Quasi-Z-source inverter (qZSI) is a new promising power conversion technology perfectly suitable for interfacing of renewable (i.e., photovoltaic, wind turbines) and alternative (i.e., fuel cells) energy sources [1-3]. The qZSI has the following advantages: 1. Boost-buck function by the one-stage conversion; 2. Continuous input current (input current never drops to zero, thus featuring the reduced stress of the input voltage source, which is especially topical in such demanding applications as power conditioners for fuel cells and solar panels); 3. Excellent reliability due to the shoot-through withstanding capability; 4. Low or no in-rush current during start up; 5. Low common-mode noise. However, the efficiency and voltage gain of the qZSI are limited and comparable with the conventional system of a voltage source inverter with the auxiliary step-up DC/DC converter in the input stage [4]. The concept of extending the qZSI gain without increasing the number of active switches was recently proposed by several authors [5-8]. These new converter topologies are commonly referred to as the extended boost qZSI or cascaded qZSI and could be generally classified as capacitor assisted and diode assisted topologies [5]. In this paper different extended boost qZSIs with continuous input current will be presented, analyzed and compared. Moreover, some problematic issues of these converters will be pointed out and discussed.
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