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Charged EVs | The way to choose the optimum transient surge safety for EV on-board chargers Unveiled: Uncover Auto Excellence at Autoxyon

On this charming article, we delve into Charged EVs | The way to choose the optimum transient surge safety for EV on-board chargers, a masterpiece crafted by Charged EVs and printed on 2023-10-20 15:50:52. Discover the world of Auto Excellence and uncover what units Autoxyon aside.

Sponsored by littelfuse.

The Automotive setting is likely one of the most extreme environments for Electronics. In the present day’s automobile designs proliferate with delicate Electronics, together with digital controls, infotainment, sensing, battery packs, battery administration, electrical automobile powertrains, and on-board chargers. Along with the warmth, voltage transients, and electromagnetic interference (EMI) within the Automotive setting, the on-board charger should interface with the AC energy grid, requiring safety from AC line disturbances for dependable operation.

In the present day’s part producers supply a number of units for safeguarding digital circuits. Because of the connection to the grid, on-board charger safety from voltage surges utilizing distinctive elements is crucial. 

Littelfuse options concentrate on superior overcurrent and overvoltage safety applied sciences, together with MOV (Metallic Oxide Varistor), TVS (Transient Voltage Suppressor), GDT (Fuel Discharge Tube), and SIDACtor® safety thyristors. The problem for design engineers? The way to optimize the part choice and decide the most effective mixture of applied sciences to achieve the most effective efficiency and value.

A singular resolution combines a SIDACtor and a Varistor (SMD or THT), reaching a low clamping voltage below a excessive surge pulse. The SIDACtor+MOV mixture permits Automotive engineers to optimize the choice and, subsequently, the price of the facility semiconductors within the design. These elements are wanted to transform the AC voltage into the DC voltage to cost the automobile’s on-board battery. 

 Determine 1. On-board charger block diagram 

The On-Board Charger (OBC) is in danger throughout EV charging on account of publicity to overvoltage occasions that will happen on the facility grid. The design should shield the facility semiconductors from overvoltage transients as a result of voltages above their most limits can injury them. To increase the EV’s reliability and lifelong, engineers should tackle growing surge present necessities and decrease most clamping voltage of their designs. 

Determine 1 exhibits the circuits requiring safety elements and blocks that may make use of high-efficiency elements. The desk lists the beneficial applied sciences.

The potential surge pulses for the OBC come from oblique lightning strikes, load switching, and failure within the system. Think about the facility of a direct lightning strike of 100kA; a excessive surge present requirement within the specification is comprehensible. Different potential root causes for a surge pulse are abrupt load switching and faults within the energy system.

Instance sources of transient voltage surges embody the next:

  • Switching of capacitive masses
  • Switching of low voltage techniques and resonant circuits
  • Brief circuits ensuing from development, visitors accidents, or storms
  • Triggered fuses and overvoltage safety. 

The coupling of the surge pulses is capacitive on parallel cables, inductive on conductor loops, and emission within the close to area. The transient surge happens over cable (on energy, information, or sign traces), and it may be symmetrical (line-to-line) or asymmetrical (line-to-ground). It’s essential to know the coupling and propagation supply to resolve the applying downside.

The IEC-61000-4-5 is the related normal for surge immunity. Desk 1 lists most surge voltages as much as 4kV. The 2Ω generator resistance leads to a 2kA surge pulse (1a). The IEEE C62.41.2-2002 normal specifies a 6 kV/3 kA surge score (1b). In the present day, most energy grid-related AC energy circuits are designed to withstand the IEEE surge requirement.

Desk 1. (1a) IEC 61000-4-5 peak voltage and peak present face up to scores and (1b)
IEEE C62.41.2-2002 Customary 1.2/50 µs-8/20 µs, anticipated voltages and present surges.

In accordance with the 6kV/3kA surge, many designers use 14mm MOVs within the AC major facet circuit.

Determine 2. Really useful circuit for differential and customary mode transient voltage circuit safety utilizing MOVs and a GDT.

A 20mm MOV is most well-liked for higher reliability and safety. The 20mm MOV handles 45 pulses of 6kV/3kA surge present, which is way more strong than the 14mm MOV. The 14mm disc can solely deal with round 14 surges over its lifetime.

Voltage transient safety efficiency comparability

Examine an MOV’s transient voltage safety efficiency with a SIDACtor+MOV mixture. Determine 3 exhibits the clamping efficiency of a 14mm MOV when struck with a 2kV and a 4kV surge. The MOV has a most working voltage of 385VACRMS. The clamping voltages are greater than 1000V, which places a excessive stress degree on the facility semiconductors.

MOV transient voltage efficiency

Determine 3. Clamping efficiency of the Littelfuse V14P385AUTO MOV below 2kV and 4kV surges. The clamping voltage exceeds 1000V.

MOV Choice Parameters

  • Rated Working Voltage—Most steady voltage of the circuit to be protected.
  • Ambient Temperature—Temperature within the space surrounding the MOV, used to find out if thermal derating is required.
  • Transient Voltage Waveform—Defines the transient pulse, together with peak voltage, period, and transient supply impedance, sometimes offered in a Customary (e.g., IEC-61000-4-5).
  • Amount of Transient Voltage Pulses—Outlined by the Customary, that is the variety of pulses that the elements should survive, and that the MOV might want to soak up.
  • Peak Pulse Present–Transient voltage pulse and the generator’s inner resistance present the height present.
  • Mounting necessities of MOV (straight, bent leads or SMD).
  • Requirement to fulfill the 6kV/3kA waveform drives MOV choice. The everyday lifetime requirement is 10 pulses.

Instance choice dedication

Stage 1 Charger—120VAC, single-phase circuit: The anticipated ambient temperature is 100°C.

Step 1: Decide the minimal voltage score of the MOV. The rule of thumb is so as to add 25% to the nominal AC line voltage to account for an imperfect energy service: 120VAC x 1.25 = 150VAC. That is the minimal steered voltage score. The utmost peak surge present should be above 3kA.

Step 2: Repetitive Surge Functionality should meet the usual necessities. The height surge present and the power score should be decreased based mostly on the temperature derating chart. The excessive potential capability will depend on the coating choice. Utilizing a GDT helps the safety configuration obtain the leakage necessities of the Excessive Potential check, which an MOV can not meet alone.

SIDACtor+MOV transient voltage efficiency

Determine 4. SIDACtor+MOV safety from voltage transients between line and impartial

The SIDACtor+MOV method has a number of benefits. The first profit is that for a 6KV/3KA surge, the clamping voltage is below 1000V as indicated in Desk 2

Determine 5 illustrates the voltage versus time response of the MOV and SIDACtor+MOV mixture, once more exhibiting that the SIDACtor+MOV mixture has a decrease clamping voltage.

Desk 2. Clamping voltage of a Littelfuse V14H385A MOV in contrast with P3800FNL SIDACtor and a V14H250A MOV below totally different surge voltage.
Determine 5. Response of the MOV and the SIDACtor+MOV mixture to a 6kV surge

An MOV alone exhibits degeneration after a number of surges. The leakage present will increase with the variety of surges the MOV should soak up. Additionally, the breakdown voltage is predicted to fall with an growing variety of surge strikes. The rising leakage and the clamping voltage change present the MOV parameters’ drift. Designer ought to choose a bigger disc measurement to keep away from this example with an MOV. This method impacts the fee and consumes essential PCB house. Nonetheless, their efficiency is extra steady with a SIDACtor+MOV mixture, and the SIDACtor extends the MOV lifetime.

SIDACtor+MOV: The superior resolution for transient surge safety

Whereas a designer will think about an MOV for voltage transient safety of downstream circuitry, Littelfuse can supply the designer a superior resolution with its SIDACtor safety thyristor positioned in sequence with an MOV. The SIDACtor+MOV mixture has a decrease clamping voltage to cut back semiconductor stress. As well as, the mix has a a lot decrease leakage present and a breakdown voltage that degrades a lot much less with growing transient strikes. Utilizing a SIDACtor+MOV mixture for transient surge safety will lead to a extra dependable, strong on-board charger.

To study extra about utilizing SIDACtor Safety Thyristors in Electrical Automobiles, obtain the The way to Choose the Optimum Transient Surge Safety for EV On-Board Chargers software notice, courtesy of Littelfuse, Inc. 

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