Electrical traction has change into a vital a part of a rising variety of methods that want environment friendly movement and place management. Motors don’t simply present the driving pressure for autos, from e-bikes to automobiles to industrial and agricultural equipment. In addition they allow a brand new technology of robots, whether or not they use wheels, propellers or legs for movement.
The opposite widespread thread for a lot of of those methods lies in the best way they’re anticipated to function in a extremely linked surroundings. As an illustration, wi-fi connectivity has enabled novel enterprise fashions for e-bike rental and delivers positioning and different important knowledge to robots as they transfer round.
However the identical connections to the Web open avenues of assault in ways in which earlier generations of motion-control methods haven’t needed to take care of. It complicates the duties of designing, certifying, and sustaining methods that guarantee secure operation.
To ensure the actuators don’t trigger damage, designers should implement safeguards for his or her management methods to forestall them being bypassed and creating unsafe conditions. In addition they want to make sure that corruption by hackers doesn’t disrupt the system’s conduct. Safety, subsequently, now performs a serious function within the design of the motor-control subsystems.
Determine 1 Connectivity in warehouse robots additionally opens vulnerabilities in motor management methods. Supply: EnSilica
Algorithmic calls for drive architectural change
Complexity within the motor management additionally arises from the novel algorithms that designers are utilizing to enhance power effectivity and to ship extra exact positioning. The drive algorithms have moved away from easy methods comparable to analog controllers that merely relate energy delivered to the motor windings to the motors rotational velocity.
They now make use of much more refined strategies comparable to field-oriented management (FOC) which can be higher capable of ship exact modifications in torque and rotor place. With FOC, a mathematical mannequin predicts with excessive precision when energy transistors ought to activate to provide energy to every of the stator windings so as to management rotor torque.
The utmost torque outcomes when the electrical and magnetic fields are offset by 90°, delivering extremely environment friendly movement management. It additionally ensures excessive positioning accuracy without having for costly sensors or encoders. As a substitute, the mathematical mannequin makes use of voltage and present inputs from the motor winding to supply the information wanted to estimate place and state precisely.
Determine 2 Using strategies like FOC delivers extremely environment friendly movement management, which ensures larger positioning accuracy with out costly sensors or encoders. Supply: EnSilica
In robotics, these algorithms are being supplemented by strategies comparable to reinforcement studying. Utilizing machine studying to reinforce movement management has confirmed extremely efficient at delivering exact traction management for each wheeled autos and legged robots. Dusty or slippery surfaces could be problematic for any automated traction management methods. Coaching the system to deal with these troublesome surfaces delivers larger stability than typical model-based strategies.
Such management methods typically name for the usage of in depth software-based algorithms operating on digital sign processors (DSPs) and different accelerators alongside high-performance microprocessors in a layered structure due to the totally different time horizons of every of the elements.
An AI mannequin educated utilizing a reinforcement studying mannequin, for instance, will usually function with an extended cycle time than the FOC algorithms and the pulse-width modulation (PWM) management alerts beneath them that make sure the motors observe the response wanted. In consequence, DSP-based fashions with very long time horizons will likely be supported by algorithms and peripherals that use {hardware} help to function and meet the deadlines required for real-time operation.
The case for customized {hardware}
The laborious real-time features are people who have direct management over the ability transistors that ship energy to the motor windings, often applied in an “inverter” comprising a half-bridge circuit for every of the motor phases. Historically, such half-bridge controllers have centered on the implementation of timing loops for PWM.
The switching frequencies are sometimes too excessive to be supported reliably by software program operating even on a devoted microprocessor with no need the processor to be clocked at extreme frequencies. The state machines used to implement PWM switching additionally deal with features comparable to dead-time insertion, which is used to make sure that every transistor doesn’t activate earlier than its counterpart transistor within the half-bridge inverter is turned off.
The timing hole prevents the shoot-through of present that will consequence if each transistors have been energetic on the identical time. The surplus present can harm the motor windings and the drive circuit board. These subsystems are so necessary that they’re typically supplied as customary constructing blocks for industrial microcontrollers.
Nonetheless, within the context of elevated threats from hackers and the necessity to assist superior algorithms, the inverter controller can change into a significant element in supporting total system resilience. By customising the inverter controller, implementors can extra simply assure security and safety, in addition to defend core traction-control IP. Partitioning of the inverter and the remainder of the drive subsystem needn’t simply assist all three goals, which may additionally scale back the price of implementation and verification.
A significant benefit of {hardware} by way of safety is its relative immutability in comparison with software program code. Attackers can not substitute necessary elements of the {hardware} algorithm in the event that they achieve entry. This simplifies some points of safety certification as well as. Strategies comparable to formal verification can decide whether or not the circuitry can ever enter a specific state. Future updates to the system won’t straight have an effect on that circuitry.
It’s attainable for code modifications to change the interactions between the microcontroller-based subsystems and the lower-level {hardware}. Nonetheless, this relationship supplies alternatives for the designer to enhance their potential to ensure secure operation, even below the worst-case circumstances the place a hacker has gained entry and changed the firmware.
{Hardware}-based lockout mechanisms and safety checks can make sure that if the upper-level software program of the system is compromised, the system will place itself right into a secure state. The lockouts can embrace assist for mechanisms comparable to safe boot. This ensures that solely the software program that passes the ASIC’s personal checks can activate the motor.
Utilizing {hardware} for security and safety safety can assist scale back the price of software program assurance, which is now topic to laws such because the European Union’s Cybersecurity Resilience Act (CRA). The brand new legislation calls for that producers and repair operators challenge software program updates for critically compromised methods.
By shifting key parts of the system design into {hardware} and minimizing the implications of a hack, the designer can scale back the necessity for frequent updates if new vulnerabilities are present in upper-level software program. Equally, shifting interlocks into {hardware} simplifies the duty of demonstrating secure operation for requirements comparable to ISO 26262 in contrast with purely software-based implementations.
Bodily assaults can typically contain energy interruptions, which supplies a approach to design an ASIC that protects towards such tampering. For instance, if energy monitoring circuitry detects a brownout, it could actually reset the microprocessor and place the remainder of the system in a secure, quiescent state.
{Hardware} selections that assist compliance and management
Alongside the extra features, an ASIC inverter controller can host extra in depth elements of the motor-control subsystem and scale back the price of the microprocessor elements. For instance, FOC depends on trigonometric and different computationally costly transforms.
Shifting these right into a coprocessor block within the ASIC can streamline the design. This mix may also scale back management latency by connecting inputs from present and voltage sensors to the low-level DSP features.
The features needn’t all be mounted. Fashionable ASICs might embrace configurable blocks comparable to programmable filters, achieve phases, and parameterizable logic to supply a stage of adaptability. Using programmable features can let a single ASIC design management varied motor configurations throughout a complete product vary.
The programming of those parts illustrates one of many many security and safety trade-offs that design groups could make. Incorporating non-volatile reminiscence into the ASIC can present the best safety. Placing the programmable parts into an ASIC that may be locked by blowing fuses after manufacturing is safer than a design the place a bunch microcontroller writes configuration values in the course of the boot course of.
The MCU-based management chips require a silicon course of appropriate for storing the firmware code, usually based mostly on flash reminiscence. This suggests some further processing masks, which enhance the price of the ultimate product, an element particularly delicate if the manufacturing quantity is excessive.
If the design requires the high-voltage functionality provided by Bipolar-CMOS-DMOS (BCD) processes for the motor-drive circuitry, a second die could also be wanted for non-volatile reminiscence. However the flash CMOS course of will usually assist a better logic density than the BCD-based elements, which permits the general price to be optimized.
Due to its potential to assist deterministic management loops and assist verification strategies that may ease safety and security certification, the usage of {hardware} is changing into more and more necessary to e-mobility and robotics designs.
By means of cautious structure choice, such {hardware} can allow the usage of software program for flexibility and its personal potential to assist novel management methods as they evolve. The result’s an surroundings the place ASIC use can provide the very best of each worlds to design groups.
David Tester, chief engineer at EnSilica, has 30+ years of expertise within the improvement of analogue, digital and mixed-signal ICs throughout a variety of semiconductor merchandise.
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