CN116260348B - MMC-based high-capacity electrolytic hydrogen production hybrid rectifier and control method - Google Patents
MMC-based high-capacity electrolytic hydrogen production hybrid rectifier and control method Download PDFInfo
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- 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
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
- H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
- H02M7/12—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/145—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means
- H02M7/155—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means using semiconductor devices only
- H02M7/162—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means using semiconductor devices only in a bridge configuration
- H02M7/1623—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means using semiconductor devices only in a bridge configuration with control circuit
- H02M7/1626—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means using semiconductor devices only in a bridge configuration with control circuit with automatic control of the output voltage or current
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- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B1/00—Electrolytic production of inorganic compounds or non-metals
- C25B1/01—Products
- C25B1/02—Hydrogen or oxygen
- C25B1/04—Hydrogen or oxygen by electrolysis of water
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- 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
- H02M1/00—Details of apparatus for conversion
- H02M1/12—Arrangements for reducing harmonics from ac input or output
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- 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
- H02M1/00—Details of apparatus for conversion
- H02M1/14—Arrangements for reducing ripples from dc input or output
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- 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
- H02M1/00—Details of apparatus for conversion
- H02M1/42—Circuits or arrangements for compensating for or adjusting power factor in converters or inverters
- H02M1/4208—Arrangements for improving power factor of AC input
- H02M1/4233—Arrangements for improving power factor of AC input using a bridge converter comprising active switches
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
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Abstract
The invention belongs to the technical field of electric power, and provides a high-capacity electrolytic hydrogen production hybrid rectifier based on MMC and a control method thereof, wherein the rectifier comprises: the auxiliary power converter is a modular multilevel converter MMC cascade phase-shifting full-bridge converter with an input series-output parallel structure, and is used for absorbing current harmonic wave at an alternating current side and compensating current ripple at a direct current side while transmitting partial power. The invention can assist the power converter to transmit a small part of power under the condition that the thyristor rectifier provides most of power support, and at the same time compensates current harmonic wave at the alternating current side and compensates current ripple at the direct current side, thereby effectively improving the electrolytic hydrogen production efficiency, and having small net side current distortion rate and large system power factor.
Description
Technical Field
The invention relates to the technical field of electric power, in particular to a high-capacity electrolytic hydrogen production hybrid rectifier based on MMC and a control method.
Background
The clean transformation process of energy is accelerated in China, the decarburization emission reduction requirements are growing increasingly, and in order to realize large-scale low-carbon and even carbon-free energy sources, the goals of carbon reaching peak and carbon neutralization are put forward in China, namely carbon dioxide emission strives to reach peak before 2030, and carbon neutralization is striven for before 2060.
The hydrogen energy is used as an energy source with great development potential in the future energy world, and has the advantages of cleanness, high energy density, high conversion efficiency and the like. The industrial chain technical equipment such as hydrogen production, hydrogen storage, hydrogen utilization and the like is accelerated to be developed in China, and the large-scale demonstration of an energy storage system is greatly promoted, so that a renewable energy power consumption mechanism is perfected and realized. The existing hydrogen production modes mainly comprise fossil fuel hydrogen production, biomass hydrogen production and water electrolysis hydrogen production. The electrolytic water hydrogen production has the advantages of zero carbon emission, high hydrogen production purity and the like, does not depend on fossil energy, and is quite environment-friendly in production process. And the high fluctuation renewable energy sources such as wind power, photovoltaic and the like can be consumed by water electrolysis and hydrogen production, the electric power of 'water abandon and wind abandon' is utilized to prepare hydrogen, the interference to a power grid is reduced, and the problems of renewable energy source consumption and grid connection stability in China can be effectively solved, so that the method has important economic and social benefits and wide development prospect.
The renewable energy high-power electrolytic hydrogen production system comprises a renewable energy micro-grid, an electrolytic water hydrogen production converter, an electrolytic stack, a hydrogen storage unit and the like. In the renewable energy electrolytic hydrogen production system with an alternating current bus structure, an AC-DC converter is used as an energy conversion device between an alternating current bus and an electrolytic hydrogen production load, and the requirements of high voltage reduction capability, continuous adjustable output, high conversion efficiency, high reliability, small output current ripple, current harmonic wave meeting the national standard and the like are required. The topology of the current grid-connected AC-DC converter for electrolytic hydrogen production mainly comprises a Silicon Controlled Rectifier (SCR) and a Pulse Width Modulation (PWM) rectifier. In high-power industrial application, a thyristor rectifier is generally adopted, a 6-pulse rectifier and a 12-pulse rectifier are commonly used, and because the power level is high, an isolation transformer is needed to realize electrical isolation, and an SCR (selective catalytic reduction) generates variable direct current by adjusting the triggering angle of the thyristor, the SCR has the advantages of simple structure, large capacity and low cost, but has serious harmonic wave and low power factor, so that an additional filter, a phase-shifting transformer or a reactive compensator is needed to be added to reduce the harmonic wave content, and the volume and the cost of the converter are increased. The PWM rectifier has good control characteristics, high power factor and good dynamic characteristics, and is widely applied to medium and small power systems along with the continuous development of power devices, and the PWM rectifier can reduce harmonic waves and improve power by applying high-frequency modulation, but the full-control type power device is high in price, so that the full-control type power device is not suitable for high-capacity hydrogen production occasions.
In recent years, partial scholars have studied the influence of the output power quality of the converter on the hydrogen production efficiency of the electrolysis stack, and the research result shows that although the hydrogen yield in the electrolysis hydrogen production is defined by the current average value, the current ripple can generate additional power loss in the electrolysis tank, the average power consumption of the electrolysis stack increases along with the increase of the current ripple factor, so that the converter with the output of low current ripple factor is beneficial to improving the hydrogen production efficiency and prolonging the service life of the electrolysis tank. The mixed rectifier combining the SCR and the VSR adopts a three-phase two-level Voltage Source Rectifier (VSR) cascading phase-shifting full-bridge converter, is integrally connected with a thyristor rectifier in parallel, can effectively solve the problems of high input current distortion and high output current ripple coefficient while improving the overall power level, and has the advantages of high hydrogen production efficiency and low harmonic. However, the VSC input side is a low-voltage ac bus, and in the case of high-capacity hydrogen production, although only a small amount of power is transmitted, a considerable current flows through the ac side, thereby increasing the difficulty and cost of manufacture. In addition, the compensation current of the single-stage phase-shifting full-bridge converter for the direct-current ripple component of the thyristor rectifier can reach hundreds of amperes, and the inductor is difficult to meet the requirement in practical application.
Disclosure of Invention
The invention aims to provide a high-capacity electrolytic hydrogen production hybrid rectifier based on MMC and a control method, which can effectively overcome the defects of the converter topology, and can meet the application scenes of high-power, high-efficiency, high-reliability and low-cost electrolytic hydrogen production.
The invention solves the technical problems and adopts the following technical scheme:
first, the invention provides a MMC-based high-capacity electrolytic hydrogen production hybrid rectifier, which comprises: the auxiliary power converter is a modular multilevel converter MMC cascade connection, adopts a phase-shifting full-bridge converter with an input-series output-parallel structure, and is used for absorbing current harmonic wave at an alternating current side and compensating current ripple at a direct current side while transmitting partial power.
Further, the input end of the MMC is the primary side of the transformer, namely an alternating current bus of a power grid, and the output end of the MMC is a public direct current bus; the comprehensive control strategy adopted during MMC operation comprises double closed-loop control and sub-module energy storage capacitance control, the MMC adopts carrier phase-shifting modulation, the modulating wave generated by the double closed-loop control is superposed with the modulating deviation amount generated by the sub-module energy storage capacitance control to form a total modulating wave, the total modulating wave is sent into the carrier phase-shifting modulation module to generate PWM signals to control the input and the cut-out of the sub-modules of the upper bridge arm and the lower bridge arm of the MMC, and the output level of the sub-modules is superposed at the output end to obtain direct-current output voltage.
Further, the dual closed loop control includes:
the voltage outer loop calculates reactive power by sampling three-phase current and three-phase voltage at the alternating current side, compares the reactive power with a reactive power reference value, and obtains fundamental wave component of an inner loop q-axis current command value through a proportional integral controllerThe method comprises the steps of carrying out a first treatment on the surface of the The fundamental component of the inner ring d-axis current command value is obtained through the PI controller after the comparison of the common DC bus voltage and the DC bus voltage reference value by sampling>；
The harmonic component of the current at the input end of the thyristor rectifier is extracted by a harmonic detection unit and used as the harmonic component of the MMC inner loop current instruction value, and the process comprises the steps of sampling the input current of the thyristor rectifierThen, obtaining +.f. in d-q coordinate system by park transformation>、/>Component, obtained by DFT sliding window iterative algorithm +.>And->Fundamental component in d-q coordinate system +.>、/>Then inputting the thyristor rectifier into the current d-q coordinate system>、/>The components being subtracted by the respective fundamental component +.>、/>Obtaining harmonic component of MMC inner loop current command value +.>、/>：
The fundamental component and the harmonic component of the MMC inner ring current command value are overlapped to form an MMC inner ring total current command value, and the MMC inner ring total current command value after overlapping is obtained according to the current flow direction of the hybrid rectifier:
the MMC current inner loop adopts a structure that a proportional integral controller and a multiple proportional resonance controller are connected in parallel, and the transfer function of the multiple proportional resonance controller is as follows:
in the method, in the process of the invention,is a proportionality factor->For resonance factor +.>For cut-off angular frequency +.>For the ith resonant angular frequency, s is the Laplace variation in the complex frequency domain.
Further, the submodule energy storage capacitor control includes: bridge arm energy equipartition control and submodule capacitor voltage equalizing control;
the bridge arm energy average control is used for ensuring that the average value of all the sub-module capacitor voltages in each phase unit is stabilized at the rated value, ensuring that the energy is distributed to each phase in an equalizing way, and simultaneously being used for inhibiting the excessive or insufficient circulation between bridge arms.
The voltage equalizing control of the capacitance voltage of each sub-module is used for ensuring that the actual value of the capacitance voltage of each sub-module is stabilized at a rated value, comparing the actual value of the capacitance voltage of each sub-module with a reference value, obtaining a positive control quantity through a proportional controller if the actual value is smaller, obtaining a modulation wave reference quantity according to the current direction of a bridge arm, sampling the current of the bridge arm, if the sampling value is positive, the sub-module is in a charging state, the modulation wave reference quantity is output by the controller to be positive, the charging time of the sub-module is increased, and then the capacitance voltage of the sub-module is increased; similarly, if the sampling value is negative, the submodule is in a discharge state, the reference quantity of the output modulation wave of the controller is negative, the discharge time of the submodule is reduced, and the capacitor voltage of the submodule is prevented from further reducing.
Further, under the condition that parameters of all modules are consistent, the phase-shifting full-bridge converter adopting the input-series output-parallel structure extracts the current direct-current ripple component at the output end of the thyristor rectifier through the ripple detection unit, and the current direct-current ripple component is overlapped to serve as a total current instruction value of the phase-shifting full-bridge converter, and the direct current is used for controlling and tracking the current instruction value to realize compensation of the direct-current ripple at the output end of the thyristor rectifier.
Further, the phase-shifting full-bridge converter adopting the input-series-output-parallel structure adopts common duty ratio control, and firstly, the ripple detection unit is used for extracting the DC ripple component of the current at the output end of the thyristor rectifierSuperimposed DC offset component->Then the total current command value is used as the total current command value of the phase-shifting full-bridge converter;
the phase-shifting full-bridge converter adopts a single current control loop, and samples the total current output by the phase-shifting full-bridge converterThe current deviation value is obtained after the comparison with the total current instruction value, the deviation value signal is compared with the carrier wave through the proportional-integral controller to generate a PWM signal, and the PWM signal is sent into each sub-module, so that the duty ratio of each sub-module is always the same.
The invention further provides a high-capacity electrolytic hydrogen production control method based on the MMC, which is applied to the high-capacity electrolytic hydrogen production mixed rectifier based on the MMC and comprises the following steps of:
connecting a thyristor rectifier in parallel with the auxiliary power converter;
the thyristor rectifier provides main power support for electrolytic hydrogen production load through low-voltage input of the secondary side of the transformer;
the auxiliary power converter is a modular multilevel converter MMC cascade connection, adopts a phase-shifting full-bridge converter with an input-series output-parallel structure, and is used for absorbing current harmonic waves at an alternating current side and compensating current ripple waves at a direct current side while transmitting partial power.
The beneficial effects of the invention are as follows: the thyristor rectifier provides main power support for electrolytic hydrogen production load, the MMC rectifier is cascaded to form an auxiliary power converter by adopting a phase-shifting full-bridge converter with an input-series-output parallel structure, the auxiliary power converter absorbs harmonic waves at an alternating current side and compensates ripple waves at a direct current side when transmitting partial power, the mixed rectifier can effectively improve electrolytic hydrogen production efficiency, the net side current distortion rate is small, the direct current side ripple wave factor is small, the system power factor is large, and the electrolytic hydrogen production application scene of high power, high efficiency and low cost is met.
Drawings
FIG. 1 is a topological structure diagram of a hybrid rectifier in embodiment 1;
FIG. 2 is a block diagram of MMC harmonic compensation control in embodiment 1;
fig. 3 is a control block diagram based on PI and MPR parallel control in embodiment 1;
fig. 4 is a bridge arm energy average control block diagram in embodiment 1;
FIG. 5 is a block diagram of a submodule capacitor voltage equalizing control in example 1;
FIG. 6 is a schematic diagram of a phase-shifting full-bridge converter employing an ISOP structure in embodiment 1 employing common duty cycle control;
FIG. 7 is a waveform diagram of the output current of the thyristor rectifier and the total output current of the hybrid rectifier in example 1;
FIG. 8 is a graph of the current waveform on the grid side of the hybrid rectifier of example 1;
fig. 9 is a flowchart of a high-capacity electrolytic hydrogen production control method based on MMC in example 2.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments of the present invention. The components of the embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations.
Example 1
As shown in fig. 1, the present embodiment provides a high-capacity electrolytic hydrogen production hybrid rectifier topology structure based on MMC, where the hybrid rectifier is formed by connecting a thyristor rectifier and an auxiliary power converter in parallel, and the present embodiment specifically describes a 6-pulse thyristor rectifier as an example; the Modular Multilevel Converter (MMC) cascade adopts a phase-shifting full-bridge converter with an input-series-output-parallel (ISOP) structure to form an auxiliary power converter; the power sub-modules are all identical in structure, and the types of the power sub-modules include, but are not limited to, half-bridge type, full-bridge type and flying capacitor type; each sub-module structure is consistent with parameters for the phase-shifting full-bridge sub-module; the input end of the MMC is the primary side of the transformer, namely an alternating current bus of the power grid, and the output end of the MMC is a public direct current bus; the comprehensive control strategy adopted during MMC operation comprises double closed-loop control and sub-module energy storage capacitance control, the MMC rectifier adopts carrier phase-shifting modulation, the modulation wave generated by the double closed-loop control is overlapped with the modulation deviation amount generated by the sub-module energy storage capacitance control to form a total modulation wave, the total modulation wave is sent into the carrier phase-shifting modulation module to generate PWM signals to control the input and the cut-out of the sub-modules of the upper bridge arm and the lower bridge arm of the MMC, and the output level of the sub-modules is overlapped at the output end to obtain direct-current output voltage.
In the double closed-loop control of the MMC, the voltage outer loop calculates reactive power by sampling three-phase current and three-phase voltage at the alternating current side, and then compares the reactive power with a reactive power reference value, and obtains the fundamental wave component of the inner loop q-axis current command value through a Proportional Integral (PI) controllerThe method comprises the steps of carrying out a first treatment on the surface of the The fundamental component of the inner ring d-axis current command value is obtained through the PI controller after the direct current bus voltage is sampled and compared with the direct current bus voltage reference value>。
Further, the harmonic component of the current at the input end of the 6-pulse thyristor rectifier is extracted by a harmonic detection unit to be used as the harmonic component of the MMC inner loop current instruction value, and the process comprises the steps of sampling the input current of the 6-pulse thyristor rectifierThen, obtaining +.f. in d-q coordinate system by park transformation>、/>Component, obtained by DFT sliding window iterative algorithm +.>And->Fundamental component in d-q coordinate system +.>、/>Then inputting the thyristor rectifier into the current d-q coordinate system>、/>The components being subtracted by the respective fundamental component +.>、/>Obtaining harmonic component of MMC inner loop current command value +.>、/>：
The harmonic component and the fundamental component of the MMC inner ring current command value are overlapped to form an MMC inner ring total current command value, and the MMC inner ring total current command value after overlapping is obtained according to the current flow direction of the mixed rectifier:
the MMC inner loop current command value comprises a fundamental component and a harmonic component, in order to realize effective tracking of current, the MMC inner loop adopts a structure that a Proportional Integral (PI) controller and a Multiple Proportional Resonance (MPR) controller are connected in parallel, and a control block diagram based on PI and MPR parallel control is shown in figure 3. And comparing the current inner loop actual value with the current inner loop instruction value to obtain a current control quantity which is a PI controller transfer function. Here, since PI control has a capability of fast tracking a given current, but has a weak tracking capability for a low-order harmonic current, MPR control is added, and after the PI control is connected in parallel with the PI controller, effective tracking for a specific subharmonic current can be achieved while ensuring dynamic characteristics of the system, and 6k±1 (k is a positive integer) subcurrent harmonics generated by a 6-pulse thyristor rectifier are changed into 6n (n is a positive integer) subharmonics in a d-q coordinate system, so that transfer functions of MPR control are:
in the method, in the process of the invention,is a proportionality factor->For resonance factor +.>For cut-off angular frequency +.>For the ith resonant angular frequency, s is the Laplace variation in the complex frequency domain.
In this embodiment, the energy storage capacitor control of the submodule includes bridge arm energy equally dividing control and voltage equalizing control of the capacitor voltage of the submodule. The bridge arm energy sharing control block diagram is shown in fig. 4, whereinIs the reference value of the capacitance voltage of the submodule and is generally set as the rated working voltage; />Is the average value of all the submodule capacitance voltages of each phase; />And->Is the current of the upper and lower bridge arms. Because the structure of the MMC rectifier is highly symmetrical, the same energy distribution in the bridge arms is beneficial to keeping the system stable, and the average value of the capacitance voltages of all the submodules in each phase unit can be ensured to be stable at the rated value of the capacitance voltage by adopting the energy equal distribution control of the bridge arms, the energy is ensured to be uniformly distributed in each phase, and meanwhile, the excessive or insufficient circulation among the bridge arms can be restrained.
A voltage equalizing control block diagram of the sub-module capacitor voltage is shown in FIG. 5, whereinIs the reference value of the capacitance voltage of the submodule and is generally set as the rated working voltage; />Is the actual value of the capacitance voltage of each sub-module; k is a proportioner parameter. Comparing the actual value of the capacitance voltage of the submodule with a reference value, if the actual value is smaller, obtaining a positive control quantity through a proportional controller, obtaining a modulation wave reference quantity according to the bridge arm current direction, sampling the bridge arm current, if the sampling value is positive, putting the submodule in a charging state, outputting the modulation wave reference quantity by the controller, and increasing the charging time of the submodule, so that the capacitance voltage of the submodule is increased; similarly, if the sampling value is negative, the submodule is in a discharge state, the reference quantity of the output modulation wave of the controller is negative, the discharge time of the submodule is reduced, and the capacitor voltage of the submodule can be prevented from further reducing.
Under the condition that parameters of all modules are consistent, the phase-shifting full-bridge converter adopting an ISOP structure extracts a current direct-current ripple component at the output end of the thyristor rectifier through the ripple detection unit, and the current direct-current ripple component is overlapped to be used as a total current instruction value of the phase-shifting full-bridge converter, and the direct current control tracking current instruction value is used for realizing compensation of the direct-current ripple at the output end of the thyristor rectifier.
Here, the phase-shifting full-bridge converter of the ISOP structure adopts a common duty ratio control, fig. 6 is a schematic diagram of the phase-shifting full-bridge converter of the ISOP structure adopting the common duty ratio control, wherein the common dc bus voltage is a phase-shifting full-bridge submodule, each submodule structure is consistent with parameters, the input end voltage-equalizing capacitor of each phase-shifting full-bridge submodule is used for outputting current for each phase-shifting full-bridge submodule. Firstly, extracting a direct current ripple component of a current at an output end of a thyristor rectifier through a ripple detection unitSuperimposed DC offset component->Then the total current command value is used as the total current command value of the phase-shifting full-bridge converter; in the embodiment, the phase-shifting full-bridge converter adopts a single current control loop, and samples the total current output by the phase-shifting full-bridge converter +.>The current deviation value is obtained after the comparison with the total current instruction value, the deviation value signal is compared with the carrier wave through the PI controller to generate a PWM signal, and the PWM signal is sent into each sub-module, so that the duty ratio of each sub-module is always the same. The system is assumed to be interfered at a certain moment, so that the input voltage of a certain module is reduced, the input current of each module is correspondingly reduced due to the consistent duty ratio of the modules, the current flowing into the corresponding voltage-dividing capacitor is increased, the voltage of the capacitor is gradually increased, the input voltage of the module is increased along with the increase until the balance is restored, the control strategy can effectively track the current instruction value, realize the compensation of the direct current ripple wave of the thyristor rectifier, and simultaneously ensure the current equalization of the output end and the voltage equalization control of the input end under the condition that the parameters of all the submodules are consistent.
To verify the working characteristics of the hybrid rectifier of the embodiment, the hybrid rectifier simulation model is built in Simulink. FIG. 7 shows the output current waveform of the thyristor rectifier and the total output current waveform of the hybrid rectifier, wherein the output current waveform of the thyristor rectifier is 6 pulse DC, the effective value of the current is 5900A, the current ripple is 500A, and the ripple component is large; after the ripple compensation of the auxiliary power converter, the total output current ripple of the hybrid rectifier is only 20A, and compared with the ripple before compensation, the ripple is reduced by 96%, so that the electrolytic hydrogen production efficiency can be effectively improved. Fig. 8 is a waveform of a grid-side current after harmonic compensation of a hybrid rectifier, wherein the input current THD of the grid-side is 3.17% after harmonic compensation, and meets grid-connected requirements (THD < 5%) of power electronic equipment.
Example 2
The embodiment provides a high-capacity electrolytic hydrogen production control method based on MMC (modular multilevel converter), which is based on embodiment 1, and a flow chart of the method is shown in fig. 9, wherein the method comprises the following steps:
s1, connecting a thyristor rectifier with an auxiliary power converter in parallel;
s2, a thyristor rectifier provides main power support for electrolytic hydrogen production load through low-voltage input of a secondary side of a transformer;
s3, the auxiliary power converter is a modular multilevel converter MMC cascade connection, adopts a phase-shifting full-bridge converter with an input-series output-parallel structure, and is used for absorbing current harmonic waves at an alternating current side and compensating current ripple waves at a direct current side while transmitting partial power.
The hybrid rectifier topological structure in the embodiment 1 is also used in the embodiment, so that the related control principle and application scene are consistent, the main power support is provided for electrolytic hydrogen production load through the thyristor rectifier, the MMC rectifier is cascaded to form an auxiliary power converter by adopting a phase-shifting full-bridge converter with an input-series-output-parallel (ISOP) structure, the auxiliary power converter absorbs harmonic waves at an alternating current side and compensates ripple waves at a direct current side when transmitting partial power, the hybrid rectifier can effectively improve electrolytic hydrogen production efficiency, the network side current distortion rate is small, the direct current side ripple factor is small, the system power factor is large, and the application scene of high power, high efficiency and low cost electrolytic hydrogen production is met. The present embodiment is not described in detail.
The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (5)
1. MMC-based high-capacity electrolytic hydrogen production hybrid rectifier is characterized by comprising: the auxiliary power converter is in cascade connection with a modular multilevel converter MMC, adopts a phase-shifting full-bridge converter with a modular multilevel converter and input-series-output-parallel structure, and is used for absorbing current harmonic wave at an alternating current side and compensating current ripple at a direct current side while transmitting partial power;
the input end of the MMC is the primary side of the transformer, namely an alternating current bus of the power grid, and the output end of the MMC is a public direct current bus; the comprehensive control strategy adopted during MMC operation comprises double closed-loop control and sub-module energy storage capacitor control, wherein the MMC adopts carrier phase-shifting modulation, modulation waves generated by the double closed-loop control are superposed with modulation deviation values generated by the sub-module energy storage capacitor control to form total modulation waves, PWM signals are generated after the total modulation waves are sent into the carrier phase-shifting modulation module to control the input and the cut-out of sub-modules of an upper bridge arm and a lower bridge arm of the MMC, and the output levels of the sub-modules are superposed at an output end to obtain direct-current output voltage;
the dual closed loop control includes:
the voltage outer loop calculates reactive power by sampling three-phase current and three-phase voltage of alternating current side, compares the reactive power with reactive power reference value, and obtains fundamental wave component of inner loop q-axis current command value through PI controllerThe method comprises the steps of carrying out a first treatment on the surface of the The fundamental component of the inner ring d-axis current command value is obtained through a proportional integral controller after the comparison of the common DC bus voltage and the DC bus voltage reference value by sampling the common DC bus voltage>；
The harmonic component of the current at the input end of the thyristor rectifier is extracted by a harmonic detection unit and used as the harmonic component of the MMC inner loop current instruction value, and the process comprises the steps of sampling the input current of the thyristor rectifierThen, obtaining the d-q coordinate system by park transformation、/>Component, obtained by DFT sliding window iterative algorithm +.>And->Fundamental component in d-q coordinate system +.>、Then inputting the thyristor rectifier into the current d-q coordinate system>、/>The components being subtracted from the respective fundamental component、/>Obtaining harmonic component of MMC inner loop current command value +.>、/>：
The fundamental component and the harmonic component of the MMC inner ring current command value are overlapped to form an MMC inner ring total current command value, and the MMC inner ring total current command value after overlapping is obtained according to the current flow direction of the hybrid rectifier:
the MMC current inner loop adopts a structure that a proportional integral controller and a multiple proportional resonance controller are connected in parallel, and the transfer function of the multiple proportional resonance controller is as follows:
in the method, in the process of the invention,is a proportionality factor->For resonance factor +.>For cut-off angular frequency +.>For the ith resonant angular frequency, s is the Laplace variation in the complex frequency domain.
2. The MMC-based high-capacity electrolytic hydrogen production hybrid rectifier of claim 1, wherein the sub-module storage capacitor control comprises: bridge arm energy equipartition control and submodule capacitor voltage equalizing control;
the bridge arm energy average control is used for ensuring that the average value of the capacitance voltage of all the submodules in each phase unit is stabilized at the rated value, ensuring that the energy is distributed to each phase in an equalizing way, and simultaneously inhibiting the circulation between bridge arms from being too large or too small;
the voltage equalizing control of the capacitance voltage of each sub-module is used for ensuring that the actual value of the capacitance voltage of each sub-module is stabilized at a rated value, comparing the actual value of the capacitance voltage of each sub-module with a reference value, obtaining a positive control quantity through a proportional controller if the actual value is smaller, obtaining a modulation wave reference quantity according to the current direction of a bridge arm, sampling the current of the bridge arm, if the sampling value is positive, the sub-module is in a charging state, the modulation wave reference quantity is output by the controller to be positive, the charging time of the sub-module is increased, and then the capacitance voltage of the sub-module is increased; similarly, if the sampling value is negative, the submodule is in a discharge state, the reference quantity of the output modulation wave of the controller is negative, the discharge time of the submodule is reduced, and the capacitor voltage of the submodule is prevented from further reducing.
3. The MMC-based high-capacity electrolytic hydrogen production hybrid rectifier is characterized in that under the condition that parameters of all modules are consistent, the phase-shifting full-bridge converter adopting an input-series output-parallel structure extracts current direct-current ripple components at the output end of the thyristor rectifier through a ripple detection unit, and the current direct-current ripple components are overlapped to be used as a total current instruction value of the phase-shifting full-bridge converter, and compensation of the direct-current ripple at the output end of the thyristor rectifier is realized through direct current control tracking current instruction value.
4. The MMC-based high-capacity electrolytic hydrogen production hybrid rectifier as in claim 3, wherein the phase-shifting full-bridge converter with input-series output-parallel structure adopts common duty ratio control, and the output end current DC ripple component of the thyristor rectifier is firstly extracted by the ripple detection unitSuperimposed DC offset component->Then the total current command value is used as the total current command value of the phase-shifting full-bridge converter;
the phase-shifting full-bridge converter adopts a single current control loop, and samples the total current output by the phase-shifting full-bridge converterThe current deviation value is obtained after the comparison with the total current instruction value, the deviation value signal is compared with the carrier wave through the proportional-integral controller to generate a PWM signal, and the PWM signal is sent into each sub-module, so that the duty ratio of each sub-module is always the same.
5. The MMC-based high-capacity electrolytic hydrogen production control method is applied to the MMC-based high-capacity electrolytic hydrogen production hybrid rectifier disclosed in any one of claims 1 to 4, and is characterized by comprising the following steps:
connecting a thyristor rectifier in parallel with the auxiliary power converter;
the thyristor rectifier provides main power support for electrolytic hydrogen production load through low-voltage input of the secondary side of the transformer;
the auxiliary power converter is a modular multilevel converter MMC cascade connection, adopts a modular multilevel rectifier and a phase-shifting full-bridge converter cascade connection with an input-series-output-parallel structure, and is used for absorbing current harmonic waves at an alternating current side and compensating current ripple waves at a direct current side while transmitting partial power.
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