Sensor-Less Five-Level Packed U-Cell (PUC5) Inverter Operating in Stand-Alone and Grid-Connected Modes


In this paper a new mode of operation has been introduced for Packed U-Cell (PUC) inverter. A sensor-less voltage control based on redundant switching states is designed for the PUC5 inverter which is integrated into switching process. The sensor-less voltage control is in charge of fixing the DC capacitor voltage at half of the DC source value results in generating symmetric five-level voltage waveform at the output with low harmonic distortion. The sensor-less voltage regulator reduces the complexity of the control system which makes the proposed converter appealing for industrial applications.


An external current controller has been applied for grid-connected application of the introduced sensor-less PUC5 to inject active and reactive power from inverter to the grid with arbitrary power factor while the PUC auxiliary DC bus is regulated only by sensor-less controller combined with new switching pattern. Experimental results obtained in stand-alone and grid-connected operating modes of proposed PUC5 inverter prove the fast response and good dynamic performance of the designed sensorless voltage control in balancing the DC capacitor voltage at desired level.


  1. Multilevel Inverter
  2. Packed U-Cell
  3. Sensor-Less Voltage Regulator
  4. PUC5
  5. 5-Level Inverter
  6. Power Quality



Fig. 1: PUC inverter topology


Fig. 2: start-up capacitor charging, 5-level voltage generating and FFT Analysis

Fig 3: adding single-phase rectifier (as nonlinear load) paralleled with the RL load to the output of PUC5

Fig. 4: DC source voltage changes and capacitor voltage is tracking the reference value

Fig. 5: switches gate pulses

Fig. 6: grid-connected PUC5 with change in current reference amplitude

Fig. 7: THD, and Crest factor computation of injected grid current

Fig. 8: PUC5 inverter operation at different power factors a) PF = 0.86, _ = 30° b) PF = 0.86, _ = 60°


The PUC5 inverter has been proposed in this paper while the capacitor voltage is balanced without involving any external controller and voltage feedback sensors. The proposed sensor-less voltage controller has been integrated into switching technique to work as open-loop system with reliable results. Moreover, another controller has been designed for the PUC5 inverter to work as unity power factor grid-connected inverter.


Low harmonics components in both voltage and current waveforms generated by PUC5, no need to bulky output filters, reliable and good dynamic performance in variable conditions (including change in DC source, load, power amount injected to the grid), requiring no voltage/current sensor in stand-alone mode


low manufacturing costs and miniaturized package due to using less components and etc are interesting advantages of the introduced PUC5 topology which have been proved by experimental results in both stand-alone and grid-connected modes. The presented PUC5 inverter can be a challenging candidate for conventional photovoltaic application inverters.


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