The Transactions of the Korean Institute of Power Electronics (전력전자학회논문지)

The Korean Institute of Power Electronics (전력전자학회)
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Accurate Calculation of RMS Value of Grid Voltage with Synchronization of Phase Angle of Sampled Data

샘플링 시점의 위상각 동기화를 이용한 계통전압 실효값의 정확한 계산 방법

  • Received : 2018.05.04
  • Accepted : 2018.06.04
  • Published : 2018.12.20
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Abstract

A novel and simple algorithm for accurate calculation of RMS voltage is proposed in a digitally controlled grid-tie inverter system. Given that the actual frequency of grid voltage is continuously changing, the constant sampling frequency cannot be a multiple number of the fundamental frequency. Therefore, the RMS of grid voltage contains periodic oscillations due to the differences in the phase angle of sampled data during calculation. The proposed algorithm precisely calculates and updates the initial phase angle of the first sampled voltage in a half-cycle period using phase-locked loop, which is commonly utilized for phase angle detection in grid-tie inverter systems. The accuracy and dynamic performance of the proposed algorithm are compared with those of other algorithms through various simulations and experiments.

Keywords

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Fig. 1. A distributed power system comprising an upper management system.

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Fig. 2. Conventional RMS calculation algorithms.(a) Block diagram of H-RMS(Half-cycle RMS) algorithm, (b) Block diagram of M-RMS(Moving average RMS) algorithm.

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Fig. 3. RMS value of classical calculation method.

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Fig. 4. Blcok diagram of the proposed RMS value calculation.(a) Overall block diagram of RMS value calculation,(b) Internal block diagram of Phase shift.

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Fig. 5. Phase compensation of Section 1 and Section 2.

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Fig. 6. Phase compensation of Section 1 and Section 2. (a) Section 1 and Section 2 (4.2ms), (b) Section 1 (50us), (c) Section 2 (50us).

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Fig. 7. Step response of voltage RMS calculation algorithm (Simulation results). (a) Phase voltage, (b) RMS calculation of methods.

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Fig. 8. Error of RMS value according to change of grid frequency(Simulation results).

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Fig. 9. Step response of voltage RMS calculation algorithm (Experimental results). (a) Phase voltage, (b) RMS calculation of methods.

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Fig. 10. Error of RMS value according to change of grid frequency(Experimental results).

TABLE I SIMULATION AND THEORY DATA ACCORDING TO PRIME NUMBER

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TABLE II SIMULATION PARAMETERS

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