In recent years, remarkable progress has been made in the high-speed railway, which has greatly changed the way of people’s daily travel and boosted the economic development. However, the bulky and low-efficiency line-frequency transformer is utilized to realize electrical isolation and voltage matching in the traditional locomotive traction unit, which leads to large energy consumption of the high-speed train and low power density of the traction onboard equipment. Thus, power electronic traction transformers (PETT) with the salient features of energy-saving, low-carbon, high-power density, environmental protection are considered as the core equipment of next generation high-speed trains [1, 2]. After many years of development, the topology of PETT has formed a representative three stage structure [3] shown in Fig. 1, consisting of a single-phase cascade H-bridge (CHB) converter, the output parallel dual active bridge (DAB) dc-dc converters with medium/high frequency transformers and a three-phase inverter. In practice, due to the circuit parameter mismatch such as storage inductor in DAB converters, transmission power unbalance problem cannot be avoided [4]. It may cause high current stress, low efficiency, large current/voltage deviation and even the breakdown of power devices if the balancing control scheme is not adopted [5, 6]. So it is significant to keep the transmission power balance between different PETT cells. In order to balance the voltage in CHB stage as well as the power in the DAB stage with parameter mismatch, a voltage and power control scheme is proposed in [7] to balance dc-link capacitor voltages of the adopted CHB converter and the actual power through the parallel DAB modules. Although the proposed scheme is simple, the high-frequency inductor current sensors are necessary in all DAB modules, which leads an increase of system cost greatly. In addition, a coordinating control solution for the CHB and DAB converters without inductor current sensors is proposed in [8]. A common duty ratio controller for the CHB stage in the single phase d-q coordinate and feedback feed-forward controller for the DAB stage are adopted in the coordinating control scheme. Although the scheme gets rid of the inductor current sensor in the DAB converters, the efficiency and dynamic performance of the scheme is a little poor.