Improvement in the Synchronization Process of the Voltage-Sourced Converters Connected to the Grid by PLL in order to Detect and Block the Double Frequency Disturbance Term

PLL Structures have many applications in power system engineering. When required the synchronous performance of Voltage Sourced Converter (VSC) with Grid, such as wind power generation system, active filters, HVDC transmission lines and FACTS devices, the most common method for accurate estimation of frequency of network, is to use a PLL. However, problems such as grid disturbances due to noise, voltage unbalances, lack of coordination, changes in grid frequency and harmonics can produce a frequency disturbance, twice the grid frequency and disturbed PLL and also the control system connected to it. In this paper, common structures of PLL is introduced. After that, unbalance and disturbance in the three phase input of PLL is studied. Then for idea and invention in PLL, a new control method based on predictive control technique is used in the control strategy of converter. Furthermore, the use of type III controller in PLL to ensure optimal performance in various conditions is proposed in this paper. How to set the parameters of the proposed controller is described by the Bode stability criterion. Conducting simulations to evaluate the performance of the proposed method is done in PSIM software. According to the proposed method and the result observed, the double frequency disturbance term is weakened and also the transient state is improved. In this article as an idea and innovation, we use a new predictive controller named Deadbeat in control circuit of PWM voltage sourced converter and a type-3 controller was used as Loop filter in PLL control circuit and the simulations were performed. Results were shown that the proposed controller is more sensitive to the problem. In the proposed method, in addition to weaken the double frequency disturbance term, in practice it is very easy to implement. In addition simulations were performed on the change of grid frequency. Simulation results confirmed the good performance of the proposed method. Some of the benefits of the proposed controller is expressed as follows: Good performance and provide the appropriate PM. While it is not so complicated. Not complicated means that it will be easily led to construction. This controller have 3 capacitors and 3 resistors with an op-amp. It is easy to implement in analog. With zero steady state error of the step, ramp and parabolic input.

Keywords:

Phase-Locked Loop (PLL) , voltage-sourced converters (VSC) , synchronization , current control , unbalanced voltage