In recent years, solar energy has gained a great deal of attention. Hence, the photovoltaic (PV) systems which convert the solar energy into electricity should achieve high efficiency, low manufacturing cost, and high quality of electric power to attract the consumers. More
In recent years, solar energy has gained a great deal of attention. Hence, the photovoltaic (PV) systems which convert the solar energy into electricity should achieve high efficiency, low manufacturing cost, and high quality of electric power to attract the consumers. Although Cascaded H-Bride (CHB) inverter is a suitable choice for injection of PV power into grid, its control issues have not been completely solved. One of the main challenges in CHB inverter is low margin of stability when the H-bridge cells are under imbalance operating conditions. In this paper, a new MPPT algorithm is proposed for a CHB photovoltaic inverter. The proposed approach not only tracks the maximum point of distinct PV arrays under symmetric insolation, but also behaves well under asymmetric insolation conditions. The latter is achieved through shifting the operating point of PV arrays and using the modulation index of H-bridge cells as a degree of freedom. The usefulness and validity of new method is confirmed by simulation and experiments on a 7-level CHB photovoltaic inverter.
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In this paper dual-loop control method is proposed for control of 400 Hz inverter. Resonant controllers are used in the outer loop to regulate the amplitude of fundamental harmonic and to remove the unwanted harmonics. To avoid phase delay and bandwidth degradation, pro More
In this paper dual-loop control method is proposed for control of 400 Hz inverter. Resonant controllers are used in the outer loop to regulate the amplitude of fundamental harmonic and to remove the unwanted harmonics. To avoid phase delay and bandwidth degradation, proportional controller is used as the inner control loop. In this paper, hybrid digital design in discrete- and continuous-time domain is introduced to design the inner and outer control loops. To decouple the control system from the load current disturbances and to improve the dynamic performance, a feed-forward path is added to the dual-loop control structure. To reduce the noise of feed-forward path, a soft-derivative term is introduced which is optimized for 400 Hz frequency. To verify the system performance, several simulations have been carried out which shows satisfactory results under dynamic and steady state conditions. Finally, the experimental results of a 20 kVA hardware prototype is presented to confirm the validity of theoretical and simulation results.
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The flying-capacitor modular multilevel converter (FC-MMC) has been introduced as a hardware development of the conventional MMC with the aim of reducing the cell capacitor ripple voltage in the application of electrical drive at low speeds. The capacitor ripple voltage More
The flying-capacitor modular multilevel converter (FC-MMC) has been introduced as a hardware development of the conventional MMC with the aim of reducing the cell capacitor ripple voltage in the application of electrical drive at low speeds. The capacitor ripple voltage of the cells in this converter is reduced only by injecting high frequency circulating current between the arms. In the conventional control method of this converter, the circulating current component is injected with the aim of complete elimination of the voltage ripple at low frequencies, which leads to an unnecessary increase of the current amplitude in the converter arms. In this paper, the converter control system is modified by finding the relationship between the cell capacitor voltage ripple and the high frequency circulating current amplitude. Then, by injecting the appropriate amplitude of the circulating current, the voltage ripple is controlled in an acceptable range. It is shown that by partial compensation (instead of full elimination of the voltage ripple), in addition to reducing the amplitude of the arm currents, the losses of the electrical system are significantly reduced. The results of simulations and experiments confirm the successful performance of the proposed method.
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