Photovoltaic panel

Photovoltaic panel model

The photovoltaic panel element is modeled as a voltage-controlled current source I_PV with module capacitance C_PV connected in parallel, as shown in Figure 1. The current source I_PV is controlled by the voltage V_PV across the PV panel, in combination with a predefined PV model I-V curve.

The voltage-controlled current source I_PV represents a nonlinear resistor with the I-V characteristics equivalent to the standard PV cell characteristics, often modeled with the equivalent circuit given in Figure 2. The standard PV cell equivalent circuit model comprises an ideal semiconductor p-n junction, a current source that models irradiance flux, and series and shunt resistance that capture internal series and shunt losses.

The PV cell IV curve is given as:

$I=I_{ph}-I_D=I_{ph}-I_0(\exp \left(\frac{e(V+I\bullet R_s)}{m\bullet k\bullet T_c}\right)-1)$

where m is an ideality factor (usually in the range of 1 to 2, with m =1 being ideal), k is the Boltzmann constant, e is the electron charge, and Tc is the junction temperature. The PV module is modeled as a compound parameterized PV cell, comprising an array of individual PV cells connected in series and/or parallel. Hence, a full module, or even a series of modules, is represented with a single PV panel element in Schematic Editor.

Photovoltaic panel component in Typhoon HIL Schematic Editor

Table 1. Photovoltaic panel component in the Schematic Editor

component	component dialog window	component parameters
Photovoltaic panel		Property tabs: Tab: General Tab: Signal Processing

Generating I-V curves in the Typhoon HIL Waveform Generator

The preview curve will be displayed for the entered irradiance and temperature.

The IV curve is a function of irradiance G, and temperature T. In particular, the parameters I_sc(STC) and V_oc(STC) are obtained under standard test conditions (G_(STC)= 1000 W/m², T_(STC)= 25°C). The relationship between the current I and the terminal voltage V of a PV panel parametrized with FFu, FFi, α, β, Cv, Cr and Cg parameters, is given as:

$I=I_{sc}-I_0(\mathrm{e}\mathrm{x}\mathrm{p}(\frac{V}{V_{oc}{C}_{aq}})-1)$

where:

I_sc is the short circuit current:

$I_{sc}=I_{sc\left(STC\right)}\frac{G}{G_{\left(STC\right)}}(1+\alpha (T-T_{\left(STC\right)}\left)\right)$ ,

V_oc is the open circuit voltage:

$V_{oc}=V_{oc\left(STC\right)}(1+\beta (T-T_{\left(STC\right)}\left)\right)(\mathrm{l}\mathrm{n}(\frac{G}{C_g}+1)C_v-C_{r}G)$ ,

I₀ is the reverse diode saturation current:

$I_0=I_{sc\left(STC\right)}{(1-{FF}_i)}^{\frac{1}{1-{FF}_u}}\frac{G}{G_{\left(STC\right)}}$ ,

and C_aq is a parameter dependent on voltage and current fill factors:

$C_{aq}=\frac{{FF}_u-1}{\mathrm{l}\mathrm{n}(1-{FF}_i)}$ .

Example: JKM220P-60

This section gives an example of reading the parameters needed for the Waveform Generator tool from a PV module datasheet given in Figure 5.

The next steps describe how to determine the ideality factor for a given PV panel. It cannot be read directly from the datasheet, rather it has to be determined experimentally. After entering all the available parameters from the datasheet to the Waveform Generator, an initial value for the ideality factor should be chosen. A good initial guess for crystalline silicon is around 2, while for amorphous silicon is less than 2. Finally, the maximum power displayed on the graph in the Waveform Generator should be compared to the maximum power provided in the datasheet. This process should be repeated until a close enough match between the maximum powers from the PV curve preview and the datasheet is obtained. PV curves for several ideality factors are shown in Figure 6.

Tab: General

• Cpv
  • PV diode capacitance. [F]

• Initial voltage
  • Initial voltage of the component. [V]

Tab: Signal Processing

If the option Enable SP-based implementation is checked, the PV panel is modelled using a signal processing based PV model. In this case, the IV curve is simulated at the execution rate of the signal processing components, defined by the Execution rate property. Conversely, if this option is unchecked, the IV curve is simulated at the basic simulation timestep defined in the circuit solver settings. In both cases, the component can be controlled through dedicated HIL API functions.

• Enable SP-based implementation
  • If checked, enables IV curve definition using the EN50530 compatible PV model.

• MPP measurement
  • Enables/disables monitoring of maximum power point (MPP). This property is available if the Enable SP-based implementation checkbox is marked.

• Execution rate
  • Type in the desired signal processing execution rate. This value must be compatible with other signal processing components of the same circuit: the value must be a multiple of the fastest execution rate in the circuit. There can be up to four different execution rates, but they must all be multiple of the basic simulation timestep. To specify the execution rate, you can use either decimal (e.g. 0.001) or exponential values (e.g. 1e-3) in seconds. Alternatively, you can type in ‘inherit’ in which case the component will be assigned execution rate based on the execution rate of the components it is receiving input from.
  • This property is available if the Enable SP-based implementation checkbox is marked.

• Enable Normalized IV curve
  • If checked, enables the IV curve definition using the Normalized IV PV model, in addition to the EN50530 compatible PV model.
  • This property is available if the Enable SP-based implementation checkbox is marked.

• Slow execution rate
  • Signal processing execution rate at which the Normalized IV curve data points are updated. The slow execution rate applies to the inputs which specify x- and y- data sets, normalizedDataV.value and normalizedDataI.value, respectively. This execution rate, however, does not apply to short circuit current iscSTC and open circuit voltage vocSTC inputs which scale the specified data sets. Instead, these inputs are updated at the faster execution rate, Execution rate.
  • This property is available if the Enable SP-based implementation and the Enable Normalized IV curve options are marked.

• CPU core
  • Specifies which User CPU core executes the signal processing portion of the component.
  • This property is available if the Enable SP-based implementation option is marked, and if the specified HIL device contains multiple User CPU cores to choose from. If the model is compiled for a HIL device which contains only one User CPU core (CPU core 0), then the value of this property is not applied, and the internal signal processing portion is mapped to CPU core 0.

Measurements and inputs internal to the PV component

Available internal measurements are given in Table 2.

The optional maximum power point (MPP) measurements, illumination, temperature, short circuit current, and open circuit voltage measurements of the signal processing based PV model are available through probes inside the component. These outputs are given in Table 3.

The references for the signal processing based PV model are provided through SCADA inputs located inside the component. An overview of the available inputs related only to the EN50530 compatible PV model type is given in Table 4.

An overview of the available inputs related only to the Normalized IV PV model type is given in Table 5.

An overview of the common inputs is available in Table 6. For the EN50530 compatible PV model type, ramping and/or scheduling can be applied to the temperature, illumination, short circuit current, and open circuit voltage references. For the Normalized IV PV model type, ramping and/or scheduling can be applied to short circuit current and open circuit voltage references.

References

[1] Overall efficiency of grid connected photovoltaic inverters, CENELEC, St. EN 50530, 2010