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With the above value of GV, the output impedance becomes capacitive. So, by selection of proper control loop and control parameter, the shaping of inverter output impedance can be effectively done. Also, the desired value of damping can be achieved. This method is known as active damping method. Like this, the

The characteristics and response of impedance of grid-connected inverter depend on various factors like selection of output filter and its parameter, controller type and its parameters, structure of PLL, the delay in switching of converter, etc. In this chapter, using first-order PI controller and different controller types, it is explained in a simple way. The complexity of impedance increases with the order of the controller and its structure. Also, the reshaping of inverter impedance can be done by selection of suitable control structure. By adding virtual impedance, the output impedance can be made inductive, capacitive or reactive without adding any additional hardware. In this work different variants of passive filter are explained, and how their output impedance behaves at different frequency is also explained with the use of Nyquist plot. The active damping method is explained, whereby damping is achieved without using resistor in the filter, which is considered as a very energy-efficient method of achieving damping. The output impedance can be reshaped either by external hardware in the form of filter or by adding virtual control loop in the controller. The stability of converter depends on how converter output impedance interacts with the grid impedance. Numerous efforts have been made and can be found in literatures to achieve the stability only by reshaping the impedance. However, the stability region can be expanded by reshaping of impedance up to a certain extent only. Only reshaping of impedance does not guarantee the converter stability with changing grid condition. Also, the converter is more likely to fall in an unstable region with weak grid condition, but reshaping of impedance helps to prevent converter-based generation from going unstable. By analysing the output impedance in the frequency domain, the controller parameters can be adjusted to reshape the output impedance. By increasing the proportional gain of the PI controller, the magnitude of the output impedance can be increased and can enhance the ability of harmonic rejection. By increasing the integral gain of the PI controller, the phase of the output impedance can be increased to improve

Switching frequency 4 kHz Switching delay 20 μS Lc 4 mH Lg 0.4 mH Cf 5 μF kp 1.2 ki 11.6

inverter can be made either L-type or R-type.

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the stability of the system [19, 20] (Table 1).

Table 1.

88

Converter parameter.

8. Conclusion

Jignesh Pravinbhai Patel and Satish Kantilal Joshi\* Department of Electrical Engineering, The Maharaja Sayajirao University of Baroda, Vadodara, Gujarat, India

\*Address all correspondence to: skjoshi@ieee.org

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
