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Based on the closed‐loop frequency domain model of permanent magnet synchronous generator–based wind power generation system (PMSG‐WPGS), the stability domain of the control parameters is constructed through the D‐partition method in this paper to acquire the range of machine‐side converter (MSC) and grid‐side converter (GSC) parameters. First, the basic stability domain of the controller parameters is established according to the control structure and transfer function of the back‐to‐back converter. Then, based on the frequency domain performance indexes, amplitude margin and phase angle margin, the obtained basic stability domain is adjusted to further gain the control parameter values that meet the frequency domain index. Furthermore, the rationality of the stability domain range is verified by drawing root locus curves of variable controller parameters on the machine side and grid side. Finally, the low‐power scale experimental platform of PMSG‐WPGS is built in the lab to validate the feasibility of the proposed stability domain construction method. [ABSTRACT FROM AUTHOR]

In the field oriented control (FOC) permanent magnet synchronous motor (PMSM) servo system, torque ripple impairs motor performance. Harmonic injection methods can suppress torque ripple by injecting additional voltage harmonic to offset the existing speed harmonic. However, since FOC is a closed-loop motion control strategy, the transfer path from injected voltage harmonic to speed harmonic is affected by FOC, especially in very low frequency. Due to the influence of FOC on the transfer function, the relation between the injected voltage harmonic and speed harmonic varies with operating conditions and motor control parameters. It causes the existing harmonic injection methods ineffective to suppress low order speed harmonics. To solve the problem, in this paper, the closed-loop transfer mechanism of injected voltage harmonics is analyzed and the closed-loop transfer function is derived. Based on the derived closed-loop transfer function, a low order speed harmonic suppression method is proposed. With the derived transfer function, the proposed method can adapt to the variations of the relation between low order injected voltage harmonic and speed harmonic under different operation conditions. Finally, the accuracy of the derived closed-loop transfer function and the effectiveness of the proposed low order speed harmonic suppression method are evaluated by experiment. [ABSTRACT FROM AUTHOR]

This article presents an iterative frequency lock loop (FLL)-assisted-phase lock loop (PLL) (FPLL) design in state space according to the minimum mean square error criterion. This is achieved by constructing a high fidelity carrier signal model with the consideration of the non-Gaussian nonwhite measurement noise characteristics. Two popular arctangent discriminators, e.g., two-quadrant (Atan) and four-quadrant (Atan2) are used to produce the PLL and FLL measurements for FPLL, respectively. The filter gain is selected to minimize the trace of the error covariance matrix and an iteration approach to quickly compute the steady-state filter gain is introduced. The nonlinearity in the discriminator and filter behaviors in FPLL at low $C/N_0$ and high dynamic conditions are investigated. The closed-form expressions of the closed-loop transfer function as well as error transfer function are clarified. The thermal noise induced tracking jitters on each carrier state, e.g., phase, doppler, and doppler rate, are derived, analyzed, and verified via Monte Carlo simulation, accordingly. The theoretical properties show that the iterative FPLL achieves the following. 1) The comparable tracking performance to the well-designed PLL-only. 2) The enhanced tracking accuracy over the well-designed FLL-only. 3) The improved tracking sensitivity over the conventional Kalman filter-based FPLL (KF-FPLL), at low $C/N_0$ condition and high dynamic conditions. [ABSTRACT FROM AUTHOR]

The current, torque, and speed harmonics caused by deadtime effect in voltage source inverter (VSI)-fed permanent magnet synchronous motor (PMSM) usually lead to undesired torque ripple and extra electrical loss, etc. In this article, a mathematical model is proposed to predict the deadtime-related harmonics in VSI-fed field-oriented control PMSM, and a deadtime-related harmonic minimization method is proposed based on proportional-integral (PI) controllers tuning and under the premise of keeping the same control strategy. The expressions of current, torque, and speed harmonics caused by deadtime effects are obtained based on the complex amplitude expression of the voltage error harmonic and the derivation of the closed-loop transfer function from the deadtime-related voltage error to the d–q axis current. Based on the derived expressions, optimization objective functions are built to search the optimal PI parameters for minimizing deadtime-related harmonics and reducing the torque ripple. The optimization constraint functions can be adjusted for transient performance requirements, so the transient performance can keep good even if the deadtime-related harmonics are minimized with the optimal PI parameters. Both simulation analysis and experimental data verify the correctness of the analytical prediction and the validity of the deadtime-related harmonic minimization method. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In this study, the problem of controlling integrating and unstable systems with long time delay is analysed in the discrete‐time domain for digital implementation. Based on a generalised predictor‐based control structure, where the plant time delay can be taken out of the control loop for the nominal plant, an analytical controller design is proposed in terms of the delay‐free part of the nominal plant model. Correspondingly, further improved control performance is obtained compared with recently developed predictor‐based control methods relying on numerical computation for controller parameterisation. The load disturbance rejection controller is derived by proposing the desired closed‐loop transfer function, and another one for set‐point tracking is designed in terms of the H2 optimal control performance specification. Both controllers can be tuned relatively independently in a monotonic manner, with a single adjustable parameter in each controller. By establishing the sufficient and necessary condition for holding robust stability of the closed‐loop control system, tuning constraints are derived together with numerical tuning guidelines for the disturbance rejection controller. Illustrative examples taken from the literature along with temperature control tests for a crystallisation reactor are used to demonstrate the effectiveness and merit of the proposed method. [ABSTRACT FROM AUTHOR]

When a classical digital controller is applied to parallel inverters, there is a tradeoff with respect to the stability, dynamic response, and control accuracy. In a practical design, the stability of the system should be considered first. To ensure sufficient margin in stability in a digitally controlled system, the proportional gains in the feedback path are limited. To solve these problems, a linear voltage-control scheme with duty-ratio feedforward is proposed. The control parameters are chosen according to the stable operating condition derived in the z-domain. In this paper, the closed-loop transfer function and output impedance for both the classical controller and the proposed controller are derived theoretically. A comparison reveals the advantages of the proposed control scheme, i.e., a unity closed-loop gain, no phase shift, good current sharing, and low total harmonic distortion of the output voltage. The theoretical results are verified by the experimental setup of a system with two digitally controlled inverters connected in parallel. [ABSTRACT FROM AUTHOR]

This paper presents a method to determine the denominator and numerator polynomials of a closed-loop transfer function in order to obtain desired transient and steady-state responses in terms of the overshoot, speed (time needed for the relative error to become less than a specific amount) and the steady-state error when the desired output is a ramp signal. Meanwhile, a controller is designed with the same characteristic equation for the closed-loop system to eliminate step and ramp disturbances. [ABSTRACT FROM AUTHOR]

In this paper the uncertainty of a robust photometer circuit (RPC) was estimated. Here, the RPC was considered as a measurement system, having input quantities that were inexactly known, and output quantities that consequently were also inexactly known. Input quantities represent information obtained from calibration certificates, specifications of manufacturers, and tabulated data. Output quantities describe the transfer function of the electrical part of the photodiode. Input quantities were the electronic components of the RPC, the parameters of the model of the photodiode and its sensitivity at 670 nm. The output quantities were the coefficients of both numerator and denominator of the closed-loop transfer function of the RPC. As an example, the gain and phase shift of the RPC versus frequency was evaluated from the transfer function, with their uncertainties and correlation coefficient. Results confirm the robustness of photodiode design. [ABSTRACT FROM AUTHOR]