Control method of DC series permanent magnet wind power system based on phase-shifted full-bridge

Abstract

The invention discloses a control method for a DC series permanent magnet wind power system based on a phase-shifted full bridge, and belongs to the technical field of power generation, power transformation or power distribution. The invention is composed of a phase-shifted full bridge and n permanent magnet wind turbines in terms of hardware, and includes a phase-shifted full bridge double-loop control, a wind turbine weak magnetic control, and a wind turbine pitch control in terms of control, and is suitable for solving the problem of overvoltage and overmodulation on the DC side of the DC series permanent magnet wind power system when the wind speed between units is unbalanced; when the wind speed between units is unbalanced but the input side voltage of the phase-shifted full bridge is greater than its lower limit voltage, weak magnetic control is adopted for the wind turbine with saturated DC side voltage, and double-loop control is adopted for the phase-shifted full bridge, and the two are combined to adjust the series loop current within the threshold range; when the wind speed is unbalanced and the input side voltage of the phase-shifted full bridge reaches its lower limit voltage, on the basis of the above control, the pitch control of the unit corresponding to the maximum value of the DC side voltage is added to adjust the series loop current within the threshold range.

Description

Technical Field

[0001] The present invention relates to the technical field of power generation, power transformation or power distribution, and in particular to a control method for a DC series permanent magnet wind power system based on a phase-shifted full-bridge. Background Art

[0002] Compared with AC transmission, HVDC has the advantages of low power loss and low reactive power requirements. In order to achieve its transmission voltage level, the series topology has been widely used in long-distance wind farms in recent years. The series structure connects the output ends of wind turbines in series to form a high-voltage output and reduce the construction cost of the step-up substation. The study of the series structure of DC wind turbines and their control strategy is of great significance.

[0003] The coupling characteristics between series-connected wind turbines increase the difficulty of controlling the system. In series-connected units, the maximum output power of a single wind turbine will vary with the wind speed at its location, and the DC bus voltage of the unit will vary with its output power. When the wind speed difference between the units exceeds a certain range, overvoltage and overmodulation problems will occur on the DC side of the wind turbine, which will not only reduce the maximum wind energy capture of the wind turbine, but also bring safety issues to the wind turbine itself.

[0004] There are three main types of existing control schemes for series-connected wind turbines. The first type is to add a DC-DC converter to the DC side of each wind turbine, and control the DC side voltage of the wind turbine to a fixed value through the converter, thereby avoiding overvoltage and overmodulation on the DC side of the unit. However, this scheme increases additional hardware investment and increases the construction cost of the wind turbine. The second type is to add an energy storage device to the DC side of each wind turbine, absorb or release energy through the energy storage device, and balance the output power of each wind turbine, so as to achieve the purpose of controlling the DC side voltage of all wind turbines to be equal, but this scheme still increases the construction cost of the wind turbine. The third type is to reduce the output power of the wind turbine running at high wind speed in the series unit, thereby increasing the proportion of the output power of the wind turbine running at low wind speed in the total output power of the series unit, and controlling its DC side voltage within a safe range. Obviously, this will reduce the total output power of the series unit.

[0005] In summary, the control technology of DC series wind power system is difficult to take into account the important indicators of safe and efficient operation and low-cost construction when the wind speed between units is unbalanced. The present invention aims to propose a control method of DC series permanent magnet wind power system based on phase-shifted full bridge to overcome the above defects. Summary of the invention

[0006] The purpose of the embodiment of the present invention is to provide a control method for a DC series permanent magnet wind power system based on a phase-shifted full-bridge, so as to solve the overvoltage and overmodulation problems on the DC side of the wind turbine when the wind speed is unbalanced between the units, while taking into account the invention's purpose of high-efficiency operation and low-cost construction of the units.

[0007] According to a first aspect of an embodiment of the present invention, a control method for a DC series permanent magnet wind power system based on a phase-shifted full bridge is provided. The system is composed of a phase-shifted full bridge and n permanent magnet wind turbines. The DC side of each wind turbine is connected in series to increase the DC bus voltage and then connected to the input side of the phase-shifted full bridge. The output side of the phase-shifted full bridge is connected to an onshore converter.

[0008] The method comprises the following steps:

[0009] The wind turbine controls its q-axis current through the converter to adjust the permanent magnet motor rotor speed, thereby achieving the maximum wind energy tracking of each unit. At the same time, in order to avoid overvoltage and overmodulation on the DC side of the wind turbine when the wind speed is unbalanced, there are two modes:

[0010] A1: The voltage at the input side of the phase-shifted full-bridge is greater than its lower limit voltage u pmin When the wind turbine is in operation, the inverter controls the d-axis current to adjust the back electromotive force of the motor stator winding, and the phase-shifted full bridge adjusts the series current i of the unit through dual-loop control. dc The size of i dc Less than its upper limit i max , greater than its lower limit i min ;

[0011] A2: The voltage on the input side of the phase-shifted full-bridge reaches its lower limit voltage u pmin When the wind turbine is in operation, the inverter controls the d-axis current to adjust the back electromotive force of the motor stator winding, and the phase-shifted full bridge reduces the series current i of the unit through dual-loop control. dc The value of i dc Less than its upper limit i max The wind turbine corresponding to the maximum DC side voltage is controlled by pitch control to reduce the current lower limit i min value, making it less than i dc .

[0012] Optionally, A1 specifically includes:

[0013] When the wind speed between the units is unbalanced but the input voltage of the phase-shifted full-bridge is greater than its lower limit voltage u pmin When the DC side voltage is not saturated, the converter adjusts its d-axis current i d = 0, for wind turbines with saturated DC voltage, the converter adjusts i through weak magnetic control dThe size of the motor stator winding is reduced to reduce the back electromotive force, thereby avoiding over-modulation of the DC side of the wind turbine. In order to achieve weak magnetic control, a phase-shifted full bridge is required to adjust the series current i of the wind turbine through dual-loop control. dc Less than its upper limit i max At the same time, in order to avoid overvoltage on the DC side of the wind turbine, the phase-shifted full bridge should also adjust i through dual-loop control dc Greater than its lower limit i min .

[0014] Optionally, A2 specifically includes:

[0015] When the wind speed between the units is unbalanced and the input voltage of the phase-shifted full-bridge reaches its lower limit voltage u pmin When the DC side voltage is not saturated, the converter adjusts its d-axis current i d = 0, for wind turbines with saturated DC voltage, the converter adjusts i through weak magnetic control d The size of the motor stator winding is reduced to reduce the back electromotive force, thereby avoiding over-modulation of the DC side of the wind turbine. In order to achieve weak magnetic control, a phase-shifted full bridge is required to adjust the series current i of the wind turbine through dual-loop control. dc Less than its upper limit i max At the same time, in order to avoid overvoltage on the DC side of the unit, i dc It should also be greater than its lower limit i min However, in this case, the phase-shifted full bridge cannot be controlled by dual loops. dc Increase so that it is greater than i min Therefore, variable pitch control is adopted for the wind turbine corresponding to the maximum DC side voltage to reduce i min value, making it smaller than the series loop current i dc , thereby avoiding overvoltage on the DC side of the wind turbine.

[0016] Optionally, the specific method of the dual-loop control of the phase-shifted full bridge is:

[0017] The phase-shifted full bridge adopts dual-loop control. The outer loop is controlled by the maximum voltage on the DC side of the wind turbine, and the reference value is the preset value u ref1 The feedback value is the maximum value of the DC side voltage of the wind turbine, and the inner loop controlled value is the series current i of the unit. dc , the reference value is the outer loop output, and the feedback value is i dc , the inner loop output is the phase shift ratio D of the phase-shifted full bridge;

[0018] Under the condition that the output power of the series wind turbine is constant, the phase shift ratio D increases, the input side voltage of the phase shift full bridge decreases, and the series current i dc Increases, the DC side voltage of the wind turbine decreases accordingly; the phase shift ratio D decreases, the input side voltage of the phase shift full bridge increases, i dcThe DC side voltage of the wind turbine increases accordingly. The dual-loop control of the phase-shifted full-bridge adjusts i dc Greater than its lower limit i min , which can avoid overvoltage on the DC side of all wind turbines, and at the same time adjust the i through the dual-loop control of the phase-shifted full bridge dc Less than its upper limit i max , in order to achieve the wind turbine weak magnetic control on the series circuit current i dc to avoid over-modulation of the DC side of the wind turbine.

[0019] Optionally, the specific method for variable pitch control of the wind turbine generator set is:

[0020] The controlled object of wind turbine pitch control is the pitch angle of the wind turbine corresponding to the maximum value of DC side voltage, and the reference value is the preset value u ref2 , the feedback value is the DC side voltage of the wind turbine;

[0021] By increasing the pitch angle of the wind turbine, reducing its wind energy capture and lowering its output power, the lower limit of the series current of the unit can be reduced. min To series current i dc The following can avoid overvoltage on the DC side of the wind turbine.

[0022] Optional, upper limit of series loop current i max The lower limit of the series circuit current i min The expression is:

[0023]

[0024] where p m is the maximum output power of the wind turbine, U m is the maximum operating voltage of the wind turbine, ψ f is the permanent magnet flux of the motor, L s is the synchronous inductance of the motor stator.

[0025] Optionally, the input side voltage lower limit u of the phase-shifted full bridge pmin The expression is:

[0026]

[0027] U T is the output side voltage of the phase-shifted full-bridge, which is controlled by the onshore converter to be a constant value, and N is the ratio of the number of turns of the output side winding of the phase-shifted full-bridge to the number of turns of the input side winding.

[0028] According to a second aspect of an embodiment of the present invention, a control device for a DC series permanent magnet wind power system based on a phase-shifted full bridge is provided. The system is composed of a phase-shifted full bridge and n permanent magnet wind turbines. The DC side of each wind turbine is connected in series to increase the DC bus voltage and then connected to the input side of the phase-shifted full bridge. The output side of the phase-shifted full bridge is connected to an onshore converter.

[0029] The control device comprises:

[0030] The control module is used to execute the wind turbine to control its q-axis current through the converter to adjust the motor rotor speed, thereby achieving the maximum wind energy tracking of each unit. At the same time, in order to avoid overvoltage and overmodulation on the DC side of the wind turbine when the wind speed is unbalanced, there are two mode modules:

[0031] The series current control module is used to execute the phase shift full bridge input side voltage greater than its lower limit voltage u pmin When the wind turbine is in operation, the inverter controls the d-axis current to adjust the back electromotive force of the motor stator winding, and the phase-shifted full bridge adjusts the series current i of the unit through dual-loop control. dc The size of the max , greater than its lower limit i min ;

[0032] The series current lower limit adjustment module is used to execute the phase-shifted full-bridge input side voltage to reach its lower limit voltage u pmin When the wind turbine is in operation, the inverter controls the d-axis current to adjust the back electromotive force of the motor stator winding, and the phase-shifted full bridge reduces the series current i of the unit through dual-loop control. dc value, making it less than its upper limit i max The wind turbine corresponding to the maximum DC side voltage is controlled by variable pitch to reduce the current lower limit i min value, making it less than i dc .

[0033] According to a second aspect of an embodiment of the present invention, there is provided an electronic device, including:

[0034] one or more processors;

[0035] A memory for storing one or more programs;

[0036] When the one or more programs are executed by the one or more processors, the one or more processors implement the method as described in the first aspect.

[0037] According to a second aspect of an embodiment of the present invention, there is provided a computer-readable storage medium on which computer instructions are stored. When the instructions are executed by a processor, the steps of the method described in the first aspect are implemented.

[0038] The technical solution provided by the embodiments of the present invention may have the following beneficial effects:

[0039] In the method, the q-axis current of the wind turbine is controlled to adjust the rotor speed, thereby improving the utilization rate of wind energy by the turbine and achieving maximum wind energy tracking of the turbine.

[0040] The unit adjusts the d-axis current through weak magnetic control, weakens the rotor magnetic field, and thereby reduces the value of the back electromotive force, so that the q-axis current of the unit can still be controlled under unbalanced wind speed conditions.

[0041] The phase-shifted full bridge uses dual-loop control to adjust the series current i dc value, making it less than i max , thereby satisfying the weak magnetic control of the unit and its series current i dc Requirements

[0042] The phase-shifted full bridge uses dual-loop control to adjust the series current i dc value, making it greater than i min , thereby avoiding overvoltage on the DC side of the unit.

[0043] The unit corresponding to the maximum DC side voltage is controlled by variable pitch to reduce the wind energy absorption of the unit, thereby reducing the lower limit of the series current i min value, making it less than i dc , which solves the problem that when the voltage on the input side of the phase-shifted full-bridge reaches its limit value, the phase-shifted full-bridge cannot increase i through dual-loop control. dc , so that it is greater than i min problem.

[0044] The control solution proposed by the present invention does not introduce additional power electronic devices, thereby reducing the construction cost of the wind turbine.

[0045] The control scheme proposed in the present invention reduces the amount of wind abandoned in a DC series wind power system when the wind speeds between units are unbalanced.

[0046] It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0048] Figure 1 An overall structural diagram of a DC series wind power system is shown according to an exemplary embodiment.

[0049] Figure 2The invention is a control block diagram of a control method of a DC series permanent magnet wind power system based on a phase-shifted full-bridge according to an exemplary embodiment.

[0050] Figure 3 is a diagram of series current simulation results under a control method according to an exemplary embodiment.

[0051] Figure 4 It is a diagram of simulation results of DC side voltage of series-connected wind turbines under a control method according to an exemplary embodiment.

[0052] Figure 5 It is a diagram showing the simulation results of the speed of a permanent magnet motor of a series unit under a control method according to an exemplary embodiment. DETAILED DESCRIPTION

[0053] Exemplary embodiments will be described in detail herein, examples of which are shown in the accompanying drawings. When the following description refers to the drawings, the same numbers in different drawings represent the same or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Instead, they are merely examples of devices and methods consistent with some aspects of the present invention as detailed in the appended claims.

[0054] The terms used in the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The singular forms "a", "the" and "the" used in the present invention and the appended claims are also intended to include plural forms unless the context clearly indicates other meanings. It should also be understood that the term "and / or" used herein refers to and includes any or all possible combinations of one or more associated listed items.

[0055] It should be understood that although the terms first, second, third, etc. may be used in the present invention to describe various information, these information should not be limited to these terms. These terms are only used to distinguish the same type of information from each other. For example, without departing from the scope of the present invention, the first information may also be referred to as the second information, and similarly, the second information may also be referred to as the first information. Depending on the context, the word "if" as used herein may be interpreted as "at the time of" or "when" or "in response to determining".

[0056] Figure 1 is an overall structural diagram of a DC series permanent magnet wind power system based on a phase-shifted full-bridge according to an exemplary embodiment, which shows the topological structure of the system proposed by the present invention, such as Figure 1 As shown, the system consists of a phase-shifted full bridge and n permanent magnet wind turbines. The DC side of each wind turbine is connected in series to increase the DC bus voltage, and then connected to the input side of the phase-shifted full bridge. The output side of the phase-shifted full bridge is connected to the onshore converter.

[0057] Figure 2 The present invention is a control block diagram of a control method of a DC series type permanent magnet wind power system based on a phase-shifted full-bridge according to an exemplary embodiment. The control method of the DC series type permanent magnet wind power system based on a phase-shifted full-bridge proposed by the present invention may include the following steps:

[0058] The wind turbine controls its q-axis current through the converter to adjust the permanent magnet motor rotor speed, thereby achieving the maximum wind energy tracking of each unit. At the same time, in order to avoid overvoltage and overmodulation on the DC side of the wind turbine when the wind speed is unbalanced, there are two modes:

[0059] A1: The voltage at the input side of the phase-shifted full-bridge is greater than its lower limit voltage u pmin When the wind turbine is in operation, the inverter controls the d-axis current to adjust the back electromotive force of the motor stator winding, and the phase-shifted full bridge adjusts the series current i of the unit through dual-loop control. dc The size of i dc Less than its upper limit i max , greater than its lower limit i min ;

[0060] A2: The voltage on the input side of the phase-shifted full-bridge reaches its lower limit voltage u pmin When the wind turbine is in operation, the inverter controls the d-axis current to adjust the back electromotive force of the motor stator winding, and the phase-shifted full bridge reduces the series current i of the unit through dual-loop control. dc The value of i dc Less than its upper limit i max The wind turbine corresponding to the maximum DC side voltage is controlled by pitch control to reduce the current lower limit i min value, making it less than i dc .

[0061] The following is a detailed description of the derivation and control scheme of the above parameters;

[0062] In the case of unbalanced wind speed between units, in order to avoid over-modulation of the DC side of the unit, the series current i dc Greater than its upper limit i max , the derivation of this conclusion and i max The expression is as follows:

[0063] In steady state, the stator voltage equation of the permanent magnet synchronous motor in the dq coordinate system is:

[0064]

[0065] R s is the stator resistance of the motor; u d 、u qare the direct-axis and quadrature-axis components of the motor stator voltage; i d 、i q are the direct-axis and quadrature-axis components of the motor stator current; L d , L q are the direct-axis and quadrature-axis components of the motor stator inductance; ω s is the synchronous angular velocity of the motor; f is the permanent magnet flux of the motor.

[0066] The maximum phase voltage amplitude that the converter can output is u max ,u max The DC side voltage u of the wind turbine dc Limitation, linear modulation strategy At the same time, the maximum current value of the motor i max Subject to its rated current I N Limitation. The voltage limit and current limit of the permanent magnet synchronous motor satisfy the following relationship:

[0067]

[0068] Where u s is the voltage vector magnitude, i s is the current vector magnitude.

[0069] Based on equations (1) and (2), ignoring the influence of stator resistance, under the condition that the current limit circle can contain the voltage limit circle, the limiting relationship between the wind turbine current and the DC side voltage in the dq coordinate system is:

[0070]

[0071] In formula (3), i d 、i q is the stator current i s The d-axis component, q-axis component, u dc is the DC side voltage of the wind turbine; L d , L q are the direct-axis and quadrature-axis components of the motor stator inductance; ω s is the synchronous angular velocity of the motor; f is the permanent magnet flux of the motor.

[0072] According to formula (3), the quadrature axis current i of the motor is q When its current limit includes voltage limit, its quadrature axis current i q The maximum value of i qmax The expression is:

[0073]

[0074] In formula (4), U DCis the sum of the DC side voltages of the series-connected wind turbines, i.e., the input side voltage u of the phase-shifted full bridge p , P e is the output power of the wind turbine. Ignoring the loss, this power is the output power of the wind turbine. s is the sum of the output power of the series-connected wind turbines, i dc is the series loop current.

[0075] For surface mounted synchronous motors,

[0076] L q =L d =L s (5)

[0077] In formula (5), L s is the motor stator synchronous inductance.

[0078] There is a maximum electromagnetic torque T emax The expression is:

[0079]

[0080] In formula (5), N p is the number of rotor pole pairs.

[0081] According to equations (4), (5), and (6), the maximum electromagnetic power P that the wind turbine can currently absorb is emax The electromagnetic power P absorbed by the e The following relations should be satisfied:

[0082]

[0083] In formula (7), w m is the mechanical angular velocity of the motor.

[0084] From formula (7), we can get that in order to avoid over-modulation of the DC side of the wind turbine, the series loop current i dc The following conditions should be met:

[0085]

[0086] In the case of unbalanced wind speed between units, in order to avoid overvoltage on the DC side of the unit, the series current i dc Less than its upper limit i min , the derivation of this conclusion is i min The expression is as follows:

[0087] For output power P e , the series circuit current is i dc The DC side voltage u of the wind turbine dc The following conditions should be met:

[0088]

[0089] In formula (9), U m It is the maximum safe voltage of the wind turbine.

[0090] From formula (9), we can get that in order to avoid overvoltage on the DC side of the wind turbine, the series loop current i dc The following conditions should be met:

[0091]

[0092] In formula (10), p m It is the maximum output power of a single wind turbine in the series unit.

[0093] Combining equations (8) and (10), we can obtain that under the weak magnetic control strategy, in order to avoid overmodulation and overvoltage on the DC side of the wind turbine due to wind speed imbalance, the series current i dc Its upper limit value i max With its lower limit i min The expression is:

[0094]

[0095] where p m is the maximum output power of a single wind turbine in the series unit, U m is the maximum safe voltage of the wind turbine, ψ f is the permanent magnet flux of the motor, L s is the synchronous inductance of the motor stator.

[0096] In one embodiment, A1 specifically includes: when the wind speed between the units is unbalanced but the input voltage of the phase-shifted full-bridge is greater than its lower limit voltage u pmin When the DC side voltage is not saturated, the converter adjusts its d-axis current i d = 0, for wind turbines with saturated DC voltage, the converter adjusts i through weak magnetic control d The size of the motor stator winding is reduced to reduce the back electromotive force, thereby avoiding over-modulation of the DC side of the wind turbine. In order to achieve weak magnetic control, a phase-shifted full bridge is required to adjust the series current i of the wind turbine through dual-loop control. dc Less than its upper limit i max At the same time, in order to avoid overvoltage on the DC side of the wind turbine, the phase-shifted full bridge should also adjust i through dual-loop control dc Greater than its lower limit i min .

[0097] The specific method of the dual-loop control of the phase-shifted full bridge is:

[0098] The phase-shifted full bridge adopts dual-loop control. The outer loop is controlled by the maximum voltage on the DC side of the wind turbine, and the reference value is the preset value u ref1 The feedback value is the maximum value of the DC side voltage of the wind turbine, and the inner loop controlled value is the series current i of the unit. dc , the reference value is the outer loop output, and the feedback value is i dc , the inner loop output is the phase shift ratio D of the phase-shifted full bridge;

[0099] Under the condition that the output power of the series wind turbine is constant, the phase shift ratio D increases, the input side voltage of the phase shift full bridge decreases, and the series current i dc Increases, the DC side voltage of the wind turbine decreases accordingly; the phase shift ratio D decreases, the input side voltage of the phase shift full bridge increases, i dc The DC side voltage of the wind turbine increases accordingly. The dual-loop control of the phase-shifted full-bridge adjusts i dc Greater than its lower limit i min , which can avoid overvoltage on the DC side of all wind turbines, and at the same time adjust the i through the dual-loop control of the phase-shifted full bridge dc Less than its upper limit i max , in order to achieve the weak magnetic control of wind turbines dc to avoid over-modulation of the DC side of the wind turbine.

[0100] In the case of unbalanced wind speed between units, overvoltage and overmodulation problems may occur on the DC side. The overvoltage phenomenon will cause irreversible damage to the electronic devices of the unit, and the overmodulation phenomenon will affect the unit's control of its q-axis current, thereby causing the rotor speed of the permanent magnet motor in the unit to operate in a non-optimal speed range, which will ultimately reduce the unit's absorption of wind energy. Therefore, the present invention proposes to solve the above problem through A1, and the phase-shifted full-bridge controls its input side voltage, thereby controlling the series current of the wind turbine unit, avoiding overvoltage and overmodulation on the DC side of the unit, and achieving safe operation of each unit under unbalanced wind conditions while achieving its maximum absorption of wind energy. At the same time, the series voltage of the unit is increased to the level of high-voltage direct current transmission through the phase-shifted full-bridge, reducing the energy loss of electricity transmitted from the sea to the shore.

[0101] The output side filter inductor L of the phase-shifted full-bridge f Analysis shows that the voltage at the end connected to the output side of the phase-shifted full bridge is U T , U T is the phase-shifted full-bridge output voltage, which is controlled by the onshore converter to be a fixed value, and the voltage at the end connected to the rectifier diode is N times u p or 0, N is the ratio of the secondary turns to the primary turns of the phase-shifted full-bridge inductor, u p is the phase-shift full-bridge input voltage, which is controlled by the phase-shift full-bridge. T >Nu p When the filter inductor L f The current decreases when UT <Nu p When the current of the filter inductor Lf increases, due to U T is a constant value, so when the output power is constant, the inductor current is a constant value, and it is obvious that there must be U T <Nu p , in order to control the inductor current to a constant value, U T =Nu p When p The value is defined as the lower limit of the input voltage u pmin

[0102] Therefore, the control range of the voltage on the input side of the phase-shifted full-bridge is u p >=u pmin , when the input power is constant, if the input side voltage u p Reach its lower limit voltage u pmin , the phase-shifted full bridge cannot reduce the input side voltage u through dual-loop control p , thereby increasing its input side current, that is, the series current i dc The value of dc Less than its lower limit i min , then overvoltage will occur on the DC side of some units;

[0103] In order to solve the above problems, the present invention proposes control scheme A2. According to the fact that the wind energy absorbed by the wind turbine decreases with the increase of the pitch angle, it is proposed that the unit corresponding to the maximum DC side voltage can reduce the wind energy absorbed by it through pitch control, thereby reducing the lower limit of the series current i min value, making it smaller than the series current i dc , avoid overvoltage on the DC side of the unit;

[0104] In one embodiment, A2 specifically includes: when the wind speed between the units is unbalanced and the input voltage of the phase-shifted full-bridge reaches its lower limit voltage u pmin When the DC side voltage is not saturated, the converter adjusts its d-axis current i d = 0, for wind turbines with saturated DC voltage, the converter adjusts i through weak magnetic control d The size of the motor stator winding is reduced to reduce the back electromotive force, thereby avoiding over-modulation of the DC side of the wind turbine. In order to achieve weak magnetic control, a phase-shifted full bridge is required to adjust the series current i of the wind turbine through dual-loop control. dc Less than its upper limit i max , and to avoid overvoltage on the DC side, i dc It should also be greater than its lower limit i min However, in this case, the phase-shifted full bridge cannot be controlled by dual loops. dc Increase so that it is greater than i minTherefore, variable pitch control is adopted for the wind turbine corresponding to the maximum DC side voltage to reduce i min value, making it smaller than the series loop current i dc , thereby avoiding overvoltage on the DC side of the wind turbine.

[0105] The specific method of variable pitch control of the wind turbine generator set is as follows:

[0106] The controlled object of wind turbine pitch control is the pitch angle of the wind turbine corresponding to the maximum value of DC side voltage, and the reference value is the preset value u ref2 , the feedback value is the DC side voltage of the wind turbine;

[0107] By increasing the pitch angle of the wind turbine, reducing its wind energy capture and lowering its output power, the lower limit value of the turbine current i can be reduced. min To the series current i dc The following can avoid overvoltage on the DC side of the wind turbine.

[0108] Phase-shifted full-bridge input side voltage u p Reach its lower limit voltage u pmin After that, the phase-shifted full bridge cannot increase the series current i through dual-loop control. dc If the series current is still less than its lower limit value i mim , there will be a problem of overvoltage on the DC side of some units, causing irreversible damage to the electronic devices inside these units. To avoid the above problem, the present invention proposes A2, the wind turbine corresponding to the maximum DC side voltage changes its pitch angle through variable pitch control to reduce the absorption of wind energy and reduce i mim value, making it less than i dc , to solve the problem of overvoltage on the DC side of the unit in this case.

[0109] It can be seen from the above embodiments that the present invention adjusts the rotor speed of the wind turbine by controlling the q-axis current of the wind turbine, thereby improving the utilization rate of the wind energy of the turbine and realizing the maximum wind energy tracking of the turbine. In the case of unbalanced wind speed between turbines, in order to realize the maximum wind energy tracking, the speed of each wind turbine is also different, and its speed is positively correlated with the wind speed. The stator winding back electromotive force of the turbine with a fast speed is high. The turbine reduces the value of the back electromotive force through weak magnetic control, thereby realizing the control of the q-axis current of the turbine under the condition of unbalanced wind speed. The weak magnetic control requires the series current i dc Greater than i mim , through the dual-loop control of the phase-shifted full-bridge, the series current i is adjusted dc value, making it less than i max , thus meeting the requirements of the weak magnetic control of the unit for the series current. At the same time, the wind turbine with a fast wind speed has a high output power and a high DC side voltage. The ratio of the unit's output power corresponding to the maximum DC side voltage to its maximum safety voltage is imin When the unit output power is constant, its DC side voltage changes with i dc The phase-shifted full bridge adjusts the series current i through dual-loop control. dc value, making it greater than i min , thereby avoiding overvoltage on the DC side of all units, but when the input voltage of the phase-shifted full-bridge reaches its lower limit u pmin When the phase-shifted full bridge cannot increase i through dual-loop control dc Therefore, the unit corresponding to the maximum DC side voltage is controlled by variable pitch, which reduces the absorption of wind energy by the unit, thereby reducing the lower limit of the series current i min value, making it less than i dc The present invention only starts from the control direction to avoid overvoltage and overmodulation on the DC side of the unit, thereby reducing the construction cost of the wind power system.

[0110] Figure 3 is a series current waveform diagram obtained by MATLAB simulation of the present invention, which shows the series current i of the unit in the case of unbalanced wind speed between units in one embodiment. dc The waveform changes are shown in the figure. In this embodiment, the series current i dc are all less than their upper limit i max , there is no over-modulation problem on the DC side of the unit, which is described in detail as follows: In this embodiment, the number of wind turbines in series is 3, and their rated wind speed is selected to be 10m / s, and the permanent magnet flux of the motor ψ f =8.5Wb motor stator inductance quadrature axis component, L q =6mH, then the upper limit of the series circuit current i max The initial wind speed of the three wind turbines is set to 6m / s. At this time, the wind speeds between the turbines are balanced, and the control mode is A1. When the system enters a steady state, i dc The value is about 160A, which is less than 1227A. Therefore, there is no overmodulation on the DC side of the three units at this time. At 0.5 seconds, the wind speed of wind turbine unit 1 rises to 7.5m / s. At this time, the wind speeds among the three series units are unbalanced, but the degree of imbalance is low. At this time, the control mode is still A1. The wind energy capture of unit 1 increases, and the output power also increases accordingly. The phase-shifted full-bridge adjusts its input side voltage through dual-loop control, thereby controlling i dc The value when re-entering the steady state is about 280A, which is less than 1227A. Therefore, there is no overmodulation on the DC side of the three units at this time. At 1.5 seconds, the wind speed of unit 1 rises to 10m / s, and the wind speed imbalance between the three series units further increases. The input side voltage of the phase-shifted full-bridge reaches its limit value. At this time, the control mode is A2. The phase-shifted full-bridge adjusts its input side voltage through dual-loop control. Unit 1 reduces its wind energy absorption through variable pitch control, reducing the lower limit value of the series current imin At this time, the series current value i dc Below, I dc The value when re-entering the steady state is about 380A, which is still less than 1227A. Therefore, at this time, the DC side of the three units has not been over-modulated. As shown in this example, within the rated wind speed range, the series current i dc are all less than their upper limit i max Therefore, when the wind speed between units is unbalanced, the control method of the present invention can effectively avoid over-modulation of the DC side of the units.

[0111] Figure 4 The DC side voltage waveform of the series wind turbines obtained by MATLAB simulation in the present invention shows the change of the DC side voltage waveform of the units when the wind speed is unbalanced between the units in one embodiment. As shown in the figure, in this embodiment, the DC side voltage of the units is less than its maximum working voltage U m , that is, there is no overvoltage problem on the DC side of the unit, which is described in detail as follows: In this embodiment, the maximum operating voltage U m Both are 2kV, the output side voltage U of the phase-shifted full bridge is T The voltage is controlled by the onshore converter to be 179.5 kV. The ratio of the secondary turns to the primary turns of the transformer is 60. Therefore, the lower limit of the input voltage is u pmin =2.99kv, the outer loop target value of the phase-shifted full-bridge dual-loop control is u ref1 =1.8kV, that is, the maximum voltage of the DC side of the three wind turbines is u ref1 =1.8kV, the target value of wind turbine pitch control is u ref2 =1.9kV, that is, the voltage u on the input side of the phase-shifted full bridge p Reach its lower limit u pmin When the DC side voltage of the three wind turbines is u ref2 =1.9kV, the initial wind speed of the three wind turbines is set to 6m / s, at this time the DC side voltage of the units is 1.8kV, u p The value of is the sum of the DC side voltages of the three units, u p =5.4kV, this value is greater than u pmin Therefore, the control mode is A1 at this time, and only the phase-shifted full bridge adjusts the series current i through dual-loop control. dc , and then control the DC side voltage of unit 1 to 1.8kV; at 0.5 seconds, the wind speed of wind turbine unit 1 rises to 7.5m / s. At this time, the wind speed between units is unbalanced. During the period of 0.5 seconds to 1.5 seconds, u p The value of is greater than u pmin Therefore, the control mode of this stage is still A1, and the phase-shifted full bridge adjusts i through dual-loop control. dc, and then control the DC side voltage of unit 1 to 1.8kV; at 1.5 seconds, the wind speed rises to 10m / s, and the sum of the input side voltages of the phase-shifted full-bridge is 2.99kV, reaching its limit value u pmin , the control mode is A2, at this time the phase-shifted full bridge cannot increase i through dual-loop control dc The DC side of unit 1 is in danger of overvoltage. Unit 1 reduces its wind energy absorption through pitch control and adjusts the unit output voltage to u ref2 =1.9kV, the simulation results show that the control method proposed in the present invention can effectively avoid overvoltage on the DC side of the wind turbine.

[0112] Figure 5 It is a waveform diagram of the permanent magnet motor speed of the series unit obtained by MATLAB simulation in the present invention. The figure shows the change of the rotor speed of the three wind turbines in the embodiment with their wind speed. The maximum speed of the three wind turbines is set to 25rpm. In the embodiment, the wind speed of wind turbines 2 and 3 remains unchanged, so their speeds have only one steady state, which is 11.2rpm. The speed of wind turbine 1 changes with the change of wind speed. The wind speed of unit 1 is increased to 7.5m / s and 10m / s at 0.5 seconds and 1.5 seconds, respectively. Correspondingly, the speed of unit 1 is increased at 0.5 seconds and 1.5 seconds, and the speed is increased to 13.5rpm and 17rpm after entering the steady state. The simulation results show that the speeds of the wind turbines are all less than their maximum speeds and can effectively track the changes in wind speed, and can achieve maximum power tracking.

[0113] Corresponding to the aforementioned embodiment of the control method of the DC series permanent magnet wind power system based on the phase-shifted full bridge, the present invention also provides an embodiment of the control device of the DC series permanent magnet wind power system based on the phase-shifted full bridge, the system is composed of a phase-shifted full bridge and n permanent magnet wind turbines, the DC side of each wind turbine is connected in series to increase the DC bus voltage, and then connected to the input side of the phase-shifted full bridge, and the output side of the phase-shifted full bridge is connected to the onshore converter; the device comprises:

[0114] The control module is used to execute the wind turbine to control its q-axis current through the converter to adjust the motor rotor speed, thereby achieving the maximum wind energy tracking of each unit. At the same time, in order to avoid overvoltage and overmodulation on the DC side of the wind turbine when the wind speed is unbalanced, there are two mode modules:

[0115] The series current control module is used to execute the phase shift full bridge input side voltage greater than its lower limit voltage u pmin When the wind turbine is in operation, the inverter controls the d-axis current to adjust the back electromotive force of the motor stator winding, and the phase-shifted full bridge adjusts the series current i of the unit through dual-loop control. dc The size of the max , greater than its lower limit i min ;

[0116] The series current lower limit adjustment module is used to execute the phase shift full bridge input side voltage less than its lower limit voltage u pmin When the wind turbine is in operation, the inverter controls the d-axis current to adjust the back electromotive force of the motor stator winding, and the phase-shifted full bridge reduces the series current i of the unit through dual-loop control. dc value, making it less than its upper limit i max The wind turbine corresponding to the maximum DC side voltage is controlled by variable pitch to reduce the current lower limit i min value, making it less than i dc .

[0117] Regarding the device in the above embodiment, the specific manner in which each module performs operations has been described in detail in the embodiment of the method, and will not be elaborated here.

[0118] For the device embodiment, since it basically corresponds to the method embodiment, the relevant parts can refer to the partial description of the method embodiment. The device embodiment described above is only schematic, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the scheme of the present invention. Ordinary technicians in this field can understand and implement it without paying creative work.

[0119] Correspondingly, the present invention also provides an electronic device, comprising: one or more processors; a memory for storing one or more programs; when the one or more programs are executed by the one or more processors, the one or more processors implement the control method of the DC series permanent magnet wind power system based on the phase-shifted full-bridge as mentioned above.

[0120] Correspondingly, the present invention also provides a computer-readable storage medium on which computer instructions are stored, and when the instructions are executed by a processor, the control method of the DC series permanent magnet wind power system based on the phase-shifted full-bridge as described above is implemented.

[0121] Those skilled in the art will readily appreciate other embodiments of the present invention after considering the specification and practicing what is disclosed herein. The present invention is intended to cover any variations, uses or adaptations of the present invention that follow the general principles of the present invention and include common knowledge or customary techniques in the art that are not disclosed by the present invention. The specification and examples are to be considered exemplary only, and the true scope and spirit of the present invention are indicated by the claims.

[0122] It should be understood that the present invention is not limited to the exact construction that has been described above and shown in the drawings and that various modifications and changes may be made without departing from the scope thereof. The scope of the present invention is limited only by the appended claims.

Claims

1. A control method for a DC series permanent magnet wind power system based on a phase-shifted full-bridge, characterized in that: The system is composed of a phase-shifted full bridge and n permanent magnet wind turbines. The DC side of each wind turbine is connected in series to increase the DC bus voltage, and then connected to the input side of the phase-shifted full bridge. The output side of the phase-shifted full bridge is connected to the onshore converter. The method comprises the following steps: The wind turbine controls its q-axis current through the converter to adjust the permanent magnet motor rotor speed, thereby achieving the maximum wind energy tracking of each unit. At the same time, in order to avoid overvoltage and overmodulation on the DC side of the wind turbine when the wind speed is unbalanced, there are two modes: A1: The voltage at the input side of the phase-shifted full-bridge is greater than its lower limit voltage u pmin When the wind turbine is in operation, the inverter controls the d-axis current to adjust the back electromotive force of the motor stator winding, and the phase-shifted full bridge adjusts the series current i of the unit through dual-loop control. dc The size of i dc Less than its upper limit i max , greater than its lower limit i min ; A2: The voltage on the input side of the phase-shifted full-bridge reaches its lower limit voltage u pmin When the wind turbine is in operation, the inverter controls the d-axis current to adjust the back electromotive force of the motor stator winding, and the phase-shifted full bridge reduces the series current i of the unit through dual-loop control. dc The value of i dc Less than its upper limit i max The wind turbine corresponding to the maximum DC side voltage is controlled by pitch control to reduce the current lower limit i min value, making it less than i dc .

2. The control method of the DC series permanent magnet wind power system based on the phase-shifted full-bridge according to claim 1 is characterized in that: A1 specifically includes: When the wind speed between the units is unbalanced but the input voltage of the phase-shifted full-bridge is greater than its lower limit voltage u pmin When the DC side voltage is not saturated, the converter adjusts its d-axis current i d = 0, for wind turbines with saturated DC voltage, the converter adjusts i through weak magnetic control d The size of the motor stator winding is reduced to reduce the back electromotive force, thereby avoiding over-modulation of the DC side of the wind turbine. In order to achieve weak magnetic control, a phase-shifted full bridge is required to adjust the series current i of the wind turbine through dual-loop control. dc Less than its upper limit i max At the same time, in order to avoid overvoltage on the DC side of the wind turbine, the phase-shifted full bridge should also adjust i through dual-loop control dc Greater than its lower limit i min .

3. The control method of the DC series permanent magnet wind power system based on the phase-shifted full-bridge according to claim 1 is characterized in that: A2 specifically includes: When the wind speed between the units is unbalanced and the input voltage of the phase-shifted full-bridge reaches its lower limit voltage u pmin When the DC side voltage is not saturated, the converter adjusts its d-axis current i d = 0, for wind turbines with saturated DC voltage, the converter adjusts i through weak magnetic control d The size of the motor stator winding is reduced to reduce the back electromotive force, thereby avoiding over-modulation of the DC side of the wind turbine. In order to achieve weak magnetic control, a phase-shifted full bridge is required to adjust the series current i of the wind turbine through dual-loop control. dc Less than its upper limit i max , and to avoid overvoltage on the DC side, i dc It should also be greater than its lower limit i min However, in this case, the phase-shifted full bridge cannot be controlled by dual loops. dc Increase so that it is greater than i min Therefore, variable pitch control is adopted for the wind turbine corresponding to the maximum DC side voltage to reduce i min value, making it smaller than the series loop current i dc , thereby avoiding overvoltage on the DC side of the wind turbine.

4. The control method of the DC series permanent magnet wind power system based on the phase-shifted full-bridge according to claim 2 is characterized in that: The specific method of the dual-loop control of the phase-shifted full bridge is: The phase-shifted full bridge adopts dual-loop control. The outer loop is controlled by the maximum voltage on the DC side of the wind turbine, and the reference value is the preset value u ref1 The feedback value is the maximum value of the DC side voltage of the wind turbine, and the inner loop controlled value is the series current i of the unit. dc , the reference value is the outer loop output, and the feedback value is i dc , the inner loop output is the phase shift ratio D of the phase-shifted full bridge; Under the condition that the output power of the series wind turbine is constant, the phase shift ratio D increases, the input side voltage of the phase shift full bridge decreases, and the series current i dc Increases, and the DC side voltage of the wind turbine decreases accordingly; The phase shift ratio D decreases, the input voltage of the phase shift full bridge increases, i dc The DC side voltage of the wind turbine increases accordingly. The dual-loop control of the phase-shifted full-bridge adjusts i dc Greater than its lower limit i min , which can avoid overvoltage on the DC side of all wind turbines, and at the same time adjust the i through the dual-loop control of the phase-shifted full bridge dc Less than its upper limit i max , in order to achieve the weak magnetic control of wind turbines dc to avoid over-modulation of the DC side of the wind turbine.

5. The control method of the DC series permanent magnet wind power system based on the phase-shifted full-bridge according to claim 3 is characterized in that: The specific method of variable pitch control of the wind turbine generator set is as follows: The controlled object of wind turbine pitch control is the pitch angle of the wind turbine corresponding to the maximum value of DC side voltage, and the reference value is the preset value u ref2 , the feedback value is the DC side voltage of the wind turbine; By increasing the pitch angle of the wind turbine, reducing its wind energy capture and lowering its output power, the lower limit of the series current of the unit can be reduced. min To series current i dc The following can avoid overvoltage on the DC side of the wind turbine.

6. The control method of the DC series permanent magnet wind power system based on the phase-shifted full-bridge according to claim 1, 2 or 3, characterized in that: The upper limit of the series circuit current i max The lower limit of the series circuit current i min The expression is: where p m is the maximum output power of the wind turbine, U m is the maximum operating voltage of the wind turbine, ψ f is the permanent magnet flux of the motor, L s is the synchronous inductance of the motor stator.

7. The control method of the DC series permanent magnet wind power system based on the phase-shifted full bridge according to claim 2 or 3, characterized in that: The input side voltage lower limit u of the phase-shifted full bridge pmin The expression is: U T is the output side voltage of the phase-shifted full-bridge, which is controlled by the onshore converter to be a constant value, and N is the ratio of the number of turns of the output side winding of the phase-shifted full-bridge to the number of turns of the input side winding.

8. A control device for a DC series permanent magnet wind power system based on a phase-shifted full bridge, characterized in that: The system is composed of a phase-shifted full bridge and n permanent magnet wind turbines. The DC side of each wind turbine is connected in series to increase the DC bus voltage, and then connected to the input side of the phase-shifted full bridge. The output side of the phase-shifted full bridge is connected to the onshore converter. The control device comprises: The control module is used to execute the wind turbine to control its q-axis current through the converter to adjust the motor rotor speed, thereby achieving the maximum wind energy tracking of each unit. At the same time, in order to avoid overvoltage and overmodulation on the DC side of the wind turbine when the wind speed is unbalanced, there are two mode modules: The series current control module is used to execute the phase shift full bridge input side voltage greater than its lower limit voltage u pmin When the wind turbine is in operation, the inverter controls the d-axis current to adjust the back electromotive force of the motor stator winding, and the phase-shifted full bridge adjusts the series current i of the unit through dual-loop control. dc The size of the max , greater than its lower limit i min ; The series current lower limit adjustment module is used to execute the phase-shifted full-bridge input side voltage to reach its lower limit voltage u pmin When the wind turbine is in operation, the inverter controls the d-axis current to adjust the back electromotive force of the motor stator winding, and the phase-shifted full bridge reduces the series current i of the unit through dual-loop control. dc value, making it less than its upper limit i max The wind turbine corresponding to the maximum DC side voltage is controlled by pitch control to reduce the current lower limit i min value, making it less than i dc .

9. An electronic device, characterized in that: include: one or more processors; A memory for storing one or more programs; When the one or more programs are executed by the one or more processors, the one or more processors implement the method according to any one of claims 1 to 7.

10. A computer-readable storage medium having computer instructions stored thereon, characterized in that: When the instruction is executed by a processor, the steps of the method according to any one of claims 1 to 7 are implemented.

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