A method for power balance and optimal voltage control in photovoltaic electrolysis of alkaline water for hydrogen production

Abstract

This invention proposes a power balance and optimal voltage control method for photovoltaic electrolysis of alkaline water to produce hydrogen, specifically for independent photovoltaic hydrogen production power equipment. It includes a main power topology circuit and a control algorithm. Addressing the fluctuating power characteristics of independent photovoltaic power generation, this invention achieves optimal efficiency in alkaline water electrolysis for hydrogen production under constant power conditions. Based on maximum power point tracking (MPPT) power balance control of the photovoltaic array, and utilizing the nonlinear characteristics of the electrolyzer current and voltage, the electrolysis efficiency model, and its principles, the invention automatically optimizes the electrolysis voltage waveform to achieve optimal hydrogen production efficiency under constant power conditions. This invention relates to algorithms for maximum power point tracking power balance control, electrolysis efficiency optimization, and smooth variation control of equal-power voltage waveforms.

Description

Technical Field

[0001] This invention belongs to the field of new energy technology, and in particular relates to a method for power balance and optimal voltage control in photovoltaic electrolysis of alkaline water for hydrogen production. Background Technology

[0002] In recent years, hydrogen energy application technologies have developed rapidly. Photovoltaic hydrogen production is a typical green hydrogen production method, and alkaline water electrolysis is also a relatively mature technology that has been widely used in industry. Currently, mainstream photovoltaic hydrogen production uses alkaline water electrolysis. Conventional alkaline water electrolysis systems use regulated power supplies, with power coming from the grid. Although there are many photovoltaic hydrogen production demonstration cases, their electrolysis power supplies are actually conventional regulated electrolysis power supplies. Because the electrolysis voltage does not change and needs to be stable, it must rely on the stability of the grid voltage. The claimed source of photovoltaic hydrogen production power is merely the distribution of photovoltaic power flow. For independent photovoltaic power generation that does not rely on the grid, its power supply has random variations or fluctuations over a large range. Conventional photovoltaic array DC / DC maximum power point tracking and power balance control generally achieve power balance by adjusting the electrolysis voltage of the alkaline electrolyzer, and this voltage must be DC and lower than the optimal DC voltage for electrolysis. Because the IV characteristic of the electrolyzer is nonlinear, under low voltage and equal power conditions, the charge-to-hydrogen conversion efficiency is not necessarily optimal, and a large portion may result in heat loss, meaning the hydrogen ion replacement efficiency is not at its optimal point. This invention achieves optimal voltage waveform control for hydrogen production through electrolysis based on the characteristics of electrolyzer IV, under the smooth voltage waveform transformation of maximum power point tracking and power balance control. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention provides a method for power balance and optimal voltage control in photovoltaic electrolysis of alkaline water for hydrogen production. This method achieves circuit topology and optimal voltage control for photovoltaic electrolysis of alkaline water for hydrogen production, taking into account real-time changes in photovoltaic power.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] A method for power balance and optimal voltage control in photovoltaic electrolysis of alkaline water for hydrogen production is disclosed. Under independent photovoltaic power supply conversion conditions, based on the nonlinear characteristics of the current and voltage of the electrolyzer and the electrolysis efficiency model and principle of the electrolyzer, a main power topology circuit and a secondary topology circuit are designed for the photovoltaic electrolysis of alkaline water for hydrogen production system. Part A of the circuit topology is the main power topology circuit, and part B is the secondary topology circuit. Part A of the circuit topology consists of a second DC / DC converter connected in parallel with the first DC / DC converter in part B of the circuit topology via a power transistor Qa and a series diode D1, and then connected to the electrolyzer through an inductor L1. The method controls and adjusts the voltage at output point a of part A, the voltage at output point b of part B, the voltage width at output point a of part A, and the waveform period T to automatically adjust the stepped electrolysis voltage waveform, thereby optimizing the efficiency of hydrogen production through electrolysis.

[0006] Furthermore, when the power of the photovoltaic array is less than the power of the electrolytic cell, while performing maximum power point tracking, the voltage at output point a of part A of the circuit topology and the voltage at output point b of part B of the circuit topology are stabilized, and the duty cycle of the power transistor Qa is adjusted to achieve the change in the average power of the load and achieve power balance.

[0007] Furthermore, the voltage stability and power balance of the photovoltaic array are controlled by the change of the duty cycle of the power transistor Qa. When the power transistor Qa is closed, the voltage output at point a of part A of the circuit topology increases, and the current of the electrolytic cell rises. When the power transistor Qa is open, part B of the circuit topology maintains the amount of reactive charge in the electrolytic cell, coordinating the control of part A of the circuit topology to achieve control of the electrolytic current waveform.

[0008] Furthermore, when the maximum power of the photovoltaic array is greater than the power of the electrolytic cell, the maximum power point tracking automatically stops, the voltage of output point a of part A of the circuit topology remains unchanged and does not exceed the optimal voltage value of the electrolytic cell, the duty cycle of power transistor Qa reaches its maximum value, at which point the load power is at its maximum, and the actual power of the photovoltaic array is balanced with the load power.

[0009] Furthermore, when the actual power of the photovoltaic array reaches a balance with the load power, the photovoltaic electrolysis alkaline water hydrogen production system, based on the current operating state, while ensuring power balance, fine-tunes the voltage of output point a in part A of the circuit topology, the voltage of output point b in part B of the circuit topology, and the duty cycle of power transistor Qa through modeling lookup or automatic search, in order to improve hydrogen production efficiency.

[0010] The advantages of this invention are:

[0011] (1) The present invention can quickly find the power balance point between photovoltaic array and electrolysis of alkaline water to produce hydrogen.

[0012] (2) Based on the smooth transformation of voltage waveform, the present invention stabilizes the voltage of photovoltaic array and adjusts the system working status in real time to achieve the optimal efficiency of electrolysis hydrogen production. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the circuit topology of the present invention;

[0014] Figure 2 This is a model diagram of the IV curve of the electrolytic cell of the present invention;

[0015] Figure 3 This is a schematic diagram illustrating the effect of duty cycle on main and auxiliary voltages when the photovoltaic array power changes according to the present invention;

[0016] Figure 4 This is a schematic diagram illustrating the effect of the PWM1 duty cycle change on hydrogen production efficiency. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0018] To achieve optimal hydrogen production efficiency under independent photovoltaic power generation conversion conditions, this invention proposes a photovoltaic electrolysis alkaline water hydrogen production power balance and optimal voltage control method, which is a four-parameter adjustable stepped electrolysis voltage waveform generation method. The embodiments of this invention are described below with reference to the accompanying drawings.

[0019] Figure 1 This is a circuit topology according to an embodiment of the present invention. Part A of the circuit topology is the main power topology circuit, and part B of the circuit topology is the sub-topology circuit. Part A of the circuit topology consists of a second DC / DC converter 2 connected in parallel with the first DC / DC converter 1 in part B of the circuit topology via a power transistor Qa and a series diode D1. Then, it passes through an inductor L1 and is connected to an electrolytic cell to achieve array power balance control.

[0020] Figure 2 This is the IV (current-voltage) curve of the electrolytic cell. As shown in the graph, when the voltage across the electrolytic cell is less than the initial inflection point holding voltage e... rev When the current changes little, it increases only slightly when the voltage exceeds the initial inflection point holding voltage e. revSubsequently, as the voltage increases, the electrolytic current increases. The output point a of part A of the circuit topology is controlled at the optimal electrolytic voltage point, which remains constant when the array power is greater than the rated electrolytic cell power. At this time, the electrolytic voltage waveform is DC. When the array power is less than the rated electrolytic cell power, the voltage Ua at output point a of part A of the circuit topology remains unchanged, and the power transistor Qa operates to perform array power balance control. At this time, part B of the circuit topology takes effect, and the voltage Ub at its output point b is the initial inflection point sustaining voltage e of the electrolytic cell's IV characteristic. rev On the one hand, it can maintain the amount of reactive charge under low power conditions, accelerate the recovery time, and reduce impact. On the other hand, it coordinates the A part of the circuit topology to control the B part of the circuit topology to achieve electrolytic current waveform control. The four adjustable parameters are the voltage amplitude at output point a of the A part of the circuit topology, the voltage amplitude at output point b of the B part of the circuit topology, the voltage width at output point a of the A part of the circuit topology, and the waveform period T.

[0021] like Figure 1 As shown, the voltage stability and power balance of the photovoltaic array are controlled by varying the duty cycle PWM1 of the power transistor Qa. The power transistor Qa is a low-on-resistance semiconductor switch. When it is closed and conducting, the voltage Ua at output point a of part A of the circuit topology is applied to the electrolytic cell, causing the current to rise rapidly. When the power transistor Qa is open, the electrolytic cell is powered by the voltage Ub at output point b of part B of the circuit topology. Since the voltage Ub at output point b of part B is lower than the voltage Ua at output point a of part A, the current decreases. Adjusting the duty cycle PWM1 of the power transistor Qa affects the average power over the entire cycle, thus enabling voltage regulation control of the array through closed-loop regulation of the first PI proportional-integral method. Under the premise of array voltage regulation control, the maximum power voltage tracking search of the array can be performed using conventional methods, such as the perturbation observation method or the incremental admittance method.

[0022] like Figure 1 As shown, in the voltage Ua control of output point a in part A of the circuit topology, due to the wide range of array power variation, the maximum power of the array may be greater than or less than the rated power of the electrolytic cell. When the maximum power exceeds the rated power of the electrolytic cell, the electrolytic cell voltage cannot exceed the optimal limit of the electrolytic voltage. Therefore, the voltage Ua control of output point a in part A of the circuit topology adopts the principle of minimum adjustment in a dual-loop input / output system to achieve stable control of the voltage Ua at output point a in part A of the circuit topology. When the array power is greater than the load power, such as... Figure 3 As shown in t k-1 ~t k During a certain period, the voltage Ua at output point a of part A of the circuit topology may exceed the limit. At this time, the duty cycle of the power transistor Qa reaches its maximum, and the voltage Ua at output point a of part A of the circuit topology achieves voltage regulation. When the array power is less than the load power, such as Figure 3As shown, t1~t2 and t n-1 ~t n During a given time period, the duty cycle of the power transistor Qa is adjusted in real time to stabilize the array voltage and achieve maximum power tracking. A small inductor can be connected to the circuit output to achieve pulse slope control.

[0023] Four-parameter optimization algorithm under power balance conditions, such as Figure 4 As shown, based on the temperature, hydrogen production per unit time, and hydrogen production efficiency model, under the current power conditions, the optimal voltage waveform parameters can be determined using modeling lookup tables or automatic search methods. With the power transistor Qa's duty cycle PWM1 unchanged, adjusting the voltage Ua at output point a of part A of the circuit topology can stabilize the array voltage through power balance. Alternatively, with the voltage Ua at output point a of part A of the circuit topology fixed, adjusting the duty cycle PWM1 of power transistor Qa can stabilize the array voltage. The voltage Ub at output point b of part B of the circuit topology can be fine-tuned. Although this has a slight impact on the voltage Ua at output point a of part A of the circuit topology or the duty cycle PWM1 of power transistor Qa, it is beneficial for current recovery; the main concern is its impact on hydrogen production efficiency.

[0024] Under the MPPT tracking array voltage stabilization control condition, the changes in the voltage Ua at output point a of part A of the circuit topology, the voltage Ub at output point b of part B of the circuit topology, and the duty cycle PWM1 of power transistor Qa will all affect the load power, and thus affect the array voltage regulation. To resolve the mutual influence, a time-division search adjustment method is adopted for the voltage Ua at output point a of part A of the circuit topology, the voltage Ub at output point b of part B of the circuit topology, and the duty cycle PWM1 of power transistor Qa to achieve decoupling control between them.

[0025] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for power balance and optimal voltage control in photovoltaic electrolysis of alkaline water for hydrogen production, characterized in that, Under independent photovoltaic power conversion conditions, based on the nonlinear characteristics of electrolyzer current and voltage and the electrolysis efficiency model and principle of electrolyzer, a main power topology circuit and a secondary topology circuit of a photovoltaic electrolysis alkaline water hydrogen production system are designed. Part A of the circuit topology is the main power topology circuit, and part B is the secondary topology circuit. Part A of the circuit topology consists of a second DC / DC converter connected in parallel with the first DC / DC converter in part B via a power transistor Qa and a series diode D1, then passing through an inductor L1 and connecting to the electrolyzer. The voltage at output point a of part A, the voltage at output point b of part B, the voltage width at output point a of part A, and the waveform period T are controlled and adjusted to automatically adjust the stepped electrolysis voltage waveform, thereby optimizing the electrolysis hydrogen production efficiency. When the power of the photovoltaic array is less than that of the electrolytic cell, while performing maximum power point tracking, the voltage of output point a of part A of the circuit topology and the voltage of output point b of part B of the circuit topology are stabilized, and the duty cycle of power transistor Qa is adjusted to achieve the change of average load power and achieve power balance. The voltage stability and power balance of the photovoltaic array are controlled by the change of the duty cycle of the power transistor Qa. When the power transistor Qa is closed, the voltage output at point a of part A of the circuit topology increases, and the current of the electrolytic cell rises. When the power transistor Qa is open, part B of the circuit topology maintains the amount of reactive charge in the electrolytic cell and coordinates the control of part A of the circuit topology to achieve control of the electrolytic current waveform.

2. The method for power balance and optimal voltage control in photovoltaic electrolysis of alkaline water for hydrogen production according to claim 1, characterized in that, When the maximum power of the photovoltaic array exceeds the power of the electrolytic cell, the maximum power point tracking automatically stops. The voltage at output point a of part A of the circuit topology remains unchanged and does not exceed the optimal voltage value of the electrolytic cell. The duty cycle of the power transistor Qa reaches its maximum value. At this time, the load power is at its maximum, and the actual power of the photovoltaic array is balanced with the load power.

3. The method for power balance and optimal voltage control in photovoltaic electrolysis of alkaline water for hydrogen production according to claim 2, characterized in that, When the actual power of the photovoltaic array reaches a balance with the load power, the photovoltaic electrolysis alkaline water hydrogen production system, based on the current operating state, while ensuring power balance, fine-tunes the voltage of output point a in part A of the circuit topology, the voltage of output point b in part B of the circuit topology, and the duty cycle of power transistor Qa through modeling lookup or automatic search, in order to improve hydrogen production efficiency.

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