Full-power converter of permanent magnet synchronous wind driven generator and control method

Abstract

The invention discloses a full-power converter of a permanent magnet synchronous wind driven generator and a control method, which can be used for solving the problems of low switching frequency, high voltage change rate, large loss and high cost during power conversion of the permanent magnet synchronous generator in the related technology. According to the topological structure of the full-power converter, a diode rectifier is adopted on the wind driven generator side, and a one-way current type modular multi-level converter is adopted on the alternating-current power grid side. The one-way current type modular multilevel converter is composed of three phases of bridge arms; wherein the alternating-current voltage which is generated by the wind driven generator side and has the frequency and the amplitude continuously changing along with time is converted into the direct-current voltage through the diode rectifier; according to the amplitude and the frequency of the power grid voltage, inversion of the direct-current voltage is completed through the one-way current type modular multi-level converter, a three-phase output voltage reference value is obtained, and the three-phase output voltage reference value is transmitted to an alternating-current power grid side.

Description

Technical Field

[0001] The present invention relates to the technical field of power control, and in particular to a full-power converter of a permanent magnet synchronous wind generator and a control method thereof. Background Art

[0002] Offshore wind energy resources are good, wind speed is stable, it is close to the onshore load center, and it has little impact on human life. It is an important part of future renewable energy power generation. Permanent Magnet Synchronous Generator (PMSG) has no brushes and slip rings, does not require frequent maintenance, and can easily reach a large capacity level. It is the mainstream generator type for offshore wind power. With the increasing demand for wind turbines and the continuous improvement of wind turbine manufacturing level, the future PMSG will gradually show the following three characteristics:

[0003] First, wind turbine capacity is getting bigger and bigger. The maximum capacity of a single wind turbine currently in operation has reached 18MW (power unit: megawatt). In the future, wind turbines with a capacity of 20MW may appear.

[0004] Second, medium-pressure fans are gradually becoming the mainstream. In order to reduce the cross-sectional area of ​​the fan's internal conductor and transmission cable, more and more fans are using medium-voltage designs such as 1140V (voltage unit: volts) and 3300V.

[0005] Third, in addition to typical three-phase motors, in order to reduce phase current, dual three-phase and multi-three-phase motors are gradually becoming the mainstream.

[0006] In actual situations, the amplitude and frequency of the PMSG output AC voltage are proportional to the rotation speed. Its rotation speed is related to the wind speed and fluctuates continuously during normal operation. Therefore, when the PMSG is operating normally, the amplitude and frequency of the output AC voltage are constantly changing, making it difficult to directly connect to the AC grid. In order to achieve variable speed constant frequency power generation, full-power AC / DC / AC converters are currently used to convert the PMSG output power. For example, a back-to-back neutral point clamped three-level converter (Back to Back Neutral Point Clamp Converter, BTB-NPC) structure or a "Diode Rectifier + DC non-isolated boost + neutral point clamped three-level converter" (Diode Rectifier + Boost Circuit + NPC, DBN) structure is used.

[0007] The BTB-NPC structure is not only limited by loss and heat dissipation, resulting in low switching frequency, but also has problems such as high cost. The DBN structure will not only cause the electromagnetic power of the generator to constantly shake, and then cause electromagnetic torque pulsation, thus affecting the life of the mechanical part of the mechanical equipment, but also has problems such as low switching frequency, high filtering difficulty, high voltage step, and large voltage change rate. Summary of the invention

[0008] The present invention provides a full-power converter and control method for a permanent magnet synchronous wind generator, which are used to solve or partially solve the technical problems of low switching frequency, high voltage change rate, large loss and high cost during power conversion of the permanent magnet synchronous generator in the related art.

[0009] The present invention provides a full-power converter for a permanent magnet synchronous wind turbine generator. The topology of the full-power converter is that a diode rectifier is used on the wind turbine generator side, and a unidirectional current type modular multilevel converter is used on the AC grid side; the unidirectional current type modular multilevel converter is composed of a three-phase bridge arm; wherein,

[0010] The diode rectifier is used to convert the AC voltage emitted by the wind generator side, the frequency and amplitude of which change continuously with time, into a DC voltage;

[0011] The unidirectional current-type modular multilevel converter is used to complete the inversion of the DC voltage according to the amplitude and frequency of the grid voltage, obtain a three-phase output voltage reference value, and transmit the three-phase output voltage reference value to the AC grid side.

[0012] Optionally, a plurality of multilevel converter modules are provided in each bridge arm of the unidirectional current-source modular multilevel converter; each of the multilevel converter modules is composed of a capacitor, a resistor, a plurality of diodes, a plurality of semiconductor switch devices, and anti-parallel diodes whose number is the same as that of the plurality of semiconductor switch devices;

[0013] The anti-parallel diode is integrated inside the semiconductor switch device, or connected to the semiconductor switch device in parallel.

[0014] Optionally, the unidirectional current-type modular multilevel converter includes a DC controller, an AC controller, a circulating current controller and a voltage linear converter; wherein,

[0015] The DC controller controls the generator speed by controlling the DC current to obtain a DC internal potential reference value;

[0016] The AC controller controls the AC active and reactive power by controlling the AC current to obtain the three-phase AC internal potential;

[0017] The circulating current controller obtains the internal potential of the circulating current by suppressing the internal circulating current;

[0018] The voltage linear conversion obtains the three-phase output voltage reference value of the unidirectional current-type modular multi-level converter by performing linear conversion based on the DC internal potential reference value, the AC internal potential, and the circulating current internal potential, wherein the three-phase output voltage reference value includes the output voltage reference values ​​of the six bridge arms of the three phases.

[0019] Optionally, the control processing process of the DC controller is:

[0020] Generate a speed reference value according to the wind speed and the grid command value;

[0021] Get the actual speed value and the actual DC current value;

[0022] After subtracting the speed reference value from the speed actual value, a DC power reference value is generated through a PI controller;

[0023] Calculating a DC current reference value according to the DC power reference value and the DC voltage;

[0024] The DC current reference value passes through a limiting link, is subtracted from the DC current actual value, and then passes through a PI controller and a DC voltage feedforward link to obtain a DC internal potential reference value.

[0025] Optionally, the AC controller includes a capacitor voltage controller, a reactive power controller and an AC decoupling controller, and the control process of the AC controller is:

[0026] Obtaining a capacitor voltage reference value, a capacitor voltage actual average value, a reactive power reference value, and a reactive power actual value;

[0027] The capacitor voltage reference value and the actual average value of the capacitor voltage are input into the capacitor voltage controller for difference, and then a d-axis current reference value is generated through a PI controller;

[0028] The reactive power reference value and the reactive power actual value are input into the reactive power controller for difference, and then a q-axis current reference value is generated through a PI controller;

[0029] Get the actual value of the d-axis current and the actual value of the q-axis current;

[0030] The d-axis current reference value, the d-axis current actual value, the q-axis current reference value and the q-axis current actual value are input into the AC decoupling controller for decoupling processing to obtain a three-phase AC internal potential, wherein the three-phase AC internal potential includes an A-phase AC internal potential, a B-phase AC internal potential and a C-phase AC internal potential.

[0031] Optionally, the control processing process of the circulation controller is:

[0032] Acquire a three-phase circulating current, wherein the three-phase circulating current includes a phase A circulating current, a phase B circulating current, and a phase C circulating current;

[0033] The circulating current suppression control is performed according to the A-phase circulating current, the B-phase circulating current and the C-phase circulating current to obtain the internal potential of the circulating current, wherein the internal potential of the circulating current includes the internal potential of the A-phase circulating current and the internal potential of the B-phase circulating current.

[0034] Optionally, the voltage linear transformation process is implemented by the following formula:

[0035]

[0036] in, , , , , , They are the output voltage reference values ​​of the six bridge arms of the three phases A, B and C respectively; , , They are the A phase AC internal potential, the B phase AC internal potential, and the C phase AC internal potential respectively; is the DC internal potential reference value; , They are the internal potential of the A phase circulating current and the internal potential of the B phase circulating current respectively.

[0037] Optionally, when the full power converter is used for dual three-phase motors, or multiple three-phase motors:

[0038] The dual three-phase motor, or each three-phase system in the multi-three-phase motor needs to be connected to the main circuit of one full-power converter; the AC side of each full-power converter is connected in parallel to the same three-phase transformer; and each full-power converter shares a speed controller.

[0039] Optionally, the unidirectional current-source modular multilevel converter is further used for:

[0040] The DC current waveform is controlled according to the DC voltage to eliminate torque pulsation.

[0041] The present invention also provides a control method for a full-power converter of a permanent magnet synchronous wind generator, comprising:

[0042] The topology structure of the full-power converter is set to adopt a diode rectifier on the wind turbine side and a unidirectional current-type modular multilevel converter on the AC grid side; wherein the unidirectional current-type modular multilevel converter is composed of a three-phase bridge arm;

[0043] The AC voltage emitted by the wind turbine generator side, whose frequency and amplitude vary with time, is converted into a DC voltage by the diode rectifier;

[0044] The unidirectional current-type modular multilevel converter completes the inversion of the DC voltage according to the amplitude and frequency of the grid voltage, obtains a three-phase output voltage reference value, and transmits the three-phase output voltage reference value to the AC grid side.

[0045] It can be seen from the above technical solutions that the present invention has the following advantages:

[0046] A full-power converter and control method for a permanent magnet synchronous wind turbine are provided. The topological structure of the full-power converter is that a diode rectifier is used on the wind turbine side, and a unidirectional current type modular multilevel converter is used on the AC grid side. The unidirectional current type modular multilevel converter is composed of three-phase bridge arms. The AC voltage with a frequency and amplitude that changes with time emitted by the wind turbine side is converted into a DC voltage by a diode rectifier; the DC voltage is inverted according to the amplitude and frequency of the grid voltage by a unidirectional current type modular multilevel converter, a three-phase output voltage reference value is obtained, and the three-phase output voltage reference value is transmitted to the AC grid side. Thus, the diode rectifier is used on the machine side, which can not only convert the AC voltage into the DC voltage, but also reduce the cost. The unidirectional current type modular multilevel converter with only one-stage switching converter is used on the grid side, which has lower loss. Moreover, the unidirectional current type modular multilevel converter has the characteristics of modular design, and medium-voltage equipment can be realized with low-voltage semiconductor devices, which is conducive to establishing a standardized design. Therefore, the technical solution proposed in the present invention can not only reduce costs and losses, but also make the redundant design very simple, and at the same time has the advantages of being able to output voltage at multiple levels, with small voltage steps, and low voltage and current change rates. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] 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 some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0048] Figure 1 A schematic diagram of the topological structure of a BTB-NPC converter in a related technology;

[0049] Figure 2 A schematic diagram of a topological structure of a DBN converter in a related technology;

[0050] Figure 3A schematic diagram of the control structure of a full-power converter of a permanent magnet synchronous wind turbine;

[0051] Figure 4 The figure is an example of the overall structure of a full-power converter of a permanent magnet synchronous wind generator when it is applied to a dual three-phase generator;

[0052] Figure 5 The figure is an example diagram of DC control when a full-power converter of a permanent magnet synchronous wind generator is applied to a multi-three-phase generator. DETAILED DESCRIPTION

[0053] The embodiment of the present invention provides a full-power converter and control method for a permanent magnet synchronous wind generator, which is used to solve or partially solve the technical problems in the related art of low switching frequency, high voltage change rate, large loss and high cost during power conversion of the permanent magnet synchronous generator.

[0054] In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described below are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0055] As an example, for the power conversion control of permanent magnet synchronous wind turbine PSMG, the currently used back-to-back neutral point clamped three-level converter BTB-NPC structure and "diode rectifier + DC non-isolated boost + neutral point clamped three-level converter" DBN structure are analyzed:

[0056] 1. Back-to-back neutral point clamped three-level converter BTB-NPC structure

[0057] The mainstream converter type used in large-capacity medium-pressure wind turbines currently in operation is BTB-NPC. Its topology is as follows: Figure 1 As shown. BTB-NPC is mainly composed of two NPC converters. Their DC sides are directly connected. The NPC on the generator side is directly connected to the wind turbine to control the electromagnetic torque and power of the wind turbine. The NPC on the grid side is connected to the grid through a transformer and outputs power to the grid.

[0058] The defects of the BTB-NPC structure are:

[0059] 1) Limited by losses and heat dissipation, the switching frequency of large-capacity BTB-NPC is usually only about 1kHz (frequency unit: kilohertz), which is only about 20 times the base frequency of 50Hz (frequency unit: hertz) (the switching frequency of small-capacity converters can reach several kHz to more than ten kHz). The low switching frequency brings great difficulties to the design of the grid-side filter.

[0060] 2) Since the NPC converter can only output three levels, for medium voltage scenarios, the voltage step of each switch is very large. For example, for a wind turbine with a rated voltage of 3.3kV (voltage unit: kilovolt), the voltage step of the NPC reaches 2.7kV, resulting in a very high voltage change rate.

[0061] 3) NPC converters are based on fully controlled devices, which are more expensive than non-controlled devices such as diodes. Using NPC converters based on fully controlled devices on both the generator and grid sides will inevitably increase the overall cost. Moreover, NPC is a PWM (Pulse Width Modulation) converter with high losses.

[0062] (II) “Diode rectifier + DC non-isolated boost + neutral point clamped three-level converter” DBN structure

[0063] In related research fields, DBN structure is also one of the research hotspots. Its topological structure is as follows Figure 2 As shown. On the fan side, a six-pulse or twelve-pulse diode rectifier is used. The fan speed is related to the wind speed. The amplitude and frequency of its output AC voltage are related to the speed. The average DC voltage of the diode rectifier is proportional to the amplitude of the fan AC voltage. Therefore, the average DC voltage output by the diode rectifier actually changes with the wind speed. The theoretical range of change is from 0 to the rated DC voltage.

[0064] The NPC converter on the grid side is the same as the BTB-NPC introduced above, and its DC voltage must always maintain the rated value. This causes a contradiction between the DC voltages of the machine-side and grid-side converters. To solve this problem, a DC non-isolated boost circuit (Boost Circuit) is added between the two. The DC voltage on the side connected to the diode is variable, while the DC voltage on the side connected to the NPC is constant.

[0065] The defects of DBN structure are:

[0066] 1) There is ripple on the DC voltage output by the diode rectifier, and the Boost circuit can usually only control the DC current to a constant value. Therefore, the DC voltage ripple of the diode will be reflected in the DC power. The DC power of the diode is essentially the electromagnetic power of the generator. Therefore, it will cause the electromagnetic power of the generator to constantly shake, and then cause electromagnetic torque pulsation. For large-capacity fans, electromagnetic torque pulsation will affect the life of the mechanical part of the mechanical equipment.

[0067] 2) Large-capacity Boost circuits and NPCs also have the same problems as the BTB-NPC solution, such as low switching frequency, difficult filtering, high voltage steps, and large voltage change rate.

[0068] Therefore, one of the core invention points of the embodiment of the present invention is: in view of the deficiencies in the related art, a full-power converter and control method for a permanent magnet synchronous wind turbine is proposed. The topological structure of the full-power converter is that a diode rectifier is used on the wind turbine side, and a unidirectional current-type modular multi-level converter is used on the AC grid side; the unidirectional current-type modular multi-level converter is composed of a three-phase bridge arm; wherein, the AC voltage emitted by the wind turbine side, whose frequency and amplitude change with time, is converted into a DC voltage by a diode rectifier; the DC voltage is inverted by a unidirectional current-type modular multi-level converter according to the amplitude and frequency of the grid voltage, and a three-phase output voltage reference value is obtained, and the three-phase output voltage reference value is transmitted to the AC grid side.

[0069] Therefore, the use of diode rectifiers on the machine side can not only convert AC voltage into DC voltage, but also reduce costs. The related technology includes at least two-stage switching conversion processes, such as the machine side and grid side of BTB-NPC are both switch conversion, and the three-level Boost and grid-side NPC of DBN are both switch conversion, and the switch conversion loss is large. However, the grid side of the present invention adopts a unidirectional current type modular multilevel converter (UC-MMC) with only one level of switch converter, which has lower losses. And the unidirectional current type modular multilevel converter UC-MMC has modular design characteristics, and medium-voltage equipment can be realized with low-voltage semiconductor devices, which is conducive to establishing a standardized design. Furthermore, based on the high control performance of the unidirectional current type modular multilevel converter UC-MMC, not only can the torque pulsation caused by the diode rectifier be eliminated, but also due to the high output AC voltage, the cable cross-sectional area between the wind turbine converter and the transformer can be reduced by 75%. Therefore, the technical solution proposed in the present invention can not only reduce costs and losses, but also make the redundant design very simple, and at the same time has the advantages of being able to output voltage at multiple levels, with small voltage steps, and low voltage and current change rates.

[0070] Reference Figure 3 , shows a schematic diagram of the control structure of a full-power converter of a permanent magnet synchronous wind generator provided in an embodiment of the present invention.

[0071] The full-power converter provided in the embodiment of the present invention is specifically named as a single-stage multilevel converter (SMC).

[0072] Among them, the full power converter SMC is a special power electronic converter. It can achieve multi-level output in a single conversion stage. Thereby providing better output waveform quality and lower harmonic distortion. Compared with the traditional two-level converter, the multi-level converter can generate more voltage levels. Thereby reducing the harmonic content in the output waveform, improving efficiency and reliability. The full power converter SMC provided by the present invention is suitable for application scenarios requiring high-quality output waveforms and high efficiency.

[0073] Specifically, combined Figure 3 It can be seen that from the overall structure point of view, the full power converter SMC is mainly composed of a main circuit and a controller.

[0074] The main circuit consists of two parts: the wind turbine side (machine side) and the AC grid side (grid side). The machine side uses a diode rectifier to reduce costs. The grid side uses a unidirectional current-type modular multilevel converter UC-MMC. That is, the topology of the full-power converter SMC is that the wind turbine side uses a diode rectifier and the AC grid side uses a unidirectional current-type modular multilevel converter UC-MMC.

[0075] In terms of the controller, since the diode rectifier on the machine side does not need to be controlled, the controller referred to in the present invention actually only includes the controller of the unidirectional current-type modular multilevel converter UC-MMC.

[0076] The main function of the diode rectifier is to convert the AC voltage emitted by the wind turbine (wind turbine side), whose frequency and amplitude vary with time, into a DC voltage.

[0077] The unidirectional current-type modular multilevel converter UC-MMC is composed of three-phase bridge arms. Each bridge arm is provided with a plurality of multilevel converter modules. Each multilevel converter module is composed of a capacitor, a resistor, a plurality of diodes, a plurality of semiconductor switch devices, and an anti-parallel diode having the same number as the semiconductor switch devices. Among them, the anti-parallel diode is integrated inside the semiconductor switch device, or connected in parallel with the semiconductor switch device.

[0078] Specifically, combined Figure 3 Each bridge arm has multiple multi-level commutation submodules (Submodule, SM, Figure 3 SM1~SM for medium n In each multi-level converter module, a diode D1, a diode D4, a semiconductor switch device S2, a semiconductor switch device S3, a semiconductor switch device S brk , capacitor C, resistor R brk constitute.

[0079] For ease of understanding, Figure 3 The multi-level converter module also shows an anti-parallel diode d S2 d S3 d Sbrk For some semiconductor switching devices with internally integrated anti-parallel diodes (such as insulated gate bipolar transistors (IGBTs)), these diodes have been integrated into S2, S3, S brk For some semiconductor switching devices that do not have an integrated anti-parallel diode (such as Integrated Gate Commuted Thyristor (IGCT)), these diodes need to be installed separately. Figure 3 As shown, the anti-parallel diodes are connected in parallel with their corresponding semiconductor switching devices.

[0080] The unidirectional current-type modular multilevel converter UC-MMC has two main functions: on the one hand, it converts the time-varying DC voltage obtained by diode rectification according to the amplitude and frequency of the grid voltage and outputs power to the AC grid. On the other hand, it uses its high controllability to control the DC current waveform according to the DC voltage of the diode rectifier, thereby eliminating torque pulsation.

[0081] In specific implementation, the unidirectional current-type modular multilevel converter is mainly used to: complete the inversion of DC voltage according to the amplitude and frequency of the grid voltage, obtain the three-phase output voltage reference value, and transmit the three-phase output voltage reference value to the AC grid side. It can also be used to: control the DC current waveform according to the DC voltage to eliminate torque pulsation.

[0082] Combined with the previous discussion, it can be seen that since the diode rectifier is uncontrolled (no need to control), the controller of SMC refers to the controller of the unidirectional current type modular multilevel converter UC-MMC in the full power converter SMC. Furthermore, the controller can be mainly divided into four parts: DC controller, AC controller, circulating current controller, and voltage linear conversion.

[0083] The DC controller can take into account the functions of fan speed control and torque pulsation elimination. The DC controller is mainly used for speed control of DC motors. It can adjust the voltage or current applied to the motor to change the speed and torque of the motor.

[0084] An AC controller is a device used to control an AC motor, especially an induction motor. It can be used to control the start, stop, direction and speed of the motor.

[0085] A circulating current controller is a device specifically designed to control circulating currents between multiple motors or power supplies. In some cases, when multiple power supplies are connected in parallel or multiple motors are connected to the same load, uneven current distribution, i.e. circulating current, may occur. The role of a circulating current controller is to ensure that the current is evenly distributed to avoid efficiency loss or equipment damage caused by circulating current.

[0086] Voltage linear transformation is actually a mathematical transformation. It is used for signal processing, filtering, amplification or transformation. In practical applications, the voltage output by the inverter usually needs to be linearly transformed to adjust the amplitude or frequency. In the inverter, voltage linear transformation can be used for signal modulation and voltage regulation.

[0087] In combination with the above-mentioned contents, in a specific implementation, the DC controller controls the generator speed by controlling the DC current to obtain a DC internal potential reference value.

[0088] Combination Figure 3 The DC controller part of the speed reference value generation module generates the square of the speed reference value according to the wind speed and the grid command value. . The square of the actual speed After the difference is made, a DC power reference value is generated through a PI controller (or other type of controller) .Then Divide the diode rectifier DC voltage , get the DC current reference value . After the limiting link, the actual value of the DC current The difference is then passed through the PI controller (or other type of controller), and then through the DC voltage feedforward link to obtain the DC internal potential reference value of the unidirectional current type modular multilevel converter UC-MMC. .

[0089] In the specific implementation, the control process of the DC controller is as follows: Generate a speed reference value according to the wind speed and the grid command value (the square of the speed reference value is actually taken in the calculation here) ; Get the actual speed value (here corresponds to the square of the actual speed) And the actual value of DC current ; Based on the speed reference The actual speed value After making the difference, the DC power reference value is generated through the PI controller ; According to the DC power reference value With DC voltage , calculate the DC current reference value ; Set the DC current reference value After the limiting link, the actual value of the DC current After the difference is made, it passes through the PI controller and then the DC voltage feedforward link to obtain the DC internal potential reference value. .

[0090] The AC controller controls the AC current to control the AC active and reactive power and obtain the three-phase AC internal potential.

[0091] Combination Figure 3 The AC controller part of the AC controller can mainly include a capacitor voltage controller, a reactive power controller and an AC decoupling controller. In the specific implementation, the control process of the AC controller is: obtain the capacitor voltage reference value (the square of the capacitor voltage reference value is actually taken when calculating here) , the actual average value of the capacitor voltage (here it corresponds to the square of the actual average value of the capacitor voltage) , reactive power reference value And the actual value of reactive power ; Set the capacitor voltage reference value And the actual average value of the capacitor voltage After inputting to the capacitor voltage controller for difference, the d-axis current reference value is generated through the PI controller ; Set the reactive power reference value And the actual value of reactive power After inputting into the reactive power controller for difference, the q-axis current reference value is generated through the PI controller ; Get the actual value of the d-axis current And the actual value of q-axis current ; Set the d-axis current reference value , Actual value of d-axis current , q-axis current reference value And the actual value of q-axis current Input to the AC decoupling controller for decoupling processing to obtain the three-phase AC internal potential, which includes the A-phase AC internal potential , B phase AC internal potential And the C phase AC internal potential .

[0092] The circulating current controller obtains the internal potential of the circulating current by suppressing the internal circulating current.

[0093] Combination Figure 3 The circulation controller part, in the specific implementation, the control process of the circulation controller is: obtain the three-phase circulation, the three-phase circulation includes the A phase circulation 、B phase circulation and C phase circulation ; According to the A phase circulation 、B phase circulation and C phase circulation Perform circulating current suppression control to obtain the internal potential of the circulating current, which includes the internal potential of the circulating current of phase A. And the potential of the B phase circulating current .

[0094] The circulating current controller part is the same as the circulating current controller of the MMC (Modular Multilevel Converter) in the related art, and is used to suppress or control the circulating current inside the MMC. Figure 3 It is not described in detail, and those skilled in the art can implement it by referring to the circulation control technology of related technology, which will not be described here.

[0095] Voltage linear transformation is based on the DC internal potential reference value 、AC internal potential( , , ), circulating current internal potential ( , ) is linearly transformed to obtain the three-phase output voltage reference value of the unidirectional current-type modular multilevel converter. The three-phase output voltage reference value includes the output voltage reference values ​​of the six bridge arms of the three phases. .

[0096] As mentioned above, the unidirectional current-type modular multilevel converter UC-MMC has six bridge arms. Each bridge arm outputs voltage by switching on and off the multilevel converter module. The bridge arm output voltage reference value refers to how much voltage the controller expects the entire bridge arm to output at every moment based on its external characteristics.

[0097] In the specific implementation, the process of voltage linear transformation is realized by the following formula:

[0098]

[0099] in, , , , , , They are the output voltage reference values ​​of the six bridge arms of the three phases A, B and C respectively; the subscripts a, b and c represent the three phases respectively; the subscripts p and n represent the upper bridge arm and the lower bridge arm respectively; , , They are the A phase AC internal potential, the B phase AC internal potential, and the C phase AC internal potential respectively; is the DC internal potential reference value; , They are the internal potential of the A phase circulating current and the internal potential of the B phase circulating current respectively.

[0100] The technical solutions and related drawings in the embodiments of the present invention are based on three-phase motors. However, large-capacity fans currently also have dual three-phase and multi-three-phase structures. Similarly, the technical solutions in the present invention can also be used for dual three-phase and multi-three-phase motors. Figure 4 , shows an overall structural example diagram of a full-power converter of a permanent magnet synchronous wind turbine generator when applied to a dual three-phase generator. Figure 5 , shows an example diagram of DC control when a full-power converter of a permanent magnet synchronous wind generator is applied to a multi-three-phase generator.

[0101] The only difference is that when the full power converter SMC is used for dual three-phase motors, or multiple three-phase motors:

[0102] (1) Each three-phase system needs to be connected to a full-power converter SMC main circuit. Each full-power converter SMC main circuit is called an SMC unit. The diode side of each SMC unit is connected to a three-phase system of the motor. The AC sides of the unidirectional current-type modular multilevel converter UC-MMC are connected in parallel and then connected to a three-phase transformer.

[0103] (2) Each SMC unit shares a speed controller. The DC power reference value output by the speed controller is divided by k (k is the number of three-phase systems) to obtain the DC power of each SMC unit. The DC power is divided by the DC voltage corresponding to the SMC unit to obtain the DC current of the SMC unit. The AC controller, circulating current control and voltage linear conversion of the unidirectional current-type modular multilevel converter UC-MMC in each SMC unit are calculated independently and do not affect each other.

[0104] In a specific implementation, when the full-power converter SMC is used for a dual three-phase motor or a multi-three-phase motor, each three-phase system in the dual three-phase motor or the multi-three-phase motor needs to be connected to the main circuit of a full-power converter SMC; the AC side of each full-power converter SMC (actually also a unidirectional current-type modular multilevel converter UC-MMC) is connected in parallel to the same three-phase transformer; each full-power converter SMC shares a speed controller.

[0105] In an embodiment of the present invention, a full-power converter for a permanent magnet synchronous wind turbine is proposed. The topological structure of the full-power converter is that a diode rectifier is used on the wind turbine side, and a unidirectional current-type modular multilevel converter is used on the AC grid side; the unidirectional current-type modular multilevel converter is composed of three-phase bridge arms; wherein the diode rectifier is used to convert the AC voltage emitted by the wind turbine side, whose frequency and amplitude change with time, into a DC voltage; the unidirectional current-type modular multilevel converter is used to complete the inversion of the DC voltage according to the amplitude and frequency of the grid voltage, obtain a three-phase output voltage reference value, and transmit the three-phase output voltage reference value to the AC grid side.

[0106] Therefore, the use of diode rectifiers on the machine side can not only convert AC voltage into DC voltage, but also reduce costs. The grid side uses a unidirectional current-type modular multilevel converter UC-MMC with only one-stage switching converter, which has lower losses. In addition, the unidirectional current-type modular multilevel converter UC-MMC has modular design characteristics, and medium-voltage equipment can be realized with low-voltage semiconductor devices, which is conducive to establishing a standardized design. Furthermore, based on the high control performance of the unidirectional current-type modular multilevel converter UC-MMC, not only can the torque pulsation caused by the diode rectifier be eliminated, but also due to the high output AC voltage, the cable cross-sectional area between the wind turbine converter and the transformer can be reduced by 75%. Therefore, the use of the technical solution proposed by the present invention can not only reduce costs and losses, but also make the redundant design very simple, and at the same time have the advantages of multi-level output voltage, small voltage steps, and low voltage and current change rates.

[0107] The embodiment of the present invention further provides a control method for a full power converter of a permanent magnet synchronous wind turbine generator, which may specifically include the following steps:

[0108] Step 201, setting the topology structure of the full-power converter to a diode rectifier on the wind turbine side and a unidirectional current-type modular multilevel converter on the AC grid side; wherein the unidirectional current-type modular multilevel converter is composed of a three-phase bridge arm;

[0109] Step 202, converting the AC voltage whose frequency and amplitude vary with time, emitted by the wind turbine generator side, into a DC voltage through the diode rectifier;

[0110] Step 203, completing the inversion of the DC voltage according to the amplitude and frequency of the grid voltage through the unidirectional current-type modular multilevel converter, obtaining a three-phase output voltage reference value, and transmitting the three-phase output voltage reference value to the AC grid side.

[0111] In an optional embodiment, a plurality of multilevel converter modules are provided in each bridge arm of the unidirectional current-source modular multilevel converter; each of the multilevel converter modules is composed of a capacitor, a resistor, a plurality of diodes, a plurality of semiconductor switch devices, and anti-parallel diodes whose number is the same as that of the plurality of semiconductor switch devices;

[0112] The anti-parallel diode is integrated inside the semiconductor switch device, or connected to the semiconductor switch device in parallel.

[0113] In an optional embodiment, the unidirectional current-type modular multilevel converter includes a DC controller, an AC controller, a circulating current controller, and a voltage linear converter; the unidirectional current-type modular multilevel converter completes the inversion of the DC voltage according to the amplitude and frequency of the grid voltage to obtain a three-phase output voltage reference value, including:

[0114] Based on the DC controller, the DC current is controlled to control the generator speed, thereby obtaining a DC internal potential reference value;

[0115] Based on the AC controller, the AC current is controlled to control the AC active and reactive power to obtain the three-phase AC internal potential;

[0116] Based on the circulating current controller, the internal circulating current potential is obtained by suppressing the internal circulating current;

[0117] Based on the voltage linear transformation, the three-phase output voltage reference value of the unidirectional current type modular multilevel converter is obtained by performing linear transformation based on the DC internal potential reference value, the AC internal potential, and the circulating current internal potential, and the three-phase output voltage reference value includes the output voltage reference values ​​of the three-phase six bridge arms.

[0118] In an optional embodiment, controlling the DC current to control the generator speed and obtaining the DC internal potential reference value includes:

[0119] Generate a speed reference value according to the wind speed and the grid command value;

[0120] Get the actual speed value and the actual DC current value;

[0121] After subtracting the speed reference value from the speed actual value, a DC power reference value is generated through a PI controller;

[0122] Calculating a DC current reference value according to the DC power reference value and the DC voltage;

[0123] The DC current reference value passes through a limiting link, is subtracted from the DC current actual value, and then passes through a PI controller and a DC voltage feedforward link to obtain a DC internal potential reference value.

[0124] In an optional embodiment, the AC controller includes a capacitor voltage controller, a reactive power controller and an AC decoupling controller, and the AC current is controlled to control the AC active and reactive power to obtain the three-phase AC internal potential, including:

[0125] Obtaining a capacitor voltage reference value, a capacitor voltage actual average value, a reactive power reference value, and a reactive power actual value;

[0126] The capacitor voltage reference value and the actual average value of the capacitor voltage are input into the capacitor voltage controller for difference, and then a d-axis current reference value is generated through a PI controller;

[0127] The reactive power reference value and the reactive power actual value are input into the reactive power controller for difference, and then a q-axis current reference value is generated through a PI controller;

[0128] Get the actual value of the d-axis current and the actual value of the q-axis current;

[0129] The d-axis current reference value, the d-axis current actual value, the q-axis current reference value and the q-axis current actual value are input into the AC decoupling controller for decoupling processing to obtain a three-phase AC internal potential, wherein the three-phase AC internal potential includes an A-phase AC internal potential, a B-phase AC internal potential and a C-phase AC internal potential.

[0130] In an optional embodiment, obtaining the inner potential of the circulating current by suppressing the inner circulating current includes:

[0131] Acquire a three-phase circulating current, wherein the three-phase circulating current includes a phase A circulating current, a phase B circulating current, and a phase C circulating current;

[0132] The circulating current suppression control is performed according to the A-phase circulating current, the B-phase circulating current and the C-phase circulating current to obtain the internal potential of the circulating current, wherein the internal potential of the circulating current includes the internal potential of the A-phase circulating current and the internal potential of the B-phase circulating current.

[0133] In an optional embodiment, the voltage linear transformation process is implemented by the following formula:

[0134]

[0135] in, , , , , , They are the output voltage reference values ​​of the six bridge arms of the three phases A, B and C respectively; , , They are the A phase AC internal potential, the B phase AC internal potential, and the C phase AC internal potential respectively; is the DC internal potential reference value; , They are the internal potential of the A phase circulating current and the internal potential of the B phase circulating current respectively.

[0136] In an optional embodiment, when the full power converter is used for dual three-phase motors, or multiple three-phase motors, the method further includes:

[0137] Connecting each three-phase system of the dual three-phase motor or the multi-three-phase motor to the main circuit of one full-power converter;

[0138] The AC sides of the full-power converters are connected in parallel to the same three-phase transformer; and the full-power converters share a speed controller.

[0139] In an optional embodiment, the method further includes:

[0140] The unidirectional current-type modular multi-level converter controls the DC current waveform according to the DC voltage to eliminate torque pulsation.

[0141] In an embodiment of the present invention, a control method for a full-power converter applied to a permanent magnet synchronous wind turbine is proposed. The topology of the full-power converter is set to use a diode rectifier on the wind turbine side and a unidirectional current type modular multilevel converter on the AC grid side; wherein the unidirectional current type modular multilevel converter is composed of a three-phase bridge arm; the AC voltage with a frequency and amplitude that changes with time emitted by the wind turbine side is converted into a DC voltage by a diode rectifier; the DC voltage is inverted by the unidirectional current type modular multilevel converter according to the amplitude and frequency of the grid voltage, and a three-phase output voltage reference value is obtained, and the three-phase output voltage reference value is transmitted to the AC grid side. Thus, the machine side is set to use a diode rectifier, which can not only convert the AC voltage into the DC voltage, but also reduce the cost. The grid side is set to use a unidirectional current type modular multilevel converter UC-MMC with only one-stage switching converter, which has lower losses. Moreover, the unidirectional current type modular multilevel converter UC-MMC has modular design characteristics, and medium-voltage equipment can be realized with low-voltage semiconductor devices, which is conducive to establishing a standardized design. Therefore, the technical solution proposed in the present invention can not only reduce costs and losses, but also make the redundant design very simple, and at the same time has the advantages of being able to output voltage at multiple levels, with small voltage steps, and low voltage and current change rates.

[0142] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working processes of the systems, devices and units described above can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0143] In the several embodiments provided by the present invention, it should be understood that the disclosed systems, devices and methods can be implemented in other ways. For example, the device embodiments described above are only schematic. For example, the division of the units is only a logical function division. There may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be an indirect coupling or communication connection through some interfaces, devices or units, which can be electrical, mechanical or other forms.

[0144] 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 units may be selected according to actual needs to achieve the purpose of the scheme of this embodiment. In addition, the functional units in the various embodiments of the present invention may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit.

[0145] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A full power converter for a permanent magnet synchronous wind turbine, characterized in that: The topological structure of the full-power converter is that a diode rectifier is used on the wind turbine generator side, and a unidirectional current-type modular multilevel converter is used on the AC grid side; the unidirectional current-type modular multilevel converter is composed of a three-phase bridge arm; wherein, The diode rectifier is used to convert the AC voltage emitted by the wind generator side, the frequency and amplitude of which change continuously with time, into a DC voltage; The unidirectional current-type modular multilevel converter is used to complete the inversion of the DC voltage according to the amplitude and frequency of the grid voltage, obtain a three-phase output voltage reference value, and transmit the three-phase output voltage reference value to the AC grid side.

2. The full power converter of the permanent magnet synchronous wind generator according to claim 1, characterized in that: A plurality of multi-level converter modules are arranged in each bridge arm of the unidirectional current-type modular multi-level converter; each of the multi-level converter modules is composed of a capacitor, a resistor, a plurality of diodes, a plurality of semiconductor switch devices, and anti-parallel diodes whose number is the same as that of the plurality of semiconductor switch devices; The anti-parallel diode is integrated inside the semiconductor switch device, or connected to the semiconductor switch device in parallel.

3. The full power converter of the permanent magnet synchronous wind generator according to claim 1, characterized in that: The unidirectional current-type modular multi-level converter includes a DC controller, an AC controller, a circulating current controller and a voltage linear converter; wherein, The DC controller controls the generator speed by controlling the DC current to obtain a DC internal potential reference value; The AC controller controls the AC active and reactive power by controlling the AC current to obtain the three-phase AC internal potential; The circulating current controller obtains the internal potential of the circulating current by suppressing the internal circulating current; The voltage linear conversion obtains the three-phase output voltage reference value of the unidirectional current-type modular multi-level converter by performing linear conversion based on the DC internal potential reference value, the AC internal potential, and the circulating current internal potential, wherein the three-phase output voltage reference value includes the output voltage reference values ​​of the six bridge arms of the three phases.

4. The full power converter of the permanent magnet synchronous wind generator according to claim 3, characterized in that: The control process of the DC controller is as follows: Generate a speed reference value according to the wind speed and the grid command value; Get the actual speed value and the actual DC current value; After subtracting the speed reference value from the speed actual value, a DC power reference value is generated through a PI controller; Calculating a DC current reference value according to the DC power reference value and the DC voltage; The DC current reference value passes through a limiting link, is subtracted from the DC current actual value, and then passes through a PI controller and a DC voltage feedforward link to obtain a DC internal potential reference value.

5. The full power converter of the permanent magnet synchronous wind generator according to claim 3, characterized in that: The AC controller includes a capacitor voltage controller, a reactive power controller and an AC decoupling controller. The control process of the AC controller is as follows: Obtaining a capacitor voltage reference value, a capacitor voltage actual average value, a reactive power reference value, and a reactive power actual value; The capacitor voltage reference value and the actual average value of the capacitor voltage are input into the capacitor voltage controller for difference, and then a d-axis current reference value is generated through a PI controller; The reactive power reference value and the reactive power actual value are input into the reactive power controller for difference, and then a q-axis current reference value is generated through a PI controller; Get the actual value of the d-axis current and the actual value of the q-axis current; The d-axis current reference value, the d-axis current actual value, the q-axis current reference value and the q-axis current actual value are input into the AC decoupling controller for decoupling processing to obtain a three-phase AC internal potential, wherein the three-phase AC internal potential includes an A-phase AC internal potential, a B-phase AC internal potential and a C-phase AC internal potential.

6. The full power converter of the permanent magnet synchronous wind generator according to claim 3, characterized in that: The control process of the circulation controller is as follows: Acquire a three-phase circulating current, wherein the three-phase circulating current includes a phase A circulating current, a phase B circulating current, and a phase C circulating current; The circulating current suppression control is performed according to the A-phase circulating current, the B-phase circulating current and the C-phase circulating current to obtain the internal potential of the circulating current, wherein the internal potential of the circulating current includes the internal potential of the A-phase circulating current and the internal potential of the B-phase circulating current.

7. The full power converter of the permanent magnet synchronous wind generator according to claim 3, characterized in that: The voltage linear transformation process is achieved through the following formula: in, , , , , , They are the output voltage reference values ​​of the six bridge arms of the three phases A, B and C respectively; , , They are the A phase AC internal potential, the B phase AC internal potential, and the C phase AC internal potential respectively; is the DC internal potential reference value; , They are the internal potential of the A phase circulating current and the internal potential of the B phase circulating current respectively.

8. The full power converter of a permanent magnet synchronous wind generator according to any one of claims 1 to 7, characterized in that: When the full power converter is used for dual three-phase motors or multiple three-phase motors: The dual three-phase motor, or each three-phase system in the multi-three-phase motor needs to be connected to the main circuit of one full-power converter; the AC side of each full-power converter is connected in parallel to the same three-phase transformer; and each full-power converter shares a speed controller.

9. The full power converter of the permanent magnet synchronous wind generator according to claim 8, characterized in that: The unidirectional current-type modular multilevel converter is also used for: The DC current waveform is controlled according to the DC voltage to eliminate torque pulsation.

10. A control method for a full power converter of a permanent magnet synchronous wind turbine generator according to claim 1, characterized in that: include: The topology structure of the full-power converter is set to adopt a diode rectifier on the wind turbine side and a unidirectional current-type modular multilevel converter on the AC grid side; wherein the unidirectional current-type modular multilevel converter is composed of a three-phase bridge arm; The AC voltage emitted by the wind turbine generator side, whose frequency and amplitude vary with time, is converted into a DC voltage by the diode rectifier; The unidirectional current-type modular multilevel converter completes the inversion of the DC voltage according to the amplitude and frequency of the grid voltage, obtains a three-phase output voltage reference value, and transmits the three-phase output voltage reference value to the AC grid side.

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