Multi-isolation output hydrogen production converter suitable for medium-voltage direct-current bus and control strategy

Abstract

The invention belongs to a power electronic electric energy conversion technology, and particularly relates to a multi-isolation output hydrogen production converter suitable for a medium-voltage direct-current bus, which comprises a medium-voltage side smoothing reactor, N power unit modules and three electrolytic cell loads, the input sides of the N power module units are connected in series, and the output sides of the N power module units are connected in parallel; each power module unit is provided with three independent outputs, and the three independent outputs are respectively connected with three electrolytic cell loads. A half-bridge sub-module series structure is matched with a medium-voltage direct-current bus, and a rear-stage isolation type buck converter is cascaded at the rear stage of the half-bridge sub-module, so that the problem that the high-voltage side and the low-voltage side of the medium-voltage side direct-current bus output large current is solved, and the voltage of the medium-voltage side bus can be flexibly matched by adjusting the number of units.

Description

Technical Field

[0001] The present invention belongs to a power electronic electric energy conversion technology, and in particular relates to a multi-isolation output hydrogen production converter suitable for a medium-voltage direct current bus and a control strategy. Background Art

[0002] Green hydrogen will be the key direction for the development of hydrogen energy in the future. The promotion of hydrogen fuel cell vehicles, hydrogen energy storage and other application links will achieve the deep integration of electricity and secondary energy such as hydrogen energy in the long term. It can be seen that in the context of global energy transformation, hydrogen energy is one of the irreplaceable and important roles in future energy strategies.

[0003] In the new energy DC microgrid hydrogen production system, according to the renewable energy power supply mode, it is coupled with the electrolyzer in two ways: direct coupling and indirect coupling. Direct coupling refers to directly connecting renewable energy to the electrolyzer. This method has a simple structure and low cost, but the renewable energy needs to match the voltage and current of the electrolyzer, and cannot be applied in large-scale engineering. Indirect coupling is that renewable energy supplies power to the electrolyzer through a controller and a DC / DC converter. It has high flexibility and is the connection method currently adopted by most new energy hydrogen production systems. However, the current indirect coupling method is based on a low-voltage DC bus, and usually uses multiple decentralized and independent two-port converters to convert power between energy ports. There are mainly the following problems: a large number of hydrogen production converters and high cost; many energy conversion stages and low efficiency; based on a low-voltage DC bus, the power is small; the dependence on renewable energy is high and the reliability is low. Therefore, the current indirect coupling method based on a low-voltage DC bus cannot meet the development needs of a new energy high-power DC microgrid hydrogen production system. Therefore, a high-power DC microgrid hydrogen production system based on a medium-voltage DC bus is an important development direction for new energy hydrogen production in the future.

[0004] The high-power new energy DC microgrid hydrogen production system based on medium-voltage DC bus mainly includes new energy module, new energy converter module, energy storage module, boost converter module, medium-voltage DC bus, hydrogen production converter module and electrolyzer, among which the main function of hydrogen production converter module is to convert ±10kV medium-voltage DC power into DC power available for electrolyzer. With the continuous increase of electrolyzer power, higher requirements are put forward for high power, wide output voltage range, high step-down conversion ratio and high reliability of hydrogen production converter.

[0005] In summary, the high-power DC microgrid hydrogen production system based on the medium-voltage DC bus is an important development direction of the future hydrogen production system; the high-power hydrogen production converter is the core equipment in the medium-voltage DC hydrogen production system that connects the medium-voltage DC grid and the low-voltage electrolyzer. Summary of the invention

[0006] The purpose of the present invention is to address the shortcomings of hydrogen production converters in existing low-voltage DC bus-based hydrogen production systems, and to propose a multi-isolated output hydrogen production converter and control strategy suitable for medium-voltage DC bus. The hydrogen production converter can realize multiple isolated output ports and provide stable, high-conversion-efficiency, steplessly adjustable DC power.

[0007] To achieve the above-mentioned object, the present invention provides a multi-isolated output hydrogen production converter suitable for a medium-voltage DC bus, comprising a medium-voltage side smoothing reactor 0, N power unit modules (N=1, 2, 3...) and three electrolyzer loads; wherein the medium-voltage side smoothing reactor 0 is connected to the positive pole of the medium-voltage bus, the N power module units are connected in series on the input side and in parallel on the output side; each power module unit has three independent outputs, and the three independent outputs are respectively connected to the three electrolyzer loads.

[0008] Each power unit module (taking power unit module 1 as an example) includes a half-bridge unit 11, a single H-bridge inverter unit 12, a four-winding high-frequency transformer 13, a rectifier bridge 14, a clamping circuit unit 15 and a filter circuit unit 16;

[0009] The half-bridge unit 11 includes a first switch device 111, a second switch device 112 and a submodule capacitor 113, the first switch device 111 and the second switch device 112 are connected in series, the midpoint of the series bridge arm is connected to the medium voltage side smoothing reactor 0, and the series bridge arm output is connected in parallel with the submodule capacitor 113;

[0010] The single H-bridge inverter unit 12 includes a first inverter bridge arm formed by a first switch 121 and a second switch 122 connected in series, and a second inverter bridge arm formed by a third switch 123 and a fourth switch 124 connected in series. The two inverter bridge arms constitute a single H-bridge inverter unit and are connected in parallel with the submodule capacitor 113; the output of the single H-bridge inverter unit is sequentially connected in series with a resonant inductor 125 (including a transformer leakage inductance), a DC blocking capacitor 126, and a high-voltage side winding 131 of a four-winding high-frequency transformer 13; the low-voltage side of the four-winding high-frequency transformer 13 has three isolated first low-voltage windings 132, a second low-voltage winding 133, and a third low-voltage winding 134;

[0011] The rectifier bridge 14 includes three independent H-bridge rectifier circuits; the first diode 1411 and the second diode 1412 are connected in series to form a first rectifier bridge arm, the third diode 1413 and the fourth diode 1414 are connected in series to form a second rectifier bridge arm, and the two rectifier bridge arms form a first H-bridge rectifier circuit, the input side of the first H-bridge rectifier circuit is connected to the first low-voltage winding 132, and the output side of the first H-bridge rectifier circuit is connected in parallel with the first RCD clamping circuit of the clamping circuit unit 15; similarly, the fifth diode 1421, the sixth diode 1422, the third diode 1413 and the fourth diode 1414 are connected in series to form a second rectifier bridge arm. The seventh diode 1423 and the eighth diode 1424 constitute a second H-bridge rectifier circuit, the input side of the second H-bridge rectifier circuit is connected to the second low-voltage winding 133, and the output side is connected in parallel with the second RCD clamping circuit of the clamping circuit unit 15; the ninth diode 1431, the tenth diode 1432, the eleventh diode 1433 and the twelfth diode 1434 constitute a third H-bridge rectifier circuit, the input side of the third H-bridge rectifier circuit is connected to the third low-voltage winding 134, and the output side is connected in parallel with the third RCD clamping circuit of the clamping circuit unit 15;

[0012] The clamping circuit unit 15 includes three independent RCD clamping circuits. The first RCD clamping circuit includes a first absorption diode 1511, a second absorption capacitor 1512 and a first absorption resistor 1513. The first absorption diode 1511 and the second absorption capacitor 1512 are connected in series, and the connection point between the first absorption diode 1511 and the first absorption resistor 1513 is connected in parallel to the positive output of the first H-bridge rectifier circuit, and the second absorption capacitor 1512 is connected to the negative output of the first H-bridge rectifier circuit; the second RCD clamping circuit and the third RCD clamping circuit are similar, and are not described in detail here.

[0013] The filter circuit unit 16 includes three independent filter circuits. The first filter circuit includes a first filter inductor 1611 and a second filter capacitor 1612, wherein the first filter inductor 1611 is connected in series with the positive output of the first H-bridge rectifier circuit, and the second filter capacitor 1612 is connected in parallel with the output of the first H-bridge rectifier circuit and connected in parallel with the first electrolytic cell 2; the second filter circuit and the third filter circuit are connected in the same way and are connected to the second electrolytic cell 3 and the third electrolytic cell 4 respectively.

[0014] The single H-bridge topology of the hydrogen production converter of the present invention can also be expanded to a multi-H-bridge topology. The biggest difference from the above-mentioned single H-bridge topology of the hydrogen production converter lies in the inverter unit and the high-frequency transformer in the power unit module. Each power unit module in the multi-H-bridge topology of the hydrogen production converter includes a first inverter unit 1210, a second inverter unit 1220 and a third inverter unit 1230. The composition and component connection method of each inverter unit are the same as those of the single H-bridge topology of the hydrogen production converter; in addition, each power unit module of the multi-H-bridge topology of the hydrogen production converter includes three dual-winding high-frequency transformers, the first high-voltage winding 1311 of the first dual-winding high-frequency transformer 131 is connected to the first inverter unit 1210, and the second high-voltage winding 1311 of the second dual-winding high-frequency transformer 132 is connected to the first inverter unit 1210. The winding 1321 is connected to the second inverter unit 1220, and the third high-voltage winding 1331 of the third double-winding high-frequency transformer 133 is connected to the third inverter unit 1230; the first low-voltage winding 1312 of the first double-winding high-frequency transformer 1310 is connected to the input side of the first H-bridge rectifier circuit, the second low-voltage winding 1322 of the second double-winding high-frequency transformer 1320 is connected to the input side of the second H-bridge rectifier circuit, and the third low-voltage winding 1332 of the third double-winding high-frequency transformer 1330 is connected to the input side of the third H-bridge rectifier circuit.

[0015] Aiming at the single H-bridge topology of hydrogen production converter, a coordinated control strategy of front-stage voltage equalization and rear-stage current equalization is proposed; the front-stage half-bridge control has three control loops, namely the sub-module capacitor voltage output outer loop, the medium-voltage side smoothing reactor current inner loop and the sub-module capacitor voltage equalization loop. The outer loop reference value of the submodule capacitor voltage output is the sum of the submodule capacitor voltage reference values ​​of N power unit modules, and the feedback value is the sum of the capacitor voltage sampling values ​​of all N submodules. The difference between the two is sent to the controller PI1, and the controller PI1 outputs the current reference value of the medium voltage side smoothing reactor; the inner loop reference value of the medium voltage side smoothing reactor current is the output value of the controller PI1, and the feedback value is the current sampling value of the medium voltage side smoothing reactor. The difference between the two is sent to the controller PI2, and the controller PI2 outputs the common duty cycle of all N half-bridge unit lower tubes; the submodule capacitor voltage equalizing loop reference value is the average value of the N submodule capacitor voltages, and the feedback value is the capacitor voltage sampling value of the kth submodule, and the difference between the two is sent to the controller PI3, and the controller PI3 outputs the duty cycle correction value of the lower tube of the half-bridge unit of the kth power unit module; the sum of the output of the controller PI2 and the output of the controller PI3 is the duty cycle of the lower tube of the half-bridge unit of the kth power unit module, and k is 1, 2, ..., N.

[0016] The control of the post-stage phase shifted full bridge converter (PSFB) is composed of the output current sharing loop of the power unit module, and its reference value is Figure 7The reference current obtained by comprehensive calculation and the feedback value are the sum of the inductor current sampling values ​​in the filter circuit unit of the kth power unit module. The difference between the two is sent to the controller PI4, and the output of the controller PI4 is the shift phase of the kth power unit module PSFB.

[0017] In addition, considering the different working conditions of multiple electrolyzers and the different upper limits of current allowed by the electrolyzers, a comprehensive calculation method for the reference current of the current loop of the filter circuit unit in each power unit module is designed, as follows:

[0018] First, the DCS system of the hydrogen production system gives the maximum current value I allowed for each of the three electrolyzers at the current temperature. max_o1 ,I max_o2 ,I max_o3 ; Determine the minimum value of the maximum current allowed by the three electrolytic cells and record it as I min_o , the number of normally operating branches N and the number of electrolytic cells M in normal operation.

[0019] Second, set the total filter inductance current setting value of the controlled object filter circuit unit to I Lfref_Dest , assuming that the initial setting value of the total filter inductance current of the filter circuit unit of the controlled object is I Lfref_start , assuming that the total filter inductance current process update value of the controlled object filter circuit unit is I Lfref_update ; The initial setting value of the total filter inductance current of the filter circuit unit of the controlled object I Lfref_start for:

[0020]

[0021] Third, suppose the real-time current values ​​of the three electrolytic cells during operation are I real_o1 ,I real_o2 ,I real_o3 ; After starting operation, the total filter inductor current is set to the initial value I Lfref_start On this basis, the total filter inductance current control process update value I of each power unit module is gradually increased according to the set current rise rate Lfref_update , and assign the updated value to the total filter inductor current setting value I in real time Lfref_Dest =I Lfref_update , until the following relationship is satisfied:

[0022]

[0023] Fourth, in dynamic operation, the real-time current values ​​of the three electrolytic cells are judged to be I real_o1 ,I real_o2 ,I real_o3 The DCS system of the hydrogen production system gives the maximum current value I allowed by the three solution cells at the current temperature. max_o1 ,I max_o2 ,Imax_o3 When the relationship between the two is satisfied and the following relationship (3) is satisfied, the total filter inductor current control process update value I is further increased according to the specified current rise rate Lfref_update , and assign the updated value to the total filter inductor current setting value I in real time Lfref_Dest =I Lfref_update , until the relation (2) is satisfied.

[0024]

[0025] Among them, const_down represents the maximum allowable value of slot undercurrent, which is adjusted to avoid jitter during operation.

[0026] If the relationship (4) is satisfied, the total filter inductance current control process update value I of each power unit module is reduced according to the set current reduction rate Lfref_update , and assign the updated value to the total filter inductor current setting value I in real time Lfref_Dest =I Lfref_update , until the relation (2) is satisfied.

[0027]

[0028] Among them, const_up represents the maximum allowable value of the slot overcurrent, which is adjusted to avoid jitter during operation.

[0029] Aiming at the multi-H-bridge topology of hydrogen production converter, a control strategy is proposed in which the voltage of the front-stage half-bridge submodule and the output current of the rear-stage electrolyzer can be independently controlled. Figure 6 The front-stage half-bridge control strategy still adopts the front-stage voltage balancing control strategy, with three control loops, namely the submodule capacitor voltage output outer loop, the medium-voltage side smoothing reactor current inner loop and the submodule capacitor voltage balancing loop. The outer loop reference value of the submodule capacitor voltage output is the sum of the reference values ​​of the capacitor voltages of the N power unit modules, and the feedback value is the sum of the capacitor voltage sampling values ​​of all N submodules. The difference between the two is sent to the controller PI5, and the output of the controller PI5 is the reference value of the current of the medium-voltage side smoothing reactor; the inner loop reference value of the current of the medium-voltage side smoothing reactor is the output value of the controller PI5, and the feedback value is the sampling value of the current of the medium-voltage side smoothing reactor. The difference between the two is sent to the controller PI6, and the output of the controller PI6 is the common duty cycle of the lower tubes of all N half-bridge units; the reference value of the submodule capacitor voltage equalizing loop is the average value of the capacitor voltages of the N submodules, and the feedback value is the sampling value of the capacitor voltage of the kth submodule. The difference between the two is sent to the controller PI7, and the output of the controller PI7 is the duty cycle correction value of the lower tube of the half-bridge unit of the kth power unit module; the sum of the output of the controller PI6 and the output of the controller PI7 is the duty cycle of the lower tube of the half-bridge unit of the kth power unit module.

[0030] The reference value of the output current loop of the post-stage module is the ratio of the total cell current of the Mth electrolytic cell to the number of branches N, and the feedback value is the sampling value of the inductor current of the filter circuit unit of the kth power unit module connected to the Mth electrolytic cell. The difference between the two is sent to the controller PI8. The output of the controller PI8 is the shift ratio of the kth power unit module PSFB connected to the Mth electrolytic cell, thereby realizing independent control of the electrolytic cell current.

[0031] The present invention adopts the above technical solution and has the following beneficial effects:

[0032] 1) A half-bridge sub-module series structure is used to match the medium-voltage DC bus, and the rear-stage isolated buck converter is cascaded at the rear stage of the half-bridge sub-module, which solves the problem of high voltage on the medium-voltage side DC bus and large output current on the low-voltage side. The medium-voltage side bus voltage can be flexibly matched by adjusting the number of units.

[0033] 2) Each unit phase-shifted full-bridge converter has a high-power high-frequency transformer inside, which realizes the electrical isolation between the medium-voltage bus and the low-voltage side electrolyzer, and ensures the power supply safety of the electrolyzer.

[0034] 3) The secondary side of the high-frequency transformer in the phase-shifted full-bridge converter has multiple independent windings, which are connected to multiple independent electrolyzers respectively. One hydrogen production power supply completes the work that originally required multiple hydrogen production power supplies, greatly improving the integration of hydrogen production power supplies and reducing equipment costs.

[0035] 4) The modular design concept is adopted. By setting up redundant modules, when some modules fail, they can be bypassed and the hydrogen production power supply can still work normally, which greatly improves the fault tolerance and power supply reliability of the equipment.

[0036] 5) When multiple electrolytic cells are in an unbalanced working state, an integrated coordinated control strategy can be adopted to consider the different operating current boundaries of multiple electrolytic cells, comprehensively calculate the current loop control instructions of each unit, and realize the safe and coordinated operation of multiple electrolytic cells.

[0037] 6) The use of the multi-H-bridge topology of the hydrogen production power supply can realize the free start and stop control of multiple electrolyzers, which are independent of each other and do not interfere with each other, greatly improving the flexibility of the operation of multiple electrolyzers. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is an H-bridge topology diagram of a multi-isolated output hydrogen production converter suitable for a medium voltage DC bus in the present invention;

[0039] Figure 2 This is a multi-H-bridge topology diagram of a multi-isolated output hydrogen production converter suitable for a medium voltage DC bus of the present invention;

[0040] Figure 3 for Figure 1The middle half-bridge submodule series structure matches the medium voltage DC bus voltage topology diagram;

[0041] Figure 4 for Figure 1 Middle phase shifted full bridge multiple independent output topology diagram;

[0042] Figure 5 This is a single H-bridge hydrogen production power supply control strategy diagram;

[0043] Figure 6 This is a multi-H-bridge hydrogen production power supply control strategy diagram;

[0044] Figure 7 This is the comprehensive calculation flow chart of reference current of single H-bridge hydrogen production power supply unit. DETAILED DESCRIPTION

[0045] The specific implementation modes of the present invention are described below in conjunction with the accompanying drawings. The following description is only for example purposes and does not limit the application scope of the present invention.

[0046] The half-bridge submodule series structure is used to match the medium voltage DC bus voltage ±10kV, such as Figure 3 As shown, it mainly includes a medium-voltage side smoothing reactor 0, a half-bridge unit 11, an equivalent load 5, etc., wherein the half-bridge unit 11 includes a first switch device 111 and a second switch device 112 connected in series, the midpoint of the series bridge arm is connected to the medium-voltage side smoothing reactor 0, and the series bridge arm output is connected in parallel with the submodule capacitor 113.

[0047] The input voltage of each half-bridge submodule during operation is 20 / N kV, where N is the number of half-bridge submodules in series. The closed-loop control strategy can keep the submodule voltage output by each half-bridge submodule consistent, greatly improving the current sharing capability on the output side of the hydrogen production power supply. A phase-shift modulation scheme is adopted to control the lower tube of each half-bridge submodule to have the same duty cycle, but the duty cycles of adjacent submodules are phase-shifted by 2π / N. Therefore, the fluctuation frequency of the DC reactor current on the medium voltage side and the output voltage of the submodule increases to Nf Ms , f Ms The half-bridge switching frequency can greatly reduce the fluctuation amplitude and improve the power efficiency.

[0048] The phase-shifted full-bridge multi-independent output topology is adopted, the input is connected to the half-bridge sub-module output, and the output multi-unit is connected in parallel to the electrolyzer. The phase-shifted full-bridge multi-independent output topology is as follows Figure 1 , 4As shown, it mainly includes a single H-bridge inverter unit 12, a four-winding high-frequency transformer 13, a rectifier bridge 14, a clamping circuit unit 15 and a filter circuit unit 16; the half-bridge unit 11 includes a first switch device 111, a second switch device 112 and a submodule capacitor 113, the first switch device 111 and the second switch device 112 are connected in series, the midpoint of the series bridge arm is connected to the medium-voltage side smoothing reactor 0, and the series bridge arm output is connected in parallel with the submodule capacitor 113;

[0049] The single H-bridge inverter unit 12 includes a first inverter bridge arm formed by a first switch 121 and a second switch 122 connected in series, and a second inverter bridge arm formed by a third switch 123 and a fourth switch 124 connected in series. The two inverter bridge arms constitute a single H-bridge inverter unit and are connected in parallel with the submodule capacitor 113; the output of the single H-bridge inverter unit is sequentially connected in series with a resonant inductor 125 (including a transformer leakage inductance), a DC blocking capacitor 126, and a high-voltage side winding 131 of a four-winding high-frequency transformer 13; the low-voltage side of the four-winding high-frequency transformer 13 has three isolated first low-voltage windings 132, a second low-voltage winding 133, and a third low-voltage winding 134;

[0050] The rectifier bridge 14 includes three independent H-bridge rectifier circuits; the first diode 1411 and the second diode 1412 are connected in series to form a first rectifier bridge arm, the third diode 1413 and the fourth diode 1414 are connected in series to form a second rectifier bridge arm, and the two rectifier bridge arms form a first H-bridge rectifier circuit, the input side of the first H-bridge rectifier circuit is connected to the first low-voltage winding 132, and the output side of the first H-bridge rectifier circuit is connected in parallel with the first RCD clamping circuit of the clamping circuit unit 15; similarly, the fifth diode 1421, the sixth diode 1422, the third diode 1413 and the fourth diode 1414 are connected in series to form a second rectifier bridge arm. The seventh diode 1423 and the eighth diode 1424 constitute a second H-bridge rectifier circuit, the input side of the second H-bridge rectifier circuit is connected to the second low-voltage winding 133, and the output side is connected in parallel with the second RCD clamping circuit of the clamping circuit unit 15; the ninth diode 1431, the tenth diode 1432, the eleventh diode 1433 and the twelfth diode 1434 constitute a third H-bridge rectifier circuit, the input side of the third H-bridge rectifier circuit is connected to the third low-voltage winding 134, and the output side is connected in parallel with the third RCD clamping circuit of the clamping circuit unit 15;

[0051] The clamping circuit unit 15 includes three independent RCD clamping circuits. The first RCD clamping circuit includes a first absorption diode 1511, a second absorption capacitor 1512 and a first absorption resistor 1513. The first absorption diode 1511 and the second absorption capacitor 1512 are connected in series, and the connection point between the first absorption diode 1511 and the first absorption resistor 1513 is connected in parallel to the positive output of the first H-bridge rectifier circuit, and the second absorption capacitor 1512 is connected to the negative output of the first H-bridge rectifier circuit; the second RCD clamping circuit and the third RCD clamping circuit are similar, and are not described in detail here.

[0052] The filter circuit unit 16 includes three independent filter circuits. The first filter circuit includes a first filter inductor 1611 and a second filter capacitor 1612, wherein the first filter inductor 1611 is connected in series with the positive output of the first H-bridge rectifier circuit, and the second filter capacitor 1612 is connected in parallel with the output of the first H-bridge rectifier circuit and connected in parallel with the first electrolytic cell 2; the second filter circuit and the third filter circuit are connected in the same way and are connected to the second electrolytic cell 3 and the third electrolytic cell 4 respectively.

[0053] The primary side is composed of a full bridge and the secondary side is composed of multiple independent rectifier bridges. The switch duty cycle in the full bridge is 0.5, and the upper and lower tubes are complementary to each other. The control of the converter transmission power is achieved by controlling the phase shift angle of the leading bridge arm and the lagging bridge arm. The phase shift modulation scheme is adopted, and the adjacent phase shift full bridge modules are staggered by π / N, which can realize the staggered superposition of the output filter inductor current and greatly reduce the output current ripple.

[0054] against Figure 1 The single H-bridge topology of the hydrogen production converter in China proposes a coordinated control strategy for the front-stage voltage equalization and the rear-stage current equalization. The control strategy is as follows Figure 5The front-stage half-bridge control has three control loops, namely the submodule capacitor voltage output outer loop, the medium-voltage side smoothing reactor current inner loop and the submodule capacitor voltage equalizing loop. The reference value of the submodule capacitor voltage output outer loop is the sum of the submodule capacitor voltage reference values ​​of N power unit modules, and the feedback value is the sum of all N submodule capacitor voltage sampling values. The difference between the two is sent to the controller PI1, and the controller PI1 outputs the reference value of the medium voltage side smoothing reactor current; the reference value of the medium voltage side smoothing reactor current inner loop is the output value of the controller PI1, and the feedback value is the medium voltage side smoothing reactor current sampling value. The difference between the two is sent to the controller PI2, and the controller PI2 outputs the common duty cycle of all N half-bridge unit lower tubes; the reference value of the submodule capacitor voltage equalizing loop is the average value of the N submodule capacitor voltages, and the feedback value is the k-th submodule capacitor voltage sampling value. The difference between the two is sent to the controller PI3, and the controller PI3 outputs the duty cycle correction value of the k-th power unit module half-bridge unit lower tube; the sum of the controller PI2 output and the controller PI3 output is the duty cycle of the k-th power unit module half-bridge unit lower tube. k is 1, 2, ... N.

[0055] Through the above control strategy, the front stage can realize the current controllability of the medium-voltage DC reactor and the voltage stability of the submodule, achieving stable transmission of power from the medium-voltage DC bus to the submodule; considering the differences in the working conditions of multiple electrolyzers, each electrolyzer has different requirements for input current. In order to achieve safe and reliable control of the electrolyzer, it is necessary to give the maximum current value allowed under each working condition according to the electrolyzer DCS system, and comprehensively calculate and update the reference instructions of the unit output current in the back-stage control. The reference current comprehensive calculation process is as follows: Figure 7 shown.

[0056] The post-stage PSFB control consists of a power unit module output current equalizing loop, whose reference value is Figure 7 The reference current obtained by comprehensive calculation and the feedback value are the sum of the inductor current sampling values ​​in the filter circuit unit of the kth power unit module. The difference between the two is sent to the controller PI4, and the output of the controller PI4 is the shift phase of the kth power unit module PSFB.

[0057] In addition, considering the different working conditions of multiple electrolyzers and the different upper limits of the current allowed by the electrolyzers, a comprehensive calculation method for the reference current of the current loop of the filter circuit unit in each power unit module is designed. Figure 7 shown.

[0058] First, the DCS system of the hydrogen production system gives the maximum current value I allowed for each of the three electrolyzers at the current temperature. max_o1 ,I max_o2 ,I max_o3 ; Determine the minimum value of the maximum current allowed by the three electrolytic cells and record it as I min_o, the number of normally operating branches N and the number of electrolytic cells M in normal operation.

[0059] Second, set the total filter inductance current setting value of the controlled object filter circuit unit to I Lfref_Dest , assuming that the initial setting value of the total filter inductance current of the filter circuit unit of the controlled object is I Lfref_start , assuming that the total filter inductance current process update value of the controlled object filter circuit unit is I Lfref_update ; Total filter current of the filter circuit unit of the controlled object

[0060] Initial setting value of sense current I Lfref_start for:

[0061]

[0062] Third, suppose the real-time current values ​​of the three electrolytic cells during operation are I real_o1 ,I real_o2 ,I real_o3 ; After starting operation, the total filter inductor current is set to the initial value I Lfref_start On this basis, the total filter inductance current control process update value I of each power unit module is gradually increased according to the set current rise rate Lfref_update , and assign the updated value to the total filter inductor current setting value I in real time Lfref_Dest =I Lfref_update , until the following relationship is satisfied:

[0063]

[0064] Fourth, in dynamic operation, the real-time current values ​​of the three electrolytic cells are judged to be I real_o1 ,I real_o2 ,I real_o3 The DCS system of the hydrogen production system gives the maximum current value I allowed by the three solution cells at the current temperature. max_o1 ,I max_o2 ,I max_o3 When the relationship between the two is satisfied and the following relationship (3) is satisfied, the total filter inductor current control process update value I is further increased according to the specified current rise rate Lfref_update , and assign the updated value to the total filter inductor current setting value I in real time Lfref_Dest =I Lfref_update , until the relation (2) is satisfied.

[0065]

[0066] Among them, const_down represents the maximum allowable value of slot undercurrent, which is adjusted to avoid jitter during operation.

[0067] If the relationship (4) is satisfied, the total filter inductance current control process update value I of each power unit module is reduced according to the set current reduction rate Lfref_update , and assign the updated value to the total filter inductor current setting value I in real time Lfref_Dest =I Lfref_update , until the relation (2) is satisfied.

[0068]

[0069] Among them, const_up represents the maximum allowable value of the slot overcurrent, which is adjusted to avoid jitter during operation.

[0070] The single H-bridge topology of the hydrogen production converter of the present invention can also be expanded to a multi-H-bridge topology, such as Figure 2 As shown above. Figure 1 The biggest difference of the single H-bridge topology of the hydrogen production converter lies in the inverter unit and high-frequency transformer in the power unit module. Each power unit module in the multi-H-bridge topology of the hydrogen production converter includes a first inverter unit 1210, a second inverter unit 1220 and a third inverter unit 1230. The composition and component connection method of each inverter unit are the same as those of the single H-bridge topology of the hydrogen production converter; in addition, each power unit module of the multi-H-bridge topology of the hydrogen production converter includes three double-winding high-frequency transformers. The first high-voltage winding 1311 of the first double-winding high-frequency transformer 131 is connected to the first inverter unit 1210, and the second high-voltage winding 1311 of the second double-winding high-frequency transformer 132 is connected to the first inverter unit 1210. The winding 1321 is connected to the second inverter unit 1220, and the third high-voltage winding 1331 of the third double-winding high-frequency transformer 133 is connected to the third inverter unit 1230; the first low-voltage winding 1312 of the first double-winding high-frequency transformer 1310 is connected to the input side of the first H-bridge rectifier circuit, the second low-voltage winding 1322 of the second double-winding high-frequency transformer 1320 is connected to the input side of the second H-bridge rectifier circuit, and the third low-voltage winding 1332 of the third double-winding high-frequency transformer 1330 is connected to the input side of the third H-bridge rectifier circuit.

[0071] The multi-H-bridge hydrogen production power supply control strategy realizes the sub-module voltage stability and medium voltage side current controllability in the front stage, and considers the differences in the working conditions of multiple electrolyzers in the back stage. According to the maximum current limit allowed by each electrolyzer, the reference instructions of the output current of each unit are calculated respectively to realize independent and flexible control. Figure 7 shown.

[0072] against Figure 2 The multi-H-bridge topology of the hydrogen production converter in China proposes a control strategy in which the voltage of the front-stage half-bridge submodule and the output current of the rear-stage electrolyzer can be independently controlled. Figure 6The front-stage half-bridge control strategy still adopts the front-stage voltage balancing control strategy, with three control loops, namely the submodule capacitor voltage output outer loop, the medium-voltage side smoothing reactor current inner loop and the submodule capacitor voltage balancing loop. The outer loop reference value of the submodule capacitor voltage output is the sum of the reference values ​​of the capacitor voltages of the N power unit modules, and the feedback value is the sum of the capacitor voltage sampling values ​​of all N submodules. The difference between the two is sent to the controller PI5, and the output of the controller PI5 is the reference value of the current of the medium-voltage side smoothing reactor; the inner loop reference value of the current of the medium-voltage side smoothing reactor is the output value of the controller PI5, and the feedback value is the sampling value of the current of the medium-voltage side smoothing reactor. The difference between the two is sent to the controller PI6, and the output of the controller PI6 is the common duty cycle of the lower tubes of all N half-bridge units; the reference value of the submodule capacitor voltage equalizing loop is the average value of the capacitor voltages of the N submodules, and the feedback value is the sampling value of the capacitor voltage of the kth submodule. The difference between the two is sent to the controller PI7, and the output of the controller PI7 is the duty cycle correction value of the lower tube of the half-bridge unit of the kth power unit module; the sum of the output of the controller PI6 and the output of the controller PI7 is the duty cycle of the lower tube of the half-bridge unit of the kth power unit module.

[0073] The reference value of the output current loop of the post-stage module is the ratio of the total cell current of the Mth electrolytic cell to the number of branches N, and the feedback value is the sampling value of the inductor current of the filter circuit unit of the kth power unit module connected to the Mth electrolytic cell. The difference between the two is sent to the controller PI8. The output of the controller PI8 is the shift ratio of the kth power unit module PSFB connected to the Mth electrolytic cell, thereby realizing independent control of the electrolytic cell current.

[0074] The hydrogen production converter of the present invention is connected to a medium-voltage busbar upward and to a low-voltage electrolyzer downward, and adopts a sub-module series structure to match the medium-voltage DC busbar voltage. The output of each half-bridge sub-module is connected to a subsequent multi-output converter, and the subsequent multi-output converter is connected in parallel to multiple electrolyzers respectively, and provides low-voltage and high-current DC power to the multiple electrolyzers at the same time; a high-frequency isolation step-down transformer is adopted in the phase-shifted full-bridge in each power unit module, so as to realize the electrical isolation between the medium-voltage side and the low-voltage side; multiple independent winding outputs on the secondary side of the transformer realize the power conversion function of multiple phase-shifted full-bridge converters; a front-stage half-bridge sub-module voltage equalization control is proposed for the single H-bridge hydrogen production power supply topology structure, and a comprehensive calculation method for the current reference instruction of the subsequent unit phase-shifted full-bridge converter is proposed considering the different requirements for the input current under different working conditions of different electrolyzers, so as to ensure the safe and reliable operation of multiple electrolyzers; a control strategy for the independent controllable output current of multiple electrolyzers is proposed for the multi-H-bridge hydrogen production power supply structure, so as to realize the independent and flexible control of multiple electrolyzers.

Claims

1. A multi-isolated output hydrogen production converter suitable for medium voltage DC bus, characterized in that: It comprises a medium voltage side smoothing reactor (0), N power unit modules and three electrolytic cell loads; the medium voltage side smoothing reactor (0) is connected to the positive pole of the medium voltage busbar, the N power module units are connected in series on the input side and in parallel on the output side; each power module unit has three independent outputs, and the three independent outputs are respectively connected to the three electrolytic cell loads.

2. The multi-isolated output hydrogen production converter suitable for medium voltage DC bus according to claim 1, characterized in that: Each of the power unit modules comprises a half-bridge unit (11), a single H-bridge inverter unit (12), a four-winding high-frequency transformer (13), a rectifier bridge (14), a clamping circuit unit (15) and a filter circuit unit (16); The half-bridge unit (11) comprises a first switch device (111), a second switch device (112) and a submodule capacitor (113); the first switch device (111) and the second switch device (112) are connected in series, the midpoint of the series bridge arm is connected to the medium-voltage side smoothing reactor (0), and the output of the series bridge arm is connected in parallel to the submodule capacitor (113); The single H-bridge inverter unit (12) comprises a first inverter bridge arm formed by a first switch (121) and a second switch (122) connected in series, and a second inverter bridge arm formed by a third switch (123) and a fourth switch (124) connected in series, the two inverter bridge arms constitute a single H-bridge inverter unit and are connected in parallel with a submodule capacitor (113); the output of the single H-bridge inverter unit is sequentially connected in series with a resonant inductor (125), a DC isolation capacitor (126), and a high-voltage side winding (131) of a four-winding high-frequency transformer (13); the low-voltage side of the four-winding high-frequency transformer (13) has three mutually isolated first low-voltage windings (132), second low-voltage windings (133), and third low-voltage windings (134); The rectifier bridge (14) comprises three independent H-bridge rectifier circuits; the first diode (1411) and the second diode (1412) are connected in series to form a first rectifier bridge arm, the third diode (1413) and the fourth diode (1414) are connected in series to form a second rectifier bridge arm, and the two rectifier bridge arms form a first H-bridge rectifier circuit, the input side of the first H-bridge rectifier circuit is connected to the first low-voltage winding (132), and the output side of the first H-bridge rectifier circuit is connected in parallel to the first RCD clamp circuit of the clamp circuit unit (15); similarly, the fifth diode (1421), the sixth diode (1422), and the seventh diode (1424) are connected in series to form a first rectifier bridge arm. The diode (1423) and the eighth diode (1424) form a second H-bridge rectifier circuit, the input side of the second H-bridge rectifier circuit is connected to the second low-voltage winding (133), and the output side is connected in parallel with the second RCD clamping circuit of the clamping circuit unit (15); the ninth diode (1431), the tenth diode (1432), the eleventh diode (1433) and the twelfth diode (1434) form a third H-bridge rectifier circuit, the input side of the third H-bridge rectifier circuit is connected to the third low-voltage winding (134), and the output side is connected in parallel with the third RCD clamping circuit of the clamping circuit unit (15); The clamping circuit unit (15) comprises three independent RCD clamping circuits, wherein the first RCD clamping circuit comprises a first absorption diode (1511), a second absorption capacitor (1512) and a first absorption resistor (1513), the first absorption diode (1511) and the second absorption capacitor (1512) are connected in series, and a connection point between the first absorption diode (1511) and the first absorption resistor (1513) is connected in parallel to the positive output of the first H-bridge rectifier circuit, and the second absorption capacitor (1512) is connected to the negative output of the first H-bridge rectifier circuit; and the second RCD clamping circuit and the third RCD clamping circuit are connected in the same manner; The filter circuit unit (16) includes three independent filter circuits, wherein the first filter circuit includes a first filter inductor (1611) and a second filter capacitor (1612), wherein the first filter inductor (1611) is connected in series with the positive output of the first H-bridge rectifier circuit, and the second filter capacitor (1612) is connected in parallel with the output of the first H-bridge rectifier circuit and connected in parallel with the first electrolytic cell (2); the second filter circuit and the third filter circuit are connected in the same manner and are connected to the second electrolytic cell (3) and the third electrolytic cell (4) respectively.

3. The multi-isolated output hydrogen production converter suitable for medium voltage DC bus according to claim 2, characterized in that: Each of the power unit modules comprises a first inverter unit (1210), a second inverter unit (1220) and a third inverter unit (1230), and the composition and component connection method of each inverter unit are the same as the single H-bridge topology of the hydrogen production converter; each power unit module comprises three double-winding high-frequency transformers, the first high-voltage winding (1311) of the first double-winding high-frequency transformer (131) is connected to the first inverter unit (1210), the second high-voltage winding (1321) of the second double-winding high-frequency transformer (132) is connected to the second inverter unit (1 220), the third high voltage winding (1331) of the third double-winding high frequency transformer (133) is connected to the third inverter unit (1230); the first low voltage winding (1312) of the first double-winding high frequency transformer (1310) is connected to the input side of the first H-bridge rectifier circuit, the second low voltage winding (1322) of the second double-winding high frequency transformer (1320) is connected to the input side of the second H-bridge rectifier circuit, and the third low voltage winding (1332) of the third double-winding high frequency transformer (1330) is connected to the input side of the third H-bridge rectifier circuit.

4. The multi-isolated output hydrogen production converter suitable for medium voltage DC bus according to claim 2, characterized in that: The control strategy of the single H-bridge topology of the hydrogen production converter includes a front-stage voltage balancing control strategy and a rear-stage current balancing control strategy; the front-stage half-bridge control has three control loops, namely, the submodule capacitor voltage output outer loop, the medium-voltage side smoothing reactor current inner loop and the submodule capacitor voltage balancing loop; the submodule capacitor voltage output outer loop reference value is the sum of the submodule capacitor voltage reference values ​​of N power unit modules, and the feedback value is the sum of all N submodule capacitor voltage sampling values, and the difference between the two is sent to the controller PI1, and the controller PI1 outputs the medium-voltage side smoothing reactor current reference value; The reference value of the inner loop of the medium-voltage side smoothing reactor current is the output value of the controller PI1, and the feedback value is the sampling value of the medium-voltage side smoothing reactor current. The difference between the two is sent to the controller PI2, and the output of the controller PI2 is the common duty cycle of the lower tubes of all N half-bridge units; the reference value of the sub-module capacitor voltage equalizing loop is the average value of the N sub-module capacitor voltages, and the feedback value is the sampling value of the k-th sub-module capacitor voltage. The difference between the two is sent to the controller PI3, and the output of the controller PI3 is the duty cycle correction value of the lower tube of the half-bridge unit of the k-th power unit module; the sum of the output of the controller PI2 and the output of the controller PI3 is the duty cycle of the lower tube of the half-bridge unit of the k-th power unit module, and k is 1, 2, ... N.

5. The multi-isolated output hydrogen production converter suitable for medium voltage DC bus according to claim 4, characterized in that: The post-stage current sharing control strategy is composed of a power unit module output current sharing loop. The difference between the reference current and the feedback value is sent to the controller PI4. The feedback value is the sum of the inductor current sampling values ​​in the filter circuit unit of the kth power unit module. The output of the controller PI4 is the PSFB shift phase of the kth power unit module.

6. The multi-isolated output hydrogen production converter suitable for medium voltage DC bus according to claim 5, characterized in that: The comprehensive calculation method of the current loop reference current of the filter circuit unit in each power unit module is as follows: First, the DCS system of the hydrogen production system gives the maximum current value I allowed for each of the three electrolyzers at the current temperature. max_o1 ,I max_o2 ,I max_o3 ; Determine the minimum value of the maximum current allowed by the three electrolytic cells and record it as I min_o , the number of normally operating branches N and the number of normally operating electrolytic cells M; Second, set the total filter inductance current setting value of the controlled object filter circuit unit to I Lfref_Dest , assuming that the initial setting value of the total filter inductance current of the filter circuit unit of the controlled object is I Lfref_start , assuming that the total filter inductance current process update value of the controlled object filter circuit unit is I Lfref_update ; The initial setting value of the total filter inductance current of the filter circuit unit of the controlled object I Lfref_start for: Third, suppose the real-time current values ​​of the three electrolytic cells during operation are I real_o1 ,I real_o2 ,I real_o3 ; After starting operation, the total filter inductor current is set to the initial value I Lfref_start On this basis, the total filter inductance current control process update value I of each power unit module is gradually increased according to the set current rise rate Lfref_update , and assign the updated value to the total filter inductor current setting value I in real time Lfref_Dest =I Lfref_update , until the following relationship is satisfied: Fourth, in dynamic operation, the real-time current values ​​of the three electrolytic cells are judged to be I real_o1 ,I real_o2 ,I real_o3 The DCS system of the hydrogen production system gives the maximum current value I allowed by the three solution cells at the current temperature. max_o1 ,I max_o2 ,I max_o3 When the relationship between the two is satisfied and the following relationship (3) is satisfied, the total filter inductor current control process update value I is further increased according to the specified current rise rate Lfref_update , and assign the updated value to the total filter inductor current setting value I in real time Lfref_Dest =I Lfref_update , until the relation (2) is satisfied; Among them, const_down represents the maximum allowable value of slot undercurrent; If the relationship (4) is satisfied, the total filter inductance current control process update value I of each power unit module is reduced according to the set current reduction rate Lfref_update , and assign the updated value to the total filter inductor current setting value I in real time Lfref_Dest =I Lfref_update , until the relation (2) is satisfied; Among them, const_up represents the maximum allowable value of the slot overcurrent.

7. The multi-isolated output hydrogen production converter suitable for medium voltage DC bus according to claim 3, characterized in that: The control strategy of the multi-H-bridge topology of the hydrogen production converter includes a front-stage half-bridge submodule voltage equalization control strategy and a control strategy for independently controllable output current of the rear-stage electrolyzer; the front-stage half-bridge control strategy adopts the front-stage voltage equalization control strategy, and there are three control loops, namely, the submodule capacitor voltage output outer loop, the medium-voltage side smoothing reactor current inner loop and the submodule capacitor voltage equalization loop; the submodule capacitor voltage output outer loop reference value is the sum of the N power unit module submodule capacitor voltage reference values, and the feedback value is the sum of all N submodule capacitor voltage sampling values, and the difference between the two is sent to the controller PI5, and the controller PI5 outputs the medium-voltage side smoothing reactor current reference value; The reference value of the inner loop of the medium-voltage side smoothing reactor current is the output value of the controller PI5, and the feedback value is the sampling value of the medium-voltage side smoothing reactor current. The difference between the two is sent to the controller PI6, and the output of the controller PI6 is the common duty cycle of the lower tubes of all N half-bridge units; the reference value of the sub-module capacitor voltage equalizing loop is the average value of the N sub-module capacitor voltages, and the feedback value is the sampling value of the k-th sub-module capacitor voltage. The difference between the two is sent to the controller PI7, and the output of the controller PI7 is the duty cycle correction value of the lower tube of the half-bridge unit of the k-th power unit module; the sum of the output of the controller PI6 and the output of the controller PI7 is the duty cycle of the lower tube of the half-bridge unit of the k-th power unit module.

8. The multi-isolated output hydrogen production converter suitable for medium voltage DC bus according to claim 7, characterized in that: The control strategy for the independent controllable output current of the rear-stage electrolytic cell is as follows: the reference value of the output current loop of the rear-stage module is the ratio of the total cell current of the Mth electrolytic cell to the number of branches N, and the feedback value is the sampling value of the inductor current of the filter circuit unit of the kth power unit module connected to the Mth electrolytic cell. The difference between the two is sent to the controller PI8, and the output of the controller PI8 is the shift ratio of the kth power unit module PSFB connected to the Mth electrolytic cell, thereby realizing independent control of the electrolytic cell current.

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