Editorís Note: I recently became interested in learning more about the current state-of-the-art with regard to Industrial Control Ė especially in the context of programmable logic in the form of CPLDs and FPGAs. As part of this, I was introduced to a company called Alizem Inc. (www.alizem.com), which specializes in providing soft IP cores for use in FPGA-based power electronics applications for home appliances, industrial, automotive and defense applications. The president of Alizem Ė Marc Perron, Ph.D., ing. Ė was kind enough to give me a crash course in Industrial Control. Marc also provided me with some useful background material, including the whitepaper that forms the basis of this article, and which is reproduced here with the kind permission of Alizem Inc.
Pumps and fans are prevalent within the industrial sector. Chemical, paper, refineries, and water treatment facilities to name a few consume about 40% of their energy driving devices of this type . Hence, pump and fan management represents a key focus area to attain significant energy savings. The most popular approach to saving energy in these applications is to implement adjustable-speed motor drive (ASD) systems, also known as variable-frequency motor drive systems (VFD). Several studies report that the use of ASD systems can reduce total power consumption by 20% to 50% in typical industrial pump and fan applications.
A typical ASD system is composed of three main components: (1) an electric motor, (2) a power converter and (3) a control system. The electric motor drives the load (fan or pump) and is powered via the power converter. The power converter controls the motor speed and hence the power delivered to the motor, by appropriately sequencing power devices within this converter that are connected to each motor phase. This speed adjustment is critically important since in applications of this type, the energy consumed increases in proportion to the cube of the motor speed - therefore operating the fan or pump at the lowest possible speed to meet the application needs results in significant energy savings.
The heart of any control system is the chip on which the control software runs. This white paper outlines how Alteraís Field-Programmable Gate Array (FPGA) chip and Alizemís Motor Control Intellectual Property (IP) core technologies are of benefit to the design of industrial ASDís for pump and fan applications in terms of increased performance, cost reductions and time-to-market.Conventional vs. FPGA-based motor control system design
As is illustrated in Figure 1, a typical motor control system is composed of four main sub-systems: (1) a motor interface which includes the PWM power converter and relevant current, speed, and position transducers, (2) a networked/remote communication interface, (3) a local interface that allows users to monitor the system on-site via handheld or laptop units and, (4) a core electronic system that binds those sub-systems together to allow their proper interaction with each other. The difference between a conventional and a FPGA-based motor control system design lies in how the control electronic system is designed.
Figure 1. Typical motor control system.
The conventional motor control system illustrated in Figure 2 implements the motor control system using a segmented architecture. A general-purpose controller chip Ė typically an MCU Ė interfaces to a networking / communication IC (a suitable hardware interface chip for local communications) and a dedicated motor control IC (motor control MCU or DSP). Specific sensor information generally feeds into the motor control IC portion of this implementation via some dedicated hardware circuitry. Managing the proper operation and hardware linkages among these dedicated ICís is an integral part of the challenge faced by designers of conventional systems of this type.
Figure 2. Control system electronics design
with PCB-integrated components.
Although in the early 90ís this approach revolutionized motor control system design, it has some fundamental limitations in terms of integration, reliability, and flexibility. The physical PCB integration of numerous components requires substantial design time and effort, and drives the need to perform extensive electrical and reliability testing before launching a production ready product. The ultimate reliability of the design is negatively affected by the number of discrete parts used in this design approach both from a manufacturing and component level perspective. Designs of this type do not offer much flexibility, if any, in terms system performance/feature upgrades and can require significant engineering effort and re-design should there be a need to substitute key components with alternate devices.
More specifically, Motor Control ICís are driven by a one-fits-all design mentality that drives volumes and ROI for the supplier. As such, they tend to restrain system flexibility that may be key to securing the most energy savings benefits for your specific application. Those limitations have an impact on system development costs where the gap between the Motor Control IC set of features and applications requirements must be worked out by the system designer.System-on-a-programmable-chip FPGA-based approach
The FPGA-based approach has the exact same system architecture as the conventional approach except that the segmented functions described in the conventional implementation are now fully integrated into a single FPGA component. The FPGA is loaded with optimized custom software/IP components tailored specifically for the application at hand as shown in Figure 3.
Figure 3. Control system electronics design
with FPGA-integrated components.
This decoupling of hardware and functionality provides a superior level of integration that translates into many well-known benefits for the system designer such as: increased design flexibility and speed, reduced component integration challenges, lower risk of component obsolescence, and lower total cost of ownership (TCO) [2,3]. Here is how value is provided to FPGA-based motor control system designers:
Alizem pump and fan motor-control IP value-added features
- Flexibility of design: the Motor Control IP can be tailored to designerís specific application needs without having to modify or add any hardware components. This also means that design modifications can be made very late in the design cycle or even in the field once the system has been released or is undergoing field trials (Field-Programmable).
- Increased speed and ease of component integration: Available FPGA IP components can be added or removed from the design within seconds through software re-programming of this versatile component. This device programmability allows designers to accelerate their design iterations within a single design environment compared to the time required by conventional design processes relying on discrete components. Hence, more time is available to focus on product differentiation and system performance testing. For motor control, this adds an opportunity to invest more time and effort to develop system diagnostics and bi-directional communications between the general controller and the Motor Control IP.
- No chip obsolescence and option to benefit from new semiconductor process technologies: The same control system can easily be ported to a different family of Altera FPGAs should there be a need to take advantage of next generation IC footprint advantages, cost, or performance aspects.
- Lower total cost of ownership: FPGA-based control systems allow ďsingle chipĒ solutions which greatly simplify the manufacturing complexity of the product and the supply chain logistics of your design. These benefits translate to lower product costs and reduced risk of supply chain issues. The ability to program these systems in the field enables the base design to be enhanced with new and improved features that can be added over time. This can be leveraged to provide a source of after-market revenues. Such an opportunity is not generally possible in a conventional discrete IC based design implementation.
Based on the FPGA-based motor control system design approach above, Alizemís Motor control IP provides the system designer with an off-the-shelf Motor Control IC in a software (IP) form factor designed for integration directly onto an FPGA device. It offers the same conventional features of Motor Control ICís such as PWM and speed regulation plus new value-added features that are enabled by the FPGA/IP combination as outlined below :
Motor control scheme and typical applications
- On-line power consumption estimator feature that provides information regarding the motorís instant power consumption or amount of total energy consumed by the controller. This information may then be used to monitor and control the energy consumption of the system and contribute to the optimal energy management of the system. This feature can be integrated into a smart-meter /smart-grid master applications.
- Power converter test and debug features that can be used by the system developer to quickly and easily test the proper operation of the power converter prior to its integration with the real motor. Rather that developing their own test module, the motor control system designers can use Alizemís Motor Control IP in debug mode to test their power converter stage operation before connecting to a real motor, enabling them to save design time.
- Customizable pin layout: By using the pin assignment flexibility inherent in an FPGA design versus the fixed constraints presented by discrete ICís, the PCB layout can be optimized to minimize its size and to optimize critical signal paths.
- On-line virtual motor simulator features emulate motor operation on the FPGA providing the software developer with a system to test their application on before initiating hardware integration with a real motor.
- Control multiple motors in parallel: multiple instances of Alizemís Motor Control IP can be housed and programmed on the same FPGA chip and controlled independently using the same software drivers. This feature is useful when one wishes to synchronize the startup of multiple motors or to minimize total peak in-rush line currents (smart-grid consideration).
- No VHDL to learn or complex motor drivers to develop: The software API is easy for non motor-control or FPGA experts to use as a system design tool.
Alizem Motor Control IP for Pump and Fan Applications is based on a V/Hz or scalar control motor scheme. This AC motor control approach is ideal for applications that have predictable and well behaved dynamics load and speed requirements such as those found in fan and pump type loads . A typical application example is a system where solar energy is hydraulically stored using a water pump .