A new deadbeat type of direct torque control is proposed, analyzed and experimentally verified in this paper. The control is based on stator and rotor flux as state variables. This choice of state variables allows a graphical representation which is transparent and insightful. The graphical solution shows the effects of realistic considerations such as voltage and current limits. A position and speed sensorless implementation of the control, based on the self-sensing signal injection technique, is also demonstrated experimentally for low speed operation. The paper first develops the new, deadbeat DTC methodology and graphical representation of the new algorithm. It then evaluates feasibility via simulation and experimentally demonstrates performance of the new method with a laboratory prototype including the sensorless methods.

Stator and Rotor Flux Based Deadbeat Direct Torque Control of Induction Machines. Revision 1

With wide application of inverters in modern industry, common-mode voltage (CMV) problems invoked severe negative effects. Hardware and software solutions have been proposed to reduce the CMV. Compared with hardware CMV mitigation solutions, software strategies based on pulse-width modulation (PWM) modifications have aroused widespread attention for their cost-effective and control flexible advantages. Up to date, various reduced CMV PWM (RCMV-PWM) strategies have been reported, such as active zero state PWM, remote state PWM, near state PWM, phase-shifted carrier PWM, carrier peak position modulation and so on. For convenience of understanding and utilising the existed RCMV-PWM strategies, this study conducts a review on this topic. According to the principle of CMV reduction algorithms, the study divides the reported RCMV-PWM strategies into three different categories. It also presents comparisons of CMV reduction techniques and output performances (like CMV value, output ripple and linearity range) between different strategies. Meanwhile, CMV suppression principles, problems in implementation and improvements of each technique are described in detail. Moreover, the inherent characteristics and development tendencies of the RCMV-PWM techniques are discussed so as to offer reference for further research.

https://ietresearch.onlinelibrary.wiley.com/doi/epdf/10.1049/iet-pel.2015.1019

Review on pulse-width modulation strategies for common-mode voltage reduction in three-phase voltage-source inverters

This paper presents a single-phase grid connected inverter with a power decoupling circuit. In the single-phase grid connected inverter, it is well known that a power pulsation with twice the grid frequency is contained in the input power. In a conventional inverter, electrolytic capacitors with large capacitance have been used in order to smooth the DC voltage. However, lifetime of those capacitors is shortened by the power pulsation with twice grid frequency. The authors have been studied a active power decoupling method that reduce the pulsating power on the input DC bus line, this enables to transfer the ripple energy appeared on the input DC capacitors into the energy in a small film capacitor on the additional circuit. Hence, extension of the lifetime of the inverter can be expected because the small film capacitor substitutes for the large electrolytic capacitors. Finally, simulation and experimental results are discussed.

A Single-Phase Grid-Connected Inverter with a Power Decoupling Function

This paper presents a single-phase grid connected inverter with a power decoupling circuit. In the single-phase grid connected inverter, it is well known that a power pulsation with twice the grid frequency is contained in the input power. In a conventional inverter, electrolytic capacitors with large capacitance have been used in order to smooth the DC voltage. However, lifetime of those capacitors is shortened by the power pulsation with twice grid frequency. The authors have been studied a active power decoupling (APD) method that reduce the pulsating power on the input DC bus line, this enables to transfer the ripple energy appeared on the input DC capacitors into the energy in a small film capacitor on the additional circuit. Hence, extension of the lifetime of the inverter can be expected because the small film capacitor substitutes for the large electrolytic capacitors. Effectiveness of the proposed method is confirmed through simulation and experimental results.

A single-phase grid-connected inverter with power decoupling function

This paper presents a novel system for producing the optimum power output from photovoltaic (PV) arrays using dynamic cell reconfiguration. The proposed approach is the first in the literature that creates strings using individual substrings that have been characterized and categorized ensuring maximum power extraction for a given irradiance profile. This optimized and decentralized PV architecture can produce significantly more power than a static equivalent (by an average of 22.6%) and also outperforms the sophisticated alternative known as an irradiance equalized dynamic photovoltaic array (IEq-DPVA) by an average of 13.7% for the relevant tests carried out. This paper identifies the hardware requirements to produce such a system and it describes an algorithm that performs the optimized-string reconfiguration strategy. Finally, a simulator programmed in MATLAB is used to compare the performance of the optimized-string DPVA against an IEq-DPVA in a series of flexibility tests.

/pdf/the-optimized-string-dynamic-photovoltaic-array-1695xdjkx5.pdf

The Optimized-String Dynamic Photovoltaic Array

Small photo-Voltaic generators for residential applications are rapidly spreading all over the world in an effort to reduce polluting emissions. In this kind of applications the AC solar module concept has recently proven to be more advantageous than the conventional string architecture. According to the AC solar module concept, single PV modules are directly connected to the AC grid through a DC/DC converter and an inverter. However, in this case a periodical power unbalance is generated because the power drawn by a single-phase residential grid features a large ripple at twice the fundamental frequency, while PV modules generate a DC power. Such a power unbalance affects the Maximum Power Point Tracking and forces the system to operate under suboptimal conditions and is faced with the introduction of bulky electrolytic capacitors. In this paper a alternative approach is presented enabling a standard DC/DC converter to also act as a power ripple damper, without the introduction of extra power devices. A hybrid PWM/unfolder approach has been also developed to reduce the switching power losses of the inverter connecting the DC/DC converter to the grid.

A solar AC module with active filter capabilities

Some of DC actuators used in home automation, office automation, medical equipment and automotive systems require a position sensor. In low power applications, the introduction of such a transducer remarkably increases the whole system cost, which justifies the development of sensorless position estimation techniques. The well-known AC motor drive sensorless techniques exploiting the fundamental component of the back electromotive force cannot be used on DC motor drives. In addition, the sophisticated approaches based on current or voltage signal injection cannot be used. Therefore, an effective and inexpensive sensorless position estimation technique suitable for DC motors is presented in this paper. This technique exploits the periodic pulses of the armature current caused by commutation. It is based on a simple pulse counting algorithm, suitable for coping with the rather large variability of the pulse frequency and it leads to the realization of a sensorless position control system for low cost, medium performance systems, like those in the field of automotive applications.

/pdf/pulse-counting-sensorless-detection-of-the-shaft-speed-and-4s1bdndq0c.pdf

Pulse Counting Sensorless Detection of the Shaft Speed and Position of DC Motor Based Electromechanical Actuators

Temperature monitoring is a major issue in induction motor drives, because temperature variations under working conditions may affect the machine lifetime and the control performance as well. The paper presents a technique for on-line monitoring the rotor and stator temperature on field-oriented induction motor drives, based on a new approach to estimate the rotor and stator winding resistances. The proposed approach exploits the injection of small additional current signals to extract the thermal status of the electrical machine, without affecting the normal drive operation. Moreover, it features a low computational effort, does not require other transducers than these already present in a standard field-oriented controlled drive and can be applied on both conventional and sensorless induction motor drives. The stator and rotor temperature estimation can be used either to prevent dangerous overheating and for on-line tuning of the control system. The practical effectiveness of the proposed approach is demonstrated by simulations and experimental tests.

A general approach to sensorless estimation rotor and stator windings temperature in induction motor drives

The on state resistance of power MOSFETs tasked to perform repetitive avalanche operations is subject to modifications caused by the growth of voids and cracks in the source metallization. Endurance tests are the traditional way to monitor these changes in order to assess the device reliability. However, they are very time expensive, requiring even months of uninterrupted operations. An interesting alternative consists in the assessment of the reliability through a suitable model, but no standard techniques have been developed up to now to accomplish this task. A possible approach is followed in this paper exploiting a dynamic analysis of the temperature distribution over the source metal. Coupling the thermodynamic analysis with a reliability model, carried out from the Coffin-Manson law, the device degradation over the time can be estimated and the level of reliability as well. The consistence of the obtained reliability prediction is confirmed by comparison with results of endurance tests. The described approach can be usefully applied to assess the reliability of MOSFETs in a large set of applications in the automotive field.

Salvatore De Caro

Papers

A solar AC module with active filter capabilities

Pulse Counting Sensorless Detection of the Shaft Speed and Position of DC Motor Based Electromechanical Actuators

A general approach to sensorless estimation rotor and stator windings temperature in induction motor drives

Reliability assessment on power MOSFETs working in energy absorption mode