MW-Chargers for Heavy-Duty EVs using Thyristors

Private and business transportation presently contributes to nearly a 3rd of greenhouse fuel (GHG) emissions. Some obstacles to the broader adoption of electrical automobiles (EVs) embrace the battery vary, the charging time, and the charging infrastructure.

Requirements for passenger electrical automobiles (EVs) at the moment are higher outlined, with the Charging Interface Initiative (CharIN) activity pressure creating the Mixed Charging System (CCS) specification, which permits for DC quick charging (DCFC) at energy ranges as much as 350 kW at bus voltages of 800 V.  These energy ranges sufficient for many EV passenger vehicles with motors within the 100 kW vary and battery capacities of fifty to 100 kWh.

Heavy-duty vans for business transportation sometimes devour about 2 kWh/km and might have battery capacities of round 500 kWh. This results in the requirement for MW charging ranges. The Megawatt Charging System (MCS) is an evolving, high-power heavy-duty truck and bus EV charging normal created by CharIN. This text will spotlight a presentation titled “MW-Chargers for heavy-duty EVs” delivered by Dr. Martin Schulz, International Principal Utility Engineer, Littelfuse on the PCIM Europe 2023 convention.

Charging Requirements

The MCS draft requirements for energy ranges, connector kinds, cooling necessities, and many others. are nonetheless in flux, although preliminary tips checklist a most voltage of 1250 V and a present degree of 3000 A (DC).  Determine 1 reveals the present CCS and MCS voltage and present ranges for EV charging.

Conventional EV Chargers

Charging programs want galvanic isolation for security and a standard strategy has taken the incoming energy provide by means of a Energy Issue Correction (PFC) rectification stage. This might be adopted with an remoted DC-DC converter corresponding to a twin lively bridge or a LLC stage, as proven in Determine 2.

Silicon carbide (SiC) gives many benefits over conventional silicon-based IGBTs within the energy conversion levels, corresponding to a lot decrease losses at a given energy ranking, the flexibility to modify quicker and therefore cut back the scale of the magnetics, and improved high-temperature operation. Every charger unit proven in Determine 2 can sometimes present 60 to 100 kW and would must be stacked to attain the online energy requirement and system redundancy. Efficiencies are reported within the 97-98% vary. Whereas these SiC chargers allow compact, excessive energy densities for passenger EV DCFC, the query is whether or not they would additionally swimsuit the upper powers required for MCS.

Thyristors

Thyristors are four-layer, three-terminal, bipolar, current-controlled gadgets first commercialized in 1958. Wonderful bipolar present conduction has allowed present and voltage rankings as excessive as 6000 A and 12000 V to be achieved in Si thyristors¹.  Rectifiers primarily based on thyristors are key parts in purposes corresponding to electrolysis. Medium voltage drives use load-commutating thyristor-based inverters in purposes corresponding to compressors and marine drives with powers ranging as much as 100 MW. Very high-power thyristor-based converters are utilized in Excessive Voltage Direct Present (HVDC) and Versatile AC Transmission Techniques (FACTS), the place they change on the line frequency of 50-60 Hz. Their bi-directional voltage-blocking functionality permits for line commutation. Excessive reliability, effectivity, overload, and surge present functionality give them unparalleled benefits in such purposes.

MW-Chargers for Heavy-Obligation EVs utilizing Thyristors

Littelfuse has proposed an MW-capable heavy-duty truck EV charger system primarily based on thyristors. Determine 3 reveals the system overview. Right here, the medium voltage transformers that obtain the incoming MV AC energy obtain galvanic isolation. This eliminates the transformer and the LLC converter stage and results in a less complicated topology.

The N1718NC200 thyristor used within the B12H or B12C topology for the thyristor has a ranking of 1718 A, and 2000 V. Determine 4 reveals a prime view of this half within the press-pack bundle, in addition to some effectivity calculations on this utility.  This high-voltage utility’s firing angle is anticipated to be between 0 – 30 levels, resulting in low reactive energy era.

A comparability to SiC-based MW charger

The thyristor-based system proven in Determine 3 would have a 2212 W loss per bridge, resulting in an total lack of 4423 W within the B12 association. This equates to an effectivity of 99.8% for the general 2.5 MW. A comparability of the same charger constructed utilizing SiC MOSFETs within the system depicted in Determine 2 results in every 60 kW unit doubtlessly needing as much as 44 dies. The two.5 MW charger would wish a complete of 1600 SiC MOSFET die. Concerning the cooling necessities, at a 97% effectivity degree, the two.5 MW charger would create a lack of 75 kW. This may therefore want a liquid cooler (chiller), which pulls round 25 kW of energy, resulting in a internet lack of 100 kW. With the a lot decrease loss, the thyristor-based charger may be air-cooled, which solely consumes round 600W to energy followers. The entire loss is due to this fact round 5 kW (4.4 kW + 0.6 kW).  Determine 5 reveals the appreciable benefit the thyristor-based system would have in dimension and quantity.

Determine 6 lists the operational value comparisons between the SiC MOSFET-based and thyristor-based MW chargers. Vital vitality and value financial savings are achieved with the thyristor-based strategy. Even when an N+1 redundancy have been added to the circuit, i.e. use of 24 thyristors as an alternative of 12, operational effectivity and cooling benefits would stay.

Conclusion

Thyristors can have a number of energy conversion benefits in line frequency and high-power purposes. The MCS for heavy-duty EVs is a major instance the place the low conduction loss, excessive energy ranking, and strong, dependable, and confirmed efficiency of those Si gadgets can be utilized vastly.

In an interview at PCIM 2023, Martin Schulz commented, “Thyristors have an extended historical past of extraordinarily dependable operation. Littelfuse thyristors span numerous energy ranges and are utilized in numerous purposes from crowbar shunt safety to energy conversion for electrolysis. They will present a extra environment friendly various to SiC in making use of MW EV-charging for heavy-duty automobiles utilized in business transportation.”

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