C. Fitzer

Dynamic voltage restorer based on voltage-space-vector PWM control

A dynamic voltage restorer (DVR) based on the voltage-space-vector pulsewidth-modulation algorithm is presented. Phase-jump compensation is achieved using a software phase-locked loop and a lead-acid battery energy store. A battery-charging control technique using the DVR itself is also described. To validate the control of the DVR, a three-phase prototype with a power rating of 10 kVA has been successfully developed. Simulation and experimental results are shown to validate the control methods.

Voltage sag detection technique for a dynamic voltage restorer

Dynamic voltage restorers (DVRs) are used to protect sensitive loads from the effects of voltage sags on the distribution feeder. This paper presents and verifies a novel voltage sag detection technique for the control system of a DVR. In some cases it may be necessary for the DVR control system to not only detect the start and end of a voltage sag but also to determine the sag depth and any associated phase shift. The DVR, which is placed in series with a sensitive load, must be able to respond quickly to a voltage sag if end users of sensitive equipment are to experience no voltage fluctuations. A problem arises when fast evaluation of these parameters is required, as standard information tracking or detection methods such as the Fourier transform or phase-locked-loop (PLL) are too slow. As a result of this the voltage sag detection method this paper proposes a new state-space matrix method, which is able to compute the phase shift and voltage reduction of the supply voltage much quicker than the Fourier transform or a PLL. The paper also illustrates that the state space matrix method returns results that can be directly interpreted whereas other methods such as the wavelet transform, which return results that can be difficult to interpret.

Dynamic voltage restorer based on voltage space vector PWM control

A dynamic voltage restorer (DVR) based on the voltage space vector PWM (VSVPWM) algorithm is presented. Phase jump compensation is achieved using a software phase-locked loop (SPLL). A battery charging control technique using the DVR itself is also described. To validate the control of DVR, a three-phase prototype with a potential power rating of 10 kVA has been successfully developed. Simulation and experimental results are shown to validate the control methods.

Mitigation of saturation in dynamic voltage restorer connection transformers

During the transient period at the start of a voltage sag, a DVR injection transformer can experience a flux-linkage that is up to twice its nominal steady-state value. In order to prevent the transformers from saturating it is normal to choose a rating flux that is double that of the steady-state limit. An alternative method is to limit the flux-linkage during the transient switch-on period, thus preventing saturation. It is shown through both simulation and experimental results that an adaptive form factor can be applied to the DVR injected voltage, which minimizes the disturbance seen by a sensitive load, while at the same time preventing saturation. The proposed method removes the need for rating the series injection transformers for the DVR transient switch-on period, and therefore removes the redundancy normally associated with their steady state operation. In economic terms, this may reduce the total cost of a DVR system, thus making it a more attractive solution for voltage sag mitigation.

Software phase-locked loop applied to dynamic voltage restorer (DVR)

In this paper, the analytical and practical design issues of a software phase-locked loop (SPLL) for DVR are presented. A SPLL model that uses a lag/lead loop controller, is derived in order to analyse the system performance and filtering characteristic by the use of bode diagrams and root-locus methods. In DVR applications, parameters of the design of the SPLL controller are not only dependent on the steady state and dynamic state, but also on practical conditions such as utility unbalance, voltage sag/swell magnitude, voltage harmonics, phase jumps and frequency variations. Therefore, the practical aspect of the SPLL implementation has also been discussed. Experimental results demonstrate its phase tracking capability.

Universal custom power conditioner (UCPC) with integrated control

This paper deals with the integrated control of a universal custom power conditioner (UCPC) applied to distribution systems. The proposed UCPC comprises a series PWM (pulse width modulation) converter and two shunt PWM converters with a battery energy storage unit for multi-function control. The goal of the UCPC is to utilize stored energy to achieve coordinated compensation functions such as short time uninterruptible power supply (UPS), voltage flicker control, dynamic voltage restorer (DVR), harmonic isolator or filter, power factor correction, system oscillation damping and interphase power controller using one device. It also manages a number of power quality and reliability problems simultaneously. The validity of the proposed UCPC with an integrated control method has been demonstrated through EMTDC/PSCAD simulation.

Novel voltage space vector PWM algorithm of 3-phase 4-wire power conditioner

This paper proposes a novel voltage space vector PWM algorithm that is applied to the control of voltage source inverters (VSI) when they operate as 3-phase 4-wire active power conditioners. The idea is based on the concept of 3-dimensional voltage space vectors (VSV) in an /spl alpha//spl beta/0 space. Under unbalanced conditions, the voltage switching state vectors are asymmetrical. A 3-dimensional voltage synthesis process can be carried out based on a normal VSV PWM method and splitting the zero vectors into different effective times, according to the 0 component. The new algorithm has been investigated thoroughly and can be implemented easily by the use of a digital-signal processor (DSP). The validity of the algorithm has been verified by the results of simulation. The proposed PWM strategy has the attractive feature that it can control 3 phases independently and flexibly in 4-wire systems.