# Transient Response Improvement of Microgrids Exploiting the Inertia of a Doubly-Fed Induction Generator (DFIG)

^{*}

## Abstract

**:**

## 1. Introduction

## 2. Architecture of the Microgrid

#### 2.1. Description and Modeling of the Hybrid System

- Hydrogen supply system to the anode.
- Air supply system to the cathode.
- De-ionized water as a coolant.
- De-ionized water to the humidifier to humidify the membrane.

^{2 s.}In the fourth system, it is assumed that the membrane of the model is fully humidified as the membrane hydration has a transient phase of about 10 s. It must be mentioned that the air flow dynamics and the humidity management define the FCS response. By assuming that the membrane is fully humidified, the designed controller for the second subsystem can safely be decoupled from the humidity. Also, the “double-layer charging effect” has been neglected, taking into account that its time constant is almost 10

^{−19}seconds. The FCS is designed to be self‑powered, i.e., every auxiliary component of the FCS must be supplied by the FCS power, especially the air supply system. At the output of the FCS, the “Chopper 1” is connected so that the DC voltage is boosted and regulates the FCS’s output, without exceeding the FCS capabilities.

_{ο}, Κ, Q, A and B denote the non load voltage, the constant voltage, the polarization voltage, the battery capacity, the exponential voltage and the exponential capacity, respectively. The battery type is given in the appendix.

#### 2.2. Description and Modeling of the DFIG

_{p}the power coefficient of the wind turbine and β the pitch angle.

_{w}being the wind turbine rotor speed.

_{p}is defined as:

## 3. Fuzzy Controller Analysis

#### 3.1. Hybrid System Controller

_{O2}, which is the ratio of oxygen supplied to oxygen used in the cathode. The optimum value of λ

_{O2}is taken as equal to 2 where, for our chosen FCS, the net deliverable power is about maximum.

_{i}) of the PWM method. The value of m

_{i}is determined by the Fc4. The control of the reactive power is achieved through shifting the phase angle on the sinusoidal reference signal of the PWM method. The Fc5 determines the shift value.

#### 3.2. DFIG System Controller

_{meas}is driven to Fc3α, whose output is the q component of the reference value of the rotor current, I

_{qrref}. The reference value is compared to the measured q component of the rotor current and drives the Fc5α, whose output is the control signal Vrq.

_{o}, forming the reference value for active power P

_{ref}. It has to be clarified that the fuzzy controllers designed for both cases are the same. This is due to the fuzzy logic adaptive nature and the design of the controllers that decrease the step size in the search of the adequate output.

_{drref}. The deviation of the measured d component of the rotor current from the reference value drives the Fc5α whose output is the control signal Vrd.

**Figure 6.**(a) Active power control of the DFIG in study case with battery included (b) active power control of the DFIG in study case without battery.

_{meas}and the reference value (P

_{opt,ref}or P

_{ref}). The output of the Fc3a is the deviations of the q component of the reference value of the rotor current, ΔI

_{qrref}whose values are added together in every simulation step in order to comprise the I

_{qrref}value at steady state (in p.u.) according to the following equation:

**Figure 8.**(a) Membership functions of the input signal of Fc3a. (b) Membership functions of the output signal of Fc3a.

- ○
- When the measured active power at the output of the DFIG is less than the reference active power, it implies that the DFIG doesn’t deliver the needed power. In order that the DFIG delivers more power, the absolute value of the component of the reference value of the rotor current has to augment.
- ○
- When the measured active power at the output of the DFIG is equal to the reference active power, it implies that the DFIG delivers the needed power. So the absolute value of the component of the reference value of the rotor current has to be the same and the output of the Fc3a has to be zero.
- ○
- When the measured active power at the output of the DFIG is larger than the reference of the active power, it implies that the DFIG delivers more than the needed power. In order that the DFIG delivers less power the absolute value of the component of the reference value of the rotor current has to decrease.

Fc3a Input | POS | POS | POS | OK | NEG | NEG | NEG |

Fc3a Output | POS_H | POS_M | POS_L | OK | NEG_L | NEG_M | NEG_H |

## 4. Simulation Results

#### 4.1. System Performance with the Battery

**Figure 9.**(a) The recorded frequency at the PCC. (b) The recorded voltage at the PCC. (c) The DFIG active power delivered. (d) The FCS-battery active power delivered at the VSI output. (e) The battery bank current in steady state and transient period. (f) The kinetic energy of the WT.

#### 4.2. System Performance without the Battery.

#### 4.3. Results Discussion

**Figure 10.**(a) The recorded frequency at the PCC. (b) The recorded voltage at the PCC. (c) The DFIG active power delivered. (d) The FCS active power delivered at the VSI output. (e) The kinetic energy of the WT.

## 5. Conclusions

## Nomenclature

- c1 = 0.5176, c2 = 116, c3 = 0.4, c4 = 5, c5 = 21 και c6 = 0.0068.
- FCS PEM: 30 kW, 200 cells, 200 A, 150 V, 280 cm
^{2}/cell. - DFIG & turbine: The electric models parameters were adopted from SimPowerSystems library for a 100 hp induction generator and the corresponding wind turbine.
- Distribution lines: AAAC type (4*185), X(Ω/km) = 0.236, R(Ω/km) = 0.204
- AC system: 380 V, 50 Hz, base p.u.:100 kW, 380 V.
- R-L load1: 37 kW, 13 kVar, 380 V
- R-L load2: 36 kW, 10 kVar, 380 V
- Squirrel-Cage Induction Motor: 20 hp, 400 V, 50 Hz, 1460 rpm
- DC Motor: 5 hp, 500 V, 1750 rpm, field: 300 V
- Battery Bank: 234 HV Nickel-Metal Hybride cells of 1.2 V, 2 Ah, 280 V.
- Transformer: 50 kVA, 190:380 V, 50 Hz.

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**MDPI and ACS Style**

Papadimitriou, C.N.; Vovos, N.A.
Transient Response Improvement of Microgrids Exploiting the Inertia of a Doubly-Fed Induction Generator (DFIG). *Energies* **2010**, *3*, 1049-1066.
https://doi.org/10.3390/en30601049

**AMA Style**

Papadimitriou CN, Vovos NA.
Transient Response Improvement of Microgrids Exploiting the Inertia of a Doubly-Fed Induction Generator (DFIG). *Energies*. 2010; 3(6):1049-1066.
https://doi.org/10.3390/en30601049

**Chicago/Turabian Style**

Papadimitriou, Christina N., and Nicholas A. Vovos.
2010. "Transient Response Improvement of Microgrids Exploiting the Inertia of a Doubly-Fed Induction Generator (DFIG)" *Energies* 3, no. 6: 1049-1066.
https://doi.org/10.3390/en30601049