Synchronous Frame Research Articles

Low-Complexity Model Predictive Power Control: Double-Vector-Based Approach

Conventional model predictive power control (MPPC) achieves good steady-state performance and quick dynamic response by minimizing a cost function relating to the power errors. However, applying single voltage vector during the whole control period fails to reduce the power ripples to a minimal value; particularly in the two-level converter with limited switching states. Recently, the concept of duty cycle control has been introduced in MPPC to achieve further power ripple reduction. Although better steady-state performance is obtained, a lot of calculations are needed when deciding the best voltage vector and its corresponding duration. This paper proposes a low-complexity MPPC with quick voltage selection and fast duty cycle calculation. Different from prior MPPC, the negative conjugate of complex power in synchronous frame is selected as the control variable. As a result, only one prediction is required to select the best voltage vector, and its duration is determined base on the principle of error minimization of both active and reactive power. Further study reveals that the proposed low-complexity MPPC is equivalent to the recently reported MPPC with duty cycle control. Simulation and experimental results obtained from a two-level three-phase ac/dc converter are presented to confirm the theoretical study and the effectiveness of the proposed method.

Low Complexity Model Predictive Control—Single Vector-Based Approach

Finite control set model predictive control (FCS-MPC) is emerging as a powerful control scheme in the control of power converters, because it takes the discrete nature of power converters into account and offers a flexible way to consider various constraints. However, conventional FCS-MPC requires to evaluate a cost function for each discrete switching states, which poses high computational burden. This paper proposes a low-complexity MPC (LC-MPC), which only requires one prediction to find the best voltage vector. The principle of LC-MPC is inherited from prior direct current control (DCC), but has been generalized by identifying its advantages, limitations, and potential application areas. Furthermore, the relationship between LC-MPC and FCS-MPC is studied and it is found that in some cases, the LC-MPC is completely equivalent to FCS-MPC. This paper presents the application example of LC-MPC in power control of three-phase ac/dc converter. To make it a success, the negative conjugate of complex power in synchronous frame is selected as the control variable. Detailed principle of vector selection is introduced and the reason for requiring only one prediction in the proposed LC-MPC is strictly proven using mathematical tools. The proposed LC-MPC is compared with conventional FCS-MPC and its effectiveness is verified by both simulation and experimental results from a two-level ac/dc converter.

A 240 × 180 130 dB 3 µs Latency Global Shutter Spatiotemporal Vision Sensor

Event-based dynamic vision sensors (DVSs) asynchronously report log intensity changes. Their high dynamic range, sub-ms latency and sparse output make them useful in applications such as robotics and real-time tracking. However they discard absolute intensity information which is useful for object recognition and classification. This paper presents a dynamic and active pixel vision sensor (DAVIS) which addresses this deficiency by outputting asynchronous DVS events and synchronous global shutter frames concurrently. The active pixel sensor (APS) circuits and the DVS circuits within a pixel share a single photodiode. Measurements from a 240×180 sensor array of 18.5 μm 2 pixels fabricated in a 0.18 μm 6M1P CMOS image sensor (CIS) technology show a dynamic range of 130 dB with 11% contrast detection threshold, minimum 3 μs latency, and 3.5% contrast matching for the DVS pathway; and a 51 dB dynamic range with 0.5% FPN for the APS readout.

Stationary Frame Equivalent Model of Proportional-Integral Controller in dq Synchronous Frame

This letter establishes the stationary frame equivalent model of proportional-integral (PI) controller in dq synchronous frame. Although both PI controller in dq synchronous frame and proportional-resonant (PR) controller in stationary frame achieve zero steady-state error when tracing fundamental frequency reference, their amplitude and phase characteristics differ greatly from each other except for fundamental frequency. Using stationary frame PR controller to replace PI controller in dq synchronous frame directly leads to analytical errors, especially in low frequency stage. Another straightforward analysis method is to use stationary frame PI controller to replace PI controller in dq synchronous frame, however the coupling terms in dq synchronous frame are ignored and the approximation is not accurate. The accurate stationary frame equivalent model of PI controller is established. For system controlled in dq synchronous frame, the established model can be used to precisely predict system performance and thus guides control parameters design process. Theoretical analysis is presented and validity of the model is evaluated by simulation.

Robust Tracking Control of a Three-Phase DC–AC Inverter for UPS Applications

This paper describes a combination of robust control techniques applied to an offset-free robust tracking control of a three-phase dc-ac inverter with an output LC filter for application to uninterruptible power supply (UPS). The control law, which employs state feedback and integration of the tracking error, is described in a synchronous dq frame and is implemented using a space vector modulation technique. The controller is designed by a linear matrix inequality (LMI)-based optimization so that the convergence rate to the steady state is maximized in the presence of the uncertainties in the LC filter. These uncertainties are expressed as possible ranges of the capacitor and inductor values. In the absence of uncertainties, the designed controller will become a deadbeat controller, whereas in the presence of uncertainties, it provides the shortest possible settling time. Thus, the proposed design method provides a systematic tool to combine the robustness to model uncertainties with the deadbeat control. The use of a one-step-ahead predictor is considered to compensate for the computation delay, and an LMI-based method to obtain an optimal gain of the state estimator is also proposed. The efficacy of the proposed approach was experimentally confirmed on a three-phase 10-kVA prototype UPS system.

Improvement of Stable Operation Ability for Large-Scale Wind Power System Based on VSC-HVDC Technology

Rigorous transmission technology is important when large-scale wind farm is connected to the power grid. Hence, a power transmission topological framework based on VSC-HVDC is proposed. The mathematical model is built in the dq synchronous frame, and the related direct current control strategy of VSC converters are designed. The doubly fed induction generator wind farm with VSC-HVDC system are modelled in DIgSILENT/PowerFactory. Ultimately, the conditions of the short-circuit fault at the receiving-end VSC AC bus is simulated. The control scheme is proved to be effective.

Voltage Compensation with Interline Power Flow Controller (IPFC) Using Control Magnitude and Phase Angle Control

The Interline Power Flow Controller (IPFC) is a voltage-source-converter (VSC)-based flexible ac transmission system (FACTS) controller for series compensation in a multiline transmission system of a substation. The capability of injecting series voltages with controllable magnitude and phase angle makes it a powerful tool for better utilization of existing transmission lines in a multiline transmission system. IPFC is used to regulate active and reactive power flow in a multiline system, usually. In this paper, a control method for IPFC is proposed to control magnitude and phase angle of one sending bus of a substation. All degrees of freedom of IPFC and decoupled synchronous frame concept are used in the proposed control structure. Simulation results in Matlab/Simulink are presented to show the capability of IPFC in compensating the bus voltage.

Sensorless Vector Control of Five-phase Induction Motor under Open-phases Fault

—This article deals with proposed solutions for five-phase induction motor drives, specifically aimed to sensorless vector control under an open-phases fault. Exploiting the modified transformation matrices for dual planes, the motor model in the synchronous frame is established under open phases. Torque ripple is reduced by particular magnitude ratio currents. Furthermore, the third harmonic current is used to improve iron utilization and torque density. The proposed sliding-mode observer method for wide-range speed estimation combined with online resistance identification is investigated, especially for low-speed operation. Experimental tests are performed to validate the effectiveness of the proposed method.

Optimised parameter design of proportional integral and resonant current regulator for doubly fed induction generator during grid voltage distortion

The study presents an optimised parameter design of the proportional integral and resonant (PIR) current regulator for doubly fed induction generator (DFIG) under distorted grid voltage conditions. Based on the mathematical model of DFIG under distorted grid voltage conditions, practical PIR current regulator under synchronous frame is developed to implement the harmonic control target of sinusoidal stator current. The optimised parameter design of PIR regulator is investigated concerning the control system gain margin and phase margin, as well as variation of the resonant bandwidth. The influence of DFIG parameters and grid frequency deviation on PIR design is also discussed. Correctness of the optimised parameter design technique of PIR regulator is validated by the MATLAB simulation and experiment results.

One-Dimensional Optimization for Proportional–Resonant Controller Design Against the Change in Source Impedance and Solar Irradiation in PV Systems

The variation in source impedance and solar irradiation effects on photovoltaic (PV) system control performance is investigated. A proportional-resonant (PR) controller in a stationary frame in place of a proportional-integral controller in a synchronous frame was adopted to modulate a single-phase grid-tied inverter for PV systems. Although the PR controllers have gained some momentum lately due to advantages such as instantaneous tracking capability and low-cost computational resources, the tracking performance may decline due to changes in source impedance and solar irradiation where the conventional PR design rule is void. To adapt PR controllers over diverse operating conditions without incurring excessive tracking error, a one-dimensional optimization (ODO) algorithm that dictates the quality of the tracking performance is proposed to search for an appropriate factor χ between the real part of dominant and nondominant eigenvalues for the PV systems. The control gains of the PR controller can be then altered in light of the optimal χ through a simple algebraic conversion. The experimental results confirm the performance of the proposed strategy.

Design and analysis of operating strategies for a generalised voltage‐source power supply based on internal model principle

This study presents a generalised voltage-source power supply to generate arbitrary shapes of voltage waveforms. The proposed voltage-source power supply can not only generate sinusoidal fundamental voltage waveforms, but also produce desired harmonic and asymmetrical voltage waveforms for applications of series active power filter, dynamic voltage regulator, uninterrupted power supply and programmable AC power source. The purpose of this study is to propose a novel operating strategy under synchronous coordinate frame based on internal model principle controllers, in such a way that it can provide more accurate tracking ability for generalised voltage references. Besides, the features of fast dynamic response, high stability and easy implementation are offered. The detailed design and analysis for the proposed strategy are given. An improved virtual resistor method is proposed to further improve the performance of the generalised voltage-source power supply. Both simulated and experimental results are given to verify the validity of the proposed approaches.

A hybrid current controller for dual three‐phase permanent magnet synchronous motors

AbstractControl of the current harmonics is a critical issue for dual three‐phase (DTP) permanent magnet synchronous motors (PMSMs). Considering the limitations of conventional synchronous frame proportional‐integral (PI) current regulator, this paper presents a hybrid current controller that combines the PI current regulator with a multiresonant controller. With the proposed hybrid current controller, precise current control can be achieved with only a slight increase in the computational effort. Theoretical analysis and experimental results confirm the effectiveness of proposed current controller. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Development of Digital Control for High Power Permanent-Magnet Synchronous Motor Drives

This paper is concerned with the development of digital control system for high power permanent-magnet synchronous motor (PMSM) to yield good speed regulation, low current harmonic, and stable output speed. The design of controller is conducted by digitizing the mathematical model of PMSM using impulse invariance technique. The predicted current estimator, which is insensitive to motor feedback currents, is proposed to function under stationary frame for harmonic current suppression. In the AC/DC power converter, mathematical model anddc-link voltage limit of the three-phase switch-mode rectifier are derived. In addition, a current controller under synchronous frame is introduced to reduce the current harmonics and increase the power factor on the input side. A digital control system for 75 kW PMSM is realized with digital signal processor (R5F5630EDDFP). Experimental results indicate that the total harmonic distortion of current is reduced from 4.1% to 2.8% for 50 kW output power by the proposed predicted current estimator technique.

On Universal Mechanics and Superluminal Velocities

In this work we continue to set up the theory of universal space and time and derive the Euclidean form of the scaling transformations. Two types of velocities emerge, inertial and universal, with the former bound by the light velocity c whereas the latter is unbound, and may accommodate consistently particles’ velocities possibly exceeding c. The inertial velocity is the ratio of the simultaneous source’s displacement and the corresponding length of the light trip to the observer, whereas the universal velocity has its familiar meaning for motion in a synchronous inertial frame. Defining the momentum as the product of universal velocity and mass, and utilizing the already established mass-energy equivalence, the mechanics constructed on the bases of the new concepts, named universal mechanics, admits superluminal velocities but yet coincides with the relativistic mechanics in its basic dynamical components and their inter-relations. The possibility of superluminal velocities provides a straight forward explanation of the presence of the μ-meson particles abundantly at the sea level despite their generation at high altitude and their short lifetime.

Complex state variable‐ and disturbance observer‐based current controllers for AC drives: an experimental comparison

In vector-controlled AC drives, the design of current controller is usually based on a machine model defined in synchronous frame coordinate, where the drive performance may be degraded by both the variation of the machine parameters and the cross-coupling between the d- and q-axes components of the stator current. In order to improve the current control performance an alternative current control strategy was proposed previously aiming to avoid the undesired cross- coupling and non-linearities between the state variables. These effects are assumed as disturbances arisen in the closed-loop path, extracted by a disturbance observer and then injected into the current controller. In this study, a revised version of a disturbance observer-based controller and a well known complex variable model-based design with a single set of complex pole are compared in terms of design aspects and performance evaluation by simulation and by experiment for two different sampling rates. Several comparative results that verify the promising performance of the proposed control scheme are presented. The advantages of the proposed controller are an easy implementation and offering a unique solution for the variation of the parameter and the cross-coupling effect. Moreover, it provides a better performance, smooth and low noisy operation with respect to the complex variable controller.

Current Control Strategy for Grid Connected Photovoltaic Inverter via LCL Filter

This paper presents a method to design a control system for grid connected photovoltaic inverter which has an LCL type filter to suppress the output current total harmonic distortion (THD). In this control system, three linear voltage and current controllers were used in a cascade configuration in order to reduce the complexity of the system. Those controllers regulate the current injected to the grid in a synchronous reference frame which transforms ac variables into dc quantities and thus possibility of applying simple PI regulators. Simulation results, using Matlab/simulink, presented for this strategy confirm the effectiveness of the control scheme in both transient and steady state operation.

Feedback Linearization Control of a Shunt Active Power Filter Using a Fuzzy Controller

In this paper, a novel feedback linearization based sliding mode controlled parallel active power filter using a fuzzy controller is presented in a three-phase three-wire grid. A feedback linearization control with fuzzy parameter self-tuning is used to implement the DC side voltage regulation while a novel integral sliding mode controller is applied to reduce the total harmonic distortion of the supply current. Since traditional unit synchronous sinusoidal signal calculation methods are not applicable when the supply voltage contains harmonics, a novel unit synchronous sinusoidal signal computing method based on synchronous frame transforming theory is presented to overcome this disadvantage. The simulation results verify that the DC side voltage is very stable for the given value and responds quickly to the external disturbance. A comparison is also made to show the advantages of the novel unit sinusoidal signal calculating method and the super harmonic treatment property of the designed active power filter.

Enhanced fault ride through performance of self‐excited induction generator‐based wind park during unbalanced grid operation

This study presents novel control design for improving the performance of large-scale wind park (LSWP) based on self-excited induction generator under unbalanced voltage conditions. A dual controller for static synchronous compensator (STATCOM) employing controller by employing positive- and negative-sequence synchronous frames is implemented and analysed in response to severely unbalanced voltage conditions. The test system simulated represents a wind park rated at 100 MW connected to a weak electrical grid. The potential of the dual STATCOM controller is evaluated and analysed for severely unbalanced voltage conditions at the grid interface of LSWP. The dual controller with STATCOM overloading capability is tested and compared with the performance of the positive-sequence controller in response to different types of asymmetrical grid faults at low short-circuit ratios. The simulations performed using PSCAD/EMTDC demonstrate superior performance of dual STATCOM control strategy for improving unbalanced operation, fault ride through capability and transient stability margin in response to severely unbalanced voltage conditions.

Performance Evaluation of R-UPQC and L-UPQC Based on a Novel Voltage Imperfections Detection Algorithm

This paper proposes a new method to detect voltage imperfections, such as balanced/unbalanced voltage sag/swell, voltage flicker and voltage disturbance in both single and three-phase electrical distribution systems with excellent performance characteristics. The proposed method is based on the single-phase synchronous d-q reference frame transformation (SPSRF). In contrast to the previous detection methods which need a measurement of the three-phase voltage for sag detection and fails to detect the voltage sag lower than a definite depth, the proposed method employs the series compensator of the unified power quality conditioner (UPQC) to inject a compensation voltage in-phase/out of phase with the source current during voltage sag/swell. The performance of the two structures of the UPQC, the right-shunt UPQC (R-UPQC) and the left-shunt UPQC (L-UPQC,) were tested under different operating conditions based on the proposed controller to improve the power quality of the single feeder distribution system. The simulation analysis and compensation performance of both UPQC topologies was implemented on a PSCAD/EMTDC platform

Improving Low Voltage Ride Through of Wind Generators Using STATCOM Under Symmetric and Asymmetric Fault Conditions

The increasing wind power integration with power system has forced the situation to revise the grid codes to improve the reliability of the system. One important problem with wind generator is the poor low voltage ride through capability. The proposed scheme is to use STATCOM which provides the wind generator the ability to remain connected in the grid during the disturbances and also provide reactive power support demanded by the power grid. The voltage dips due to symmetrical and asymmetrical faults are considered for analysis. The synchronous reference frame based control scheme is employed for fault compensation which uses software phase locked loop scheme and park dq0 transformation technique. Extensive simulation results are included to illustrate the control and operation of STATCOM.