Phase Margin Research Articles

Fast and low power SiPM amplifier operating in a wide temperature range

The next generation of Ring Imaging CHerenkov detectors in high energy physics experiments may use SiPMs as photon sensing elements. This upgrade is necessary to achieve greater detector granularity and speed, however SiPMs need to be cooled down to cryogenic temperatures to detect single photons in high-radiation environments and avoid being overwhelmed by the presence of “dark signals”. It is therefore necessary to study and characterize SiPM models in dedicated campaigns, using a custom-built amplifying chain that can also operate in an extended temperature range, between 80 K and 300 K, for detector characterization purposes. The proposed amplifier configuration consists of two amplifying stages and achieves low jitter values (<10−20psRMS) thanks to the low electronic noise and the high amplifier bandwidth. The circuit achieves a signal bandwidth of 500MHz<BW<1GHz, a phase margin of approximately 45° and a power consumption of about 65−135mW. The amplifier prototype unit can be adjusted to cover the considered temperature range and still achieve low jitter values.

Ultra-low-power super class-AB adaptive biasing operational transconductance amplifier with enhanced gain for biomedical applications

The operational transconductance amplifier (OTA) proposed in this article is a bulk-driven (BD), single-stage, super-class-AB, adaptive biasing, functioning in the subthreshold region (ST) with an enormously low power supply of ± 0.25 V, providing high-gain. The input core of the OTA circuit is composed of adaptively biased BD differential input pairs based on flipped voltage follower (FVF), which drive in class-AB mode with a partial positive feedback (PPF) approach. The circuit additionally employs FVF and self-cascode (SC)-based low-power current mirror loads at its output to obtain significantly high gain and unity gain frequency. In addition, using adaptive loads based on source-degenerated metal oxide semiconductor (MOS) resistors raises dynamic current more efficiently, consequently improving the slew rate and unity gain frequency (UGF) without drawing additional power. Employing the cadence spectre tool and the UMC 0.18 μm complementary metal oxide semiconductor (CMOS) process technology, the designed OTA has been simulated. The simulation outcomes substantiate that the amplifier provides high open loop DC gain of 75 dB, 18.75 kHz UGF with a phase margin of 63.93º, and input-referred noise (IRN) of 0.734 µV/Hz0.5 at 1 kHz frequency. The proposed OTA consumes just 60.15 nW of power. The performance results confirmed that the proposed OTA circuit is appropriate in biomedical applications.

A decentralized optimal PID controller with disk margin-based robust stability analysis for higher-order industrial systems

ABSTRACT Decentralized control systems are frequently employed to tackle control challenges in multi-input multi-output (MIMO) systems. Hence, this paper proposes a decentralized PID controller that relies on frequency domain specifications. This controller is designed to minimize the loop interactions and fulfill the design criteria of the MIMO system. The PID parameters are calculated based on gain and phase margin specifications. Additionally, a first-order plus dead time model is derived for each of the decoupled subsystems. Furthermore, robust stability is analysed using disc margin analysis, which overcomes the constraints of traditional margins. Moreover, the paper determines a secure range of uncertainty for various levels of gain and phase uncertainties. The findings suggest that the proposed controller achieves robust stability over a broader range of margins when compared to alternative control methods.

Relay feedback identification and PI-PD control of asymmetrical heating and cooling processes

A common type of nonlinear system in the field of process industry is asymmetrical heating and cooling processes. These systems have two operating modes, heating and cooling, each with a particular dynamic feature. This study deals with identifying and controlling such processes. The relay feedback identification method based on the state-space approach, which results in exact estimates, is used in the identification procedure to achieve two first-order plus dead time (FOPDT) process models. Following process identification, two sets of PI-PD controller parameters are acquired in line with the user-defined gain and phase margin specifications, and the system is controlled using a gain-scheduled PI-PD control method. Some simulation examples are provided to demonstrate the use and profitability of the suggested identification and control approaches. Comparisons with a similar study are provided for both identification and control approaches to clearly demonstrate the benefits of the suggested procedures.

Efficient voltage regulation: An RW-ARO optimized cascaded controller approach

This work introduces novel advancements in automatic voltage regulator (AVR) control, addressing key challenges and delivering innovative contributions. The primary motivation lies in enhancing AVR performance to ensure stable and reliable voltage output. A crucial innovation in this work is the introduction of the random walk aided artificial rabbits optimizer (RW-ARO). This novel optimization strategy incorporates a random walk approach, enhancing the efficiency of AVR control schemes. The proposed cascaded RPIDD2-PI controller, fine-tuned using the RW-ARO, stands out as a pioneering approach in the AVR domain. It demonstrates superior stability, faster response times, enhanced robustness, and improved efficiency compared to existing methods. Comparative analyses with established controller approaches reaffirm the exceptional performance of the proposed method. The new approach results in shorter rise times, quicker settling times, and minimal overshoot, highlighting its effectiveness and speed in achieving desired system responses. Moreover, the novel approach attains higher phase and gain margins, showcasing its superior performance in the frequency domain. The disturbance rejection and harmonic analysis are performed in order to demonstrate the efficacy of the proposed approach for potential real-world applications. The latter analyses further cement the superior capability of the proposed approach for the automatic voltage regulation.

Grid-Connected Inverter Grid Voltage Feedforward Control Strategy Based on Multi-Objective Constraint in Weak Grid

In weak grid, feedforward of grid voltage control is widely used to effectively suppress grid-side current distortion of inverters caused by harmonics in point of common coupling (PCC) voltage. However, due to its introduction of a positive feedback loop related to the grid impedance, it results in a significant reduction in the system phase margin. In view of this, in this paper, the output impedance of a three-phase LCL grid-connected inverter under a quasi-proportional resonant (QPR) controller is first modeled. Instead of the traditional grid voltage feedforward control strategy, a band-pass filter is added to the grid voltage feedforward channel. Secondly, a multi-objective constraint method is proposed to make improvements to the feedforward function. Then, a multi-objective constraint function is established with the constraints of base-wave current tracking performance, system stability margin, and low-frequency amplitude, and the feasibility of its function optimization design method is verified. Theoretical analysis shows that the optimized grid voltage feedforward control strategy can effectively reshape the phase characteristics of the system output impedance, which greatly broadens the adaptation range of the system to the grid impedance. Finally, the effectiveness of the proposed control strategy is verified by building a semi-physical simulation experimental platform based on RT-LAB OP4510.

IMC based robust and innovative control strategies for higher-order DC-DC converter in DC microgrid applications

The extensive practice of DC-DC converter interfacing circuits to maintain DC link voltage in DC microgrid applications introduces unavoidable voltage regulation problems due to its nonlinearity. These unregulated voltages demean the performance and result in an unstable system. This brief proposes an internal model control (IMC) non-linear approach based robust proportional-integral-lead (PI-Lead) controller design for regulating a practical fifth-order DC-DC boost converter. The main innovation of this paper is the developed procedure for designing controller. The prominent feature of IMC filter coefficient is to fulfil the desired level of gain margin and phase margin to show the trade-off between performance and robustness. The proposed controller's performance is evaluated in the presence of uncertain disruptions and its effectiveness is verified by comparing it with the some conventional proportional-integral (PI) as well as with recently published IMC-proportional-integral-derivative (IMC-PID) and IMC-proportional integral derivative double derivative (IMC-PIDD2) controllers. The applicability of the proposed control methodology has been validated under varying supply and load current levels in presence of parametric uncertainty using a MATLAB/Simulink tool along with a low-cost microcontroller DSP F280379D based laboratory prototype.

A compensator design and stability margin monitor for digitally controlled DC-DC converters

ABSTRACT In this paper, an automatic direct digital design approach for compensators is presented to achieve a lookup table proportional – integral – derivative controller. Additionally, a correlation-based stability margin monitor with adaptive sliding window smoothing is proposed to increase the identifiable range for bandwidth detection. The proposed automatic compensator design approach meets the expected phase margin and crossover frequency and considers limit-cycle oscillation conditions throughout the design process. The digital controller with the direct digital design was implemented on a field programmable gate array to validate the approach and alternative design capabilities. Experimental results show that the direct digital design yields a higher crossover frequency than digital redesign. The best transient response performance can be obtained if a proper integral gain is designed. The digital controller with ASWS was fabricated using the TSMC 1P6M 0.18-μm standard CMOS process. Further experimental results show that the proposed ASWS provides a significantly more accurate identified frequency response by using narrow windows at low frequencies and expansive windows at high frequencies.

LQR control strategy for virtual synchronous generator adapted to stiff grid

Virtual synchronous generators (VSG) exhibit good small-signal stability in low short-circuit ratio (SCR) grids. However, the small-signal stability of the grid decreases as its SCRs increase, and there is even a risk of sub-synchronous resonance (SSR). The VSG sequence impedance model considering the frequency coupling effect is developed. The reasons for SSR caused by VSG integration into a stiff grids are analyzed using the sequence impedance analysis method and the Nyquist criterion. To enhance the grid-connected stability of VSG under stiff grids conditions, a linear quadratic regulator (LQR) control strategy with full-state feedback was proposed. The control strategy of LQR can effectively improve the phase margin of VSG output impedance in the low-frequency region, and it also exhibits strong robustness to variations in grid short-circuit ratios. It can also significantly improve the stability margin of the grid-tied system consisting of VSG and stiff grid, and effectively suppress the occurrence of SSR. Finally, the effectiveness and reliability of LQR control strategy are verified by OPAL-RT experimental platform.

Control stability analysis of dynamic model with time delay for quadrotor UAV

For the first-order unstable object with time delay, the PD control parameter tuning method based on the traditional definition lacks consideration of the lower boundary of amplitude margin, resulting in a certain deviation between the result and the reality. In this paper, through analyzing the control loop of quadrotor UAV (QUAV), the integral link is moved from the controlled object to the controller, and the QUAV becomes a first-order unstable object, realizing the conversion of PD to PI in the hovering state. The system stability margin remains unchanged, and the position and attitude control objectives can be realized synchronously. By means of parameter setting method, the upper boundary of stability margin is obtained. Pade approximation is carried out for the time delay link, and then the lower margin of the amplitude margin is deduced according to Routh stability criterion, so as to obtain a more accurate reachable stability margin region. To avoid the high gain feedback of attitude angular velocity of QUAV, a numerical analytical setting formula for PD attitude control is derived to meet the requirements of gain and phase margin. The graph shows that the reachable region obtained by the strict definition of stability margin analysis decreases significantly. The proposed method can not only give the reachable region intuitively, but also give the tuning formula of the control parameters concisely, which has important engineering application value.

Parametric Sensitivity Analysis of Stability Margins of Holos-Quad Microreactor

An analysis of the stability margins of the innovative Holos-Quad microreactor design is presented. This high-temeprature gas-cooled reactor (HTGR) system is designed to operate fully autonomously with passive safety mechanisms. Therefore, the inherent stability of the reactor is of great importance. Using a point-reactor model, which couples point kinetics to thermal-hydraulic heat balance equations and includes reactivity feedback effects of the fuel and moderator temperatures, the closed-loop transfer function of the reactor is derived. Applying the approach of linear systems and control theory, both the gain and phase margins of the Holos-Quad design are obtained. The analysis demonstrates that the design is stable, with an infinite gain margin and a finite phase margin. A parametric uncertainty quantification study is also performed using a total Monte Carlo approach. The stability of the reactor for different power levels, such as during reactor startup or load-following transients, is also explored. Finally, two sensitivity analysis methods are applied, namely, multiple regression (deriving standardized regression coefficients) and variance-based sensitivity analysis (known as the Sobol method), to study the contribution of each of the parameters to the stability margins’ uncertainty. This analysis improves our understanding of the role of each of the parameters in the stability of the reactor.

16.2-μW Super Class-AB OTA with current-reuse technique achieving 130.3-μA/μA FoM

In this paper, a single-stage Super Class-AB operational transconductance amplifier (OTA) using current reuse technique is presented. It is based on two scaled current mirrors located at the tail current nodes of input pairs, reusing the current through the cross-coupled input pairs by a current gain factor of α, and delivering new currents to the output branch, enhancing the overall transconductance (Gm) by a factor of (1+α). With adaptive biasing and local common mode feedback (LCMFB), slew rate (SR), open loop gain (AOL) and gain-bandwidth product (GBW) are improved. An prototype has been designed in TSMC 0.18-μm CMOS process. Post-simulation shows the positive and negative slew rate of 22V/μs and −38.3V/μs, respectively, a GBW of 3.72 MHz, a DC gain of 65.6 dB with a phase margin of 69.2° for a capacitive load of 70 pF. The proposed OTA consumes a total power of 16.2 μW under a 1.8V supply voltage.

Segment-compensated Bandgap Reference Generator with Low-temperature Drift

Abstract In this paper, a segment-compensated low-temperature-drift bandgap reference generator is proposed and designed to get the high-order nonlinear temperature characteristics for the bandgap reference circuit. Based on the Nuvoton 0.35 μm BCD process, the circuit is simulated and analyzed. The result is that a temperature coefficient of 1.12 ppm/℃ over the range of -40℃ to 125℃ is obtained, which is much lower than the 6.88 ppm/℃ before compensation. It is demonstrated that the power supply rejection ratio is 141.3 dB at 1, 000 HZ, low-frequency open-loop gain is 75 dB, and a phase margin is 57°.

A Transient-Enhanced Capacitorless LDO Design

Abstract This paper introduces a capacitor-less low drop-out voltage regulator (LDO) designed for fast transient response. Traditional capacitor-less LDOs often suffer from suboptimal transient responses, leading to unstable outputs during load transitions. To address this challenge, the circuit employs voltage rise and fall suppression circuits to mitigate voltage spikes. It utilizes slew rate enhancement techniques to improve the transient response characteristics of the LDO. Miller compensation is applied to achieve phase margin compensation with a smaller capacitor area. Simulation outcomes indicate that within the voltage range of 2.2 V to 3.3 V, the circuit provides a stable output voltage of 1.8 V while accommodating a peak load current of 100 mA. When the load current undergoes a step change between 1 mA and 100 mA, the transient enhancement circuit reduces the undershoot of the output voltage by 58 mV, a decrease of 39%, with a response time of 1.13 μs. The overshoot amplitude is reduced by 212 mV, a decrease of 70.6%, with a response time of 1.21 μs.

Simulation and Controller Design for a Fish Robot with Control Fins.

In this paper, a nonlinear simulation block for a fish robot was designed using MATLAB Simulink. The simulation block incorporated added masses, hydrodynamic damping forces, restoring forces, and forces and moments due to dorsal fins, pectoral fins, and caudal fins into six-degree-of-freedom equations of motion. To obtain a linearized model, we used three different nominal surge velocities (i.e., 0.2 m/s, 0.4 m/s, and 0.6 m/s). After obtaining output responses by applying pseudo-random binary signal inputs to a nonlinear model, an identification tool was used to obtain approximated linear models between inputs and outputs. Utilizing the obtained linearized models, two-degree-of-freedom proportional, integral, and derivative controllers were designed, and their characteristics were analyzed. For the 0.4 m/s nominal surge velocity models, the gain margins and phase margins of the surge, pitch, and yaw controllers were infinity and 69 degrees, 26.3 dB and 85 degrees, and infinity and 69 degrees, respectively. The bandwidths of surge, pitch, and yaw control loops were determined to be 2.3 rad/s, 0.17 rad/s, and 2.0 rad/s, respectively. Similar characteristics were observed when controllers designed for linear models were applied to the nonlinear model. When step inputs were applied to the nonlinear model, the maximum overshoot and steady-state errors were very small. It was also found that the nonlinear plant with three different nominal surge velocities could be controlled by a single controller designed for a linear model with a nominal surge velocity of 0.4 m/s. Therefore, controllers designed using linear approximation models are expected to work well with an actual nonlinear model.

Model‐based adaptive control of modular DAB converter for EV chargers

AbstractThis paper presents the discrete‐time modelling and control of modular input‐parallel–output‐parallel (IPOP) dual‐active‐bridge (DAB) converters for electric vehicle (EV) charging. The proposed adaptive control system ensures adequate current‐sharing among parallel modules while minimizing DAB current stress by adopting dual phase‐shift modulation. Driven by the growing need for fast EV charging options, the paper highlights the importance of achieving top‐notch control performance, especially with varying load conditions. Specifically, it introduces a discrete‐time model for adjusting controller parameters adaptively, which simplifies the typically cumbersome manual tuning process associated with these systems. The proposed PI formulae are derived to satisfy specifications on the frequency domain as phase margin and the gain crossover frequency of the open loop gain transfer function, ensuring stability and robustness in operation. Moreover, the implementation of these formulae in discrete microcontrollers facilitates seamless PI autotuning for precise current, voltage, or power control. Notably, the proposed control strategy effectively mitigates current overshot issues commonly encountered during module engagement and shedding operations in modular EV chargers. To validate its efficacy, the proposed controller is evaluated through extensive testing and comparisons within the PLECS environment, particularly focusing on a two‐module IPOP‐DAB converter scenario, and including comparisons with classical offline model‐based pole placement methodology. Furthermore, real‐time hardware‐in‐the‐loop experiments are conducted to confirm the feasibility and performance of the proposed controller under realistic EV charging profiles.

Analysis, Simulation, and Experiments of Dynamics and Control of a Hydrostatic Wind Turbine Under Partial Load

Abstract Kω2 control, also called torque control, is a popular method for maximizing wind turbine power. For hydrostatic wind turbines, torque control becomes pressure control with pc=K'ω2 because pressure is proportional to torque. Inverse Kω2 control is an alternative approach using rotor speed control with pc=(p/K')1/2. This work analyzes the dynamics of hydrostatic wind turbines using forward and inverse Kω2 control with P-, PD-, PI-, and PID-control for feedback. Dimensionless, linearized models are used. Analysis shows that the mechanical rotor dynamics are much slower than the hydrostatic transmission dynamics and that frictional and leakage losses are negligible. Linear perturbation of the nonlinear model reveals that the closed-loop control is not in Evan's form, so that closed-loop poles and zeros both vary with the loop gain. Pole and zero root locus analysis shows how systems responses change with controller gains. Both control approaches require derivative controller action to sufficiently dampen their responses; both are also fundamentally limited in speed of response by a slow stable pole regardless of controller loop gains. Nonlinear system simulation shows that both control approaches track the maximum power point with nearly identical transient behavior and have nearly identical power losses when using suboptimal values of the control law gain, K. Pressure control has a gain margin of infinity and a phase margin of 99.3 degrees, while speed control has a gain margin of 22.4 dB and a phase margin of 73.8 degrees showing that pressure control is more robust than speed control. Experiments using the power regenerative hydrostatic test stand at the University of Minnesota show that the control approaches have different transient responses but capture comparable power under steady and turbulent conditions.

Experimentally validated predictive PI-PD control strategy for delay-dominant chemical processes

Controlling delay dominant chemical processes is a challenging control problem. Hence, a new method for designing a Smith predictor (SP)-based proportional-integral proportional-derivative (PI-PD) control strategy is proposed in this study. The inner-loop PD parameters are determined using the phase margin (PM) and maximum sensitivity (Ms) specifications. To determine the outer-loop PI parameters, the moment matching technique is augmented with maximum sensitivity considerations. The performance and robustness of this design is compared with that of its contemporaries using four benchmark chemical process models including that of a stirred tank reactor and a heat exchanger. The resilience of this control strategy amid uncertainties in process parameters is studied and performance improvement achieved over contemporary works is quantified. Finally, the proposed design is also experimentally validated on a two-tank level control loop.

PID controller tuning based on PSO and dominant pole placement

This paper proposed a new approach for proportional integral derivative (PID) controller tuning. particle swarm optimization (PSO) algorithm and dominant pole placement were used for PID controller tuning. Minimizing the estimation criterion with integral of absolute error (IAE) and overshoot by PSO algorithm, we determined the dominant pole and crossover frequency satisfying the maximum sensitivity and phase margin. This dominant pole and crossover frequency were used in order to design the PID controller. It satisfied robust stability and improves the control effect of the system to balance the trade-off between overshoot and settling time. We simulated this approach for SOPDT model. A simulation results were given to demonstrate the effectiveness of this approach.

Sensorimotor adaptation to destabilizing dynamics in weakly electric fish

Humans and other animals can readily learn to compensate for changes in the dynamics of movement. Such changes can result from an injury or changes in the weight of carried objects. These changes in dynamics can lead not only to reduced performance but also to dramatic instabilities. We evaluated the impacts of compensatory changes in control policies in relation to stability and robustness in Eigenmannia virescens, a species of weakly electric fish. We discovered that these fish retune their sensorimotor control system in response to experimentally generated destabilizing dynamics. Specifically, we used an augmented reality system to manipulate sensory feedback during an image stabilization task in which a fish maintained its position within a refuge. The augmented reality system measured the fish's movements in real time. These movements were passed through a high-pass filter and multiplied by a gain factor before being fed back to the refuge motion. We adjusted the gain factor to gradually destabilize the fish's sensorimotor loop. The fish retuned their sensorimotor control system to compensate for the experimentally induced destabilizing dynamics. This retuning was partially maintained when the augmented reality feedback was abruptly removed. The compensatory changes in sensorimotor control improved tracking performance as well as control-theoretic measures of robustness, including reduced sensitivity to disturbances and improved phase margins.