High-power alternating-current impedance excitation circuit, control method thereof and electrolysis test system

Abstract

The invention discloses a high-power alternating-current impedance excitation circuit, a control method thereof and an electrolysis test system, and belongs to the technical field of power supplies and power electronics, the circuit is used as an alternating-current power supply in a high-capacity electrolysis test power supply, and the circuit is controlled by a controller to output an alternating-current signal so as to carry out an impedance test on an electrolytic bath. Compared with a full-bridge circuit, the alternating-current impedance excitation circuit adopts the multi-level converter, so that the output current harmonic content is low, the electrolysis efficiency is improved, the equipment loss is reduced, the economical efficiency of an electrolysis system is improved, stable operation of an electrolytic bath is ensured, and electrolysis interruption or faults caused by voltage fluctuation are reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of power supply and power electronics, and particularly relates to a high-power AC impedance excitation circuit, a control method thereof, and an electrolysis test system. Background Art

[0002] As a key path to integrating renewable energy consumption with the hydrogen energy industry, PEM electrolysis hydrogen production technology features high electrolysis efficiency, fast dynamic response, and a wide load regulation range. The test performance of its core equipment, the electrolysis power supply, directly affects the efficiency and stability of the hydrogen production system. However, current high-power electrolysis power supplies face the following technical bottlenecks that need to be overcome when testing megawatt-class PEM electrolysis equipment: 1. Poor performance of fine control of electrolytic test power supply The dynamic response characteristics of PEM electrolyzers require power supply with millisecond-level power regulation accuracy. For example, in wind-solar coupling scenarios, electrolyzers need to switch quickly within the load range of 30%-100%. Traditional power supplies have difficulty in achieving accurate tracking due to control algorithm lag (PID regulation error of more than ±5%). Studies have shown that when the current density is increased from 1A / cm 2 Jumped to 2A / cm 2 When the electrolyzer efficiency is increased by 30% to current fluctuations, the ripple factor of existing power supplies generally exceeds 2%, leading to the risk of membrane electrode overload. In addition, when testing multiple electrolyzers in parallel, the power supply current sharing error exceeds 10%, which cannot meet the coordinated control requirements of the balancing strategy.

[0003] 2. High-power electrolysis test power supply with high grid-connected harmonic content While the IGBT rectifier topology enables high-frequency switching (above 10kHz), its nonlinear characteristics result in total harmonic distortion (THD) as high as 15%-25%, far exceeding the 5% limit specified in the GB / T 14549 standard. Harmonics such as the 5th and 7th orders account for over 60% of the total harmonics, causing not only grid voltage distortion but also electromagnetic interference within the electrolyzer, leading to localized overheating of the proton exchange membrane. For example, field measurements in a 1MW electrolysis system revealed that harmonic currents caused electrolyzer voltage fluctuations of up to ±3V, directly impacting hydrogen purity. Furthermore, insufficient reactive power compensation (power factor <0.8) in the high-power thyristor rectifiers further exacerbated system energy efficiency losses.

[0004] 3. Electrolytic power supplies generally lack high-power AC impedance excitation capabilities Existing electrolysis power supplies generally lack the ability to superimpose high-frequency (1kHz-1MHz) AC signals, making it impossible to obtain real-time electrochemical impedance spectroscopy (EIS) of the electrolyzer. Research has shown that the aging state of the proton exchange membrane is directly related to the capacitive reactance characteristics in the high-frequency range (>10kHz) of the impedance spectrum, while traditional DC power supplies are unable to output AC excitation signals with stable amplitude (error <1mV) and adjustable frequency (resolution ≤1Hz). For example, tests have shown that when a local "hot spot" appears in the electrolyzer, the imaginary part of the impedance changes by as much as 20mΩ, but conventional equipment is unable to capture such microscopic failure characteristics. Furthermore, under high current (>1000A) conditions, the measurement error of the charge transfer impedance at the electrode-electrolyte interface exceeds 15%, seriously affecting the evaluation of catalyst activity.

[0005] 4. AC / DC coupling during AC impedance measurement leads to inaccurate AC measurement results When an AC signal is superimposed on a DC bias (>100V), the coupling capacitor (typically in the μF range) at the power supply output introduces a phase shift (up to 10° or more), leading to errors in the analysis of the real and imaginary parts of the impedance. Experimental data shows that when the DC component exceeds 90%, the measurement error of the AC impedance modulus increases sharply from 1% to 8%. Furthermore, switching noise from power electronic devices (such as IGBTs with dV / dt up to 10kV / μs) can alias the excitation signal, causing impedance spectrum distortion in the high-frequency range (>10kHz). For example, in testing a 2MW electrolysis system, AC / DC coupling resulted in data dispersion of the imaginary part of the membrane electrode interface impedance as high as 30%, making it impossible to accurately assess the proton conductivity performance of the membrane electrode.

[0006] It can be seen that the existing high-power electrolysis power supply cannot meet the testing requirements of electrolysis equipment.

[0007] In summary, there is an urgent need to carry out research on online excitation technology that integrates high-power AC impedance broadband testing to achieve a wide-range integrated output of high-power broadband AC and DC, and meet the flexible testing requirements of megawatt-level PEM electrolysis hydrogen production systems with wide-range regulation under multiple working conditions. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to address the deficiencies in the above-mentioned prior art and provide a high-power AC impedance excitation circuit, a control method thereof, and an electrolysis test system, so as to solve the technical problems of insufficient control accuracy caused by high harmonic content, limited adjustment range, and AC / DC coupling interference of high-power electrolysis power supply.

[0009] The present invention adopts the following technical solutions: A high-power AC impedance excitation circuit includes a single-phase five-level stacked multi-unit converter. The single-phase five-level stacked multi-unit converter is composed of four basic commutation units, each of which includes a pair of complementary conductive switching tubes. Adjacent basic commutation units are connected via floating capacitors, with one floating capacitor provided on each layer, for a total of two floating capacitors. The positive and negative electrodes of the floating capacitors are respectively connected to the source and gate electrodes of the switching tubes of adjacent basic commutation units. The output end of the single-phase five-level stacked multi-unit converter is connected to an LCL filter and a bias capacitor for providing a broadband AC current signal with a superimposed DC bias to the load.

[0010] Preferably, the switch tubes in the basic commutation unit are SiC MOSFET devices, and each switch tube is anti-parallel connected with a diode.

[0011] Preferably, the rated voltage of the suspension capacitor is 1 / 4 of the DC side voltage.

[0012] Preferably, the first filter inductor of the LCL filter is connected to the positive pole of the output end of the single-phase five-level stacked multi-unit converter; after the second filter inductor is connected in parallel with the filter capacitor, its first end is connected to the second end of the first filter inductor, and its second end is connected to the positive pole of the electrolytic cell, and the bias capacitor is connected to the negative pole of the output end of the single-phase five-level stacked multi-unit converter and the negative pole of the electrolytic cell.

[0013] Preferably, the frequency of the AC current output by the single-phase five-level stacked multi-unit converter is 100 Hz to 10 kHz.

[0014] Another technical solution of the present invention is a high-power AC impedance excitation circuit control method, which uses the circuit and includes the following steps: Generate five-level output and nine switch state combinations based on carrier stack modulation; Real-time detection of load current direction and suspension capacitor voltage; Dynamically select redundant switch states based on the output voltage level, load current direction, and floating capacitor voltage state to achieve floating capacitor voltage balance. Specifically, the following steps are performed: When the output level is ±E / 4, the charge and discharge switch combination is selected according to the current direction and the capacitor voltage deviation; When the output level is 0, a fixed switch combination is used.

[0015] Preferably, when the output level is When the lower switch tube and At the same time, the upper switch tube The conduction conditions are: when the load current flows in a positive direction, the upper floating capacitor is charged; when the load current flows in a negative direction, the upper floating capacitor is discharged; Upper switch tube The conduction condition is: when the load current flows in a positive direction, the upper floating capacitor is discharged; when the load current flows in a negative direction, the upper floating capacitor is charged.

[0016] Preferably, when the output level is When the switch The conduction conditions are: when the load current flows in a positive direction, the lower floating capacitor is charged; when the load current flows in a negative direction, the lower floating capacitor is discharged; Switching tube The conduction conditions are: When the load current flows in a positive direction, the lower floating capacitor is discharged; when the load current flows in a negative direction, the lower floating capacitor is charged.

[0017] Preferably, the carrier stacking modulation uses an in-phase carrier.

[0018] Another technical solution of the present invention is an electrolysis testing system, comprising: A first power supply and a second power supply are connected in parallel, the output ends of the first power supply and the second power supply are both connected to the electrolytic cell, and the DC bias voltage matches the AC signal amplitude; the second power supply adopts the high-power AC impedance excitation circuit described in any one of claims 1 to 5; The first power supply outputs a first direct current and a direct current bias voltage to the electrolytic cell according to the three-phase alternating current voltage, and the second power supply provides a broadband alternating current for impedance testing.

[0019] Preferably, the second power supply includes: A power module, configured to generate a second direct current and output the second direct current to the inverter module; The inverter module is used to convert the second direct current into a third alternating current and transmit the third alternating current to the filter module.

[0020] A filtering module, configured to filter the third alternating current and output a second alternating current to the electrolytic cell; The bias module is used to convert the first DC current output into a bias signal with the same amplitude as the DC bias voltage and transmit it to the negative electrode of the electrolytic cell.

[0021] Preferably, the bias module includes a capacitor C, the positive electrode of the capacitor C is connected to the negative electrode of the output end of the inverter module, and the negative electrode is connected to the negative electrode of the electrolytic cell, and is used to convert the first direct current into a constant amplitude bias voltage.

[0022] Preferably, the system supports parallel testing of multiple electrolytic cells.

[0023] Compared with the prior art, the present invention has at least the following beneficial effects: A high-power AC impedance excitation circuit utilizes a single-phase, five-level stacked multi-cell converter. This circuit generates a stepped output voltage through the series connection of four basic commutation cells and coupling with floating capacitors. The floating capacitors achieve inter-cell voltage balance, making the output waveform nearly sinusoidal. The five-level output concentrates harmonic energy at the carrier frequency, where it is filtered by an LCL filter to reduce THD and eliminate the risk of electromagnetic interference in the electrolyzer. The floating capacitors absorb switching spikes, supporting wideband AC output and covering the high frequency range required for proton exchange membrane aging testing. The layered floating capacitor design prevents voltage drift, ensuring that electrolyzer voltage fluctuations meet design requirements.

[0024] Furthermore, the switching frequency of SiC MOSFET is >10kHz, the reverse recovery time is <100ns, and the anti-parallel diode provides a low-loss freewheeling path; the switching speed is faster than IGBT, shortening the load switching response time and solving the power tracking problem in wind-solar coupling scenarios; it reduces on-resistance, reduces device temperature rise, and extends equipment life; and supports high-frequency operation of carrier stacking modulation to avoid impedance spectrum distortion caused by switching noise aliasing.

[0025] Furthermore, the first filter inductor suppresses high-frequency harmonics; the filter capacitor is connected in parallel to the ground to absorb common-mode noise; and the second filter inductor blocks low-frequency ripple. The bias capacitor provides a DC ground path, cutting off the coupling path of the DC component to the AC signal, reducing phase shift and minimizing impedance real part measurement errors; and the parasitic resistance dissipates high-frequency energy, avoiding LCL resonance.

[0026] A high-power AC impedance excitation circuit control method uses carrier stacking modulation to generate five levels, detects current direction and capacitor voltage deviation in real time, and dynamically selects redundant switch states to meet EIS testing requirements. A fixed switch combination is used for level 0 to prevent short-circuiting of the switch tube.

[0027] Furthermore, the current direction is strongly correlated with the switching action, which improves the charging and discharging efficiency, and the charging and discharging combinations are mutually exclusive, thus avoiding capacitor overvoltage / undervoltage.

[0028] An electrolysis test system. A first DC power supply provides a DC bias (matching the AC amplitude), a second AC power supply outputs a broadband excitation, and a bias module synchronizes the DC component to eliminate phase shift caused by coupling capacitance. The dual power supplies are connected in parallel and superimposed. SiC devices and LCL filtering reduce system losses and improve overall energy efficiency.

[0029] Furthermore, the power module, the inverter module, and the filter module form a cascade link, and the bias module directly samples the DC output of the first power supply; the inverter module and the filter module are physically separated, and the switching noise is attenuated; the bias module tracks the DC power supply voltage in real time to reduce the amplitude matching error.

[0030] In summary, the present invention adopts a combined structure of a single-phase five-level stacked multi-unit converter, an LCL filter, and a bias capacitor, and adopts dynamic selection of redundant switch states to achieve voltage balance of the floating capacitor. It can output a wide-band AC current signal with a superimposed DC bias, and has the technical effects of improving the control accuracy of the electrolysis test power supply, reducing the grid-connected harmonic content, and realizing the superposition capability of high-frequency AC signals.

[0031] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings to be used in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0033] Figure 1 This is a schematic structural diagram of a power supply in an embodiment of the present application; Figure 2 This is another schematic structural diagram of the power supply in the embodiment of the present application; Figure 3 This is a schematic structural diagram of the second power supply in an embodiment of the present application. DETAILED DESCRIPTION

[0034] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0035] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "one side", "one end", "one side" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0036] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0037] It will be understood that when used in this specification and the appended claims, the terms “comprises” and “comprising” indicate the presence of described features, integers, steps, operations, elements and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups thereof.

[0038] It should also be understood that the terms used in the present specification are only for the purpose of describing particular embodiments and are not intended to limit the present invention. As used in the present specification and the appended claims, the singular forms "a", "an", and "the" are intended to include the plural forms unless the context clearly indicates otherwise.

[0039] It should be further understood that the term "and / or" used in the present description and the appended claims refers to and includes any and all possible combinations of one or more of the associated listed items.

[0040] The accompanying drawings illustrate various schematic diagrams of structures according to embodiments disclosed herein. These figures are not drawn to scale; for clarity, some details are exaggerated and some details may be omitted. The shapes of the various regions and layers shown in the figures, as well as their relative sizes and positional relationships, are merely exemplary and may deviate in practice due to manufacturing tolerances or technical limitations. Those skilled in the art may design regions / layers with different shapes, sizes, and relative positions as needed.

[0041] The present invention provides a high-power AC impedance excitation circuit, a control method thereof, and an electrolysis test system. These circuits serve as the AC power source in a high-capacity electrolysis test power supply, providing an AC current signal for impedance testing of an electrolytic cell. The high-power AC impedance excitation circuit comprises a single-phase five-level stacked multi-cell converter, which includes four basic commutation units, each with two cells and two layers. Each basic commutation unit includes a pair of switching transistors in complementary states. The two cells of the single-phase five-level stacked multi-cell converter are connected by a floating capacitor, with each layer having one floating capacitor, for a total of two floating capacitors. Compared to a full-bridge circuit, the multi-level converter reduces the harmonic content of the output current, improves electrolysis efficiency, reduces equipment losses, and enhances the economic efficiency of the electrolysis system. This helps ensure stable operation of the electrolytic cell and reduces electrolysis interruptions or failures caused by voltage fluctuations.

[0042] See also Figure 1 The present invention provides an electrolysis test system, which serves as an AC power supply in a large-capacity electrolysis test power supply, and is used to provide an AC current signal for performing an impedance test on an electrolytic cell; the large-capacity electrolysis test power supply includes a first power supply 1 and a second power supply 2.

[0043] The first power supply 1 is used to be connected to a load L, and the second power supply 2 is also used to be connected to the load L. The first power supply 1 and the second power supply 2 are connected in parallel.

[0044] The first power supply 1 is used to: u A 、 u B 、 u C ) outputs a first direct current and a first alternating current to a load L.

[0045] The second power supply 2 is configured to output the second direct current into a second alternating current to the load L. The second power supply 2 may also be configured to output a bias voltage to the load according to the first direct current.

[0046] The amplitude of the DC voltage generated by the load L according to the first DC current is the same as the amplitude of the bias voltage.

[0047] Optionally, the load L is an electrolytic cell; of course, the load L can also be other types, and this application takes the electrolytic cell as an example for explanation.

[0048] The electrolyzer is driven by the first direct current to produce hydrogen through electrolysis. The electrolyzer can also be driven by the first alternating current and the second alternating current to measure the alternating current impedance of the electrolyzer.

[0049] For example, the frequency range of the first alternating current (which is a sinusoidal current) may be 0.1 Hz to 100 Hz, and the frequency range of the second alternating current (which is a sinusoidal current) may be 100 Hz to 10 kHz.

[0050] Therefore, an AC current of 0.1 Hz to 10 kHz is provided to the load L through the first power supply 1 and the second power supply 2 , and the load L then measures the wide-band AC impedance according to the AC current of 0.1 Hz to 10 kHz.

[0051] In order to improve the stability of the power supply, the power supply includes a plurality of first power supplies connected in parallel and a second power supply, such as Figure 2 The plurality of first power supplies include a first power supply 1-1 to a first power supply 1-N. The first power supply and each second power supply are described with reference to the following: See also Figure 3 In some embodiments, the second power supply 2 includes a power module 21 , an inverter module 22 , a filter module 23 and a bias module 24 .

[0052] The power module 21 is used to generate a second direct current and output it to the inverter module 22; The inverter module 22 is configured to convert the second direct current into a third alternating current and transmit the alternating current to the filter module 23 .

[0053] The filtering module 23 is used to filter the third alternating current and output a second alternating current to the electrolytic cell; The bias module 24 is configured to output a bias voltage to the electrolytic cell according to the first direct current.

[0054] Exemplarily, the first output end of the power module 21 is connected to the first input end of the inverter module 22, and the second output end of the power module 21 is connected to the second input end of the inverter module 22; the output end of the inverter module 22 is connected to the input end of the filter module 23, the second output end of the filter module 23 is connected to the input end of the bias module 24, the first output end of the filter module 23 is connected to the first input end of the electrolytic cell, and the output end of the bias module 24 is connected to the second input end of the electrolytic cell.

[0055] See also Figure 3 In some embodiments, the power supply module 21 includes a voltage source E and a resistor R.

[0056] The first end of the resistor R is connected to the first output end (which can be the positive end) of the voltage source E, the second end of the resistor R serves as the first output end of the power module 21, and the second output end (which can be the negative end) of the voltage source E serves as the second output end of the power module 21.

[0057] See also Figure 3 In other embodiments, the inverter module 22 includes a first basic commutation unit ( ), the second basic commutation unit ( ), the third basic commutation unit ( ), the fourth basic commutation unit ( ), the switching states of a pair of switch tubes in the commutation unit must be strictly complementary. To ensure the normal operation of the SMC, it is required and , and Cannot be turned on at the same time.

[0058] Optionally, the switch tubes in the four basic commutation units all use SiC MOSFETs, which are anti-parallel connected to the diodes.

[0059] C 1 and C 2 is the DC side capacitor, the working voltage is E / 2, O is the DC side midpoint, C 12 and C 11 For a suspension capacitor, the rated voltage is E / 4. DC side upper capacitor C 2's positive electrode and switch tube The source is connected to The gate and upper floating capacitance C 12 The positive electrode is connected to the upper capacitor on the DC side C 2's negative electrode and lower capacitor C 1 is connected to the positive pole, the DC side midpoint O and switch tube The gate of the switch is connected to The source and The source is connected to The gate and upper floating capacitance C 12 The negative pole is connected to the DC side lower capacitor C 1 negative electrode and The gate is connected to The source and lower floating capacitor C 11The negative electrode is connected to the upper floating capacitor C 12 The negative electrode and the lower capacitor C 11 The positive electrode is connected to the upper floating capacitor C 12 The positive electrode and the switching tube The source is connected to the upper floating capacitor C 12 The negative electrode and the switch tube The gate is connected to The source and The source is connected to the lower floating capacitor C 11 The negative electrode and the switch tube The gate of the switch is connected to The gate, The gate and The source of the two terminals are connected together to form the positive terminal of the converter output, and the DC side midpoint O It forms the negative pole of the converter output.

[0060] The present invention provides a control method for a high-power AC impedance excitation circuit, comprising the following steps: Single-phase five-level stacked multi-unit converter output E / 2、 E / 4, 0, - E / 4,- E / 2 has five levels and 9 switch states, among which the output level E / 4,- E / 4 and 0 have two or three redundant switch states respectively. ) is binary coded, where "1" indicates that the switch is on and "0" indicates that it is off.

[0061] When the output level is E / 2, the load current only flows through the outermost switches in the upper layer, and the charge and discharge current of the floating capacitor is 0. When the output level is -E / 2, the load current only flows through the outermost switches in the lower layer, and the charge and discharge current of the floating capacitor is still 0. When the output level is E / 4, the load current flows through the upper switch tubes. At this time, the upper floating capacitor The charge and discharge current is the load current. The direction of the load current and the switch state determine the direction of the charge and discharge current. The switch combination (1011) and (0111) have two switching states on the upper floating capacitor. The charging and discharging effects are opposite; When the output level is When the load current flows through the lower switch tubes, the lower floating capacitor The charge and discharge current is the load current. The direction of the load current and the switch state determine the direction of the charge and discharge current. The switch combination (0001) and (0010) have two switching states on the lower floating capacitor. The charging and discharging effects are opposite.

[0062] When the output level is 0, the switch combination (0101) has no effect on the voltage balance of the floating capacitor because the current only flows through the inner switch tube.

[0063] The stable operation of the stacked multi-unit converter requires ensuring the voltage balance of the suspended capacitor, which depends on the corresponding active balancing control strategy - logical expression; the logical expression control strategy is designed based on carrier stacking modulation.

[0064] In carrier stacking modulation, all carriers are in phase. The resulting harmonics at the phase voltage output carrier frequency concentrate the vast majority of the carrier band's energy, while the harmonic energy in the sidebands is minimal. This carrier harmonic energy is offset between phases during line voltage synthesis, resulting in optimal line voltage harmonic performance, and consequently, optimal line current harmonic performance. Therefore, the logical expression control strategy is designed based on the advantages of carrier stacking modulation.

[0065] The logic expression control strategy is to detect the direction of the load current, sample the voltage of the floating capacitor, calculate the output voltage of the converter, and substitute the values ​​of the variables obtained above into the logic equation to generate the appropriate switching state to achieve the balance of the floating capacitor voltage.

[0066] In the active capacitor voltage balancing technology based on logical expressions, the following parameters need to be defined: (1) (2) (3) in, Indicates the direction of load current; Represents floating capacitance The measured voltage at each sampling moment, Represents floating capacitance The reference voltage at each sampling moment, Represents floating capacitance Deviation from reference voltage The size of Represents the floating capacitor The voltage state, when When , it means that the floating capacitor voltage is higher than the reference voltage value, and the current capacitor is in an overcharge state. When , it means that the floating capacitor voltage is lower than the reference voltage value and the capacitor is currently in an over-discharge state.

[0067] For the single-phase five-level SMC topology, when the output phase voltage is 、 When the voltage is 0, there is only one switch state corresponding to it; When the output phase voltage is and When the level is set, there are two redundant switching states with opposite charging and discharging effects on the floating capacitor, which need to be selected carefully. The output phase voltage of the single-phase five-level SMC is converted to the level function ( , , , , ) to indicate.

[0068] When the output level is When When all switches 、 、 and They must be turned on simultaneously to ensure the correct phase voltage output.

[0069] When the output level is When When the lower switch tube and Must be turned on at the same time, the upper switch tube and The conduction condition of the floating capacitor needs to be determined by the following analysis. The measured voltage is compared to the expected reference voltage By comparison, it can be seen from formulas (2) and (3) that if the measured value is greater than the reference value, that is, , indicating that the floating capacitor needs to be discharged.

[0070] Therefore, when the load current flows in the positive direction, that is, hour, and The switch state is ; When the load current flows in the negative direction, that is, hour, and The switch state is .

[0071] On the other hand, if the measured value is less than the reference value, that is , indicating that the floating capacitor needs to be charged. Therefore, when the load current flows in the positive direction, that is, in formula (1) hour, and The switch state is ; When the load current flows in the negative direction, that is, hour, and The switch state is .

[0072] Summary of switch tube The conduction conditions are as follows: (1) The load current flows in the positive direction The upper floating capacitor needs to be charged , which is expressed in logical expressions as ; (2) The load current flows in the negative direction The upper floating capacitor needs to be discharged when , which is expressed in logical expressions as .

[0073] Switching tube The conduction conditions are as follows: (1) The load current flows in the positive direction The upper floating capacitor needs to be discharged when , which is expressed in logical expressions as ; (2) The load current flows in the negative direction The upper floating capacitor needs to be charged , which is expressed in logical expressions as .

[0074] When the output level is 0, that is, When the upper switch tube and The lower switch tube must be turned off at the same time. and They must be turned on at the same time to ensure the correct phase voltage output.

[0075] When the output level is When When the switch is turned on, the analysis of the output level is same.

[0076] Summary of switch tube The conduction conditions are as follows: (1) The load current flows in the positive direction The lower floating capacitor needs to be charged , which is expressed in logical expressions as ; (2) The load current flows in the negative direction The lower floating capacitor needs to be discharged , which is expressed in logical expressions as .

[0077] Switching tube The conduction conditions are as follows: (1) The load current flows in the positive direction The lower floating capacitor needs to be discharged , which is expressed in logical expressions as ; (2) The load current flows in the negative direction The lower floating capacitor needs to be charged , which is expressed in logical expressions as .

[0078] When the output level is When When all switches 、 、 and They must be turned off simultaneously to ensure the correct phase voltage output.

[0079] In summary, the power switch tube 、 、 and The switching state can be expressed by the following logic equation: (4) (5) (6) (7) In a logic equation, the '+' signifies 'OR', the '×' signifies 'AND', and the '-' sign above a variable signifies 'NOT'.

[0080] The four pairs of switch tubes in the four basic commutation units of the stacked multi-unit converter are all SiC MOSFET devices.

[0081] The AC impedance excitation circuit serves as the AC power source in a large-capacity electrolysis test power supply, and is used to provide an AC current signal for impedance testing of the electrolytic cell.

[0082] The AC power supply in the large-capacity electrolysis test power supply includes an LCL filter and a capacitor C. One end of the LCL filter is connected to the output end of the single-phase five-level stacked multi-unit converter, and the other end is connected to the positive electrode of the electrolytic cell; one end of the capacitor C is connected to the midpoint of the upper and lower layers of the DC side, and the other end is connected to the negative electrode of the electrolytic cell.

[0083] The AC power supply in the large-capacity electrolytic test power supply can achieve wide-band AC impedance measurement based on the output AC current. For example, the AC power supply can provide an AC current of 100 Hz to 10 kHz to the load.

[0084] In some embodiments, the filter module 23 includes a filter inductor L f1 and parasitic resistance R Lf1 , filter capacitor C f and parasitic resistance R Cf , filter inductor L f2 and parasitic resistance R Lf2 .

[0085] filter inductors L f1 The positive pole of the inverter is connected to the positive pole of the inverter output. L f1 The negative electrode and L f2 The positive pole of the filter capacitor C f The positive electrode is connected to C f The negative pole of the inverter is connected to the negative pole of the inverter output. L f2 The negative electrode of the electrolyzer is connected to the positive input terminal of the electrolyzer.

[0086] In some embodiments, the bias module 24 includes a capacitor C and a parasitic resistor R C .

[0087] The positive electrode of capacitor C is connected to the negative electrode of the inverter output terminal, and the negative electrode of C is connected to the negative input terminal of the electrolytic cell.

[0088] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments of 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.

[0089] Existing electrolysis test power supplies suffer from severe harmonic interference and large AC / DC coupling errors. Traditional power supplies utilize an IGBT rectifier topology, and its nonlinear characteristics lead to excessive high-order harmonic content, causing electrolytic cell voltage fluctuations and electromagnetic interference. Furthermore, when the DC bias and AC signal are superimposed, the output coupling capacitor causes phase shift, resulting in impedance measurement errors. Existing technology struggles to achieve stable superposition of broadband AC signals while maintaining high power output, hindering the accurate acquisition of electrochemical impedance spectroscopy in the electrolytic cell.

[0090] To address these issues, a circuit structure is needed that effectively suppresses harmonics and achieves AC / DC decoupling. Analysis of the topological characteristics of multilevel converters reveals that a stacked structure reduces voltage stress on switching devices and minimizes harmonic content in the output waveform. To address the challenge of voltage balance on the floating capacitors, a dynamic adjustment strategy for redundant switching states is employed to ensure stable voltages across the capacitors. To address AC / DC coupling, a combination of an LCL filter and a bias capacitor is introduced to effectively separate high-frequency AC and DC components.

[0091] Therefore, this application proposes a circuit structure comprising a single-phase, five-level stacked multi-unit converter. This converter consists of four basic commutation units, each of which contains a pair of complementary switching transistors. Adjacent units are connected via floating capacitors, with one floating capacitor provided for each layer. The converter output is connected to an LCL filter and bias capacitor to provide a broadband AC signal with a superimposed DC bias to the load.

[0092] Among them, the single-phase five-level stacked multi-unit converter refers to a topology that realizes a five-level output by connecting multiple commutation units in series. Specifically, four basic commutation units can be stacked and connected. Each unit contains two complementary conductive switching tubes, and different voltage steps are generated by controlling the switch state combination. The floating capacitor connection method refers to the connection of the source and gate of the switching tube of adjacent commutation units to the positive and negative poles of the capacitor respectively. Specifically, a metallized film capacitor can be used to bridge between adjacent units to form a natural voltage support point. The LCL filter refers to a filter network composed of two-stage inductors and one-stage capacitors. Specifically, a combination of an iron silicon aluminum core inductor and a polypropylene film capacitor can be used to filter out high-frequency switching harmonics and isolate AC and DC components. The bias capacitor refers to an energy storage element used to superimpose the DC voltage component. Specifically, an electrolytic capacitor parallel structure can be used, connected between the output end of the converter and the load.

[0093] Specifically, the four basic commutation units are connected in series step by step through the floating capacitor, and the complementary switch tubes in each unit are alternately turned on to form a current path. When the switch tube of the upper unit is turned on, the lower unit forms a freewheeling loop through the floating capacitor to achieve a five-level voltage output. The first inductor of the LCL filter is connected in series with the positive pole of the converter output, and forms a low-pass filter network with the parallel capacitor and the second inductor, which effectively suppresses the transmission of high-frequency harmonics to the load side. The bias capacitor is connected in parallel between the negative pole of the output end and the load, and the DC bias voltage is maintained stable by charging and discharging the capacitor. The floating capacitor adjusts the charge and discharge by dynamically selecting the redundant switch state. When it is detected that the capacitor voltage deviates from the set value, the switch combination is switched according to the current direction to achieve voltage balance.

[0094] Compared with existing technologies, traditional IGBT rectifier circuits use a two-level output structure, which has a large voltage jump amplitude and high harmonic content. However, this solution reduces the voltage step amplitude to one-fourth of the traditional structure through a five-level stacked structure, significantly reducing current ripple. Existing technologies use LC filters to process harmonics, which cannot effectively isolate AC and DC components. After introducing LCL filters, this solution uses the synergistic effect of two-stage inductors and capacitors to filter out high-frequency harmonics while achieving decoupled transmission of AC signals and DC bias. In traditional solutions, the voltage balance of the suspended capacitor relies on a passive voltage equalization circuit. This solution actively adjusts the capacitor charging and discharging process while maintaining the output voltage by dynamically selecting redundant switch states.

[0095] Through the above technical solution, this application effectively reduces the harmonic content of the output current, reduces the measurement error caused by AC / DC coupling, and achieves a stable superposition of broadband AC signals and DC bias. This circuit structure can meet the demand for broadband impedance excitation signals in high-power electrolysis testing scenarios and provides the hardware foundation for accurately obtaining the electrochemical impedance spectrum of the electrolytic cell.

[0096] The present application further proposes that the switch tubes in the basic commutation unit adopt SiC MOSFET devices, and each switch tube is anti-parallel connected with a diode.

[0097] SiC MOSFET devices are metal-oxide semiconductor field-effect transistors made of silicon carbide. They are typically implemented in models with low on-resistance and high switching speeds. Their wide bandgap allows for stable operation in high-temperature environments. Antiparallel diodes are diode elements connected in reverse parallel across the switch. These diodes can be implemented as Schottky barrier diodes integrated into the SiC MOSFET chip package, providing a freewheeling path for inductive load current during the switch's off period.

[0098] Specifically, in a single-phase, five-level stacked multi-unit converter, each basic commutation unit utilizes SiC MOSFET devices instead of traditional silicon-based IGBTs or MOSFETs, enabling it to withstand higher operating temperatures and faster switching speeds. When the converter switches at high frequencies, the fast switching characteristics of the SiC MOSFET effectively reduce switching losses, while its low on-resistance reduces conduction losses. The anti-parallel diode automatically conducts at the moment the switch is turned off, preventing damage to the device caused by voltage spikes caused by sudden changes in inductive load current and ensuring current continuity in the commutation unit during charging and discharging.

[0099] Compared to existing technologies, traditional electrolysis test power supplies generally use silicon-based power devices. Their switching frequency is limited by device characteristics, resulting in high harmonic content. Furthermore, the separate placement of the freewheeling diode and the main switch can easily generate parasitic inductance. This solution, by integrating SiC MOSFETs with anti-parallel diodes, not only increases the upper switching frequency limit but also reduces loop inductance through optimized device packaging.

[0100] Through the above technical solution, this application can significantly reduce switching losses and electromagnetic interference during converter operation, improving the waveform quality of the system's broadband AC signal output. Furthermore, the integrated design of anti-parallel diodes effectively suppresses voltage oscillations during commutation, ensuring the stability of the suspended capacitor voltage balance control and providing a more accurate current excitation signal for electrolytic cell impedance testing.

[0101] The present application further proposes that the rated voltage of the suspension capacitor is 1 / 4 of the DC side voltage.

[0102] The suspended capacitor is an energy storage element connected in series between adjacent basic commutation units. Specifically, it can be implemented using a metallized polypropylene film capacitor. Its positive and negative electrodes are connected to the source and gate of adjacent switching transistors, respectively, to balance the potential difference between the commutation units. The rated voltage is set based on the ratio of the total DC side voltage to the number of commutation unit levels. By limiting the suspended capacitor voltage to 1 / 4 of the DC side voltage, it ensures that each commutation unit experiences balanced voltage stress.

[0103] Specifically, in a single-phase five-level stacked multi-unit converter, four basic commutation units are connected in series via a floating capacitor to form a five-level output structure. Each floating capacitor is connected between two adjacent commutation units, and its voltage value directly affects the conduction state of the switch tube and the system harmonic characteristics. When the rated voltage of the floating capacitor is set to 1 / 4 of the DC side voltage, the voltage distribution of each commutation unit forms a strict correspondence with the switching timing, so that the floating capacitor always maintains the target voltage value during the charging and discharging process, avoiding level distortion caused by voltage offset. This voltage proportional relationship ensures that the charging and discharging rate of the floating capacitor remains synchronized with the switching frequency when a wide-band AC signal is output through a hierarchical voltage distribution mechanism.

[0104] Compared to existing technologies, traditional multilevel converters lack a clear proportional relationship between the floating capacitor voltage and the DC link voltage, resulting in cumulative deviations in the capacitor voltage as load fluctuates. This solution, however, limits the rated voltage of the floating capacitor to 1 / 4 of the DC link voltage, establishing mathematical constraints for voltage distribution. This ensures that the capacitor voltage remains stable under dynamic conditions, thereby reducing phase shift and noise interference during AC / DC coupling.

[0105] Through the above technical solution, the present application effectively solves the problem of AC measurement error caused by AC-DC coupling. By precisely controlling the voltage of the suspended capacitor, the influence of switching noise of power electronic devices on high-frequency impedance measurement is reduced, providing a stable broadband AC excitation environment for the accurate measurement of the electrochemical impedance spectrum of the electrolytic cell.

[0106] The present application further proposes a high-power AC impedance excitation circuit, in which the first filter inductor of the LCL filter is connected to the positive output terminal of the single-phase five-level stacked multi-unit converter; after the second filter inductor is connected in parallel with the filter capacitor, its first end is connected to the second end of the first filter inductor, and its second end is connected to the positive pole of the electrolytic cell, and the bias capacitor is connected to the negative output terminal of the single-phase five-level stacked multi-unit converter and the negative pole of the electrolytic cell.

[0107] Among them, the LCL filter refers to a low-pass filter composed of two inductors and one capacitor. Specifically, it can be implemented using a ferrite core inductor and a metallized polypropylene film capacitor. It is used to filter out high-frequency switching harmonics and suppress current mutations.

[0108] The bias capacitor refers to an energy storage element used to carry the DC component, and can be specifically implemented as an electrolytic capacitor, which is used to block the DC component in the AC signal path and maintain the stability of the DC bias voltage.

[0109] Specifically, the broadband AC current output by the single-phase five-level stacked multi-unit converter enters the LCL filter through the first filter inductor. The parallel branch formed by the second filter inductor and filter capacitor further filters out high-frequency harmonic components, ultimately delivering the filtered AC current to the positive electrode of the electrolytic cell. A bias capacitor is connected between the negative electrode of the converter output and the negative electrode of the electrolytic cell, forming an independent DC bias circuit, which physically isolates the AC excitation signal from the DC bias voltage at both ends of the electrolytic cell.

[0110] Compared to existing technologies, traditional electrolytic test systems typically use a single inductor filter without a bias capacitor, resulting in direct coupling of AC and DC signals in the transmission path. This leads to phase shift in the AC measurement signal due to interference from the DC component. This solution uses a multi-stage LCL filter structure to reduce residual high-frequency harmonics. It also utilizes a bias capacitor to block the DC component from penetrating the AC measurement loop, achieving decoupled transmission of AC and DC signals at the circuit topology level.

[0111] Through the above technical solution, the present application effectively suppresses the phase shift and signal aliasing caused by AC / DC coupling, so that the amplitude and phase of the high-frequency AC excitation signal at both ends of the electrolytic cell remain stable, providing a pure test signal environment for accurately obtaining the electrochemical impedance spectrum of the electrolytic cell.

[0112] The present application further proposes that the frequency of the output AC current of the single-phase five-level stacked multi-unit converter is 100 Hz to 10 kHz.

[0113] The AC current frequency range refers to the adjustable frequency band of the inverter's output current signal. This is achieved using carrier stacking modulation technology, which generates AC components of varying frequencies by adjusting the carrier frequency and modulation wave parameters. This frequency band covers the high-frequency range required for electrochemical impedance spectroscopy testing of electrolyzers, meeting the requirements for monitoring proton exchange membrane aging.

[0114] Specifically, the converter generates a five-level staircase waveform under the complementary action of the switching tubes through time-sharing conduction control of the multi-unit topology. During the carrier modulation process, the fundamental frequency is controlled in the range of 100Hz to 10kHz. The low frequency band is used to maintain the stability of the electrolyzer operation, and the high frequency band is used to stimulate the charge transfer response at the membrane electrode interface. For example, when it is necessary to detect the impedance characteristics above 10kHz, the harmonic components of the converter output current can penetrate the double-layer structure of the electrolyzer, where the fundamental frequency is set close to the target test frequency, and the high-frequency carrier component is used to realize the impedance spectrum data acquisition.

[0115] Compared with existing technologies, traditional electrolysis power supplies are limited by IGBT switching losses and topological constraints, with an AC output frequency limit typically below 1kHz, making them unable to meet the high-frequency impedance testing requirements associated with proton exchange membrane aging characteristics. This solution utilizes a stacked multi-unit structure to reduce stress on individual switching transistors. Combined with suspended capacitor voltage balance control, this solution extends the output current frequency to 10kHz, effectively capturing microscopic failure characteristics of electrolyzers.

[0116] Through the above technical solution, this application solves the problem of excessive error in measuring the electrode-electrolyte interface impedance under high current conditions. Through the broadband AC excitation signal output capability, the detection accuracy of the charge transfer impedance inside the electrolytic cell is improved, providing a reliable data basis for catalyst activity evaluation.

[0117] The present application further proposes a high-power AC impedance excitation circuit control method, including the following steps: generating a five-level output and nine switch state combinations based on carrier stacking modulation; detecting the load current direction and the suspension capacitor voltage in real time; dynamically selecting redundant switch states according to the output voltage level, load current direction and suspension capacitor voltage state to achieve suspension capacitor voltage balance, specifically including: when the output level is ±E / 4, selecting the charge and discharge switch combination according to the current direction and capacitor voltage deviation; when the output level is 0, using a fixed switch combination.

[0118] Among them, carrier stacking modulation refers to the technology of using multiple in-phase carriers for signal modulation. Specifically, a triangle wave or a sawtooth wave can be used as the carrier signal. By adjusting the carrier phase relationship, a multi-level output waveform is generated. This technology can effectively reduce switching losses and improve the output waveform quality. Redundant switching state refers to the existence of multiple switch tube conduction combinations at the same output voltage level. Specifically, the charge and discharge control of the floating capacitor can be achieved by switching different switch tube combinations, thereby providing adjustment freedom for voltage balance. The voltage balance of the floating capacitor refers to maintaining the voltage of each floating capacitor within the set value range by controlling the charge and discharge path under different switching states. Specifically, the switch combination can be dynamically adjusted according to the current direction and voltage deviation to avoid output distortion caused by capacitor voltage imbalance.

[0119] Specifically, under the five-level output condition, after the target level is determined by carrier stacking modulation, the load current direction and the floating capacitor voltage state are collected in real time. When the output level is at ±E / 4, the conduction mode that can charge or discharge the target capacitor is selected from the redundant switch combination according to the positive or negative current direction and the deviation direction of the capacitor voltage. For example, if the upper floating capacitor voltage is detected to be lower than the rated value in the positive current direction, the switch combination that puts the capacitor in the charging circuit is selected; if the voltage is higher than the rated value, it is switched to the discharge circuit. When the output level is 0, a fixed switch combination is used to avoid invalid switching of the capacitor voltage, thereby maintaining system stability. The control logic ensures that the floating capacitor voltage is always within a controllable range by dynamically adjusting the charging and discharging path.

[0120] Compared with existing technologies, traditional control methods typically use fixed switching strategies or a single redundant state selection mechanism, which cannot dynamically adjust the charge and discharge paths according to real-time operating conditions, resulting in voltage imbalance in the suspended capacitor and output waveform distortion. This method, however, establishes a correlation model between output voltage level, current direction, and capacitor voltage state to achieve multi-dimensional parameter coordinated control. It can automatically match the optimal switching combination under different operating conditions, effectively solving the problem of capacitor voltage fluctuation under high-power conditions.

[0121] Through the above technical solution, the present application realizes the precise balance control of the suspended capacitor voltage, suppresses the output harmonic distortion caused by voltage imbalance, and at the same time ensures the stability of the broadband AC signal output by dynamically selecting the redundant switching state, providing a high-precision excitation signal basis for the electrolytic cell impedance spectrum measurement.

[0122] The present application further proposes that when the output level is a specific value, the lower switch tubes and are turned on at the same time, and the conduction condition of the upper switch tube is: when the load current flows in a positive direction, the upper floating capacitor is charged; when the load current flows in a negative direction, the upper floating capacitor is discharged; The conduction condition of the upper switch tube is: when the load current flows in a positive direction, the upper floating capacitor is discharged; when the load current flows in a negative direction, the upper floating capacitor is charged.

[0123] The lower-level switch tube refers to the power semiconductor device located at the bottom of the circuit topology. Specifically, it can be implemented using a SiC MOSFET device, and its conduction state is directly driven by a control signal. The upper-level switch tube refers to the power semiconductor device located in the upper layer of the circuit topology. Specifically, it can be implemented by connecting an anti-parallel diode in parallel with the switch tube to construct a multi-level output path. The load current flow direction refers to the direction of the current flowing through the electrolytic cell. Specifically, it can be detected in real time by a Hall sensor to determine the direction of energy flow. The suspended capacitor refers to the energy storage element connected between adjacent commutation units. Specifically, it can be implemented using a metallized film capacitor. Its charge and discharge state is related to the action of the switch tube.

[0124] Specifically, when the output level is in a specific range, the lower switch tube remains continuously turned on to establish a basic current path. When the load current flows in the forward direction, the conduction of the upper switch tube will guide the current to charge the upper floating capacitor. At this time, the capacitor voltage rises to compensate for energy loss; when the load current flows in the reverse direction, the conduction of the same switch tube will cause the capacitor to enter a discharge state, thereby maintaining voltage balance. For the other set of upper switch tubes, their conduction logic is inversely related to the current direction. When the current is forward, they actively release the energy stored in the capacitor, and when the current is reversed, they turn to absorb energy. This bidirectional energy regulation mechanism dynamically adjusts the charging and discharging timing by matching the current direction and the capacitor state in real time.

[0125] Compared with existing technologies, traditional control methods use only fixed switch combinations under AC / DC coupling conditions, making it impossible to adjust the charging and discharging strategy based on real-time operating conditions, resulting in increased voltage fluctuations in the suspended capacitor. This solution establishes a dynamic mapping between current direction and switch state, actively adjusting capacitor energy while maintaining multi-level output, effectively suppressing the increase in harmonic components caused by voltage imbalance.

[0126] Through the above technical solution, the present application can significantly reduce the impact of phase offset on impedance measurement during AC / DC coupling, especially when working in the high-frequency band. By precisely controlling the charging and discharging timing of the suspended capacitor, the aliasing interference of switching noise and excitation signal is reduced, thereby improving the accuracy of the electrolytic cell impedance spectrum measurement data.

[0127] The present application further proposes a high-power AC impedance excitation circuit control method. When the output level is E / 4, the conduction conditions of the switch tubes Q5 and Q6 are: when the load current flows in a positive direction, the lower floating capacitor is charged; when the load current flows in a negative direction, the lower floating capacitor is discharged; the conduction conditions of the switch tubes Q7 and Q8 are: when the load current flows in a positive direction, the lower floating capacitor is discharged; when the load current flows in a negative direction, the lower floating capacitor is charged.

[0128] The output level of E / 4 means that the voltage amplitude at the converter output relative to the reference point is one-quarter of the DC side voltage. This can be achieved by using the level division method in multi-level modulation technology. The level value corresponds to the output voltage state under a specific switch combination.

[0129] The lower floating capacitor refers to an energy storage element located in the lower layer of the converter structure, which can be implemented by a metallized film capacitor. Its voltage state is adjusted by the switching action of the adjacent commutation unit.

[0130] Among them, when the load current flows in a positive direction, it means that the current flows from the positive electrode of the converter output end to the positive electrode of the electrolytic cell. Specifically, this can be achieved by using a Hall current sensor to detect the polarity. This direction determines the energy flow path of the capacitor charging and discharging.

[0131] Specifically, when the converter output level is in the E / 4 state, the conduction combination of Q5-Q8 switches is dynamically selected by detecting the load current direction and combining it with the real-time voltage state of the lower floating capacitor. When the load current flows in the forward direction, Q5 and Q6 are turned on to connect the lower floating capacitor to the charging circuit, using the positive component of the current to replenish the capacitor's energy. When the current direction reverses, Q7 and Q8 are switched on, allowing the capacitor to discharge through the load circuit to maintain voltage balance. This control logic ensures that the lower floating capacitor voltage remains stable at the set operating point by matching the current direction with the capacitor's charging and discharging requirements in real time.

[0132] Compared to existing technologies, traditional methods, with fixed switch combinations, cannot dynamically adjust the capacitor charge and discharge paths based on current direction, causing suspended capacitor voltage fluctuations to exceed the permitted range. This solution achieves closed-loop regulation of the capacitor voltage by establishing a direct mapping between current direction and switch state, effectively suppressing voltage offsets caused by sudden changes in current direction.

[0133] Through the above technical solution, this application solves the measurement error problem caused by the instability of the floating capacitor voltage in the AC-DC coupling scenario. By dynamically adjusting the charging and discharging path of the floating capacitor, it ensures that the multi-level converter maintains capacitor voltage balance when outputting a wide-band AC signal, thereby reducing the impact of phase offset and switching noise on the impedance measurement accuracy.

[0134] The present application further proposes that carrier stacking modulation adopts an in-phase carrier.

[0135] In-phase carriers refer to multiple carrier signals with the same phase angle. This can be achieved using sine or triangular wave signals with the same frequency and zero phase difference. During carrier stacking modulation, in-phase carriers are superimposed to form a composite modulated signal with continuous phase characteristics, which effectively reduces high-frequency harmonic components.

[0136] Specifically, during the five-level output generation process, the phase consistency of the in-phase carrier ensures that the switching actions of each basic commutation unit maintain synchronous timing. When the modulated wave is compared with the in-phase carrier, the rising and falling edges of the switch tube trigger pulse are completely aligned on the time axis, and the resulting level jump process does not introduce additional phase differences. This synchronous triggering mechanism causes the high-order harmonic components of the output voltage waveform to be concentrated near integer multiples of the carrier frequency, facilitating targeted attenuation by the LCL filter. For example, when generating nine switching state combinations of ±E / 4 and 0 levels, the in-phase carrier ensures that the duration of the charging and discharging process of each floating capacitor is strictly matched, avoiding cumulative deviations in capacitor voltage due to phase differences.

[0137] In some specific implementations, the in-phase carrier wave can use a triangular wave as its base waveform, with its peak and valley values ​​corresponding to the on and off thresholds of the switching transistors, respectively. When the amplitude of the modulated wave exceeds the carrier wave amplitude, the system automatically switches to the switching state combination corresponding to the adjacent level. At this time, the phase consistency of the in-phase carrier wave maintains the symmetry of the operating state of each commutation unit.

[0138] Compared to existing technologies, traditional carrier stacking modulation often uses phase-shifted carrier technology, which has a fixed phase difference between carrier signals. While phase-shifted carriers can disperse harmonic energy, they can cause misalignment in the switching timing, creating asymmetric current paths during the charging and discharging of the suspended capacitor. This solution's in-phase carrier eliminates phase differences, simplifying control logic and reducing the complexity of capacitor voltage balance regulation, while also avoiding harmonic aliasing caused by phase shifts.

[0139] Through the above technical solution, the present application effectively suppresses the high-frequency harmonic interference generated during the switching process of power electronic devices, reduces the phase offset error caused by AC / DC coupling, and significantly improves the analysis accuracy of the real and imaginary parts of the electrolytic cell impedance spectrum measurement results, providing a reliable data basis for accurately evaluating the aging status of the proton exchange membrane.

[0140] The present application further proposes an electrolysis testing system, comprising a first power supply and a second power supply connected in parallel, wherein the output ends of the first power supply and the second power supply are both connected to an electrolytic cell, and the DC bias voltage matches the AC signal amplitude; the second power supply adopts a high-power AC impedance excitation circuit including a single-phase five-level stacked multi-unit converter; the first power supply outputs a first DC current and a DC bias voltage to the electrolytic cell according to the three-phase AC voltage, and the second power supply provides a broadband AC current for impedance testing.

[0141] The parallel connection of the first and second power supplies refers to two independent power supply devices that are electrically connected to jointly output power to the electrolyzer. This can be achieved using a dual-bus parallel structure, with independent control circuits regulating the DC and AC components. This structure prevents coupling of AC and DC signals within the same circuit, thereby reducing phase offset errors.

[0142] Matching the DC bias voltage to the AC signal amplitude means that the peak voltage of the AC signal does not exceed a set percentage of the DC bias voltage. This can be achieved through closed-loop voltage control, for example, by limiting the AC signal amplitude to within 10% of the DC bias voltage. This matching relationship suppresses the attenuation effect of the coupling capacitor on the AC measurement signal.

[0143] The single-phase five-level stacked multi-unit converter is a power electronics topology consisting of multiple cascaded commutation units. Specifically, a commutation unit consisting of four switching transistors and a floating capacitor achieves a five-level output. This topology uses multi-level modulation to reduce output harmonics, thereby minimizing electromagnetic interference (EMI) on the electrolyzer.

[0144] Specifically, the first power supply converts AC power into DC power through a three-phase rectifier circuit and provides a stable DC bias voltage and main operating current to the electrolytic cell. The second power supply generates a broadband AC signal based on a five-level converter. This signal is filtered through an LCL filter to remove high-frequency switching noise and then superimposed on the electrolytic cell. Because the output terminals of the two power supplies are directly connected in parallel to the positive and negative poles of the electrolytic cell, the DC bias voltage is independently provided by the first power supply, while the AC excitation signal is output separately by the second power supply. The two achieve voltage superposition at the electrolytic cell end but separate current paths. This design prevents the AC signal from flowing through the filter capacitor of the first power supply during transmission, thereby avoiding the phase offset problem introduced by the μF coupling capacitor.

[0145] Compared to existing technologies, traditional electrolysis test systems use a single power supply to output both DC and AC components. This results in AC and DC signals sharing the same power electronic converter and filtering circuit. This causes the high-frequency AC component to charge and discharge the DC-side capacitor, leading to impedance measurement errors. This solution uses independent power supplies to perform the DC bias and AC excitation functions, fundamentally eliminating the AC / DC coupling path. It also leverages the low harmonic characteristics of the five-level converter to reduce the impact of high-frequency interference on the electrolytic cell.

[0146] Through the above technical solution, the present application can realize the physical isolation transmission of DC bias voltage and AC excitation signal, effectively suppress the phase shift and harmonic aliasing problems caused by coupling capacitance, thereby improving the measurement accuracy of electrolytic cell impedance spectrum; at the same time, the dual power supply parallel structure supports synchronous testing of multiple electrolytic cells, and meets the test requirements under different working conditions by independently adjusting the output parameters of each power supply.

[0147] In summary, the present invention provides a high-power AC impedance excitation circuit, a control method thereof, and an electrolysis test system. Through a five-level stacked converter and dynamic capacitor balancing control, the five-level step output is combined with LCL filtering to reduce THD and eliminate the electrolytic cell voltage fluctuation and membrane electrode overheating risk caused by high-order harmonics; μs-level capacitor voltage control based on logical expressions achieves 100Hz-10kHz wide-band AC output, amplitude error <1mV, frequency resolution 1Hz, and accurately captures the proton exchange membrane >10kHz aging characteristics; the dual-power parallel architecture compresses phase offset, reduces impedance measurement error, and solves the spectrum distortion problem caused by coupling capacitance; the full SiC MOSFET device makes the load switching response <10ms, and the current sharing error of multiple electrolytic cells in parallel <3%, meeting the millisecond-level power tracking requirements of wind-solar coupling scenarios.

[0148] The above content is only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A high-power AC impedance excitation circuit, characterized in that: The single-phase five-level stacked multi-unit converter comprises four basic commutation units, each of which comprises a pair of complementary conductive switching tubes; adjacent basic commutation units are connected via suspension capacitors, with one suspension capacitor provided on each layer, for a total of two suspension capacitors, with the positive and negative poles of the suspension capacitors respectively connected to the source and gate electrodes of the switching tubes of adjacent basic commutation units; The output end of the single-phase five-level stacked multi-unit converter is connected to an LCL filter and a bias capacitor for providing a broadband AC current signal with a superimposed DC bias to the load.

2. The high-power AC impedance excitation circuit according to claim 1, characterized in that: The switching tubes in the basic commutation unit use SiC MOSFET devices, and each switching tube is connected in anti-parallel with a diode.

3. The high-power AC impedance excitation circuit according to claim 1, characterized in that: The rated voltage of the suspension capacitor is 1 / 4 of the DC side voltage.

4. The high-power AC impedance excitation circuit according to claim 1, characterized in that: The first filter inductor of the LCL filter is connected to the positive pole of the output end of the single-phase five-level stacked multi-unit converter; after the second filter inductor is connected in parallel with the filter capacitor, its first end is connected to the second end of the first filter inductor, and its second end is connected to the positive pole of the electrolytic cell; the bias capacitor is connected to the negative pole of the output end of the single-phase five-level stacked multi-unit converter and the negative pole of the electrolytic cell.

5. The high-power AC impedance excitation circuit according to claim 1, characterized in that: The single-phase five-level stacked multi-unit converter outputs an AC current with a frequency of 100 Hz to 10 kHz.

6. A high-power AC impedance excitation circuit control method, applied to the circuit according to any one of claims 1 to 5, characterized in that: The following steps are involved: Generate five-level output and nine switch state combinations based on carrier stack modulation; Real-time detection of load current direction and suspension capacitor voltage; Dynamically select redundant switch states based on the output voltage level, load current direction, and floating capacitor voltage state to achieve floating capacitor voltage balance. Specifically, the following steps are performed: When the output level is ±E / 4, the charge and discharge switch combination is selected according to the current direction and the capacitor voltage deviation; When the output level is 0, a fixed switch combination is used.

7. The high-power AC impedance excitation circuit control method according to claim 6, characterized in that: When the output level is When the lower switch tube and At the same time, the upper switch tube The conduction condition is: when the load current flows in the positive direction, the upper floating capacitor is charged; When the load current flows in the negative direction, the upper floating capacitor is discharged; Upper switch tube The conduction condition is: when the load current flows in the positive direction, the upper floating capacitor is discharged; When the load current flows in the negative direction, the upper floating capacitor is charged.

8. The high-power AC impedance excitation circuit control method according to claim 7, characterized in that: When the output level is When the switch The conduction condition is: when the load current flows in the positive direction, the lower floating capacitor is charged; When the load current flows in the negative direction, the lower floating capacitor is discharged; Switching tube The conduction conditions are: When the load current flows in the positive direction, the lower floating capacitor is discharged; When the load current flows in the negative direction, the lower floating capacitor is charged.

9. The high-power AC impedance excitation circuit control method according to claim 6, characterized in that: Carrier stacking modulation uses the same-phase carrier.

10. An electrolysis testing system, characterized in that: include: A first power supply (1) and a second power supply (2) are connected in parallel, the output ends of the first power supply (1) and the second power supply (2) are both connected to the electrolytic cell, and the DC bias voltage matches the AC signal amplitude; the second power supply (2) adopts the high-power AC impedance excitation circuit described in any one of claims 1 to 5; The first power supply (1) outputs a first direct current and a direct current bias voltage to the electrolytic cell according to the three-phase alternating current voltage, and the second power supply (2) provides a broadband alternating current for impedance testing.

11. The electrolysis testing system according to claim 10, characterized in that: The second power supply (2) comprises: A power module (21) is used to generate a second direct current and output the second direct current to the inverter module (22); An inverter module (22) is used to convert the second direct current into a third alternating current and transmit the third alternating current to the filter module (23); A filtering module (23) is used to filter the third alternating current and output a second alternating current to the electrolytic cell; The bias module (24) is used for converting the first DC current output into a bias signal having the same amplitude as the DC bias voltage and transmitting the bias signal to the negative electrode of the electrolytic cell.

12. The electrolysis testing system according to claim 11, characterized in that: The bias module (24) includes a capacitor C, the positive electrode of the capacitor C is connected to the negative electrode of the output end of the inverter module (22), and the negative electrode is connected to the negative electrode of the electrolytic cell, and is used to convert the first direct current into a constant amplitude bias voltage.

13. The electrolysis testing system according to claim 10, characterized in that: The system supports parallel testing of multiple electrolyzers.

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