阅读说明：本技术 一种电-电混合电源系统的燃料电池效率优化方法 (Fuel cell efficiency optimization method of electricity-electricity hybrid power system ) 是由 王亚雄 张晨阳 陈铨 于 2019-11-28 设计创作，主要内容包括：本发明涉及一种电-电混合电源系统的燃料电池效率优化方法,提供一种电-电混合电源系统,采用燃料电池与变结构蓄电池作为电源,将燃料电池与变结构蓄电池直接并联接入母线并经直流/交流逆变器与负载电机相连；包括以下步骤：步骤S1:通过离线测量和计算获取燃料电池电源的各工作点的相关参数,并通过多项式拟合的形式获取燃料电池电源的电压、电流、功率与效率之间的函数关系；步骤S2:通过函数逆运算获取燃料电池电源最大效率点的电压与功率;步骤S3:匹配变结构蓄电池电源的串并联分组结构;步骤S4:计算变结构蓄电池电源所需串联单体数与并联支路数。本发明通过将燃料电池稳定在效率最大点工作,能够有效提高燃料电池的利用率。(The invention relates to a fuel cell efficiency optimization method of an electricity-electricity hybrid power system, and provides the electricity-electricity hybrid power system, wherein a fuel cell and a variable structure storage battery are used as power supplies, and the fuel cell and the variable structure storage battery are directly connected in parallel to a bus and are connected with a load motor through a direct current/alternating current inverter; the method comprises the following steps: step S1, obtaining relevant parameters of each working point of the fuel cell power supply through off-line measurement and calculation, and obtaining the functional relation between the voltage, the current, the power and the efficiency of the fuel cell power supply through a polynomial fitting form; the method comprises the steps of S2, obtaining the voltage and the power of the maximum efficiency point of the fuel cell power supply through function inverse operation, S3, matching the series-parallel connection grouping structure of the variable-structure storage battery power supply, and S4, calculating the number of series-connected monomers and the number of parallel-connected branches required by the variable-structure storage battery power supply. The invention can effectively improve the utilization rate of the fuel cell by stabilizing the fuel cell to work at the maximum efficiency point.)

1. A fuel cell efficiency optimization method of an electricity-electricity hybrid power system is characterized in that an electricity-electricity hybrid power system is provided, a fuel cell and a variable structure storage battery are used as power supplies, the fuel cell and the variable structure storage battery are directly connected in parallel to a bus and are connected with a load motor through a direct current/alternating current inverter, and the specific method comprises the following steps:

step S1, obtaining relevant parameters of a specific working point of the fuel cell power supply through off-line measurement and calculation, and obtaining a functional relation among the voltage, the current, the power and the efficiency of the fuel cell power supply through a polynomial fitting form;

step S2, obtaining the voltage and the power of the maximum efficiency point of the fuel cell power supply through the function inverse operation according to the functional relation among the voltage, the current, the power and the efficiency of the fuel cell power supply;

step S3, matching the serial-parallel connection grouping structure of the storage battery power supply according to the storage battery monomer voltage obtained by real-time measurement and the maximum efficiency point power of the fuel;

and step S4, calculating the number of the series-connected monomers required by each branch of the variable structure storage battery according to the output voltage of the maximum efficiency point of the fuel cell and the voltage of the storage battery monomer obtained by real-time measurement, and meanwhile, calculating the number of the parallel branches according to the load power, increasing or reducing the number of the parallel branches of the variable structure storage battery in real time, and ensuring that the power supply of the variable structure storage battery is supplied safely and stably under the condition that the current of each branch of the storage battery does not exceed the current discharge limit.

2. The method for optimizing the fuel cell efficiency of an electric-electric hybrid power supply system according to claim 1, wherein the step S1 is specifically as follows:

step S11, obtaining the current, voltage and actual hydrogen consumption flow of the fuel cell stack at each specific working point through off-line measurement;

step S12, calculating the power of the fuel cell at each operating point by the formula (1)

Wherein:Pis the power of the fuel cell;Uis the voltage of the fuel cell;Iis the current flowing through the fuel cell;

step S13, calculating the efficiency of the fuel cell at each specific operating point:

wherein:Q(H₂) Actual hydrogen consumption flow rate (g/s) for fuel cell power;M _H2molar mass of hydrogen (g/mol);. DELTA.HIs the enthalpy change (kJ/mol) of the hydrogen reaction in the fuel cell;

step S14, according to the calculated efficiency of the fuel cell power supply and the voltage value and the power value of the fuel cell at the working point, fitting a voltage-efficiency and power-efficiency curve of the fuel cell by a polynomial, wherein the curve is shown in the formulas (3) and (4):

wherein:a,a ₂ ,a ₃ ,…a _N as a fitting coefficient to the fuel cell supply voltage-efficiency polynomial,b ₁ ,b ₂ ,b ₃ …b _N as a fitting coefficient to the fuel cell power-efficiency polynomial,G、Frespectively, voltage-efficiency and power-efficiency.

3. The method of claim 2, wherein the operating voltage of the fuel cell corresponding to the highest efficiency point of the fuel cell is the operating voltage of the fuel cellU _mOperating powerP _m：

Wherein:

4. The method for optimizing the fuel cell efficiency of an electric-electric hybrid power supply system according to claim 3, wherein the step S4 is specifically as follows:

step S41 Preset series connection

wherein:

step S42, calculating the number of parallel branches needed by the variable-structure storage battery power supplyL _pI.e. closingL _pA branch in parallelL _pWhen it is a decimal number, the ratio is takenL _pThe largest minimum integer is shown in formula (8):

wherein:L _pthe number of the parallel branches required by the variable-structure storage battery power supply,P _sfor the cell voltage of the accumulator to beU _sAnd the current is the power when the battery reaches the discharge limit current.

Technical Field

The invention relates to a fuel cell hybrid power supply, in particular to a fuel cell efficiency optimization method of an electricity-electricity hybrid power supply system.

Background

The fuel cell is an energy conversion device for directly converting chemical energy into electric energy, the electric energy generation mode of the fuel cell is mainly realized through chemical reaction, and the reaction process is not limited by Carlo cycle, so that the fuel cell has higher energy conversion efficiency compared with the traditional internal combustion engine for providing power, and the fuel cell has low noise and basically no pollution in the power generation process. Compared with a storage battery, the fuel cell has the advantages that the storage battery is prevented from being overcharged and over-discharged in order to guarantee the durability of the storage battery in the energy supply process, a shallow charging and shallow discharging mode is generally adopted, the effective capacity is small, the energy density is low, the discharging process of the fuel cell only needs to meet the requirement of fuel supply, the capacity problem does not need to be considered under the general condition, the higher energy density is realized, and the fuel cell is widely favored as an energy supply mode. However, considering that the discharge efficiency of the fuel cell varies at different operating points during the discharge process, when the fuel cell is applied to a vehicle, although the fuel cell vehicle can achieve zero emission and low noise, if the discharge efficiency and the operating point of the fuel cell cannot be considered together, the economical efficiency of the fuel cell vehicle will be greatly reduced.

Therefore, aiming at the structural design of a power source of a fuel cell electric automobile, stable power supply and strategy optimization are usually realized by mixing various power sources and connecting the power sources through a converter, and the power source of the fuel cell electric automobile mainly comprises a fuel cell + storage battery, a fuel cell + super capacitor, and a fuel cell + storage battery + super capacitor. For these power supply configurations, the fuel cell is typically connected to the bidirectional dc/dc boost converter, which is connected to the battery or super capacitor.

In such a hybrid power source structure, there are two main problems, one of which is that the stability of the control of the dc/dc converter is required to be good, otherwise the system is likely to run away. Secondly, the dc/dc converter as a power conversion device also causes a large amount of energy consumption due to its own structure. Meanwhile, the energy efficiency of the fuel cell is also affected by the unreasonable design of the operating point of the fuel cell.

Disclosure of Invention

In view of the above, an object of the present invention is to provide a method for optimizing the efficiency of a fuel cell of an electric-electric hybrid power system, which can effectively improve the utilization rate of the fuel cell by stabilizing the fuel cell to operate at the maximum efficiency point.

In order to achieve the purpose, the invention adopts the following technical scheme:

a fuel cell efficiency optimization method of an electricity-electricity hybrid power system provides an electricity-electricity hybrid power system, which adopts a fuel cell and a variable structure storage battery as power supplies, and the fuel cell and the variable structure storage battery are directly connected in parallel to a bus and are connected with a load motor through a direct current/alternating current inverter; the method comprises the following steps:

step S1, obtaining relevant parameters of a specific working point of the fuel cell power supply through off-line measurement and calculation, and obtaining a functional relation among the voltage, the current, the power and the efficiency of the fuel cell power supply through a polynomial fitting form;

step S2, obtaining the voltage and the power of the maximum efficiency point of the fuel cell power supply through the function inverse operation according to the functional relation among the voltage, the current, the power and the efficiency of the fuel cell power supply;

step S3, matching the series-parallel connection grouping structure of the variable-structure storage battery power supply according to the storage battery monomer voltage obtained by real-time measurement and the maximum efficiency point power of the fuel;

step S4, calculating the number L of series monomers needed by the variable-structure storage battery according to the output voltage of the maximum efficiency point of the fuel cell and the voltage of the storage battery monomer obtained by real-time measurement_SMeanwhile, the number L of the parallel branches is calculated according to the magnitude of the load power_PThe number of parallel branches of the variable-structure storage battery power supply is increased or reduced in real time, and the current of each branch storage battery is ensured to be safe and stable in power supply under the condition that the current discharge limit is not exceeded.

Further, the step S1 is specifically:

step S11, obtaining the current, voltage and actual hydrogen consumption flow of the fuel cell stack at each specific working point through off-line measurement;

step S12, calculating the power of the fuel cell at each operating point by the formula (1)

P＝U·I (1)

Wherein: p is the power of the fuel cell; u is the voltage of the fuel cell; i is the current flowing through the fuel cell;

step S13, calculating the efficiency of the fuel cell at each specific operating point:

wherein: q (H)₂) Actual hydrogen consumption flow rate (g/s) for fuel cell power; m_H2The molar mass (g/mol) of hydrogen, the Delta H is the enthalpy change (kJ/mol) of the hydrogen reaction in the fuel cell, and η is the efficiency of the fuel cell power supply;

step S14, according to the calculated efficiency of the fuel cell power supply and the voltage value and the power value of the fuel cell at the working point, fitting a voltage-efficiency and power-efficiency curve of the fuel cell by a polynomial, wherein the curve is shown in the formulas (3) and (4):

η＝G(U)＝a₁+a₂·U¹+a₃·U²+……a_N·U^N(3)

η＝F(P)＝b₁+b₂·P¹+b₃·P²+……b_N·P^N(4)

wherein: a, a₂，a₃，...a_NFitting coefficients for fuel cell supply voltage-efficiency polynomial, b₁，b₂，b₃...b_NFor the fitting coefficients of the fuel cell power-efficiency polynomial, G, F are the voltage-efficiency and power-efficiency functional maps, respectively.

Further, the fuel cell operates according to the maximum efficiency pointVoltage U_mOperating power P_m：

U_m＝G^-1(max(η)) (5)

P_m＝F^-1(max(η)) (6)

Wherein max (η) is a maximum function of η, U_mIs the maximum efficiency point voltage, P, of the fuel cell_mThe power corresponding to the maximum efficiency point of the fuel cell.

Further, the step S4 is specifically:

step S41: preset series connection L_SThe single storage battery is used as a storage battery branch, as shown in fig. 3, the voltage of the power supply end of the variable-structure storage battery is enabled to be consistent with the voltage of the maximum efficiency point of the fuel cell power supply, when L is_SFractional number of decimal fraction L_SThe largest minimum integer:

wherein: l is_SThe number of the storage battery monomers in series connection required by each branch storage battery module of the variable-structure storage battery power supply is U_sThe voltage is the real-time voltage of the storage battery monomer.

Step S42: calculating the number L of parallel branches required by the variable-structure storage battery power supply_pI.e. L is closed in FIG. 3_pA branch in parallel, when L_pWhen it is a decimal number, take the ratio L_pThe largest minimum integer is shown in formula (8):

wherein: l is_PNumber of parallel branches, P, required for variable-structure battery power supply_sFor the cell voltage of the storage battery to be U_sTime and current is the power at which the battery limits the current.

Compared with the prior art, the invention has the following beneficial effects:

1. the fuel cell and the storage battery are directly connected to the bus in parallel and are connected to the load motor through the direct current/alternating current inverter, so that the structure that a traditional power supply is connected with the bus through the direct current/direct current converter is avoided, the power loss of the direct current/direct current converter is reduced, and the utilization rate of energy can be effectively improved.

2. The invention stabilizes the fuel cell at the maximum efficiency point, can effectively improve the hydrogen utilization rate of the fuel cell, and ensures the high-efficiency and stable operation of the fuel cell.

3. The invention adopts the variable-structure storage battery to stabilize the working state of the fuel cell and realize high-efficiency energy recovery.

Drawings

FIG. 1 is a diagram of a powertrain according to one embodiment of the present invention;

FIG. 2 is a structural diagram of a variable-structure battery according to an embodiment of the present invention;

fig. 3 is a series-parallel connection matching structure diagram of the variable-structure storage battery.

Detailed Description

The invention is further explained below with reference to the drawings and the embodiments.

Referring to fig. 1, the present invention provides an electric-electric hybrid power system, which uses a fuel cell and a variable structure battery as power sources, and connects the fuel cell and the variable structure battery directly in parallel to a bus and to a load motor through a dc/ac inverter; the efficiency optimization method comprises the following steps:

in this embodiment, as shown in fig. 2, a structure diagram of a variable-structure battery power supply is shown, wherein series-parallel grouping inside the battery power supply can be realized by closing corresponding switches, for example: the switches Spu1, Spu2, Sdu1 and Sdu2 are closed to realize parallel connection of the storage battery monomer 1 and the storage battery monomer 2; the switches Ss1, Ss3, Spu2, Spd2 and Spd4 are closed, so that the parallel connection of the storage battery cells 1 and 2 and the storage battery cells 3 and 4 can be realized;

in this embodiment, an automobile is taken as an example, and according to an automobile dynamics model, the driving condition of the automobile is calculated to obtain the required power of the automobile, as shown in formula (1):

step S1, obtaining relevant parameters of each working point of the fuel cell power supply through off-line measurement and calculation, and obtaining the functional relation between the voltage, the current, the power and the efficiency of the fuel cell power supply through a polynomial fitting form;

the step S1 specifically includes:

step S11, obtaining the current, voltage and actual hydrogen consumption flow of the fuel cell stack at each specific working point through off-line measurement;

step S12, calculating the power of the fuel cell at each operating point by the formula (1)

p＝U·I (1)

Wherein: p is the power of the fuel cell; u is the voltage of the fuel cell; i is the current flowing through the fuel cell;

step S13, calculating the efficiency of the fuel cell at each specific operating point:

wherein: q (H)₂) Actual hydrogen consumption flow rate (g/s) for fuel cell power; m_H2The molar mass (g/mol) of hydrogen, the Delta H is the enthalpy change (kJ/mol) of the hydrogen reaction in the fuel cell, and η is the efficiency of the fuel cell power supply;

step S14: according to the calculated efficiency of the fuel cell power supply and the voltage value and the power value of the fuel cell at the working point, fitting a fuel cell voltage-efficiency and power-efficiency curve by a polynomial, wherein the polynomial is shown in the formulas (3) and (4):

η＝G(U)＝a₁+a₂·U¹+a₃·U²+……a_N·U^N(3)

η＝F(P)＝b₁+b₂·P¹+b₃·P²+……b_N·P^N(4)

wherein: a, a₂，a₃，...a_NFitting coefficients for fuel cell supply voltage-efficiency polynomial, b₁，b₂，b₃...b_NFor power-efficiency polynomials for fuel cell power sourcesThe fitting coefficients, G, F, are voltage-efficiency and power-efficiency functional maps, respectively.

Step S2: obtaining the voltage and the power of the maximum efficiency point of the fuel cell power supply through function inverse operation according to the functional relation among the voltage, the current, the power and the efficiency of the fuel cell power supply;

the operating voltage U of the fuel cell corresponding to the maximum efficiency point of the fuel cell_mOperating power P_m：

U_m＝G^-1(max(η)) (5)

P_m＝F^-1(max(η)) (6)

Wherein max (η) is a maximum function of η, U_mIs the maximum efficiency point voltage, P, of the fuel cell_mThe power corresponding to the maximum efficiency point of the fuel cell.

Step S3: matching a series-parallel connection grouping structure of a storage battery power supply according to the storage battery monomer voltage obtained by real-time measurement and the maximum efficiency point power of the fuel;

step S4, calculating the number L of series-connected single cells needed by the storage battery according to the output voltage of the maximum efficiency point of the fuel cell and the voltage of the storage battery single cell obtained by real-time measurement_SMeanwhile, the number L of the parallel branches is calculated according to the magnitude of the load power_PThe number of parallel branches of the variable-structure storage battery power supply is increased or reduced in real time, and the current of each branch storage battery is ensured to be safe and stable in power supply under the condition that the current discharge limit is not exceeded. Step S41 Preset series connection L_SThe single storage battery is used as a storage battery branch, as shown in fig. 3, the voltage of the power supply end of the variable-structure storage battery is enabled to be consistent with the voltage of the maximum efficiency point of the fuel cell power supply, when L is_SFractional number of decimal fraction L_SThe largest minimum integer:

wherein: l is_SThe number of the storage battery monomers, U, required to be connected in series for each branch storage battery module of the storage battery power supply_sFor storage battery monomerTime-voltage.

Step S42, calculating the number L of parallel branches needed by the variable-structure storage battery power supply_pI.e. L is closed in FIG. 3_pA branch in parallel, when L_pWhen it is a decimal number, take the ratio L_pThe largest minimum integer is shown in formula (8):

wherein: l is_pNumber of parallel branches, P, required for variable-structure battery power supply_sFor the cell voltage of the storage battery to be U_sAnd the current is the power at which the battery limits the discharge current.

When the automobile is in braking energy recovery or the variable-structure storage battery power supply is in charging, the variable-structure storage battery power supply works independently. When energy is recovered or low-voltage charging is carried out, the number of parallel batteries of the variable-structure storage battery power supply is increased, and the number of series batteries is reduced; when the variable-structure storage battery power supply is charged at high voltage, the series number of the variable-structure storage battery power supply is properly increased, and relatively safe charging current is maintained.

According to the design, the series-parallel connection structure of the variable-structure storage battery power supply is switched, the working voltage of the fuel battery power supply at the maximum efficiency point is maintained, the fuel battery can work at the maximum efficiency point stably all the time, and the variable-structure storage battery power supply reasonably maintains the change requirement of load power and is charged and discharged efficiently and safely.

The above description is only a preferred embodiment of the present invention, and all equivalent changes and modifications made in accordance with the claims of the present invention should be covered by the present invention.