Phase-locked Loop Method Research Articles

Design and real-time implementation of a sliding mode observer utilizing voltage signal injection and PLL for sensorless control of IPMSMs

In this study, a sliding mode observer (SMO) based on high-frequency (HF) voltage signal injection and a phase-locked loop (PLL) is proposed for estimating the extended electromotive force (EEMF), rotor position, and rotor velocity of an interior permanent magnet synchronous machine (IPMSM).This approach addresses real-time estimation challenges associated with standard SMO and PLL at very low speeds and standstill. A reliable and accurate sensorless speed control system for IPMSM is then developed and implemented in real time using the proposed SMO and PLL, covering a wide range of speeds, including low-speed and standstill conditions. The SMO effectively estimates the EEMF, while the PLL extracts the rotor velocity and position based on these estimates. Compared to conventional SMO and PLL methods, real-time results from an 8-pole, 0.4 kW IPMSM demonstrate the superior efficiency of the proposed system.

Current-Oriented Phase-Locked Loop Method for Robust Control of Grid-Connected Converter in Extremely Weak Grid

Current-Oriented Phase-Locked Loop Method for Robust Control of Grid-Connected Converter in Extremely Weak Grid

DSP implementation and discretization of phase locked loop methods in presence of grid imperfections

DSP implementation and discretization of phase locked loop methods in presence of grid imperfections

Grid synchronization method based on three novel types of third-order generalized integrators

Phase-locked loop (PLL) is widely used to estimate synchronous information such as amplitude and phase angle of grid voltage. It plays a crucial role in distributed renewable energy grid-connected power generation. However, the presence of grid harmonics and DC offset voltage (DCOV) can affect the accurate extraction of the fundamental voltage component, leading to phase-locked deviation. This paper introduces three novel or improved third-order generalized integrators (TOGI) with DCOV rejecting function to address this issue. A unified dual third-order generalized integrator (DTOGI) structure is designed based on the three TOGI structures. This DTOGI structure is further combined with a moving average filter (MAF) to propose three innovative three-phase PLLs. Unlike other PLL filtering methods that inadequately consider DCOV, the proposed PLL methods not only reject DCOV but also eliminate the fundamental voltage negative sequence component (FVNSC) and each order harmonic component. They demonstrate strong robustness and excellent filtering performance even under abnormal grid conditions. Among the three methods, the DII-TOGI based PLL exhibits superior dynamic performance compared to the other two methods, it can improve dynamic characteristics by about 10 % compared to the other two methods. The effectiveness of the proposed methods is verified through extensive Matlab/Simulink simulations and experiments.

Fast hybrid islanding detection for DGs with inverters using maximum likelihood-based ROCOF and SFS

The present study introduces an unconventional and fast hybrid strategy for islanding detection in Distributed Generators (DGs) based on inverters. The active method utilized in this work is Sandia Frequency Shift (SFS), while the passive method is the Rate Of Change Of Frequency (ROCOF) Relay. The key contribution of this paper is the use of Maximum Likelihood to estimate the ROCOF as opposed to the conventional Phase-Locked-Loop (PLL) method. The objective of this paper is to improve the responsiveness of detection across various conditions by providing fast detection without compromising accuracy. Several simulation investigations, adhering to the anti-islanding test standards of IEEE 1547 and UL1741, have been carried out on a system integrated with the suggested hybrid method. These studies aim to showcase the high sensitivity and specificity of the proposed technique for detecting islanding. In addition, pertinent comparisons are made between the proposed technique and the PLL-based method. The simulation results illustrate that the proposed control system effectively complies with the DG islanding protection requirements. In Furthermore, compared to the PLL, the proposed technique mitigates the common drawbacks associated with other islanding detection techniques by reducing the Non-Detection Zone, enhancing the power quality of the system, and, most significantly, producing fast detection under different conditions. The proposed approach exhibits a response time nearly three times faster than the PLL method, while in less demanding conditions, it provides an instantaneous response.

A Rotor Position Detection Method for Permanent Magnet Synchronous Motors Based on Variable Gain Discrete Sliding Mode Observer

The purpose of this paper is to study the sensor-less rotor position estimation method for permanent magnet synchronous motors, and to achieve accurate estimation of rotor position in different conditions. Firstly, the traditional super-twisting observer algorithm is analyzed, and a new discrete variable gain sliding mode observer is designed to solve the buffeting problem in discrete systems, taking the reaction force as the disturbance signal. By estimating the back potential of the observer, the buffeting problem in the sliding mode algorithm can be effectively improved as shown by the simulation results. Then, to solve the problem of phase delay in rotor position estimation, an adaptive orthogonal phase-locked loop method is used to compensate the estimation error caused by the change in motor speed and increase the estimation accuracy of rotor position. The stability of the method can be proven by Lyapunov’s second method. Simulation experiments verify the accuracy of the proposed PMSM rotor position estimation method.

Control strategy for three-phase four-switch active power filter based on positive sequence extraction in stationary coordinate fundamental reference frame

Traditional three-phase four-switch active power filter often uses the method of phase-locked loop (PLL) and low-pass filter for harmonic detection, which seriously affects the detection accuracy. In order to improve the detection accuracy, a lock-free three-phase four-switch active power filter based on fundamental positive sequence extraction is proposed. The harmonic detection adopts the fundamental positive sequence extraction method, and the rotation coordinate axis transformation adopts the phase-locked loop (PLL) free method. Compared with the traditional three-phase four-switch active power filter, this method does not require a phase-locked loop and a low-pass filter, and does not need complex coordinate transformation[2].The control method is simpler. Finally, simulation results prove the effectiveness of the control method.

Simultaneous BPSK classical communication and continuous variable quantum key distribution with a locally local oscillator regenerated by optical injection phase locked loop

This paper proposes a scheme for simultaneous classical communication and continuous variable quantum key distribution with a true local oscillator. In this scheme, the emitter’s laser, after binary phase-shift keying (BPSK) modulation, is multiplexed in polarization with the quantum signal and sent to the receiver. After BPSK demodulation and correction, this signal is used for local oscillator regeneration by an optical injection phase-locked loop method. Comparing the effective noise sources in this scheme with typical local local oscillator schemes revealed that continuous variable quantum key distribution (CV-QKD) with a true local oscillator based on the optical injection phase-locked loop encounters lower levels of noise in comparison to the pre-existing genuine local oscillator CV-QKDs.

Research and implementation of debugging method of digital phase-locked loop

This paper studies the commissioning method of phase-locked loops to enable the phasemeters to achieve the required frequency and phase accuracy. The influence of different phasemeter structures on performance is explored. Through theoretical analysis and experiments, the debugging process of the phase-locked loop is clarified, which can meet its basic indexes, especially frequency and phase accuracy, and is optimized for its traditional structure.

Phase Demodulation Strategy Based on Kalman Filter for Sinusoidal Encoders

Phase demodulation strategy based on Kalman filter for sinusoidal encoders is proposed in this paper. For the state equation and observation equation in the constructed phase demodulation model, the phase angle, the phase angular speed, and the speed fluctuation are the system states, and the sine and cosine signals output by the encoder are the system observations. In addition, due to the nonlinear relationship between the observations and the system states, the observation function is linearized by the extended Kalman approach. In order to implement the Kalman filter on the hardware platform with a field programmable gate array (FPGA), the matrix model of the Kalman filter is further derived into an algebraic model, which only contains sine, cosine, and basic algebraic operations. Compared to the arctangent method, the proposed method has the noise suppression capability, and compared to the conventional phase-locked loop (PLL) method, the proposed method has the better dynamic performance without the acceleration-associated phase error. Both simulation and experimental results can prove the effectiveness of the proposed method.

Point of Common Coupling Voltage Modulated Direct Power Control of Grid-Tied Photovoltaic Inverter for AC Microgrid Application

A direct power control (DPC) approach is proposed in this study for a grid-tied photovoltaic (PV) voltage source inverter (VSI) to regulate active and reactive power flow directly in between utility grid and microgrid (MG) by controlling point of common coupling (PCC) voltage. The proposed PCC voltage modulated (PVM) theory-based DPC method (PVMT-DPC) is composed of nonlinear PVM, nonlinear damping, conventional feedforward, and feedback PI controllers. For grid synchronization rather than employing phase-locked-loop (PLL) technology, in this study, direct power calculation of the PCC voltage and current is adopted. Subsequently, at PCC, the computed real and reactive powers are compared with reference powers in order to generate the VSI’s control signals using sinusoidal pulse width modulation (SPWM). Because of the absence of the PLL and DPC method adoption, the suggested controller has a faster convergence rate compared to traditional VSI’s power controllers. Additionally, it displays nearly zero steady-state power oscillations, which assure that MG’s power quality is improved significantly. To validate the proposed PVMT-DPC method’s performance, real-time simulations are conducted via real-time digital simulator (RTDS) for a variety of cases. The obtained results demonstrate that using the proposed PVMT-DPC approach, PV VSI can track the reference power within 0.055 s where the output power has low steady-state oscillations and output current has lower total harmonic distortion (THD) of 1.68%.

Phase Measurement Method Based on Digital Dual Frequency Comb for High-Precision High-Speed Heterodyne Interferometry

The heterodyne interferometer is widely used as a precise displacement sensor in ultraprecision processing. However, there is a trade-off between measurement speed and measurement precision in the existing interference signal processing methods. In this work, a novel phase measurement method based on digital dual frequency comb is proposed. The proposed method uses the intrinsic frequency comb signal and a narrowband low-pass filter to form a band-pass filter bank, which divides the broadband brought by high-speed movement into multiple narrow bands. The signal-to-noise ratio (SNR) is improved for phase calculation. In addition, two groups of intrinsic frequency comb signals are used simultaneously for phase measurement and the rotation of the output, preventing the inaccurate phase measurement of the input signal whose frequency is the average of two frequencies in the frequency comb signal. The heterodyne laser interferometer can maintain high precision at high measurement speed. The simulation results show that the precision of the proposed method is more than 50% higher than that of the phase-locked loop method. The experiment with a circuit board combined with 100 Msps sampling 16-bit A/D converter shows that the phase measurement precision of the input signal frequency in the bandwidth range of 2.5–37.5 MHz can reach 0.77 mrad, equivalent to the displacement measurement precision of the double-pass interferometer (19 pm) at a measurement speed of less than 2.77 m/s.

A novel Phase-Lock-Loop algorithm for Three-Phase grid voltage Distortion-Connected electric vehicle chargers

A new phase-lock-loop (PLL) method is proposed to deal with the unusable angle for feeding into the current control in three-phase grid voltage distortion-connected electric vehicle (EV) charger systems. The development of the proposed PLL method is the modification by means of doubly cascading the PLL modules, called the double PLL (DPLL) method. The superiority of the proposed DPLL method is that it provides a more correct approach to the phase angle for the control system. This makes this system a good candidate for bidirectional power quality control with grid-to-vehicle and vehicle-to-grid modes and constant current, voltage, and power modes for charging batteries. With its third-order system, it is more attractive due to the ability to design a better cut-off frequency and better oscillator filtering performance. A mathematical transfer function of the proposed DPLL method is fully derived and compared with the existing PLL methods by numerically analyzing them in the theory of the bode plot schematic. To verify the feasibility of the proposed DPLL method, the simulation of the 12.5 kW-battery EV charger systems under the ideal and non-ideal grid voltage conditions with the two-level and multi-level converters is tested by comparing between the proposed and existing PLL methods.

An Improved PLL-Based Speed Estimation Method for Induction Motors through Harmonic Separation

The real-time speed estimation of induction motors (IMs) is important for the motors’ state monitoring and control. The utilization of rotor slot harmonics (RSHs) due to the inherent cogging effect is regarded as a promising way to realize the speed estimation of IMs. The key to the RSH-based speed estimation method is how to accurately and quickly identify the frequency of an RSH signal. However, as the RSH signal always consists of two side-frequency components that are adjacent to each other, it is actually improper to directly use the conventional phase-locked loop (PLL) method designed for single-frequency tracking. Furthermore, the form of the two side components in the frequency domain also leads to a significant amplitude fluctuation in the time-domain waveform of RSHs, thus resulting in the obvious frequency tracking errors of the conventional PLL method. In this paper, we proposed an improved PLL through harmonic separation to further improve the performance of the RSH-based speed estimation method of multiphase IMs, so that the dynamic tracking errors of PLL due to the reasons mentioned above can be significantly reduced. Simulations and experiments in a wide speed range were also performed, with their results presented as verifications of the proposed method.

Three-Phase PLL Based on Adaptive Clarke Transform Under Unbalanced Condition

This letter proposes a three-phase phase-locked loop (PLL) algorithm relying on an adaptive Clarke transform (CT) under amplitude and/or phase angle unbalanced condition. Analytical expressions for coefficients of matrix associated with the adaptive CT are derived and used to generate orthogonal signals. An auxiliary algorithm is also proposed to track the actual amplitudes and phase angle deviations. Unlike the conventional CT relying on constant coefficients, the adaptive CT can generate accurate orthogonal signals from the three-phase voltages including phase angle and/or amplitude imbalances. As a result, the proposed PLL is not affected by the unbalanced phase angles with/without amplitude imbalances. The advantages of the proposed adaptive CT-based PLL method is illustrated by both simulation and experimental results.

Sensorless DPCC of PMLSM Using SOGI-PLL-Based High-Order SMO With Cogging Force Feedforward Compensation

In order to reduce the adverse effect of the large thrust ripple of permanent magnet linear synchronous motor (PMLSM) on mover position estimation accuracy and solve the sliding mode chattering problem of the traditional sensorless algorithm based on sliding mode observer (SMO), this article proposes a systematic method to solve above issues. First, the high-order SMO method is used to suppress harmonic generation from the source of sliding mode chattering. Second, an adaptive filter based on a second-order generalized integrator (SOGI) is constructed to filter out the harmonics. Then, the normalized quadrature phase-locked loop (PLL) method is used to realize the closed-loop extraction of position information. Finally, the deadbeat predictive current control (DPCC) with the current feedforward compensation strategy is proposed to further improve the dynamic performance and mover position estimation accuracy. The simulation model and experimental platform are built. The simulation analyses and test results show that the proposed method has a better performance than conventional techniques.

Direct Power Control Based on Point of Common Coupling Voltage Modulation for Grid-Tied AC Microgrid PV Inverter

In this paper, a direct power control (DPC) approach is proposed for grid-tied AC MG’s photovoltaic (PV) voltage source inverter (VSI) to regulate directly active and reactive powers by modulating microgrid’s (MG) point of common coupling (PCC) voltage. The proposed PCC voltage modulated (PVM) theory-based DPC method (PVMT-DPC) is composed of nonlinear PVM, nonlinear damping, conventional feedforward and feedback PI controllers. For grid synchronization rather than employing phase-locked-loop (PLL) technology, in this study, direct power calculation of the PCC voltage and current is adopted. Subsequently, at PCC, the computed real and reactive powers are compared with reference powers in order to generate the VSI’s control signals using sinusoidal pulse width modulation (SPWM). Because of the absence of the PLL and DPC method adoption, the suggested controller has a faster convergence rate compared to traditional VSI’s power controllers. Additionally, it displays nearly zero steady-state power oscillations, which assures that MG’s power quality is improved significantly. To validate the proposed PVMT-DPC method’s performance real-time simulations are conducted via real-time digital simulator (RTDS) for a variety of cases. The results demonstrate that PV VSI using the suggested PVMT-DPC approach can track the reference power quicker (0.055 s) along with very low steady-state power oscillations, and lower total harmonic distortion (THD) of 1.697% at VSI output current.

A Novel Adaptive Bandpass Filter Based PLL for Grid Synchronization Under Distorted Grid Conditions

In the current scenario, the integration of a renewable energy sources (RESs) with variable power production into power grids requires a power converter with robust control techniques. In order to formulate the control strategy meticulously, a fast and accurate detection of grid phase angle is necessary. Hence, frequency and phase angle of the grid voltages are vital components to guarantee the synchronization for grid-connected converter. Additionally, a phase locked loop (PLL)-based control algorithm is needed to generate the accurate reference current for the grid-connected converter. The conventional adaptive low-pass filter (ALPF)-based PLL is used as a synchronization tool but requires more settling time during interharmonics and dc offset grid conditions in addition to higher THD of the grid currents/voltages. In this article, a novel adaptive bandpass filter (ABPF) is proposed and can be added as a prefilter of PLL structures without modifying the base design. To confirm the adaptive nature of the ABPF the gradient algorithm is used to maximize the normalized mean square output and self-adjust the center frequency of the filter during distorted grid conditions. The 3-D surface plot can be used to provide the system stability and dynamic response of the filter. For effectiveness of the proposed study, ABPF is added as prefilter to dq-frame cascaded delayed signal cancellation (dqCDSC) PLL and MAF PLL and detailed comparative study is made in this article. In addition to that, the proposed ABPF-based dqCDSC PLL and ABPF-based MAF PLL methods are analyzed using MATLAB/Simulink environment. Finally, performance is tested with real-time via dSPACE-1104 hardware-in-loop (HIL) simulation.

Control of grid side converter in wind power based PMSG with PLL method

Wind power is one of the most promising renewable energy sources. Due to a constantly increasing penetration rate in power grids in order to comply with interconnection requirements. This article targets the impact of a permanent magnet synchronous generator (PMSG) which is the subject of most attention due to low cost and maintenance requirements, driven by a wind turbine with the necessary power electronic converters that allow wind turbines to operate at variable speed, and connected to the grid for power generation more efficiently by the phase-locked loop (PLL) method in order to synchronize it. Thus, the proposed control technicals are based on vector control (VC) to achieve maximum power point tracking (MPPT), keep the DC link voltage constant, and control the speed and current at the generator side and grid side in PMSG which provides controllability of the reactive power supplied to the network. Therefore, the response of the PLL is analyzed and the simulation results of the dynamic model of the system is developed in Matlab / Simulink. The study results exhibit the excellent performance with high robustness, by improving the system efficiency to 98.72%.

An investigation on fronthaul and millimeter wave technologies for 5G

.The growing demand for communications and the emergence of new applications have put the capacity, transmission rate and latency of communications systems to a more severe test. In this context, 5G communication technology has emerged. 5G applications are divided into three typical application scenarios: eMBB, URLLC and mMTC. In order to support these applications, the key technologies of 5G need to be studied in depth. This paper firstly investigates the networking architecture of 5G bearer networks, and carries out a detailed analysis and comparison of 5G fronthaul technology, including the optical fibre direct connection solution, passive WDM solution, active WDM/OTN solution and WDM-PON solution. Secondly, this paper introduces 5G millimetre wave technology to achieve large capacity and high spectral efficiency transmission, including direct intensity modulation method, external modulation method, optical heterodyne method, optical injection locking method and optical phase-locked loop method. Finally, this paper provides an outlook on 5G fronthaul technology and millimetre wave technology.