Ensure Robust, Reliable Controllers and Powertrains in the Next Generation Automotive Control Architecture

­An electronic control unit (ECU) manages each vehicle function, and their numbers are rising with the growth in features. High-end vehicles can now contain up to 150 ECUs, which are critical for communicating information and responding to the main control system.

Automotive control architectures

Automotive control architectures are evolving from single-layer to multi-layer designs to handle the complexity of integrating numerous ECUs into a responsive, reliable system.

• Distributed Architecture: Refers to early systems in which each ECU communicates directly with a master controller.
• Domain Architecture: Emerged as vehicles became more complex, introducing domain controllers to manage specific functions and offload tasks from the master controller.
• Zonal Architecture: In this latest evolution, grouping ECUs by physical zones and using advanced zonal controllers (ZCUs) to manage all functions within those zones results in improved efficiency, reduced wiring complexity, and enhanced scalability.

Zonal architecture offers several advantages:

·      Improved vehicle response times, enhancing safety.

·      Modular, scalable zone additions or modifications.

·      Faster, more efficient Ethernet-based communication.

·      Reduced wiring and complexity.

Figure 1 illustrates the evolution of these architectures.

In EVs, zonal control improves efficiency and scalability. Zonal distribution optimizes battery management, energy recovery, and power control for powertrains. ZCUs also monitor and regulate thermal conditions and sensor data to maximize powertrain performance.

As ZCUs become integral to vehicle operations, their reliability is paramount. They should be designed to withstand harsh automotive conditions, including overcurrent, overvoltage, and electrostatic discharge (ESD) hazards.

In addition to ZCUs, other key powertrain components—such as the traction motor inverter and onboard battery charger—face similar risks from electrical hazards. The following sections provide recommendations to protect these circuits and enhance their reliability.

Protecting the Zonal Control Unit

Given its critical role, the ZCU should be robust and capable of operating reliably in harsh conditions. Figure 2 presents a block diagram of the circuits in a typical ZCU. This article details how to protect these circuits from electrical hazards, ensuring longevity and safe operation of the vehicle. The figure also lists recommended components that protect the individual ZCU circuits.  

The ZCU needs protection from faults impacting the Power Supply, such as an overcurrent condition caused by a fault in the supply or a fault in the load circuitry. Either fast-responding fuses or polymer positive temperature coefficient resettable fuses can provide the necessary protection. One-time and resettable fuses that are AEC-Q200 qualified are available to withstand the severe conditions of the automotive environment.

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The Power Supply is also subject to high voltage transients, particularly from load dumps that create inductive spikes when power is interrupted. A transient voltage suppression (TVS) diode or a metal oxide varistor (MOV) can clamp the transient to protect downstream circuitry. MOVs can handle higher load dump energies, but TVS diodes respond much faster to a transient and clamp to a lower voltage. Models of both the MOV and the TVS diode are AEC-qualified.

Ensuring the numerous communication and control interfaces in the ZCU will not experience damage in the harsh automotive environment is essential for safe vehicle operation. ESD and voltage transients are the primary hazardous energy sources. ESD diodes and polymer ESD suppressors provide appropriate protection for communication data lines and control lines. Many types of these components have low capacitance to minimize signal distortion. The appendix describes models of ESD protection solutions that will ensure reliable data transmission through the communication and control ports that the ZCU uses to interface with functions in its zone of control and other ZCUs in the zonal control architecture.

Protecting the Onboard Battery Charger

The Onboard Battery Charger (Figure 3) converts AC line voltage to DC for charging the main battery pack, which typically operates at 400–800 volts when fully charged. As consumers demand faster charging, higher-power circuits, including 3-phase power, are increasingly required. This example illustrates a single-phase circuit. Each circuit block requires protection components, with two blocks needing control components to optimize efficiency.

In addition to protecting against transients inherent to the EV environment, the charger must also handle AC power line risks, such as overloads and transients. Designers should safeguard the onboard charger as they would any line-powered product and protect communication circuits to prevent data corruption. Minimizing internal power consumption is also crucial to reduce battery charge time.

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The Protection circuit intercepts transients such as a lightning strike and surges on the AC line. 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 MOV as close to the input connections of the charger as possible. The MOV will absorb the transient energy and prevent it from damaging the downstage circuit blocks. If the onboard charger uses 3-phase power, the designer should consider adding MOVs for phase-phase transient protection and phase-neutral transient protection.

For even better protection of downstream circuits, designers can place a bipolar thyristor in series with the MOV. A protection thyristor has a very low clamping voltage and can have high holding currents. A thyristor allows the 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.

A gas discharge tube (GDT) is a fourth safety element for superior circuit protection. It provides high electrical isolation between the hot and neutral lines and the vehicle's chassis ground, providing an additional level of protection against fast-rising transients from lightning disturbances.

A residual current monitor detects differences between the power or high and neutral lines to avoid hazardous AC or DC leakage currents or insulation breakdown currents. Models of residual current monitors can detect DC current differentials of 6 mA and AC differentials of 10 mA.  

For fast, high-power charging, designers should select thyristors for the Rectifier block with sufficient current handling capacity to supply the necessary power. Thyristors also can safely withstand high in-rush current transients that have passed through the Protection and EMI Filter stages.

The Power Factor Correction circuit improves the charger's efficiency 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 select a gate driver with a sufficient operating voltage range to control the IGBT. Designers should select a gate driver with a sufficient operating voltage range to control the IGBT. Designers should also consider selecting a gate driver with high immunity to latch-up and fast rise and fall times to quickly switch the IGBT. Fast rise and fall times combined with a gate driver's low supply current minimize the power consumption of this circuit block. The gate driver also needs ESD protection; designers should 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. 

The DC/DC circuit steps up the output charge voltage and generates the charge current for the battery. 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 Ldi/dt effects from internal parasitic inductance. 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. 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 increase its potential. The TVS diode continues to conduct until the transient is eliminated. Using a TVS diode as a collector-gate feedback element is known as active clamping, and this approach keeps the IGBT stable. More information on active clamping is available in the referenced application note.² Some IGBTs have built-in active clamping TVS diodes. Designers should select that IGBT type or add TVS diodes to their circuit.

The Output Voltage stage may require 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. In some instances, because other modules incorporate protection, it is unnecessary here. Designers should consider employing a fuse to protect from an overcurrent resulting from a short in the battery pack or the wires that carry the battery voltage. Using an MOV or a TVS diode protects against potentially damaging voltage transients.  

The charger's Control Unit communicates with the ZCU. To avoid damage to the communication circuit block and data corruption, designers should provide ESD and transient voltage protection on the input/output lines. The same type of ESD diode that protects the ZCU CAN bus can protect the control Unit I/O lines.   

The recommended components will enable a charger that is robust to electrical hazards. The table in Figure 3 summarizes the recommended components for the charger circuitry.

Protecting the Traction Motor inverter

The Traction Motor Inverter converts the battery DC to AC current to drive the traction motor. Operation of this circuit block requires safe, efficient, and reliable propulsion.  Figure 4 shows the circuit blocks of the Traction Motor Inverter, and the table lists the recommended protection, control, and sensing components.

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As with the power supply in the ZCU circuit, the supply in the traction inverter circuit requires overcurrent and transient voltage protection. A fuse and a TVS diode will provide the necessary protection.

The CAN Transceiver needs an ESD diode array for protection from ESD strikes. The same TVS diode array recommended for the CAN/CAN FD circuit in the ZCU will protect this circuit.

The Gate Driver circuit controls the power transistors. Gate driver ICs control the switching of power transistors such as IGBTs and SiC MOSFETs to minimize power loss and maximize efficiency. Protecting the Gate Driver ICs involves using ESD diode arrays to absorb ESD strikes safely.

The Inverter block generates the power drive for the propulsion motor. Ensuring reliable operation of the Inverter requires overcurrent, voltage transient, and thermal protection for the power transistors. Preventing the power transistors from operating at dangerously high temperatures requires a device such as a thermal protector, which will interrupt the supply current to the power transistor circuit.

When using SiC MOSFETs, a TVS diode between the gate and source of the MOSFET will protect the MOSFET from transients. For IGBTs, a TVS diode between the collector and the gate will prevent damage to the IGBT from a transient rise in voltage at the collector. The TVS diode will clamp the collector-gate voltage to a safe level for the IGBT. This approach is the active clamping technique for protecting IGBTs in the Onboard Battery Charger circuitry.

Monitoring the motor load current indicates the health of the motor. A common option for monitoring current is a current sensor that uses Hall effect technology which uses magnetic detection to sense load current. The load current wire threads through an aperture, or under the Hall effect sensor allowing isolated monitoring of motor current without adding power loss to the circuit. 

The components presented will ensure protection, sensing, and efficient control for the Traction Motor Inverter circuitry. The table in Figure 4 provides component recommendations.

Available resources for achieving reliable ZCU and powertrain circuitry

As automotive control architectures transition to zonal control, reliable operation of the ZCU, onboard charger, and traction motor inverter are critical for achieving the safety and efficiency benefits of zonal designs. The recommended overcurrent, overvoltage, and temperature protection components ensure robust performance in the harsh automotive environment.

Partnering with circuit protection experts like Littelfuse helps designers save development time and costs. Littelfuse application engineers provide recommendations for cost-effective, efficient protection, control, and sensing components while assisting with compliance to automotive standards. This support includes pre-compliance testing to streamline certification processes, avoiding delays with standards organizations. With Littelfuse expertise, designers can confidently create reliable, robust automotive control and power electronics.

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