Reinforced Droop for Active Current Sharing in Parallel NPC Inverter for Islanded AC Microgrid Application
Abstract
:1. Introduction
- The droop function enables to share current accurately with both linear and nonlinear loads;
- The cascaded control loop improves the system dynamics;
- Robustness of the system is achieved;
- Performance analysis of NPC inverter with droop control is investigated.
2. System Model and Cross Current Analysis in Islanded Microgrid
2.1. Circulating Current Analysis of Parallel NPC Inverter
2.2. Conventional Droop Analysis
3. Proposed Reinforced Multi Loop Control Strategy
3.1. Reinforced Droop
3.2. Multi Loop Feedback Control
4. Results and Discussion
4.1. Simulation Results
4.1.1. Under Linear Load Conditions
4.1.2. Under Non-Linear Load Conditions
4.2. Experimental Validation
4.2.1. Experimental Setup
4.2.2. Under Linear Load Conditions
4.2.3. Under Non-Linear Load Conditions
4.3. Performance Analysis of NPC Inverter
5. Conclusions
Author Contributions
Funding
Conflicts of Interest
References
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Description | Parameter | Value |
---|---|---|
Nominal Voltage | E0l-l | 208 Vl-l(V)(rms) |
Filter parameters | Lf, Cf | 5 mH, 50 µF |
Line resistance | Rl1, Rl2 | 1, 1.2 ohms |
Switching frequency | fs | 5 kHz |
Droop Coefficient | mp1, mp2 | 0.0012, 0.00168 |
Linear Load current | IL | 3 A(rms) Maximum |
Nonlinear Load current | IL | 3 A(rms) |
Cut off frequency | Fcutoff | 2 kHz |
DC Droop correction | Kcr | 0.35 |
Voltage Compensation | Kp, Ki | 0.02, 0.5 |
Multi loop- Voltage PR controller | Kpv, Kiv | 0.68, 100 |
Multi loop current P control | Kp | 1.36 |
The feedback resistance | Rci | 1 (Since the rating of inverters are identical) |
Load Type | ILa1—Output Current of Inverter-1 in A (pk-pk) | ILa2—Output Current of Inverter-2 in A (pk-pk) | ILoada—Total Load Current at the Common Bus in A (pk-pk) | Pictorial Depiction | Inference | |
---|---|---|---|---|---|---|
Linear Load | Steady state operation with constant load | 1.75 | 1.75 | 3.5 | Figure 21 | Accurate current sharing is achieved |
Transient operation with constant load | 1.8 | 1.75 | 3.5 | Figure 22 | When inverter -2 is switched on at 500 ms, the current sharing is achieved much accurately in less than 50 ms | |
Parallel operation for step change in load | 2.1 | 2.1 | 4.2 | Figure 24, | For increment of load current from 3.2 to 4.2 A, the rapid and accurate current sharing is achieved | |
1.6 | 1.6 | 3.2 | Figure 25 | For a decrement of load current, rapid sharing is achieved | ||
Nonlinear Load | Steady state operation with constant load | 2.75 | 2.8 | 5.56 | Figure 27 | Accurate current sharing is achieved with 6.3% of total harmonic distortion |
Transient operation with constant load | 2.8 | 2.75 | 5.56 | Figure 28, Figure 29 and Figure 30 | For Sudden momentary switching of inverter, accurate current sharing is achieved and the system retains its stability in less than 50 ms. |
Validation Type | Control Strategy | Output Current in the System | Percentage of Current Sharing Error (%) | ||
---|---|---|---|---|---|
ILa1—Output Current of Inverter-1 in A (pk-pk) | ILa2—Output Current of Inverter-2 in A (pk-pk) | ILoada—Total Load Current at the Common Bus in A (pk-pk) | |||
Simulation by MATLAB | Conventional droop method | 2.0 | 1.6 | 3.6 | 11 |
Proposed reinforced droop method | 1.8 | 1.76 | 3.6 | 1.2 | |
Real time Validation | Conventional droop method | 1.95 | 1.6 | 3.55 | 11.2 |
Proposed reinforced droop | 1.8 | 1.75 | 3.55 | 1.4 |
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Purushotham, M.; Muniswamy, K. Reinforced Droop for Active Current Sharing in Parallel NPC Inverter for Islanded AC Microgrid Application. Energies 2019, 12, 3090. https://doi.org/10.3390/en12163090
Purushotham M, Muniswamy K. Reinforced Droop for Active Current Sharing in Parallel NPC Inverter for Islanded AC Microgrid Application. Energies. 2019; 12(16):3090. https://doi.org/10.3390/en12163090
Chicago/Turabian StylePurushotham, Monica, and Kowsalya Muniswamy. 2019. "Reinforced Droop for Active Current Sharing in Parallel NPC Inverter for Islanded AC Microgrid Application" Energies 12, no. 16: 3090. https://doi.org/10.3390/en12163090
APA StylePurushotham, M., & Muniswamy, K. (2019). Reinforced Droop for Active Current Sharing in Parallel NPC Inverter for Islanded AC Microgrid Application. Energies, 12(16), 3090. https://doi.org/10.3390/en12163090