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A sliding mode control strategy for a grid-supporting and grid-forming power converter in autonomous AC microgrids
(2019-03-01)
Khongkhachat, S.
;
Khomfoi, S.
– This paper presents a sliding mode control technique combined with voltage orientation for grid-supporting and grid-forming (GSGFm) function in a power converter, used in AC microgrid during island operation. The robustness sliding mode control method (SMC) can provide stability control system and fast dynamic response. Therefore, a control law is designed using sliding mode techniques, which is based on the combination of continuous and discrete signals to generate the robustness system from uncertainties and disturbances. A sliding mode control approach is adopted in this paper in order to enhance for the inner control loops (level 0) to improve the dynamic response of a lowest hierarchical level based on droop regulated-microgrids. The main objectives of the proposed SMC technique are to keep frequency and voltages at normal values, according to the actual real-reactive power loads absorption. SMC has also produced the reference frequency and the voltage signals. Thereupon, the dynamic frequency and voltage can be regulated with a new control approach and can guarantee power reliability, quality and efficiency during this mode. Finally, the model and the controller design are validated by simulation and experimental results. The results show that the proposed SMC technique can be implemented in a GSGFm power converter for AC microgrid.
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Ramp rate consideration of a BESS using active power control for PV generation
(2016-01-18)
Prompinit, K.
;
Khomfoi, S.
Ramp rate consideration of a BESS using active power control for PV generation is proposed in this paper. Battery energy storage system (BESS) in ac microgrid is used in this research. The design of controller is verified by PSIM 9.0 under unstable of solar energy each day. This paper presents the output power control of PV generation by using BESS, which help to compensate active power to fulfill output of active power from PV generation. This paper presents optimal method to smooth active power curve and compares with traditional moving average method in ramp rate control. The validation result is verified by data from ac microgrid. The design of controller consists of profile from PV generation profile of real time microgrid application. The simulation results show that proposed ramp rate control could reduced BESS equipment size and also compensate active power of PV generation in ac microgrid.
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Solid state transformer using a modular multilevel inverter for PV farm applications
(2016-01-18)
Khemmook, P.
;
Khomfoi, S.
The aim of this paper is to present the solid state transformer integrated with PV farm applications in the distribution system of PEA grid. A Modular Multilevel Inverter (MMI) circuit, which can be connected to a 22 kVL-L transmission system is also presented in this paper. The MMI has the capability of current limit if the short circuit fault occurs. The topology of the proposed MMI is the three-level three-phase inverter with the reduced voltage for laboratory use. The proposed idea focusing only on the MMI is validated by simulation and substantiate by the experiment.
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An EV quick charger based on CHAdeMO standard with grid-support function
(2016-01-18)
Jampeethong, P.
;
Khomfoi, S.
An electric vehicle (EV) quick charger based on CHAdeMO standard with grid-support function is proposed in this paper. The current source modular converter configuration is used to perform the charging pulses with both positive and negative pulse to achieve required time for an EV which is less than 30 minutes. The use of current source converter can offer the inherit fault tolerance capability and bidirectional power flow. CHAdeMO protocol is modified for grid-support function. The 50 kW prototype is developed to validate the proposed notion. The simulation and experimental results illustrate that the proposed pulse frequency charging technique requires about 16 minutes to fully charge of the battery from 20% of SOC to 80% of SOC. The results suggest that the proposed technique can be applied for an electric vehicle quick charger station.
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Application of the DC-link current sensors of the back-to-back converters for the operation of a doubly-fed induction generator
(2016-01-18)
Suwan-Ngam, W.
;
Khomfoi, S.
The aim of this paper is to propose the application of the DC-link current sensors of the back-to-back converters for operation of a doubly-fed induction generator (DFIG). The operation of the DFIG is first discussed. The measured DC-link currents are used reconstruct the AC current waveforms for operation of the DFIG under different operating modes. The feasibility of the proposed application is investigated by simulation and experiment. The limitations of the proposed topology are discussed. The fault tolerant operation while the fault occurs at the AC current sensors is also discussed.
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Droop control strategy of AC microgrid in islanding mode
(2016-01-18)
Khongkhachat, S.
;
Khomfoi, S.
The droop control strategy of an AC microgrid in islanding mode is presented in this paper. The frequency reference of islanding mode is recalculated from proposed droop control technique due to the loss of grid reference frequency. The fast response of both voltage and frequency of the AC microgrid during an islanding operation is required in order to maintain the frequency and voltage stability. The understanding of control strategy of each inverter needs to investigate for better application which is also explained. The Matlab/Simulink is used to validate the proposed droop control. The simulation result shows that proposed droop control strategy can control active and reactive power of an AC microgrid satisfactory.
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Influence of PWM characteristics on the core losses due to harmonic voltages in PWM fed induction motors
(2000-01-01)
Khomfoi, S.
;
Kinnares, V.
;
Viriya, P.
The paper focuses on mechanisms of harmonic core losses due to PWM characteristics. The influence of PWM characteristics such as switching frequency, modulation depth and PWM strategy on core losses has been examined. The investigation into harmonic core losses based on no-load input power measurement with minimized rotor copper loss and rotational loss has been made. The experimental results show that the increment of core losses due to PWM harmonic voltages is significant compared to a sinusoidal supply and the modulation depth has significant effect on machine core losses.
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Investigation into core losses due to harmonic voltages in PWM fed induction motors
(1999-01-01)
Khomfoi, S.
;
Kinnares, V.
;
Viriya, P.
The paper focuses on mechanisms of harmonic core losses due to PWM characteristics. The relationship between modulation depth particularly at higher value of PWM strategies and loss characteristics are discussed. The PWM voltage spectra at higher modulation depth are examined for interpreting core losses associated with the interaction between individual harmonic voltages and machine features. The investigation into harmonic core loss based on no-load tests with minimized rotor copper loss and rotational loss has been made. The experimental results have shown that the increment of core losses due to PWM harmonic voltages is significant compared to a sinusoidal supply and the modulation depth has significant effect on machine core losses.

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