# Power-Split Hybrid Train Configuration Design Based on a Single-Row Star Row
## 2 Configuration Choice
### Single-Row Star-Row Power-Split Configuration  
The planetary row gear set ratio and the placement of the motor both impact the power-split characteristics. Depending on the different motor locations, the single-row star-row power-split mechanism can be classified as an input power-split mechanism or an output power-split mechanism. Power splitting causes a unique power cycling phenomenon between power components. As a result, the proportion of power in the electromechanical path increases and the system efficiency decreases. The transmission ratio of the transmission system is defined as \(i=\omega_{\text{E}}/\omega_{\text{Out}}\) and the mechanical point of the working state of the transmission ratio is referred to as \(i_{\text{MP}}\). The magnitude of the relationship between the two impacts the production of the power cycle phenomena. A single row of a star row in one of the nodes in this study can only be connected to two power components simultaneously, and the power components include the motor, the engine, and the output shaft, when designing the configuration scheme. The selection process begins from the perspective of the connecting nodes and considers that the design configuration must achieve variable speed adjustment. Figure 2 illustrates an input split arrangement with six connection options when the motor and output are linked at the same node. An MG2 motor is connected to the output in the configuration indicated in Figure 2, and the speed-torque coupling equation for the planetary row is presented in Equation (3), which determines the torque-speed relationship between the input power element and the output element. \[\left\{ \begin{array}{l}T_{\text{M2}}=-\frac{1}{\alpha}T_{\text{E}}\\ T_{\text{M1}}=T_{\text{Out}}-\frac{\alpha-1}{\alpha}T_{\text{E}}\\ \omega_{\text{M2}}=\omega_{\text{Out}}\\ \omega_{\text{MI}}+(\alpha-1)\omega_{Out}-\alpha\omega_{\text{E}}=0\end{array} \right. \tag{3}\]  
The ratio of the electromechanical path power to the engine output power for the input distributed configuration is shown in Equation (4). \[\left\{ \begin{array}{l}\eta_{\text{M}_{1}}=\frac{T_{\text{M1}}\omega_{\text{ MI}}}{T_{\text{E}}\omega_{\text{E}}}=\frac{1}{\alpha}-1-\frac{1}{\alpha l}= \frac{i\text{MP}}{l}-1\\ \eta_{\text{M}_{2}}=\frac{T_{\text{M2}}\omega_{\text{ME}}}{T_{\text{E}}\omega_{ \text{E}}}=1-\frac{1}{l}+\frac{1}{\alpha l}=1-\frac{i\text{MP}}{l}\end{array} \right. \tag{4}\]  
\(\alpha\) in Equation (4) is related to the characteristic parameter \(K\) of the planetary row. The corresponding \(\alpha\) values for the six input distributive configurations are \(\alpha_{1}=K/(1+K)\), \(\alpha_{2}=-K\), \(\alpha_{3}=1/(1+K)\), \(\alpha_{4}=(1+K)/K\), \(\alpha_{5}=-1/K\), and \(\alpha_{6}=1+K\). Option (f) was chosen for analysis. Equation (4) indicates that the power-split phenomenon happens when \(i>i_{\text{MP}}\), \(\eta_{\text{M1}}<0\), and \(\eta_{\text{M2}}>0\). At this time, MG1 is the generator, MG2 is the motor, electrical power flows from MG1 to MG2, and the output mechanical power of MG2 converges to that of the output shaft. The power circulation phenomenon happens when \(i<i_{\text{MP}}\), \(\eta_{\text{M1}}>0\), and \(\eta_{\text{M2}}<0\); then, MG2 is the generator, MG1 is the motor,  
Figure 2: Configurations for the input split arrangement. (**a**,**d**) Motor MG2 and output shaft are connected to the sun gear; (**b**,**e**) Motor MG2 and output shaft are connected to the planetary carrier; (**c**,**f**) Motor MG2 and output shaft are connected to the gear ring. electrical power flows from MG2 to MG1, and the direction of power flow is opposite that of the mechanical power flow. Figure 3 illustrates an output distribution configuration with six possible connections for the engine and the motor at the same node. Equation (5) describes the torque-speed relationship between the power input element and the output element of the output split configuration according to the analysis of the input split configuration. \[\left\{