A hydrogen energy, electrochemical energy and multi-energy fusion energy storage system and control strategy

Abstract

The present invention discloses a multi-energy fusion energy storage system and control strategy of hydrogen energy and electrochemical energy, belonging to the field of new energy. The energy storage system includes a new energy power station, an electrolyzer, a proton exchange membrane fuel cell, and a supercapacitor. The new energy power station, the electrolyzer, the proton exchange membrane fuel cell, and the supercapacitor are connected in parallel with the DC bus through a DC converter, and the DC bus is connected to the power grid. The supercapacitor of the present invention can both absorb and release electrical energy, and can better ensure the controllable output of the hybrid energy storage system, make the output of the grid-connected system more stable, stabilize the DC bus voltage, and improve the power quality of the power grid.

Description

Technical Field

[0001] The present invention belongs to the field of new energy, and more specifically relates to a hydrogen energy, electrochemical energy and multi-energy fusion energy storage system and control strategy. Background Art

[0002] Renewable energy generation is widely used. The use of solar energy resources has the disadvantages of randomness, volatility and intermittency, which leads to increased fluctuations in grid-connected power and increased abandonment of solar and wind power. Therefore, adding energy storage devices to the power generation system can effectively solve the above shortcomings. In Chapter 4, we combine batteries and supercapacitors to form a hybrid energy storage system to maintain power balance and bus voltage stability. However, batteries have low specific energy, short cycle life, and cumbersome equipment maintenance. The more important reason is that batteries are not conducive to the development trend of green environmental protection.

[0003] The country is currently also vigorously advocating the use of new hydrogen energy storage methods in renewable energy power generation. In the context of promoting the development of green energy, hydrogen energy storage is the most ideal energy storage unit choice. As a green and clean energy source, hydrogen has the characteristics of high energy density, long cycle life, large storage capacity, and easy storage and transportation. It has become one of the best solutions for the development, storage and utilization of green development concepts in renewable energy power generation. When there is an excess of renewable energy power generation, hydrogen can be produced by electrolyzers, and when there is insufficient power generation, the hydrogen produced by electrolysis can be used in proton exchange membrane fuel cells to generate electricity. Hydrogen is clean and pollution-free during the combustion process, which is in line with the green development concept advocated by the country. Summary of the invention

[0004] The present invention combines green hydrogen energy storage methods to build a hybrid energy storage system based on hydrogen energy storage and electrochemical energy in a new energy power generation system. Considering the upper and lower voltage limits of supercapacitors and the frequent start and stop of electrolyzers that cause great loss to their lifespan, a power coordination control strategy is given. And under three different operating conditions of the hybrid system, the bus voltage is guaranteed to be stable and energy balance is achieved. The DC bus voltage is stable and the maximum utilization of solar energy resources is achieved.

[0005] In order to achieve the above-mentioned purpose, the present invention is implemented by adopting the following technical scheme: the energy storage system includes a new energy power station, an electrolyzer, a fuel cell, and a supercapacitor. The new energy power station, the electrolyzer, the fuel cell, and the supercapacitor are connected in parallel with a DC bus through a DC converter, and the DC bus is connected to the power grid.

[0006] Furthermore, the fuel cell is connected to a DC bus through a DC / DC converter, and the fuel cell is a proton exchange membrane fuel cell.

[0007] Furthermore, the electrolyzer is connected to a DC bus through a DC / DC converter, and the DC bus provides electrolysis power to the electrolyzer; the energy storage system also includes a hydrogen storage tank, and the hydrogen electrolyzed by the electrolyzer is sent to the hydrogen storage tank for storage.

[0008] Furthermore, the DC bus is connected to the power grid through a DC / AC converter to convert the DC power on the DC bus into AC power; the output power of the new energy power station is connected to the DC bus through a DC / DC converter.

[0009] On the other hand, a control strategy for a hydrogen energy, electrochemical energy and multi-energy fusion energy storage system is provided. The control strategy is applicable to the energy storage system. The control strategy is established in the following steps:

[0010] S1. Construct the control strategy equation of the new energy power station; construct the control strategy equation of the electrolyzer and the fuel cell; construct the control strategy equation of the supercapacitor;

[0011] S2. Construct the grid-connected control strategy equation and power transmission equation of the hybrid energy storage system;

[0012] S3. Divide the energy storage system control strategy into three working conditions for analysis.

[0013] Furthermore, the control strategy equation of the new energy power station constructed by S1 is shown as follows (1):

[0014]

[0015] Among them, m pv Represents the trigger pulse signal of the DC / DC converter in the renewable energy power station, k ppv、 k ipv They represent the proportion and integral coefficient of the PI controller in the maximum power point tracking process of the new energy power station, U mpp , U pv They respectively represent the voltage value of the maximum power point of the DC / DC converter of the new energy power station and the measured voltage value.

[0016] Furthermore, the control strategy equations of the electrolyzer and fuel cell constructed by S1 are expressed as (2);

[0017]

[0018] Among them, m el Represents the trigger pulse signal of the converter of the electrolytic cell, m fc represents the trigger pulse signal of the fuel cell converter, k pel , k iel They represent the proportional and integral coefficients of the PI regulator in the electrolyzer power loop, Pel , P el_ref They are respectively represented by the actual value and reference value of the electrolytic cell outer ring power, k pfc , k ifc They represent the proportional and integral coefficients of the PI regulator in the fuel cell power loop, P fc , P fc_ref They respectively represent the actual value and reference value of the fuel cell outer ring power.

[0019] Furthermore, the control strategy equation of the S1 supercapacitor is as follows:

[0020] (1) When the supercapacitor is in boost mode

[0021]

[0022] (2) When the supercapacitor is in buck mode

[0023]

[0024] Among them, m sc1 、m sc2 represents the trigger pulse signal of the converter in the supercapacitor, k psc , k isc They represent the proportional and integral coefficients of the PI regulator of the supercapacitor current loop, U dcsc ,I dcsc They represent the voltage value and current value at both ends of the supercapacitor respectively.

[0025] Furthermore, the grid-connected control strategy equation in S2 is:

[0026]

[0027] Among them are:

[0028]

[0029] In the formula, m d 、m q Indicates the trigger pulse signal of the d-axis and q-axis of the grid-connected DC / AC converter, k pq , k id Indicates the proportional and integral coefficients of the PI regulator in the d-axis current, k pdc , k idc represents the proportional and integral coefficient of the PI regulator in the q-axis current, and L represents the inductance on the AC side of the power grid;

[0030] Then in the dq coordinate system, the power transfer expression in the hybrid energy storage system is as follows:

[0031]

[0032] Among them, P s , Q s Respectively represent the active power and reactive power at the grid connection point, I d ,I q They represent the d-axis and q-axis components of the current value at the grid side, respectively, and P grid represents the power value at the grid-connected location, Ud represents the d-axis component of the voltage value at the grid side, P pv Represents the maximum power point tracking power of the renewable energy power station, P fc Represents the fuel cell output power, P el Indicates the power absorbed by the electrolytic cell, P sc Indicates the power absorption value of the supercapacitor.

[0033] Furthermore, the three working conditions of S3 are as follows:

[0034] (1) When the output of a new energy power station is greater than the load, the electrolyzer is started first because the hydrogen energy storage device should have a higher startup priority than the supercapacitor, and its electrolysis of water consumes the excess electricity to produce hydrogen;

[0035] (2) The output of the new energy power station is slightly less than the load demand due to its own fluctuations or load changes. Instead of shutting down the electrolyzer, its output power is adjusted. The fuel cell and supercapacitor are coordinated to achieve power stability and DC bus voltage stability.

[0036] (3) When the new energy power station cannot produce power on rainy days, at night, or in the absence of wind, the electrolyzer will be shut down. Since the startup priority of the hydrogen energy storage device should be higher than that of the supercapacitor, the fuel cell will be started to release electricity to meet the load demand. Since the power shortage is too large, the supercapacitor should also be started in time to provide the required power to the load together with the fuel cell.

[0037] Beneficial effects of the present invention:

[0038] The present invention combines green hydrogen energy storage methods to build a composite energy storage system based on hydrogen energy storage and electrochemical energy in a new energy power generation system. Considering the upper and lower voltage limits of supercapacitors and the frequent start and stop of electrolyzers that cause great loss to their lifespan, a power coordination control strategy is given. And under three different operating conditions of the hybrid system, the bus voltage is guaranteed to be stable and energy balance is achieved. The DC bus voltage is stable and the maximum utilization of solar energy resources is achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a structural diagram of the energy storage system of the present invention;

[0040] Figure 2 This is a diagram of the grid-connected control strategy of the energy storage system of the present invention. DETAILED DESCRIPTION

[0041] In order to facilitate understanding of the present invention, the present invention will be described more fully below with reference to the relevant drawings. Typical embodiments of the present invention are provided in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described in the present invention. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thorough and comprehensive.

[0042] Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0043] Embodiment 1:

[0044] like Figure 1 As shown, an energy storage system is constructed including a new energy power station, an electrolyzer, a fuel cell, and a supercapacitor. The new energy power station, the electrolyzer, the fuel cell, and the supercapacitor are connected in parallel with a DC bus through a DC converter, and the DC bus is connected to a power grid.

[0045] The fuel cell is connected to the DC bus through a DC / DC converter, and the fuel cell adopts a proton exchange membrane fuel cell. The electrolyzer is connected to the DC bus through a DC / DC converter, and the DC bus provides electrolysis power to the electrolyzer; the energy storage system also includes a hydrogen storage tank, and the hydrogen electrolyzed by the electrolyzer is sent to the hydrogen storage tank for storage. The DC bus is connected to the power grid through a DC / AC converter, and the DC / AV converter is an inverter that converts the DC power on the DC bus into AC power; the output power of the new energy power station is connected to the DC bus through a DC / DC converter.

[0046] In this example, the new energy power station uses photovoltaic power generation, and the photovoltaic array uses maximum power point tracking technology to achieve real-time transmission of energy to the DC bus as the photovoltaic output changes with changes in light intensity. When there is excess electricity, the electrolyzer electrolyzes water to produce hydrogen, consumes excess electricity, and stores the hydrogen for use with proton exchange membrane fuel cells. When electricity is insufficient, the proton exchange membrane fuel cell burns hydrogen to generate electricity and supply the system. Supercapacitors can both absorb and release electricity, and when combined with hydrogen energy storage, they can better ensure the controllable output of the hybrid energy storage system, make the grid-connected system output more stable, stabilize the DC bus voltage, and improve the quality of power grid electricity.

[0047] The relationship between the DC bus voltage and each unit current is as follows:

[0048]

[0049] In the formula, C dc Indicates the DC bus capacitance, U dc Indicates the DC bus voltage, i pv Indicates the current emitted by the renewable energy power station, i el represents the outflow current of the electrolytic cell unit, i fc represents the current flowing into the fuel cell unit, i sc Supercapacitance refers to the current flowing into and out of the supercapacitor cell.

[0050] Embodiment 2:

[0051] like Figure 2 As shown, according to the energy storage system of Example 1, a control strategy for a hydrogen energy, electrochemical energy and multi-energy fusion energy storage system is established. The control strategy is applicable to the energy storage system. The control strategy is established in the following steps:

[0052] S1. Construct the control strategy equation of the new energy power station;

[0053] The control strategy equation of the S1 new energy power station is as follows (1):

[0054]

[0055] Among them, m pv Represents the trigger pulse signal of the DC / DC converter Conv.1 in the new energy power station, k ppv , k ipv They represent the proportion and integral coefficient of the PI controller in the maximum power point tracking process of the new energy power station, U mpp , U pv They respectively represent the voltage value of the maximum power point of the DC / DC converter of the new energy power station and the measured voltage value.

[0056] Construct the control strategy equations of the electrolyzer and the fuel cell; the expressions are as follows (2);

[0057]

[0058] Among them, m el Represents the trigger pulse signal of the electrolytic cell converter Conv.2, m fc represents the trigger pulse signal of the fuel cell converter Conv.3, k pel , k iel They represent the proportional and integral coefficients of the PI regulator in the electrolyzer power loop, P el , P el_ref They are respectively represented by the actual value and reference value of the electrolytic cell outer ring power, k pfc , k ifcThey represent the proportional and integral coefficients of the PI regulator in the fuel cell power loop, P fc , P fc_ref They respectively represent the actual value and reference value of the fuel cell outer ring power.

[0059] Construct the control strategy equations for supercapacitors;

[0060] (1) When the supercapacitor is in boost mode

[0061]

[0062] (2) When the supercapacitor is in buck mode

[0063]

[0064] Among them, m sc1 、m sc2 represents the trigger pulse signal of Conv.4 of the converter in the supercapacitor, k psc , k isc They represent the proportional and integral coefficients of the PI regulator of the supercapacitor current loop, U dcsc ,I dcsc They represent the voltage value and current value at both ends of the supercapacitor respectively.

[0065] S2. Construct the grid-connected control strategy equation and power transmission equation of the hybrid energy storage system;

[0066] The grid-connected control strategy equation in the dq synchronous coordinate system is:

[0067]

[0068] Among them are:

[0069]

[0070] In the formula, m d 、m q Indicates the trigger pulse signal of the d-axis and q-axis of the grid-connected DC / AC converter Conv.5, k pq , k id Indicates the proportional and integral coefficients of the PI regulator in the d-axis current, k pdc、 k idc It represents the proportion and integral coefficient of the PI regulator in the q-axis current, and L represents the inductance on the AC side of the power grid.

[0071] Under the control of the grid-connected inverter, the DC bus voltage value U dc There is a small fluctuation around its set value, so the dynamic expression of the DC bus voltage is:

[0072]

[0073] Where U dc Indicates the DC bus voltage value, C indicates the DC bus capacitance, I pv Indicates the current emitted by the renewable energy power station, I fc Represents the fuel cell output current, I el Represents the working current of the electrolytic cell, I sc Supercapacitor represents the supercapacitor current, I grid Indicates the grid-connected current value.

[0074] Then in the dq coordinate system, the power transfer expression in the hybrid energy storage system is as follows:

[0075]

[0076] Among them, P s、 Q s Respectively represent the active power and reactive power at the grid connection point, I d ,I q They represent the d-axis and q-axis components of the current value at the grid side, respectively, and P grid represents the power value at the grid-connected location, Ud represents the d-axis component of the voltage value at the grid side, P pv Represents the maximum power point tracking power of the renewable energy power station, P fc Represents the fuel cell output power, P el Indicates the power absorbed by the electrolytic cell, P sc Indicates the power absorption value of the supercapacitor.

[0077] Power coordination control is the core of the hybrid energy storage system based on hydrogen energy storage. The so-called power coordination control of the hybrid energy storage system is to reasonably coordinate the power of the complex hybrid system composed of new energy power stations, supercapacitors, hydrogen energy storage (electrolyzers and fuel cells), operating loads and various power converters.

[0078] In a hybrid energy storage system, the energy density of hydrogen is much higher than that of a supercapacitor, so during operation, the startup priority of the hydrogen energy storage device should be higher than that of the supercapacitor. When unbalanced electrical energy appears in the hybrid system, the hydrogen energy storage device will be started first, and the electrolyzer or fuel cell will be put into operation to balance the DC bus power. Supercapacitors also need to absorb and release electrical energy, and need to coordinate with hydrogen energy storage, so after the hydrogen energy storage device has been started for a period of time, the supercapacitor will be started in time to maintain the balance of the DC bus power. Considering that the supercapacitor has upper and lower voltage limits, it will exit operation after exceeding its voltage upper limit, and the hydrogen energy storage unit will continue to work.

[0079] S3. Divide the energy storage system control strategy into three working conditions for analysis.

[0080] (1) When the output of a new energy power station is greater than the load, the electrolyzer is started first because the startup priority of the hydrogen energy storage device should be higher than that of the supercapacitor. The electrolyzer electrolyzes water to consume excess electricity to produce hydrogen. The supercapacitor itself does not produce electricity, so if you want it to release electricity, you must first let it absorb electricity. After a period of time, the supercapacitor is started and absorbs the extra excess electricity for storage. However, the supercapacitor itself has an upper voltage limit. When the electricity it absorbs reaches the upper voltage limit, it can no longer continue to work. At this time, the supercapacitor will exit operation and increase the power of the electrolyzer to consume the remaining electricity.

[0081] (2) When the output of a new energy power station is slightly less than the load demand due to its own fluctuations or load changes, the electrolyzer is not shut down but its output power is adjusted. The fuel cell and supercapacitor are coordinated to achieve power stability and DC bus voltage stability.

[0082] When the output of renewable energy generation is slightly less than the load demand, the fuel cell is started because the startup priority of the hydrogen energy storage device should be higher than that of the supercapacitor. The supercapacitor also needs to release electrical energy to maintain balance. At the same time, in order to have sufficient storage space when absorbing electricity, the supercapacitor starts and releases energy after a period of time. However, the supercapacitor itself has a lower voltage limit. When the electrical energy released reaches the lower voltage limit, it can no longer continue to work. At this time, the supercapacitor will exit work and adjust the power of the electrolyzer to maintain power balance.

[0083] (3) When the new energy power station cannot produce power on rainy days, at night, or in windless conditions, the electrolyzer will be shut down. Since the startup priority of the hydrogen energy storage device should be higher than that of the supercapacitor, the fuel cell will be started to release electricity to meet the load demand. Since the power shortage is too large, the supercapacitor should also be started in time to provide the required power to the load together with the fuel cell. However, the supercapacitor itself has a lower voltage limit. When the electricity it releases reaches the lower voltage limit, it can no longer continue to work. At this time, the supercapacitor will shut down. In order to balance the system power, the load is reduced step by step.

[0084] When the new energy source remains in the output state but is far less than the load demand, the electrolytic cell should also be shut down. The subsequent working conditions are similar to those in condition three, so no further analysis will be given.

[0085] Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiments can be implemented by instructing related hardware through a computer program, and the program can be stored in a computer-readable storage medium, and when the program is executed, it can include the processes of the embodiments of the above-mentioned methods. The storage medium can be a disk, an optical disk, a read-only memory (ROM) or a random access memory (RAM), etc.

[0086] It should be understood that the detailed description of the technical solutions of the present invention by means of the preferred embodiments is illustrative rather than restrictive. A person skilled in the art may modify the technical solutions described in the embodiments, or replace some of the technical features by equivalents, based on reading the specification of the present invention; and these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A multi-energy storage system integrating hydrogen energy and electrochemical energy. Features: The energy storage system includes a new energy power station, an electrolyzer, a fuel cell, and a supercapacitor. The new energy power station, the electrolyzer, the fuel cell, and the supercapacitor are connected in parallel with a DC bus through a DC converter, and the DC bus is connected to a power grid; The fuel cell is connected to the DC bus through a DC / DC converter, and the fuel cell is a proton exchange membrane fuel cell; The electrolyzer is connected to the DC bus through a DC / DC converter, and the DC bus provides electrolysis power to the electrolyzer; the energy storage system also includes a hydrogen storage tank, and the hydrogen electrolyzed by the electrolyzer is sent to the hydrogen storage tank for storage; The DC bus is connected to the power grid through a DC / AC converter to convert the DC power on the DC bus into AC power; the output power of the new energy power station is connected to the DC bus through a DC / DC converter; The control strategy is established in the following steps: The control strategy is established in the following steps: S1. Construct the control strategy equation of the new energy power station; construct the control strategy equation of the electrolyzer and the fuel cell; construct the control strategy equation of the supercapacitor; S2. Construct the grid-connected control strategy equation and power transmission equation of the hybrid energy storage system; S3, divide the energy storage system control strategy into three working conditions for analysis; The control strategy equation of the S1 new energy power station is as follows (1): Among them, m pv Represents the trigger pulse signal of the DC / DC converter in the renewable energy power station, k ppv , k ipv They represent the proportion and integral coefficient of the PI controller in the maximum power point tracking process of the new energy power station, U mpp , U pv Respectively represent the voltage value of the maximum power point of the DC / DC converter of the new energy power station and the measured voltage value; The control strategy equations of the electrolyzer and fuel cell constructed by S1 are expressed as (2); Among them, m el Represents the trigger pulse signal of the converter of the electrolytic cell, m fc Represents the trigger pulse signal of the fuel cell converter, k pel , k iel They represent the proportional and integral coefficients of the PI regulator in the electrolyzer power loop, P el , P el_ref They are respectively represented by the actual value and reference value of the electrolytic cell outer ring power, k pfc , k ifc They represent the proportional and integral coefficients of the PI regulator in the fuel cell power loop, P fc , P fc_ref They represent the actual value and reference value of the outer ring power of the fuel cell respectively; the control strategy equation for constructing the supercapacitor by S1 is as follows: (1) When the supercapacitor is in boost mode (2) When the supercapacitor is in buck mode Among them, m sc1 、m sc2 represents the trigger pulse signal of the converter in the supercapacitor, k psc , k isc They represent the proportional and integral coefficients of the PI regulator of the supercapacitor current loop, U dcsc ,I dcsc Respectively represent the voltage value and current value of the supercapacitor; The grid-connected control strategy equation in S2 is: Among them are: In the formula, m d 、m q Indicates the trigger pulse signal of the d-axis and q-axis of the grid-connected DC / AC converter, k pq , k id Indicates the proportional and integral coefficients of the PI regulator in the d-axis current, k pdc , k idc represents the proportional and integral coefficient of the PI regulator in the q-axis current, and L represents the inductance on the AC side of the power grid; Then in the dq coordinate system, the power transfer expression in the hybrid energy storage system is as follows: Among them, P s , Q s Respectively represent the active power and reactive power at the grid connection point, I d ,I q They represent the d-axis and q-axis components of the current value at the grid side, respectively, and P grid represents the power value at the grid-connected location, Ud represents the d-axis component of the voltage value at the grid side, P pv Represents the maximum power point tracking power of the renewable energy power station, P fc Represents the fuel cell output power, P el Indicates the power absorbed by the electrolytic cell, P sc Indicates the power absorption value of the supercapacitor; The S3 described has three working conditions as follows: (1) When the output of a new energy power station is greater than the load, the electrolyzer is started first because the hydrogen energy storage device should have a higher startup priority than the supercapacitor, and its electrolysis of water consumes the excess electricity to produce hydrogen; (2) The output of the new energy power station is slightly less than the load demand due to its own fluctuations or load changes. Instead of shutting down the electrolyzer, its output power is adjusted. The fuel cell and supercapacitor are coordinated to achieve power stability and DC bus voltage stability. (3) When the new energy power station cannot produce power on rainy days, at night, or in windless conditions, the electrolyzer will be shut down. Since the startup priority of the hydrogen energy storage device should be higher than that of the supercapacitor, the fuel cell will be started to release electricity to meet the load demand. Since the power shortage is too large, the supercapacitor should also be started in time to provide the required power to the load together with the fuel cell.

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