针对积分器入射面的辐照不均匀度高导致的太阳模拟器辐照均匀性较差的问题，设计了一种自由曲面聚光镜。基于点光源模型，根据能量守恒定律和非成像光学中的边光理论，建立光源出射角度与目标面对应点的映射关系；依据菲涅耳定律结合映射关系推导出微分方程，通过龙格-库塔法求解微分方程，计算出离散点数据；拟合离散点数据得到自由曲面聚光镜的母线，旋转母线获得自由曲面聚光镜的初始结构。使用贝塞尔曲线表征自由曲面母线，利用模拟退火算法对引入扩展光源的自由曲面进行反馈优化，从而得到连续的自由曲面面形。采用LightTools软件仿真太阳模拟器光学系统，结果表明：自由曲面聚光镜的辐照均匀性较椭球聚光镜的辐照均匀性显著提升，辐照面?50 mm内辐照不均匀度优于±0.32%，辐照面?100 mm内辐照不均匀度优于±0.53%；通过误差仿真分析，依据现有自由曲面加工与检测水平，验证了所设计自由曲面聚光镜加工、检测与装调的可行性。

Results and Discussions According to the analysis results, the target surface of the developed free-form surface condenser displays a uniform irradiation distribution, which indicates an ideal improvement in the irradiation uniformity of the optical integrator's incident surface. In the design proposal, the generatrix is rotated to obtain the free-form surface condenser. After multiple parameters of the Bézier curve are optimized, the irradiation uniformity within ?60 mm of the target surface of the free-form surface condenser rises from 52% before optimization to 92% (Fig. 7). By contrast, the irradiation nonuniformity of the solar simulator using the free-form surface condenser is significantly lower than that of the solar simulator using the ellipsoidal condenser. In the case of the free-form surface condenser, the irradiation nonuniformity within ?50 mm of the irradiation surface is better than 0.32%, and the irradiation nonuniformity within ?100 mm of the irradiation surface is better than 0.53% (Table 1). When the surface accuracy of the free-form surface condenser is controlled within ±15 μm (Fig. 12), the axial position deviation is controlled within 0.3 mm (Fig. 13), the vertical-axis position deviation is controlled within 0.3 mm (Fig. 14), and the angle deviation is controlled within 0.4° (Fig. 15), the irradiance within ?100 mm of the irradiation surface of the solar simulator can be greater than S₀, and the irradiation nonuniformity is less than 1.5%.

The solar simulator is a device that simulates solar irradiation characteristics indoors. In the design of the solar simulator, the irradiation uniformity is an important indicator, which directly determines the accuracy of the device. Hence, improving irradiation uniformity has become a key research direction. In a solar simulator, the concentrator system is one of the key components, which typically uses an ellipsoidal condenser. By the ellipsoidal condenser, the radiation flux from the light source placed on the first focal plane will be focused on the second focal plane. As a result, a convergent spot is formed on the incident surface of the optical integrator, which is dense at the center, sparse at the edge, and Gaussian in shape. This uneven illuminance distribution is detrimental to the irradiation uniformity of the entire system. To address the poor performance of the solar simulator due to the low irradiation uniformity of the optical integrator's incident surface, this paper proposes and designs a free-form surface condenser as the concentrator system of the solar simulator. On the premise that the focusing efficiency is ensured, the irradiation uniformity on the second focal plane is effectively improved as the irradiation uniformity of the solar simulator is improved through better irradiation distribution on the optical integrator's incident surface.

In this paper, the free-form surface condenser used in the solar simulation system is studied. First, the mapping relationship between the outgoing angle of the light source and the corresponding point on the target surface is determined. According to Fresnel's law and the mapping relationship, the differential equation is derived, which is solved by the Runge-Kutta method to calculate the discrete point data. After curve fitting of the discrete point data, the bus line of the free-form surface condenser is obtained. Second, the generatrix of the free-form surface is generated by the Bézier curve. A simulated annealing algorithm is employed to conduct feedback-oriented optimization on the free-form surface condenser with an extended light source. Third, the optical system of the solar simulator is modeled by the software LightTools, and the ellipsoidal condenser and the free-form surface condenser are configured in the same optical system of a solar simulator for comparative analysis. Fourth, the irradiance and the irradiation nonuniformity within ?100 mm of the irradiation surface are taken as the evaluation indexes, and error simulation analyses are performed to investigate the influence of surface accuracy, axial position offset, vertical-axis position offset, and angle offset of the free-form surface condenser on the irradiance and the irradiation nonuniformity.

In this paper, a free-form surface condenser is proposed and designed. The point light source model is used to construct a reasonable initial structure according to the law of conservation of energy, the edge light theory, and the mapping method. In the design proposal, the generatrix of the free-form surface condenser is represented by the Bézier curve. The parameters of the Bézier curve are selected as the optimization variables, and the irradiation uniformity on the target surface is selected as the evaluation function. In the meantime, a simulated annealing algorithm is used to optimize the free-form surface with an extended light source. The simulation results of LightTools show that the irradiation uniformity on the irradiation surface of the solar simulator is significantly improved when the free surface condenser is used. The irradiation nonuniformity within ?50 mm of the irradiation surface is better than 0.32%, and that within ?100 mm of the irradiation surface is better than 0.53%. When the surface and pose errors of the free-form surface condenser are taken into account according to the existing processing, assembly, and adjustment level, the irradiance greater than S₀ is considered feasible on the irradiation surface, and the irradiation nonuniformity is less than 1.5%. This verifies the feasibility of the processing, detection, assembly, and adjustment of the free-form surface condenser.