Power Control Strategies in Industries
Electronic applications make use of a wide variety of materials, knowledge, and devices, which help to pave the road to creative design, development, and the creation of innumerable electronic circuits with the purpose of incorporating them in electronic products. This is where power electronics have been fully introduced in industry, in applications such as power supplies, converters, inverters, battery chargers, temperature control, variable speed motors. Power electronics has become an integral part for any industry to flourish, right from chemical industries to high level multinational companies, the effective usage of power is of prime importance.
The reality (looking at the current scenario) is that the demand for electrical energy is a direct proportionate to the improvement in quality of life. As a result, the design, development, and optimization of power electronics and controller devices are essential to face forthcoming challenges. There are 2 major trends that can be clearly seen in industries in the recent past in the power systems field of study. The first trend is the increasing in the employment of renewable energy resources for power generation as well as control. The second trend is decentralized energy generation. Decentralized energy is the energy that is generated off the main grid and is produced close to where it will be used rather than at a large plant elsewhere and sent through the national grid.
Recently, there has been increase in the usage of Transformer-less voltage sources. Transformer less Voltage source inverters (VSI) are the standard choice instead of Current source inverters (CSIs), because they possess better conversion efficiency, smaller size, and lower manufacturing costs for the same power rating. These transformer less inverters are generally classified into two classes such as galvanic or non-galvanic categories. When a high-frequency and low-size transformer is used on the DC side, the electric connection between the circuit components is removed, which implies there is an electrical isolation between the two electrical systems. The same can also be thought of from the perspective of AC side i.e. when a low-frequency large-size transformer on the AC side are used. This electrical separation helps improve operation security and reliability.
Power electronics deals with the problem of Common Mode Current (CMC), which is cause multiple conductors to act or behave like a single conductor. CMC circulation is only possible, since there is no galvanic isolation which, when combined with the stray capacitance that appears between the photovoltaic installation and the DC side ground, which allows a path for ground current to be injected into the neutral point at the AC side. To eliminate the possibility of power leakage and the common mode current, different topologies for the design of Transformer-less inverters have been used in many industries. Fig.1 represents an H7 topology. Similarly, there are H6, H5, half bridge, full bridge, HERIC, etc. to name a few.
Detection of faults in power systems is also another parameter to be considered in power systems. They can lead to high transients and thermal stresses on power system equipment such as overhead lines, cables, transformers, and switch gears. Therefore, the fault current protection schemes are important. The most simple solution to problem of limit short-circuit current would be the application of a source with high impedance. However, the main drawback of this solution is that it also influences the system during normal operation conditions, and this results in a considerable voltage drop for high current loads
A fast fault current limiter and circuit breaker is the solution for rapid voltage recovery of sensitive loads that is predominantly used in industries. This methodology consists of a compound type of Current Limiter and Circuit Breaker (CLCB) which can limit fault current and fast break to adjust voltage sags at the protected buses.
This device acts by dual-function protection. These include limiting the fault current and also opening the faulty line, whose functionality is similar to a circuit breaker. Therefore, in practice, its fast response to faults helps to successfully limit the first peak of the fault current. In addition, the CLCB also assists to recover the protected buses voltage to a near acceptable level. Therefore, the sensitive loads do not experience a significant voltage sag.
Whenever a fault occurs inside a circuit, the fault current naturally increases which is detected when its value passes the threshold current level (IL). In this case, the control circuit detects the fault and turns on the IGBTs which are connected in anti parallel manner. As a result, the secondary side of the resonance transformer is short-circuited and the resonance transformer shows negligible impedance. The series capacitor impedance then limits the fault current. In this way, the CLCB is successful in not only detection of a fault, but also to act as a fuse, by disconnecting the faulty connection.
Overall, the rise of power electronic equipment in our power grids as well as different industries can be seen as a major technological trend. Besides this, the coupling of the electrical power system to other energy sectors, like the heat/cold supply or the transportation infrastructure via electro-mobility, will have significant impact to the requirements for the control system. The rising trends in industrial development has also sown the seeds for an improportionate rise of power electronics devices as well as power control strategies. Technologies like Transformer less voltage sources and CLCB helps to monitor and regulate the power consumption throughout the circuit and consequently the entire system.
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