# Quasi-Z Source T-Type Power Converter for PV Based Commercial and Industrial Nanogrids with Active Functions Strategy

^{1}

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## Abstract

**:**

## 1. Introduction

- The integration of PV inverters, based on a three-phase Quasi-Z-Source Three-Level T-Type topology as part of a PV based commercial and industrial nanogrid. The control strategy (i) integrates several functions so far partially implemented on this specific power topology [22,24]: active and reactive power control and harmonics and imbalance mitigation; (ii) propose a collaborative operation between inverters inside the CIN and (iii) in any case, working well under distorted and unbalanced grid voltage, extending the achievements reported in [26].
- The control approach is straightforward and can achieve optimized injection of PV power into the grid, reactive power compensation, and harmonic and imbalance mitigation, in a coordinated or independent manner. Even more, the AC/DC converters from PV, which includes the DC link capacitors, are suitable to be used as active filters even when there is no solar irradiation. The idea tries to take maximum advantage of power electronics equipment, regardless of the process they are involved in.

## 2. Power Structure and Control System

#### 2.1. Topology

#### 2.2. Proposed Control Strategy

#### 2.2.1. Active Power Control (P Mode)

#### 2.2.2. Reactive Power Control (Q Mode)

#### 2.2.3. Load Current Harmonics and Imbalance Reduction (HI Mode)

#### 2.3. Current Controller and Modulation Method

#### 2.4. DC Bus Voltage Regulation

## 3. Simulation Results and Analysis

- Case A. PV voltage set to ${U}_{PV}$= 1060 V. MPPT mode. Injecting active power close to rated power and no reactive power: ${P}^{*}$ = 50 kW; ${Q}_{1}^{*}$= 0. CIN load without harmonics nor imbalance.
- Case B. PV voltage set to ${U}_{PV}$ = 850 V. RPPT mode. Injecting active and reactive power: ${P}^{*}$ = 45 kW; ${Q}_{1}^{*}$ = 21.7 kVAr. CIN’s load without harmonics nor imbalance.
- Case C. PV voltage set to ${U}_{PV}$ = 850 V. RPPT mode. Injecting active and reactive power: ${P}^{*}$ = 45 kW; ${Q}_{1\text{}}^{*}$= 15 kVAr. CIN’s load with odd harmonic currents up to 9th order as the maximum established by the IEC TS 61000-3-4 standard [40]. Harmonic and imbalance content are shown in Table 3. For this load, the RMS value of the equivalent current, calculated according to Std. IEEE-1459:2010 [41] is ${I}_{Le}=31.53\text{}\mathrm{A}$. The HI compensation function is not activated.
- Case D. PV voltage set to ${U}_{PV}$ = 850 V. RPPT mode. Injecting active and reactive power: ${P}^{*}$ = 45 kW; ${Q}_{1}^{*}$ = 15 kVAR. Harmonic and unbalanced content of CIN’s load as in case C. The HI compensation function is activated.
- Case E. PV voltage set to ${U}_{PV}$ = 850 V. RPPT mode. Injecting active and reactive power: ${P}^{*}$ = 45 kW; ${Q}_{1}^{*}$ = 21.7 kVAr. Harmonic and unbalanced content of CIN’s load as in cases C and D. The HI compensation function is activated.

_{1}in kVAr, non-active power N in kVA, the power factor PF, and the displacement power factor dPF.

## 4. Conclusions

## Author Contributions

## Funding

## Conflicts of Interest

## References

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**Figure 2.**Three-phase topology for one PV inverter (PVI) and the assigned fraction of the facility’s unbalanced and non-linear loads.

**Figure 5.**Switching signal generation with the level-shifted Pulse Width Modulation (LS-PWM) in phase disposition with the constant boost control (CBC) scheme.

**Figure 6.**Simulation results. Case A. CIN setpoints (sent at t = 0.2 s): ${P}^{*}$ = 50 kW, ${Q}_{1}^{*}$ = 0. CIN load without harmonics nor imbalance: ${I}_{L}$ = 30 A. From left to right and top to bottom: grid voltages (${u}_{a},{u}_{b},{u}_{c})$ and grid currents (${i}_{ga},{i}_{gb},{i}_{gc})$; PVI output currents (${i}_{a},{i}_{b},{i}_{c})$; load currents (${i}_{La},{i}_{Lb},{i}_{Lc})$; phase-to-phase PVI output voltage before filtering (${u}_{{a}^{\prime}{b}^{\prime}}$ ); harmonics and imbalance compensation PVI reference currents (${i}_{HI,a}^{*},{i}_{HI,b}^{*},{i}_{HI,c}^{*});$ and PV voltage (${U}_{PV}$ ), DC-link voltage (${U}_{PN}$ ) and reference DC-link voltage (${\widehat{U}}_{PN}^{*}$ ).

**Figure 7.**Simulation results. Case B. ${P}^{*}$ = 45 kW, ${Q}_{1}^{*}$ = 21.7 kVAr. CIN load without harmonics. ${I}_{L}$ = 30 A. From left to right and top to bottom as in Figure 6.

**Figure 10.**Simulation results. Case E. ${P}^{*}$ = 45 kW and ${Q}_{1}^{*}$ = 21.7 kVAr. CIN load containing harmonic and unbalanced components as in Case D. From left to right and top to bottom as in Figure 6.

**Figure 11.**Behavior under changing setpoint conditions. From top to bottom: grid voltages (${u}_{a},{u}_{b},{u}_{c})$; grid currents (${i}_{ga},{i}_{gb},{i}_{gc})$; PVI output currents (${i}_{a},{i}_{b},{i}_{c})$; PV voltage (${U}_{PV}$ ), DC-link voltage (${U}_{PN})$; and phase-to-phase PVI output voltage before filtering (${u}_{{a}^{\prime}{b}^{\prime}}$ ).

Parameter | Value | Unit |
---|---|---|

Inductors ${L}_{1}\dots {L}_{4}$ | $0.5$ | mH |

Capacitors ${C}_{1}\dots {C}_{4}$ | $2.2$ | mF |

Output Filter ${L}_{f}$ | $0.75$ | mH |

PV voltage ${U}_{PV}$ | $800\u20131100$ | V |

Output voltage (phase-to-neutral) ${U}_{g}$ | $230$ | V |

${K}_{L}$ and ${K}_{C}$ | 0.05 | p.u. |

${U}_{inv}({h}_{sw})$ | 0.05 | p.u. |

$TH{D}_{I}$ | 0.05 | p.u. |

Rated output power ${P}_{out}$ | 50 | kW |

Voltage Harmonic Distortion (%) | Voltage THD (%) | ${\mathit{U}}^{-}/{\mathit{U}}^{+}$ | ${\mathit{U}}^{0}/{\mathit{U}}^{+}$ | ||
---|---|---|---|---|---|

HD3 | HD5 | HD7 | (%) | (%) | |

5 | 4.5 | 4 | 7.83 | 2 | 2 |

Individual Harmonic Distortion (% Respect to the Positive-Sequence Fundamental Component) | Total Harmonic Distortion THD (%) | $\begin{array}{c}{\mathit{I}}^{-}/{\mathit{I}}^{+}\\ (\%)\end{array}$ | $\begin{array}{c}{\mathit{I}}^{0}/{\mathit{I}}^{+}\\ (\%)\end{array}$ | |||
---|---|---|---|---|---|---|

HD3 | HD5 | HD7 | HD9 | |||

21.6 | 10.7 | 7.2 | 3.8 | 25.44 | 10 | 10 |

Current | Harmonics | Imbalance | |||||||
---|---|---|---|---|---|---|---|---|---|

${\mathit{I}}_{1}$$\text{}(\mathbf{A})$ | ${\mathit{I}}_{3}$$\text{}(\mathbf{A})$ | ${\mathit{I}}_{5}$$\text{}(\mathbf{A})$ | ${\mathit{I}}_{7}$$\text{}(\mathbf{A})$ | ${\mathit{I}}_{9}$$\text{}(\mathbf{A})$ | $\mathit{I}$$\text{}(\mathbf{A})$ | THD (%) | ${\mathit{I}}^{-}$$\text{}(\mathbf{A})$ | ${\mathit{I}}^{0}$$\text{}(\mathbf{A})$ | |

${i}_{La}$ | 36 | 6.48 | 3.21 | 2.16 | 1.14 | 36.80 | 21.20 | 3 | 3 |

${i}_{Lb}$ | 27 | 6.48 | 3.21 | 2.16 | 1.14 | 28.06 | 28.27 | ||

${i}_{Lc}$ | 27 | 6.48 | 3.21 | 2.16 | 1.14 | 28.06 | 28.27 | ||

${i}_{ga}$ | 37.59 | 7.02 | 3.66 | 2.54 | 1.16 | 38.56 | 22.92 | 3.26 | 3.19 |

${i}_{gb}$ | 45.19 | 6.88 | 3.62 | 2.56 | 1.14 | 45.97 | 18.79 | ||

${i}_{gc}$ | 45.25 | 6.84 | 3.59 | 2.53 | 1.16 | 46.03 | 18.65 | ||

${i}_{a}$ | 68.59 | 0.54 | 0.45 | 0.38 | 0.02 | 68.61 | 3.04 | 0.26 | 0.19 |

${i}_{b}$ | 69.21 | 0.41 | 0.41 | 0.40 | 0.01 | 69.23 | 3.00 | ||

${i}_{c}$ | 69.25 | 0.36 | 0.38 | 0.37 | 0.04 | 69.27 | 2.97 |

Current | Harmonics | Imbalance | |||||||
---|---|---|---|---|---|---|---|---|---|

${\mathit{I}}_{1}$$\text{}(\mathbf{A})$ | ${\mathit{I}}_{3}$$\text{}(\mathbf{A})$ | ${\mathit{I}}_{5}$$\text{}(\mathbf{A})$ | ${\mathit{I}}_{7}$$\text{}(\mathbf{A})$ | ${\mathit{I}}_{9}$$\text{}(\mathbf{A})$ | $\mathit{I}$$\text{}(\mathbf{A})$ | THD (%) | ${\mathit{I}}^{-}$$\text{}(\mathbf{A})$ | ${\mathit{I}}^{0}$$\text{}(\mathbf{A})$ | |

${i}_{La}$ | 36 | 6.48 | 3.21 | 2.16 | 1.14 | 36.80 | 21.20 | 3 | 3 |

${i}_{Lb}$ | 27 | 6.48 | 3.21 | 2.16 | 1.14 | 28.06 | 28.27 | ||

${i}_{Lc}$ | 27 | 6.48 | 3.21 | 2.16 | 1.14 | 28.06 | 28.27 | ||

${i}_{ga}$ | 42.89 | 0.32 | 0.15 | 0.15 | 0.20 | 42.93 | 4.60 | 0.14 | 0.20 |

${i}_{gb}$ | 42.39 | 0.41 | 0.15 | 0.18 | 0.21 | 42.43 | 4.80 | ||

${i}_{gc}$ | 42.47 | 0.46 | 0.15 | 0.21 | 0.18 | 42.51 | 4.82 | ||

${i}_{a}$ | 74.96 | 6.72 | 3.17 | 2.10 | 1.29 | 75.39 | 10.75 | 3.13 | 3.20 |

${i}_{b}$ | 66.04 | 6.88 | 3.20 | 2.05 | 1.31 | 66.54 | 12.43 | ||

${i}_{c}$ | 66.10 | 6.88 | 3.18 | 2.06 | 1.28 | 66.60 | 12.41 |

Current | Harmonics | Imbalance | |||||||
---|---|---|---|---|---|---|---|---|---|

${\mathit{I}}_{1}$$\text{}(\mathbf{A})$ | ${\mathit{I}}_{3}$$\text{}(\mathbf{A})$ | ${\mathit{I}}_{5}$$\text{}(\mathbf{A})$ | ${\mathit{I}}_{7}$$\text{}(\mathbf{A})$ | ${\mathit{I}}_{9}$$\text{}(\mathbf{A})$ | $\mathit{I}$$\text{}(\mathbf{A})$ | THD (%) | ${\mathit{I}}^{-}$$\text{}(\mathbf{A})$ | ${\mathit{I}}^{0}$$\text{}(\mathbf{A})$ | |

${i}_{La}$ | 36 | 6.48 | 3.21 | 2.16 | 1.14 | 36.80 | 21.20 | 3 | 3 |

${i}_{Lb}$ | 27 | 6.48 | 3.21 | 2.16 | 1.14 | 28.06 | 28.27 | ||

${i}_{Lc}$ | 27 | 6.48 | 3.21 | 2.16 | 1.14 | 28.06 | 28.27 | ||

${i}_{ga}$ | 48.32 | 2.51 | 1.41 | 0.98 | 0.41 | 48.45 | 7.49 | 1.19 | 1.09 |

${i}_{gb}$ | 50.50 | 2.35 | 1.34 | 1.03 | 0.36 | 50.62 | 6.95 | ||

${i}_{gc}$ | 50.56 | 2.37 | 1.42 | 1.09 | 0.39 | 50.68 | 7.07 | ||

${i}_{a}$ | 76.91 | 3.97 | 1.80 | 1.18 | 0.75 | 77.06 | 6.46 | 1.81 | 1.91 |

${i}_{b}$ | 71.97 | 4.13 | 1.89 | 1.14 | 0.79 | 72.15 | 7.13 | ||

${i}_{c}$ | 71.98 | 4.12 | 1.79 | 1.08 | 0.76 | 72.15 | 7.05 |

Cases | S (kVA) | P (kW) | ${\mathit{Q}}_{1}$ (kVAr) | N (kVA) | PF | dPF |
---|---|---|---|---|---|---|

$\mathrm{A}$ | 50.48 | 50.09 | 0.757 | 6.28 | 0.99 | 0.99 |

$\mathrm{B}$ | 51.03 | 44.13 | 25.07 | 25.62 | 0.86 | 0.87 |

$\mathrm{C}$ | 47.86 | 44.22 | 17.55 | 18.30 | 0.92 | 0.93 |

$\mathrm{D}$ | 49.13 | 44.73 | 17.54 | 20.25 | 0.91 | 0.93 |

$\mathrm{E}$ | 51.45 | 44.40 | 25.08 | 26.00 | 0.86 | 0.87 |

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**MDPI and ACS Style**

Barrero-González, F.; Roncero-Clemente, C.; Milanés-Montero, M.I.; González-Romera, E.; Romero-Cadaval, E.; Husev, O.
Quasi-Z Source T-Type Power Converter for PV Based Commercial and Industrial Nanogrids with Active Functions Strategy. *Electronics* **2020**, *9*, 1233.
https://doi.org/10.3390/electronics9081233

**AMA Style**

Barrero-González F, Roncero-Clemente C, Milanés-Montero MI, González-Romera E, Romero-Cadaval E, Husev O.
Quasi-Z Source T-Type Power Converter for PV Based Commercial and Industrial Nanogrids with Active Functions Strategy. *Electronics*. 2020; 9(8):1233.
https://doi.org/10.3390/electronics9081233

**Chicago/Turabian Style**

Barrero-González, Fermín, Carlos Roncero-Clemente, María Isabel Milanés-Montero, Eva González-Romera, Enrique Romero-Cadaval, and Oleksandr Husev.
2020. "Quasi-Z Source T-Type Power Converter for PV Based Commercial and Industrial Nanogrids with Active Functions Strategy" *Electronics* 9, no. 8: 1233.
https://doi.org/10.3390/electronics9081233