Novel high-power low-ripple-output hydrogen production converter and control method

Abstract

The invention provides a novel high-power low-ripple-output hydrogen production converter and a control method. The novel high-power low-ripple-output hydrogen production converter comprises a six-pulse conversion unit, a filter circuit and a three-phase stacked interleaved Buck circuit. The six-pulse commutation unit is connected in series with the filter circuit, then is connected in series with the three-phase stacked interleaved parallel Buck circuit 3, and finally is connected with a load. And the direct-current voltage of the converter is changed by controlling the phase of the trigger pulse of the thyristor valve so as to realize six-pulse direct-current power transmission. The main branch of the three-phase stacked interleaved parallel auxiliary branch is used for realizing power transmission, and the auxiliary branch is used for eliminating output current ripples. A voltage-current double closed-loop control strategy can ensure that each phase of the main branch realizes a good current sharing effect; alternating current component complementation and ripple complementation of the current IAX and the current IdcMain can be achieved by controlling the auxiliary branch switching tubes SAX1 and SAX2, then zero ripple of the output current Idco of the converter is achieved, and control over the auxiliary branch is completed. According to the invention, high-power low-current ripple output can be realized in a low-voltage high-current scene.

Description

Technical Field

[0001] The present invention relates to the technical field of hydrogen production from renewable energy, and in particular to a novel high-power low-ripple output hydrogen production converter and a control method thereof. Background Art

[0002] With the rapid development of social economy, the traditional energy system dominated by fossil energy is facing the development dilemma of resource depletion and environmental pollution. Energy transformation aimed at developing renewable energy, reducing the use of traditional fossil energy and reducing carbon emissions is an effective way to break the deadlock. Clean fuel hydrogen has the advantages of high efficiency and no pollution. As a high-quality secondary energy, it has great application potential in energy storage and utilization. The development of clean energy hydrogen production technology such as wind and light can not only alleviate the impact of intermittent new energy power generation, but also greatly reduce the cost of hydrogen production.

[0003] As a key device for connecting the electrolyzer to the DC microgrid, the selection and design of high-power DC hydrogen converters are particularly important. The DC output current of traditional hydrogen power sources has a large ripple, resulting in low hydrogen production efficiency, which makes it difficult to meet the use requirements of some high-demand occasions. The LLC resonance method is adopted in "High-frequency and high-efficiency LLC resonant converter based on GaN devices", and the efficiency and power density of the inverter are greatly improved with the help of soft switching technology. However, it is worth noting that soft switching circuits usually use MOSFETs, and the power level of the circuit is limited. The research team of Liaoning University of Engineering and Technology used an interleaved parallel magnetic integrated Buck converter in the document "Analysis of intrinsically safe output ripple voltage of interleaved parallel magnetic integrated Buck converters". The equivalent inductance of the actual inductance is increased by inductive coupling, which can effectively reduce the inductance in the converter, but the equivalent inductance is limited, and the switching frequency is high, which will lead to increased losses and costs. Therefore, it is particularly important to study power electronic converters with low voltage and high current, high step-down capability, high reliability, high efficiency and low current ripple. Summary of the invention

[0004] The present invention provides a novel high-power low-ripple output hydrogen production converter and a control method, aiming to solve the above technical problems.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: A novel high-power low-ripple output hydrogen production converter includes a six-pulse commutation unit, a filter circuit, and a three-phase stacked interleaved parallel Buck circuit connected in sequence. The six-pulse commutation unit and the filter circuit are connected in series to output a filtered DC voltage. U dc , at this time U dcThe harmonic content is high, so the filter circuit is connected in series with the three-phase stacked interleaved parallel Buck circuit. The output voltage of the three-phase stacked interleaved parallel Buck circuit is V o , and finally to the load R powered by.

[0006] The above-mentioned six-pulse commutation unit uses a three-phase bridge-type fully controlled commutation circuit as a basic unit. The three-phase stacked staggered parallel Buck circuit is divided into a main branch and a compensation branch. The main branch is composed of three Buck circuits in parallel. The compensation branch includes a half-bridge and a compensation capacitor that plays a role of voltage division and DC isolation. C AX , and a filter inductor L AX .

[0007] The three Buck circuits of the main branch in the above three-phase stacked interlaced parallel Buck circuit are composed of three parallel DC voltage U dc The series branch at both ends is composed of a switch tube S n and diode D n ,n=1,2,3;Switching tube S n and diode D n The inductor L is drawn between n , the other ends of the three inductors L1, L2 and L3 are connected in parallel and the output current I dcmain To capacitor C, capacitor C is connected to inductor L n The parallel terminals and DC voltage U dc negative electrode.

[0008] The above load R In parallel with capacitor C.

[0009] The half bridge of the compensation branch in the above three-phase stacked staggered parallel Buck circuit includes a DC voltage U dc The switch tube S at both ends AX1 and S AX2 , switch tube S AX1 and S AX2 The midpoint output and filter inductor L AX And compensation capacitor C AX Connect and source current I AX To capacitor C, current I AX and current I dcmain Composition output current I dcoTo load R， Compensation capacitor C AX Both ends of the load R Connected to the positive terminal of capacitor C.

[0010] The above filter circuit consists of a smoothing reactor L d and DC filter capacitors C d Series structure, smoothing reactor L d and DC filter capacitors C d The two ends of the series connection are connected to the output of the six-pulse commutation unit, and the DC filter capacitor C d Output filtered DC voltage U dc .

[0011] The control method of the novel high-power low-ripple output hydrogen production converter mentioned above includes six-pulse commutation unit voltage control, three-phase stacked staggered parallel Buck circuit main branch current equalization double closed-loop control and compensation branch control.

[0012] The above-mentioned six-pulse commutation unit voltage control realizes the control of the output voltage of the six-pulse rectifier by changing the DC voltage of the converter through the phase control of the thyristor valve trigger pulse.

[0013] The above-mentioned three-phase stacked staggered parallel Buck circuit main branch current equalization dual closed-loop control adopts voltage-current dual closed-loop control to ensure that each phase of the main branch achieves a good current equalization effect. The carrier phase shift pulse width modulation is added, and the first-phase triangle wave is used as a reference to make the second phase phase shift 120° and the third phase phase shift 240° to achieve precise phase shift of each phase drive signal.

[0014] The above three-phase stacked interleaved parallel Buck circuit compensation branch control is controlled by controlling the switch tube S AX1 and S AX2 To achieve current I AX and I dcmain The AC components and ripples are complementary, thereby achieving the output current of the converter I dco Zero ripple; if the output current ripple slope is positive, the compensation branch current ripple slope is negative, corresponding to S AX1 Shutdown and S AX2 On; On the contrary, S AX1 Conducting and S AX2 Finally, the compensation branch switch S is realized through signal conversion. AX1 and S AX2Complementary conduction control.

[0015] The present invention provides a novel high-power low-ripple output hydrogen production converter and control method. Compared with the prior art, the present invention has the following beneficial effects: 1. High output power and high hydrogen production efficiency; the hydrogen production converter in the low-voltage and high-current scenario of the present invention has a small output current ripple, which reduces the impact of the ripple on the inside of the electrolyzer and prolongs the service life of the electrolyzer; 2. Small harmonics and good economy: By adding a multi-phase stacked interleaved parallel Buck circuit, the input current harmonic distortion rate can be effectively reduced while also reducing the filter inductance, thereby avoiding harmonic pollution to the power grid and improving economy. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The present invention will be further described below in conjunction with the accompanying drawings and embodiments: Figure 1 It is a schematic diagram of the high-power and low-ripple output hydrogen production converter of the present invention.

[0017] Figure 2 This is a schematic diagram of the 6-pulse rectifier working during the VT1 and VT2 conduction phase.

[0018] Figure 3 It is a schematic diagram of the operation of the 6-pulse rectifier during the conduction phase of VT1, VT2, and VT3.

[0019] Figure 4 This is a schematic diagram of the six-pulse rectifier working during the VT2 and VT3 conduction phase.

[0020] Figure 5 For a three-phase stacked interleaved parallel Buck circuit in [0,t 10 ] Schematic diagram of circuit status within time.

[0021] Figure 6 For a three-phase stacked interleaved parallel Buck circuit, 10 ,T s / 3] Schematic diagram of circuit status during time.

[0022] Figure 7 For a three-phase stacked interleaved parallel Buck circuit in [T s / 3,T s / 2] Schematic diagram of circuit status during time.

[0023] Figure 8 For a three-phase stacked interleaved parallel Buck circuit in [T s / 2,t 20 ] Schematic diagram of circuit status within time.

[0024] Fig. 9For a three-phase stacked interleaved parallel Buck circuit, [t 20 ,2T s / 3] Schematic diagram of circuit status during time.

[0025] Fig.10 For a three-phase stacked interleaved parallel Buck circuit in [2T s / 3,T s ] Schematic diagram of circuit status within time.

[0026] Fig.11 This is the control block diagram of the six-pulse rectifier unit.

[0027] Fig.12 It is a block diagram of the main branch voltage-current dual closed-loop control of a three-phase stacked interleaved parallel Buck circuit.

[0028] Fig.13 This is the overall control logic diagram of the main branch of the three-phase stacked interleaved parallel Buck circuit.

[0029] Fig.14 This is the control logic diagram of the compensation branch of the three-phase stacked interleaved parallel Buck circuit.

[0030] Fig.15 This is the three-phase stacked interleaved parallel Buck main branch drive signal waveform.

[0031] Fig.16 This is the inductor current waveform of the three-phase stacked interleaved parallel Buck main branch.

[0032] Fig.17 The driving signal waveform of the three-phase stacked interleaved parallel Buck compensation branch.

[0033] Fig.18 The inductor current waveform of the three-phase stacked interleaved parallel Buck compensation branch.

[0034] Fig.19 This is a waveform diagram of the output voltage, output current and output power of a high-power, low-ripple output hydrogen production converter.

[0035] Fig. 20 This is a comparison chart of the output current waveforms of the high-power low-ripple hydrogen production converter and the traditional hydrogen production converter.

[0036] Among them: six-pulse commutation unit 1, filter circuit 2, three-phase stacked staggered parallel Buck circuit 3. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solutions and advantages of the present invention clearer, the following content will systematically and completely describe the specific technical solutions of the present invention in combination with the drawings provided according to the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0038] A novel high-power low-ripple output hydrogen production converter comprises a six-pulse commutation unit 1, a filter circuit 2 and a three-phase stacked staggered parallel Buck circuit 3 connected in sequence. The six-pulse commutation unit 1 and the filter circuit 2 are connected in series to output a filtered DC voltage. U dc , at this time U dc The harmonic content is high, so the filter circuit 2 is connected in series with the three-phase stacked interleaved parallel Buck circuit 3, and the output voltage of the three-phase stacked interleaved parallel Buck circuit 3 is V o , and finally to the load R powered by.

[0039] The above-mentioned six-pulse commutation unit 1 uses a three-phase bridge-type fully controlled commutation circuit as a basic unit. The three-phase stacked staggered parallel Buck circuit 3 is divided into a main branch and a compensation branch. The main branch is composed of three Buck circuits in parallel. The compensation branch includes a half bridge and a compensation capacitor that plays a role of voltage division and DC isolation. C AX , and a filter inductor L AX .

[0040] The six-pulse converter unit 1 is composed of six-pulse converters. VT1~VT6 are the 1st to 6th bridge arms. u a , u b , u c is the equivalent fundamental phase voltage of the AC system; L r is the equivalent commutation inductance of each phase, which is composed of the leakage inductance of the converter transformer and the equivalent inductance of the AC system; the conduction order of the six bridge arms of the converter valve is VT1, VT2 on → VT1, VT2, VT3 on → VT2, VT3 on → VT2, VT3, VT4 on → VT3, VT4 on → VT3, VT4, VT5 on → VT4, VT5 on → VT4, VT5, VT6 on → VT5, VT6 on → VT5, VT6, VT1 on → VT6, VT1 on → VT6, VT1, VT2 on → VT1, VT2 on → (repeated cycle).

[0041] The operation mode in which two valve arms and three valve arms are turned on alternately is called "operating condition 2-3". The prerequisite for the 6-pulse rectifier to work in "operating condition 2-3" is: the trigger delay angle 0 < α <90°- μ / 2, while the commutation angle is 0≤ μ <60°. Assuming that the 6-pulse circuit works under the ideal condition of no ripple in DC current and equal interval triggering with an electrical angle interval of 60°, it is reasonable to assume that the two valve arms VT1 and VT2 are in the on state, so as to analyze the conduction process of each valve arm in the subsequent time.

[0042] 1VT1, VT2 conduction stage At this time, the three-phase current is Figure 2 The reference directions shown are: i a = i d , i b =0, i c =- i d Since we assume that the DC current i d There is no ripple, so the DC current is in the equivalent commutation inductance L r , there will be no voltage drop, so the output voltage of the 6-pulse rectifier, that is, the rectified voltage u q = u mN - u nN , equal to the power line voltage u ac When the potential at point b is higher than that at point c, the conduction condition of the thyristor valve arm VT3 is met, and the valve arm VT3 is triggered to conduct, thus forming a pattern in which the three valve arms VT1, VT2, and VT3 are simultaneously conducted.

[0043] 2VT1, VT2, VT3 conduction stage At this time, in the upper half bridge of the 6-pulse rectifier, the valve arms VT1 and VT3 form a closed loop through the two phases a and b of the AC system, such as Figure 3 As shown. VT1 and VT3 form a two-phase short circuit, and the short circuit current is called i sc , its value gradually increases with time, the current in the valve arm VT3 is i sc In the same direction, the current passing through the valve arm VT1 i VT1 = i d - i sc , its value gradually decreases with time.i VT1 When the thyristor is turned off, the DC current decreases to below the holding current (the value is close to zero). i d It is completely provided by the valve arm VT3. At this point, the commutation process of the AC system is completed, and the rectifier works in the conduction state of the converter valves VT2 and VT3.

[0044] 3) VT2, VT3 conduction stage Figure 4 As shown, i a =0, i b = i d , i c =- i d . Since the DC current i d No ripple, DC current in equivalent commutation inductance L There is no voltage drop across r, so the rectified voltage u d Equal to the power line voltage u bc .

[0045] The above analysis discusses the process before and after the commutation of the valve arm VT1 to the valve arm VT3 in the upper half bridge, that is, the process of VT1, VT2 conduction → VT1, VT2, VT3 conduction → VT2, VT3 conduction. Similarly, the process before and after the commutation of the lower half bridge can be analyzed, such as VT2, VT3 conduction → VT2, VT3, VT4 conduction → VT3, VT4 conduction process. In each power frequency cycle, the forward current lasts for 120°+ μ Electrical angle, off 60°- μ Electrical angle, then reverse continuously for 120°+ μ Electrical angle, then shut off 60°- μ In each power frequency cycle, the rectified voltage consists of 6 waveforms with a duration of 60° and the same shape, hence the name 6-pulse wave.

[0046] The above-mentioned filter circuit 2 is composed of a smoothing reactor L d and DC filter capacitors C d Series structure, smoothing reactor L d and DC filter capacitors C d The two ends of the series connection are connected to the output of the six-pulse commutation unit 1, and the DC filter capacitor C dOutput filtered DC voltage U dc The smoothing reactor can reduce the DC current ripple and offset the instantaneous difference between the six-pulse output voltage and the output voltage of the three-phase stacked Buck converter. The DC filter capacitor also plays a role in suppressing the harmonics injected into the DC line by the converter.

[0047] The three Buck circuits of the main branch in the above three-phase stacked interlaced parallel Buck circuit 3 are composed of three parallel DC voltage U dc The series branch at both ends is composed of a switch tube S n and diode D n ,n=1,2,3;Switching tube S n and diode D n The inductor L is drawn between n , the other ends of the three inductors L1, L2 and L3 are connected in parallel and the output current I dcmain To capacitor C, capacitor C is connected to inductor L n The parallel terminals and DC voltage U dc negative electrode.

[0048] The above load R In parallel with capacitor C.

[0049] The half bridge of the compensation branch in the three-phase stacked staggered parallel Buck circuit 3 includes a DC voltage U dc The switch tube S at both ends AX1 and S AX2 , switch tube S AX1 and S AX2 The midpoint output and filter inductor L AX And compensation capacitor C AX Connect and source current I AX To capacitor C, current I AX and current I dcmain Composition output current I dco To load R， Compensation capacitor C AX Both ends of the load R Connected to the positive terminal of capacitor C.

[0050] The main branch is a traditional three-phase staggered parallel Buck converter. The switch devices of the main branch are S1, S2, S3, D1, D2 and D3. Among them, S1 and D1 are the switch tubes of the first branch, and the same applies to other branches. The switch tubes of each branch are complementary, and S1, S2 and S3 are turned on successively with an interval of 120°. The compensation branch includes a half bridge, a compensation capacitor that acts as a voltage divider and DC isolation C AX , and a filter inductor L AX . C is the total supporting capacitance of the main branch; U dc and V o are the input and output voltages of the converter, respectively; I dcmain is the main branch output current, I AX is the compensation branch current, I dco is the converter output current. Let us assume that the compensation branch filter inductance L AX and main branch N Phase inductance L 1. L 2…… L N The inductance values ​​are the same, that is L 1= L 2=......= L N = L ax = L The present invention is based on the number of phases of the main branch N =3, and the operating modal analysis of the multi-phase stacked interleaved parallel Buck converter with a duty cycle of 0.5 is performed. The analysis of other duty cycles is similar.

[0051] 1) If Figure 5 As shown, in [0,t 10 ] time, S AX2 , S1, S3 and D2 are turned on, S AX1 , S2, D1 and D3 are turned off. L 1 and L 3 Absorbing energy, inductor current I 3 in t 10 The inductance rises to the maximum value at any time. L AX and L 2Release energy, current I AX and I 2 is in a decreasing state, and at t 10time I AX drops to a minimum value; 2) If Figure 6 As shown, in [t 10 ,T s / 3] time, S AX1 conduction, S1 continues to conduct, S AX2 , S2 and S3 are all off, correspondingly D1 is off, and D2 and D3 are on. I AX and I 1 linear increase, I 2 and I 3 linear decrease. At T s / 3 Moment I 2 drops to the minimum value first, and I AX rise to maximum value; 3) If Figure 7 As shown, at time [T s / 3,T s / 2], S AX2 conduction, S1 continues to conduct, S2 starts to conduct, S AX1 and S3 are both off, the current I 1 and I 2 Linear rise, current I AX and I 3 linear decrease, at Ts / 2, the current I 1 reaches the maximum value, the current I AX Dropped to minimum value.

[0052] 4) If Figure 8 As shown, at time [T s / 2,t 20 ]Inside, S AX1 , S2, D1 and D3 are turned on, S AX2 , S1, S3, and D2 are turned off. Current I AX and I 2 is in the rising state, and at t 20 Current at all times I AX rises to its maximum value. I 1 and I 3 linear decrease, at t 20 time I 3 reaches the minimum value.

[0053] 5) If Figure 9 As shown, at time [t 20 ,2T s / 3], SAX2 , S2, S3 and D1 are turned on, S AX1 , S1, D2 and D3 are turned off. Current I AX and I 1 Linear decrease, current I 2 and I 3 linear increase. At 2T s / 3 moment, current I 2 reaches the maximum value, the current I AX Dropped to minimum value.

[0054] 6) If Figure 10 As shown, at time [2T s / 3,T s ]Inside, S AX1 , S3, D1 and D2 are turned on, S AX2 , S1, S2 and D3 are turned off. Current I AX and I 3 Linear rise, current I 1 and I 2 linearly decreases. At T s time I 1 drops to the minimum value first, and I AX Rise to maximum value.

[0055] Therefore, the inductor current ripple of each phase can be obtained as shown in formula 1: ; (1) The total output current ripple Δ of the three-phase interleaved parallel Buck part is obtained by linear superposition I dcmain for: ; (2) When the duty cycle is 0.5, V AX =(2-3 D ) U dc - DU dc ,but ; (3) Therefore, the total output current ripple of the proposed converter Δ I dco for: ; (4) The above describes in detail the proposed converter in terms of the number of phases in the main branch. N=3, the working mode when the duty cycle is 0.5 in steady state operation. From theoretical analysis, it can be seen that the converter can eliminate the output current ripple.

[0056] The control method of the novel high-power low-ripple output hydrogen production converter includes voltage control of six-pulse commutation unit 1, main branch current equalization double closed-loop control of three-phase stacked staggered parallel Buck circuit 3 and compensation branch control.

[0057] The voltage control of the six-pulse commutation unit 1 mentioned above realizes the control of the output voltage of the six-pulse rectifier by changing the DC voltage of the converter through the phase control of the thyristor valve trigger pulse.

[0058] The above-mentioned three-phase stacked staggered parallel Buck circuit 3 main branch current equalization dual closed-loop control adopts voltage-current dual closed-loop control to ensure that each phase of the main branch achieves a good current equalization effect, and finally adds carrier phase shift pulse width modulation, taking the first phase triangular wave as a reference, so that the second phase is phase shifted by 120° and the third phase is phase shifted by 240°, so as to achieve accurate phase shift of each phase drive signal.

[0059] The compensation branch of the three-phase stacked interleaved parallel Buck circuit 3 is controlled by controlling the switch tube S AX1 and S AX2 To achieve current I AX and I dcmain The AC components and ripples are complementary, thereby achieving the output current of the converter I dco Zero ripple; if the output current ripple slope is positive, the compensation branch current ripple slope is negative, corresponding to S AX1 Shutdown and S AX2 On; On the contrary, S AX1 Conducting and S AX2 Finally, the compensation branch switch S is realized through signal conversion. AX1 and S AX2 Complementary conduction control.

[0060] The primary goal of the three-phase stacked staggered parallel main branch control is to achieve current sharing between parallel circuits to ensure stable and efficient operation of the main branch. The voltage-current dual closed-loop control strategy can ensure that each phase of the main branch achieves a good current sharing effect: the voltage loop is used as the control outer loop to stabilize the converter output voltage, and three independent current loops with the same structure are connected in parallel to form the control inner loop. Finally, carrier phase shift pulse width modulation is added, and the first phase triangle wave is used as a reference to shift the second phase by 120° and the third phase by 240° to achieve accurate phase shift of each phase drive signal.

[0061] The three-phase stacked staggered parallel compensation branch main branch is used to achieve power transmission, and the compensation branch is used to eliminate output current ripple.I dcmain All the DC and AC currents required to flow through the load. On the other hand, in the compensation branch, the DC component is C AX Block, so I AX There is only AC component in the circuit. Therefore, we can control the compensation branch switch S AX1 and S AX2 To achieve current I AX and I dcmain The AC components and ripples are complementary, thereby achieving the output current of the converter I dco Zero ripple. If the output current ripple slope is positive, the compensation branch current ripple slope is negative, corresponding to S AX1 Shutdown and S AX2 On; On the contrary, S AX1 Conducting and S AX2 Compare the number of positive slopes of the inductor currents in each phase of the main branch R rate The number of inductor currents in each phase of the main branch with negative slopes D rate , we can get the positive and negative slope of the main branch output current ripple at any time. Finally, the compensation branch switch S is realized through signal conversion. AX1 and S AX2 Complementary conduction control.

[0062] Since S1, S2...S N Staggered conduction, so the driving signal G S1 , G S2 , G S3 It can be linearly superimposed, so we can count the number of S1, S2, and S3 that are turned on at any time. N 1 and the number of S1, S2, and S3 turned off N 0 in respectively and U dc - V o and V o Multiplying them together, we can get the number of three-phase inductor current ripples with positive slopes at any time. R rate The sum is negative D rate , and then R rate and D rateBy comparing the two, we can get the positive and negative slope of the total output current ripple at any time, and finally realize S AX1 and S AX2 Complementary conduction control. R rate > D rate When S AX1 If S is turned off AX2 Conductivity (G SAX1 =0,G SAX2 =1); when R rate ≤ D rate When S AX1 If conduction S AX2 Turn off (G SAX1 =1,G SAX2 =0).

[0063] Embodiment 1: See attached Figure 1 As shown, the present invention provides a low-ripple hydrogen production converter structure and control method for low-voltage and high-current scenarios, including a six-pulse commutation unit 1, a filter circuit 2 and a three-phase stacked interlaced parallel Buck circuit 3; the three-phase stacked interlaced parallel Buck circuit is divided into a main branch and a compensation branch, the main branch is composed of three Bucks in parallel, and the compensation branch includes a half-bridge, a compensation capacitor that plays a role of voltage division and DC isolation C AX , and a filter inductor L AX .

[0064] Attached Figure 1 As shown in the figure, the three-phase voltage power frequency fundamental sinusoidal phase electromotive force of the power grid input is u a , u b , u c , L r is the equivalent commutation reactance of each phase, VT 1~6 The code for the six converter valves that make up the six-pulse converter, and the numbers 1 to 6 are the conduction sequence numbers of the converter valves. The filter circuit consists of a smoothing reactor L d and a DC filter capacitor C d The 6-pulse rectifier is connected in series with the filter circuit to output a filtered DC voltage. U dc , at this time U dcThe harmonic content is high, so we connect the three-phase stacked interleaved parallel Buck circuit in series to reduce the ripple output voltage V o , and finally to the load R The three-phase stacked staggered parallel Buck circuit consists of a main branch and an auxiliary branch. The main branch consists of three Buck circuits in parallel, and each Buck circuit branch includes a switch device S k , diode D k And inductor L k , k=1,2,3. The total capacitance of the three branches in parallel is C Each parallel Buck circuit uses the same switching frequency, but the conduction time differs by 1 / 3 of the switching cycle; the compensation branch includes the auxiliary branch switch tube S AX1 and S AX2 A half bridge is formed, and the compensation capacitor plays the role of voltage division and DC isolation C AX , and a filter inductor L AX , this branch can compensate the output ripple through a certain control strategy.

[0065] In order to make the DC voltage have a higher level, the rectifier generally adopts a smaller trigger delay angle. α The average value of the ideal no-load DC voltage of the six-pulse rectifier U dc0 Available rectifier valve side winding no-load line voltage effective value U 1 means: ; (5) Conduction Angle α represents the time delay from when the valve voltage becomes positive to when the thyristor is turned on. α As the DC output voltage increases, it decreases accordingly. Figure 10 As shown in Figure 1, we can control the conduction angle α To achieve the purpose of continuously adjusting the DC output voltage, and thus controlling the power transfer. α As the DC output voltage of the converter gradually decreases and approaches zero, the control generates a firing angle command value according to the need for a constant DC voltage.

[0066] The main branch of three-phase stacked interleaved parallel connection is a three-phase interleaved parallel Buck converter. The primary goal of the main branch control is to achieve current sharing between the parallel circuits to ensure stable and efficient operation of the main branch. Figure 10 As shown in the second G c ( s) represents the controller transfer function; the transfer function from duty cycle to inductor current is G id ( s ), the transfer function from duty cycle to output voltage G vd ( s ) and the transfer function from inductor current to output voltage G vi ( s ). The average mathematical equations for the average rate of change of the inductor current and capacitor voltage during the switching period are listed. After Laplace transform and linearization, the transfer functions under the ideal condition of continuous conduction mode of the inductor current are obtained through small signal modeling: ; (6) in, N is the phase number, N =3, R It is the equivalent load of the three-phase stacked interleaved parallel Buck circuit.

[0067] The stable output voltage of the interleaved parallel Buck converter is the prerequisite for current sharing control. Only when the output voltage can be stabilized at the target voltage, it is meaningful to control the current sharing of the three-phase branches. Figure 10 As shown in Figure 3, the voltage loop is used as the outer control loop to stabilize the converter output voltage, and the DC bus voltage at its output end is V o With a given reference voltage V ref By comparison, a voltage error signal is obtained; after PI adjustment, the reference current is obtained I ref , divide the reference current by the number of phases and compare it with the inductive current of the inductive element at the input end of each phase I 1. I 2. I 3 for comparison, thus, three independent current loops with the same structure are connected in parallel to form the inner control loop. After that, they are regulated by PI and input into the carrier phase shift pulse width modulation. Taking the first phase triangle wave as a reference, the second phase is shifted by 120° and the third phase is shifted by 240° to achieve the precise phase shift of each phase drive signal and generate the trigger signals of each switch device S1, S2, and S3 of the main branch.

[0068] As attached Figure 10 As shown in Figure 4, the auxiliary branch S AX1 and S AX2 The conduction state of S1, S2, S3 and the output voltage V o and input voltage U dc The relationship between the main branch multi-phase staggered parallel output current is used to determineI dcmain The positive or negative condition of the ripple slope determines the output current. I dcmain The ripple slope is positive, and the auxiliary branch current I AX The ripple slope is negative, corresponding to S AX1 Shutdown and S AX2 If the output current I dcmain If the ripple slope is negative, the auxiliary branch current I AX The ripple slope is positive, corresponding to S AX1 Conducting and S AX2 In this way, the converter output current ripple can be zero under wide duty cycle conditions. The specific method is: estimate the current main branch output current I dcmain The rate of change d I dcmain / d t : ; in R rate and D rate They are respectively the number of inductor currents of each phase in the main branch with positive slopes and the number of inductor currents of each phase in the main branch with negative slopes, and they are: ; ; In the above formula, S k ( k =1~ N ), N =3 is the main branch k The switching function of a switch tube is 1 when it is turned on and 0 when it is turned off.

[0069] Then R rate and D rate By comparing the two, we can get the output current of the main branch at any time. I dcmain The ripple slope is positive or negative, and finally the auxiliary branch switch tube S is realized through signal conversion AX1 and S AX2 Complementary conduction control.

[0070] Attached Figure 10 Five ~ Attachment Figure 10 Eighth, the three-phase stacked interleaved parallel Buck driving signals at each level and the inductor current waveforms of each branch.

[0071] (1) In [0,t 10 ] time, S AX2 , S1, S3 and D2 are turned on, S AX1 , S2, D1 and D3 are turned off. L 1 and L 3 Absorbing energy, inductor current I 3 in t 10 The inductance rises to the maximum value at any time. L AX and L 2Release energy, current I AX and I 2 is in a decreasing state, and at t 10 time I AX drops to a minimum value; (2) In [t 10 ,Ts / 3] time, S AX1 conduction, S1 continues to conduct, S AX2 , S2 and S3 are all off, correspondingly D1 is off, and D2 and D3 are on. I AX and I 1 linear increase, I 2 and I 3 linearly decreases. At Ts / 3 I 2 drops to the minimum value first, and I AX rise to the maximum value; (3) Within the time [Ts / 3, Ts / 2], S AX2 conduction, S1 continues to conduct, S2 starts to conduct, S AX1 and S3 are both off, the current I 1 and I 2 Linear rise, current I AX and I 3 linear decrease, at Ts / 2, the current I 1 reaches the maximum value, the current I AX drops to a minimum value; (4) At time [Ts / 2,t 20 ]Inside, S AX1 , S2, D1 and D3 are turned on, S AX2 , S1, S3, and D2 are turned off. Current I AX and I 2 is in the rising state, and at t 20 Current at all times I AXrises to its maximum value. I 1 and I 3 linear decrease, at t 20 time I 3 reaches the minimum value; (5) At time [t 20 ,2Ts / 3], S AX2 , S2, S3 and D1 are turned on, S AX1 , S1, D2 and D3 are turned off. Current I AX and I 1 Linear decrease, current I 2 and I 3 linearly increases. At 2Ts / 3, the current I 2 reaches the maximum value, the current I AX drops to a minimum value; (6) Within the time [2Ts / 3,Ts], S AX1 , S3, D1 and D2 are turned on, S AX2 , S1, S2 and D3 are turned off. Current I AX and I 3 Linear rise, current I 1 and I 2 linearly decreases. At time Ts I 1 drops to the minimum value first, and I AX Rise to the maximum value.

[0072] The above simulation model was built in PSCAD / EMTDC. The output voltage, output power and output current waveforms of the hydrogen production converter of the present invention are shown in the attached figure. Figure 10 9 shown.

[0073] and Figure 10 Under the same working conditions, when the low ripple hydrogen production power supply described in the embodiment of the present invention and the traditional six-pulse rectifier unit and three-phase staggered parallel Buck circuit are used to produce hydrogen, the output current waveform is shown in the attached figure. Figure 2 10. The average DC current output by the traditional hydrogen production power supply is 39.14kA, and the current ripple accounts for 0.2%, while the high-power low-ripple hydrogen production converter proposed in this patent outputs an average DC current of 39.1325kA, and the current ripple accounts for 0.04%. By comparison, it can be seen that the output current ripple of the hydrogen production converter in the low-voltage and high-current scenario described in the present invention is small, which reduces the impact of the ripple on the inside of the electrolyzer and extends the service life of the electrolyzer; by adding a multi-phase stacked staggered parallel Buck circuit, the input current harmonic distortion rate can be effectively reduced while also reducing the filter inductance, thereby avoiding harmonic pollution to the power grid and improving economic efficiency.

[0074] The above-mentioned embodiments only express the specific implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the protection scope of the present application. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the technical solution concept of the present application, and these all belong to the protection scope of the present application.

Claims

1. A new type of high-power low-ripple output hydrogen production converter, characterized in that: The invention comprises a six-pulse commutation unit (1), a filter circuit (2) and a three-phase stacked interlaced parallel Buck circuit (3) which are connected in sequence. The six-pulse commutation unit (1) and the filter circuit (2) are connected in series to output a filtered DC voltage. U dc , the filter circuit (2) is connected in series with the three-phase stacked interleaved parallel Buck circuit (3), and the output voltage of the three-phase stacked interleaved parallel Buck circuit (3) is V o , and finally to the load R powered by.

2. According to the novel high-power low-ripple output hydrogen production converter described in claim 1, it is characterized in that: The six-pulse commutation unit (1) uses a three-phase bridge-type fully controlled commutation circuit as a basic unit. The three-phase stacked staggered parallel Buck circuit (3) is divided into a main branch and a compensation branch. The main branch is composed of three Buck circuits in parallel. The compensation branch includes a half bridge and a compensation capacitor that plays a role of voltage division and DC isolation. C AX , and a filter inductor L AX .

3. According to the novel high-power low-ripple output hydrogen production converter described in claim 2, it is characterized in that: The three-phase stacked interlaced parallel Buck circuit (3) of the main branch consists of three parallel DC voltage U dc The series branch at both ends is composed of a switch tube S n and diode D n ,n=1,2,3;Switching tube S n and diode D n The inductor L is drawn between n , the other ends of the three inductors L1, L2 and L3 are connected in parallel and the output current I dcmain To capacitor C, capacitor C is connected to inductor L n The parallel terminals and DC voltage U dc negative electrode.

4. According to the novel high-power low-ripple output hydrogen production converter described in claim 3, it is characterized in that: The load R In parallel with capacitor C.

5. According to the novel high-power low-ripple output hydrogen production converter described in claim 4, it is characterized in that: The half bridge of the compensation branch in the three-phase stacked staggered parallel Buck circuit (3) includes a DC voltage U dc The switch tube S at both ends AX1 and S AX2 , switch tube S AX1 and S AX2 The midpoint output and filter inductor L AX And compensation capacitor C AX Connect and source current I AX To capacitor C, current I AX and current I dcmain Composition output current I dco To load R， Compensation capacitor C AX Both ends of the load R Connected to the positive terminal of capacitor C.

6. According to the novel high-power low-ripple output hydrogen production converter described in claim 5, it is characterized in that: The filter circuit (2) is composed of a smoothing reactor L d and DC filter capacitors C d Series structure, smoothing reactor L d and DC filter capacitors C d The two ends of the series connection are connected to the output of the six-pulse commutation unit (1), and the DC filter capacitor C d Output filtered DC voltage U dc .

7. A control method for a novel high-power low-ripple output hydrogen production converter according to claim 6, characterized in that: It includes six-pulse commutation unit (1) voltage control, three-phase stacked staggered parallel Buck circuit (3) main branch current equalization double closed-loop control and compensation branch control.

8. The control method of a novel high-power low-ripple output hydrogen production converter according to claim 7 is characterized in that: The voltage control of the six-pulse commutation unit (1) achieves control of the output voltage of the six-pulse rectifier by changing the DC voltage of the converter through phase control of the thyristor valve trigger pulse.

9. The control method of a novel high-power low-ripple output hydrogen production converter according to claim 8 is characterized in that: The main branch current equalization dual closed-loop control of the three-phase stacked staggered parallel Buck circuit (3) adopts voltage-current dual closed-loop control, input carrier phase shift pulse width modulation, and uses the first phase triangle wave as a reference to make the second phase phase shift 120° and the third phase phase shift 240°.

10. The control method of a novel high-power low-ripple output hydrogen production converter according to claim 9 is characterized in that: The compensation branch of the three-phase stacked interleaved parallel Buck circuit (3) is controlled by controlling the switch tube S AX1 and S AX2 To achieve current I AX and I dcmain The AC components and ripples are complementary, thereby achieving the output current of the converter I dco Zero ripple; if the output current ripple slope is positive, the compensation branch current ripple slope is negative, corresponding to S AX1 Shutdown and S AX2 On; On the contrary, S AX1 Conducting and S AX2 Finally, the compensation branch switch S is realized through signal conversion. AX1 and S AX2 Complementary conduction control.

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