Improving The Power Quality Of A Marine Automated Digital Substation By Using An Active Filter

One of the aspects of digital power grids development is the provision of high quality electricity. The effectiveness of control and load management by software and hardware complexes predetermines an increase in the stringency of the requirements for power quality parameters affecting the operation of power equipment and the transmission of information signals, thereby implying the need to study ways to compensate for current and voltage distortions. As an object of research, marine power plants are considered as developing digital substations. The paper considers the issue of documentary control harmonic components level in electricity supply networks. The control of the voltage curve deviation from the sinusoid in onshore general-purpose networks is carried out in the Russian Federation in accordance with GOST (Russian National Standard) 30804.4.7-2013 (IEC 61000-4-7: 2009). At offshore facilities, these indicators and their standards are defined in the Rules for the Classification and Construction of Sea-Going Ships.Electric drives are one of the interharmonic components sources of current and voltage on ships. The non-linearity of the electric drives load of reciprocating compressors lies in the fact that they set in motion a mechanical load with an uneven moment of resistance, thereby creating current ripples in the windings of the electric motor. According to the carried out experimental and analytical studies, it was revealed that the current distortions during the operation of reciprocating compressors are interharmonic and reach the highest amplitude at a frequency lower than the network frequency.The use of active filters is proposed to improve the quality of electric power in the ship electric power system and to compensate for interharmonic components. The methods of designing power electronic devices have been studied. A design of an active filter on the platform of the STM32F4 debug board has been developed. The device includes a control system, power amplifiers, galvanic isolation, power supply units and power components. The elements have a replaceable modular construction, which allows the device to be used for a wide range of electric drive capacities. The controller software was developed in the MATLAB programming environment using the Simulink visualization simulation package and the Aimagin Waijung blockset. The board was also debugged and flashed. This method of implementing the software of an active filter allows not only its off-line operation, but also continuous real time data transmission to a personal computer to monitor the operation of the device.An algorithm feature of the designed active filter is the principle of operation by disturbing the reference form of the load current. The level of deviation from the reference form is read over several periods of the current sinusoid. The control system calculates the pattern of current distortion by performing a spectral analysis, and the following periods compensate for the current. At the same time, new possible deviations are read and the compensating signal is corrected for subsequent periods. The number of read cycle and compensation cycle times may vary depending on the drive capacity and the expected compensation accuracy.The experiment showed that the designed device is capable of generating periodic balanced three-phase signal and unbalanced three-phase signal of various harmonic spectrum. In laboratory conditions, the device made it possible to reduce the level of interharmonic components of the electric drive current of an air compressor by 2.5%. With the addition of high-power transformers and stand-alone rectifiers, such an active filter can compensate for both harmonic and interharmonic distortions that appear in ship networks when electric drives operate with uneven loads. Improving the quality of electrical energy in marine automated substation will reduce the negative impact of harmonics on digital information and control systems, thereby extending the service life and providing a greater uptime factor for electronic and power equipment.