e-ISSN(Online): 2460-8122 pp 53-58
Analysis of Rotor-Side Control and Grid-Side Control for Grid Voltage Improvement in a
DFIG-Based Wind Turbine System
Mus Ali Alsabah1, Rini Nur Hasanah2, Wijono3, Corina Martineac4
1,2,3 Department of Electrical Engineering, Universitas Brawijaya, Malang, Indonesia
4 Electrical Engineering Faculty, Technical University of Cluj-Napoca, Cluj-Napoca, Romania Email: [email protected], [email protected], [email protected], [email protected]
Abstract-Wind Power Plant (WPP) has received a lot of attention from public, researchers, and many governments because of its advantageous role in fulfilling the energy need and reducing the environmental damage being caused by fossil-based electrical energy generations. Unlike power plants that use fossil-based resources as primary energy, WPP uses wind kinetic energy to generate electricity. Many problems arise because the wind speed is always changing every time. The resulting output voltage instability in the generator can affect the electric power system where the output electricity of the generator is injected. This paper analyzes control the generator output voltage control on a WPP. The considered generator in this study is a doubly- fed induction generator (DFIG). The control method is applied on both the rotor side as well as the grid side converters, with the aim of maintaining the output voltage injected into the power grid within a certain level of voltage oscillation. The study results show the advantages given by the applied control to achieved the desired condition of generator output voltage.
Index Terms: DFIG, grid-side converter, rotor-side converters, voltage oscillation, wind energy generator.
Abstrak-Pembangkit Listrik Tenaga Bayu (PLTB) mendapat banyak perhatian dari masyarakat, para peneliti, maupun pemerintah karena kelebihan dan perannya dalam mengurangi penyebab kerusakan lingkungan akibat pembangkitan energi listrik. Tidak seperti pembangkit listrik yang menggunakan energi primer dari bahan bakar fosil, PLTB menggunakan energi kinetik angin untuk menghasilkan listrik. Banyak permasalahan yang timbul karena kecepatan angin yang selalu berubah setiap saatnya. Ketidakstabilan tegangan keluaran yang diakibatkannya pada generator pembangkit dapat mempengaruhi sistem daya listrik tempat listrik keluaran pembangkit tersebut diinjeksikan. Pada makalah ini diuraikan cara menganalisis pengendalian tegangan keluaran generator pada PLTB. Generator yang digunakan adalah jenis generator induksi dengan dua masukan (Doubly-Fed Induction Generator, DFIG), sedangkan cara analisisnya dilakukan dengan menggunakan alat bantu simulasi PSIM dari Powersim, Inc. Pengendalian dilakukan baik pada sisi rotor (Rotor Side Converter, RSC) maupun pada sisi grid (Grid Side Converter), dengan tujuan untuk mempertahankan tegangan keluaran yang diinjeksikan ke jaringan listrik dengan tingkat osilasi tegangan tertentu.
Hasil pengendalian menunjukkan bahwa tegangan keluaran generator dapat dipertahankan sesuai dengan yang dikehendaki.
Kata kunci: DFIG, konverter sisi jaringan, converter sisi rotor, osilasi tegangan, PLTB.
I. INTRODUCTION
Wind Power Plant (PLTB) is one type of renewable energy power plant. It is one of the alternative energy sources that are developing quite rapidly. Its utilization has not been much maximized, but its development has been increasing very rapidly in both developed and developing countries [1], [2], and [3]. WPP received much attention from government and researchers due to its offered advantages. It uses wind energy as its primary source [4]. Wind is one of the unlimited energies in the universe [5], [6], and [7]. WPP convert wind kinetic energy into electrical energy using wind turbines or windmills.
Among the widely applied wind energy conversion system configurations, there are four most common types, namely: Type A which uses a fixed-speed turbine connected to a squirrel-cage induction generator (SCIG) via a gearbox; Type B which uses a variable-speed turbine connected via a gearbox to a wound-rotor induction generator (WRIG) whose rotor is connected with a variable resistance; Type C which is also a variable speed turbine connected via a gearbox to a WRIG but whose rotor output is fed to the grid via a frequency converter at a less than rated rating, which is also known as a doubly-fed induction generator (DFIG); and Type D which uses a variable-speed turbine connected either directly or via a gearbox to the WRIG [8],[9].
Currently, the most widely used wind turbine in WPP is the DFIG type. It offers several advantages such as reduced inverter costs, potential for torque control, and increased wind energy extraction efficiency. However, wind turbines with DFIG are very sensitive to network disturbances, especially to voltage drops [10].
In a DFIG there is a combination of aerodynamic, mechanical, electromagnetic, and electronic systems.
The related control on various subsystems both during transient as well steady-state conditions is quite complex.
The continuously increasing penetration of wind power generation into the existing grids demands more and more stringent Grid Code to ensure the reliability and safety of power system. The wind energy conversion system (WECS) should be able to remain connected to the system even when a fault occurs, so that it demands the availability of reactive currents to support network voltage conditions [11].
This paper discusses the analysis of DFIG control in wind turbines to maintain the output voltage conditions.
The analysis was carried out by utilizing the PSIM simulation software. The simulation is based on the design of the DFIG generator control system model to obtain the output voltage injected into the network under certain oscillation conditions.
II. METHODS A. A. Simulation Model Parameters
The method used to analysis the doubly-fed induction generator control in this paper is shown in the flowchart of Fig. 1. The required data include wind turbine data, generator data and network model data. The study is based on a 380V electrical system voltage. Parameters of the wind turbine, generator, and the considered network are shown in Fig. 2, 3 and 4 respectively.
Fig. 1. Method to analyze the DFIG control
Fig. 2. Wind turbine parameters [12]
Fig. 3. DFIG parameters [12]
Fig. 4. Voltage source parameters [12]
B. Simulation Models
The model of the DFIG simulation circuit using the PSIM software is shown in Fig. 5. The circuit making is based on the default PSIM module with several components added to get the circuit and results as needed.
DFIG control is carried out simultaneously on the rotor side and the grid side, with the aim of maintaining and correcting voltage and current oscillations.
The DFIG control simulation model is equipped with current and voltage sensor models to provide input quantities to the control system and also to monitor changes in current and voltage. The current sensor is installed at the input and output of the converter while the voltage sensor is placed at the network section. The power converter model consists of three parts, namely the stator converter, the rotor converter and a DC link capacitor, as shown in Fig. 6.
Fig. 5. DFIG circuit model [13,14]
Fig. 6. Sensor placement and converter modeling
Fig. 6 indicates the sensors placement and the converter modelling. The AC-DC-AC converter model is equipped with several current and voltage sensors. Part A is the rotor converter input current sensor which is used for RSC input, part B is the DC link voltage sensor which is used as the sum of inputs for the RSC and GSC, part C is the grid converter output current sensor which is used for GSC input, while part D is grid voltage sensor used for RSC and GSC input as voltage monitoring.
The RSC and GSC models are shown in Fig. 7. The RSC functions to control the DFIG rotor input section which is connected to the AC/DC/AC converter by utilizing the rotor input sensor, while the GSC functions to control and monitor the output of the converter which is injected into the grid.
Fig. 7. RSC and GSC modeling
III. RESULTS AND DISCUSSION
Analysis was performed on the DFIG control simulation results in time domain. Observations were made on the operation of RSC, GSC, and control circuits in close-loop mode with time domain simulation. The observation results are displayed in the form of a graph of the voltage oscillation response. Fig. 8 is the result of oscillations from the DFIG circuit model that has not been controlled (Fig. 5). It can be seen that there is a voltage drop in each phase, where the voltage drop lasts for 0 to 0.01 seconds.
Fig. 8. DFIG voltage output oscillation [8]
A. A. RSC Modeling Simulation
Fig. 9 is a complete simulation circuit for observing voltage oscillations on the RSC. The simulation was carried out in the time range of 0 to 0.1 seconds, at a DFIG voltage of 380VAC and a constant voltage reference source in the RSC control circuit with a value of 12VDC. The simulation results are given in Fig. 10. In accordance with the procedure described, namely installing the control system only on the rotor block without involving the grid control block, additional components are provided in the form of several voltage probes to observe the results of the circuit in the form of voltage oscillations.
Fig. 9. RSC circuit in DFIG
Fig. 10. RSC voltage output oscillation
Fig. 11. GSC circuit on DFIG
Fig. 12. GSC output voltage oscillation
B. GSC Voltage Oscillation
Figure 11 is the form of the GSC circuit which is directly connected to the grid network without involving the output voltage of the DFIG rotor. The simulation is carried out on a 380VAC electrical system and a constant voltage reference source on the GSC control circuit with a value of 12VDC, with a simulated running time of 0 seconds to 0.1 seconds. The simulation results are given in Fig. 12. In accordance with the procedure described above, namely installing the control system only on the grid block without involving the rotor control block.
Additional components are provided in the form of several voltage probes to observe the results of the circuit
in the form of voltage oscillations.
C. C. Close-loop control of DFIG
The DFIG control circuit in the DFIG close-loop is shown in Fig. 13. The simulation results are given in Fig.
14. The two sets of RSC and GSC function together in control according to the procedures described. Each paired sensor is enabled to send signals to the RSC and GSC control systems according to the initial modeling procedure. The simulation is carried out on a 380VAC
electrical system and a constant voltage reference source on the RSC and GSC control circuits with the same value of 12VDC, the simulation running time is carried out for 0 seconds to 0.1 seconds.
Fig. 13. Close-loop DFIG circuit
Fig. 14. DFIG voltage oscillation results of close-loop Control
IV. CONCLUSION
In this study, DFIG control was examined in wind power generation systems with the aim that the voltage generated by the generator can be maintained stable for injection into the electricity grid. Control is carried out both on the rotor side converter and the grid side converter on the generator. The control system modeling
the experimental method using references from the supporting literature. Control system modeling is made using PSIM software. The control results show that the output voltage of the generator injected into the grid can be maintained, which is indicated by the uniformity of the waveforms and the peaks of the oscillations in each phase.
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