AM263x Benchmark and Analysis for Traction Systems

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1 Introduction

This application note presents AM2634 benchmarks obtained from a demo of the traction inverter framework, AM263x for Traction Inverters. The document also discusses typical application scenarios based on the benchmarks. The goal is to help users understand the performance of AM2634 in traction inverters.

System resources and diagram are presented in Figure 1-1 and Figure 1-2 for the following discussion. AM2634 is operated at 400 MHz core frequency and 200 MHz peripheral frequency, the program is compiled with TI Clang v1.3.0.LTS and O3 optimization for the best processing time, and the Field Oriented Control Interrupt Service Routine (FOC ISR) is assigned to FIQ of ARM Cortex R5F in order to achieve low latency. The performance of FOC ISR, FOC Run triggered by ADC INT1 in Figure 1-2, is the focus of the following discussion.

Figure 1-1 Resources in the Traction Inverter Framework

Figure 1-2 Traction Inverter System Diagram

2 AM26x FOC ISR Benchmarks

This section presents benchmarks of major functions in FOC ISR. They are visualized in Figure 2-1, Figure 2-2, Figure 2-3 and Figure 2-4. The order of items, top to bottom, in Bar Charts at Figure 2-3 and Figure 2-4 follows the execution flow. The Sunburst Charts in Figure 2-3 and Figure 2-4 are organized to have execution time from long to short in a clockwise direction. More details are summarized in Table 2-1. From Figure 2-4, the FOC ISR with TI R5F math library takes 3.9us from PWM time base counting Zero to PWM duty cycle updated. As shown in Figure 2-2, among the 3.9 µs, hardware interface costs 40% or 1.565 µs, and computation consumes 60% or 2.335 µs. Within the computation time, trigonometric functions take 26% or 600 ns. The Field Oriented Control excluding trigonometric functions and hardware operation is less than 1 µs, roughly 42% of computation time. The software resolver example without trigonometric functions requires 150 ns, 7% of computation time. The rest 25% computation time is spent on processing feedback and generating control reference in demo logic. The log function at the end of ISR is not counted in this benchmark as it is part of debug function.

Figure 2-1 AM26x Software Computation vs Hardware Interface for FOC Loop With Standard C lib

Figure 2-2 AM26x Software Computation vs Hardware Interface for FOC Loop With TI R5F lib

Figure 2-3 AM26x Time Consumption Breakdown for FOC Loop With Standard C lib

Figure 2-4 AM26x Time Consumption Breakdown for FOC Loop With TI R5F lib

Table 2-1 AM26x FOC Loop Benchmarks

Field Oriented Control Interrupt Service Routine	Description	Operation Type	Execution Time (ns)
ADC Acquisition and Conversion	PWM hardware trigger ADC ADC hardware sample, convert, and trigger interrupt	Hardware Interface	300
ISR Entry	R5F hardware process interrupt Interrupt handler load ISR	Hardware Interface	600
Read Feedback	Read 8 ADC results including 3-phase currents, resolver sin and cos, dc link voltage and others	Hardware Interface	440
Process Feedback	Remove effects, adjust scales, and filter noises	Computation	300
Run Trigonometric Functions - Option 1, Standard C Library	Run 3 times of sinf() and cosf() from libc.a Run one time for software resolver Run one time for Park transformation Run one time for iPark transformation	Computation	2400
Run Trigonometric Functions - Option 2, TI R5F Math	Run 3 times of ti_r5fmath_sincos() from TI R5F Math Run one time for software resolver Run one time for Park transformation Run one time for iPark transformation	Computation	600
Get Rotor Position with Software Resolver	resolver_run() is given as an example to take resolver feedback at the excitation frequency	Computation	150
Update PWM	Write PWM Duty Cycle	Hardware Interface	225
Field Oriented Control	Speed Loop Controller Slip Compensation for Induction Motor Park and Clark Transformation Id Controller Iq Controller Output Limiter iPark Transformation Space Vector Generation Duty Cycle Limiter	Computation	985
Demo Logic	Dummy theta generator for open loop and current loop tests Test profile generator for speed loop test	Computation	300
Total	From PWM time base count Zero to PWM duty cycle update	Hardware Interface and Computation	3900

3 Typical Application Scenarios for Traction Inverters

There are many ways to design traction inverters but most share the similar ADC sample and PWM update scheme. This section provides two typical design examples for traction inverters operated in up-down counting or center-lined timing PWM. The cases are listed below. Unless new frequencies are specified in the following sections, the cases are analyzed in the condition of both PWM and resolver sinusoidal excitation frequency at 10 kHz.

Sample ADC in cycle 0 and update PWM in cycle 1
Sample ADC in first half of cycle 0 and update PWM in second half of cycle 0