^{1}

^{1}

^{1}

Renewable power generation is a suitable technology used to deliver energy locally to customers especially in remote regions. Wind energy based on induction generator situates in a foreground position in the total energy produced using renewable sources. In the last few decades, a new self- excitation generator was based on multi-stator induction strongly emerges. This article presents a systematic modelling, a detailed analysis and the performance analysis of self-excitation dual stator winding induction generator (SE-DSWIG). The modelling of the SE-DSWIG was done with taking in account the common mutual leakage inductance between stators and the magnetizing inductance, which played a principal role in the stabilization of the output voltage in the steady state. The generator feeds the end user emulated by an inductive-resistive load. In order to simulate the weather conditions’ variation, a step change of the prime mover speed was applied on the SE-DSWIG. A passive series and shunt compensator was used to mitigate the voltage sag and swell appeared in the power system due to wind variation and the lack of reactive power consumed by the inductive load.

Nowadays, distributed generation systems (DGs) impose themselves as an attractive research area. According to a study done by the Electric Power Research Institute (EPRI), the distributed generation systems participated with 25% in the energy production by the end of 2010 [

In the last century, a new generation of self-excitation induction machine strongly emerged in AC applications. It constitutes of multi-stators topology. A self-excitation dual stator windings induction generator (SE- DSWIG) belongs to this category and it brings a lot of advantages compared to the traditional three-phase induction generator such as the minimization of rotor losses and torque ripples, the reduction of harmonic, reducing current without increasing voltage in each phase and the power segmentation [

The main drawback of the self-excitation induction generator in distributed generation energy systems is the terminal voltage poor stability [

In this sense, due to its topologies, the self-excitation dual stator windings induction generator can play both of the roles of power generation and maintain the PCC voltage at an optimal level. The first stator produces voltage and the second connected to a compensator that can inject the reactive power necessary to maintain the output voltage of the first stator. The harmonics generated by the second stator cannot propagate to the first one because there is no physical link between both of stators.

A literature survey on the SE-DSWIG utilisation leads to conclude that it is still in the first steps for the wind power generation. However, it is remarkable that it made important strides in the high-speed AC-application for the airborne, ships and vehicles that need self-power support. In [

It is remarkable in former works, that the SE-DSWIG performance was explored in high and enough constant speed to generate power that means it was not exposed to the critical condition in term of speed and power issues. While in speed variation applications such as wind power, it is necessary to use several topologies of inverters and compensators to sustain the power quality and to mitigate issues that appear in variable speed AC application such as voltage collapse, sag, and swell.

This article deals with voltage collapse, sag, and swell issues. For that, a systematic modeling, a detailed analysis and the performance study of SE-DSWIG in stand-alone operating mode are presented. The end user is modeled by an inductive-resistive load. A step variation of the prime mover speed is applied to the generator to emulate the wind speed variation in order to illustrate its influence on SE-DSWIG behavior. A passive compensator is used to mitigate the voltage sag and swell caused by the insertion of the inductive load and due to the prime mover speed variation. The article starts by an introduction that contains the state of the art on the SE-DSWIG, then in section two, the passive shunt and series compensator operation mode are discussed. In the third section, the mathematical modeling of the SE-DSWIG is presented, in addition to the equating of self- excitation capacity bank systems connected in shunt to the generator terminals to get the reactive power necessary for starting. The fourth section contains also the mathematical modeling of the end user represented by an inductive-resistive load with the modeling of passive shunt compensator connected in series and in parallel. In the fifth section, numerical are performed and results are displayed for the SE-DSWIG operation in different operating modes. Then, a conclusion summarises our work and presents the unforeseen challenges.

The passive compensator is a mature technique that been used since the beginning of the use of electricity [

The direct-quadratic synchronous referential frame representation of the dual stator windings induction generator is proposed in

The schema shown in

The flux linkage of both stators and rotor in (dq)-axis are given by the following equations [

L is the dynamic inductance.

And it defined by the following nonlinear expression [

The magnetizing current is calculated by the next expression [

The electromagnetic torque is estimated by the afterward expression [

The SE-DSWIG belongs to the self-excitation machines category. It needs a capacity bank connected at the stator terminals to get the necessary reactive power to start working.

At the presence of the residual magnetism and a sufficient rotating speed, the SE-DSWIG engenders enough current that stimulates the self-excitation capacity bank to generate reactive power into the windings. This operation will be repeated until arrivingat an equality between the SE-DSWIG output voltage and capacity bank terminal voltage. This will be the DSWIG operating point.

The following equation represents the excitation capacity bank modeled by the voltage and current relationship equations at the machine’s terminals [

The nd user is modeled by an inductive load in order to evaluate its influence on the main power supplier performance which is the SE-DSWIG. The end user is represented by the following system of equations:

The direct and quadratic load currents for both of stators are:

with

The wind speed variation and the presence of loads connected across the stators terminalsprovoke voltage disturbance, especially with poor voltage regulation feature that characterises induction generator. This situation requires the use of a compensator to fix the trouble.

In this work, we deal with a parallel passive compensator represented by a capacity bankconnected in parallel with SE-DSWIG terminals and a series passive compensator connected in series with SE-DSWIG terminals. Both of case are used to sustain the power quality and to mitigate issues that appear in the power system.

The current and voltage equations of the power system in DQ-frame at the presence of the series passive compensator are given as following:

First stator

Second stator

The current and voltage equations of the power system in dq-frame at the presence of the series passive compensator are given as following:

First stator

Second stator

injected by the parallel passive compensator to adjust the voltage at the point of common coupling.

In this section, we present the performance of SE-DSWIG in different situation such as prime mover speed variation, custom load variation, etc. The simulation of this work has been built up in Matlab^{®}/Sim Power Systems. Note that, the simulation of SE-DSWIG is very difficult due to the complexity of its equations. These are

constituted of ten differential equations with periodic and variable coefficients and took into account the magnetizing inductance. The passive compensator performance was evaluated. The parameters used in this simulation study are presented in

Symbol | Parameters | ||
---|---|---|---|

Entity | Quantity | Unity | |

A stator per-phase resistance | 1.9 | Ω | |

A rotor per-phase resistance | 2.1 | Ω | |

Stator per-phase leakage inductance | 0.0132 | H | |

Rotorper-phase leakage inductance | 0.0132 | H | |

Mutual leakage inductance | 0.011 | H | |

Nominal speed | 1500 | tr/min | |

Excitation capacity | 40 | μF | |

Parallel passive compensator capacity | 10 | μF | |

Series passive compensator capacity | 35 | μF | |

Load resistance | 200 | Ω | |

Load inductance | 0.05 | H |

Symbol | Definition |
---|---|

DGs | Distributed generation systems |

EPRI | Electric Power Research Institute |

SE-DSWIG | Self-excitation dual stator windings induction generator |

PCC | Point of common coupling |

Series passive compensator engendered voltage | |

Stator I terminal voltage | |

Load terminal voltage | |

Parallel compensator injected current | |

Rotor three phase windings sets | |

Stator I three phase windings sets | |

Stator II three phase windings sets | |

Stator I voltage in dq-frame | |

Stator II voltage in dq-frame | |

Rotor voltage in dq-frame | |

Stator I current in dq-frame | |

Stator II current in dq-frame | |

Rotor current in dq-frame | |

The flux linkage of stator I | |

The flux linkage of stator II | |

The flux linkage of rotor | |

The frequency | |

The rotating speed | |

Direct and quadratic magnetizing inductances | |

Dynamic inductance | |

The inter saturation cyclic inductance | |

The magnetizing inductance | |

The inductance and resistance of load |

In this case, inductive-resistive loads are connected with the terminals of stators I and II at t = 3 s. The presence of these loads decreases the output current and voltage of stators due to the lack of reactive power consumed by

the loads (Figures 12-20). At t = 4 s, a passive compensator is connected in series in the first test and in parallel in the second test the passive compensator consists of a capacity bank switched on between the generator and the loads. The compensator either in series or parallel rectifies the trouble, which is translated by augmentation of the current and voltage at the terminals of stators I and II until reaching the ideal values. The series passive compensator intervention was done by engendering an alternative voltage into the SE-DSWIG terminals as illustrated in

In this case, several speed values are applied to investigate their influence on the SE-DSWIG operation.

In this case, we applied a speed step variation on the prime mover emulating the variation of wind speed in real condition. At t = 3 s, the speed decreases from 314.5 rad/s to 310 rad/s.

In the other case, the prime mover speed changes from 314.5 rad/s to 320 rad/s. This speed variation provokes a voltage swell as shown in

Voltage sag and swell phenomena are the most influential issue on distributed generation system, especially with wind turbine systems.

Wind energy based distribution generation systems occupy forefront position in total energy production using renewable sources. Induction generator based wind systems are widely used because of their advantages. A new self-excitation induction generator consisting of two stators was presented in this work. We started by the mathematical modeling of the SE-DSWIG with taking into account the common mutual leakage inductance between stators and also magnetizing inductance which plays a principal role in the stabilization of the output voltage in the steady state. The SE-DSWIG was studied at no-load and connected to the end user, modeled by an inductive-resistive load. A step variation of the prime mover speed was applied at the SE-DSWIG start-up and

after reaching saturation. A passive shunt compensator was connected in series in firstly and in parallel secondly between the generator and the end user in order to mitigate the voltage disturbance caused by the presence of load or due to the prime mover speed variation. The SE-DSWIG shows a good performance in different operating modes and gives the opportunity to build several topologies such as feeding two different end users or a stator connected to the grid utility and the other one feeding a particular customer. The compensator supervised perfectly the power system stability and it intervened to mitigate the voltage sag and swell. Nevertheless, the passive compensator needs to be adapted for every intervention, depending on the prime mover speed and the load size. The drawback of this technique is its slowness comparing with the rapidity variation of both of loads size and weather conditions, so new technique is needed to allow better adapting with these requirements. Customer power devices (CPD) and flexible AC transmission system (FACTS) connected in series or in parallel such as D-STATCOM, DVR or hybrid such as UPFC, UPQC are proposed to meet the demands in term of rapidity and efficiency. In addition, the use of an advanced control algorithm is necessary to supervise the function of the active compensators (DVR, D-STATCOM, etc.) that participate in the improvement of the power flow and the mitigation of power quality issues that happen in AC applications.

Faris Hamoud,Mamadou Lamine Doumbia,Ahmed Cheriti, (2016) Performance Study of a Self-Excitation Dual Stator Winding Induction Generator for Renewable Distributed Generation Systems. Smart Grid and Renewable Energy,07,197-215. doi: 10.4236/sgre.2016.76016