Subhajyoti Mukherjee

Control of a Single-Phase Standalone Inverter Without an Output Voltage Sensor

This paper analyzes the possibility of controlling the output voltage of a standalone single-phase inverter by directly controlling the output filter capacitor current without using a dedicated output voltage sensor. The plant modeling and controller design are presented. The proposed method depends on having the value of the output filter capacitance. A method to estimate the output filter capacitance is also presented. Rigorous analysis is done to show that the proposed sensorless scheme is largely insensitive to parameter variations and ensure that the output voltage is within specified regulations at utility level. It is also demonstrated in this paper that compared to the conventional voltage control scheme the proposed control scheme ensures an improved total harmonic distortion of the output voltage waveform. Experimental results presented validate the proposed scheme.

Grid Voltage Estimation and Current Control of a Single-Phase Grid-Connected Converter Without Grid Voltage Sensor

This paper investigates the possibility of estimating the grid voltage and controlling a single-phase grid-connected converter without a dedicated grid voltage sensor. The main focus is given to current-controlled architectures which need phase-locked loops (PLL) for their operation. The grid voltage estimation method is proposed based on the active and reactive power delivered by the converter to the grid. In addition to the estimation of the grid voltage, the proposed method also generates the unit vectors and frequency information similar to a conventional PLL structure. The influence of various parameters like the dead time, equivalent loss resistance, and the filter inductance on the proposed estimation method is studied in details. Experimental results validate the feasibility of the proposed scheme.

Impedance shaping for improved load sharing among inverters in AC microgrids

In this paper, a control scheme to improve load sharing among inverters of different power ratings in an ac microgrid is proposed. The proposed control scheme shapes the output impedance of the inverters independent of the voltage controller parameters and minimizes the requirement of the virtual impedance for proper load sharing. Results show that system stability improves. Simulation and experimental results presented show the effectiveness of the scheme.

Power-Angle Synchronization for Grid-Connected Converter With Fault Ride-Through Capability for Low-Voltage Grids

In this paper, the power-angle synchronization control of a grid-tied bidirectional dc–ac converter is investigated for low-voltage grids. The power flow equations for the low-voltage grid are analyzed and compensators are designed to ensure the decoupled control of active and reactive power. The proposed control system operates without the need for a phase-locked loop during balanced and unbalanced grid conditions. It is shown that during balanced conditions the compensators ensure stable operation controlling the desired power flow to and from the grid. It is also demonstrated that the compensators are immune to grid fluctuations and to a large extent can cater grid unbalanced conditions. Experimental results verify the performance of the proposed control scheme.

An improved control scheme for stand-alone inverters in the stationary frame of reference with a zero sequence controller

In this paper, a control scheme for stand-alone voltage source inverters using resonant controllers in the 2-phase stationary frame of reference with a zero sequence controller is proposed. The proposed control scheme reduces the number of resonant controllers while achieves the same performance as existing control methods. The total harmonic distortion (THD) of the output voltage is improved over conventional control methods by using an improved feed-forward term. Experimental results presented show the effectiveness of the proposed scheme.

Filter capacitor current estimation and grid current control in LCL based grid connected inverter

The control of the grid side current in an LCL filter based grid connected converter is generally complex and involve multi loop structure. This paper presents a method to control the grid current indirectly by controlling the converter side current with compensation of the filter capacitor current. The proposed control algorithm uses only one current sensor to measure the converter side current. The filter capacitor current need to be estimated and an estimation method is presented to do the same. Simulation and experimental results are presented to confirm the feasibility of the proposed scheme.

Control of a three-phase inverter under unbalanced grid conditions

A control strategy for a three-phase grid connected inverter with LCL filter based on Lyapunov energy function during unbalanced grid conditions is presented in this paper. To reduce complexity and number of variables the control strategy is accomplished in a stationary two phase reference frame. Dual second-order generalized integrator structure (DSOGI) is utilized to extract the positive and negative sequence components of voltages and currents for unbalanced operation. A virtual resistor based active damping methodology based on indirect capacitor current feedback is employed to nullify the resonance oscillations due to the third order (LCL) filter. By using Lyapunov energy function based control, a direct grid current control architecture is achieved at the desired power factor.

Indirect voltage control of a stand-alone inverter

This paper discusses the control of the output voltage of a stand-alone single-phase inverter by directly controlling the output filter capacitor current. Compared to the conventional voltage control scheme, the proposed control approach has the potential of achieving higher bandwidth and hence improved total harmonic distortion (THD) of the output voltage. The proposed method depends on the value of the output filter capacitance. A method to estimate the output filter capacitor based on a rms control loop is also presented. Simulation and experimental results presented validate the proposed scheme.

Estimation of parameters in single phase grid connected and stand-alone inverter system

The control of single phase grid connected and stand-alone inverters are very important for power electronics and power systems applications. The controller design for each topology needs an accurate plant model. The plant model depends on the system parameters (equivalent loss resistance, filter inductance and capacitance) which are not fixed. This paper proposes model reference based adaptive control (MRAC) to estimate the system parameters for accurate plant modeling. Simulation and experimental results presented validate the proposed scheme.

Resonant controller based power-angle synchronization control in low voltage grids

In this paper, power-angle synchronization based control of grid connected converter is studied for low voltage grids under grid unbalanced conditions. The active and reactive power controllers used for power-angle synchronization are augmented with resonant peaks to suppress the oscillations in power under grid unbalanced conditions. The controller structure and design are presented. Simulation and experimental results presented validate the proposed scheme.