TY  - JOUR
T1  - Digital Current Sensing in Modular Multilevel Converter for HVDC Applications
AU - Yahaya, J.A. AU - Mansor, Muhamad AU - Hadi, Abdul 
JO  - Journal of Engineering and Applied Sciences
VL  - 12
IS  - 3
SP  - 617
EP  - 621
PY  - 2017
DA  - 2001/08/19
SN  - 1816-949x
DO  - jeasci.2017.617.621
UR  - https://makhillpublications.co/view-article.php?doi=jeasci.2017.617.621
KW  - MMC
KW  -HVDC
KW  -voltage sensor
KW  -hysteresis control
KW  -Malaysia
AB  - For long-distance transmission, HVDC (High-Voltage, Direct-Current) is proven to be less expensive
and have lower electrical losses as compared to HVAC (High-Voltage, Alternating-Current). Now a days, the
advancement of power electronic switches such as IGBT’s and MOSFET enables the use of converters for
HVDC applications. Among the well-known converters used for HVDC are Voltage Source Converter (VSC) Line
Commutated Converter (LCC) and Modular Multilevel Converter (MMC). The MMC is still new and a promising
technology for HVDC application. The MMC has many advantages such as controlling high amount of
active/reactive power and possess lower losses as compared to other converters. To control the active/reactive
power in a MMC, control scheme such as free-running hysteresis uses the reference voltage and the inductor
current to produce the required switching pulses. This study proposed a technique in which a voltage sensor
is use to measure the inductor current. Conventionally, the inductor current is sensed either with a resistor or
Current Transformer (CT). This method is associated with some disadvantages; requires additional circuitry
which introduces some power loss and requires higher bandwidth in order to sense accurately. This study
instead, measures the current indirectly by using the information of the phase inductor voltage. As the voltage
sensor is placed in parallel to the inductor, this measuring technique is immune to I<sup>2</sup>R loss. The proposed
technique will be investigated using MATLAB simulation to determine its current sensing capability in a MMC
for HVDC applications. To design an improved current-less sensing method using a digital RC network. To
extract the inductor current values from the phase inductor voltage an RC filter is required and placed in parallel
across the inductor. In this way, all the high frequency harmonics will be filtered out and only the low frequency
inductor current can be seen across the capacitor. The selection of RC values, however is dependent on the
inductor value and inductor DC-Resistance (R<sub>DCR</sub> ). The main concern with this technique is that selection of DCR
RC values sometimes can be unavailable for hardware implementation. To further improve the implementation
of RC network and eliminate the problems of selecting suitable RC values for hardware implementation. This
paper proposed the used of digital filter based on the RC network concept. Instead of using the actual
components for filtering the high frequency harmonics, this technique uses only the DSP for filtering to remove
the high frequency harmonics. The proposed technique is able to convert the high frequency voltage V<sub>L1</sub> measured from the phase inductor L<sub>1</sub> into the phase inductor current i<sub>L1</sub>without any delay or difficulty. By 1 L1
comparing the signals of proposed method to the series sensing method and the conventional RC filter method
the waveforms of both signals are almost identical. However, the proposed method eliminates the need for RC
components as compared to the conventional RC filter method. This technique improves the efficiency of the
system in terms of improve signal noise ratio and eliminates the need for passive component on the system.
ER  -