Flexible Compensation of Voltage and Current Unbalance and Harmonics in Microgrids
Abstract
:1. Introduction
- Simultaneous control of fundamental positive and negative sequences, as well as harmonic components of voltage and current, is achieved for three-phase DG-interfacing inverters.
- A flexible voltage or current compensation of nonlinear and unbalanced loads is proposed.
- The proposed method is applicable in both grid-connected and islanded modes of three-phase MGs.
- Four unbalanced and harmonic voltage or current compensation strategies can be achieved using this method.
2. Control Approach for DG-Interface Inverter
2.1. Power Control and Virtual Impedance
2.2. Proposed Flexible Controller for Unbalance and Harmonic Compensation
- Mode 1—unbalance and harmonic compensation of Point of Common Coupling (PCC) voltage (VPCC): in this mode, the unbalance and harmonic voltage compensation is achieved by using the following equation as input of flexible power quality controller (FPQC):
- Mode 2—unbalance and harmonic compensation of DG output voltage (VC): The capacitor voltage will be balanced if the (0-VC,αβ) is applied as the input of FPQC. The unbalance and harmonic compensation of VC is obtained by injecting FNS&H sequences of VC; hence, the performance of the inverter acts in voltage controlled mode (VCM) in FNS&H sequences. The compensation is important when a sensitive load is connected near the DG. The selection of Modes 1 or 2 is dependent on the location of the sensitive load.
- Mode 3—local unbalanced and nonlinear loads compensation: in this mode, the aim of the compensation is the unbalance and harmonic compensations of MG-injected current (Iinj). Using (Ilcaoal-I2) as input of FPQC, the multifunctional inverter acts as an active filter in negative and harmonic sequences, therefore, the FNS&H parts of unbalanced and nonlinear loads are supplied by the DG-interfacing inverter and Iinj will be balanced. The mode can be activated when there is a limitation for the unbalance and harmonics current of an MG, since each system has limitations in harmonic and unbalance injections according to IEEE 519 and EN 50160 standards.
- Mode 4—the output current compensation of DG unit (I2): in this mode, which is called the unbalance and harmonics rejection mode, the output current of DG will be compensated. This mode is important when the DG delivers maximum power to the grid, and injection of unbalance and harmonics current can increase the current of one/two phase(s) higher than the rated one.
3. Control System Design
4. Simulation Results
4.1. Grid-Connected Operation
- Step 1 (0 s ≤ t < 3.5 s): activation of Mode 1 for VPCC compensation.
- Step 2 (3.5 s ≤ t < 6.5 s): activation of Mode 2 for VC compensation.
- Step 3 (6.5 s ≤ t < 9.5 s): activation of Mode 3 for Iinj compensation.
- Step 4 (9.5 s ≤ t < 12.5 s): activation of Mode 4 for IDG compensation.
- Step 5 (12.5 s ≤ t < 16 s): disabling the harmonic and unbalance compensation (no compensation).
4.2. Islanded Operation of the MG
- Mode X: unbalance and harmonic compensation of PCC.
- Mode Y: unbalance and harmonic compensation of VC.
- ✓
- Step I:
- ✓
- Step II:
- ✓
- Step III:
- ✓
- Step IV:
5. Conclusions
Author Contributions
Conflicts of Interest
References
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DC Link Voltage | LCL Filter (L1/C/L2) | Voltage/Frequency | ||||
---|---|---|---|---|---|---|
650 V | 2.5 mH/20 μF/1.5 Mh | 230 V/50 Hz | ||||
Nonlinear load | Line impedance | Unbalanced linear local and PCC load | ||||
CNL (μF) | RNL (Ω) | LNL (mH) | ZLG (Ω) | Runb (Ω) | ||
235 | 114 | 0.084 | 0.95j + 1 | 20 | ||
active and reactive power powers refrence power | Switching frequency | Pulse Width modulatin (PWM) delay | ||||
Active power reference | Reactive power reference | fs | Ts | |||
20 kW | 5 kVAR | 10 kHz | 100 μs | |||
Parameters of controller | ||||||
Active power droop coefficients | Reactive power droop coefficients | |||||
mP | mI | nP | nI | |||
1 × 10−5 rad·s−1 | 1 × 10−4 ω | 0.05 | 0.1 | |||
Voltage and current controllers parameters | ||||||
KV | KUUC | KI,3/KI,5/KI,7 | KP | KD | ||
4 | 700 | 500/300/300 | 4 | 20 | ||
Virtual admittance for harmonic and unbalance compensation | Virtual impedance for fundamental component | |||||
G− | Gh | Rv | Lv | |||
25 Ω−1 | 1 Ω−1 | 0.1 Ω | 2 mH |
Harmonics | VPCC | VC | IDG | Iinj | |||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Steps | H3− | H3+ | H5− | H5+ | H3− | H3+ | H5− | H5+ | H3− | H3+ | H5− | H5+ | H3− | H3+ | H5− | H5+ | |
Step 1 | 1.1 | 1 | 0.8 | 0.8 | 2.1 | 2.1 | 2.2 | 2.15 | 8 | 7.5 | 5.5 | 5.25 | 5 | 4.9 | 3.75 | 3.5 | |
Step 2 | 1.5 | 1.3 | 1.5 | 1.2 | 0.05 | 0.05 | 0.05 | 0.03 | 6 | 5.5 | 3.85 | 3.25 | 2.2 | 2 | 1.5 | 1 | |
Step 3 | 2.2 | 1.75 | 2 | 1.55 | 1.5 | 1.05 | 1.15 | 0.9 | 4.2 | 3.8 | 2.3 | 1.9 | 0.3 | 0.2 | 0.2 | 0.2 | |
Step 4 | 3.75 | 2.8 | 2.8 | 2 | 3.8 | 3 | 2.85 | 2 | 0.15 | 0.08 | 0.1 | 0.1 | 5.3 | 4.15 | 2.5 | 1.75 | |
Step 5 | 3.3 | 2.6 | 2.5 | 2 | 3.15 | 2.7 | 2.3 | 2 | 1.75 | 1.4 | 1.3 | 1 | 4 | 2.9 | 1.85 | 1.6 |
DC Link Voltage | LCL Filter (L1/C/L2) for Both DGs | Voltage/Frequency | |||
---|---|---|---|---|---|
650 V | 2.5 mH/20 μF/1.5 mH | 230 V/50 Hz | |||
Nonlinear load | Line impedance for both DGs | Unbalanced linear local and PCC load | |||
CNL (μF) | RNL (Ω) | LNL (mH) | ZLG (Ω) | ZL (Ω) | |
235 | 114 | 0.084 | 0.95j + 1 | 40/20 | |
Parameter of controller | |||||
Active power droops coefficients | Reactive power droops coefficients | ||||
mP | mI | nP | nI | ||
1 × 10−5 rad·s−1 | 1 × 10−4 | 0.05 | 0 | ||
Voltage and current controllers parameters | |||||
KV | KUUC | KI,3/KI,5/KI,7 | KP | KD | |
4 | 700 | 500/300/300 | 4 | 20 | |
Virtual admittance for harmonics and unbalance compensation | Virtual impedance for fundamental component | ||||
G− | Gh | Rv | Lv | ||
1.8 Ω−1 | 0.8 Ω−1 | 0.1 Ω | 2 mH |
Harmonics | VPCC | VC1 | VC2 | ||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Steps | H3− | H3+ | H5− | H5+ | H3− | H3+ | H5− | H5+ | H3− | H3+ | H5− | H5+ | |
Step I | 0.65 | 0.65 | 0.45 | 0.45 | 1.1 | 0.95 | 1.05 | 1.03 | 1 | 0.95 | 1.05 | 1.04 | |
Step II | 1.05 | 1 | 1 | 0.95 | 0.02 | 0.042 | 0.013 | 0.02 | 0.015 | 0.04 | 0.015 | 0.015 | |
Step III | 1.1 | 1.05 | 1.05 | 0.9 | 0.025 | 0.05 | 0.018 | 0.03 | 0.02 | 0.05 | 0.02 | 0.025 | |
Step IV | 4 | 1 | 1.2 | 1.6 | 3.3 | 3 | 0.6 | 1.05 | 3.3 | 3 | 0.6 | 1.5 |
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Mousazadeh Mousavi, S.Y.; Jalilian, A.; Savaghebi, M.; Guerrero, J.M. Flexible Compensation of Voltage and Current Unbalance and Harmonics in Microgrids. Energies 2017, 10, 1568. https://doi.org/10.3390/en10101568
Mousazadeh Mousavi SY, Jalilian A, Savaghebi M, Guerrero JM. Flexible Compensation of Voltage and Current Unbalance and Harmonics in Microgrids. Energies. 2017; 10(10):1568. https://doi.org/10.3390/en10101568
Chicago/Turabian StyleMousazadeh Mousavi, Seyyed Yousef, Alireza Jalilian, Mehdi Savaghebi, and Josep M. Guerrero. 2017. "Flexible Compensation of Voltage and Current Unbalance and Harmonics in Microgrids" Energies 10, no. 10: 1568. https://doi.org/10.3390/en10101568