Study On Optimal Flux-weakening Control Of Permanent Magnet Synchronous Motors For Electric Vehicle In High-speed Range

The automotive industry is not only a pillar industry of the national economy, but also iconic industry which plays an important role in the national economy and social development. New energy vehicles are a major upgrading and breakthrough that acts as method that automobile industry deal with energy security, climate change, environmental protection and structure Upgrade. New energy vehicles have become green industry with a great market potential in 21st century. The electric drive system which consists of a motor, an inverter and a controller as a link between the wheels and the energy storage system is the heart of the electric car. It determines vehicles’ performs. PMSM (permanent magnet synchronous motor),specially rare-earth permanent magnet synchronous motor, has simple structure, reliable operation, small size, low weight, low loss, high efficiency, flexible shape and size and other significant advantages. So PMSM has a high value in the electric drive system of electric vehicles.Frequent acceleration and deceleration, complex operating conditions and high-speed operation of electric vehicle require electric drive system to have higher robust and dynamic response. At the same time, limited power of electric vehicle and high cost of storing power require electric drive system to have high operating efficiency in flux-weakening operation. Based on the above requirements, this article carries out optimization studies in motor control and inverter control.Firstly, the paper summarizes the flux-weakening control method of PMSM and its PWM modulation technique, which provides a theoretical basis of flux-weakening control of PMSM and its PWM modulation.In the level of motor control, this paper focuses on the single current weakening control method, and proposes a novel weakening control method based on gradient descent by using single current regulator. On the basis of single current control, this method optimize online automatically to update q-axis voltage by comparing the current gradient descent direction and constant torque direction in current value of the load and speed, so that the current reaches the minimum to improve operational efficiency, while this method retains the original advantages of single current control, such as fast dynamic response, high depth of field-weakening, good robustness of the DC bus voltage and load variations. The simulation and experimental results show that:compared with linearization method, the method proposed in this paper can improve efficiency of the electric drive system, providing an effective and efficient way for the operation of the PMSM drive system.In the level of inverter control, considering permanent magnet synchronous motors that work in field-weakening control work is close to the maximum modulation for general, this paper proposes a novel minimum switching loss PWM modulation based on vector control in order to work with PMSM in field-weakening control. The method combines with vector control principle and synthetically uses a variety of discontinuous PWM (DPWM) strategy, reaching the aim of saving the switching losses, reducing the harmonic content of the inverter output voltage in field-weakening control and reducing the torque ripple. The simulation and experimental results show that this method helps reduce the harmonic content of the inverter of electric vehicle and improve system performance and operational efficiency.