coupling network construction according to claim 1, wherein the wind turbine grid-side converter adopts the network construction control strategy based on active-frequency coupling, is responsible for establishing the sending-end AC grid voltage, and maintains the stability of the sending-end AC power grid in the running process, and the active power reference value is given according to the maximum power tracking module; the specific implementation mode of the network construction control strategy of the wind turbine grid-side converter is as follows: ​ In the active-frequency coupling control module, the reference phase θ is calculated according to the following method g : θ g (k+1) = ∫ω g (k+1)dt where θ g (k+1) is the reference phase of the next sampling period, ω g (k+1) is the angular frequency of the next sampling period, ω g (k) is the angular frequency of the current sampling period, ω n is the rated angular frequency, P gref is the active power reference value, P g (k) is the active power of the current sampling period, J is the virtual rotor moment of inertia, D p is the active damping coefficient; In the reactive-voltage coupling control module, the d-axis voltage reference value u is calculated according to the following method gdref : wherein, u gdref (k+1) is the d-axis voltage reference value of the next sampling period, |U g (k) is the voltage amplitude of the current sampling period, U ref is the voltage amplitude reference value, Q gref is the reactive power reference value, Q g (k) is the reactive power of the current sampling period, K is the virtual excitation coefficient, D q is the reactive power damping coefficient.

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