## 1 Introduction  
Electric vehicles (EVs) are promising alternatives to conventional vehicles that use fossil fuels [1]. Benefiting from the wide operating range of the electric motor and minimizing the cost, volume, and mass of the power train, most EVs in the market are equipped with fixed-ratio single reduction rather than multispeed transmission, e.g., Nissan Leaf, Renault ZOE, and Tesla Model 3. However, motor operating points may deviate from the high-efficiency region under actual driving conditions for daily use and the ratio of single reduction on EVs must be designed as a trade-off between dynamic and economic performances [2]. Researchers have proved benefits of using multispeed transmissions on EVs through simulations and experiments [3; 4; 5; 6; 7]. Integrating a multiple-speed transmission into EVs can make optimum use of high-efficiency motor operating ranges, which means that the motor and battery can be downsized compared to the baseline drivetrain configuration consisting of a single-speed transmission [3; 4]. Reference [2] indicated that choosing a suitable two-speed transmission not only improves EVs' dynamic performance with little additional initial manufacturing cost, but also saves customers' money in the long term. The application of a multispeed transmission for EVs consists of dual clutch transmission (DCT) [8; 9], continuous variable transmission (CVT) [5], automatic transmission (AT) [10; 11], and automated manual transmission (AMT) [6; 11; 12; 13]. Each of the above transmission configurations has its own merits and demerits. The first three can achieve a seamless gearshift by clutch-to-clutch control, but this makes the control system complex and expensive. The AMT used in EVs has a simpler mechanical structure and lower cost, in which the gearshift is mainly achieved through active motor speed synchronization, while torque interruption is inevitable during the gearshift process. Gear ratio optimization of the multispeed transmission is necessary in order to balance the dynamic and economic performance. In [2], the gear ratios of a two-speed DCT and a simplified CVT are designed according to target vehicle performance characteristics, i.e., top speed, max grade, and acceleration. The selection of the optimal gear ratio for the CVT-based two-speed system has been carried out via an optimization procedure which takes into account the efficiency characteristics of the whole vehicle power-train [14]. However, the above design optimizations are based on fixed drive cycle, which may not be necessarily optimal when applied to different drive cycle or to the entire driving profile of a vehicle [15]. Therefore, reference [6] designed a composite gear shifting schedule under the combined urban and suburban drive cycles in the optimization process. Researches on gearshift control of transmissions for EVs have also been observed. In [16], optimal control methods are used to fulfill the constant-output speed and constant-output torque shift control, with the actuator limits considered. This work is further improved by complementing with a backstepping controller which serves as the feedback component [17]. Hybrid Minimum Principle (HMP) is used to handle state jumps at the switching points of different stages in gearshift [10]. PID (Proportional-integral-derivative) controllers are applied in references [18; 19]. Effects of the slip speed reference in the inertia phase are discussed in reference [20]. In [21], torque observers are adopted to facilitate shifting control of a two-speed transmission for EV. Novel configurations and control strategies are brought about with the rapid development of EV. For high-performance models, intermittent power loss is unacceptable. In such cases, planetary-gear-based transmissions (PGTs) may be more promising candidates. In this paper, we propose a two-speed transmission based on dual planetary gear mechanism and introduce an integrated gearshift strategy using feedforward-feedback control with disturbance compensation, for both torque phase and inertia phase.