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In modern electrical networks thyristor-switched capacitors (TSC) are most used devices
for VAR compensation. These devices don’t contain rotating parts and mechanical contacts,
provide a stepwise control of reactive power and no generation of harmonics to the
network. However, with the help of TSC it’s not possible to ensure smooth control of reac...
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Citations
... Пристрої компенсації реактивної потужності (ПКРП) мають відповідати наступним критеріям: забезпечувати плавне регулювання реактивної потужності та при цьому мати відносно невелику вартість. Сучасним рішенням для компенсації реактивної потужності (РП) є використання ПКРП зі ступеневим перемиканням, СТАТКОМів, активних фільтрів [1]. Останнім часом все більше уваги приділяється проектуванню ПКРП на базі безпосередніх АС/АС перетворювачів, які отримали назву «динамічний конденсатор» (ДК) [2 -4]. ...
Purpose. Modern approaches of VAR compensation are: using
compensators with stepped regulation, STATCOMs, active power
filters. Recently, more attention is paid to VAR compensator’s
design based on the direct AC / AC converters, which are called
dynamic capacitors. Methodology. The dynamic capacitor (DCAP)
is the capacitor bank, which is connected to the mains
through direct AC / AC buck converter. By varying the duty
cycle of bidirectional switches, smooth control of reactive power
can be achieved. However, in case of distorted mains voltage,
D-CAP mains current will have a high THD. This is due to the
fact that the D-CAP affects the frequency response of electric
grid thus leading to the appearance of resonances. With nonsinusoidal
mains voltage, capacitors are affected by harmonics.
This reduces the reliability of the D-CAP, increasing the probability
of their failure. To eliminate these drawbacks it is suggested
to improve the D-CAP control system so that the input
current of the dynamic capacitor is forced to be close to sinusoidal.
This can be achieved if the duty cycle of the switching bidirectional
switches is changed according to the proposed expression.
Results. The research is done on a single-phase DCAP
with the proposed control system, its input current diagrams
are shown. In contrast to the D-CAP with a constant duty
cycle control, the resulting THD of its input current is much
lower. Thus, the control system provides a form of the input
current that is close to a sine wave. This reduces the influence of
mains voltage harmonics on the D-CAP operation, increases its
reliability and improves power quality. Originality. The proposed
D-CAP control system ensures reliable operation with
non-sinusoidal mains voltage. Practical value. Application of DCAPs
with the proposed control system allows for improved
energy efficiency of electrical mains by providing VAR compensation
and improving power quality. References 4, figures 6.
Key words: VAR compensation, dynamic capacitor, control
system, thin AC/AC converter, bidirectional switch.
