Solar simulator is a device for simulating the space solar radiation characteristics and geometric characteristics on the ground, and its irradiation uniformity index directly determines the performance of the solar simulator. Traditional light homogenizing devices include optical integrator and integrating sphere. Optical integrator is constrained by the angle of incident light, and has the disadvantage that the angle is sensitive to the effect of light homogenization. Although the integrating sphere has a wide range of incident light angles, it will result in the large irradiance surface at a long distance, and the irradiance and irradiation uniformity will be reduced by the influence of the divergent light angle of the integrating sphere. In the present study, we propose a method to modulate the angle of the light emitted from the integrating sphere by inverting the compound parabolic concentrator into a compound parabolic reflector. This compound parabolic reflector can utilize the light emitted by the integrating sphere that cannot enter the effective irradiation surface, improve the energy utilization of the light source, and realize the simulation of light spot with large irradiation surface and high irradiation uniformity at a distance.
In this paper, the design of compound parabolic reflector is carried out. Firstly, the parabolic equation is derived by studying the principle of beam modulation of compound parabolic reflector. Then, the influence of the parameters of the compound parabolic reflector on the irradiation uniformity and irradiance on the irradiation surface is analyzed, and the size parameters such as the divergence angle and intercept ratio of the compound parabolic reflector are determined. Finally, the optical system model of the divergent solar simulator is established and simulated.
The designed compound parabolic reflector modulates the light half angle of the divergent light of the integrating sphere from 82° to 25° (Fig. 8). With the increase of the maximum divergence half angle from 20° to 30°, the irradiance drops sharply, and its value even drops by nearly 40%; the irradiation uniformity shows a trend of rising first and then stabilizing (Fig.6). The irradiance of the effective irradiation surface decreases gradually with the increase of the length intercept ratio of the compound parabolic reflector. The irradiation uniformity is almost stable when the intercept ratio is not greater than 20%, and the decline is steeper when the intercept ratio is greater than 20% (Fig.9). With the diameter of the effective irradiation surface of solar simulator being 1000 mm, when the intercept ratio of the compound parabolic reflector used is 20%, the irradiation uniformity on the effective surface is increased by 0.24 times, to 97.30%, and the irradiance is increased by 5.1 times, to 553.54 W/m2 compared with the system without the composite parabolic reflector (Table 2).
In this paper, a compound parabolic reflector is designed for the purpose of modulating the divergence angle of the light hole of the integrating sphere to improve the utilization of the light energy of the xenon lamp and the irradiation uniformity of the large irradiance surface. The compound parabolic reflector can modulate the half angle of the divergent light of the integrating sphere from 82° to 25°. Through the analysis of the length intercept ratio of the compound parabolic reflector, the results show that when the length intercept ratio is 20%, the irradiation uniformity of the intercepted compound parabolic reflector on the effective irradiation surface is still 97.30%, a value comparable to that of the compound parabolic reflector without interception. The overall simulation analysis of the optical system of the solar simulator shows that when the working distance of the solar simulator is 3000 mm and the diameter of the effective irradiation surface is 1000 mm, the irradiation uniformity is 97.30%, and the maximum irradiance is 553.54 W/m2, realizing the simulation of large irradiance with high irradiation uniformity.
