## 2 Overview of Shunt Regulation Design for Satellite Power Supply Systems  
The power system of a certain MEO orbit satellite consists of a solar array, a lithium-ion battery pack, a power controller, etc. The main function of the power subsystem is to realize the energy transfer and power balance between the solar array and the battery pack, ensuring the normal power supply of the primary power system [24; 25; 26; 27]. The power controller adopts a three-domain full-regulation control bus scheme using a voltage error signal. The MEA uniformly manages the power regulation modules inside the power controller to keep the bus voltage constant, whether in the light period or the shadow period [28; 29; 30]. The main function of the MEA error amplifier is to collect the 42 V bus voltage, compare it with a set reference value after transformation to generate an MEA control signal, and then send it to the shunt circuit through a two-out-of-three voting circuit to stabilize the primary bus. The principle block diagram is shown in Figure 1[31; 32; 33]. Figure 1: Principal block diagram of main error amplifier (MEA). The bus error signal can be expressed by Equation (1). \[\mathrm{Vmea}=\mathrm{A}(\mathrm{K}\mathrm{Vbus}-\mathrm{Vref}) \tag{1}\]  
Vmea: Bus error signal; A: Amplifier gain; Vbus: Bus voltage; Vref: Circuit voltage reference. K represents the voltage division factor. The shunt regulator of the power controller is used for power regulation of the solar array during the light period [34]. The entire shunt regulator consists of 12 identical shunt circuits, each with a single-stage shunt capacity of 7 A. When the system is balanced, only one of the 12 shunt circuits is in the adjustment state, while the others are in the cutoff or conduction state. During the light period, the solar array current is constant. When the load decreases, the bus voltage increases, the MEA voltage rises, and the 12 shunt circuits sequentially enter the shunt state; conversely, when the load increases, the bus voltage decreases, the MEA voltage drops, and the shunt circuits sequentially exit the shunt state. The solar cell circuits are shorted to ground or supply power to the bus according to the load demand, maintaining the stability of the bus voltage by regulating the supply current of the solar array [35; 36; 37; 38]. The circuit reference of the shunt circuits is formed by a series-connected resistor network. All shunt circuits correspond to 12 voltage references in total, with the lowest voltage corresponding to the first-stage shunt circuit. The threshold voltage data for each stage of the shunt regulator, obtained through experiments, are shown in Table 1 below. By referring to Table 1 and combining it with the actual measured \(\mathrm{V}_{\mathrm{MEAASR}}\) data, the real-time status of each shunt circuit in the shunt regulator can be determined. In response to the 12-stage shunt operation mode of the PCU, the solar array is designed with 12 sub-arrays in total. Sub-arrays 1-12 sequentially correspond to the controller's 1-12 shunt stages. Each wing contains six sub-arrays: the +Y wing houses sub-arrays 1, 3, 5, 7, 9, and 11; the \(-\mathrm{Y}\) wing houses sub-arrays 2, 4, 6, 8, 10, and 12. The distribution of thermistors on the +Y wing of the solar array is as follows: Thermistor 1 is located in the first-stage shunt circuit (PC1, inner panel), Thermistor 2 in the seventh-stage shunt circuit (PC9, inner panel), and Thermistor 3 in the fifth-stage shunt circuit (PC7, outer panel). For the \(-\mathrm{Y}\) wing of the solar array, the thermistor distribution is Thermistor 1 in the first-stage shunt circuit (PC2, inner panel), Thermistor 2 in the seventh-stage shunt circuit (PC10, inner panel), and Thermistor 3 in the fifth-stage shunt circuit (PC8, outer panel). Whether the circuit at the temperature measurement point is shunting is controlled by the shunt regulator (S3R).