A converter and control method for direct-drive wind power generation

Abstract

The present invention discloses a converter and control method for direct-drive wind power generation, which relates to the technical field of power electronic conversion, and includes: 3N single-phase isolated AC / DC conversion units, three single-phase isolated AC / DC conversion units form a three-phase isolated AC / DC conversion unit; the single-phase isolated AC / DC conversion unit includes an input uncontrolled rectifier bridge and an isolated DC / DC resonant conversion circuit; the AC input end of the input uncontrolled rectifier bridge is used as the AC input end of the single-phase isolated AC / DC conversion unit, the DC output end of the input uncontrolled rectifier bridge is connected to the DC input end of the isolated DC / DC resonant conversion circuit, the DC output end of the isolated DC / DC resonant conversion circuit is used as the DC output end of the single-phase isolated AC / DC conversion unit, and capacitors are connected in parallel to the AC input end and the DC output end of the input uncontrolled rectifier bridge. The unit power factor operation and isolated DC output of the direct-drive wind generator and the soft switch control of the converter are realized, and the efficient power conversion of the direct-drive wind power generation is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronic conversion, and in particular to a converter for direct-drive wind power generation and a control method thereof. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] In the existing direct-drive wind power generation system, the machine-side AC / DC converter includes a fully controlled PWM (Pulse Width Modulation) converter. This type of machine-side converter can arbitrarily adjust the current size and phase of the wind turbine generator, and has good control performance, but it is not easy to achieve soft switching, has large losses, and requires two-level high-frequency PWM conversion and control on the machine side and the grid side. At the same time, the DC bus between the machine-side converter and the grid-side converter requires a large-capacity electrolytic capacitor to maintain the DC bus voltage, so the cost is high. The large-capacity electrolytic capacitor also restricts the life of the system. The two-level high-frequency conversion also reduces the power conversion efficiency. At the same time, it requires two-level coordinated control, which is complex to control. Summary of the invention

[0004] In order to solve the problems existing in the above-mentioned direct-drive wind power generation system, the present invention proposes a converter and control method for direct-drive wind power generation, which adopts the DC output terminals of N three-phase isolated AC / DC conversion units to be connected in parallel or in series, so that the output power between the three phases is superimposed on each other, and the pulsating power output by the single-phase isolated AC / DC conversion unit is eliminated. At the same time, the step-up and step-down characteristics of the resonant converter are utilized, and the AC input current is controlled by the current controller to track its input voltage waveform, so as to realize the unity power factor control of the wind turbine.

[0005] In order to achieve the above object, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a control method for a converter for direct-drive wind power generation, wherein the converter comprises 3N single-phase isolated AC / DC conversion units, where N is the number of three-phase windings; the AC input terminals and DC output terminals of the three single-phase isolated AC / DC conversion units are connected in a set connection mode to form a three-phase isolated AC / DC conversion unit; the DC output terminals of the N three-phase isolated AC / DC conversion units are connected to an external device in a set connection mode;

[0007] Acquire the AC input voltage, AC input current and DC output voltage of 3N single-phase isolated AC / DC conversion units, and thereby obtain an AC current amplitude control signal;

[0008] Performing unitization processing on the AC input voltage of each single-phase isolated AC / DC conversion unit to obtain an AC input voltage unitization signal;

[0009] A filtered signal is obtained by filtering the AC input voltage unitized signal, and an absolute value reference signal of the AC input current is obtained according to the AC input voltage unitized signal, the AC current amplitude control signal and the filtered signal;

[0010] A switch control signal is obtained according to the absolute value of the AC input current of each single-phase isolated AC / DC conversion unit and the absolute value reference signal.

[0011] As an optional implementation, the unitization process includes: dividing the AC input voltage of each single-phase isolated AC / DC conversion unit by its rated voltage effective value to obtain an AC input voltage unitization signal.

[0012] As an optional implementation, the product of the AC input voltage normalization signal and the AC current amplitude control signal is added to the filtered signal, and then the absolute value is taken to obtain the absolute value reference signal of the AC input current.

[0013] As an optional implementation, the AC input voltage unitized signal is processed by a bandpass filter to obtain a filtered signal, and the center frequency f0 of the bandpass filter satisfies Among them, L sr is the winding leakage inductance of the direct-drive wind turbine generator, C ac For the filter capacitor.

[0014] As an optional implementation, the process of obtaining the AC current amplitude control signal includes:

[0015] Calculate the average AC input voltage effective value, average AC input current effective value and total active power of 3N single-phase isolated AC / DC conversion units;

[0016] According to the output connection mode of 3N single-phase isolated AC / DC conversion units, the average total DC output voltage is calculated; when the outputs are connected in parallel, the DC output voltages are averaged; when the outputs are connected in series, the DC output voltages are summed;

[0017] According to the average AC input voltage effective value, the average AC input current effective value and the total active power, the control quantity I is obtained through maximum power tracking control. m1 ;

[0018] According to the average AC input voltage effective value, total active power and total active power given value, the control quantity I is obtained through constant power control. m2 ;

[0019] According to the average AC input voltage effective value, the average total DC output voltage and the rated output voltage given value, as well as the total active power and the total active power given value, the control quantity I is obtained through output voltage droop control. m3 ;

[0020] The control quantity I m1 ,I m2 and I m3 After selection by the three-to-one switch, an AC current amplitude control signal is obtained.

[0021] As an optional implementation, the process of obtaining the switch control signal includes:

[0022] According to the absolute value of the AC input current of each single-phase isolated AC / DC conversion unit and the absolute value reference signal, the switching period signal T is obtained. s ; According to the switching cycle signal T s The switching period is T s The square wave pulse signal is outputted, thereby outputting the switch control signal.

[0023] As an optional implementation, the process of obtaining the switch control signal includes:

[0024] According to the absolute value of the AC input current of each single-phase isolated AC / DC conversion unit and the absolute value reference signal, the output voltage pulse width signal T of the high-frequency DC / AC converter is obtained. pw ;

[0025] According to the phase difference time signal T between the output voltage and output current of the high-frequency DC / AC converter q With its reference signal, the switching period signal T of the high-frequency DC / AC converter is obtained. s , where the reference signal is greater than the switch signal dead time;

[0026] According to the switching cycle signal T s And the output voltage pulse width signal T pw , and obtain the switch control signal so that the output voltage of the high-frequency DC / AC converter is s and the pulse width is T pw The voltage pulse makes the output current phase lag by T q .

[0027] In a second aspect, the present invention provides a converter for direct-drive wind power generation, comprising: 3N single-phase isolated AC / DC conversion units, N being the number of three-phase windings; the AC input terminals and DC output terminals of the three single-phase isolated AC / DC conversion units are connected in a set connection mode to form a three-phase isolated AC / DC conversion unit; the DC output terminals of the N three-phase isolated AC / DC conversion units are connected to an external device in a set connection mode;

[0028] The single-phase isolated AC / DC conversion unit includes an input uncontrolled rectifier bridge and an isolated DC / DC resonant conversion circuit connected in sequence, and capacitors are respectively connected in parallel to the AC input end and the DC output end of the input uncontrolled rectifier bridge; the single-phase isolated AC / DC conversion unit uses the method described in the first aspect to control the action of the isolated DC / DC resonant conversion circuit.

[0029] As an optional implementation, the AC input end of each three-phase isolated AC / DC conversion unit adopts a star or triangle connection mode.

[0030] As an optional implementation, the DC output end of each three-phase isolated AC / DC conversion unit is connected in parallel or in series.

[0031] As an optional implementation, the DC output ends of the N three-phase isolated AC / DC conversion units are connected in parallel or in series.

[0032] As an optional implementation, the AC input end of the input uncontrolled rectifier bridge serves as the AC input end of the single-phase isolated AC / DC conversion unit, the DC output end of the input uncontrolled rectifier bridge is connected to the DC input end of the isolated DC / DC resonant conversion circuit, and the DC output end of the isolated DC / DC resonant conversion circuit serves as the DC output end of the single-phase isolated AC / DC conversion unit.

[0033] As an optional implementation, a filter capacitor is connected in parallel to the AC input end of the single-phase isolated AC / DC conversion unit.

[0034] As an optional implementation, an absorption capacitor is connected in parallel to the DC input terminal of the isolated DC / DC resonant conversion circuit.

[0035] As an optional implementation, the isolated DC / DC resonant conversion circuit includes a high-frequency DC / AC converter, a resonant network, a high-frequency isolation transformer and an output uncontrolled rectifier bridge;

[0036] The DC output end of the input uncontrolled rectifier bridge is connected to the DC input end of the high-frequency DC / AC converter, the AC output end of the high-frequency DC / AC converter is connected to the resonant network, the resonant network is connected to the primary side of the high-frequency isolation transformer, the secondary side of the high-frequency isolation transformer is connected to the AC input end of the output uncontrolled rectifier bridge, and the DC output end of the output uncontrolled rectifier bridge serves as the DC output end of the isolated DC / DC resonant conversion circuit.

[0037] As an optional implementation, the isolated DC / DC resonant conversion circuit includes a high-frequency DC / AC converter, a high-frequency isolation transformer, a resonant network and an output uncontrolled rectifier bridge;

[0038] The DC output end of the input uncontrolled rectifier bridge is connected to the DC input end of the high-frequency DC / AC converter, the AC output end of the high-frequency DC / AC converter is connected to the primary side of the high-frequency isolation transformer, the secondary side of the high-frequency isolation transformer is connected to the resonant network, the resonant network is connected to the AC input end of the output uncontrolled rectifier bridge, and the DC output end of the output uncontrolled rectifier bridge serves as the DC output end of the isolated DC / DC resonant conversion circuit.

[0039] As an optional implementation, the high-frequency DC / AC converter adopts a half-bridge, full-bridge, three-level or multi-level structure.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] The present invention proposes a converter and control method for direct-drive wind power generation. For a wind turbine with N three-phase windings, 3N single-phase isolated AC / DC conversion units are required. The single-phase isolated AC / DC conversion unit adopts a single-stage high-frequency conversion topology structure to replace Figure 1 The machine-side PWM converter and grid-side PWM converter of the existing typical direct-drive wind power system converter topology shown in the figure reduce one level of high-frequency conversion compared with the existing two-level high-frequency conversion, thereby improving the power conversion efficiency and realizing high power factor AC-DC power conversion of direct-drive wind power generation.

[0042] In the single-phase isolated AC / DC conversion unit designed by the present invention, the filter capacitor and the leakage inductance of the direct-drive wind motor winding constitute a second-order filter circuit, which can effectively filter out the switching ripple and has lower voltage and current harmonics than the existing system (only the leakage inductance filtering of the direct-drive wind motor winding). At the same time, the absorption capacitor is used to absorb the high-frequency switching voltage spikes of the isolated DC / DC resonant conversion circuit, omitting large-capacity electrolytic capacitors, reducing costs and increasing the service life of the system.

[0043] The present invention proposes a converter and control method for direct-drive wind power generation, which adopts an isolated DC / DC resonant conversion circuit for power transmission to realize soft switching operation control, and adopts a high-frequency transformer to realize electrical isolation and boost, thereby reducing the volume and output current and improving power conversion and transmission efficiency.

[0044] The present invention proposes a converter and control method for direct-drive wind power generation, which utilizes the voltage step-up and voltage step-down characteristics of a resonant converter, controls the AC input current of a single-phase isolated AC / DC conversion unit to track its input voltage waveform through a current controller, realizes unity power factor control of a wind generator, reduces low-order current harmonics of the wind generator, and simultaneously omits large-capacity electrolytic capacitors, eliminates the influence of large-capacity electrolytic capacitors on system life, and reduces costs.

[0045] The present invention proposes a converter and control method for direct-drive wind power generation, which uses a filter capacitor and a leakage inductance of a direct-drive wind motor winding to form a second-order filter circuit to filter out switching ripple. However, it is also easy to cause resonance in the output of the direct-drive wind generator under light load. For this reason, the control method proposed in the present invention uses a bandpass filter to increase the load current at the resonant frequency point, increase its damping, and effectively weaken the resonance caused by the input filter capacitor.

[0046] The present invention proposes a converter and a control method for direct-drive wind power generation. For a wind turbine with N three-phase windings, the DC output ends of its N three-phase isolated AC / DC conversion units are connected in parallel or in series, so that the output power between the three phases is superimposed on each other, which can eliminate the pulsating power output by the single-phase isolated AC / DC conversion unit.

[0047] The present invention proposes a converter and control method for direct-drive wind power generation, which integrates machine-side control and grid-side control to achieve single-stage integrated control of direct-drive wind power generation. At the same time, only the input / output voltage and current of the converter need to be detected to achieve maximum power tracking control, constant power control and output voltage droop control, without the need to detect the rotor position or speed of the direct-drive wind generator, thus simplifying the system design.

[0048] Advantages of additional aspects of the present invention will be given in part in the following description, and in part will become obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0050] Figure 1 The topological structure diagram of the "back-to-back" converter of the existing direct-drive wind power system;

[0051] Figure 2 A topological structure diagram of a single-phase isolated AC / DC conversion unit provided in Example 1 of the present invention;

[0052] FIG3( a ) is a wiring diagram of an embodiment of a three-phase isolated AC / DC conversion unit provided in Embodiment 1 of the present invention;

[0053] FIG3( b ) is a wiring diagram of another embodiment of the three-phase isolated AC / DC conversion unit provided in Embodiment 1 of the present invention;

[0054] FIG3( c ) is a wiring diagram of another embodiment of the three-phase isolated AC / DC conversion unit provided in Embodiment 1 of the present invention;

[0055] FIG3( d ) is a wiring diagram of another embodiment of the three-phase isolated AC / DC conversion unit provided in Embodiment 1 of the present invention;

[0056] FIG4(a) is a wiring diagram of a conversion unit embodiment of N three-phase wind turbine windings provided in Embodiment 1 of the present invention;

[0057] FIG4( b ) is a wiring diagram of another embodiment of a conversion unit of N three-phase wind turbine windings provided in Embodiment 1 of the present invention;

[0058] FIG5(a) is an embodiment of an isolated DC / DC resonant conversion circuit provided in Embodiment 1 of the present invention;

[0059] FIG5( b ) is another embodiment of the isolated DC / DC resonant conversion circuit provided in Embodiment 1 of the present invention;

[0060] Figure 6 A flow chart of a control method for a converter for direct-drive wind power generation provided in Embodiment 2 of the present invention;

[0061] Figure 7 for Figure 6 Flowchart of the integrated controller in;

[0062] Figure 8 for Figure 7 Flow chart of the constant power control method in;

[0063] Fig. 9 for Figure 7 Flow chart of the output voltage droop control method in;

[0064] Fig.10 for Figure 6 A flow chart of a current controller in;

[0065] Fig.11 for Fig.10 Output voltage and current waveforms of high frequency DC / AC converters in the control method;

[0066] Fig.12 for Figure 6 Flow chart of another current controller in;

[0067] Fig.13 for Fig.12 Output voltage and current waveforms of high frequency DC / AC converters in the control method;

[0068] Among them, 1. Single-phase isolated AC / DC conversion unit, 2. Input uncontrolled rectifier bridge, 3. Isolated DC / DC resonant conversion circuit, 4. Three-phase isolated AC / DC conversion unit, 5. High-frequency DC / AC converter, 6. Resonant network, 7. High-frequency isolation transformer, 8. Output uncontrolled rectifier bridge, 9. Integrated controller, 10. Current controller, 11. Maximum power tracking control, 12. Constant power control, 13. Output voltage droop control, 14. Three-choice switch. DETAILED DESCRIPTION

[0069] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0070] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0071] It should be noted that the terms used herein are only for describing specific embodiments, and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that the terms "include" and "comprise" and any of their variations are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0072] In the absence of conflict, the embodiments of the present invention and the features of the embodiments may be combined with each other.

[0073] Example 1

[0074] like Figure 1 The figure shows the topological structure of the "back-to-back" PWM converter of the existing direct-drive wind power system. Figure 1In the invention, both the machine side and the grid side use high-frequency fully controlled PWM converters, and the intermediate DC bus uses large-capacity electrolytic capacitors to maintain the DC voltage. As described in the background technology, the machine side high-frequency PWM converter is not easy to achieve soft switching, and the DC bus between the machine side converter and the grid side converter requires large-capacity electrolytic capacitors to maintain the DC bus voltage, so the cost is high. Large-capacity electrolytic capacitors also limit the life of the system, and the two-stage high-frequency conversion also reduces the power conversion efficiency.

[0075] Therefore, for Figure 1 The typical existing direct-drive wind power system shown in the figure, this embodiment provides a converter for direct-drive wind power generation, which realizes the unit power factor AC-DC power conversion of direct-drive wind power generation. It includes: 3N single-phase isolated AC / DC conversion units 1; wherein N is the number of three-phase windings of the wind turbine;

[0076] like Figure 2 As shown, the single-phase isolated AC / DC conversion unit 1 includes a filter capacitor C ac , input uncontrolled rectifier bridge 2, absorption capacitor C s And isolated DC / DC resonant conversion circuit 3.

[0077] Specifically:

[0078] The two AC input terminals of the input uncontrolled rectifier bridge 2 serve as the two AC input terminals of the single-phase isolated AC / DC conversion unit 1. ac Connected in parallel to two AC input terminals of the single-phase isolated AC / DC conversion unit 1;

[0079] The two DC output ends of the input uncontrolled rectifier bridge 2 are connected to the two DC input ends of the isolated DC / DC resonant conversion circuit 3. The two DC output ends of the isolated DC / DC resonant conversion circuit 3 serve as the two DC output ends of the single-phase isolated AC / DC conversion unit 1. The absorption capacitor C s It is connected in parallel to the two DC input terminals of the isolated DC / DC resonant conversion circuit 3.

[0080] In this embodiment, for a wind turbine with N three-phase windings, 3N single-phase isolated AC / DC conversion units are required. The single-phase isolated AC / DC conversion unit proposed in this embodiment uses a single-stage high-frequency conversion to achieve AC / DC unity power factor conversion of direct-drive wind power. Figure 1 The machine-side PWM converter and the grid-side PWM converter.

[0081] As an optional implementation, the filter capacitor C ac It forms a filter circuit with the leakage inductance of the direct-drive wind motor winding to filter out the switching ripple.

[0082] As an optional implementation, the absorption capacitor C s Used to absorb the high-frequency switching voltage spike of the isolated DC / DC resonant conversion circuit 3, omitting the large-capacity electrolytic capacitor C dc .

[0083] In this embodiment, the three single-phase isolated AC / DC conversion units 1 are grouped into N groups, and each group of single-phase isolated AC / DC conversion units 1 is combined into a three-phase isolated AC / DC conversion unit 4;

[0084] Among them, the AC input end of each three-phase isolated AC / DC conversion unit 4 adopts a star or triangle connection method, the DC output end of each three-phase isolated AC / DC conversion unit 4 adopts a parallel or series connection method, and the DC output ends of N groups of three-phase isolated AC / DC conversion units 4 are connected to the DC grid or load in parallel or series.

[0085] FIG3( a ) is a wiring diagram of an embodiment of a three-phase isolated AC / DC conversion unit, wherein the AC input terminals of three single-phase isolated AC / DC conversion units are connected in a triangle manner, and the DC output terminals are connected in parallel.

[0086] FIG3( b ) is a wiring diagram of another embodiment of a three-phase isolated AC / DC conversion unit, wherein the AC input terminals of three single-phase isolated AC / DC conversion units are connected in a triangle manner, and the DC output terminals are connected in series.

[0087] FIG3( c ) is a wiring diagram of another embodiment of a three-phase isolated AC / DC conversion unit, wherein the AC input terminals of the three single-phase isolated AC / DC conversion units are connected in star connection and the DC output terminals are connected in parallel.

[0088] FIG3( d ) is a wiring diagram of another embodiment of a three-phase isolated AC / DC conversion unit, wherein the AC input terminals of the three single-phase isolated AC / DC conversion units are connected in star connection and the DC output terminals are connected in series.

[0089] FIG4( a ) is a wiring diagram of a converter embodiment of N three-phase wind turbine windings, wherein the DC output ends of the N three-phase isolated AC / DC conversion units are connected in parallel.

[0090] FIG4( b ) is a wiring diagram of another embodiment of a converter for N three-phase wind turbine windings, wherein the DC output ends of the N three-phase isolated AC / DC conversion units are connected in series.

[0091] In this embodiment, as shown in FIG. 5( a ), the isolated DC / DC resonant conversion circuit 3 includes a high-frequency DC / AC converter 5 , a resonant network 6 , a high-frequency isolation transformer 7 and an output uncontrolled rectifier bridge 8 .

[0092] Among them, the DC output end of the input uncontrolled rectifier bridge 2 is connected to the DC input end of the high-frequency DC / AC converter 5, the AC output end of the high-frequency DC / AC converter 5 is connected to the resonant network 6, the resonant network 6 is connected to the primary side of the high-frequency isolation transformer 7, the secondary side of the high-frequency isolation transformer 7 is connected to the AC input end of the output uncontrolled rectifier bridge 8, and the DC output end of the output uncontrolled rectifier bridge 8 serves as the DC output end of the isolated DC / DC resonant conversion circuit 3.

[0093] As an optional implementation, in FIG. 5( a ), the resonant network 6 adopts an LLC resonant network; wherein the inductor L m represents the excitation inductance of the high-frequency isolation transformer 7, and the inductance L r is the resonant inductor, which may be the leakage inductance of the high-frequency isolation transformer 7 .

[0094] In this embodiment, as shown in FIG. 5( b ), the isolated DC / DC resonant conversion circuit 3 includes a high-frequency DC / AC converter 5 , a high-frequency isolation transformer 7 , a resonant network 6 and an output uncontrolled rectifier bridge 8 .

[0095] Among them, the DC output end of the input uncontrolled rectifier bridge 2 is connected to the DC input end of the high-frequency DC / AC converter 5, the AC output end of the high-frequency DC / AC converter 5 is connected to the primary side of the high-frequency isolation transformer 7, the secondary side of the high-frequency isolation transformer 7 is connected to the resonant network 6, the resonant network 6 is connected to the AC input end of the output uncontrolled rectifier bridge 8, and the DC output end of the output uncontrolled rectifier bridge 8 serves as the DC output end of the isolated DC / DC resonant conversion circuit 3.

[0096] As an optional implementation, in FIG. 5( b ), the resonant network 6 adopts an LC resonant network; wherein the inductor L m represents the excitation inductance of the high-frequency isolation transformer 7, and the inductance L r is the resonant inductor, which may be the leakage inductance of the high-frequency isolation transformer 7 .

[0097] As an optional implementation, in FIG. 5( a ) and FIG. 5( b ), the high-frequency DC / AC converter 5 adopts a half-bridge, full-bridge, three-level or multi-level structure.

[0098] It can be understood that the resonant network 6 is not limited to the LLC resonant network and the LC resonant network shown in FIG. 5( a ) and FIG. 5( b ) above.

[0099] Example 2

[0100] This embodiment provides a control method for the above-mentioned converter for direct-drive wind power generation, such as Figure 6 As shown, specifically including:

[0101] Step 1): Detect the DC output voltage U of 3N single-phase isolated AC / DC conversion units o , and the AC input voltage u of the uncontrolled rectifier bridge ac and AC input current i ac .

[0102] Step 2): The DC output voltage U of the 3N single-phase isolated AC / DC conversion units detected is o , and the AC input voltage u ac and AC input current i ac After being processed by the integrated controller 9, the AC current amplitude control signal I is obtained. m .

[0103] Step 3): The AC input voltage u of each single-phase isolated AC / DC conversion unit ac Perform unitization processing to obtain the AC input voltage unitization signal u uint .

[0104] The unitization process is as follows: the AC input voltage u of each single-phase isolated AC / DC conversion unit is converted into ac Divide by its rated voltage effective value U acN , to perform unitization processing and obtain the input voltage unitization signal u uint ,Right now:

[0105] Step 4): Normalize the AC input voltage signal u uint After being processed by a bandpass filter, the filtered signal u is obtained. bp , according to the AC input voltage unit signal u uint , AC current amplitude control signal I m and the filtered signal u bp Get the AC input current i ac The absolute value of the reference signal |i ac * .

[0106] Among them, the AC input voltage is normalized to signal u uint and the AC current amplitude control signal I m The product of the AC input voltage unit signal u uint The filtered signal u after being processed by the bandpass filter bp , and then take the absolute value as the AC input current i ac The absolute value of the reference signal |i ac |* ,Right now:

[0107] |i ac | * =|I m ·u unit +u bp |.

[0108] The center frequency f0 of the bandpass filter is approximately equal to the winding leakage inductance L of the direct-drive wind turbine generator. sr With filter capacitor C ac The resonant frequency is

[0109] Step 5): According to the AC input current i of each single-phase isolated AC / DC conversion unit ac The absolute value of |i ac |With AC input current i ac The absolute value of the reference signal |i ac | * After being processed by the current controller 10, a switch control signal Ks of the isolated DC / DC resonant conversion circuit is obtained, thereby performing frequency conversion or frequency conversion + width modulation control and realizing soft switching control.

[0110] In this embodiment, if Figure 7 As shown, the processing process of the integrated controller 9 specifically includes:

[0111] Step 2-1): Calculate the average AC input voltage effective value U of 3N single-phase isolated AC / DC conversion units ac , average AC input current effective value I ac And the total active power P, that is:

[0112]

[0113] Step 2-2): Calculate the average total DC output voltage U of the fan converter according to the output wiring mode of 3N single-phase isolated AC / DC conversion units. out .

[0114] The calculation principles include:

[0115] When the outputs are connected in parallel, the voltage is averaged, that is, when M outputs are connected in parallel,

[0116] When the outputs are connected in series, the voltage is summed, that is, when M outputs are connected in series,

[0117] Specific basis Figure 3(a)-Figure 3(d) 4(a) and 4(b) output connection combinations, calculate the average total output voltage U according to the above calculation principleout .

[0118] Step 2-3): According to the calculated average AC input voltage effective value U ac , average AC input current effective value I ac And the total active power P, after the maximum power tracking control 11, the control quantity I is obtained m1 ;

[0119] According to the calculated average AC input voltage effective value U ac , total active power P and total active power given value P * , after constant power control, the control quantity I is obtained m2 ;

[0120] According to the calculated average AC input voltage effective value U ac , average total DC output voltage U out and rated output voltage given value As well as the total active power P and the total active power given value P * , after output voltage droop control, the control quantity I is obtained m3 .

[0121] Step 2-4): The obtained control amount I m1 ,I m2 and I m3 After the three-to-one switch 14 selects, the AC current amplitude control signal I is obtained. m .

[0122] Among them, the total active power given value P * and rated output voltage given value Given by the upper system.

[0123] Among them, the maximum power point tracking (MPPT) control can adopt the existing MPPT algorithms, such as the conductance increment method, the interference observation method, etc.

[0124] In this embodiment, if Figure 8 As shown, the implementation scheme of the constant power control 12 specifically includes:

[0125] Step 1): Compare the calculated total active power P with the given value of total active power P * After being processed by the power regulator W1, the control quantity U W1 .

[0126] Step 2): Set the control quantity U W1 Divide by the rated input voltage RMS U acN , then multiply by the effective value of the input voltage U ac Get the control quantity I m2 ,Right now

[0127] Wherein, the power regulator W1 can be a PI regulator.

[0128] In this embodiment, if Fig. 9 As shown, the implementation scheme of the output voltage droop control 13 can realize the output voltage droop control with droop characteristics and inertia, specifically including:

[0129] Step 1): Set the rated output voltage to a given value Subtract the total output voltage U out After and droop coefficient K u The product of the active power given value P * The difference between the active power P (P * -P), and then pass through integrator G1 to get the output reference voltage Right now J u is the integration time constant.

[0130] Step 2): Calculate the output voltage U out With output reference voltage After being processed by the voltage regulator W2, the control quantity U W2 .

[0131] Step 3): Set the control quantity U W2 Divide by the rated input voltage RMS U acN , then multiply by the effective value of the input voltage U ac Get the control quantity I m3 ,Right now

[0132] Wherein, the voltage regulator W2 may be a PI regulator.

[0133] In this embodiment, if Fig.10 As shown, the current controller 10 can realize the tracking control of the input AC current through frequency conversion control, and its specific implementation process includes:

[0134] Step 5-1): Convert the AC input current i of each single-phase isolated AC / DC conversion unit ac The absolute value of |i ac | and its reference signal |i ac | * After being processed by the current regulator W3, the switching cycle signal T of the high-frequency DC / AC converter is obtained. s .

[0135] Step 5-2): Based on the switching cycle signal T s The switching signal generating unit UT1 generates a switching cycle T sThe square wave pulse signal is output and the switch control signal Ks is output.

[0136] For the embodiment shown in FIG. 5( a ), the switching period T s The maximum value of is limited to the LLC circuit output no-load resonant period, that is, To achieve soft switching operation of the converter;

[0137] For the embodiment shown in FIG. 5( b ), the switching period T s The maximum value of is limited to the LC circuit output no-load resonant period, that is, To achieve soft switching operation of the converter.

[0138] Wherein, the current regulator W3 can be a PI regulator.

[0139] Fig.11 Gives the corresponding Fig.10 The high-frequency DC / AC converter output voltage and current waveform of the current controller. In the figure, U T is the output voltage, i T is the output current, T s is the switching cycle.

[0140] In this embodiment, another implementation scheme of the current controller 10 is also provided. Fig.12 As shown in the figure, the tracking control of input AC current can be achieved through frequency conversion + width modulation control, which includes:

[0141] Step 5-1): Convert the AC input current i of each single-phase isolated AC / DC conversion unit ac The absolute value of |i ac | and its reference signal |i ac | * After being processed by the current regulator W4, the high-frequency DC / AC converter output voltage pulse width signal T is obtained. pw .

[0142] Step 5-2): The high frequency DC / AC converter output voltage U T With the output current i T The phase difference time signal T q With its reference signal After being processed by the phase regulator W5, the switching cycle signal T of the high-frequency DC / AC converter is obtained. s , reference signal It is greater than the dead time of the switching signal and can be twice the dead time.

[0143] Step 5-3): The switching cycle signal T s And the output voltage pulse width signal T pwThe switch signal generating unit UT2 outputs the switch control signal Ks, which makes the high frequency DC / AC converter output voltage U T The switching period is T s and the pulse width is T pw The voltage pulse makes the output current i T Phase time lag T q .

[0144] For the embodiment shown in FIG. 5( a ), the switching period T s The maximum value of is limited to the LLC circuit output no-load resonant period, that is, To achieve soft switching operation of the converter;

[0145] For the embodiment shown in FIG. 5( b ), the switching period T s The maximum value of is limited to the LC circuit output no-load resonant period, that is, To achieve soft switching operation of the converter.

[0146] Wherein, the current regulator W4 and the phase regulator W5 can be PI regulators.

[0147] Fig.13 Gives the corresponding Fig.12 The high frequency DC / AC converter output voltage and current waveform of the current controller 10, in which U T is the output voltage, i T is the output current, T s is the switching period, T pw is the voltage pulse width, T q is the output voltage U T With the output current i T The phase difference time signal.

[0148] Although the above describes the specific implementation mode of the present invention in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solution of the present invention without creative work are still within the scope of protection of the present invention.

Claims

1. A control method for a converter for direct-drive wind power generation, characterized in that: The converter includes 3N single-phase isolated AC / DC conversion units, where N is the number of three-phase windings; the AC input terminals and DC output terminals of the three single-phase isolated AC / DC conversion units are connected in a set connection mode to form a three-phase isolated AC / DC conversion unit; the DC output terminals of the N three-phase isolated AC / DC conversion units are connected to an external device in a set connection mode; Acquire the AC input voltage, AC input current and DC output voltage of 3N single-phase isolated AC / DC conversion units, and thereby obtain an AC current amplitude control signal; Performing unitization processing on the AC input voltage of each single-phase isolated AC / DC conversion unit to obtain an AC input voltage unitization signal; A filtered signal is obtained by filtering the AC input voltage unitized signal, and an absolute value reference signal of the AC input current is obtained according to the AC input voltage unitized signal, the AC current amplitude control signal and the filtered signal; A switch control signal is obtained according to the absolute value of the AC input current of each single-phase isolated AC / DC conversion unit and the absolute value reference signal.

2. A control method for a converter for direct-drive wind power generation according to claim 1, characterized in that: The unitization process includes: dividing the AC input voltage of each single-phase isolated AC / DC conversion unit by its rated voltage effective value to obtain an AC input voltage unitization signal; The product of the AC input voltage unitization signal and the AC current amplitude control signal is added to the filtered signal, and then the absolute value is taken to obtain the absolute value reference signal of the AC input current; The AC input voltage unitized signal is processed by a bandpass filter to obtain a filtered signal, and the center frequency f0 of the bandpass filter satisfies Among them, L sr is the winding leakage inductance of the direct-drive wind turbine generator, C ac For the filter capacitor.

3. A control method for a converter for direct-drive wind power generation according to claim 1, characterized in that: The process of obtaining the AC current amplitude control signal includes: Calculate the average AC input voltage effective value, average AC input current effective value and total active power of 3N single-phase isolated AC / DC conversion units; According to the output connection mode of 3N single-phase isolated AC / DC conversion units, the average total DC output voltage is calculated; when the outputs are connected in parallel, the DC output voltages are averaged as the average total DC output voltage; when the outputs are connected in series, the DC output voltages are summed as the average total DC output voltage; According to the average AC input voltage effective value, the average AC input current effective value and the total active power, the control quantity I is obtained through maximum power tracking control. m1 ; According to the average AC input voltage effective value, total active power and total active power given value, the control quantity I is obtained through constant power control. m2 ; According to the average AC input voltage effective value, the average total DC output voltage and the rated output voltage given value, as well as the total active power and the total active power given value, the control quantity I is obtained through output voltage droop control. m3 ; The control quantity I m1 、Control quantity I m2 and control quantity I m3 After selection by the three-to-one switch, an AC current amplitude control signal is obtained.

4. A control method for a converter for direct-drive wind power generation according to claim 1, characterized in that: The process of obtaining the switch control signal includes: According to the absolute value of the AC input current of each single-phase isolated AC / DC conversion unit and the absolute value reference signal, the switching period signal T is obtained. s ; According to the switching cycle signal T s The switching period is T s The square wave pulse signal is outputted, thereby outputting the switch control signal.

5. The control method of a converter for direct-drive wind power generation according to claim 1, characterized in that: The process of obtaining the switch control signal includes: According to the absolute value of the AC input current of each single-phase isolated AC / DC conversion unit and the absolute value reference signal, the output voltage pulse width signal T of the high-frequency DC / AC converter in each single-phase isolated AC / DC conversion unit is obtained. pw ; According to the phase difference time signal T between the output voltage and output current of the high-frequency DC / AC converter q With its reference signal, the switching period signal T of the high-frequency DC / AC converter is obtained. s , where the reference signal is greater than the switch signal dead time; According to the switching cycle signal T s And the output voltage pulse width signal T pw , and obtain the switch control signal so that the output voltage of the high-frequency DC / AC converter is s and the pulse width is T pw The voltage pulse makes the output current phase lag by T q .

6. A converter for direct-drive wind power generation, characterized in that: include: 3N single-phase isolated AC / DC conversion units, N is the number of three-phase windings; the AC input terminals and DC output terminals of the three single-phase isolated AC / DC conversion units are connected in a set connection mode to form a three-phase isolated AC / DC conversion unit; the DC output terminals of the N three-phase isolated AC / DC conversion units are connected to an external device in a set connection mode; The single-phase isolated AC / DC conversion unit includes an input uncontrolled rectifier bridge and an isolated DC / DC resonant conversion circuit connected in sequence, and capacitors are respectively connected in parallel to the AC input end and the DC output end of the input uncontrolled rectifier bridge; the single-phase isolated AC / DC conversion unit adopts the control method described in any one of claims 1 to 5 to control the action of the isolated DC / DC resonant conversion circuit.

7. A converter for direct-drive wind power generation according to claim 6, characterized in that: The AC input terminals of the three single-phase isolated AC / DC conversion units are connected in a star or delta configuration; The DC output terminals of the three single-phase isolated AC / DC conversion units are connected in parallel or in series; The DC output ends of the N three-phase isolated AC / DC conversion units are connected in parallel or in series.

8. A converter for direct-drive wind power generation according to claim 6, characterized in that: The AC input end of the input uncontrolled rectifier bridge is used as the AC input end of the single-phase isolated AC / DC conversion unit, the DC output end of the input uncontrolled rectifier bridge is connected to the DC input end of the isolated DC / DC resonant conversion circuit, and the DC output end of the isolated DC / DC resonant conversion circuit is used as the DC output end of the single-phase isolated AC / DC conversion unit; Connect a filter capacitor in parallel to the AC input terminal of the single-phase isolated AC / DC conversion unit; An absorption capacitor is connected in parallel to the DC input terminal of the isolated DC / DC resonant conversion circuit.

9. A converter for direct-drive wind power generation according to claim 6, characterized in that: The isolated DC / DC resonant conversion circuit includes a high-frequency DC / AC converter, a resonant network, a high-frequency isolation transformer and an output uncontrolled rectifier bridge; The DC output end of the input uncontrolled rectifier bridge is connected to the DC input end of the high-frequency DC / AC converter, the AC output end of the high-frequency DC / AC converter is connected to the resonant network, the resonant network is connected to the primary side of the high-frequency isolation transformer, the secondary side of the high-frequency isolation transformer is connected to the AC input end of the output uncontrolled rectifier bridge, and the DC output end of the output uncontrolled rectifier bridge serves as the DC output end of the isolated DC / DC resonant conversion circuit.

10. A converter for direct-drive wind power generation according to claim 6, characterized in that: The isolated DC / DC resonant conversion circuit includes a high-frequency DC / AC converter, a high-frequency isolation transformer, a resonant network and an output uncontrolled rectifier bridge; The DC output end of the input uncontrolled rectifier bridge is connected to the DC input end of the high-frequency DC / AC converter, the AC output end of the high-frequency DC / AC converter is connected to the primary side of the high-frequency isolation transformer, the secondary side of the high-frequency isolation transformer is connected to the resonant network, the resonant network is connected to the AC input end of the output uncontrolled rectifier bridge, and the DC output end of the output uncontrolled rectifier bridge serves as the DC output end of the isolated DC / DC resonant conversion circuit.

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