CN113889998A - Direct-current wind power plant switch reluctance motor current transformation system and control method thereof - Google Patents

Direct-current wind power plant switch reluctance motor current transformation system and control method thereof Download PDF

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CN113889998A
CN113889998A CN202111219241.1A CN202111219241A CN113889998A CN 113889998 A CN113889998 A CN 113889998A CN 202111219241 A CN202111219241 A CN 202111219241A CN 113889998 A CN113889998 A CN 113889998A
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diode
phase winding
switching tube
main circuit
direct current
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CN113889998B (en
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孙冠群
李璟
王颖
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China Jiliang University
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China Jiliang University
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J1/00—Circuit arrangements for dc mains or dc distribution networks
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/3353—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having at least two simultaneously operating switches on the input side, e.g. "double forward" or "double (switched) flyback" converter
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P9/00—Arrangements for controlling electric generators for the purpose of obtaining a desired output
    • H02P9/14—Arrangements for controlling electric generators for the purpose of obtaining a desired output by variation of field
    • H02P9/26—Arrangements for controlling electric generators for the purpose of obtaining a desired output by variation of field using discharge tubes or semiconductor devices
    • H02P9/30—Arrangements for controlling electric generators for the purpose of obtaining a desired output by variation of field using discharge tubes or semiconductor devices using semiconductor devices
    • H02P9/305—Arrangements for controlling electric generators for the purpose of obtaining a desired output by variation of field using discharge tubes or semiconductor devices using semiconductor devices controlling voltage
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P9/00—Arrangements for controlling electric generators for the purpose of obtaining a desired output
    • H02P9/14—Arrangements for controlling electric generators for the purpose of obtaining a desired output by variation of field
    • H02P9/38—Self-excitation by current derived from rectification of both output voltage and output current of generator
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P2101/00—Special adaptation of control arrangements for generators
    • H02P2101/15—Special adaptation of control arrangements for generators for wind-driven turbines
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/70—Wind energy
    • Y02E10/76—Power conversion electric or electronic aspects

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Control Of Eletrric Generators (AREA)

Abstract

A direct current wind power plant switch reluctance motor current transformation system and a control method thereof, the direct current wind power plant is composed of Z fans, Z switch reluctance generator systems and a lifting type direct current converter, each switch reluctance generator system is composed of a switch reluctance generator, the converter system comprises a converter main circuit and an isolation type reversible direct current conversion circuit, wherein the converter system comprises a converter main circuit and the isolation type reversible direct current conversion circuit, the Z switched reluctance generator systems are connected with direct current boosting in series after direct current output, the converter main circuit adopts different excitation power generation modes according to different rotating speed regions during working, the isolation type reversible direct current conversion circuit can be excited during forward working or charge a storage battery in the converter main circuit, the reverse working can assist safe ride-through during low voltage fault, the whole system device is high in utilization rate, strong in controllability and high in cost performance, and the isolation type reversible direct current conversion circuit is suitable for being applied to the field of wind power, particularly offshore direct current wind power.

Description

Direct-current wind power plant switch reluctance motor current transformation system and control method thereof
Technical Field
The invention relates to the field of a switched reluctance motor system, in particular to a converter system which adopts a switched reluctance motor as a wind driven generator of a direct current wind power plant and can realize direct voltage boosting, excitation voltage changing, continuous power generation in a three-speed area, consideration of low voltage ride through multi-stage protection and the like, and a control method thereof.
Background
Wind power is a clean power generation mode, which is the main power in the field of clean energy power generation at present and in the future, but in China, large-scale land wind power development is close to the top, and offshore wind resources of numerous coastal provinces are abundant, and the offshore wind speed is relatively stable, however, offshore wind power development in China is just in the starting stage, and meanwhile, according to experience at home and abroad, offshore wind power is often converged and transmitted in a direct current mode more economically and practically, so that on the aspect of investment cost which is one of bottleneck problems hindering offshore wind power construction development, the choice is not lost in an intelligent way, namely, offshore wind power adopts a direct current mode different from alternating current, but because the current mainstream generators are alternating current generators, the direct current cables are transmitted to the shore after the rectification of a transformer substation is required to be built at sea, and a land power grid is mostly alternating current, therefore, the land needs to be provided with the inverter station, which is a problem of increasing investment cost, however, a local area type direct current power grid is already available, so that the cost problem of the inverter station can be at least reduced.
The switched reluctance motor has a simple and firm structure, and a rotor derived from the switched reluctance motor is only formed by laminating concave-convex groove silicon steel sheets, and has no winding or permanent magnet, so the switched reluctance motor is also resistant to high temperature and high speed, has higher reliability and low maintenance workload, more importantly, the switched reluctance motor can directly send out direct current when being used as a generator, and can directly increase direct current voltage if a plurality of switched reluctance generators are connected in series after being output; however, the current engineering application of the switched reluctance generator for wind power is not available at home and abroad, a few test properties are available, the key point is the operation of the motor, the operation of the motor is greatly dependent on a converter and control thereof, and the operation is some but not mature, so that the defects are more.
When the switched reluctance generator is used for wind power, a plurality of problems in the wind power field, such as low voltage ride through, are faced, and the requirements on a current transformation system of the switched reluctance generator are necessarily required; such as Maximum Power Point Tracking (MPPT) control problems; in addition to controlling the switching angle at which the switched reluctance generator phase winding is energized, other parameters such as field voltage issues can be controlled.
In addition, the switched reluctance generator has the problems that an excitation power supply is separately excited or self-excited in operation, and how to adapt to a current transformation system under the wind power working condition is achieved under the advantages and the disadvantages of the excitation power supply, the reliability of manual labor amount reduction is greatly improved if a storage battery is additionally charged in the case of separate excitation, and the problem of how to start the switched reluctance generator is also achieved in the case of self excitation; whether the converter system can be reused or not, otherwise, the number of hardware is greatly increased, the reliability is reduced, and the loss of the converter system is increased; and so on.
Finally, the most concerned problems of investment cost and return rate in the field of offshore wind power are the core problem of cost performance.
Disclosure of Invention
According to the background technology, the invention provides a switched reluctance motor converter system which adopts a switched reluctance motor as a wind power plant generator, performs direct current power generation and convergence, adopts a multi-switched reluctance generator system output series connection direct voltage boost controllable grid connection, adopts different excitation power generation modes in a multi-speed area, adopts a three-level low voltage ride through scheme, can change excitation voltage and has ultrahigh comprehensive cost performance, and a control method thereof.
The technical scheme of the invention is as follows:
a direct current wind farm switch reluctance motor converter system, at first, the direct current of the direct current wind farm assembles the network and is made up of Z fans, Z switch reluctance generator systems, and a lift-type direct current converter, each said fan connects a said switch reluctance generator system through the mechanical way, such fans and switch reluctance generator systems of Z group totally, Z is greater than 2, the direct current that these switch reluctance generator systems output connects in series, then input to said lift-type direct current converter and export to the direct current electric wire netting, the lift-type direct current converter is a controllable converter, namely regulate the lift-type direct current converter to control its output value according to the direct current electric wire netting needs;
each switched reluctance generator system has the same structure and consists of a switched reluctance generator, a current transformation system and a controller, wherein the current transformation system consists of a current transformation main circuit (containing each phase winding of the switched reluctance generator) and an isolated reversible direct current conversion circuit, the output end of the current transformation main circuit is also used as the input end of the isolated reversible direct current conversion circuit except for being used as the output end of the current transformation system and the switched reluctance generator system, and the output end of the isolated reversible direct current conversion circuit is used as the input end of the current transformation main circuit; the controller receives wind speed, the rotating speed of the switched reluctance generator, output voltage and current of the converter system, and input voltage and current and output voltage and current signals of the isolated reversible direct current conversion circuit, and outputs and controls each switch tube in the converter system;
the converter main circuit consists of a first phase winding converter main circuit, a second phase winding converter main circuit, a third phase winding converter main circuit, a storage battery and a first switch tube, wherein the input ends of the first phase winding converter main circuit, the second phase winding converter main circuit and the third phase winding converter main circuit are connected in parallel, the output ends of the first phase winding converter main circuit, the second phase winding converter main circuit and the third phase winding converter main circuit are also connected in parallel, the X negative pole of the storage battery is used as the input negative pole end of the converter main circuit, the X positive pole of the storage battery is connected with one end of the first switch tube, and the other end of the first switch tube is used as the input positive pole end of the converter main circuit; the first switching tube is a bidirectional controllable power electronic switching device;
the first phase winding current transformation main circuit consists of a first diode, a second diode, a third diode, a fourth diode, a fifth diode, a first inductor, a second switch tube, a third switch tube, a first phase winding and a first capacitor, wherein the anode of the first diode is used as the input positive end of the first phase winding current transformation main circuit, namely the input positive end of the current transformation main circuit, and is connected with the other end of the first switch tube, the input positive end of the second phase winding current transformation main circuit, the input positive end of the third phase winding current transformation main circuit and the output positive end of the isolated reversible direct current transformation circuit, the cathode of the first diode is connected with one end of the first inductor and the anode of the second switch tube, the other end of the first inductor is connected with the anode of the third switch tube, and the cathode of the third switch tube is connected with the cathode of the second switch tube, the anode of the second diode, the cathode of the fourth diode, And one end of the first phase winding, the other end of the first phase winding is connected with the anode of the third diode and the cathode of the fifth diode, and is used as the input cathode end of the first phase winding current transformation main circuit, namely the input cathode end of the current transformation main circuit, the cathode end of the storage battery, the input cathode end of the second phase winding current transformation main circuit, the input cathode end of the third phase winding, and the output cathode end of the isolation type reversible direct current transformation circuit, the cathode of the second diode is connected with the cathode of the third diode and one end of the first capacitor, and is used as the output anode end of the first phase winding current transformation main circuit, namely the output anode end of the current transformation main circuit, and is also the output anode end of the current transformation system and the switched reluctance generator system, and is connected with the output anode end of the second phase winding current transformation main circuit, the output anode end of the third phase winding current transformation main circuit, and the input anode end of the isolation type reversible direct current transformation circuit, the anode of the fourth diode is connected with the anode of the fifth diode and the other end of the first capacitor, is used as the output negative end of the first phase winding current transformation main circuit, namely the output negative end of the current transformation main circuit, and is also the output negative end of the current transformation system and the switched reluctance generator system, and is connected with the output negative end of the second phase winding current transformation main circuit, the output negative end of the third phase winding current transformation main circuit and the input negative end of the isolated reversible direct current transformation circuit;
the second phase winding current transformation main circuit consists of a sixth diode, a seventh diode, an eighth diode, a ninth diode, a twelfth diode, a second inductor, a fourth switching tube, a fifth switching tube, a second phase winding and a second capacitor, wherein the anode of the sixth diode is used as the input positive end of the second phase winding current transformation main circuit, the cathode of the sixth diode is connected with one end of the second inductor and the anode of the fourth switching tube, the other end of the second inductor is connected with the anode of the fifth switching tube, the cathode of the fifth switching tube is connected with the cathode of the fourth switching tube, the anode of the seventh diode, the cathode of the ninth diode and one end of the second phase winding, the other end of the second phase winding is connected with the anode of the eighth diode and the cathode of the twelfth diode and is used as the input negative end of the second phase winding current transformation main circuit, and the cathode of the seventh diode is connected with the cathode of the eighth diode and one end of the second capacitor, the anode of a ninth diode is connected with the anode of a twelfth diode and the other end of the second capacitor and is used as the output negative end of the second phase winding current transformation main circuit;
the third phase winding current-converting main circuit consists of an eleventh diode, a twelfth diode, a thirteenth diode, a fourteenth diode, a fifteenth diode, a third inductor, a sixth switching tube, a seventh switching tube, a third phase winding and a third capacitor, wherein the anode of the eleventh diode is used as the input positive terminal of the third phase winding current-converting main circuit, the cathode of the eleventh diode is connected with one end of the third inductor and the anode of the sixth switching tube, the other end of the third inductor is connected with the anode of the seventh switching tube, the cathode of the seventh switching tube is connected with the cathode of the sixth switching tube, the anode of the twelfth diode, the cathode of the fourteenth diode and one end of the third phase winding, the other end of the third phase winding is connected with the anode of the thirteenth diode and the cathode of the fifteenth diode and is used as the input negative terminal of the third phase winding current-converting main circuit, and the cathode of the twelfth diode is connected with the cathode of the thirteenth diode and one end of the third capacitor, the anode of the fourteenth diode is connected with the anode of the fifteenth diode and the other end of the third capacitor and is used as the output negative end of the third phase winding current transformation main circuit;
the voltage at the output end of the isolated reversible direct current conversion circuit is called excitation voltage and is used for exciting a phase winding in each phase winding current transformation main circuit or charging a storage battery, and the input voltage of the isolated reversible direct current conversion circuit is also called power generation voltage, namely the voltage at the output end of each current transformation main circuit and the output voltage of each switched reluctance generator system;
the isolated reversible direct current conversion circuit is composed of a fourth capacitor, a fifth capacitor, a sixth capacitor, a seventh capacitor, a sixteenth diode, a seventeenth diode, an eighth switch tube, a ninth switch tube, a tenth switch tube, an eleventh switch tube, a twelfth switch tube, a thirteenth switch tube, a fourteenth switch tube, a fifteenth switch tube, a sixteenth switch tube, a seventeenth switch tube, a transformer and a fourth inductor, one end of the fourth capacitor is connected with one end of the sixth capacitor, a cathode of the sixteenth diode and an anode of the sixteenth switch tube and serves as an input positive end of the isolated reversible direct current conversion circuit, one end of the fifth capacitor is connected with one end of the seventh capacitor, an anode of the seventeenth diode and a cathode of the seventeenth switch tube and serves as an input negative end of the isolated reversible direct current conversion circuit, one end of a secondary side winding of the transformer is connected with the other end of a fourth capacitor, the anode of a sixteenth diode, the cathode of a sixteenth switching tube, the other end of a fifth capacitor, the cathode of a seventeenth diode and the anode of a seventeenth switching tube, the other end of the secondary side winding of the transformer is connected with the other end of a sixth capacitor and the other end of a seventh capacitor, one end of a primary side winding of the transformer is connected with the cathode of an eighth switching tube, the anode of a ninth switching tube, the anode of a tenth switching tube and the cathode of an eleventh switching tube, the other end of a primary side winding of the transformer is connected with the cathode of a twelfth switching tube, the anode of a thirteenth switching tube, the anode of a fourteenth switching tube and the cathode of a fifteenth switching tube, the anode of an eighth switching tube is connected with the cathode of a ninth switching tube, the anode of a twelfth switching tube, the cathode of a thirteenth switching tube and one end of a fourth inductor, the other end of the fourth inductor is used as an output positive end of the isolated reversible direct current conversion circuit, and the cathode of the tenth switching tube is connected with the anode of the eleventh switching tube, the cathode of the fourteenth switching tube and the anode of the fifteenth switching tube and is used as an output negative end of the isolated reversible direct current conversion circuit.
The invention discloses a control method of a direct-current wind power plant switch reluctance motor current transformation system, which comprises the following steps:
the common excitation power supply of each phase winding of the switched reluctance generator is divided into the following schemes:
1) when the storage battery provides an excitation power supply, the first switch tube is conducted reversely, and the scheme has the premise that the electric energy stored in the storage battery is higher than the minimum limit value, excitation is not required to be changed into excitation voltage, and the excitation voltage is equal to the voltage of the storage battery;
2) when the isolated reversible direct current conversion circuit provides an excitation power supply and the storage battery does not need to be charged, the two directions of the first switching tube are both in a turn-off state, and on the other premise, the electric energy stored by the storage battery is higher than the minimum limit value, the generating voltage is within the normal value range required by the system, and the excitation voltage needs to be adjusted to realize the performance required by the system;
3) when the isolated reversible direct current conversion circuit provides an excitation power supply and the storage battery needs to be charged, the first switching tube is conducted in the forward direction, and on the other premise, the electric energy stored in the storage battery is lower than the minimum limit value, the excitation voltage and the current accord with the range of the charging parameters of the storage battery, the generating voltage is also in the range of the normal value required by the system, and the system needs to adjust the excitation voltage to realize the performance required by the system;
when the switched reluctance motor is to operate according to the working condition of the switched reluctance generator, an excitation power supply is required to provide excitation electric energy for a phase winding of the switched reluctance motor, but when a system is started, the switched reluctance motor is started according to a switched reluctance motor mode, the excitation power supply is also required necessarily at the moment and is used as a power supply when the motor is in the working condition, and after the starting is finished according to the operating principle of the switched reluctance motor and the power generation operation condition of a fan is met, the switched reluctance motor is put into the working condition of the generator to operate;
during the working condition operation of the switched reluctance generator, firstly detecting and judging the rotating speed of the rotor, and dividing the rotating speed of the rotor into three areas, namely a low-speed area, a medium-speed area and a high-speed area;
according to the rotor position information, when the first phase winding needs to be put into operation, the first phase winding current transformation main circuit is put into operation under the supply of an excitation power supply, firstly, the rotating speed is judged, when the first phase winding is in a low-speed area, a second switch tube is closed and conducted, an excitation stage is started, the excitation power supply supplies power and excites the first phase winding through a first diode and the second switch tube, when the excitation stage needs to be finished according to the rotor position information, the second switch tube is turned off, and the first phase winding outputs electric energy to the first capacitor side through a third diode and a fourth diode, namely the output end of the current transformation main circuit; when the rotating speed is in a medium-speed region, the third switching tube is closed and conducted, an excitation stage is started, an excitation power supply supplies power and excites the first phase winding through the first diode, the first inductor and the third switching tube, the third switching tube is turned off when the excitation stage needs to be finished according to the position information of the rotor, and the first phase winding outputs electric energy to the output end of the converter main circuit through the third diode and the fourth diode; when the converter main circuit is in a high-speed region, the third switch tube is always in a closed conduction state, namely the third switch tube is always in a closed state in the working universe of the first phase winding in an excitation stage and a power generation stage, when the third switch tube is in the excitation stage at the beginning of the closed conduction, except that the excitation power supply supplies power and excites the first phase winding through the first diode, the first inductor and the third switch tube, when the voltage at two ends of the first phase winding is greater than the power generation voltage at the output end of the converter main circuit, the electric energy of the excitation power supply can output electric energy to the output end of the converter main circuit through the second diode and the fifth diode, when the first phase winding discharges, namely in the power generation stage, the first phase winding outputs electric energy to the output end of the converter main circuit through the third diode and the fourth diode, and simultaneously feeds back the electric energy to the excitation power supply and the first inductor through the first diode;
according to the rotor position information, when a second phase winding needs to be put into operation, the second phase winding current conversion main circuit is put into operation under the supply of an excitation power supply, firstly, the rotating speed is judged, when the second phase winding is in a low-speed area, a fourth switch tube is closed and conducted, an excitation stage is started, the excitation power supply supplies power and excites the second phase winding through a sixth diode and the fourth switch tube, when the excitation stage needs to be finished according to the rotor position information, the fourth switch tube is turned off, and the second phase winding outputs electric energy to the side of a second capacitor, namely the output end of the current conversion main circuit, through an eighth diode and a ninth diode; when the rotating speed is in a medium-speed region, the fifth switching tube is closed and conducted, an excitation stage is started, an excitation power supply supplies power and excites the second-phase winding through the sixth diode, the second inductor and the fifth switching tube, the fifth switching tube is turned off when the excitation stage needs to be finished according to the position information of the rotor, and the second-phase winding outputs electric energy to the output end of the converter main circuit through the eighth diode and the ninth diode; when the second phase winding discharges, namely in the power generation stage, the second phase winding outputs electric energy to the output end of the main converter circuit through an eighth diode and a ninth diode, and simultaneously feeds back the electric energy to the excitation power supply and the second inductor through the sixth diode;
according to the rotor position information, when a third-phase winding needs to be put into operation, the third-phase winding current transformation main circuit is put into operation under the supply of an excitation power supply, firstly, the rotating speed is judged, when the third-phase winding is in a low-speed area, a sixth switching tube is closed and conducted, an excitation stage is started, the excitation power supply supplies power and excites the third-phase winding through an eleventh diode and the sixth switching tube, when the excitation stage needs to be finished according to the rotor position information, the sixth switching tube is turned off, and the third-phase winding outputs electric energy to the side of a third capacitor, namely the output end of the current transformation main circuit, through a thirteenth diode and a fourteenth diode; when the rotating speed is in a medium-speed region, the seventh switch tube is closed and conducted, an excitation stage is started, an excitation power supply supplies power and excites the third-phase winding through the eleventh diode, the third inductor and the seventh switch tube, the seventh switch tube is turned off when the excitation stage needs to be finished according to the rotor position information, and the third-phase winding outputs electric energy to the output end of the current transformation main circuit through the thirteenth diode and the fourteenth diode; when the converter is in a high-speed region, the seventh switching tube is always in a closed conduction state, namely the seventh switching tube is always in a closed state in the working universe of the third phase winding in an excitation stage and a power generation stage, except that the excitation power supply supplies power and excites the third phase winding through the eleventh diode, the third inductor and the seventh switching tube in the excitation stage when the seventh switching tube is started to be closed and conducted, when the voltage at two ends of the third phase winding is greater than the power generation voltage at the output end of the converter main circuit, the electric energy of the excitation power supply can output electric energy to the output end of the converter main circuit through the twelfth diode and the fifteenth diode, when the third phase winding discharges, namely the power generation stage, the third phase winding outputs electric energy to the output end of the converter main circuit through the thirteenth diode and the fourteenth diode, and simultaneously feeds back the electric energy to the excitation power supply and the third inductor through the eleventh diode;
when the voltage of a direct current power grid at the output end of the system suddenly drops in an extreme condition during operation, starting the three-stage low-voltage ride-through protection system according to the following sequence:
a first stage: regulating and controlling the lifting type direct current converter, and quickly recovering the voltage of the output end of the lifting type direct current converter through regulation and control;
and a second stage: when the voltage is reduced to a second level, namely is further lower than the low voltage faced by the first level, the isolated reversible direct current conversion circuits in the current conversion main circuits of the switched reluctance generator systems are started to work reversely except for regulating the lifting type direct current converter, and the premise is that the storage battery has the stored electric energy higher than the lower limit value, the storage battery provides electric energy to the output side of the system through the isolated reversible direct current conversion circuits, and meanwhile, the storage battery serves as an excitation power supply to maintain the power generation operation of the switched reluctance generator systems;
a third pole: when the voltage is further lower than the low voltage faced by the second stage, except for the two measures of the second stage, no matter in which region the rotating speed of the switched reluctance generator is, in the control of the excitation and power generation working process of each phase winding, the corresponding second switching tube, the corresponding fourth switching tube and the corresponding sixth switching tube are in an open state, and the corresponding third switching tube, the corresponding fifth switching tube and the corresponding seventh switching tube are in a closed and conductive state;
the isolated reversible direct current conversion circuit is used as an excitation power supply for supplying power in the forward direction and protecting the system during reverse operation;
when the isolated reversible direct current conversion circuit works in the forward direction, the structure of the right side of the transformer is equivalent to half-bridge inversion, the structure of the left side of the transformer is equivalent to staggered rectification, the output side of the transformer is equivalent to a direct current source, and when the main converter circuit is in a working state, excitation electric energy is also provided, and the isolated reversible direct current conversion circuit specifically comprises the following eleven switching working steps and circulation:
the method comprises the following steps: the ninth switching tube and the fifteenth switching tube are simultaneously closed and conducted;
step two: the thirteenth switching tube is closed and conducted;
step three: the ninth switching tube is disconnected;
step four: the eleventh switch tube and the seventeenth switch tube are closed and conducted;
step five: the fifteenth switching tube is disconnected;
step six: the seventeenth switching tube is disconnected;
step seven: the ninth switching tube is closed and conducted;
step eight: the thirteenth switching tube is disconnected;
step nine: the fifteenth switching tube and the sixteenth switching tube are closed and conducted;
step ten: the eleventh switching tube is disconnected;
step eleven: the sixteenth switching tube is disconnected;
based on the working steps, the duty ratio of each switching tube in eleven steps from the first step to the eleventh step is adjustable within the adjustable range, the principle is that the working is carried out on the premise of the steps, and the requirements for charging a storage battery and exciting a main converter circuit are met;
when the electric quantity of the storage battery is higher than the lower limit value and the voltage on the output side of the system is too low to need safe ride through as described above, and the second-stage protection system and the third-stage protection system as described above are started, the isolated reversible direct current conversion circuit works in a reverse conversion mode, the left structure of the transformer is equivalent to double-bridge inversion, the right structure is equivalent to boost rectification, the output side is equivalent to a voltage source, and the reverse conversion work time of the isolated reversible direct current conversion circuit is divided into the following eleven switching work steps and is circulated:
the method comprises the following steps: the tenth switching tube and the twelfth switching tube are closed and conducted;
step two: the fourteenth switching tube is closed and conducted;
step three: the tenth switching tube is disconnected;
step four: the eighth switching tube and the seventeenth switching tube are closed and conducted;
step five: the twelfth switching tube is disconnected;
step six: the seventeenth switching tube is disconnected;
step seven: the tenth switching tube is closed and conducted;
step eight: the fourteenth switching tube is turned off;
step nine: the twelfth switching tube and the sixteenth switching tube are closed and conducted;
step ten: the eighth switching tube is disconnected;
step eleven: the sixteenth switching tube is disconnected;
based on the above operation steps of the isolated reversible direct current conversion circuit, the duty ratio of each switching tube in eleven steps from the first step to the eleventh step is adjustable within the adjustable range, so as to meet the requirement when voltage dip occurs and ride-through protection is required.
The invention has the following main technical effects:
the invention relates to the field, which is the current hot point of the wind power industry, such as offshore wind power, direct current electric energy convergence, direct current transmission and direct current power grid, a switched reluctance generator directly generates direct current without a rectification link, a plurality of switched reluctance generators are connected in series after generating and outputting to obtain the effect of direct voltage boosting, and the voltage boosting link is reduced.
Controllable lift type DC converter at first need not the contravariant link, and the controllability has very big reinforcing again to direct current electric wire netting's adaptability, flexibility, especially to unstable wind-powered electricity generation field, can greatly promote the stability of system and electric wire netting to also promote the reliability, and when electric wire netting voltage dip trouble appears, lift type DC converter can pass through the protection as one-level, has further strengthened the reliability and the stability of electric wire netting.
The switched reluctance generator converter system has self-starting capability, does not need special equipment and circuits during starting, and reduces cost.
The storage battery can be used as a starting power supply, an excitation power supply, and a ride-through protection function under voltage dip can be reversely implemented through the isolated reversible direct-current conversion circuit, and meanwhile, a special charging device is not needed to charge the storage battery, so that the utilization rate of the storage battery is greatly improved, and the cost performance is extremely high.
The switched reluctance power generation has different working control modes in three low-speed, medium-speed and high-speed areas of each phase winding, particularly in the high-speed area, besides greatly reducing the switching frequency of a related switching tube, reducing the switching loss and improving the reliability, the switched reluctance power generation can provide electric energy for an output end while exciting, so that the current of the variable current output end of each phase winding is continuous and uninterrupted, and the energy can be fed back to charge a storage battery and a first inductor (taking the first phase winding as an example) in the power generation stage, thereby obviously improving the power generation output capacity and the electric energy quality and reducing the cost; in addition, in the medium-speed region, the first inductor is involved in the excitation stage to help improve the excitation capacity, and the requirement that more electric energy is obtained and balanced with the input of the fan is met in the medium-speed region at a relatively low speed, and meanwhile, the first inductor mainly plays a central role in the high-speed region to realize that the excitation electric energy of the storage battery or the isolated reversible direct current conversion circuit and the stored energy of the first inductor can be excited together and simultaneously supply power to the power generation output end as described above.
The isolation type reversible direct current conversion circuit is internally provided with an isolation link, so that a current conversion system does not need to be provided with a special isolation converter in a common structure in the industry, and the volume, the weight and the cost are reduced;
one circuit of the isolated reversible direct current conversion circuit can work in two directions, although the number of switching tubes is large, the circuit can be used as an excitation power supply and a storage battery charging power supply when the circuit works in the forward direction, when a system does not need to change excitation voltage, the system does not need to work in the forward direction, the reverse working probability is lower and shorter, and the circuit is started to work in the reverse direction only when the voltage dip fault occurs and is serious, so that the circuit is usually in an out-of-operation state in the overall view;
in addition, the output of the isolated reversible direct current conversion circuit is adjustable no matter the isolated reversible direct current conversion circuit works in the forward direction or in the reverse direction, and particularly the isolated reversible direct current conversion circuit is equivalent to a direct current source when the isolated reversible direct current conversion circuit outputs in the forward direction, so that the isolated reversible direct current conversion circuit is very beneficial to constant current charging of a storage battery and gives consideration to variable excitation voltage; when the circuit works reversely, the circuit is equivalent to a direct current voltage source, is particularly suitable for the constant voltage power transmission and supply requirements of a direct current power grid, and is more suitable for low voltage ride through protection, so that the function diversification and flexibility are realized by the same circuit, and the cost performance is extremely high.
For wind power generation, Maximum Power Point Tracking (MPPT) control is basically standard configuration, and besides the control of a switching angle, the method can be realized by adjusting the excitation voltage, so that diversified selection of system control is enhanced.
When voltage dip fault occurs, the control method of the invention provides three-stage protection recovery measures, and codes are added step by step so as to ensure that the fault is passed through without stopping, and the three-stage measures are realized not by adding devices specially but by a control method, so that the utilization rate and efficiency benefit of the equipment device are improved, and the cost is also reduced.
In a word, the system and the control method thereof adopt direct current in the whole system, have high utilization rate and relatively simpler structure, have considerable application value in the field of variable-speed wind power, particularly variable-speed offshore wind power direct current power generation and transmission and direct current power grid, and have economic and social double meanings.
Drawings
Fig. 1 is a diagram showing a structure of a dc aggregation network of a dc wind farm according to the present invention.
Fig. 2 is a circuit structure diagram of a switched reluctance wind turbine converter system according to the present invention.
Fig. 3 is a model diagram of the position relationship between the stator and the rotor of the switched reluctance motor and the inductance of the phase winding according to the present invention.
Wherein in fig. 2, 1: a current transformer main circuit; 101: a first phase winding current transformation main circuit; 102: a second phase winding current transformation main circuit; 103: a third phase winding current transformation main circuit; 2: an isolated reversible DC conversion circuit.
Detailed Description
In the direct current wind farm switched reluctance motor converter system and the control method thereof of the embodiment, a direct current convergence network structure of a direct current wind farm is shown in figure 1 and comprises Z fans, Z switched reluctance generator systems and a lifting type direct current converter, each fan is mechanically connected with one switched reluctance generator system, namely, the fan 1 is coaxial with the switched reluctance generator system 1 or mechanically connected through a gear box, the fan 2 is coaxial with the switched reluctance generator system 2 or mechanically connected through the gear box, Z groups of fans and the switched reluctance generator systems are summed, Z is more than 2, direct currents output by the switched reluctance generator systems are connected in series, so that the total direct current voltage is increased after series connection, then the direct current is input to the lifting type direct current converter and then output to a direct current power grid, the lifting type direct current converter is a controllable converter, the output value of the internal switching tube of the buck-boost type direct current converter is adjusted according to the requirement of a direct current power grid, and the output can be increased or reduced compared with the input, so the buck-boost type direct current converter is defined as the buck-boost type direct current converter.
Each switched reluctance generator system of the embodiment has the same structure, and is composed of a switched reluctance generator, a current transformation system and a controller, wherein the current transformation system is composed of a current transformation main circuit 1 (including windings of each phase of the switched reluctance generator) and an isolated reversible direct current conversion circuit 2, as shown in fig. 2, the output end of the current transformation main circuit 1 is also used as the input end of the isolated reversible direct current conversion circuit 2 in addition to being used as the output end of the current transformation system, namely the switched reluctance motor system, and the output end of the isolated reversible direct current conversion circuit 2 is used as the input end of the current transformation main circuit 1; the controller receives signals of wind speed, the rotating speed of the switched reluctance generator, output voltage and current of the converter system, input voltage and current and output voltage and current of the isolated reversible direct current conversion circuit 2 and the like, and outputs and controls each switch tube in the converter system; the switched reluctance generator of the embodiment is a switched reluctance motor with three-phase windings;
the converter main circuit 1 of the embodiment is composed of a first phase winding converter main circuit 101, a second phase winding converter main circuit 102, a third phase winding converter main circuit 103, a storage battery X and a first switch tube K1, wherein the input ends of the first phase winding converter main circuit 101, the second phase winding converter main circuit 102 and the third phase winding converter main circuit 103 are connected in parallel, the output ends of the three are also connected in parallel, the negative electrode of the storage battery X is used as the input negative electrode end of the converter main circuit 1, the positive electrode of the storage battery X is connected with one end of a first switch tube K1, the other end of the first switch tube K1 is used as the input positive electrode end of the converter main circuit 1, and the first switch tube K1 is a bidirectional controllable power electronic switch device;
the first phase winding converter main circuit 101 is composed of a first diode D1, a second diode D2, a third diode D3, a fourth diode D4, a fifth diode D5, a first inductor L1, a second switch tube K2, a third switch tube K3, a first phase winding M and a first capacitor C1, wherein the anode of the first diode D1 is used as the input positive end of the first phase winding converter main circuit 101, namely the input positive end of the converter main circuit 1, and is connected with the other end of the first switch tube K1, the input positive end of the second phase winding converter main circuit 102, the input positive end of the third phase winding converter main circuit 103, and the output positive end of the isolated reversible direct current conversion circuit 2, the cathode of the first diode D1 is connected with one end of the first inductor L1 and the anode of the second switch tube K2, the other end of the first inductor L1 is connected with the anode of the third switch tube K3, and the cathode of the second switch tube K3 is connected with the cathode of the second switch tube K2, The other end of the first phase winding M is connected with the anode of a third diode D2, the cathode of a fourth diode D4 and one end of a first phase winding M, the other end of the first phase winding M is connected with the anode of a third diode D3 and the cathode of a fifth diode D5 and is used as the input negative end of the first phase winding converter main circuit 101, namely the input negative end of the converter main circuit 1, the input negative end of a storage battery X, the input negative end of the second phase winding converter main circuit 102, the input negative end of the third phase winding converter main circuit 103 and the output negative end of an isolated reversible direct current converter circuit 2, the cathode of a second diode D2 is connected with the cathode of a third diode D3 and one end of a first capacitor C1 and is used as the output positive end of the first phase winding converter main circuit 101, namely the output positive end of the converter main circuit 1 and is also used as the output positive end of the converter system and the output positive end of the switched reluctance generator system and is connected with the output positive end of the second phase winding converter main circuit 102, The positive output end of the third phase winding current transformer main circuit 103 and the positive input end of the isolated reversible direct current conversion circuit 2 are connected, the positive electrode of a fourth diode D4 is connected with the positive electrode of a fifth diode D5 and the other end of a first capacitor C1 and serves as the negative output end of the first phase winding current transformer main circuit 101, namely the negative output end of the current transformer main circuit 1, and simultaneously the negative output ends of the current transformer system and the switched reluctance generator system are also connected with the negative output end of the second phase winding current transformer main circuit 102, the negative output end of the third phase winding current transformer main circuit 103 and the negative input end of the isolated reversible direct current conversion circuit 2;
the second phase winding converter main circuit 102 is composed of a sixth diode D6, a seventh diode D7, an eighth diode D8, a ninth diode D9, a twelfth diode D10, a second inductor L2, a fourth switching tube K4, a fifth switching tube K5, a second phase winding N and a second capacitor C2, the anode of the sixth diode D6 serves as the input positive terminal of the second phase winding converter main circuit 102, the cathode of the sixth diode D6 is connected with one end of the second inductor L2 and the anode of the fourth switching tube K4, the other end of the second inductor L2 is connected with the anode of the fifth switching tube K5, the cathode of the fifth switching tube K5 is connected with the cathode of the fourth switching tube K4, the anode of the seventh diode D7, the cathode of the ninth diode D9 and one end of the second phase winding N, the other end of the second phase winding N is connected with the anode of the eighth diode D8 and the cathode of the twelfth diode D10 and serves as the input negative terminal of the second phase winding converter main circuit 102, the cathode of the eighth diode D8656 and the cathode 86 8, the anode of a ninth diode D9 is connected with the anode of a twelfth diode D10 and the other end of a second capacitor C2 and is used as the output negative end of the second phase winding current transformer main circuit 102;
the third main circuit 103 is composed of an eleventh diode D11, a twelfth diode D12, a thirteenth diode D13, a fourteenth diode D14, a fifteenth diode D15, a third inductor L3, a sixth switch tube K6, a seventh switch tube K7, a third phase winding P and a third capacitor C3, the anode of the eleventh diode D11 is used as the input positive terminal of the third main circuit 103, the cathode of the eleventh diode D11 is connected with one end of a third inductor L3 and the anode of a sixth switch tube K6, the other end of the third inductor L3 is connected with the anode of the seventh switch tube K7, the cathode of the seventh switch tube K7 is connected with the cathode of the sixth switch tube K6, the anode of the twelfth diode D12, the cathode of the fourteenth diode D14 and one end of the third phase winding P, the other end of the third phase winding P is connected with the anode of the thirteenth diode D13 and the anode of the fifteenth diode D15 as the input negative terminal of the main circuit 103, the cathode of the twelfth diode D12 is connected with the cathode of the thirteenth diode D13 and one end of the third capacitor C3 and serves as the output positive end of the third phase winding current transformer main circuit 103, and the anode of the fourteenth diode D14 is connected with the anode of the fifteenth diode D15 and the other end of the third capacitor C3 and serves as the output negative end of the third phase winding current transformer main circuit 103;
the inductance values of the first inductor L1, the second inductor L2, and the third inductor L3 are required to be sufficiently large.
The voltage at the output end of the isolated reversible direct current conversion circuit 2 is called excitation voltage and is used for exciting phase windings in each phase winding current transformation main circuit or charging a storage battery X, the input voltage of the isolated reversible direct current conversion circuit is also called power generation voltage, namely the voltage at the output end of the current transformation main circuit 1 and the output voltage of each switched reluctance generator system, and the power generation voltage of each switched reluctance generator system is connected in series and boosted and then is converted by a lifting type direct current converter to be used as grid-connected voltage output to a direct current power grid;
the isolated reversible direct current conversion circuit 2 is composed of a fourth capacitor C4, a fifth capacitor C5, a sixth capacitor C6, a seventh capacitor C7, a sixteenth diode D16, a seventeenth diode D17, an eighth switch tube K8, a ninth switch tube K9, a tenth switch tube K10, an eleventh switch tube K11, a twelfth switch tube K12, a thirteenth switch tube K13, a fourteenth switch tube K14, a fifteenth switch tube K15, a sixteenth switch tube K16, a seventeenth switch tube K17, a transformer T and a fourth inductor L4, one end of the fourth capacitor C4 is connected with one end of the sixth capacitor C6, a sixteenth diode D16 cathode and a sixteenth switch tube K16 anode and serves as an isolated reversible direct current conversion circuit 2 input positive terminal, one end of the fifth capacitor C5 is connected with one end of the seventh capacitor C7, the seventeenth diode D17, the seventeenth switch tube K16 anode and the cathode 17 and serves as an isolated reversible direct current conversion circuit input terminal, one end of a secondary winding n2 of the transformer T is connected with the other end of a fourth capacitor C4, the anode of a sixteenth diode D16, the cathode of a sixteenth switching tube K16, the other end of a fifth capacitor C5, the cathode of a seventeenth diode D17 and the anode of a seventeenth switching tube K17, the other end of a secondary winding n2 of the transformer T is connected with the other end of a sixth capacitor C6 and the other end of a seventh capacitor C7, one end of a primary winding n1 of the transformer T is connected with the cathode of an eighth switching tube K8, the anode of a ninth switching tube K9, the anode of a tenth switching tube K10 and the cathode of an eleventh switching tube K11, the other end of a primary winding n1 of the transformer T is connected with the cathode of a twelfth switching tube K12, the anode of a thirteenth switching tube K13, the anode of a fourteenth switching tube K14 and the cathode of a fifteenth switching tube K15, the anode of the eighth switching tube K8 is connected with the cathode of the ninth switching tube K9, the anode of the twelfth switching tube K12, the anode of the thirteenth switching tube K13 and the cathode of the seventeenth switching tube K539, One end of a fourth inductor L4 is connected, the other end of the fourth inductor L4 serves as the output positive end of the isolated reversible direct current conversion circuit 2, and the cathode of a tenth switching tube K10 is connected with the anode of an eleventh switching tube K11, the cathode of a fourteenth switching tube K14 and the anode of a fifteenth switching tube K15 and serves as the output negative end of the isolated reversible direct current conversion circuit 2; the transformation ratio of the transformer T, namely the ratio of the turns of windings on two sides, is determined according to the requirements of the rated voltage of the storage battery X and the output generating voltage of the system, and is not necessarily equal to 1 and only plays an isolation role;
the common excitation power supply of each phase winding of the switched reluctance generator of the embodiment is divided into the following schemes:
1) when the storage battery X provides an excitation power supply, the first switch tube K1 is conducted reversely, and the scheme is characterized in that the electric energy stored in the storage battery X is higher than the minimum limit value, and excitation is not required to be changed by excitation voltage, and the excitation voltage is equal to the voltage of the storage battery X;
2) when the isolated reversible direct current conversion circuit 2 provides an excitation power supply and the storage battery X does not need to be charged, the first switch tube K1 is in a turn-off state in both directions, the scheme is characterized in that the electric energy stored in the storage battery X is higher than a minimum limit value, the generating voltage is within a normal value range required by a system, and the control performance required by the system, such as the requirements of Maximum Power Point Tracking (MPPT) control and the like, needs to be realized through excitation with variable excitation voltage;
3) when the isolated reversible direct current conversion circuit 2 provides an excitation power supply and the storage battery X needs to be charged, the first switch tube K1 is conducted in the forward direction, the scheme is that the electric energy stored in the storage battery X is lower than the lowest limit value, the excitation voltage and the current are in accordance with the range of charging parameters of the storage battery X, the generating voltage is in the range of normal values required by the system, and the system needs to realize the control performance required by the system through excitation of variable excitation voltage, such as MPPT control and other requirements;
in any case, the switched reluctance motor is required to be provided with an excitation power supply to provide excitation electric energy for a phase winding of the switched reluctance motor when the switched reluctance motor operates according to the working condition of the switched reluctance motor, and when the system is started, the switched reluctance motor is started according to the mode of the switched reluctance motor, the excitation power supply is also required necessarily and is used as a power supply for the working condition of the motor;
during the working condition operation of the switched reluctance generator, firstly detecting and judging the rotating speed of the rotor, and dividing the rotating speed of the rotor into three areas, namely a low-speed area, a medium-speed area and a high-speed area;
when the switched reluctance generator operates, according to rotor position information, when the first phase winding M is required to be put into operation, the first phase winding current transformation main circuit 101 is put into operation under the supply of an excitation power supply, firstly, the rotating speed is judged, when the first phase winding M is in a low-speed area, the second switching tube K2 is closed and conducted, an excitation stage is entered, the excitation power supply supplies power and excites the first phase winding M through the first diode D1 and the second switching tube K2, when the excitation stage is required to be ended according to the rotor position information, the second switching tube K2 is turned off, and the first phase winding M outputs electric energy to the first capacitor C1 side through the third diode D3 and the fourth diode D4, namely the output end of the current transformation main circuit 1; when the rotating speed is in a medium-speed region, the third switching tube K3 is closed and conducted, an excitation stage is started, an excitation power supply supplies power and excites the first phase winding M through the first diode D1, the first inductor L1 and the third switching tube K3, the third switching tube K3 is turned off when the excitation stage needs to be finished according to the position information of the rotor, and the first phase winding M outputs electric energy to the output end of the converter main circuit 1 through the third diode D3 and the fourth diode D4; when in the high-speed region, the third switch tube K3 is always in the closed conducting state, that is, the third switch tube K3 is always in the closed state in the whole working range of the first phase winding M in the excitation stage and the power generation stage, since the first inductor L1 is required to be large enough, during the excitation phase beginning when the third switch tube K3 is turned on, in addition to the excitation power supply supplying excitation to the first phase winding M via the first diode D1, the first inductor L1 and the third switch tube K3, meanwhile, the power is output to the output end of the main converter circuit 1 through the second diode D2 and the fifth diode D5, namely, the voltage at two ends of the first phase winding M is larger than the voltage at the output end of the main converter circuit 1, namely the generating voltage value, since the second diode D2 and the fifth diode D5 can be turned on only when this condition is satisfied, the rotation speed value at the critical point where the phase winding voltage is equal to the generated voltage is defined as the boundary point between the intermediate speed region and the high speed region;
the switched reluctance motor stator and rotor position relation and phase winding inductance model according to fig. 3 is shown in combination with the following switched reluctance motor phase winding voltage equation (1):
Figure BSA0000255425640000081
in the formula: e is phase winding induced electromotive force, psi is flux linkage, omega is angular velocity of the switched reluctance motor,
Figure BSA0000255425640000091
named transformer electromotive force;
Figure BSA0000255425640000092
denominated as kinetic electromotive force; formula (1) is a voltage balance equation in the excitation stage;
it can be seen that, for the high speed region of the first phase winding M, in combination with the basic principle of the switched reluctance generator, the starting point of the excitation phase for starting to energize should be before θ 3 and after θ 2 in the inductance model of fig. 3, i.e. the inductance is in the rising phase at the beginning of the excitation phase, since the rotation speed is in the high speed region, the moving electromotive force is large and positive, the current of the first phase winding M will not rise, and may even be in the falling state to balance the voltage equation, when the angle θ 3 and the central line θ a of the salient poles of the stator and rotor are exceeded, especially after the angle θ 4 is exceeded, the inductance of the first phase winding M falls, the moving electromotive force is reversed, the current of the first phase winding M will rise, and then the power generation phase is automatically entered, i.e. the first phase winding M enters the discharging state (the mechanical energy of the moving electromotive force is converted into electrical energy), the third diode D3 and the fourth diode D4 are turned on, the voltage balance equation at this time becomes:
Figure BSA0000255425640000093
it can be seen that the sign of entering the power generation phase is that the current through the second diode D2 and the fifth diode D5 is zero, and at this time, the first phase winding M outputs electric energy to the output end of the converter main circuit 1 through the third diode D3 and the fourth diode D4, and simultaneously feeds back electric energy to the excitation power supply and the first inductor L1 through the first diode D1; when the first inductor L1 is large enough and the rotation speed is high enough, the current of the first phase winding M in the power generation phase continuously rises to the angle θ 5, i.e. the area between the minimum inductance areas θ 1 and θ 2 at the beginning of the next cycle, and then falls, i.e. although the excitation and power generation phases of the third switch tube K3 are continuously closed and conducted, the conventional mode of exciting and supplying power and cutting off power (cutting off the excitation power supply) in the conventional mode and medium and low speed areas is broken, but in the high speed area, the excitation phase can increase the power output (simultaneously, the second diode D2 and the fifth diode D5 conduct and output power) without cutting off the power generation phase of the third switch tube K3, and the first phase winding M can reversely feed power to the excitation power supply end or the storage battery X while outputting power through the third diode D3 and the fourth diode D4, so that the power generation capacity is greatly enhanced, Efficiency and benefit of power generation;
the above is directed to the working process of the first phase winding M according to the rotor position information and the rotation speed, when the second phase winding N is required to be put into operation according to the rotor position information, the second phase winding current transformer main circuit 102 is put into operation under the supply of the excitation power supply, and the working process is substantially the same as that of the first phase winding M, except that the sixth diode D6 corresponds to the first diode D1, the second inductor L2 corresponds to the first inductor L1, the fourth switching tube K4 corresponds to the second switching tube K2, the fifth switching tube K5 corresponds to the third switching tube K3, the second phase winding N corresponds to the first phase winding M, the seventh diode D7 corresponds to the second diode D2, the eighth diode D8 corresponds to the third diode D3, the ninth diode D9 corresponds to the fourth diode D4, the twelfth diode D10 corresponds to the fifth diode D5, and the second capacitor C2 corresponds to the first capacitor C1;
similarly, when the third phase winding P needs to be put into operation, the third phase winding converter main circuit 103 is put into operation under the excitation power supply, which is also substantially the same as the operation process of the first phase winding M, the eleventh diode D11 corresponds to the first diode D1, the third inductor L3 corresponds to the first inductor L1, the sixth switching tube K6 corresponds to the second switching tube K2, the seventh switching tube K7 corresponds to the third switching tube K3, the third phase winding P corresponds to the first phase winding M, the twelfth diode D12 corresponds to the second diode D2, the thirteenth diode D13 corresponds to the third diode D3, the fourteenth diode D14 corresponds to the fourth diode D4, the fifteenth diode D15 corresponds to the fifth diode D5, and the third capacitor C3 corresponds to the first capacitor C1.
If the rotating speed of the switched reluctance motor is too high and exceeds the upper limit value required by the system, a pitch angle control system of the fan is started, the rotating speed of the fan is increased, the rotating speed is reduced, when the method is not enough to control the rotating speed to be lower than the upper limit value, the wind speed is too high, the system is stopped, all the switch tubes are in a disconnected state, and the fan and the switched reluctance generator system start a brake system together to stop the system.
When the total generated voltage of all the switched reluctance generator systems after being connected in series is out of the range of the normal value required by the system and is higher than the normal value, the system is shut down for partial switched reluctance generator systems, and the number of the shut-down switched reluctance generator systems is determined by taking the requirement of the input voltage of the buck-boost direct current converter of the direct current convergence network of the direct current wind power plant as a reference.
When the total output voltage of the system, namely the output voltage of the buck-boost direct-current converter, suddenly drops, which is a difficulty that needs to be solved in the field of wind power working conditions, is called low-voltage ride through, the three-level low-voltage ride through protection system is started according to the following sequence, often because of factors such as overlarge load, instantaneous short-circuit fault of a power grid and the like:
a first stage: the regulation and control system of the lift-type direct current converter is used for quickly recovering the voltage of the output end by regulating and controlling a switch tube in the lift-type direct current converter;
and a second stage: when the direct current voltage at the output end of the buck-boost direct current converter is reduced to a second level, namely when the direct current voltage is lower than the low voltage faced by the first level, the isolated reversible direct current conversion circuit 2 is started to work reversely except for regulating and controlling an internal switching tube of the buck-boost direct current converter, and the precondition is that the storage battery X has the reserve electric energy higher than the lower limit value, because the storage battery X actually provides the electric energy to the output side of the system through the isolated reversible direct current conversion circuit 2 at the moment, and meanwhile, the storage battery X is required to be used as an excitation power supply to maintain the operation of the switched reluctance generator system;
a third pole: when the dc voltage at the output end of the buck-boost dc converter is reduced to the third level, i.e. lower than the low voltage faced by the second level, in addition to the above two measures taken by the second level, on the premise that the generated voltage at the output end of the main converter circuit 1 is lower than the average voltage value of the windings of each phase (in fact, the voltage drops suddenly to the third level, which means that the generated voltage output by the main converter circuit of each phase winding is extremely low), no matter what region the rotational speed of the switched reluctance generator is in, during the excitation and generation process control of the windings of each phase, the second switching tube K2, the fourth switching tube K4, and the sixth switching tube K6 are all in the off state, while the third switching tube K3, the fifth switching tube K5, and the seventh switching tube K7 are all in the on state, i.e. similar to the regulation mode of the high speed region in the normal operation state, at this time because of no matter in the excitation or generation stage, the first capacitor C1, the second capacitor C2 and the third capacitor C3 can receive continuous current instead of intermittent current during the operation of the corresponding phase windings, and the lower the generated voltage at the output side is, the larger the current is, and the better the compensation ride-through effect is naturally.
As described above, no matter the isolated reversible dc converter circuit 2 is used as an excitation power supply for forward power supply or a reverse protection system, the forward and reverse operation processes are not simple, when the isolated reversible dc converter circuit is operated in the forward direction, the right side structure of the transformer T is equivalent to half-bridge inversion, the left side structure is equivalent to interleaved rectification, and the output side is equivalent to a dc current source, so as to facilitate continuous constant current charging of the storage battery X, when the main converter circuit 1 is in the operating state, excitation electric energy is also provided, and when the isolated reversible dc converter circuit 2 is operated in the forward direction, the isolated reversible dc converter circuit is specifically divided into the following eleven switching operation steps, and the switching operation steps are circulated:
the method comprises the following steps: the ninth switch tube K9 and the fifteenth switch tube K15 are closed and conducted simultaneously;
step two: the thirteenth switching tube K13 is closed and conducted;
step three: the ninth switching tube K9 is open;
step four: the eleventh switch tube K11 and the seventeenth switch tube K17 are closed and conducted;
step five: the fifteenth switching tube K15 is open;
step six: the seventeenth switching tube K17 is turned off;
step seven: the ninth switching tube K9 is closed and conducted;
step eight: the thirteenth switching tube K13 is open;
step nine: the fifteenth switching tube K15 and the sixteenth switching tube K16 are closed and conducted;
step ten: the eleventh switching tube K11 is off;
step eleven: the sixteenth switching tube K16 is turned off;
based on the working steps, the duty ratio of each switching tube in eleven steps from the first step to the eleventh step is adjustable within the adjustable range, the principle is that the duty ratio is adjusted on the premise of meeting the steps, and the requirements of charging a storage battery X and exciting a main converter circuit 1 are met;
when the X electric quantity of the storage battery is higher than the lower limit value and the system output side voltage is too low to cause a fault and need safe ride-through, and the second-stage protection system and the third-stage protection system are started, the isolated reversible direct current conversion circuit 2 works in a reverse conversion mode, the left side structure of the transformer T is equivalent to double-bridge inversion, the right side structure of the transformer T is equivalent to boost rectification, and the output side is equivalent to a voltage source, so that the recovery of the load side faults such as low voltage ride-through is facilitated; the operation of the isolated reversible direct current conversion circuit 2 is divided into the following eleven switching operation steps in a reverse conversion mode, and the switching operation is circulated:
the method comprises the following steps: the tenth switching tube K10 and the twelfth switching tube K12 are closed and conducted;
step two: the fourteenth switching tube K14 is closed and conducted;
step three: the tenth switching tube K10 is open;
step four: the eighth switch tube K8 and the seventeenth switch tube K17 are closed and conducted;
step five: the twelfth switching tube K12 is open;
step six: the seventeenth switching tube K17 is turned off;
step seven: the tenth switching tube K10 is closed and conducted;
step eight: the fourteenth switching tube K14 is turned off;
step nine: the twelfth switching tube K12 and the sixteenth switching tube K16 are closed and conducted;
step ten: the eighth switching tube K8 is open;
step eleven: the sixteenth switching tube K16 is turned off;
based on the above inverse conversion working steps of the isolated reversible direct current conversion circuit 2, the duty ratio of each switching tube in eleven steps from step one to step eleven is adjustable within the adjustable range thereof, so as to meet the requirement on outputting the generated voltage, especially the requirement when voltage dip occurs and needs to be crossed as described above;
although the work control process of the isolated reversible direct current conversion circuit 2 is complex, during the normal power generation work of the system, if the wind energy is stable, the excitation voltage does not need to be changed to meet the performance requirements of MPPT and the like, the storage battery X is often adopted as the excitation power supply, and at the moment, the isolated reversible direct current conversion circuit 2 does not need to be subjected to current conversion work; the probability and the time of extreme conditions such as sudden voltage drop on the load side are very rare and short, even if the extreme conditions occur, the extreme conditions are required to be completed in a very short time when the second-level and the third-level pass through protection requirements, otherwise, the system is required to be completely shut down, so the reverse working time is shorter and rarer; therefore, although the number of the switch tubes of the isolated reversible direct current conversion circuit 2 is large, the loss in operation is generally high, but the loss can be almost ignored when the isolated reversible direct current conversion circuit is placed in the overall system.
It can be seen from this embodiment and the drawings that, when the number of the phase windings of the switched reluctance motor is the number of the non-three-phase windings, the number of the phase winding current transformation main circuits which are identical in addition, subtraction, structure and control is merely a problem, so that the present invention should be within the protection range for the non-three-phase winding switched reluctance motor.

Claims (2)

1. A direct current wind farm switch reluctance motor converter system, the direct current of the direct current wind farm assembles the network and is made up of Z fans, Z switch reluctance generator systems, and a lift type direct current converter, its technical characteristic is, each said fan connects a said switch reluctance generator system through the mechanical way, such fans and switch reluctance generator systems of Z group totally, Z is greater than 2, the direct current that these switch reluctance generator systems output connects in series, then input to said lift type direct current converter and export to the direct current electric wire netting, the lift type direct current converter is a controllable converter, namely regulate the lift type direct current converter to control its output value according to the direct current electric wire netting needs;
each switched reluctance generator system has the same structure and consists of a switched reluctance generator, a current transformation system and a controller, wherein the current transformation system consists of a current transformation main circuit and an isolated reversible direct current transformation circuit, the output end of the current transformation main circuit is also used as the input end of the isolated reversible direct current transformation circuit except for being used as the output end of the current transformation system and the switched reluctance generator system, and the output end of the isolated reversible direct current transformation circuit is used as the input end of the current transformation main circuit; the controller receives wind speed, the rotating speed of the switched reluctance generator, output voltage and current of the converter system, and input voltage and current and output voltage and current signals of the isolated reversible direct current conversion circuit, and outputs and controls each switch tube in the converter system;
the converter main circuit consists of a first phase winding converter main circuit, a second phase winding converter main circuit, a third phase winding converter main circuit, a storage battery and a first switch tube, wherein the input ends of the first phase winding converter main circuit, the second phase winding converter main circuit and the third phase winding converter main circuit are connected in parallel, the output ends of the first phase winding converter main circuit, the second phase winding converter main circuit and the third phase winding converter main circuit are also connected in parallel, the X negative pole of the storage battery is used as the input negative pole end of the converter main circuit, the X positive pole of the storage battery is connected with one end of the first switch tube, and the other end of the first switch tube is used as the input positive pole end of the converter main circuit; the first switching tube is a bidirectional controllable power electronic switching device;
the first phase winding current transformation main circuit consists of a first diode, a second diode, a third diode, a fourth diode, a fifth diode, a first inductor, a second switch tube, a third switch tube, a first phase winding and a first capacitor, wherein the anode of the first diode is used as the input positive end of the first phase winding current transformation main circuit, namely the input positive end of the current transformation main circuit, and is connected with the other end of the first switch tube, the input positive end of the second phase winding current transformation main circuit, the input positive end of the third phase winding current transformation main circuit and the output positive end of the isolated reversible direct current transformation circuit, the cathode of the first diode is connected with one end of the first inductor and the anode of the second switch tube, the other end of the first inductor is connected with the anode of the third switch tube, and the cathode of the third switch tube is connected with the cathode of the second switch tube, the anode of the second diode, the cathode of the fourth diode, And one end of the first phase winding, the other end of the first phase winding is connected with the anode of the third diode and the cathode of the fifth diode, and is used as the input cathode end of the first phase winding current transformation main circuit, namely the input cathode end of the current transformation main circuit, the cathode end of the storage battery, the input cathode end of the second phase winding current transformation main circuit, the input cathode end of the third phase winding, and the output cathode end of the isolation type reversible direct current transformation circuit, the cathode of the second diode is connected with the cathode of the third diode and one end of the first capacitor, and is used as the output anode end of the first phase winding current transformation main circuit, namely the output anode end of the current transformation main circuit, and is also the output anode end of the current transformation system and the switched reluctance generator system, and is connected with the output anode end of the second phase winding current transformation main circuit, the output anode end of the third phase winding current transformation main circuit, and the input anode end of the isolation type reversible direct current transformation circuit, the anode of the fourth diode is connected with the anode of the fifth diode and the other end of the first capacitor, is used as the output negative end of the first phase winding current transformation main circuit, namely the output negative end of the current transformation main circuit, and is also the output negative end of the current transformation system and the switched reluctance generator system, and is connected with the output negative end of the second phase winding current transformation main circuit, the output negative end of the third phase winding current transformation main circuit and the input negative end of the isolated reversible direct current transformation circuit;
the second phase winding current transformation main circuit consists of a sixth diode, a seventh diode, an eighth diode, a ninth diode, a twelfth diode, a second inductor, a fourth switching tube, a fifth switching tube, a second phase winding and a second capacitor, wherein the anode of the sixth diode is used as the input positive end of the second phase winding current transformation main circuit, the cathode of the sixth diode is connected with one end of the second inductor and the anode of the fourth switching tube, the other end of the second inductor is connected with the anode of the fifth switching tube, the cathode of the fifth switching tube is connected with the cathode of the fourth switching tube, the anode of the seventh diode, the cathode of the ninth diode and one end of the second phase winding, the other end of the second phase winding is connected with the anode of the eighth diode and the cathode of the twelfth diode and is used as the input negative end of the second phase winding current transformation main circuit, and the cathode of the seventh diode is connected with the cathode of the eighth diode and one end of the second capacitor, the anode of a ninth diode is connected with the anode of a twelfth diode and the other end of the second capacitor and is used as the output negative end of the second phase winding current transformation main circuit;
the third phase winding current-converting main circuit consists of an eleventh diode, a twelfth diode, a thirteenth diode, a fourteenth diode, a fifteenth diode, a third inductor, a sixth switching tube, a seventh switching tube, a third phase winding and a third capacitor, wherein the anode of the eleventh diode is used as the input positive terminal of the third phase winding current-converting main circuit, the cathode of the eleventh diode is connected with one end of the third inductor and the anode of the sixth switching tube, the other end of the third inductor is connected with the anode of the seventh switching tube, the cathode of the seventh switching tube is connected with the cathode of the sixth switching tube, the anode of the twelfth diode, the cathode of the fourteenth diode and one end of the third phase winding, the other end of the third phase winding is connected with the anode of the thirteenth diode and the cathode of the fifteenth diode and is used as the input negative terminal of the third phase winding current-converting main circuit, and the cathode of the twelfth diode is connected with the cathode of the thirteenth diode and one end of the third capacitor, the anode of the fourteenth diode is connected with the anode of the fifteenth diode and the other end of the third capacitor and is used as the output negative end of the third phase winding current transformation main circuit;
the voltage at the output end of the isolated reversible direct current conversion circuit is called excitation voltage and is used for exciting a phase winding in each phase winding current transformation main circuit or charging a storage battery, and the input voltage of the isolated reversible direct current conversion circuit is also called power generation voltage, namely the voltage at the output end of each current transformation main circuit and the output voltage of each switched reluctance generator system;
the isolated reversible direct current conversion circuit is composed of a fourth capacitor, a fifth capacitor, a sixth capacitor, a seventh capacitor, a sixteenth diode, a seventeenth diode, an eighth switch tube, a ninth switch tube, a tenth switch tube, an eleventh switch tube, a twelfth switch tube, a thirteenth switch tube, a fourteenth switch tube, a fifteenth switch tube, a sixteenth switch tube, a seventeenth switch tube, a transformer and a fourth inductor, one end of the fourth capacitor is connected with one end of the sixth capacitor, a cathode of the sixteenth diode and an anode of the sixteenth switch tube and serves as an input positive end of the isolated reversible direct current conversion circuit, one end of the fifth capacitor is connected with one end of the seventh capacitor, an anode of the seventeenth diode and a cathode of the seventeenth switch tube and serves as an input negative end of the isolated reversible direct current conversion circuit, one end of a secondary side winding of the transformer is connected with the other end of a fourth capacitor, the anode of a sixteenth diode, the cathode of a sixteenth switching tube, the other end of a fifth capacitor, the cathode of a seventeenth diode and the anode of a seventeenth switching tube, the other end of the secondary side winding of the transformer is connected with the other end of a sixth capacitor and the other end of a seventh capacitor, one end of a primary side winding of the transformer is connected with the cathode of an eighth switching tube, the anode of a ninth switching tube, the anode of a tenth switching tube and the cathode of an eleventh switching tube, the other end of a primary side winding of the transformer is connected with the cathode of a twelfth switching tube, the anode of a thirteenth switching tube, the anode of a fourteenth switching tube and the cathode of a fifteenth switching tube, the anode of an eighth switching tube is connected with the cathode of a ninth switching tube, the anode of a twelfth switching tube, the cathode of a thirteenth switching tube and one end of a fourth inductor, the other end of the fourth inductor is used as an output positive end of the isolated reversible direct current conversion circuit, and the cathode of the tenth switching tube is connected with the anode of the eleventh switching tube, the cathode of the fourteenth switching tube and the anode of the fifteenth switching tube and is used as an output negative end of the isolated reversible direct current conversion circuit.
2. The control method of the direct-current wind power plant switched reluctance motor converter system according to claim 1, wherein the technical characteristics are that firstly, the excitation power supply common to each phase winding of the switched reluctance generator is divided into the following schemes:
1) when the storage battery provides an excitation power supply, the first switch tube is conducted reversely, and the scheme has the premise that the electric energy stored in the storage battery is higher than the minimum limit value, excitation is not required to be changed into excitation voltage, and the excitation voltage is equal to the voltage of the storage battery;
2) when the isolated reversible direct current conversion circuit provides an excitation power supply and the storage battery does not need to be charged, the two directions of the first switching tube are both in a turn-off state, and on the other premise, the electric energy stored by the storage battery is higher than the minimum limit value, the generating voltage is within the normal value range required by the system, and the excitation voltage needs to be adjusted to realize the performance required by the system;
3) when the isolated reversible direct current conversion circuit provides an excitation power supply and the storage battery needs to be charged, the first switching tube is conducted in the forward direction, and on the other premise, the electric energy stored in the storage battery is lower than the minimum limit value, the excitation voltage and the current accord with the range of the charging parameters of the storage battery, the generating voltage is also in the range of the normal value required by the system, and the system needs to adjust the excitation voltage to realize the performance required by the system;
when the switched reluctance motor is to operate according to the working condition of the switched reluctance generator, an excitation power supply is required to provide excitation electric energy for a phase winding of the switched reluctance motor, but when a system is started, the switched reluctance motor is started according to a switched reluctance motor mode, the excitation power supply is also required necessarily at the moment and is used as a power supply when the motor is in the working condition, and after the starting is finished according to the operating principle of the switched reluctance motor and the power generation operation condition of a fan is met, the switched reluctance motor is put into the working condition of the generator to operate;
during the working condition operation of the switched reluctance generator, firstly detecting and judging the rotating speed of the rotor, and dividing the rotating speed of the rotor into three areas, namely a low-speed area, a medium-speed area and a high-speed area;
according to the rotor position information, when the first phase winding needs to be put into operation, the first phase winding current transformation main circuit is put into operation under the supply of an excitation power supply, firstly, the rotating speed is judged, when the first phase winding is in a low-speed area, a second switch tube is closed and conducted, an excitation stage is started, the excitation power supply supplies power and excites the first phase winding through a first diode and the second switch tube, when the excitation stage needs to be finished according to the rotor position information, the second switch tube is turned off, and the first phase winding outputs electric energy to the first capacitor side through a third diode and a fourth diode, namely the output end of the current transformation main circuit; when the rotating speed is in a medium-speed region, the third switching tube is closed and conducted, an excitation stage is started, an excitation power supply supplies power and excites the first phase winding through the first diode, the first inductor and the third switching tube, the third switching tube is turned off when the excitation stage needs to be finished according to the position information of the rotor, and the first phase winding outputs electric energy to the output end of the converter main circuit through the third diode and the fourth diode; when the converter main circuit is in a high-speed region, the third switch tube is always in a closed conduction state, namely the third switch tube is always in a closed state in the working universe of the first phase winding in an excitation stage and a power generation stage, when the third switch tube is in the excitation stage at the beginning of the closed conduction, except that the excitation power supply supplies power and excites the first phase winding through the first diode, the first inductor and the third switch tube, when the voltage at two ends of the first phase winding is greater than the power generation voltage at the output end of the converter main circuit, the electric energy of the excitation power supply can output electric energy to the output end of the converter main circuit through the second diode and the fifth diode, when the first phase winding discharges, namely in the power generation stage, the first phase winding outputs electric energy to the output end of the converter main circuit through the third diode and the fourth diode, and simultaneously feeds back the electric energy to the excitation power supply and the first inductor through the first diode;
according to the rotor position information, when a second phase winding needs to be put into operation, the second phase winding current conversion main circuit is put into operation under the supply of an excitation power supply, firstly, the rotating speed is judged, when the second phase winding is in a low-speed area, a fourth switch tube is closed and conducted, an excitation stage is started, the excitation power supply supplies power and excites the second phase winding through a sixth diode and the fourth switch tube, when the excitation stage needs to be finished according to the rotor position information, the fourth switch tube is turned off, and the second phase winding outputs electric energy to the side of a second capacitor, namely the output end of the current conversion main circuit, through an eighth diode and a ninth diode; when the rotating speed is in a medium-speed region, the fifth switching tube is closed and conducted, an excitation stage is started, an excitation power supply supplies power and excites the second-phase winding through the sixth diode, the second inductor and the fifth switching tube, the fifth switching tube is turned off when the excitation stage needs to be finished according to the position information of the rotor, and the second-phase winding outputs electric energy to the output end of the converter main circuit through the eighth diode and the ninth diode; when the second phase winding discharges, namely in the power generation stage, the second phase winding outputs electric energy to the output end of the main converter circuit through an eighth diode and a ninth diode, and simultaneously feeds back the electric energy to the excitation power supply and the second inductor through the sixth diode;
according to the rotor position information, when a third-phase winding needs to be put into operation, the third-phase winding current transformation main circuit is put into operation under the supply of an excitation power supply, firstly, the rotating speed is judged, when the third-phase winding is in a low-speed area, a sixth switching tube is closed and conducted, an excitation stage is started, the excitation power supply supplies power and excites the third-phase winding through an eleventh diode and the sixth switching tube, when the excitation stage needs to be finished according to the rotor position information, the sixth switching tube is turned off, and the third-phase winding outputs electric energy to the side of a third capacitor, namely the output end of the current transformation main circuit, through a thirteenth diode and a fourteenth diode; when the rotating speed is in a medium-speed region, the seventh switch tube is closed and conducted, an excitation stage is started, an excitation power supply supplies power and excites the third-phase winding through the eleventh diode, the third inductor and the seventh switch tube, the seventh switch tube is turned off when the excitation stage needs to be finished according to the rotor position information, and the third-phase winding outputs electric energy to the output end of the current transformation main circuit through the thirteenth diode and the fourteenth diode; when the converter is in a high-speed region, the seventh switching tube is always in a closed conduction state, namely the seventh switching tube is always in a closed state in the working universe of the third phase winding in an excitation stage and a power generation stage, except that the excitation power supply supplies power and excites the third phase winding through the eleventh diode, the third inductor and the seventh switching tube in the excitation stage when the seventh switching tube is started to be closed and conducted, when the voltage at two ends of the third phase winding is greater than the power generation voltage at the output end of the converter main circuit, the electric energy of the excitation power supply can output electric energy to the output end of the converter main circuit through the twelfth diode and the fifteenth diode, when the third phase winding discharges, namely the power generation stage, the third phase winding outputs electric energy to the output end of the converter main circuit through the thirteenth diode and the fourteenth diode, and simultaneously feeds back the electric energy to the excitation power supply and the third inductor through the eleventh diode;
when the voltage of a direct current power grid at the output end of the system suddenly drops in an extreme condition during operation, starting the three-stage low-voltage ride-through protection system according to the following sequence:
a first stage: regulating and controlling the lifting type direct current converter, and quickly recovering the voltage of the output end of the lifting type direct current converter through regulation and control;
and a second stage: when the voltage is reduced to a second level, namely is further lower than the low voltage faced by the first level, the isolated reversible direct current conversion circuits in the current conversion main circuits of the switched reluctance generator systems are started to work reversely except for regulating the lifting type direct current converter, and the premise is that the storage battery has the stored electric energy higher than the lower limit value, the storage battery provides electric energy to the output side of the system through the isolated reversible direct current conversion circuits, and meanwhile, the storage battery serves as an excitation power supply to maintain the power generation operation of the switched reluctance generator systems;
a third pole: when the voltage is further lower than the low voltage faced by the second stage, except for the two measures of the second stage, no matter in which region the rotating speed of the switched reluctance generator is, in the control of the excitation and power generation working process of each phase winding, the corresponding second switching tube, the corresponding fourth switching tube and the corresponding sixth switching tube are in an open state, and the corresponding third switching tube, the corresponding fifth switching tube and the corresponding seventh switching tube are in a closed and conductive state;
the isolated reversible direct current conversion circuit is used as an excitation power supply to supply power in a forward direction and protect a system during reverse work;
when the isolated reversible direct current conversion circuit works in the forward direction, the structure of the right side of the transformer is equivalent to half-bridge inversion, the structure of the left side of the transformer is equivalent to staggered rectification, the output side of the transformer is equivalent to a direct current source, and when the main converter circuit is in a working state, excitation electric energy is also provided, and the isolated reversible direct current conversion circuit specifically comprises the following eleven switching working steps and circulation:
the method comprises the following steps: the ninth switching tube and the fifteenth switching tube are simultaneously closed and conducted;
step two: the thirteenth switching tube is closed and conducted;
step three: the ninth switching tube is disconnected:
step four: the eleventh switch tube and the seventeenth switch tube are closed and conducted;
step five: the fifteenth switching tube is disconnected;
step six: the seventeenth switching tube is disconnected;
step seven: the ninth switching tube is closed and conducted;
step eight: the thirteenth switching tube is disconnected;
step nine: the fifteenth switching tube and the sixteenth switching tube are closed and conducted;
step ten: the eleventh switching tube is disconnected;
step eleven: the sixteenth switching tube is disconnected;
based on the working steps, the duty ratio of each switching tube in eleven steps from the first step to the eleventh step is adjustable within the adjustable range, the principle is that the working is carried out on the premise of the steps, and the requirements for charging a storage battery and exciting a main converter circuit are met;
when the electric quantity of the storage battery is higher than the lower limit value and the voltage on the output side of the system is too low to need safe ride through as described above, and the second-stage protection system and the third-stage protection system as described above are started, the isolated reversible direct current conversion circuit works in a reverse conversion mode, the left structure of the transformer is equivalent to double-bridge inversion, the right structure is equivalent to boost rectification, the output side is equivalent to a voltage source, and the reverse conversion work time of the isolated reversible direct current conversion circuit is divided into the following eleven switching work steps and is circulated:
the method comprises the following steps: the tenth switching tube and the twelfth switching tube are closed and conducted;
step two: the fourteenth switching tube is closed and conducted;
step three: the tenth switching tube is disconnected;
step four: the eighth switching tube and the seventeenth switching tube are closed and conducted;
step five: the twelfth switching tube is disconnected;
step six: the seventeenth switching tube is disconnected;
step seven: the tenth switching tube is closed and conducted;
step eight: the fourteenth switching tube is turned off;
step nine: the twelfth switching tube and the sixteenth switching tube are closed and conducted;
step ten: the eighth switching tube is disconnected;
step eleven: the sixteenth switching tube is disconnected;
based on the above operation steps of the isolated reversible direct current conversion circuit, the duty ratio of each switching tube in eleven steps from the first step to the eleventh step is adjustable within the adjustable range, so as to meet the requirement when voltage dip occurs and ride-through protection is required.
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