FPGA-based High Performance AC Servo Motor Drive – Accelerator configurable servo drive design platform

In recent years, a Digital Signal Processor (DSP) or Microcontroller has been widely used for implementing the digital motor control algorithm in the motor drive industry. Application spans widely from a low performance appliance AC inverter drive to a high performance servo drive. Today’s digital AC drive consists of the implementation of torque control by means of regulating the motor current which requires very high speed computation in the range of tens of microseconds, and speed control which requires relatively moderate computation intensity in the range of hundreds of microseconds. All these functions have been implemented in one DSP or one microcontroller with/without a separate motion ASIC which performs much faster tasks such as the PWM (Pulse Width Modulated waveform generator), encoder signal interface, etc. This popularity has been due partly to availability and flexibility of desired algorithm implementation. However, as the performance envelope is further expanded and application is further diversified, new issues arise to satisfy the need for new performance challenges. 1) Traditional DSP and microcontroller have the fixed motion peripheral hardware logic and communication ports. Constraint on these fixed hardware logics inside a DSP and microcontroller imposes limit on the adaptation of different types of feedback devices and network connectivity, and unique customization of motion peripheral hardware logics. 2) Inadequate performance due to a lack of computation power for highend servo torque control results in a multiple DSP or microcontroller implementation mixed with specific motion peripheral ASIC(s); One for torque control and the other for other controls. This creates additional complexity associated with functional partitioning and interconnectivity among split modules/functions. 3) Impeded process and challenge to meet faster time-to-market development. Exponential effort in programming is already inevitable in today’s drive development process. A Specific coding technique is often used to meet demanding challenges, and to satisfy new computational speed requirements. Code maintenance ability is further deteriorated if a cryptic assembly language is used as opposed to a high level language, such as C, in order to meet the speed requirement. In reality, the torque control algorithm is particularly written in the dedicated assembly language, which adversely affects programming productivity. In order to solve the arising problems stemmed from the traditional DSP and microcontroller approach, a new method of hardware control has been developed. International Rectifier recently introduced the Accelerator design platform for a flexible high performance servo drive system. The system is based on the latest generation of the FPGA which recently became affordable for implementing complicated closed loop current control and velocity control with desired motion peripheral and communication ports. Review of the today’s servo drive digital control architecture and functional partitioning Today, most servo motor drive systems are implemented by digital closed loop control