為下一代電動汽車創(chuàng)建安全可靠的電路

Fig.1.In hybrid-electric vehicle electrical architectures,the on-board charger must contend with the AC power line and its potential for generating overloads and transients.(Littelfuse)

圖1 在混合動力電動汽車電氣結構中，車載充電器必須與交流電源線及其可能產(chǎn)生的過載和瞬態(tài)過壓相匹配。（Littelfuse）　　       Design considerations for building robust circuit protection in electrified and increasingly automated vehicles.

　　在電動化和自動化程度更高的車輛中建立可靠電路保護的設計注意事項。

　　Fig.2.On-board charger block diagram and recommended protection and control components.(Littelfuse)

　　圖2 車載充電器框圖和推薦的保護和功率控制器件。(Littelfuse)

Fig.3.TVS diode array for protection of CAN bus lines.(Littelfuse)

圖3 用于保護CAN總線的TVS二極管陣列。(Littelfuse)

　　Designing circuits for electrified vehicles is extremely challenging.To ensure robust and safe designs that can withstand overloads,transients,and electrostatic discharge(ESD),designers need to ensure their circuits have the necessary components that will prevent damage.This article presents recommendations for both circuit protection and efficient control using the on-board charger as an example circuit.

　　為電動車輛設計電路極具挑戰(zhàn)性。為了確保能夠承受過載，瞬態(tài)和靜電放電（ESD）的可靠和安全設計，設計人員需要確保其電路具有必要的器件以防止損壞。本文以車載充電器為例，提出了電路保護和高效功率控制的建議。

　　Hybrid vehicles,as seen in the Fig.1 schematic,represent the worst-case scenario for designers who must develop circuitry that can withstand transients from both the internal combustion engine and the high-power electric motors.In this environment,the on-board charger must contend with the AC power line and its potential for generating overloads and transients.

　　如圖1示意圖所示，對于必須開發(fā)能夠承受來自內(nèi)燃發(fā)動機和大功率電動機瞬變的電路設計人員而言，混合動力汽車代表了最壞的情況。在這種環(huán)境下，車載充電器必須與交流電源線及其可能產(chǎn)生的過載和瞬變相匹配。

　　Designers should protect the on-board charger just as they would protect any line-powered product.They also will want to protect communication circuits to avoid corruption of data while minimizing internal power consumption,so that battery charge time is as short as possible.

　　設計人員應該保護車載充電器，就像保護任何線路供電產(chǎn)品一樣。他們還希望保護通信電路以避免數(shù)據(jù)損壞，同時將內(nèi)部功耗降至最低，從而使電池充電時間盡可能短。

　　The on-board charger converts the AC line voltage into the DC voltage required for charging the main battery pack which,when fully charged,can contain voltage in the range of 300 to 500 V.Consumers want faster EV charging,thus the demand for higher-power charging circuits which can include 3-phase power.

　　車載充電器將交流線路電壓轉換為主電池組充電所需的直流電壓，當電池充滿時，主電池組的電壓范圍為300至500 V。消費者希望電動汽車充電更快，因此需要更高功率的充電電路，包括三相電源。

　　Fig.2 shows a block diagram of an on-board charger.In this example,a single-phase circuit is represented.Each circuit block requires protection components,and two blocks require control components to optimize the charger for efficiency.

　　圖2顯示了車載充電器的框圖。在此例子中，表示了一個單相電路。每個電路子框圖都需要保護元件，兩個電路子框圖需要功率控制元件來優(yōu)化充電器的效率。

MOVing to transient protection

轉到瞬態(tài)保護

　　The input voltage section is susceptible to transients such as a lightning strike and surges on the AC line.The first line protection is a fuse to provide overload protection.Designers should consider fuses with a high interrupting current rating and a high voltage rating to ensure the fuse will open under the worst-case current overload.To protect against a surge transient or a lightning strike,designers should place a metal oxide varistor(MOV)as close to the input connections of the charger as possible.The MOV will absorb the transient energy and can prevent it from damaging the downstage circuit blocks.

　　輸入電壓部分容易受到瞬變的影響，如雷擊和交流線路上的浪涌。第一種線路保護是提供過載保護的熔斷器。設計人員應考慮具有高中斷電流額定值和高電壓額定值的保險絲，以確保保險絲在最壞的電流過載情況下斷開。為了防止電涌瞬變或雷擊，設計人員應將金屬氧化物變阻器（MOV）放置在盡可能靠近充電器輸入連接的位置。MOV將吸收瞬態(tài)能量，并可防止其損壞下游電路。

　　If the on-board charger uses 3-phase power,the designer should consider adding MOVs for phase-phase transient protection as well as phase-neutral transient protection.For even greater protection of downstream circuits,designers can place a bipolar thyristor in series with the MOV.A thyristor has a very low clamping voltage of around 5 V.Use of a thyristor allows a designer to select an MOV with a lower standoff voltage.The net effect is the reduction of the peak transient voltage to which the downstage circuitry is momentarily subjected.

　　如果車載充電器使用三相電源，則設計人員應考慮添加MOV進行相-相瞬態(tài)保護以及相-中性點瞬態(tài)保護。為了更好地保護下游電路，設計人員可以將半導體放電管與MOV串聯(lián)。半導體放電管的箝位電壓非常低，約為5 V。半導體放電管的使用允許設計者選擇具有較低工作電壓的MOV。好處是可以降低下游電路瞬間承受的峰值瞬態(tài)電壓。

　　A fourth protection element for superior circuit protection is a gas discharge tube.The gas discharge tube provides high resistance,electrical isolation between the hot and neutral lines and the vehicle’s chassis ground.Gas discharge tubes provide an additional level of protection against fast-rising transients from lightning disturbances.

　　用于高級電路保護的第四種保護元件是氣體放電管。氣體放電管在火線和中性線與車輛底盤接地之間提供高電阻電氣隔離。氣體放電管可提供更高級別的保護，以防止雷電干擾引起的快速上升的瞬變。

IGBTs to the rescue

IGBT保護和控制

　　For fast,high power charging,designers should select rectifier block thyristors with sufficient current handling capacity to supply the necessary power.Thyristors also can absorb safely surge current transients that may have passed through the input voltage and EMI filter stages.

　　對于快速、大功率充電，設計者應選擇具有足夠電流處理能力的整流塊晶閘管來提供必要的電源。晶閘管還可以安全地吸收可能通過輸入電壓和EMI濾波器級的浪涌電流瞬變。

　　The power factor correction(PFC)circuit improves the efficiency of the charge by reducing the total power drawn from the AC power line.Designers can use a gate driver and an insulated gate bipolar transistor(IGBT)to control the amount of inductance in the circuit.Designers should ensure that they select a gate driver with a sufficient operating voltage range for control of the IGBT.Designers also should consider selecting a gate driver with high immunity to latch-up and with fast rise-and-fall times to quickly switch the IGBT.

　　功率因數(shù)校正（PFC）電路通過降低從交流電源線吸取的總功率來提高充電效率。設計人員可以使用柵極驅動器和絕緣柵雙極晶體管（IGBT）來控制電路中的電感量。設計人員應確保選擇具有足夠工作電壓范圍的柵極驅動器來控制IGBT。設計人員還應考慮選擇一個具有高抗擾度的柵極驅動器來鎖定，并具有快速上升和下降時間來快速切換IGBT。

　　Fast rise-and-fall times combined with a low supply current minimize power consumption of this circuit block.The gate driver should be protected from ESD;designers should either select a gate driver with built-in ESD protection or add an external ESD diode.Versions of ESD diodes can be either bi-directional or uni-directional and can withstand ESD transients as high as 30 kV.

　　快速上升和下降時間與較低的電源電流相結合，最大限度地降低了該電路塊的功耗。柵極驅動器應提供防靜電保護。設計人員應該選擇具有內(nèi)置ESD保護的柵極驅動器，或者添加一個外部ESD二極管。ESD二極管可以是雙向的也可以是單向的，并且可以承受高達30 kV的ESD瞬變。

Know the key diodes

了解關鍵二極管

　　The DC link consists of the capacitor bank that stabilizes the ripple generated by the high-power DC/DC converter.Designers concerned about large voltage transients reaching the DC link can employ a high-voltage TVS diode to protect the capacitor bank.直流鏈路由電容器組組成，用于穩(wěn)定大功率直流/直流變換器產(chǎn)生的紋波。擔心到達直流鏈路的大電壓瞬變的設計人員可以采用高壓TVS二極管來保護電容器組。

　　The DC/DC section steps up the output charge voltage and generates the charge current for the battery.This circuit block requires a robust gate driver similar to the PFC circuit block.If a gate driver selection does not include internal ESD protection,designers can select an ESD diode to protect the gate driver.Addition of an external ESD diode does not degrade the performance of the gate driver.

　　直流/直流部分會提高輸出充電電壓，并為電池產(chǎn)生充電電流。該電路模塊需要與PFC電路模塊相似的可靠的柵極驅動器。如果柵極驅動器選擇不包括內(nèi)部ESD保護，則設計人員可以選擇一個ESD二極管來保護柵極驅動器。添加外部ESD二極管不會降低柵極驅動器的性能。

　　Designers should also ensure that their power IGBTs are protected from voltage transients.In addition to protection from external transients,the IGBT creates turn-off switching transients due to L·di/dt effects from internal parasitic inductance(L being the inductance and di/dt the rate of current change).To eliminate the potential damage to an IGBT from this transient,designers should place a TVS diode between the collector and gate of each IGBT.

　　設計人員還應確保其電源IGBT免受電壓瞬變的影響。除了防止外部瞬變，由于內(nèi)部寄生電感的L·di/dt效應（L是電感，di/dt是電流變化率），IGBT還會產(chǎn)生關斷開關瞬變。為了消除這種瞬態(tài)對IGBT的潛在損害，設計人員應該在每個IGBT的集電極和柵極之間放置一個TVS二極管。

　　The TVS diode reduces the di/dt of the current transient by raising the gate voltage.When the collector-emitter voltage exceeds the breakdown voltage of the TVS diode,current flows through the TVS diode into the gate to raise its potential.The TVS diode continues to conduct until the transient is eliminated.

　　TVS二極管通過提高柵極電壓來降低電流瞬變的di/dt。當集電極-發(fā)射極電壓超過TVS二極管的擊穿電壓時，電流通過TVS二極管流入柵極以提高其電勢。TVS二極管繼續(xù)導通，直到瞬態(tài)消除。

　　Use of a TVS diode as a collector-gate feedback element is known as active clamping and keeps the IGBT in a stable state.More information on active clamping is available in the referenced application note.1 Some IGBTs have built-in active clamping TVS diodes.Designers either should select that type of IGBT or add TVS diodes to their circuit.

　　使用TVS二極管作為集電極-柵極反饋元件被稱為有源鉗位，并可將IGBT保持在穩(wěn)定狀態(tài)。有關有源鉗位的更多信息，請參閱參考應用說明1。一些IGBT具有內(nèi)置有源鉗位TVS二極管。設計人員應選擇該類型的IGBT或在其電路中添加TVS二極管。

Protecting CAN bus signals

保護CAN總線信號

　　The output voltage stage requires protection from current overloads and in-vehicle voltage transients when motors turn on and off or when current is instantaneously interrupted by a break in a cable.Designers should consider employing a fuse to protect from an overcurrent resulting from a short in the battery pack or in the cables that carry the battery voltage.Use of an MOV or a TVS diode protects against the potentially damaging voltage transients.

　　當電機打開和關閉或電流因電纜斷裂而瞬時中斷時，輸出電壓側需要提供保護，以防止電流過載和車內(nèi)電壓瞬變。設計人員應考慮使用熔斷器，以防止因電池組或承載電池電壓的電纜短路而引起的過電流。使用MOV或TVS二極管可防止?jié)撛诘钠茐男噪妷核沧儭?/p>

　　The control unit for the charger communicates with the data network via the CAN bus.To avoid damage to the communication circuit block and avoid corruption of data,designers should provide ESD and transient protection.They can implement the protection with a single,space-saving component.Fig.3 shows a dual-line TVS diode array designed for protection of CAN bus signal lines.Diode arrays designed for protecting communication lines contain minimal capacitance and do not degrade the transmitter/receiver I/O states.

　　充電器的控制單元通過CAN總線與數(shù)據(jù)網(wǎng)絡聯(lián)系。為避免通信電路塊和數(shù)據(jù)損壞，設計人員應提供ESD和瞬態(tài)保護。他們可以使用單個節(jié)省空間的元件來實現(xiàn)保護。圖3顯示了設計用于保護CAN總線信號線的雙線TVS二極管陣列。設計用于保護通信線路的二極管陣列包含較小的電容，并且不會降低發(fā)送器/接收器的I/O狀態(tài)。

　　Designers who follow the recommendations for protection and control will have robust,reliable and safe circuits for their companies’EV customers.Whenever possible,designers should use AEC-Q qualified components that have been certified for use in the automotive environment.For example,AEC-Q101 covers discrete semiconductors,and AEC-Q200 covers passive components such as varistors.Furthermore,designers should consider taking advantage of the manufacturers’experts for assistance in selection of appropriate protection components.

　　遵循保護和功率控制建議的設計人員將為其公司的電動汽車客戶提供可靠和安全的電路。設計人員應盡可能使用經(jīng)AEC-Q認證且可在汽車環(huán)境中使用的合格元件。例如，AEC-Q101覆蓋分立半導體，和AEC-Q200覆蓋無源元件，如壓敏電阻。此外，設計人員應考慮利用制造商的專家的幫助來選擇合適的保護元件。