Simulation analysis of P–U characteristics
At a constant temperature of 25°C, the P–U characteristics of the PV panel were simulated and analyzed, when the light intensity was 1000 W/m2800W/m2and 600 W/m2, respectively. The simulation model is shown in Fig. 8.
As shown in Fig. 8, the output voltage and output power of the PV array are sent to workspaces a and b respectively, which are used to draw the P–U characteristic curve of the PV array. The parameters of the PV panel simulation model are shown in Table 1.
The P–U characteristic curve under different light intensities is shown in Fig. 9.
It can be obtained from Fig. 9: The maximum power point power and voltage under different light intensities as shown in Table 2.
System simulation model
The system simulation model is shown in Fig. 10, which includes PV subsystem, Boost circuit, R load, MPPT subsystem and PWM subsystem. The traditional incremental conductance method is a fixed step, the step value ΔU1* is 0.01, the variable step incremental conductance method is variable step and the step factors α1α2α3 are fixed values of 0.05, 0.02, 0.01, respectively. In Figure 10, L1 = 5e−4H, C1=C2 = 5e−4F, R = 10Ω.
The MPPT subsystem collects the voltage and current and obtains the reference voltage command signal Uref, via the MPPT algorithm. The control signal Urefis compared to the sawtooth wave with a frequency of 10 kHz through a comparator. If the relation is greater than, it outputs high, and if it is less than the relation, it outputs low, thus generating a PWM signal. The PWM signal drives the IGBT to realize the pulse width modulation of the Boost circuit. Therefore, the Boost circuit can produce different voltages.
System simulation analysis
In order to simulate the MPPT tracking effect of the system under rapidly changing lighting conditions, a Simulink simulation was performed for the system. During the simulation, the temperature was constant at 25°C, but the light intensity changed rapidly.
During the simulation, the rule of light intensity change is: in 0~0.3s, the light intensity is constant at 1000W/m2; in 0.3~0.6s, the light intensity is constant at 600W/m2; in 0.6~1s, the light intensity is constant at 800W/m2; The simulation time is 1 s, the ode45 algorithm is used and the sampling time is 1e−6 s.
Output voltage simulation analysis
The MPPT simulation analysis of the PV array output voltage was performed using the traditional incremental conductance method and the enhanced incremental conductance method respectively. The MPPT simulation results of the two incremental conductance methods are shown in Fig. 11.
It can be seen from Fig. 11 that the output voltage curves of the traditional conductance incremental method and the enhanced conductance incremental method almost overlap, and the voltage values are almost the same. The output voltage and error are shown in Table 3.
From Table 3, it can be concluded that under different lighting conditions, the maximum power point voltage tracking error of the incremental conductance method and the incremental enhanced conductance method are both within the error range of 4.66%, the error is small, and the voltage tracking effect is good and stable.
Output power simulation analysis
The MPPT simulation analysis of the PV array output power was performed using the traditional incremental conductance method and the enhanced incremental conductance method respectively. The MPPT simulation results of the two incremental conductance methods are shown in Fig. 12.
It can be seen from Fig. 12 that the output power curves of the traditional conductance incremental method and the enhanced conductance incremental method almost overlap, and the voltage values are almost the same. Output power and error are shown in Table 4.
From Table 4, it can be concluded that under different lighting conditions, the power tracking errors of the Incremental Conductance Method and the Incremental Conductance Enhanced Method are both within the error range of 3, 48%, the error is small, and the power tracking effect is good and stable.
The enlarged views from area A to area D in FIG. 12 are shown in Figs. 13, 14, 15 and 16, respectively.
As shown in Fig. 13, when the light intensity is 1000W/m2, the traditional incremental conductance method enters steady-state at 0.01 s; However, the improved incremental conductance method entered a stable state at 0.005s, the adjustment time is short, and the response speed is fast.
As shown in Fig. 14, at this time, the light intensity is 1000W/m2, and the system is already in a stable state at about 0.2 s. In steady state, the output power of the traditional incremental conductance method fluctuates greatly, and the peak-to-peak value is about 0.96 W; The output power of the enhanced incremental conductance method also has no steady-state oscillation.
As shown in Fig. 15, when the light intensity changes from 600 to 800 W/m2 at 0.6 s, the output power of the traditional incremental conductance method oscillates strongly and the system enters the steady state at 0.612 s; while the output power of the enhanced incremental conductance method oscillates less, the system entered the steady state at 0.607s, the adjustment time is short, and the response speed is fast.
As shown in Fig. 16, at this time, the light intensity is 800W/m2, and the system is already in a stable state at about 0.8 s. In steady state, the output power of the traditional incremental conductance method oscillates greatly, and the peak-to-peak value is about 0.87 W; The output power of the enhanced incremental conductance method also has no steady-state oscillation.
From Figs. 11, 12, 13, 14, 15 and 16, it can be seen that when the light intensity changes rapidly, the new and improved incremental conductance method not only has the advantages of no steady-state oscillation and fast response speed, but also the efficiency of photovoltaic power generation is improved, and the fast and accurate tracking of MPP is better realized.