Simplified Control Technique Research Articles

Capacitor voltage balancing in neutral-point clamped rectifier using modified modulation index technique

In this paper, a simplified control technique is proposed to control capacitor voltages of three-phase Neutral-Point Clamped bi-directional rectifier based on the modified modulation index technique. The modified modulation index technique generates new position of the reference vector in the space vector hexagon keeping both capacitor voltages constant. The modified reference vector is made either large or small enough so that the effects of redundant switching patterns become prominent to balance capacitor voltages. Changing commutation state for the adoption of redundant switching patterns is dictated by reference vector. The modulation index is modified in proportion to the mean difference in the capacitor voltages plus calculated modulation index. The calculated modulation index is due to change in duty cycle of redundant switching states of the three nearest reference vectors in the sectors in which reference vector lies. The proposed algorithm maintains minimum neural point potential variations and also keeps source side and load side parameters within acceptable limits.

Optimising the performance of three-phase neutral-point clamped rectifier under disturbed AC mains

In this paper, a novel simplified control technique is proposed to control three-phase neutral-point clamped bidirectional rectifier using optimised switching sequences for disturbed AC mains. In space-vector modulation (SVM) technique using optimised switching sequences, duty ratio and sampling periods in each region are very important. In other words, reference vector trajectory shape and the time spent by the reference vector in each region are very important to obtain exact switching under any supply conditions. With the use of optimised switching sequences, even under ideal supply conditions, it is depicted that source-side and load-side parameters deviate from acceptable limits, and a DC-bus capacitor voltage unbalance occurs. Under the influence of disturbed AC supply, source-side and load-side parameters deviate more beyond acceptable limits which cause a very large unbalance in DC bus capacitor voltages. This non-ideal performance of the converter is responsible for the deterioration of quality of source currents and a large stress on power semiconductor devices. A new algorithm is proposed in this paper to make the converter performance ideal even under ideal and non-ideal supply conditions. According to supply conditions, the proposed technique varies the speed of the reference vector and, also at the same time, forms a required trajectory while passing through the most effective regions of SVM hexagon. The proposed technique maintains parameters within acceptable limits for source side and load side in terms of unity power factor, low input current total harmonic distortion (THD), minimum switching losses and reduced-rippled, well-regulated DC-bus voltage and also at the same time DC-bus capacitor voltage balance. The simulation results are presented to demonstrate the effectiveness of the proposed control technique.

A novel adaptive control approach for three-phase improved power quality converter under distorted and unbalanced AC mains

In this paper, a novel simplified control technique is proposed to control three-phase improved power quality converter for disturbed AC mains. The proposed technique is based on retransformation of Clarke transformation. The trajectory of reference vector is very important for SVM technique to obtain exact switching times. Due to disturbed supply in a three-phase system, the trajectory of reference vector gets affected which results in low input power factor, high input current THD and high ripple factor of the DC output voltage in power converters. In the proposed technique, PI operation is implemented for the retransformation of Clarke transformation. The modified Clarke transformation generates a required shape of the trajectory of reference vector so that the system performs satisfactorily even under disturbed AC mains. Moreover, the proposed scheme has the advantage of fast response and is simple enough to be implemented in a single-chip microcontroller. The simulation results are presented to demonstrate the effectiveness of the new proposed control technique.

A Simplified Control Technique for a Dual Unified Power Quality Conditioner

This paper presents a simplified control technique for a dual three-phase topology of a unified power quality conditioner—iUPQC. The iUPQC is composed of two active filters, a series active filter and a shunt active filter (parallel active filter), used to eliminate harmonics and unbalances. Different from a conventional UPQC, the iUPQC has the series filter controlled as a sinusoidal current source and the shunt filter controlled as a sinusoidal voltage source. Therefore, the pulse width modulation (PWM) controls of the iUPQC deal with a well-known frequency spectrum, since it is controlled using voltage and current sinusoidal references, different from the conventional UPQC that is controlled using nonsinusoidal references. In this paper, the proposed design control, power flow analysis, and experimental results of the developed prototype are presented.

Simplified control technique for unity-power-factor boost pre-regulator

A simple implementation of the average-current-mode control technique for a single-phase boost power-factor pre-regulator is presented to give good line current correction. The controller avoids use of a multiplier, a sample-and-hold circuit, and a line voltage sensor. It provides an effective solution when a low-cost control circuit is required.

Simplified control technique for high-power-factor flyback Cuk and Sepic rectifiers operating in CCM

Control techniques for high-power-factor rectifiers which do not need input voltage sensing are gaining considerable attention due to their simpler implementation and inherently superior stability, as compared to conventional average or peak current mode control. Among these, the solutions based on the integration of a current signal (switch, diode, or inductor current) provide an inherent noise immunity, which makes them further appealing. This paper proposes a simple implementation of one such control technique for high-power-factor flyback, Cuk, or Sepic rectifiers, which, while still retaining a high power factor, further reduces the control complexity, thus making the solution very attractive for smart-power integration. A 200 W flyback rectifier with the proposed control technique was implemented and tested. The achieved results are in good agreement with the expected performance.