June-Hee Lee, “고효율 태양광 마이크로인버터 시스템의 제어기 설계,” 아주대학교 공학박사 학위 논문, 2018. > Paper

This paper proposes the design and control methods for photovoltaic microinverter systems. The microinverter is a type of photovoltaic

inverter that can be attached to individual solar panels behind the railing at the array area. The microinverter offers a much more

generation efficiency because it is connected to each separate solar panel. Therefore, the other solar panels not affected by shade or

debris can still produce maximum power. In comparison, the central photovoltaic inverter is paired together so if shade or debris is on

just one solar panel, the output power of the entire inverter can be dramatically decreased. Two studies for the design and control of

the miciroinverter are contained in this paper: sensorless maximum power point traking (MPPT) method and dead-beat control (DBC)

for the high efficiency microinverter. Firstly, this paper proposes a current sensorless MPPT control method for the microinverter system.

The conventional MPPT control method is essential in photovoltaic power generation systems. After obtaining the value from many

sensors, the system operates the P&O MPPT control method. At this time, the expensive isolated voltage and current sensor are used

in the microinverter system. In a small photovoltaic power generation system, the cost and size of the microinverter are important

factors to compete other products. Therefore, by reducing the number of parts, for example the input current sensor, the system

advantage is a smaller size and a lower cost. Secondly, this paper proposes a method to reduce the distortion of the grid current using

a DBC method for bridgeless inverter systems. In the case of the general PI current controller for power factor correction (PFC) scheme,

the grid current is generally distorted due to the slow dynamic response of the PI controller. The PI current controller is affected by

the bandwidth. If the bandwidth of the PI controller increases to improve the dynamic response, the PI controller performs a fast

dynamic response, but it becomes unstable because the wide bandwidth leads to the control of unnecessary values such as a grid

current noise. However, the proposed PFC-DBC method has a fast response for the reference current and accuracy compared to the

conventional PFC-PI controller due to the optimal duty cycle for the next state reference current value. In addition, since the inaccurate

system modeling due to the mismatch in parameter, the proposed PFC-DBC controller can be unstable state. In this paper,

the proposed PFC-DBC method can operate robust control by using the estimation method for actual filter inductance. The

simulations are carried out to verify the effectiveness of the proposed methods: sensorless MPPT method and PFC-DBC method for

the high efficiency microinverter. Moreover, the experiments are carried out to verify the performance and effectiveness of the

proposed methods on a 110 [W] prototype current-fed microinverter and 300 [W] voltage-fed microinverter.