Mark Sumner

Evaluation of three-phase transformerless photovoltaic inverter topologies

This paper analyzes and compares three transformerless photovoltaic inverter topologies for three-phase grid connection with the main focus on the safety issues that result from the lack of galvanic isolation. A common-mode model, valid at frequencies lower than 50 kHz, is adopted to study the leakage current paths. The model is validated by both simulation and experimental results. These will be used to compare the selected topologies, and to explain the influence of system unbalance and the neutral conductor inductance on the leakage current. It will be demonstrated that the later has a crucial influence. Finally, a comparison of the selected topologies is carried out, based on the adopted modulation, connection of the neutral and its inductance, effects of unbalance conditions, component ratings, output voltage levels, and filter size.

A Fast Adaptive Memetic Algorithm for Online and Offline Control Design of PMSM Drives

A fast adaptive memetic algorithm (FAMA) is proposed which is used to design the optimal control system for a permanent-magnet synchronous motor. The FAMA is a memetic algorithm with a dynamic parameter setting and two local searchers adaptively launched, either one by one or simultaneously, according to the necessities of the evolution. The FAMA has been tested for both offline and online optimization. The former is based on a simulation of the whole system-control system and plant-using a model obtained through identification tests. The online optimization is model free because each fitness evaluation consists of an experimental test on the real motor drive. The proposed algorithm has been compared with other optimization approaches, and a matching analysis has been carried out offline and online. Excellent results are obtained in terms of optimality, convergence, and algorithmic efficiency. Moreover, the FAMA has given very robust results in the presence of noise in the experimental system

Hybrid rotor position observer for wide speed-range sensorless PM motor drives including zero speed

This paper addresses the problem of wide speed-range sensorless control of a surface-mount permanent-magnet (SMPM) machine including zero-speed operation. A hybrid structure integrating a flux observer and signal-injection techniques is proposed, which results in a rotor position signal independent of motor parameters at low and zero speed. Although the SMPM machine typically has a very low geometric saliency, the injection technique is effective in tracking the saturation-induced saliency produced by the stator flux. Experimental results are presented showing an excellent performance for both the sensorless speed and position control using an off-the-shelf SMPM machine.

Comparative analysis of experimental performance and stability of sensorless induction motor drives

This paper compares the experimental performance of three flux and speed observers for speed-sensorless induction motor drives and discusses the cause of their differences. The small signal analysis using the linearized model is carried out to analyze stability. Three methods are generally accepted to be representative candidates for high sensorless performance, namely: 1) rotor-flux model reference adaptive system (MRAS); 2) torque-current MRAS; and 3) adaptive nonlinear flux observer. Many other sensorless methods improved these methods. The paper discusses baseline conditions for the experiments and the stability analysis, which include matched load inertia, specified speed estimator dynamics, and sensorless operation within a speed control loop. For the comparison tests in the paper, the speed estimation dynamics of the methods are the same; this is important for parameter sensitivity. The paper concentrates on the low-speed performance, and all results shown are under sensorless speed control.

Real-Time Estimation of Fundamental Frequency and Harmonics for Active Shunt Power Filters in Aircraft Electrical Systems

A novel algorithm for fundamental frequency and harmonic components detection is presented in this paper. The technique is based on a real-time implementation of discrete Fourier transform, and it allows fast and accurate estimation of fundamental frequency and harmonics of a distorted signal with variable fundamental frequency. It is suitable for active shunt filter applications, when fast and accurate tracking of the reference signal is required to achieve a good control performance. The main application for the algorithm is aircraft ac power systems, where the fundamental frequency can be either fixed on 400 Hz and its actual value fluctuates around the nominal value, or variable in the range 360-900 Hz. Hence, a real-time estimation of fundamental frequency is essential for active filter control. The proposed algorithm has been at first implemented in Matlab/Simulink for computer simulation, and it has been compared with a Phase Locked Loop (PLL) algorithm for frequency detection and the synchronous dq reference method for harmonic detection. Experimental tests have been carried out in order to validate the simulation results. The distorted current absorbed by a nonlinear load is analyzed and processed by means of a digital implementation of the algorithm running on the active shunt power filter control DSP, in order to calculate the active filter compensating current.

Suppression of saturation saliency effects for the sensorless position control of induction motor drives under loaded conditions

This paper presents an automated commissioning procedure used for the elimination of the saturation saliency effects in the sensorless position control of field-orientated cage induction motor drives. The position control itself is based on extracting a rotor position estimate from a high-frequency signal injection interacting with natural or engineered rotor position saliencies within the machine. The paper shows that this estimate cannot be robustly or accurately obtained if saturation saliencies are present. The paper introduces a method for suppressing the effects of the saturation saliency through information gained in a prior commissioning procedure. The effectiveness of the procedure is demonstrated through experimental results showing both good suppression of the saturation harmonics and true sensorless position control under high load torques.

A technique for power supply harmonic impedance estimation using a controlled voltage disturbance

A method for power system impedance estimation is presented. The method employs a power converter to inject a voltage transient onto the supply system. As the technique employs controlled power electronic devices it may be used as a stand alone piece of a portable measurement equipment, or it may be embedded into the functions of an active shunt filter for improved harmonic control. The impedance is estimated through correlation of the measured voltage and current transients. Simulations and experimental results demonstrate the measurement technique is highly accurate and effective.

Analysis and suppression of high-frequency inverter modulation in sensorless position-controlled induction machine drives

This paper focuses on the modulation of high-frequency (HF) currents required for sensorless position control of induction machine drives. Such drives can be realized by using the modulating effect of the rotor slots or from an engineered rotor saliency. Distortion due to saturation is known to cause a deterioration in the rotor position estimate. This paper reports a hitherto unreported distortion arising from inverter deadtime that will affect all sensorless drives using HF injection techniques. The deadtime distortion behaves in a similar way to that of saturation but has some specific characteristics that are presented in this work. Standard deadtime compensation techniques reduce but do not eliminate the distorting modulation. The residual distortion should be suppressed for good position estimation. The paper presents a new compensation strategy termed space modulation profiling which is effective in suppressing the HF modulations due to inverter deadtime and saturation saliencies. Experimental results show the sensorless drive under heavy load for zero-speed and transient operation.

Sensorless Position and Speed Control of Induction Motors Using High-Frequency Injection and Without Offline Precommissioning

This paper addresses the sensorless speed and position control of induction motors using high-frequency injection at zero and low frequencies. A novel algorithm is presented which allows the rejection of saturation and nonlinear inverter effects without the need for an offline precommissioning process. The method is based on a set of synchronous filters to identify the disturbance waveforms and a memory algorithm that refines the quality of the disturbance waveforms as the motors operational history is increased. The algorithm is entirely sensorless. Experimental results show sensorless low-frequency operation with and without the memory algorithm.

Performance of HF signal injection techniques for zero-low-frequency vector control of induction Machines under sensorless conditions

A number of HF signal injection techniques have been proposed for the sensorless zero-low-frequency control of induction machines (IMs). This paper reviews these methods and experimentally investigates their performance under true sensorless conditions for a standard cage IM with closed rotor slots. Implementation techniques covering hybrid methods, saliency decoupling, and saliency orientation are discussed. The paper concludes that, while HF techniques can outperform observer-based methods at low frequencies, the robust performance required for industrial application still presents a research challenge.