DC grid-connected double-fed wind power generation system with rotor-side energy storage and control method thereof

Abstract

The present invention relates to a DC grid-connected double-fed wind power generation system and control method with rotor-side energy storage. The rotor side of the double-fed wind generator is connected to an energy storage device via a rotor-side converter RSC, and the stator side of the double-fed wind generator is connected to a DC grid via a diode rectifier bridge; a control unit signal input terminal is connected to the signal output terminal of the current sensor, voltage sensor, and optical encoder, and the control unit controls the rotor-side converter RSC according to the rotor voltage reference value obtained by the PI adjustment unit, thereby controlling the charging and discharging of the energy storage device. The present invention can flexibly and effectively control the charging and discharging of the energy storage device.

Description

Technical Field

[0001] The invention relates to a direct current grid-connected double-fed wind power generation system with rotor-side energy storage and a control method thereof. Background Art

[0002] Developing new energy is an important measure to solve the energy crisis and achieve my country's carbon neutrality goal. Wind energy reserves are abundant and it is one of the new energy sources with the greatest development potential. Doubly-fed wind turbines (DFIG) have high power generation efficiency, small power converter capacity and low cost.

[0003] Due to the intermittent and unstable characteristics of wind power, energy storage is often used in wind power generation systems to smooth out wind power fluctuations and improve the stability of the power system. Energy storage connected to wind power generation systems usually requires additional equipment such as DC-DC converters for energy storage charge and discharge control. This additional equipment will increase system costs and increase the difficulty of control. Rotor-side energy storage uses the rotor-side converter RSC in the doubly-fed wind power generation system to connect the energy storage device, and controls the battery charge and discharge by controlling the RSC. Therefore, in rotor-side energy storage, the energy storage device can be directly connected to the wind power generation system without other equipment, which can save this part of the cost.

[0004] In a doubly-fed wind power generation system with rotor-side energy storage, the battery charge and discharge status depends on the magnitude and direction of the rotor-side slip power. Figure 1 As shown, when the wind power generation system is connected to the grid, the battery charging and discharging state cannot be flexibly controlled. This is because the stator voltage frequency can only be kept constant at the industrial frequency, and the synchronous speed is also a fixed value. The battery can only be charged when the speed is higher than the synchronous speed. The battery discharges when the speed is lower than the synchronous speed. It cannot be flexibly charged and discharged according to the battery's own state. Even if the wind speed is too low or too high, the battery discharge and charging current may exceed the maximum charge and discharge current allowed by the battery, affecting the battery life. Summary of the invention

[0005] The object of the present invention is to provide a DC grid-connected doubly-fed wind power generation system with rotor-side energy storage and a control method, which can flexibly and effectively control the charging and discharging of the energy storage device.

[0006] Based on the same invention purpose, the present invention has two independent technical solutions:

[0007] 1. A DC grid-connected doubly-fed wind power generation system with rotor-side energy storage, comprising a doubly-fed wind generator and an energy storage device, wherein the rotor side of the doubly-fed wind generator is connected to the energy storage device via a rotor-side converter RSC, and the stator side of the doubly-fed wind generator is connected to a DC grid via a diode rectifier bridge; and further comprising:

[0008] A current sensor and a voltage sensor, wherein the current sensor and the voltage sensor are used to detect the stator side current, the rotor side current and the stator side voltage of the doubly-fed wind generator respectively;

[0009] An optical encoder disk, the optical encoder disk is used to detect the rotor speed of the doubly-fed wind turbine generator;

[0010] A PI regulating unit, wherein the PI regulating unit is used to perform PI regulation on the stator flux and stator-side output power of the doubly-fed wind generator, and output a rotor voltage reference value of the doubly-fed wind generator;

[0011] A control unit, wherein a signal input terminal of the control unit is connected to the signal output terminals of the current sensor, the voltage sensor, and the optical encoder disk. The control unit controls the rotor-side converter RSC according to the rotor voltage reference value obtained by the PI adjustment unit, thereby controlling the charging and discharging of the energy storage device.

[0012] Furthermore, the control unit determines a current current reference value of the energy storage device according to current wind parameters and current energy storage device parameters; obtains a current stator voltage frequency reference value of the doubly-fed wind generator according to the current rotor speed and the current current reference value of the energy storage device; and obtains a rotor voltage reference value of the doubly-fed wind generator through PI adjustment of the PI adjustment unit according to the current stator voltage frequency reference value.

[0013] Furthermore, the control unit obtains a stator flux reference value and a stator side output power reference value based on a current stator voltage frequency reference value; the control unit calculates and obtains a current stator flux value and a stator side output power value based on current voltage and current values ​​of the doubly-fed wind turbine generator and the DC power grid.

[0014] Furthermore, the PI adjustment unit sequentially performs PI adjustment on the stator flux and the d-axis component of the rotor current of the doubly fed wind generator to obtain a reference value of the d-axis component of the rotor voltage; and sequentially performs PI adjustment on the stator side output power and the q-axis component of the rotor current of the doubly fed wind generator to obtain a reference value of the q-axis component of the rotor voltage.

[0015] Furthermore, the control unit implements PI regulation through a PI regulation algorithm.

[0016] Furthermore, the diode rectifier bridge is an uncontrollable diode rectifier bridge, so that the stator side of the doubly-fed wind generator outputs power unidirectionally, and the doubly-fed wind generator is in a super-synchronous power generation operation state or a sub-synchronous power generation operation state.

[0017] 2. A control method for the above-mentioned DC grid-connected doubly-fed wind power generation system with rotor-side energy storage, comprising the following steps:

[0018] Step 1: obtaining the stator and rotor side currents and the stator side voltage of the doubly-fed wind turbine generator through a current sensor and a voltage sensor; obtaining the rotor speed of the doubly-fed wind turbine generator through an optical encoder;

[0019] Step 2: Determine the current current reference value of the energy storage device according to the current wind force parameters and the current energy storage device parameters; obtain the current stator voltage frequency reference value according to the current rotor speed and the current current reference value of the energy storage device;

[0020] Step 3: According to the current stator voltage frequency reference value, obtain the rotor voltage reference value of the doubly-fed wind generator through PI regulation;

[0021] Step 4: According to the rotor voltage reference value, the control unit outputs a PMW signal to control the rotor-side converter RSC, thereby controlling the charging and discharging of the energy storage device.

[0022] Furthermore, in step 2, the current stator voltage frequency reference value is obtained by the following formula:

[0023]

[0024] Where n r is the rotor speed, P n is the number of motor pole pairs, f s is the stator voltage frequency reference value, P cus is the stator copper loss, P cur is the rotor copper loss, I b is the current reference value of the energy storage device, U b is the voltage reference value of the energy storage device, k s is the setting coefficient.

[0025] Further, in step 2, when the current charge amount of the energy storage device is within a normal range, a current current reference value of the energy storage device is determined so that the doubly-fed wind turbine generator tracks the maximum wind energy and operates in a power generation operation mode;

[0026] When the current charge of the energy storage device is lower than a normal range, a current current reference value of the energy storage device is determined so that the energy storage device is charged and the doubly-fed wind turbine generator is in a super-synchronous power generation operation state;

[0027] When the current charge amount of the energy storage device is higher than the normal range, the current current reference value of the energy storage device is determined, so that the energy storage device is discharged, and the doubly-fed wind turbine generator is in a subsynchronous power generation operation state.

[0028] Furthermore, step 3 includes the following steps:

[0029] Step 3.1: The control unit obtains a stator flux reference value and a stator side output power reference value according to a current stator voltage frequency reference value;

[0030] Stator flux reference value ψ s * Obtained by the following formula,

[0031]

[0032] In the formula, ψ s * is the stator flux reference value, u d is the DC grid voltage value, f s is the stator voltage frequency reference value;

[0033] Stator side output power reference value P S * Obtained by the following formula:

[0034] P S * =k s n r 2 f s +P cus

[0035] In the formula, k s is the setting coefficient, n r is the rotor speed, f s is the stator voltage frequency reference value, P cus is the stator copper loss;

[0036] Step 3.2: The PI adjustment unit performs PI adjustment on the stator flux and the d-axis component of the rotor current of the doubly fed wind generator in turn to obtain a reference value of the d-axis component of the rotor voltage; and performs PI adjustment on the stator side output power and the q-axis component of the rotor current of the doubly fed wind generator in turn to obtain a reference value of the q-axis component of the rotor voltage.

[0037] The present invention has the beneficial effects:

[0038] The rotor side of the doubly-fed wind generator of the present invention is connected to the energy storage device through the rotor side converter RSC, and the stator side of the doubly-fed wind generator is connected to the DC grid through the diode rectifier bridge; it also includes a PI adjustment unit, which outputs the rotor voltage reference value of the doubly-fed wind generator after PI adjustment by the PI adjustment unit; a control unit, the signal input end of the control unit is connected to the signal output end of the voltage sensor, the current sensor, and the optical encoder, and the control unit controls the rotor side converter RSC according to the rotor voltage reference value obtained by the PI adjustment unit, thereby controlling the charging and discharging of the energy storage device. The doubly-fed wind generator of the present invention is connected to the DC grid, and the stator voltage frequency does not need to be constant to the industrial frequency. The adjustability of the stator voltage frequency of the doubly-fed wind generator is utilized to flexibly and effectively control the charging and discharging of the energy storage device through the rotor side converter RSC, which has a simple structure, reasonable design, and effectively reduces costs. The present invention directly connects the energy storage device through the rotor side converter RSC, which can save the cost of the DC-DC converter, further reduce the system cost, and can directly play the role of flexibly adjusting the power generation without multiple energy conversions. The energy storage device of the present invention is connected through the rotor side. When the wind is insufficient, the energy storage device can discharge to drive the DFIG unit to generate electricity. When the wind is excessive, the excess wind energy is absorbed to charge the energy storage device. While improving the utilization rate of wind energy, the problem of wind power fluctuation can be solved directly on-site, which is more direct and more efficient. At the same time, due to the presence of the battery energy storage device on the rotor side, the rotor side is not affected when the DC bus fails. The energy storage device can be used to establish initial excitation to drive the wind turbine to generate electricity. The doubly-fed wind turbine generator set is used as a black start power supply, so that the DFIG can start automatically and help the wind power microgrid to achieve black start, thereby improving the reliability of the system. The DC grid-connected doubly-fed wind power generation system with rotor-side energy storage of the present invention has the advantages of low cost, high reliability, simple control, and convenient start-up.

[0039] The control unit of the present invention determines the current current reference value of the energy storage device according to the current wind force parameters and the current energy storage device parameters; obtains the current stator voltage frequency reference value of the doubly fed wind generator according to the current rotor speed and the current current reference value of the energy storage device; obtains the rotor voltage reference value of the doubly fed wind generator through PI adjustment by the PI adjustment unit according to the current stator voltage frequency reference value; the control unit obtains the stator flux reference value and the stator side output power reference value according to the current stator voltage frequency reference value; the control unit calculates the current stator flux value and the stator side output power value according to the current voltage and current values ​​of the doubly fed wind generator and the DC power grid; the PI adjustment unit sequentially performs PI adjustment on the stator flux and the d-axis component of the rotor current of the doubly fed wind generator to obtain the rotor voltage d-axis component reference value; sequentially performs PI adjustment on the stator side output power and the q-axis component of the rotor current of the doubly fed wind generator to obtain the rotor voltage q-axis component reference value. The present invention obtains the rotor voltage reference value through the above method, and then controls the rotor side converter RSC to control the charging and discharging of the energy storage device, taking into account the current wind force (parameters) and the current energy storage device (parameters) requirements, and controlling the charging and discharging of the energy storage device more flexibly and effectively. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a schematic diagram of an existing AC grid-connected double-fed wind power generation system;

[0041] Figure 2 It is a circuit principle diagram of the DC grid-connected double-fed wind power generation system of the present invention;

[0042] Figure 3 It is a control principle diagram of the DC grid-connected double-fed wind power generation system of the present invention. DETAILED DESCRIPTION

[0043] The present invention is described in detail below in conjunction with the various embodiments shown in the accompanying drawings, but it should be noted that these embodiments are not limitations of the present invention, and any equivalent transformations or substitutions in functions, methods, or structures made by ordinary technicians in the field based on these embodiments are all within the scope of protection of the present invention.

[0044] Embodiment 1:

[0045] DC grid-connected doubly-fed wind power generation system with rotor-side energy storage

[0046] like Figure 2As shown, it includes a doubly-fed wind turbine generator DFIG and an energy storage device. In this embodiment, the energy storage device adopts an energy storage battery 1, but it is not limited to battery energy storage, and also includes energy storage devices such as supercapacitors and solid-state batteries. The battery energy storage is composed of 70-200 battery cells connected in series, with a voltage range of 200V to 600V and a battery current range of 20Ah-300Ah. The rotor side of the doubly-fed wind turbine is connected to the energy storage device via the rotor-side converter RSC 4, and the stator side of the doubly-fed wind turbine is connected to the DC power grid via the diode rectifier bridge 8. In this embodiment, the diode rectifier bridge is an uncontrollable diode rectifier bridge, so that the stator side of the doubly-fed wind turbine outputs power unidirectionally, and the doubly-fed wind turbine is in a super-synchronous power generation operation state or a sub-synchronous power generation operation state.

[0047] Also includes:

[0048] The current sensor 5 and the voltage sensor 7 are used to detect the stator side current i of the double-fed wind turbine generator. sa 、i sb 、i sc , rotor side current i ra 、i rb 、i rc and stator side voltage u sa 、u sb 、u sc The DC grid can also be equipped with a voltage sensor to collect the DC grid voltage u d .

[0049] The optical code disk 6 is used to detect the rotor speed n of the doubly-fed wind turbine generator. r ;

[0050] A PI regulating unit (PI regulator) 3, wherein the PI regulating unit is used to output a rotor voltage reference value of the doubly-fed wind generator after PI regulation;

[0051] The control unit 2, in this embodiment, adopts a DSP control unit, the signal input end of the control unit is connected to the signal output end of the voltage sensor, the current sensor, and the optical encoder, and the control unit controls the rotor side converter RSC 4 according to the rotor voltage reference value obtained by the PI adjustment unit, thereby controlling the charging and discharging of the energy storage device.

[0052] The control unit determines a current current reference value of the energy storage device according to current wind parameters and current energy storage device parameters; and obtains a current stator voltage frequency reference value of the doubly-fed wind generator according to the current rotor speed and the current current reference value of the energy storage device.

[0053] The control unit obtains a stator flux reference value and a stator side output power reference value according to a current stator voltage frequency reference value; the control unit calculates and obtains a current stator flux value and a stator side output power value according to current voltage and current values ​​of the doubly-fed wind turbine generator and the DC power grid.

[0054] The PI adjustment unit sequentially performs PI adjustment on the stator flux and the d-axis component of the rotor current of the doubly fed wind generator to obtain a reference value of the d-axis component of the rotor voltage; and sequentially performs PI adjustment on the stator side output power and the q-axis component of the rotor current of the doubly fed wind generator to obtain a reference value of the q-axis component of the rotor voltage.

[0055] The PI regulation unit may be hardware, and the control unit is in communication connection with the PI regulation unit; or, the PI regulation unit may be a PI regulation algorithm, and the control unit implements PI regulation through the PI regulation algorithm.

[0056] Embodiment 2:

[0057] Control method of DC grid-connected doubly-fed wind power generation system with rotor-side energy storage

[0058] like Figure 3 As shown, the following steps are included:

[0059] Step 1: Obtain the stator side current i of the doubly-fed wind turbine generator through a current sensor and a voltage sensor sa 、i sb 、i sc , rotor side current i ra 、i rb 、i rc and stator side voltage u sa 、u sb 、u sc ; Obtain the rotor speed n of the doubly fed wind turbine generator by the optical encoder r .

[0060] Figure 3 In, θ s represents the stator position angle, θ r represents the rotor position angle, θ sl represents the slip angle, ω r represents the rotor angular velocity.

[0061] Step 2: Determine the current reference value of the energy storage device according to the current wind force parameters and the current energy storage device parameters; obtain the current stator voltage frequency reference value according to the current rotor speed and the current current reference value of the energy storage device.

[0062] Determine the current reference value of the energy storage device:

[0063] When the current charge of the energy storage device is within a normal range, the current current reference value of the energy storage device is determined, so that the doubly-fed wind generator tracks the maximum wind energy and operates in a power generation operation mode; when the current charge of the energy storage device is lower than the normal range, the current current reference value of the energy storage device is determined, so that the energy storage device is charged, and the doubly-fed wind generator is in a super-synchronous power generation operation state; when the current charge of the energy storage device is higher than the normal range, the current current reference value of the energy storage device is determined, so that the energy storage device is discharged, and the doubly-fed wind generator is in a sub-synchronous power generation operation state.

[0064] When the energy storage battery is discharged, the DFIG is in a subsynchronous power generation state, and when the energy storage battery is charged, the DFIG is in a supersynchronous power generation state. When the rotor speed is lower than the synchronous speed, the DFIG runs subsynchronously, the slip rate is positive, and the slip power flows from the battery to the rotor, so the battery discharges; when the rotor speed is higher than the synchronous speed, the DFIG runs supersynchronously, the slip rate is negative, and the slip power flows out from the rotor side, so the battery charges. Moreover, the battery charge and discharge control should match the battery's own needs, and should be able to be flexibly controlled according to its charge and discharge needs. For example, if the battery has too much power, it needs to be discharged, and if the power is insufficient, it needs to be charged.

[0065] Get the current stator voltage frequency reference value:

[0066] The stator and rotor are both based on the motor convention. In this article, the number of motor pole pairs is Pn, so the slip rate expression can be calculated by the speed:

[0067]

[0068] Where n s , n r ——synchronous speed, rotor speed;

[0069] f s ——Stator frequency.

[0070] Under the dual motor convention, in a doubly fed wind turbine generator, the output power of the wind turbine is:

[0071] P v =-0.5ρSv 3 C p

[0072] P v =P M -sP M

[0073] Where P V ——fan output power;

[0074] P M ——Electromagnetic power.

[0075] Taking into account the copper loss of the stator and rotor, the stator and rotor sides have the following power relationships:

[0076] P M +P cus =P s

[0077] -sP M +P cur =P r

[0078] Where Ps, Pr - the power flowing out of the stator and rotor sides, referred to as stator and rotor power;

[0079] P cus , P cur ——Copper loss of stator and rotor,

[0080]

[0081] From this, the relationship between the stator and rotor power can be obtained as follows:

[0082] P r -P cur =-s(P s -P cus )

[0083] Energy exchange between the energy storage battery and the rotor side can be expressed as follows, taking into account the rotor side converter loss:

[0084] P r +P RSC =U b I b

[0085] Where P RSC ——Rotor-side converter losses;

[0086] U b , I b ——Battery voltage and current.

[0087] In summary, the current stator voltage frequency reference value f s Obtained by the following formula:

[0088]

[0089] Where n r is the rotor speed, P n is the number of motor pole pairs, f s is the stator voltage frequency reference value, P cus is the stator copper loss, P cur is the rotor copper loss, I bis the current reference value of the energy storage device, U b is the voltage reference value of the energy storage device, k s is the setting coefficient.

[0090] Step 3: According to the current stator voltage frequency reference value, a rotor voltage reference value of the doubly-fed wind generator is obtained through PI regulation.

[0091] Step 3.1: The control unit obtains a stator flux reference value and a stator side output power reference value according to a current stator voltage frequency reference value.

[0092] Stator flux reference value ψ s * Obtained by the following formula,

[0093]

[0094] In the formula, ψ s * is the stator flux reference value, u d is the DC grid voltage value, f s is the stator voltage frequency reference value.

[0095] Stator side output power reference value P S * Obtained by the following formula:

[0096] P S * =k s n r 2 f s +P cus

[0097] In the formula, k s is the setting coefficient, n r is the rotor speed, f s is the stator voltage frequency reference value, P cus is the stator copper loss.

[0098] The control unit calculates and obtains the current stator flux value and the stator-side output power value according to the current voltage and current values ​​of the double-fed wind turbine generator and the DC power grid.

[0099] Magnetic flux equation:

[0100] ψ s =L s i sd +L m i rd

[0101] Where ψs——stator flux;

[0102] Ls, Lm——stator self-inductance and mutual inductance between stator and rotor in dq coordinate system;

[0103] Isd——d-axis component of stator current;

[0104] Ird——d-axis component of rotor current.

[0105] Under the dual motor convention, the stator flux is d-axis oriented, and the stator power equation is:

[0106]

[0107] Where Ps——stator power;

[0108] Usd, Usq——d-axis component and q-axis component of stator voltage;

[0109] Isq——q-axis component of stator current.

[0110] Step 3.2: The PI adjustment unit sequentially performs PI adjustment on the stator flux and the d-axis component of the rotor current of the doubly-fed wind turbine generator, and obtains the reference value i of the d-axis component of the rotor current by adjusting the stator flux PI. rd * , by adjusting the PI of the rotor current d-axis component, the rotor voltage d-axis component reference value u is obtained rd * ; The stator side output power and the rotor current q-axis component of the doubly fed wind turbine are sequentially PI-regulated, and the rotor current q-axis component reference value i is obtained by adjusting the stator side output power PI. rq * , by adjusting the PI of the rotor current q-axis component, the rotor voltage q-axis component reference value u is obtained rq * .

[0111] Step 4: Set the rotor voltage d-axis component reference value u rd * , rotor voltage q-axis component reference value u rq * After coordinate transformation, the rotor voltage reference value u is obtained ra * 、u rb * 、u rc * Based on the rotor voltage reference value, the control unit outputs a PMW signal to control the rotor-side converter RSC, thereby controlling the charging and discharging of the energy storage device.

[0112] The series of detailed descriptions listed above are only specific descriptions of feasible implementation methods of the present invention. They are not intended to limit the scope of protection of the present invention. Any equivalent implementation methods or changes that do not deviate from the technical spirit of the present invention should be included in the scope of protection of the present invention.

[0113] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-restrictive in all respects, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present invention.

Claims

1. A DC grid-connected doubly-fed wind power generation system with rotor-side energy storage, comprising a doubly-fed wind generator and an energy storage device, wherein the rotor side of the doubly-fed wind generator is connected to the energy storage device via a rotor-side converter RSC, characterized in that: The stator side of the double-fed wind turbine generator is bridge-connected to a DC grid via diode rectification, and the system further comprises: A current sensor and a voltage sensor, wherein the current sensor and the voltage sensor are used to detect the stator side current, the rotor side current and the stator side voltage of the doubly-fed wind generator respectively; An optical encoder disk, the optical encoder disk is used to detect the rotor speed of the doubly-fed wind generator; A PI regulating unit, the PI regulating unit is used to perform PI regulation on the stator flux and stator-side output power of the doubly-fed wind generator, and output a rotor voltage reference value of the doubly-fed wind generator; A control unit, wherein a signal input terminal of the control unit is connected to the signal output terminals of the current sensor, the voltage sensor, and the optical encoder, and the control unit controls the rotor-side converter RSC according to the rotor voltage reference value obtained by the PI adjustment unit, thereby controlling the charging and discharging of the energy storage device; The control unit determines the current current reference value of the energy storage device according to the current wind force parameters and the current energy storage device parameters; obtains the current stator voltage frequency reference value of the doubly-fed wind generator according to the current rotor speed and the current current reference value of the energy storage device; obtains the rotor voltage reference value of the doubly-fed wind generator through PI adjustment by the PI adjustment unit according to the current stator voltage frequency reference value; Wherein, when the current charge amount of the energy storage device is within a normal range, a current current reference value of the energy storage device is determined so that the doubly-fed wind turbine generator tracks the maximum wind energy and operates in a power generation operation mode; When the current charge of the energy storage device is lower than a normal range, a current current reference value of the energy storage device is determined so that the energy storage device is charged and the doubly-fed wind turbine generator is in a super-synchronous power generation operation state; When the current charge amount of the energy storage device is higher than the normal range, the current current reference value of the energy storage device is determined, so that the energy storage device is discharged, and the doubly-fed wind turbine generator is in a subsynchronous power generation operation state.

2. The DC grid-connected doubly-fed wind power generation system with rotor-side energy storage according to claim 1, characterized in that: The control unit obtains a stator flux reference value and a stator side output power reference value according to a current stator voltage frequency reference value; the control unit calculates and obtains a current stator flux value and a stator side output power value according to current voltage and current values ​​of the doubly-fed wind turbine generator and the DC power grid.

3. The DC grid-connected doubly-fed wind power generation system with rotor-side energy storage according to claim 2, characterized in that: The PI adjustment unit sequentially performs PI adjustment on the stator flux and the d-axis component of the rotor current of the doubly fed wind generator to obtain a reference value of the d-axis component of the rotor voltage; and sequentially performs PI adjustment on the stator side output power and the q-axis component of the rotor current of the doubly fed wind generator to obtain a reference value of the q-axis component of the rotor voltage.

4. The DC grid-connected doubly-fed wind power generation system with rotor-side energy storage according to claim 1, characterized in that: The control unit is communicatively connected with the PI regulation unit.

5. The DC grid-connected doubly-fed wind power generation system with rotor-side energy storage according to claim 1, characterized in that: The diode rectifier bridge is an uncontrollable diode rectifier bridge, so that the stator side of the doubly-fed wind generator outputs power in one direction, and the doubly-fed wind generator is in a super-synchronous power generation operation state or a sub-synchronous power generation operation state.

6. A control method for the DC grid-connected doubly-fed wind power generation system with rotor-side energy storage as claimed in claim 1, characterized in that: The steps include: Step 1: obtaining the stator side current, rotor side current and stator side voltage of the doubly-fed wind generator through a current sensor and a voltage sensor; obtaining the rotor speed of the doubly-fed wind generator through an optical encoder; Step 2: Determine the current current reference value of the energy storage device according to the current wind force parameters and the current energy storage device parameters; obtain the current stator voltage frequency reference value according to the current rotor speed and the current current reference value of the energy storage device; Step 3: According to the current stator voltage frequency reference value, obtain the rotor voltage reference value of the doubly-fed wind generator through PI regulation; Step 4: According to the rotor voltage reference value, the control unit outputs a PWM signal to control the rotor-side converter RSC, thereby controlling the charging and discharging of the energy storage device.

7. The control method according to claim 6, characterized in that: In step 2, the current stator voltage frequency reference value is obtained by the following formula: Where n r is the rotor speed, P n is the number of motor pole pairs, f s is the stator voltage frequency reference value, P cur is the rotor copper loss, I b is the current reference value of the energy storage device, U b is the voltage reference value of the energy storage device, k s is the setting coefficient, P RSC is the rotor side converter loss.

8. The control method according to claim 6, characterized in that: Step 3 includes the following steps: Step 3.1: The control unit obtains a stator flux reference value and a stator side output power reference value according to a current stator voltage frequency reference value; Stator flux reference value ψ s * Obtained by the following formula, In the formula, ψ s * is the stator flux reference value, u d is the DC grid voltage value, f s is the stator voltage frequency reference value; Stator side output power reference value P S * Obtained by the following formula: P S * =k s n r 2 f s +P cus In the formula, k s is the setting coefficient, n r is the rotor speed, f s is the stator voltage frequency reference value, P cus is the stator copper loss; Step 3.2: The PI adjustment unit performs PI adjustment on the stator flux and the d-axis component of the rotor current of the doubly fed wind generator in turn to obtain a reference value of the d-axis component of the rotor voltage; and performs PI adjustment on the stator side output power and the q-axis component of the rotor current of the doubly fed wind generator in turn to obtain a reference value of the q-axis component of the rotor voltage.

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