Power inverter safety system concept for ISO 26262

Just one of the indisputable specifics about the automotive field is that the overall digital

Just one of the indisputable specifics about the automotive field is that the overall digital program written content in motor vehicles is expanding.

As motor vehicles come to be much more sophisticated and involve characteristics that sense, feel and act for the driver, the form of digital written content variations. In particular, there will be significant expansion in hybrid electric powered auto and electric powered auto written content, as perfectly as for automated travel functions.

On the other hand, a crucial problem that desires to be resolved is that the present-day small business design for electric powered motor vehicles is not lucrative lengthy time period for OEMs. The average believed cost for foundation electric powered motor vehicles is continue to a major problem.

OEMs will be hunting to shut this gap by bringing much more design back in-household, or by bypassing Tier 1 suppliers to talk specifically to IC suppliers. The disrupter below will be to integrate embedded digital architectures by combining ECUs and clustering functions in a new way.

This is why NXP is working intently with companions throughout the field to accelerate how these constraints are satisfied. Just one way is by producing reference models that mix our program know-how with our safety skills. This means that reference models involve crucial safety program elements from the outset.

To develop safety principles for program reference models, NXP has to be capable to determine the safety targets, concept and functions for the supposed item to be capable to recognize the proper program implementation into our program design.

We do this by subsequent the ISO 26262 growth system. This gives tips for each and every action together the growth system for safety program items with a V cycle venture administration resource.

The V cycle teams each and every action as a Part and precise work items are expected at each and every degree. IC suppliers like NXP can anticipate and develop program ECUs just like a Tier 1 supplier does. By carrying out this, we can pace growth time and provide conventional deliverables that are of benefit in the course of the growth chain.

The objective is not automatically to provide a solution with the identical degree of maturity that a Tier 1 could provide, somewhat to accelerate the growth of the work items for the Tier 1.

Let us look at as an instance, how to develop a safety concept for a electricity inverter module as a SEooC for an EV software. As an IC supplier, we would work by means of areas 3, four, 5, 6 and seven of the V cycle and provide the work items connected to each and every component. We start off by defining the item in the goal program – i.e. what are the possible hazards and safety targets that we want to apply to our reference design?

Figure 1: HV Inverter for EVs

As determine 1 shows, the electricity inverter is the key traction program of an electric powered auto. It controls the power conversion in between the electric powered power resource and the mechanical shaft of the electric powered motor, primarily based on the torque ask for from the Vehicle Command Device (VCU).

The VCU interprets the driver desires into acceleration or deceleration of the electric powered motor. The inverter translates the torque ask for into phase currents likely into the traction motor.

In a battery electric powered auto, this connection is typically created with a straightforward gearbox without having a clutch. This is our very first assumption. It is essential to be precise below, considering that the safety situation would be distinctive if the auto has a clutch.
In our situation, if a hazard really should happen, it is unattainable for the driver or the electrical program to prevent the traction of the auto by only opening the connection in between the electric powered motor and the wheels of the car or truck.

We also need to recognize possible resources of EE malfunction – regardless of whether owing to driving or non-driving eventualities. These hazards are then ranked by danger degree according to the ASIL degrees laid out in ISO 26262. As demonstrated in determine 2, in this situation a safety objective could be to stay clear of unintended acceleration if the auto is stopped.

Figure 2: Illustrations of hazards and safety targets for an EV HV inverter

These safety targets guide to a purposeful safety architecture with purposeful specifications (FR) and purposeful safety specifications (FSR) with connected ASIL degrees and FTTI these kinds of as:

FR1 The Inverter shall review the ask for from VCU, then command the subsequent functions accordingly: traction, brake and battery regeneration. ASIL D FTTI
200 ms
FSR1 The inverter shall check the torque ask for from the VCU and notify in situation of unanticipated value. ASIL D FTTI
200 ms


Figure 3: Purposeful safety architecture

Now that we have the purposeful safety architecture, determine 3, we need to reveal that the program architecture will be capable to fulfil the safety specifications and design constraints.

To do this, we derived a specialized safety concept from the purposeful safety concept. This combines the hardware and software package sub-aspect functions that will be made use of to attain the supposed item and program performance.

A safety evaluation is then run to check that all possible program failures have been discovered and that the proper safety mechanisms are in location. This could consequence in new safety specifications being allocated to the safety architecture.

By carrying out this, the specialized definition can provide the essential evidence that the proper reactions have been discovered and that a secure condition can be accomplished in a lot less time than FTTI: as a result that there is no violation of the safety targets of the item.

In our instance, secure condition is sophisticated because of the high quantity of power flowing into the electric powered motor. A secure condition below means stopping the propulsion of the auto, by opening or shorting the a few phases of the motor relying on the pace of the motor.

As we progress by means of the V cycle, the work items are designed to ensure the safety considerations a consumer could have are fulfilled. A hardware design is lined by the system in the identical way the safety concept cuts down the growth and prototyping phase for clients by a few to 6 months.

In the NXP reference design, the complete safety architecture is crafted out using NXP ICs and diagnostics and reaction to secure condition are tested. The reference design aids to pace growth and gives a degree of specialized safety architecture, together with evidence of the safety integrity degree as component of the overall package.

Obtain out much more about the electricity inverter reference design below.