Robust Digital Control Research Articles

Robust digital voltage mode control of buck converter with enhanced tracking performance

The digital voltage controller of power converters is used because it has many advantages over its analog counterparts. Thus, in this paper, a controller of digital voltage mode is designed and analyzed for a non-isolated DC-DC buck converter in continuous conduction mode (CCM). First, an analog controller is designed using a Bode plot to achieve the desired stability margins in the frequency domain. Next, the analog controller is discretized using bilinear transformation with the pre-warping method. The characteristics of the discretized compensator can be maintained close to the corresponding analog compensator as long as a proper sampling time is selected. The digital control scheme is simulated with a nonlinear DC-DC buck converter model in MATLAB/Simulink to investigate the controller performance. The simulation results demonstrated the validation of the proposed digital voltage-mode control design approach. The developed digital controller eliminates DC error by tracking the reference voltage, achieving a fast transient response, maintaining specified stability margins, and effectively rejecting large disturbances.

Methodology for Designing Cyber-Physical Multi-Operation Robot Systems Operating in the Conditions of Digital Robust Control

Abstract The article proposes an original interdisciplinary approach to the design and construction of cyber-physical robot systems for mechanical processing. From a methodological aspect, the goal is the unification of modeling/synthesis and simulation software of a robot system for mechanical processing operating under the conditions of digital robust control. The system includes industrial robots; modules for implementing technological operations and transport systems. Adherence to the principle of modular construction, reconfiguration, and multi-operation ensures high flexibility and quick response when readjusting the system, and the optimization criteria – minimizing idle moves of the robot, leads to a reduction in the work cycle. The robust control, simultaneously in the instrumental, configurational, and system direction, is a counteraction in the mode of uncertainty, both to external signal disturbances and to possible constantly acting, system reparametrizing factors. This creates prerequisites for maintaining and implementing in online mode both the technological and geometric parameters of the details processed.

A Note on the Robustness of the Disturbance Observer-Based Robust Control Systems

Abstract This brief shows that the design constraints on the plant-model mismatch and the bandwidth of the disturbance observer (DOb) become more severe when the robust controller is implemented using computers. This brief also shows that continuous-time analysis methods fall-short in explaining the fundamental design constraints of the DOb-based robust digital control systems, therefore leading to unexpected stability and performance problems in practice.

Real-Time testing of novel robust digital pitch controller for digital hydraulic pitch system in wind turbine

ABSTRACT This research work draws insight on developing a novel digital hydraulic pitch system for a large-scale wind turbine. Digital hydraulic pitching can be appropriate for wind turbine application due to its high response, high power-to-weight ratio, and robustness. To perform digital pitch control, a machine learning-based robust digital pitch controller was designed and implemented in the developed real-time test setup. The proposed real-time test setup consist of sub-systems such as digital hydraulic system hardware, real-time interface, robust digital pitch controller, and 5 MW benchmark wind turbine model. Real-time testing was conducted on proposed controller using the developed test setup. Robustness test exhibited robust pitch control tracking when subjected to high wind gusts/fluctuations. In this test, the proposed controller reduced the pitch control error (mean absolute) by 68.10% and 51.75% when compared to feed forward and Elman controller, respectively. Subsequently, a power regulation test was performed on the proposed controller under real-time turbulence wind speed. Relative to the feed-forward and Elman controller, the proposed controller regulates power close to the rated value and improved the mean generator power by 3.39%, and 3.72%, respectively. A comparative study conducted with existing controllers (in the literature) demonstrate the superior performance of the proposed controller. This study reports that intelligent digital pitching action of proposed controller generates power close to rated power when compared to existing controllers in the literature.

Robust laser positioning in a mobile robot machine vision system

Problem. Laser scanning devices are widely used in Machine Vision Systems (MVS) of an autonomous mobile robot for solving SLAM problems. One of the concerns with MVS operation is the ability to detect relatively small obstacles. This requires scanning a limited sector within the field of view or even focusing on a specific point of space. The accuracy of the laser beam positioning is hampered by various kinds of uncertainties both due to the model simplifying and using inaccurate values of its parameters, as well as lacking information about perturbations. Goal. This paper presents the improvement of the MVS, described in previous works of the authors, by robust control of the DC motor, which represents the Positioning Laser drive. Methodology. For this purpose, a DC motor model is built, taking into account the parametric uncertainty. A robust digital PD controller for laser positioning is designed, and a comparative evaluation of the robust properties of the obtained control system with a classical one is carried out. The PWM signal formation by the microcontroller and processes in the H-bridge are also taken into account. Results. The obtained digital controller meets the transient process and accuracy requirements and combines the simplicity of a classic controller with a weak sensitivity to the parametric uncertainties of the drive model. Originality. The originality of the paper is in its focus on the MVS of the autonomous mobile robot developed by the authors. Practical value. The implementation of the MVS with the proposed controller will increase the reliability of obstacles detection within a robot field of view and the accuracy of environment mapping.

Breaking adiabatic quantum control with deep learning

In the era of digital quantum computing, optimal digitized pulses are requisite for efficient quantum control. This goal is translated into dynamic programming, in which a deep reinforcement learning (DRL) agent is gifted. As a reference, shortcuts to adiabaticity (STA) provide analytical approaches to adiabatic speed up by pulse control. Here, we select single-component control of qubits, resembling the ubiquitous two-level Landau-Zener problem for gate operation. We aim at obtaining fast and robust digital pulses by combining STA and DRL algorithm. In particular, we find that DRL leads to robust digital quantum control with operation time bounded by quantum speed limits dictated by STA. In addition, we demonstrate that robustness against systematic errors can be achieved by DRL without any input from STA. Our results introduce a general framework of digital quantum control, leading to a promising enhancement in quantum information processing.

Robust Digital Control Strategy Based on Fuzzy Logic for a Solar Charger of VRLA Batteries

This paper presents the design and implementation of a digital control strategy for a Buck converter, used as a solar charger of valve-regulated lead acid (VRLA) batteries. The control system consists of two fuzzy logic controllers (FLCs), which adjust the appropriate increment of the converter duty cycle based on battery state of charge according to a three-stage charging scheme. One FLC works as a maximum power point tracker (FLC-MPPT), while the other regulates the battery voltage (FLC-VR). This approach of using two different set of membership functions overcomes the limitations of the battery chargers with a single control function, where the voltage supplied to the battery is either not constant due to the operation of the MPPT algorithm (possibly damaging the battery) or is constant due to the operation of the voltage control (hence, MPP cannot be achieved). In this way, the proposed control approach has the advantage of extracting the maximum energy of the PV panel, preventing battery damage caused by variable MPPT voltage, thereby extending the battery’s lifetime. Moreover, it allows overcoming of the drawbacks of the conventional solar chargers, which become slow or inaccurate during abrupt changes in weather conditions. The strategy is developed to be implemented in a low-cost AT91SAM3X8E Arduino Due microcontroller. Simulations by MATLAB/Simulink and experimental results from hardware implementation are provided and discussed, which validate the reliability and robustness of the control strategy.

A New Robust Digital Non-Linear Control for Power Factor Correction—Arc Welding Applications

A welding power source is commonly assimilated to a non-linear load. Arc welding market being in full growth, the resulting harmonic pollution is becoming an increasingly difficult problem to ignore. Therefore, the main purpose of this work is to define and implement the most suitable solution for power factor correction in a welding power source. Due to the high non-linearity of the electric arc, the current controller used to control grid current need to show high robustness. Consequently, this paper focuses on the digitization of a very robust Phase-Shift Self-Oscillating Current Controller (PSSOCC), which only exists in its analog version until then, to carry out this task. After quick descriptions of the entire energy conversion chain and the PSSOCC operation principle, a model of the digital PSSOCC is proposed. Then, the quality and the accuracy of the aforementioned model are evaluated and its operating limits are identified. Afterwards, the behavior of the digital controller is studied within a Power Factor Correction (PFC) regulation for several specific arc welding operating modes. Finally, excellent robustness of this new FPGA-based digital current controller, named DPSSOCC, is confirmed on a three-phase Vienna converter test bench.

Synthesizing robust control systems for mechatronic objects with digital state controllers and observers

Currently, digital controllers with state observers are widely applied in automatic control systems for mechatronic objects, which great potential abilities are caused by structural flexibility and developed methods of synthesis. However, during design and practical implementation of the systems there is problem of robustness, associated with parametrical uncertainty of typical mechatronic objects. Most methods for synthesis of robust control systems are based on application of continuous mathematical models and do not take into account specific of digital realization of controllers with state observers. Methods of state space, modal control, digital system design, numerical optimization algorithms and simulation in MatLab environment were used. We propose a method of synthesizing robust digital modal control systems with state observers based on generating dynamic system characteristics within the areas of parametric robustness. Further, low sensitivity of the system to changes in controlled object parameters is ensured by the minimal phase character of the complex controller transfer function, while low sensitivity to changing parameters of the controller itself is ensured by excluding positive feedback in both control and adjustment circuits. Developed recommendations of choosing dynamic characteristics of state controller with observer loops within robustness areas and of forming rational state observer structure allow us to synthesize digital automatic control system with low sensitivity for variation of both control object parameters and inherent controller parameters.

Stability and Robustness of the Disturbance Observer-Based Motion Control Systems in Discrete-Time Domain

This article analyses the robust stability and performance of the disturbance observer (DOb) based digital motion control systems in the discrete-time domain. It is shown that the phase margin and the robustness of the digital motion controller can be directly adjusted by tuning the nominal plant model and the bandwidth of the observer. However, they have the upper and lower bounds due to robust stability and performance constraints as well as the noise sensitivity. The constraints on the design parameters of the DOb change when the digital motion controller is synthesized by measuring different states of a servosystem. For example, the bandwidth of the DOb is limited by the noise sensitivity and waterbed effect when the velocity and position measurements are employed in the digital robust motion controller synthesis. The robustness constraint due to the waterbed effect is removed when the DOb is implemented by acceleration measurement. The design constraints on the nominal plant model and the bandwidth of the observer are analytically derived by employing the generalized Bode integral theorem in discrete time. The proposed design constraints allow one to systematically synthesize a high-performance DOb-based digital robust motion controller. The experimental results are given to verify the proposed analysis and synthesis methods.

Direct Form Digital Robust RST Control Based on Chebyshev Sphere Optimization Applied in a DC-DC Power Converter

This paper presents a novel direct form to design a digital robust control using RST structure (i.e., name given because of the R, S and T polynomials computed) based on convex optimization such as Chebyshev sphere; this approach was applied to a DC-DC Buck converter. This methodology takes into account parametric uncertainties and a Chebyshev sphere constraint in order to ensure robust performance and stability of the system in the discrete domain. For this purpose, a mathematical model for the DC-DC Buck converter is presented when considering uncertainties in electrical variables, such as load resistance, inductance, capacitance, and source voltage variation, also to obtain the discrete model of the system by using the bilinear transformation. The proposed methodology is compared with two other approaches designed in a discrete domain: the classical pole placement and the robust methodology based on the Kharitonov theorem. Wide-ranging experiments are performed in order to evaluate the behavior of the control methodologies when the system is subject to parametric variations of the load resistance and voltage setpoint variation. The results show that the proposed methodology outperforms the other approaches in 90% of the tests and ensures robust stability and robust performance when the system is subjected to a parametric uncertainties family.

Low power analogue equaliser with adaptive digital tuning for fast ethernet

This work presents an analogue equaliser with digital tuning. It compensates the losses introduced by up to 120 m long category 5 unshielded twisted pair cables and baseline wander (BLW). The equaliser is designed for Fast Ethernet with a symbol rate of 125 MHz. A g m -C filter, based on three first-order high pass filters, is used to compensate the cable loss. To minimise power consumption, three operational transconductance amplifiers (OTAs) are merged into a novel multi-input OTA structure. Additionally, a robust digital control logic is presented to automatically adjust the parameters of the equaliser for different cable lengths. A fast settling time below 250 µs is demonstrated for different scenarios. The equaliser is fabricated as part of a Fast Ethernet PHY chip in a 180 nm CMOS technology of GLOBALFOUNDRIES. Measurement results demonstrate error-free data transmission (bit error rate below 10 −12 ) for cable lengths up to 120 m. The power consumption of the analogue equaliser ranges from 2.3 mW (short cable) to 6.5 mW (120 m cable). To the best of the authors’ knowledge, this is the lowest power consumption of an analogue equaliser for Fast Ethernet, supporting additional BLW and flat loss compensation reported to date.

Robust digital control for autonomous skid-steered agricultural robots

There are two main issues to consider when designing a controller for autonomous off-road vehicles: velocity and terrain irregularities. Whereas the first one is measurable, the second one is very difficult to determine. Solutions to cover these issues could be very complex and difficult to implement in an embedded system with limited resources. The results obtained in our previous research for an adaptive approach implemented in a tractor with varying hitch forces, lead to the improvements presented here. This paper proposes a robust digital RST pole placement controller design for the lateral position, with sensitivity functions tuned to cover uncertainties and non-linearities not considered in the model. Simulations were implemented to assess the performance of the system and the controller implementation was applied to a skid-steered agricultural robot with limited computational resources and a state-of-the-art navigation system, which delivered satisfactory results.

A Robust Digital Control Strategy Using Error Correction Based on the Discrete Lyapunov Theorem

This paper presents a robust digital control strategy using error correction techniques to improve the robustness of conventional deadbeat control methods. The proposed control method, based on the discrete converter models, determined control law using an error correction technique based on the discrete Lyapunov stability theorem. The steady-state performance and dynamic response of the presented method was analyzed and verified. The experimental results showed that the method derived in this paper not only offered improved robustness, but also endowed the grid current with lower Total Harmonic Distortion (THD), while still maintaining a fast, dynamic response.

Two Degree-of-Freedom Robust Digital Controller Design With Bouc-Wen Hysteresis Compensator for Piezoelectric Positioning Stage

The compensation of nonlinear hysteretic behavior is one of the mandatory requirements in order to achieve precise reference tracking performance from a piezoelectric positioning stage. A common practice of employing an inverse hysteresis model as a feed-forward compensator must deal with modeling complexity; consequently, real-time tracking performance suffers due to modeling errors. In this paper, a two degree-of-freedom robust digital feedback controller design scheme in the presence of a simple Bouc-Wen hysteresis feed-forward compensator is proposed to deal with the dual challenge of modeling complexity and modeling errors. The proposed control scheme takes into account the performance and robustness requirements simultaneously. The desired performance and robustness requirements are expressed by means of constraints on the shapes of closed-loop sensitivity functions (CLSFs). Then, pole placement with sensitivity function shaping methodology is adopted so that the CLSFs respect their respective constraints and the desired performance with robustness could be achieved. The presented experimental results verify the effectiveness of the proposed control scheme in achieving the peak-to-peak reference tracking error of 0.36% for the desired displacement of $12~\mu \text{m}$ with tracking frequency of 10 Hz, whereas the peak-to-peak tracking error of 4.33% is observed with a Bouc-Wen hysteresis feed-forward compensator (without the feedback controller). Overall, 91% improvement is achieved in reducing the reference tracking error with the proposed control scheme.

Design of a Robust Digital Control System for the Rectification Column Used in the Production of Divinyl

A complex optimization criterion that takes into account the integral quadratic error and the stability margin of a robust digital control system for the rectification column used for the butylene-divinyl fraction is proposed. The influence of the weight coefficient, taking into account the ratio of the performance and stability indicators, on the dynamic characteristics of the system is investigated. High system performance and system stability indices over a sufficiently broad range of variation of the parameters of the rectification column are achieved through the use of the proposed optimization criterion and a stability estimation algorithm in the synthesis of a robust digital control system.

Application of Robust Control to a Cryogenic Current Comparator

This paper describes the implementation of a digital robust controller in a cryogenic current comparator. The controller was designed applying $ {\cal {H}_\infty }$ control theory and it was programmed in a home-made digital unit. Experimental comparisons of the new robust controller with the conventional analog integrator have showed a significant improvement of stability robustness and noise rejection in the system.

Robust digital pole-placer for electric drives based on uncertain diophantine equation and interval mathematics

In this paper, a novel robust digital controller design is proposed and implemented for induction motor speed control. The objective is to design a robust output feedback controller that places the closed-loop poles in a specified region in order to achieve the desired dynamic performance for a system with variable load. The design is carried out in the frequency domain by solving the uncertain Diophantine equation using interval mathematics and non-linear optimization method. In order to capture the load variations, the characteristic equation is relaxed and enlarged from a fixed-point to an interval set. A simple model-based design methodology is adopted in this work and implemented experimentally using a Hardware-in-the-Loop environment. The proposed design is simulated and then validated using real induction drive system. The proposed controller is compared with two other controllers: the auto tuned PID and a least-square-based robust controller. Experimental results show that the designed robust controller provides a better dynamic response than conventional controllers used in the industry when the motor’s load is varied. These results validate the proposed design as the plant’s output follows the reference signal with minimal overshoot and settling time.

Robust digital deadbeat control design technique for 3 phase VSI with disturbance observer

Robust digital deadbeat control design technique for 3 phase VSI with disturbance observer

Robust Control of High-Speed Synchronous Reluctance Machines

High-speed regimes allow an increase in the power density of electrical drives, which is a necessary characteristic in aeronautical applications. In such a context, together with the typical nonlinearities of low-speed drives, i.e., core saturation, phenomena related to high fundamental to sampling frequency ratios appear increasingly significant. This paper applies methodologies based on modern robust control to high-speed synchronous reluctance machines. The proposed method is based on a reformulation of the motor model as a linear parameter varying system. This allows transforming the current controller design in a multivariable optimization problem, which is solved with efficient numeric tools. The mathematical formulation of a robust digital controller directly designed in the discrete time domain is proposed. The controller performance are experimentally compared to of its counterpart designed in the continuous-time domain, and subsequently, discretized, as proposed in a previous work by the same authors, to have agreement a more standard decoupled current control using proportional-integral regulators. Results demonstrate the effectiveness of the proposed controller structure in current regulation, especially at high-speed regimes.