Abstract
The converter in a microgrid uses the active power and reactive power (PQ) control strategy when connected to the grid. In the case of failure of large power grid, the converters are required to be connected in parallel under the condition of island to provide power to the load. In this paper, a new control method for the parallel operation of converters based on V/F control is proposed. The V/F control is used to ensure the output voltages have the same amplitude and frequency, then the converters will only produce circulating current caused by phase angle inconsistency. The phase angle self-synchronization strategy is proposed to make sure the phase angle of output voltage of all converters in the system are consistent. First, a large inductor is added to the end of the converter to ignore the line reactance, through this, the measured voltage at the terminal of the converter roughly equals to the voltage of the load, thus, every converter has the same reference of phase angle. Using the proposed phase angle self-synchronization strategy allows the output voltage of every converter to have the same phase angle, so that there is no circulating current between converters, and the power is evenly distributed among the converters. The simulation verification was carried out on the Power Simulation (PSIM) simulation platform, and the experimental verification was implemented on the hardware experimental platform. Both results demonstrate the effectiveness of the proposed strategy. This method is highly reliable and easy to implement, and the circulating current can be reduced effectively.
Highlights
Energy has always been the basic resource for human survival
Based on the existing study of parallel operation strategy of converters, a new control method for the parallel operation of converters based on V/F control is proposed
In order to solve the problem of the difference of the phase angle between the output voltages of each converter, this paper proposes a phase angle self-synchronization strategy
Summary
Energy has always been the basic resource for human survival. Due to the energy crisis and the environmental security, governments all over the world have begun to attach great importance to renewable energy generation [1]. With the development of distributed generation, higher requirements were put forward for converter capacity, operational performance, and expansibility. References [4,5] studied the parallel strategy of centralized control In this method, the centralized controller needs to collect the output current of the system, and the current reference of the single converter is obtained after calculation, and the centralized controller will generate the voltage reference of each converter. The master-slave control is simpler to implement, but once the main converter fails, the system voltage is not supported, and the current reference signal from each converter is lost, which will cause the parallel system to collapse. The parallel control strategy of the converter proposed in this paper does not require the use of communication lines, and the operation is stable and reliable, the implementation principle is simple, and the hardware is easy to implement. The circulation of the system is small, and the load power is evenly distributed
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