Energy management with dual droop plus frequency dividing coordinated control strategy for electric vehicle applications

In this paper,a dual droop-frequency diving coordinated control strategy is proposed for electric vehicle(EV)applications,where the hybrid energy storage system(HESS)with supercapacitors and batteries is integrated to prolong the life time of storage elements.The dynamic power allocation between the supercapacitor and batteries are obtained through the voltage cascaded control,upon which the high and low frequency power fluctuation are absorbed by the supercapacitors and batteries respectively to fully exploit the advantages of the supercapacitors and batteries.Moreover,the power capacity is scaled up by connecting storage blocks in parallel.A dual droop control scheme for parallel-connected energy storage system and its operation principle is introduced on the aspect of current sharing characteristic and state-of-charging(SOC)management.After detailed analysis and formula derivation,the corresponding loop parameters are designed.Through this control method,the current sharing performance is ensured and each block makes the self-adaptive adjustment according to their SOC.Consequently,the load power can be shared effectively,which helps to avoid the over-charge/over-discharge operation and contributes to the life cycle of the energy storage system.Each module is autonomous controlled without the necessity of communication,which is easy,economic and effective to realize.Finally,the simulation and experimental results are exhibited to verify the effectiveness of the proposed control scheme.

Elimination of Collector Current Impact in TSEP-based Junction Temperature Extraction Method for High-Power IGBT Modules

Insulated gate bipolar transistor(IGBT)modules are widely employed in high-power conversion systems.Their junction temperature ranks as one of the most important factors in the reliability of power semiconductor devices.Thermo-sensitive electrical parameter(TSEP)is regarded as the promising solution to extract the junction temperature due to its non-invasion measurement,fast response and high accuracy.However,accurate collector current measurement is required if only the individual TSEP is adopted,which increases the complexity and cost.In this paper,the combined TSEP method is proposed to eliminate the influence of collector current(/c),where the turn-off delay time(tdoff)and maximum decrease rate of/c(max d/c/dt)are adopted and combined.The two TSEPs both have linear relationships withjunction temperature and/c.When they are combined mathematically,the influence of/c is eliminated.Experiments have been implemented to validate the effectiveness of the proposed approach.The comparison between combined TSEP and two individual TSEP methods are illustrated and analyzed.

Non-isolated stacked bidirectional soft-switching DC-DC converter with PWM plus phase-shift control scheme

In this paper, a non-isolated stacked bidirectional DC-DC converter with zero-voltage-switching(ZVS) is introduced for the high step-up/step-down conversion systems. The extremely narrow turn-on and/or turn-off duty cycle existing in the conventional bidirectional buck-boost converters can be extended due to the stacked module configuration for large voltage conversion ratio applications. Furthermore, the switch voltage stress is halved because of the series connection of half bridge modules. The PWM plus phase-shift control strategy is employed, where the duty cycle is adopted to regulate the voltages between the input and output sides and the phaseshift angle is applied to achieve the power flow regulation.This decoupled control scheme can not only realize seamless bidirectional transition operation, but also achieve adaptive voltage balance for the power switches. In addition, ZVS soft-switching operation for all active switches is realized to minimize the switching losses. Finally, a prototype of 1 kW operating at 100 kHz is built and tested to demonstrate the effectiveness of the proposed converter and the control strategy.

Comparison of Cost-effective Distances for LFAC with HVAC and HVDC in Their Connections for Offshore and Remote Onshore Wind Energy

For a cost-effective connection of large-scale longdistance wind energy,a low frequency alternating current(LFAC)transmission scheme(16.7 Hz or 20 Hz)is proposed as an alternative to the conventional high voltage alternating current(HVAC)transmission scheme(50 Hz or 60 Hz)and the recently popular high voltage direct current(HVDC)transmission scheme(0 Hz).The technical feasibility of the LFAC system is demonstrated but the basis for identifying the distance ranges for which LFAC would be preferable to HVAC and HVDC are not established and the dependence of this range on factors,such as power transfer rating,voltage rating and cable/line type,is not investigated.This paper presents an in-depth analysis for the overall cost of LFAC system and then provides an extensive comparison with HVAC and HVDC,to explore the distance ranges over which LFAC is cost-effective over both HVAC and HVDC in connections of offshore and remote onshore wind energy.The results demonstrate that the LFAC system does possess ranges in the intermediate distance for which it is more cost-effective than both HVAC and HVDC,and its overall cost advantage is generally larger in the overhead line(OHL)connection of remote onshore wind energy than the cable connection of offshore wind energy.

Hierarchical Control of DC Microgrids Robustness and Smartness

This paper investigates the hierarchical control of DC microgrids.Compared to AC microgrids,DC microgrids encounter complicated converter-level control,and simplified system-level management.To address these characteristics,a new three-level control hierarchy is introduced.The converter control level encapsulates sophisticated converter topologies and inner control loops into a black-box representation.The voltage coordination level uses DC voltage signals to coordinate both static and transient power sharing.The energy management level optimizes the power flow and power quality in a broader scope through communication.This architecture lowers the focus of control to bottom levels.More functions are allocated to the converter control and voltage coordination levels.They can maintain basic microgrid performance with fully local control,thereby ensuring reliable power supply in case of communication failures.Moreover,taking advantage of DC microgrids’simplified system-level operation patterns,the energy management level uses straightforward algorithms to achieve intelligent functions.As a result,this architecture achieves both robust and smart control by exploring DC microgrids’critical features.