# A Novel Energy Optimization Control Strategy for Electric Drive System Based on Current Angle
## 1 Introduction
### Literature Review  
Recently, the efficiency of motor has been improved by motor structure optimizing, vehicle control strategy, and motor loss minimization algorithm (LMA). In the motor manufacturing stage, the energy consumption characteristics of the motor can be improved by optimizing the structure of the motor, including the shape, material, geometric dimension, and so on [3; 4; 5; 6]. When the motor is manufactured and installed on the vehicle, the working point of the motor can be changed as much as possible through different vehicle structures and vehicle control strategies to improve the power and economy of the vehicle, such as dual motor drive system and corresponding coordinated control strategy [7; 8], two-speed automated manual transmission (AMT)-motor system with shift controlstrategy [9]. In addition, the most widely used method to improve the efficiency of the motor is LMA [10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23; 24], which search the optimal control variables (usually dq-axis current \(i_{d}\)/\(i_{q}\)) of the motor through the loss model, so that the efficiency of the motor is the highest under the given speed and torque. At present, LMAs to improve the motor efficiency can be divided into two categories: Online search control (OSC) and loss model control (LMC). OSC is less affected by the motor parameters. According to the state feedback of the machine, different methods were proposed to give the increment of the optimal direction of motor current vector during each iteration, such as neural network [10], golden section search (GSS) [11], collaborative optimization control strategy based on sliding mode controller [12], and online optimization [13]. The electric time constant of the motor is very small, which can reach microsecond level, so the OSC will occupy a lot of computing resources and its response speed is slow. Compared with it, LMC has the advantages of fast response speed, good dynamic characteristics, and so on. It is often used in motor in practical application. LMC uses the motor loss model to calculate the optimal control parameters of the motor, so that the motor efficiency is the highest. Some scholars used methods like formula calculation [14], linear optimization [15], and nonlinear programming [16] to optimize the of motor armature current vector, which improved the efficiency of motor. However, in reality, the characteristics of motor are complex and changeable, and such LMC means are no longer suitable for the current needs. Now, scholars put more interest in table lookup control (LUTC). This kind of LMC obtains the optimal control value of each working point through the motor loss model to make an offline look-up table, and then control the motor by looking up the offline look-up table according to the current state of the motor. In light of different optimization objects, LUTC is divided into DC bus voltage \(U_{dc}\) optimization control [17; 18], inverter switching frequency \(f_{purm}\) optimization control [19], and furthermore, the optimization control of DC bus voltage combined with inverter switching frequency was proposed [20]. It should be mentioned that in order to better control the motor, the optimization objects of most LUTC are flux linkage \(\varphi_{f}\)[21; 22] and dq-axis current \(i_{d}\)/\(i_{q}\)[23], which is more effective for the control of copper loss and iron loss in motor. Furthermore, inverter switching frequency \(f_{purm}\) was added to the optimization [24], but \(i_{d}\)/\(i_{q}\) and \(f_{purm}\) were considered separately. In brief, most of the above LMA studies focus on the control strategy of \(i_{d}\)/\(i_{q}\), which can effectively reduce the loss of motor itself. However, it is still of great potential and reference value to explore effective motor control strategies. Moreover, the above LMA studies often focus on the loss of the motor, and few studies consider the loss of the inverter at the same time. Other works solely consider the efficiency of the inverter. One method is adopting advanced power devices [25; 26].