[0069] The preferred embodiments will be described in detail below in conjunction with the accompanying drawings. It should be emphasized that the following description is only exemplary and not intended to limit the scope of the invention and its application.
[0070] The specific steps of the modeling method are:
[0071] Step 1: Establish a single exponential 5-parameter initial model that comprehensively reflects the output characteristics of photovoltaic cells, wherein the 5 parameters in the above initial model are all values to be obtained.
[0072] The equivalent circuit of a single exponential 5-parameter model of a photovoltaic cell is as figure 2 shown, according to figure 2 Available:
[0073] I = I pv - I 0 [ exp ( V + R s I aV t ) - 1 ] - V + R s I R p - - - ( 1 )
[0074] Among them: I pv is the photogenerated current; I 0 is the reverse saturation leakage current flowing through the diode; V t =N s kT/q,N s is the number of single cells contained in the photovoltaic cell module, k is the Boltzmann constant: 1.38×10 -23 J/K, T is the battery temperature, q is the unit charge, 1.6×10 -19 C; R s and R p are the equivalent series resistance and parallel resistance; a is the ideality factor; I and V are the output current and output voltage of the photovoltaic cell, respectively.
[0075] Step 2: Use the Lambert W function to make the photovoltaic cell model explicit in step 1 to obtain an explicit photovoltaic cell model. The output current (voltage) can be obtained directly by inputting a given voltage (current).
[0076] It can be seen that formula (1) is an implicit transcendental equation about I and V, which is inconvenient to solve, so the Lambert W function is used to make it explicit:
[0077] I = R p ( I pv + I 0 ) - V R s + R p - aV t R s W ( Y ) - - - ( 2 )
[0078] V=R p (I pv +I 0 -I)-IR s -aV t W(Z) (3)
[0079] Among them, W(Y) and W(Z) are both Lambert W functions, satisfying the property W(X)exp(W(X))=X
[0080] Y = R s R p I 0 aV t ( R s + R p ) exp [ R p ( R s I pv + R s I 0 + V ) aV t ( R s + R p ) ]
[0081] Z = R p I 0 aV t exp ( R p ( I pv + I 0 - I ) aV t )
[0082] It should be noted that explicitization refers to equivalently transforming the photovoltaic cell model in step 1 into a simple and easy-to-apply model. There is no simplification of the model.
[0083] Step 3: Use the data provided by the manufacturer and the parameter calculation algorithm to extract the parameter values to be obtained in the initial model under standard working conditions.
[0084] Usually, photovoltaic cell manufacturers only provide users with standard operating conditions (irradiance S=1000W/m 2 , battery temperature T=25°C), photovoltaic cell short-circuit current I sc，n , open circuit voltage V oc，n , maximum power point current I m，n and voltage V m,n (Note: The parameter subscript with n indicates the corresponding value under standard working conditions, which will not be explained below).
[0085] Correspondingly, the short-circuit point V=0, I=I sc，n :
[0086] I pv , n ≈ R p , n + R s , n R p . n I sc , n - - - ( 4 )
[0087] Open circuit point V=V oc，n , I=0:
[0088] I 0 , n = ( R p , n + R s , n ) I sc , n - V oc , n C 1 R p , n - - - ( 5 )
[0089] Among them: C 1 =exp[V oc,n /(a n V t，n )]-1
[0090] Maximum power point V=V max，n , I=I max，n :
[0091] R p , n = V max , n + R s , n I max , n - C 1 V oc , n / C 2 ( C 2 - C 1 ) / C 2 I sc , n - I max , n - - - ( 6 )
[0092] Among them: C 2 =exp[(V max，n +I max，n R s,n )/(a n V t，n )]-1;
[0093] Another by image 3 The P-V characteristic curve of the photovoltaic cell shown:
[0094] dP dV | V m = V m dI dV | V m + I m = 0 - - - ( 7 )
[0095] Among them, P is the battery output power; V is the output voltage value; V m is the voltage value corresponding to the maximum output power; I m is the current value corresponding to the maximum output power;
[0096] It is further deduced that:
[0097] R p , n = V max , n - aV t , n + I max , n R s , n + V oc , n / C 1 ( C 1 + 1 ) / C 1 I sc , n + [ aV t , n / ( I max , n R s , n - V m , n ) - 1 ] I max , n - - - ( 8 )
[0098] The above two explicit equations contain a total of 3 unknown parameters R p，n 、a n and R s，n , the analytical solution cannot be obtained directly, and the following algorithm can be used for optimal solution:
[0099] min|R p1,n (R s，n , a n )-R p2，n (R s，n , a n )|
[0100] s.t.a min ≤a n ≤a max R s，min s，n s,max (9)
[0101] For photovoltaic cells of different materials, a n The typical value of is also different, and photovoltaic cells of different materials are combined in the algorithm a n The typical value of a min =1.0, a max =3.5; From a physical point of view, R s，n Describes the resistance of the photovoltaic cell substrate, the resistance of the diffusion layer, and the contact resistance between the grid line and the photovoltaic cell, so that R s,n Impossible to be less than 0, preferably R s，min =0; for general photovoltaic cells, R s,n Small, desirable R s，max =2.
[0102] Step 4: Use the parameter values under standard working conditions obtained in step 3 and the parameter conversion algorithm to obtain the parameter values under given working conditions.
[0103] Photovoltaic cell model parameters vary with irradiance and temperature. Photogenerated current is mainly affected by irradiance and temperature:
[0104] I pv = [ I pv , n + K I ( T - T n ) ] S S n - - - ( 10 )
[0105] Among them: K I is the current temperature coefficient; S n Irradiance under standard conditions.
[0106] Diode reverse saturation leakage current is mainly affected by temperature:
[0107] I 0 = I 0 , n ( T T n ) 3 exp [ qE g a n k ( 1 T n - 1 T ) ] - - - ( 11 )
[0108] Among them: E g For the forbidden band width, different photovoltaic cell materials take different values (eg: Si: 1.12eV, GaGs: 1.35eV).
[0109] For a, R under normal working conditions s , R p , which can be obtained by the following formula:
[0110] a=a n (12)
[0111] R s =R s，n (13)
[0112] R p = S S n × R p , n - - - ( 14 )
[0113] When R is obtained under the standard working condition through the optimization algorithm p，n 、a n and R s,n After that, the corresponding parameter values under general working conditions can be obtained through the above conversion formula. When the above algorithm is used to calculate the model parameters, the corresponding values of the five parameters under any irradiance and temperature can be obtained through the corresponding conversion formulas after only one off-line calculation of the five parameters under the standard working condition of the photovoltaic cell, so that it can be easily It is convenient for real-time simulation of photovoltaic cells.
[0114] Step 5: Substituting the parameter values obtained above into the explicit model of the photovoltaic cell in step 2 to obtain a photovoltaic cell model that comprehensively reflects the output characteristics of the photovoltaic cell under a given working condition.
[0115] The above is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed in the present invention can easily think of changes or Replacement should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be determined by the protection scope of the claims.
