High-capacity hydrogen production power supply suitable for medium-voltage alternating current power grid and control method thereofTechnical Field
The invention relates to the technical field of high-power electronics, in particular to a high-capacity hydrogen production power supply suitable for a medium-voltage alternating current power grid and a control method thereof.
Background
The hydrogen energy is clean energy with environmental protection, no pollution and high heat value. The hydrogen production and energy storage industry is greatly developed to meet the requirements of improving the flexibility of an electric power system, improving the new energy consumption capability and reducing the waste wind and light.
In the field of high-power hydrogen production power supply at present, the balance between cost and performance is difficult to achieve. The traditional hydrogen production power supply usually adopts a rectifier composed of a transformer and a thyristor, has the defects of large capacity, serious harmonic pollution, low power factor, slow response and low efficiency, is easy to influence the electric energy quality and stability of the power grid, and even can lead the system to be inoperable if the thyristor rectifier fails. If the PWM rectification scheme is adopted, although the power factor can be improved, the harmonic pollution can be reduced, and the response speed can be improved, the capacity of the PWM rectification scheme is smaller, and the PWM rectification scheme is not suitable for being applied to a high-capacity hydrogen production power supply.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a high-capacity hydrogen production power supply suitable for a medium-voltage alternating current power grid and a control method thereof, and aims to solve the problems of high input voltage, large electrolytic capacity and high power quality requirement in the prior art during the hydrogen production of renewable energy sources.
The aim of the invention can be achieved by the following technical scheme:
The invention provides a high-capacity hydrogen production power supply suitable for a medium-voltage alternating current power grid.
The multi-pulse rectification current is positioned at the starting end of the hydrogen production equipment and connected with the medium-voltage power grid, and is formed by cascading a multi-pulse phase-shifting rectification transformer and an uncontrolled rectification circuit. The multi-pulse phase-shifting rectifier transformer is connected with a medium-voltage alternating current power grid and outputs phase-shifting voltage, the number of windings on the low-voltage side of the multi-pulse phase-shifting rectifier transformer is m, and phase-shifting voltages with the same phase angles of m groups of phase-shifting line voltages and with the same amplitude values and phase differences pi/(3 m) are generated. The medium-voltage power grid can be a 10KV or 35KV power grid, is certainly not limited to the description, and can be used according to actual conditions, and the medium-voltage power grid is within the protection scope of the application. The multi-pulse rectifier transformer may be a 12-pulse rectifier transformer, an 18-pulse rectifier transformer, a 24-pulse rectifier transformer, or other multi-pulse rectifier transformers. The uncontrolled rectifying circuit is a three-phase diode rectifying bridge, the input end of the uncontrolled rectifying circuit is connected with the multi-pulse phase-shifting rectifying transformer, the number of the diode rectifying bridges is the same as the number of windings on the low-voltage side of the multi-pulse phase-shifting rectifying transformer, the number of the diode rectifying bridges is m, and the output ends of the diode rectifying bridges are connected in parallel to achieve the purpose of harmonic cancellation, so that a (6 m) pulse wave rectifying circuit is formed and connected with a rear-stage direct-current transformer module. The uncontrolled rectifying circuit reduces the harmonic content of the output voltage by improving the pulse wave number of the output direct-current voltage, reduces the cost by adopting uncontrolled devices, improves the reliability and does not need an additional control circuit. Optionally, an additional passive filter may be installed at the input of the uncontrolled rectifying circuit to enhance the filtering capability.
The direct-current transformer module adopts an input series-output parallel structure. The input side of the direct current transformer is connected in series by k sub-modules, so that the voltage division burden of the switching device is reduced, the voltage withstand requirement and the voltage stress of the switching device are reduced, and the output side of the direct current transformer is connected in parallel by k sub-modules, so that the high current requirement of the hydrogen production electrolytic tank is met. The submodule of the direct current transformer adopts one or more of an isolated direct current converter such as a DAB converter, a CLLLC converter, a phase-shifting full-bridge converter, an LLC converter and the like, and realizes the voltage conversion of higher voltage transformation ratio while realizing electric isolation.
And the input end of the hydrogen production electrolytic tank is connected with the direct current transformer module, and the input end of the hydrogen production electrolytic tank is connected with the direct current transformer module in series and output and is connected with the direct current transformer in parallel to supply power and carry out electrolytic hydrogen production.
The control module consists of a sampling circuit, a DSP controller and a driving circuit. The sampling circuit converts the electric quantities such as capacitance voltage of each submodule at the input side of the direct-current transformer, capacitance voltage at the output side of the direct-current transformer, output current of each submodule at the output side of the direct-current transformer and the like into 0-3.3V analog signal quantity, and the analog signal quantity is further output to an ADC port of the DSP controller. The DSP controller is responsible for realizing a control algorithm and a protection algorithm, outputs PWM signals to the driving circuit through EPWM ports after calculating the duty ratio, and can be properly expanded if the number of the DC transformer submodules is large. The driving circuit adopts optical isolation or magnetic isolation to realize electrical isolation and level conversion, and drives the I GBT module.
Further, the invention also provides a control method of the high-capacity hydrogen production power supply suitable for the medium-voltage alternating-current power grid, which comprises a three-closed loop decoupling control algorithm and an overcurrent protection algorithm for the direct-current transformer. The three-closed loop control algorithm comprises an input equalizing ring, an output voltage ring and a current inner ring, and the input equalizing ring and the output voltage ring are required to be decoupled in order to avoid interference of the input equalizing ring on the output voltage loop. In the input equalizing ring, the input voltage equalizing control signal dsn corresponding to the nth basic circuit unit is not obtained directly, but is obtained by adding the output signals of the first n-1 input equalizing rings, so as to realize decoupling control, avoid the influence of the input equalizing ring on the output voltage ring, and facilitate the control parameter design of each loop. The protection algorithm comprises overvoltage protection, overcurrent protection, short-circuit protection and the like and is used for protecting the direct-current transformer.
The invention has the beneficial effects that:
The hydrogen production power supply has the advantages of small output voltage ripple, good working condition of the hydrogen production electrolytic tank, high hydrogen production efficiency, wide output current regulation range, low harmonic pollution to the power grid and investment saving in harmonic treatment. The hydrogen production power supply front-stage multi-pulse rectification circuit adopts an uncontrolled device, reduces the cost, improves the reliability, reduces the harmonic current injected into a power grid by adopting a phase-shifting rectification technology, and improves the electric energy quality. The hydrogen production power supply rear-stage direct current transformer adopts an isolated power supply scheme, and has better control precision and high safety. The high-voltage power supply is suitable for high-voltage transformation ratio occasions, and can simultaneously meet the requirements of inputting high voltage and outputting low voltage and large current.
Drawings
The invention is further described below with reference to the accompanying drawings.
FIG. 1 is a schematic diagram of a rectifying device according to the present invention;
FIG. 2 is a schematic diagram of a system topology of an embodiment of the present invention;
FIG. 3 is a system control schematic of an embodiment of the present invention;
FIG. 4 is a simulated waveform diagram of a pre-stage rectification circuit according to an embodiment of the present invention;
fig. 5 is a simulation waveform diagram of a post-stage dc transformer according to an embodiment of the present invention.
Detailed Description
Embodiments of the present invention will now be described with reference to the accompanying drawings and an example of a hydrogen generation power source having a voltage rating of 35kVAC/346V DC and a capacity of 1MVA, it being apparent that the examples described are only some, but not all, examples of the present invention. Based on the embodiments of the present invention, all other embodiments that a person of ordinary skill in the art would obtain without inventive faculty to fig. 1 are within the scope of the present invention. Embodiments employ PLECS software for simulation verification of the system.
As shown in FIG. 1, the invention is composed of a multi-pulse phase-shifting rectifier transformer, an uncontrolled rectifier circuit, a DC transformer module and a hydrogen production electrolytic tank.
As shown in FIG. 2, the embodiment of the invention adopts a scheme of cascading a 24-pulse rectification circuit and an ISOP-DAB DC transformer. A front-stage 24-pulse rectifying circuit in the hydrogen production power supply rectifies 35kV alternating current ug into 4kV direct current uin. The 24 pulse wave rectifying circuit of the preceding stage is composed of 2 three-winding phase-shifting rectifying transformers and 4 three-phase uncontrolled rectifying circuits. The low-voltage side windings of each three-winding transformer respectively adopt y-type windings and d-type windings, the line voltages of the windings form a phase difference of 30 degrees, the high-voltage side windings of the 2 three-winding phase-shifting rectifier transformers respectively generate phase displacement of +7.5 degrees and-7.5 degrees by adopting a side-extending triangle connection method, and therefore four sets of low-voltage side winding line voltages uabc,1,uabc,2,uabc,3,uabc,4 of the two three-winding phase-shifting rectifier transformers are mutually different by 15 degrees. The input sides of the 4 uncontrolled rectifying circuits are respectively connected with the windings of the low-voltage side of the 2 three-winding phase-shifting transformers, and the output sides of the 4 uncontrolled rectifying circuits are connected in parallel to obtain medium-voltage direct-current voltage uin, so that a 24-pulse rectifying circuit is formed. In order to reduce the ripple of uin, the passive filter Zfilter is additionally arranged at the rear stage of uncontrolled rectification. The ISOP-DAB direct current transformer comprises 6 DAB modules, so that each DAB only needs to bear voltage smaller than 1kV, and the IGBT of each DAB can be in parallel connection with the output side to disperse and output current required by electrolytic hydrogen production, and the system safety is improved. For a single DAB module, the transformation ratio of the isolation transformer is n 1, Lr is the leakage inductance of the isolation transformer, Rp is the parasitic resistance, and Co is the output capacitance. The ISOP-DAB direct current transformer converts 4kV direct current into 346V direct current so as to meet the requirement of low-voltage and high-current of the hydrogen production power supply. The control module of the hydrogen production power supply comprises a DSP controller, a driving circuit and a sampling circuit. The sampling circuit converts the electric quantity of the direct-current transformer into 0-3.3V analog quantity and transmits the analog quantity to the ADC module of the DSP controller. And after the analog signals are input into the ADC module of the DSP controller, the operation of a three-closed loop decoupling control algorithm is carried out. In the protection algorithm of the direct current transformer, the command current in the current inner loop is increased by a limiting value to prevent the output current from being overlarge and prevent the IGBT from overflowing, and meanwhile, the input voltage and the output voltage are detected to realize overvoltage protection. The DSP controller updates the PWM duty ratio value in real time in each switching period and outputs PWM signals to the driving circuit. The driving circuit electrically isolates the DSP controller from the switching device of the direct-current transformer, performs level conversion and outputs a driving signal to drive the switching device in the direct-current transformer. In this example, the hydrogen production electrolyzer is replaced with a resistive load RL.
As shown in FIG. 3, the control scheme of the embodiment of the invention adopts a three-closed loop decoupling control strategy, and comprises an input voltage equalizing controller Gui, an output voltage controller Guo and an output current controller Gi, wherein the three-closed loop control is implemented by adding a current inner loop on the basis of the traditional double-closed loop control strategy so as to achieve the purposes of improving dynamic response and preventing overcurrent. The control signal dsn of the last DAB input voltage equalizing is determined by the previous ds1,ds2…dsn-1, so that decoupling control is realized, and the influence of the input voltage equalizing ring on the output voltage ring is avoided. For the jth DAB module, the output voltage loop and the input equalizing loop jointly determine the output current reference value i× oj, the difference between i× oj in the current loop and the actual output current i oj is obtained by Gi to obtain a shift dj, and then the shift unit obtains the switching signal s1,s2,s3,s4,s5,s6,s7,s8 to drive the DAB module. In this embodiment, n=6, i.e. 6 DAB modules are used to form the ISOP-DAB converter.
As shown in fig. 4, in the embodiment of the present invention, the 24-pulse rectification circuit rectifies the medium-voltage ac voltage ug to output a medium-voltage dc voltage uin, and the medium-voltage dc voltage uin contains a smaller ripple component after being filtered by the passive filter Zfilter. ua1,ua2,ua3,ua4,ub1,ub2,ub3,ub4,uc1,uc2,uc3,uc4 in the figure is the line voltage output from each phase-shifting rectifier transformer.
As shown in FIG. 5, in the embodiment of the invention, the ISOP-DAB direct current transformer converts the direct current voltage uin output by the front-stage rectifying circuit into the direct current voltage uo,iout required by the hydrogen production electrolytic tank to be the output current of the direct current transformer, the ISOP-DAB direct current transformer has better dynamic response, and after the system is started, uo and iout can reach a steady state in a shorter time.
The foregoing has shown and described the basic principles, principal features and advantages of the invention. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, and that the above embodiments and descriptions are merely illustrative of the principles of the present invention, and various changes and modifications may be made without departing from the spirit and scope of the invention, which is defined in the appended claims.