Sanzhong Bai

Review of non-isolated bi-directional DC-DC converters for plug-in hybrid electric vehicle charge station application at municipal parking decks

There is a growing interest on plug-in hybrid electric vehicles (PHEVs) due to energy security and green house gas emission issues, as well as the low electricity fuel cost. As battery capacity and all-electric range of PHEVs are improved, and potentially some PHEVs or EVs need fast charging, there is increased demand to build high power off-board charging infrastructures. A charge station architecture for municipal parking decks has been proposed, which has a DC microgrid to interface with multiple DC-DC chargers, distributed renewable power generations and energy storage, and provides functionalities of normal and rapid charging, grid support such as reactive and real power injection (including V2G), current harmonic filtering and load balance. Several non-isolated bidirectional DC-DC converters suited for charge station applications have been reviewed and compared, as the major focus of this paper. Half bridge converter is a good candidate but it is difficult to maintain high efficiency in wide battery pack voltage range. A variable frequency pulse width modulation (VFPWM) scheme is proposed to mitigate this issue. Finally three-level bi-directional DC-DC converter is suggested to be employed in this application. A 10kW prototype verifies that 95.1–97.9% full load efficiency can be achieved in charging mode with 180–360V battery pack voltage. In addition, the inductor size is only one third of the half bridge counterpart, which is a great advantage for high power converters.

ZCS

Inductive power transfer (IPT) is commonly used to transmit power from an extended loop (track) to a number of galvanically isolated movable pick-ups. To maximize the power transfer and minimize converter requirements, various compensation circuits have been proposed for both the track (primary) and the pick-up (secondary). This paper investigates the suitability of the LCC series-parallel compensation for IPT primary design. A new compensation-circuit design procedure is proposed that considers high-order current harmonics and results in inverter zero-current switching. The proposed compensation is compared with the classical compensation designed for zero phase angle between the inverter voltage and current fundamental components. Expressions for the bifurcation boundary, voltampere rating of reactive-compensation elements, and the current at the moment of switching are derived and analyzed. Analytical results are verified both via PSpice simulations and experimentally using a 1-hp MOSFET-based prototype.

LCC

In this paper the optimum design of a fast-charging station for PHEVs and EVs is proposed to minimize the strain on the power grid while supplying the vehicles with the required power. By studying the power demand of the charging station, a conclusion is reached that the size of the grid tie can be reduced substantially by sizing the grid tie for the average rather than the peak power demand. Therefore the charging station architecture with a single AC/DC conversion and a DC distribution to DC/DC charging units is proposed. An energy storage system is connected to the DC bus to supply power when the demand exceeds the average that can be provided from the grid. Various topologies for both the AC/DC and DC/DC conversion are studied to find the optimum design for this application.

-Compensated Resonant Inverter for Inductive-Power-Transfer Application

A network of fast-charging stations is of great importance for widespread adoption of electric vehicles (EV) if the so-called range anxiety issue is to be resolved. As with petrol stations, we expect that multiple chargers will be co-located to form charging stations. This layout allows for the fast-charging station to make use of a common rectifier stage and several dc/dc stages to charge multiple EVs. This paper builds on our previous work where we proposed a novel dc-side filter for the 12-pulse rectifier and investigated the power profile for a MW fast-charging station. In this paper, we propose a novel control approach for the filter, based on the virtual resistor injection, which results in further reduction in dc ripple, ac-side harmonics, and filter VA ratings. We also demonstrate that, with the proposed topology and control, the filter stage can be used as dc-side energy storage system.

Optimum design of an EV/PHEV charging station with DC bus and storage system

Economic and environmental issues are main motivation for developing efficient and sustainable electrical vehicle for urban transportation. Electrical vehicles (EV) have two main advantages compared to hybrid and gasoline vehicle: eliminated tailpipe emissions and simplified drive-train. However, electric vehicles have a limited range between recharges when fitted with the current state-of-the-art energy storage. To mitigate the limitations of the energy storage technology, we propose to use inductively coupled power transfer (ICPT) to supply power to the vehicle while it is moving. ICPT is an efficient technique for transferring power with no physical connection between the source and the load. In this paper we investigate the ICPT requirements for two types of vehicles operating in combination with ICPT system. The first vehicle makes use of a battery as primary and ICPT as secondary energy source for electric vehicle supplying. The goal is to achieve 300 miles range of covering. The second uses electrochemical capacitors (Ultracapacitors) as the power source and ICPT as the energy source. The goal is to provide unlimited range for the vehicle. The result is system analysis of feasibility of battery-ICPT and ultracapacitor-ICPT combinations for different driving conditions and vehicles as well as rough evaluation of expected length and optimal positions of ICPT track for specified driving cycles.

Unified Active Filter and Energy Storage System for an MW Electric Vehicle Charging Station

The 12-pulse rectifier is often used to supply high-power industrial loads. Its ability to effectively and cheaply mitigate the harmonics on the ac side has ensured its dominance in the industry even as active front ends become cheaper and more reliable. Despite its many benefits, the 12-pulse rectifier is not able to reduce the ac-side harmonics to a level acceptable by the pertinent IEEE standards without additional filtering. In this paper, we outline a novel method to profile the rectifier output current to be triangular which results in low ac-side harmonics. The novelty in the proposed approach is that we exploit the dc-side filter design to minimize the volt-amperes (VA) rating of the current source used to profile the dc-side rectifier current. Additional benefits of the proposed method include lower VA rating of the dc filter, simple integration of dc energy storage, and effective ac harmonic control even when the initial rectifier current is discontinuous.

Inductively coupled power transfer for continuously powered electric vehicles

This paper studies three fundamental switching patterns for resonant converters to achieve Zero Voltage Switching (ZVS) operation. To evaluate the performance of the three control methods, three resonant topologies are taken into consideration: series resonant, parallel resonant and seriesparallel resonant. The criteria functions for ZVS operation are derived for each control method and topology. The results show that the Asymmetrical Clamped Mode control (ACM) can guarantee lower switching frequency than other two control methods while keeping ZVS operation. Moreover, the circulating power for each control method is analyzed. The relationships between the switching frequency and the maximum power transfer of the three resonant topologies are derived and the series-parallel resonant topology shows a superior characteristic. Experiment results are given to verify some of the results.

New Method to Achieve AC Harmonic Elimination and Energy Storage Integration for 12-Pulse Diode Rectifiers

This paper looks at the optimizing the electric vehicle supply equipment (EVSE) design for level 3 DC charging stations. By studying the power demand of the charging station, we conclude that the size of the grid tie can be reduced substantially by sizing for average rather than the peak power demand. Therefore the charging station architecture with a single AC/DC conversion and a DC distribution to DC/DC charging units is proposed. An energy storage system connected to the DC bus is used to supply power when the demand exceeds the capability of the grid tie. Specifically, this paper looks at the integration of energy storage on the DC bus to (1) provide power to the chargers in instances when their requirements exceed the grid tie capability (2) eliminate DC side ripple and (3) eliminate AC side harmonics.

A comparison study of control strategies for ZVS resonant converters

The total harmonic distortion (THD) of a waveform is a standard way to quantify its deviation from a sinusoid. In three-phase systems, we are interested in minimizing 3THD: the component of THD produced by odd nontriplen harmonics. However, its definition involves an infinite sum, making it difficult to evaluate and analyze. This paper solves the problem of finding equivalent closed-form expressions for the 3THD of a staircase waveform. In particular, two expressions are rigorously derived, which reveal 3THD to be a piecewise differentiable function. One expression is shorter but describes the pieces implicitly. The other is longer but describes the pieces explicitly. We minimize 3THD using the closed-form expression and provide a comparison with previous techniques. Finally, we provide experimental results that show close agreement with the theoretical results.

Design considerations for DC charging station for plug-in vehicles

In this paper we present a new circuit design for multi-pickup high-power inductive power transfer systems. The proposed design combines parallel compensated resonant tank with tri-state boost converter. By synchronizing tri-state boost switching period with the half-period of resonant tank voltage, we position the inherently discontinuous current pulse drawn by tri-state boost to control both active and reactive power flow from the resonant circuit to tri-state boost. Controllable reactive current can be used effectively to emulate appropriate inductance or capacitance to tune the resonant tank and achieve optimal power transfer.