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Differing from a two-level voltage source converter (TL-VSC), the internal dynamics of a modular multilevel converter (MMC) are much more complicated. Since the fluctuation of submodule capacitor voltage is unavoidable when transmitting power, the MMCs output voltages cannot track the references perfectly. The interaction between the time-varying capacitor dynamics and controllers may lead to self-instability of the MMCs. In order to address this self-instability issue, this paper first establishes the small-signal closed loop transfer function matrices (TFMs) of the external and internal control loop by the harmonic linearization method. Further, a novel design principle of MMC controllers is proposed. Then, the critical impact factors on the stability of circulating current controller and AC voltage controller are investigated based on the generalized Nyquist criterion(GNC). The proposed models and analysis methods are validated by time-domain simulations in PSCAD/EMTDC.

A novel flexible fuel thermal management architecture with a switched mode control strategy is proposed that provides a framework for increasing the thermal endurance of aircraft that use fuel as a...

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Commonly used variants of the proportional-integral, PI, and the integral-proportional, IP, compensator gains selections, merged with the $\mathfrak {D}$ -decomposition technique are presented in this paper. The motivation to this work is the willingness to check whether such a combination can lead to unified and perhaps simplified approach in this matter. Therefore, the $\mathfrak {D}$ -decomposition technique has been effectively combined with the frequency- and the time-domain driven requirements regarding the control dynamics. Criteria such as the gain- and phase-margins, $(GM, PM)$ , the sensitivity, $M_{\text {S}}$ , the pole placements by means of the $(\sigma, \omega _{\text {d}})$ and the $(\xi, \omega _{\text {n}})$ , and the overshoot with the rise time $(\delta, t_{\text {r}})$ are considered. It has been shown that the control design effort can be reduced by the means of the $\mathfrak {D}$ -decomposition to intuitive judgments in the proportional and integral gains coordinates $(K_{\text {P}}, K_{\text {I}})$ with parametric curves. As such it can be thought of as a promising scenario in a case considered. The analyses are presented and discussed in details. They are conducted basing on example of output voltage closed loop control of the Dual Active Bridge, DAB, converter. The circuit operates under the phase shift control scheme. The control-to-output transfer function identification and the control circuit delays are included in the analyses. The case analysis have shown that the time domain requirements are less effectively met with the PI regulator when compared to its IP configuration. This is due to the commonly used simplifications during conversion between the $(\xi, \omega _{\text {n}})$ and the $(\delta, t_{\text {r}})$ in presence of uncompensated zero of the closed loop transfer function. The paper contains complete and intelligible approach to dedicated mathematical investigations verified experimentally.

The parameter perturbation of grid-side equivalent inductance is a significant feature of the uncertainty in the single-phase pulse-width modulation rectifiers system for the electric locomotive. This characteristic tends to reduce the robustness of the rectifier system. This study handles these problems in the framework of the structured singular value, which helps to reduce the influence of model parameter perturbation, caused by measurement error and operation condition change, on the robustness. However, the conventional μ-synthesis robust controls only reflect tracking and anti-disturbance performance by weighting functions and ignoring the dynamic response performance. Herein, a direct current control (DCC) scheme based on improved μ-synthesis is proposed. A desired closed-loop transfer function is introduced to the conventional μ-synthesis control structure to ameliorate the performance of the dynamic response. Furthermore, considering the external disturbances on the system control output, a suitable weighting function is used to restrict the external disturbance. The input–output relationship of the generalised open-loop plant can thus be constructed accordingly. The proposed control scheme is compared with the widely applied proportional–integral-based DCC scheme and the conventional μ-synthesis DCC scheme. Hardware-in-the-loop experiment results show promising dynamic performance as well as stronger robustness against parameter perturbation and external disturbances.

Although all six Apollo lunar landings were successful, the multiple landing site redesignations and landing near hazards suggest crewed planetary landings can be challenging and demand high pilot ...

Background: Manual drug infusion during surgeries is inaccurate and timeconsuming which has been adopted technique in most of the hospitals. Methods: Based on clinical data, it is evident that the manual control is inaccurate and takes prolonged time to bring into effect, if any change in infusion rate is required during clinical practice. Considering this drawback, the modeling of cardiovascular system (CVS) and baroreceptor (BR) is developed using miscellaneous differential equations based on compartmental approach. The control variables are mean arterial pressure (MAP) and cardiac output (CO) obtained from CVS-BR model. Findings: The manipulated variables are noradrenaline (NAR) and nitroglycerine (NG) infusion rate which is modeled using the relationship between volume and drug mass effect equations on CVS-BR model. For the open loop transfer function derived from the model, relative gain array (RGA) analysis is performed to identify the influence of maximum effect of manipulated variables on the physiological parameters. The simulation results obtained from MATLAB are correlated using time domain specifications and error criteria. The performance index reveals the least error and facilitates in accurate infusion of drugs to the patient during cardiovascular surgeries. Novelty: The automatic controller during surgery provides safe operating condition and speedy recovery of the patients and also helps the anaesthetist to monitor and regulate the physiological variables. Keywords: Control strategy; Error criteria; Drug infusion; Modeling; Relative gain array; Simulation

Nonlinear dynamic inversion (NDI) is a nonlinear feedback linearization technique that has been widely applied to flight control systems [1,2]. Using state feedback and the inverted nonlinear system dynamics, NDI can significantly reduce controller development costs by avoiding gain scheduling and Jacobian linearization at a multitude of operating points. However, the control performance of NDI is directly dependent on required detailed knowledge of the model. As a simplified and enhanced NDI method [3], incremental nonlinear dynamic inversion (INDI) [4,5] has been proposed to reduce the model dependency and improve the robustness against model uncertainties. Instead of using a global nonlinear model, in INDI the dynamic inversion is implemented on a locally linearized system model that is updated at every sampling period, for which the control input is calculated in an incremental manner. Unlike NDI, for which full knowledge of the complete system dynamics is needed, INDI only requires explicit knowledge of the system’s control effectiveness matrix.

This work aims to introduce a tuning-free PID controller for stable FOPTD and FOLIPD systems. The objective was achieved using a partial model-matching strategy; matching the coefficients of corresponding powers of s of the closed loop response of the model to the desired closed loop transfer function. Closed-loop performance is evaluated by considering a unit step change in the process model and compared the results with other methods reported earlier in the literature. Input and output performances were evaluated using error analyses and total variation. The robustness of the proposed method was assessed via incorporation of uncertainties in the process model parameters. The proposed method was also experimentally validated for FOPTD model using a temperature controlled lab. It was concluded that the method was analytically derived and model based with a key advantage that the resultant PID required no tuning parameter.

In this paper we derive some new and useful conditions on the open loop transfer function, necessary for closed loop stability. The derivation is based on imposing the sign-invariance of the closed loop characteristic polynomial evaluated on the real axis. Although this is a simple necessary condition for closed loop stability, it leads to fairly stringent requirements on the open loop transfer function. Also, the results can be stated only in terms of the numbers of real poles and zeros of the open loop system even though the system may have complex poles and zeros. Using the same approach new necessary conditions for stabilizability by P, PI and PID controllers as well as by arbitrary controllers are also presented.

This paper presents an intuitive analysis of a class of conditionally stable feedback circuits, that are stable although the Bode stability criteria indicates otherwise: at the frequencies their loop gain phase characteristics first reach -180°, the magnitudes of their magnitude characteristics are far larger than unity. An easy-to-use stability criterion is introduced by means of two circuit examples. Only the usual loop gain Bode plots are required to apply this criterion, but it suits only conditionally stable systems with no right-hand plane (RHP) poles in the open loop transfer function, T(s), and no integrators. A separate, three-step method for assessing the stability of feedback circuits with RHP poles and integrators is also proposed. It applies to all conditionally stable circuits and involves extracting the poles and zeros of T(s) and plotting the corresponding Nyquist contour.

Positive position feedback is an attractive control law for the control of plants having no high frequency roll-off. The tuning of the parameters of the positive position feedback to obtain the desired closed-loop performance is quite challenging. This paper presents a technique to design the positive position feedback controller with the optimal damping. The technique is demonstrated on a single degree-of-freedom system. The poles of the positive position feedback are tuned using the method of maximum damping, which states that the maximum damping is achieved when both closed-loop poles of the system are merged. The parameters of the positive position feedback are dependent on the desired target damping in the closed-loop system. However, arbitrary choice of target damping results in high response at the frequencies lower than the tuning frequency. The optimal value of the target damping is obtained by minimizing the [Formula: see text] norm of the closed-loop transfer function of the system. The influence of the various parameters of the positive position feedback on the closed-loop response of the system is also studied. Finally, the experiments are conducted to verify the effectiveness of the proposed technique.

This article studies the mechanics of reusable retro-propelled flight of slender low lift to-drag bodies via integrated guidance and control simulations. To do this, a simulation benchmark focused on the coupling between flight mechanics, guidance and control must be developed, as opposed to mission-optimisation oriented ones that simplify (or directly ignore) these couplings. The developed simulator covers vertical take-off and landing of a first stage booster for return to launch site and downrange landing missions. In order to steer it towards a controlled entry, followed by descent and precision landing, the vehicle is configured with a deep throttling thrust vector control system, fins and cold gas thrusters. Comparative performance results are derived in terms of aerodynamic loads and heat fluxes for both recovery scenarios, as well as through a detailed closed-loop controllability analysis. The latter demonstrates that the configuration has sufficient authority and resolution to perform stable flight and adequate wind gust rejection. The developed benchmark (because of the coupled flight mechanics, guidance and control) allows to provide a first assessment of operational limits, as well as mission and GNC specifications. This in turn paves the way for the synthesis and assessment of more sophisticated reusable launcher guidance and control algorithms.

In this paper, improved design of a decentralized PID controller for the multivariable time delay processes is proposed. In this method, the Haalman method is extended for each single input and single output process. The method is based on keeping the open loop transfer function same as that required for an integrating with time delay transfer function model. The method does not involve any tuning parameter. The design of MIMO PID controllers is based on detuning only the proportional gain. The controller performance study has been carried out on three multivariable stable transfer function models. The proposed method provides better closed loop performances for the perfect and uncertainties in the process model parameters compared with the recently reported methods. The closed loop performances are assessed in terms of Integral Square Error (ISE), Integral Absolute Error (IAE) values and Total variance (TV).

A common topic of discussion among members of the flight-test community is pilot gain. Every seasoned flight-test professional is capable of identifying test pilots that are considered to be either...

The goal of this paper is to introduce an adaptive load frequency control (LFC) technique for power systems. The concept of the proposed adaptive technique is built on the on-line tuning of the gain of an integral controller using Electro-Search optimization (ESO) supported by a modification called the ‘balloon effect’. The main target is to regulate the frequency of isolated and interconnected power systems. The balloon effect is designed to obtain the input/output signals of the power system plant at any moment; then, these signals are utilized to calculate the value of the open loop transfer function of the plant at the same time. This will emphatically affect the specified objective function of the ESO approach and increase its sensitivity to and effect on system difficulties such as system step load changes, parameter uncertainties and the effect of the penetrations resulting from renewable sources. Delayed time resulting from the communication process between the area and control center is considered in the dynamic model of interconnected MGs, and nonlinearities, such as governor dead bands (GDBs) and generation rate constraints (GRCs), are included in the simulation model. The simulation results demonstrate the effectiveness and success of the proposed controller tuned by the ESO approach with a balloon effect and provide better performance of frequency regulation than a fixed controller, as well as other methods such as standard Jaya and ESO methods.

Voltage source converter (VSC)-based high-voltage dc (HVDC) transmission is widely utilised nowadays. However, a VSC-HVDC connected to a weak ac system still faces the problem of phase-locked loop (PLL) synchronisation. To tackle this problem, this study proposes a dc voltage synchronisation control (DCSC) based on the power synchronisation control and the power balance equation of the virtual synchronous generator. To analyse the dynamic stability of DCSC, voltage sensitivity indicator (VSI) is used to reflect the voltage fluctuations. Considering the deviations of dc voltage and converter losses, a closed-loop transfer function of dc voltage is designed. Three important parameters including VSI, virtual damping coefficient and inertia time constant are investigated. The dynamic stability analysis shows DCSC has strong controllability. Then, a three terminals VSC-MTDC model is simulated in PSCAD/EMTDC. Herein, DCSC is used in one inverter and PLL is used in another inverter. The waveforms obtained by using DCSC are compared with that by using PLL. Simulation results clearly depict that the inverter with DCSC has a normal steady state and a better transient response than using PLL when connected to a strong ac system, also provides better power transfer capability when connected to a weak ac system.

This paper addresses the design of a two-dimensional guidance scheme in the vertical plane, using robust and gain-scheduling control methods, for a fin-stabilized canard-guided projectile. Given th...

We propose a multimodal PAM4/nonreturn to zero (NRZ) transceiver, including an adaptive ultra-wide range receiver and power noise-stabilized transmitter. The multimodal transmitter features a PAM4 emphasis driver and stabilizer, which are applied to reduce distortion impact and power-induced jitter. Installing an aggressor circuit allowed us to analyze the influence on the input buffer of the interface block and the influence on the whole system by varying the frequency and activation rate. The multi-modal receiver features a wide-range phase detector to optimize jitter tolerance at each speed while supporting both clock-forward and clock-embedded modes. Our proposed RX supports three selectable modes, each of which has a tradeoff between jitter tolerance and power. An adaptive clock data recovery (CDR) controller selects the optimum CDR mode according to transmitter jitter performance to reduce power consumption while ensuring interoperability. We also derived CDR power and the effect of latency accompanying it from an open loop transfer function. A test chip was fabricated using a 28-nm CMOS process that achieved 0.25–27-Gb/s wide-range operation and a 33% power reduction compared to conventional architecture without the adaptive controller, resulting in 3.8-pJ/bit energy efficiency for TX and 6.2-pJ/bit for RX.

As control precision for Earth-orbiting formations increases, the required ΔV can quickly become infeasible. Missions have demonstrated approximately 5 m/s/yr for 10-m control (TanDEM-X), but that...

PID controllers are the most common type of controllers used in industry. However, to find the best PID performance is a challenging task. Assessment of the best PID performance leads to the minimization of the deviation from set point as indicated by closed loop transfer function. This is a non-convex optimization problem and there is no direct solution for finding this benchmark. Solving this problem iteratively as proposed in literature requires long calculation times. Furthermore, iterative methods are not guaranteed to find the minimum value. Using as many as possible infinite impulse response coefficients, or increasing the number of finite impulse coefficients gradually, causes undesirably large calculation times. We propose a fast method to evaluate the minimum variance by a fixed number of finite impulse response coefficients. This finite impulse model is double the size of the stable system impulse response (it contains the transient response and the same duration of steady state). Thus it avoids undesired iteration, and consequently, the PID minimum variance is quickly evaluated. Time is a critical factor as the purpose to assess this index is for use in online monitoring. The proposed method is tested on benchmark simulation examples from literature.

Cuk and SEPIC are some of the important DC-DC converters used for charging batteries. In this paper, a generalized circuit averaging technique is employed for Cuk and SEPIC converters. The derived equations are used to obtain the frequency response of open loop transfer function. The ratio of perturbed output voltage to duty cycle (C vd ) is simulated using LTSpice software package. The derived averaged models of the converters aids in faster and simpler simulation. The behavior of the converters in CCM and DCM was also simulated. The derived expressions can be generalized to power converters with two switches.

In this paper we derive the control parameter gains required to guarantee a stable human-robot interaction (HRI). One goal in HRI research field is to reduce the robot mechanical impedance and enable humans to easily manipulate the robot. Force feedback is an effective way to reduce robot inertia and friction, but stability is paramount especially when interacting with humans. This paper discusses gains and stability boundaries. The phase response of the open loop transfer function that represents the human robot interaction is used to derive the gains. The environment is modeled as a second-order spring-mass-damper system. The stability boundaries correspond to the region when the phase response of the transfer function becomes greater than –180° at all frequencies. This enables the system to interact stably regardless of the environment second-order system parameters. One of the interesting results is that the virtual spring used to generate the impedance field has nothing to do with the stability condition. The experimental results show the validity of our method.

Physical systems are normally characterized by high uncertainty which makes it difficult for the closed loop system to have good stability margins and meet required performance specifications. Quantitative feedback theory (QFT) is a method of robust control which deals with the effects of uncertainty systematically. In the proposed work, QFT methodology is being adopted to design the autopilot for a launch vehicle with rigid body dynamics and flexibility dynamics. The conventional approach to QFT is to manually manipulate the poles and zeros of the nominal open loop transfer function. This is an adhoc approach as it greatly depends on the experience of the designer. To overcome this problem, an algorithm has been implemented that gives a set of feasible PID controllers. Based on the gain margin, phase margin, transient response and closed loop tracking specifications, the controller that closely satisfies the given performance specifications is selected. Further, a notch filter is also incorporated to complete the autopilot design.

The multi-rotor aircraft is more and more widely used. In this paper, the mathematical model of Transfer Function is established for the pitching channel model of multi-rotor aircraft. The Transfer Function of the system is an unstable function. Then PID controller is applied to the system to establish the Closed Loop Transfer Function of the system. The stability control of the system is realized by using Routh-Hurwitz criterion and selecting proper PID parameters. Finally, MATLAB is used for simulation.

Haptic support systems have been widely used for supporting human operators when performing a manual control task. These systems are commonly designed to track known target trajectories. However, the trajectory to track is not known in many realistic cases. For instance, the pilot-intended trajectory is not known beforehand when considering a helicopter pilot flying in free-flight. This paper proposes a possible approach to design a haptic shared control system when the target trajectory is not known a priori. Especially, the aim of the proposed design is to help minimally trained pilots during a 2-degree-of-freedom lateral/longitudinal helicopter free-flight task. To accomplish this goal, first, a Pilot Intent Estimator (PIE) is developed to infer pilot intent. Then, the corresponding intended trajectory is generated. Finally, a haptic feedback is designed to track the estimated intended trajectory. The designed PIE was evaluated in a preliminary test with an experienced helicopter pilot. Then, a human-in-the-loop experiment with minimally trained participants was conducted to assess the proposed shared control system. Results showed the effectiveness of the PIE to estimate the correct direction of motion chosen by the pilot. Furthermore, the haptic feedback helped participants to accomplish the control task with better task performance (i.e., lower tracking errors and lower amount of control activity) compared with manual control.

Phase-locked loop (PLL) is a circuit that can synchronize the output signal with the input signal in frequency and phase. Generally, it consists of three parts: Phase Detector (PD), Loop Filter (LF) and Voltage Controlled Oscillator (VCO). In modern technology, it is widely used in various fields, such as modulation and demodulation, frequency synthesis, power system, laser ranging, image processing and so on. According to the number of zero and pole in open loop transfer function, PLL can be divided into two types: TYPE I and TYPE II (Charge Pump). In TYPE I PLL, there is only one zero and pole produced by VCO. Therefore, when the loop is locked, there is always a phase error between input and output. However, in TYPE II phase-locked loop, not only does it contain a zero and a pole generated by VCO, but it also introduces a charge pump into the phase-locked loop and provides another pole for the whole loop together with a phase detector, thus making the phase error zero when the loop is locked. Charge Pump Phase-Locked Loop (CPPLL) has a large phase-locked range. Charge pump phase-locked loop (CPPLL) is widely used because of its large capture range and relatively simple structure. In this paper, the principle of charge pump phase locked loop (CPPLL) in phase laser ranging is analyzed, the linear model is built, and the performance of speed conversion is studied. The frequency-locked, phase-locked precision and conversion speed of the loop are analyzed, and the charge pump phase-locked loop circuit is designed. Experiments show that the circuit effectively prevents the charge sharing effect and improves the accuracy and speed of the system.

The island microgrid is composed of a large number of inverters and various types of power equipment, and the interaction between inverters with different control methods may cause system instability, which will cause the power equipment to malfunction. Therefore, effective methods for analyzing the stability of the microgrid system have become particularly important. Generally, impedance modeling methods are used to analyze the stability of power electronic converter systems. In this paper, the impedance models of a PQ-controlled inverter and droop-controlled inverter are established in d-q frame. In view of the difference of output characteristics between the two control methods, the island microgrid is equivalent to a double closed-loop system. The impedance model of the parallel system is derived and the open loop transfer function of the system is extracted. Based on the generalized Nyquist criterion (GNC), the stability of parallel system working in island microgrid mode is analyzed using this proposed impedance model. The simulation and experiment results are presented to verify the analysis.

This paper suggests a simple approach to design a proportional-integral-derivative (PID) controller for regulating the turbine speed of the oscillation water column (OWC) system. The objective of PID controller is to achieve the maximum wave energy extraction from OWC. The first prerequisite for PID controller development is to reduce and linearize the OWC plant because the plant dynamics are highly complicated and nonlinear in nature. The reduced OWC plant model is therefore developed and compared to the nonlinear OWC plant model. Afterwards, the linear OWC plant model is derived and the closed loop transfer function of the OWC plant with the PID control is obtained which is followed by the determination of the unknown PID variables by pole placement. Simulations are performed to create an open and closed loop response of the linear OWC plant model to verify the performance of the PID controller. The efficiency of the PID controller on a JONSWAP irregular wave model for a nonlinear OWC plant is also validated. Lastly, for regulated and unregulated OWC plants, essential parameters such as turbine flow coefficient and turbine output power are evaluated. The PID controller functions very well for the nonlinear OWC model as well.

Vibration is a problem for many mechanical systems. Although there are many sources of vibration, simply moving a flexible system will generally cause it to vibrate. One technique for limiting unde...

This paper presents an on-line chatter detection method in milling using drive motor current commands supplied by the CNC system in real-time. The methodology is described by using the spindle drive motor current command although it has been applied to the feed drives as well which is demonstrated in the results section. The transfer function of spindle velocity controller is constructed by reading the control law parameters and measuring the Frequency Response Function (FRF) of the system automatically using an external computer communicating with the CNC in real time. By subtracting the rigid body based FRF from the measured FRF of the velocity controller that includes the flexibilities, the structural modes of the spindle drive are identified. The closed loop transfer function between the cutting torque at the tool and corresponding noise free digital current commanded by the CNC is formed. The effects of structural dynamic modes of the spindle are compensated via a proposed observer. The bandwidth of the compensated FRF of the current command over cutting torque disturbance has been increased to 2.5 kHz with 10 kHz communication speed limit of the CNC with external PC. After removing the forced vibration components, the frequency and presence of chatter are detected from the Fourier Spectrum of the current commands supplied by CNC in real time. The proposed system is experimentally validated in milling tests.

Proton Exchange Membrane (PEM) fuel cell is one of the possible green solutions for energy generation. The response of the fuel cell system depends on the air and hydrogen feed, flow and heat/ water management. The main control task is to maintain the supply manifold pressure at the cathode side of PEMFC. In this article, an approximation of First Order plus Time Delay (FOPTD) model is obtained from the PEMFC dynamic model by process reaction curve method. The analysis of uncertainty for the FOPTD model was carried out. From the FOPTD model, a simple PID controller was designed and compared with other techniques like: ZN-PI, Skogestad – Internal Model Control (SIMC)-PI, Improved SIMC-PID and Smith Predictor. Also, MPC and decoupler design were implemented. The simulation results are obtained using MATLAB® which shows that the response of supply manifold pressure is well controlled. The gain and phase margins were found out from the Bode plots of open loop transfer function and closed loop transfer...

In this article, a performance assessment method that measures the performances of set point tracking as well as disturbance rejection characteristics of PID controllers designed for unstable processes is proposed. The lower bounds of integral absolute errors (IAEo) are derived from the desired closed loop transfer function subjected to set point changes which may be of step or ramp types. The performance index is developed by considering Direct Synthesis (DS) method for PID controller design. Based on the theoretical bound IAE0, a dimensionless index is elucidated as the ratio between IAE0 and the actual IAE obtained from closed loop response under step set point changes and load variable changes. Considering this IAE based index as the performance measure of PI/PID control loops, the effectiveness of the controller is evaluated and tested on different types of unstable first order or second order plus time delay processes. Simulation studies for both set-point changes and disturbance rejection on various numerical examples are performed to prove the validity of the suggested performance benchmark.