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A new all-digital current control technique is presented in this paper. The current control is based on Ramptime current control technique, where multisampling is chosen as the sampling strategy due to its ability to provide higher accuracy. The resultant current control is called Digital Ramptime current control. The performance of the new current control is compared with the original Ramptime in an active power filter experiment. Results show that with sufficient sampling, the performance of Digital Ramptime is satisfactory.

This paper investigates the static and dynamic performance of current sense methods, which exploit the resistive voltage drop across the current carrying copper trace. This approach promises very low cost since no dedicated shunt resistor is required, no additional power losses occur and no extra space on the printed-circuit-board (PCB) is necessary. A microcontroller can be used to calibrate the copper trace resistance and implement a temperature drift compensation by means of a temperature sensor. Given that today almost every electronic device has at least one microcontroller that can provide the small computation power required for this current sensing technique, the additional cost of such a technique is small.While the proposed technique appears straightforward, theoretical modeling and hardware experiments revealed two unexpected obstacles. First, the thermal resistance between the busbar and the temperature sensor notably alters correction for the temperature drift. We found that it is possible to rectify this behavior by implementing a more sophisticated temperature compensation method inside the microcontroller. Second, it is demonstrated that the self-inductance of the busbar arrangement is not important for the dynamic behavior (frequency response) of this measurement method, and the response is determined by the mutual inductance between main loop and sense loop. Based on simulation and measurements, we demonstrated that a simple RC-compensation network can significantly improve the frequency response.

The lossless inductor current sensing method is well-known and is frequently applied in the measurement of output current in DC-DC converters due to its low cost and simplicity. This technique uses a low-pass filter that is matched to the inductance (L) and winding resistance to compensate for induced voltages due to the inductor. However, the waveform fidelity above the corner frequency of the inductor is generally poor due to large production tolerances and thermal drift. In this letter, we propose the use of a coupled sense winding, which increases the corner frequency of the sensing circuit by more than two orders of magnitude. We show, as an example, that for a 3.85 muH inductor the corner frequency of the measurement circuit can be increased from 36 Hz using the conventional approach to 5.8 kHz using the coupled sense winding method. Above the new corner frequency, a low-pass filter is still required but may now be constructed using a smaller capacitor and with improved high-frequency response.

This paper provides a thorough review of state-of-the-art current sensing techniques. It catalogues the current sensors according to the underlying physical principle in order to point out their strengths and weaknesses.

Twenty years ago, R. Severns presented a transformer based circuit which is able to measure DC currents. However, this circuit did not experience a break-through in the industry or even academic world because it requires too many components and is unable to measure small currents. This paper enhances this circuit so that it becomes feasible to measure currents down to zero. The circuit complexity is no longer an obstacle because in digital controlled power supplies the DSP provides the required auxiliary functionalities. The feasibility of the proposed circuit has been proven by hardware experiment.

In this paper, the implementation of a shunt active power filter with a small series inductor for a three-phase system is presented. The filter consists of a three-phase current-controlled voltage source inverter (CC-VSI) with a filter inductance at the ac output and a dc-bus capacitor. The series inductor is primarily used to handle the harmonic voltage source. The main concern is the size of the series inductance so that it is as small as possible but effective in compensating the harmonics. In order to select the proper value of the series inductance, the simulation is conducted to evaluate the value for different types of load.

In this paper a novel space vector modulation method for single-phase inverters is presented. Mathematical analysis, simulation and comparison of conventional sinusoidal pulse width modulation (SPWM) techniques with the proposed space vector modulation for single-phase inverter are included. These modulation techniques are compared, evaluated and classified for different single-phase applications, including deadband effects. The proposed modulation method combines the flexibility of the well-known unipolar PWM scheme for single-phase inverters result in maximum harmonic mitigation. The new technique is suitable for simple digital implementation. Experimental results, obtained by a digital signal processor (DSP) board, are included.

A prototype current-controlled power conditioning system has been developed and tested on a weak rural feeder line at Kalbarri, about 600 km northwest of Perth in Western Australia. This system sources 20 kW of power from a photovoltaic array with maximum power point tracking control. In addition, it provides voltage support for the power grid at Kalbarri by varying its reactive power in response to the measured voltage at the point of connection. This paper describes the development and testing of the power conditioning system.

Unity and controlled power factor AC-DC power converters require a current control technique with zero average current error (ZACE) in each switching period. Acting on the current error signal alone, a ZACE controlled converter offers complete real and reactive power flow control with negligible low order current harmonics, a narrow switching frequency band, and relative immunity to DC link or AC line voltage harmonics. Slope-generated hysteresis, a new ZACE current control method is introduced. Simulation and experimental results in a three phase converter are presented. >

The most widely used configuration of DC machines is series-wound type. The main advantages are simpler control system design and no separately excited field windings. However, the use of DC motors in electric vehicles has declined dramatically in the current decade. Unless the efficiency of such a system can be improved significantly the use of DC motors in electrical vehicles becomes unattractive. One possible way of improving the efficiency is to include regenerative braking. Regenerative braking is an energy recovery mechanism used to improve the drive distance of electric vehicles. Hence in this paper, a regenerative braking mechanism for a series-wound dc motor system is proposed. The simulation results are also presented to show the effectiveness of the proposed regenerative braking system.

This paper presents an experimental comparison of three current control techniques, namely Hysteresis, PI and Ramptime Current Control Techniques. The testing platform is a 300 W shunt active power filter with diode rectifier load. Results are analysed both in the time domain and the frequency domain. The pros and cons of each of the above mentioned current control techniques are discussed. It is found that Ramptime Current Control is capable of incorporating the advantages of the two other control techniques with negligible shortcomings.

Simulations of voltage source inverters often only consider the ideal system performance, but in the real-world there are always non-ideal characteristics too. To provide insight into performance under non-ideal conditions and to make comparable analyses, particular levels of non-ideal characteristics can be introduced as a benchmark in simulation of current control strategies for voltage source inverters. The overall aim is to offer some implementation guidance so that control method suitability and associated issues/limitations are quickly identified (via knowledge of particular non-ideal characteristics that a certain control is susceptible to) - which hopefully saves time and/or cost during prototype development and verification.

The output current of contemporary AC-DC front-end converters is steadily increasing due to higher power density requirements. The use of shunt resistors to sense the output current is becoming unacceptable due to high power losses and new techniques for current sensing need to be investigated. In this paper, we investigate the possible use of the voltage drop across the trace resistance to sense the output current. This approach promises very low cost since no dedicated shunt resistor is required, no additional power losses occur and no extra space on the printed-circuit-board (PCB) is necessary. To overcome the problems associated with the temperature drift of the copper, and variability in the trace resistance of the copper track, a digital controller can be used to calibrate the trace resistance and implement a temperature drift compensation. This form of microcontroller is readily available on todaypsilas AC-DC front-end converters. However, theoretical and practical investigations revealed that the parasitic inductance and skin effect may limit the bandwidth of this measurement principle down to several hundred Hz. To overcome this limitation, we proposed a compensation technique that has the potential to increase the bandwidth beyond ten kilohertz. Experiments with output currents of up to 240 A demonstrated that the measurement uncertainty for DC currents is less than plusmn1 A for temperatures between 25 to 60 degrees, and that the effective bandwidth can be enhanced using a compensation technique.

In this paper, the implementation of a three-phase shunt active power filter is presented. The filter is essentially three independent single-phase current-controlled voltage source inverters (CC-VSI) with a common DC bus. The CC- VSI is operated to directly control the AC grid current to be sinusoidal and in phase with the grid voltage. The APF consists of a current control loop, which uses polarized ramptime current control and a voltage control loop, which employs a simple Proportional Integral control. The experimental results indicate that the active filter is able to handle predominantly the harmonics, as well as the unbalance and reactive power, so that the grid currents are sinusoidal, in phase with the grid voltages and symmetrical.

This paper presents a comparative analysis of the parallel operation of different switches in a switch mode power converter. In high power applications, multi-switch PWM power conditioners may be preferred despite a higher component count, due to the absence of low frequency filters, reduced switching losses and fault tolerance. The paper demonstrates how current sharing (CSH) and time sharing (TSH) lead to the reduction of switching stress in the parallel operation of switches in any converter. The solutions proposed in this study can be applied on different scales to other power conditioners for renewable energy applications. Discussions of the concepts, hypotheses and computer simulations are verified by 1 kW experimental results

This paper describes a novel space vector modulation method for single-phase inverters suitable for an uninterruptible power supply (UPS) and other applications. This modulation method combines the flexibility of the wellknown unipolar PWM for single-phase inverters with the maximum harmonic mitigation. Six switching methods are presented, evaluated and classified for different single-phase applications, including deadband effects. Simulations using Matlab/Simulink confirm the validity of the proposed PWM. Mathematical analysis and comparison of SPWM with the proposed space vector modulation for single-phase inverter are presented.

An improved variation of ramptime current control, implemented in programmable logic, is applied to a bidirectional three-phase "voltage source inverter". Named "polarized" ramptime, it is a zero average current error (ZACE) method with a more controlled and narrow switching frequency band. Only the polarity of the decoupled current error signal and the desired switching frequency are used in this current regulator to determine switching instants. Switching signals are adjusted immediately and automatically for variations in system parameters without manipulation, prediction or direct measurement. Polarized ramptime is applied in each of two current regulators in a balanced three-phase voltage source inverter operating with a standing phase. Simulation and prototype inverter results are presented showing negligible low order AC current harmonics. The synchronization of the two polarized ramptime current regulators is controlled in the prototype inverter so as to minimize the AC current ripple, with a similar result to that achieved with symmetrical pulse patterns in voltage space vectors.

In this paper a novel multifunctional power processing unit capable of extracting maximum power from solar photovoltaic panels is described. It employs a combination of a voltage controlled voltage source inverter (VCVSI) and a current controlled voltage source inverter (CCVSI), connected in series on the DC side and in parallel on the AC side Chem Nayar et al. (2003), H. Dehbonei et al. (2002), H. Dehbonei (2003). This power processing unit is able to provide an uninterruptible power supply feature, load voltage stabilisation, unity power factor operation, maximum power point tracking, higher efficiency for charging the battery from renewable energy sources and more reactive power support. The experimental results from the prototyped system confirm the validity of the proposed topology.

This paper proposes a systematic procedure for designing a single-phase H-bridge inverter. It includes mathematical calculations, computer simulations and experimental verification on a scaled down prototype inverter.

A prototype current controlled power conditioning system has been developed and is being tested on a weak rural feeder line at Kalbarri, about 600 kilometers north-west of Perth in Western Australia. This system sources 20 kW of power from three photovoltaic arrays with a maximum power point tracking control. In addition, it provides voltage support for the grid at Kalbarri by varying its reactive power in response to the measured voltage at the point of connection. This paper describes the development and testing of the power conditioning system.

Unity and controlled power factor AC-DC power converters require a current control technique with zero average current error (ZACE) in each switching period. Acting on the current error signal alone, a ZACE controlled converter offers complete real and reactive power flow control with negligible low order current harmonics, a narrow switching frequency band, and relative immunity to DC link or AC line voltage harmonics. Slope-generated hysteresis, a new ZACE current control method is introduced. Simulation and experimental results in a three phase converter are presented. >

A soft-switching AC to DC converter that employs a continuously resonating L-C circuit in a single-phase single-switch boost rectifier circuit is presented. The phase of the resonant tank when the switch is turned on is used as the controlling variable for shaping the rectifier input current. This phase control technique, when used together with a current estimator, is demonstrated as an effective means for generating sinusoidal AC-line currents in phase with the AC-line voltage. The quality of the control scheme is assessed, and experimental results are obtained for an 800 W, 20 kHz rectifier using an IGBT switch. >

This paper describes the current control method and the switching scheme of a cascaded five level inverter based grid connected single phase photovoltaic system. For the current control a dual polarised ramptime zero average current error control method is applied, which provides good current regulation, and a narrow ripple current frequency band. Simulation results which demonstrate the method are presented. The redundant inverter states of the five level cascaded inverter allow for a cyclic switching scheme which minimises the switching frequency, equalises stress evenly on all switches and minimises the voltage ripple on the DC capacitors. Simulation and experimental results of a multi carrier PWM voltage controller showing the effectiveness of the switching scheme are presented.

This paper describes the implementation of a shunt active power filter for a three-phase four-wire system to overcome the power quality problems generated by mixed non-linear loads which are a combination of harmonic , reactive and unbalanced components. The filter consists of a three-phase current-controlled voltage source inverter (CC-VSI) with a filter inductor at the AC output and a DC-bus capacitor. T he CC-VSI is operated to directly control the grid current in order to be sinusoidal and in phase with the grid voltage without sensing the load currents. The switching is controlled by using polarized ramp-time current control, which is based on the concept of zero average current error (ZACE) with a fixed switching frequency. The laboratory experiment results indicate that the filter is able to mitigate the harmonics and the reactive power, so that the grid currents are sinusoidal, in phase with the grid voltages, and symmetric although the grid voltage contains harmonics .

This paper describes an application of the space vector modulation (SPM) technique to a photovoltaic assisted single-phase line-interactive inverter operating as an uninterruptible power supply (UPS). The performance of this inverter is comparable to a unipolar sinusoidal pulse width modulation (SPWM) operating at higher switching frequencies. Preliminary experimental results using a DSP-based system and simulation using Matlab/Simulink confirm the validity of the proposal. This UPS has built in features such as active filtering, demand side management and integration of renewable energy sources such as photovoltaic (PV). In this paper, comparison of SVM and SPWM in single-phase together with simulation and experimental results are also included.

This paper reports on the application of a zero average current error (ZACE) control method in single-phase five level cascaded inverter based systems. The dual ramptime method and its adaptation to the five level cascaded converter are described in detail. Recommendations on the choice of control parameters and how to improve noise immunity are included. Experimental results demonstrate the suitability of the control method, since the lower order harmonics are negligible and the ripple current frequency is kept within a narrow band.

In this paper, a novel power converter capable of extracting maximum power from solar photovoltaic panels is described. It employs a combination of a voltage controlled voltage source inverter and a current controlled voltage source inverter, connected in series on the DC side and in parallel on the AC side. This dual converter is able to provide uninterruptible power supply feature, load voltage stabilisation, unity power factor operation, maximum power point tracking as well as reactive power support. The overall efficiency of the proposed converter is higher than the conventional system with a DC-DC converter between the PV panels and the battery.

This paper investigates and analyses different multicarrier PWM methods for a single phase five level cascaded inverter. Carrier disposition methods, phase shifted and a hybrid method are discussed with respect to resulting switching frequencies, complexity of implementation, spectrum of the output waveform, and the use of inverter state redundancies to perform additional application specific control tasks, such as power flow control from each DC source. A concept of separating the waveshaping function from the switch selection is explored and selected experimental results are presented.