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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.

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. >

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.

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 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.

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 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.

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.