Abstract
The conventional grid-connected inverters require a sophisticated digital signal processor to generate the demanded reference signal as a feedforward signal for the sinusoidal pulse width modulation (SPWM) control. However, the reference signal needs to be re-calculated to maintain the demanded power control as the ac mains varies. It increases the computation burden of the controller and has become a major obstacle of the grid connected energy storage system with demanded power flow control. Therefore, a simplified approach to reduce the computation burden of the controller is proposed in this paper. With the proposed simplified equation for the power flow control, the usage of a low cost microcontroller unit becomes possible. In additional, no additional sensors or circuitries are needed. Meanwhile, the performance of desired power flow control by using the simplified control is almost unaffected. The proposed simplified algorithm is validated via mathematical calculations, computer simulation and experimental results. By using the proposed simplified control, 52.3% of the computational clock cycles can be reduced. Different operation scenarios were tested to validate the performance of the proposed simplified control via the MATLAB/Simulink simulations and the 1kVA prototype experiments.
Highlights
The renewable energy source has drawn a lot of attention due to the energy shortage and environment issues
The grid-connected voltage source inverter (GVSI) plays an important role for the energy storage component to connect to the microgrid
To deliver the demanded power to the grid, the reference signal of the controller needs to be calculated based on the variation of the ac mains voltage
Summary
The renewable energy source has drawn a lot of attention due to the energy shortage and environment issues. Three parameters, ac mains voltage vac, dc voltage Vdc and reference ac current iac,re f , are required to generate the feedforward sinusoidal control signal vre f for the PWM gate signal comparator. Since the objective of the proposed simplified control method is to transfer the demanded constant power under the fluctuated ac mains voltage, the reference signal generator in the feedforward loop is focused. To generate the sinusoidal reference signal, vre f , for the SPWM control, it requires the information of dc voltage, ac mains voltage, and line current. Because the objective of the GVSI is to maintain the consistent power control under the variable line voltage condition, the amplitude of the new ac mains voltage and current can be expressed by the summation of the nominal value and the variation as shown below:. The proposed simplified control algorithm can achieve similar computing time reduction for high-level DSPs with hardware acceleration units and various programming languages
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