Cost-Effective APF/UPS System with Seamless Mode Transfer

Lee, Woo-Cheol The Korean Institute of Electrical Engineers 2015 Journal of Electrical Engineering & Technology Vol.10 No.1

In this paper, the development of a cost-effective active power filter/uninterruptible power supply (APF/UPS) system with seamless mode transfer is described. The proposed scheme employs a pulse-width-modulation (PWM) voltage-source inverter and has two operational modes. First, when the source voltage is normal, the system operates as an APF, which compensates for the harmonics and power factor while boosting the DC-link voltage to be ready for the disturbance, without an additional DC charging circuit. A simple algorithm to detect the load current harmonics is also proposed. Second, when the source voltage is out of the normal range (owing to sag, swell, or outage), it operates a UPS, which controls the output voltage constantly by discharging the DC-link capacitor. Furthermore, a seamless transfer method for the single-phase inverter between the APF mode and the UPS mode is also proposed, in which an IGBT switch with diodes is used as a static bypass switch. Dissimilar to a conventional SCR switch, the IGBT switch can implement a seamless mode transfer. During the UPS operation, when the source voltage returns to the normal range, the system operates as an APF. The proposed system has good transient and steady-state response characteristics. The APF, charging circuit, and UPS systems are implemented in one inverter system. Finally, the validity of the proposed scheme is investigated with simulated and experimental results for a prototype APF/UPS system rated at 3 kVA.

Cost-Effective APF/UPS System with Seamless Mode Transfer

Woo-Cheol Lee 대한전기학회 2015 Journal of Electrical Engineering & Technology Vol.10 No.1

In this paper, the development of a cost-effective active power filter/uninterruptible power supply (APF/UPS) system with seamless mode transfer is described. The proposed scheme employs a pulse-width-modulation (PWM) voltage-source inverter and has two operational modes. First, when the source voltage is normal, the system operates as an APF, which compensates for the harmonics and power factor while boosting the DC-link voltage to be ready for the disturbance, without an additional DC charging circuit. A simple algorithm to detect the load current harmonics is also proposed. Second, when the source voltage is out of the normal range (owing to sag, swell, or outage), it operates a UPS, which controls the output voltage constantly by discharging the DC-link capacitor. Furthermore, a seamless transfer method for the single-phase inverter between the APF mode and the UPS mode is also proposed, in which an IGBT switch with diodes is used as a static bypass switch. Dissimilar to a conventional SCR switch, the IGBT switch can implement a seamless mode transfer. During the UPS operation, when the source voltage returns to the normal range, the system operates as an APF. The proposed system has good transient and steady-state response characteristics. The APF, charging circuit, and UPS systems are implemented in one inverter system. Finally, the validity of the proposed scheme is investigated with simulated and experimental results for a prototype APF/UPS system rated at 3 kVA.

Strategy for the Seamless Mode Transfer of an Inverter in a Master-Slave Control Independent Microgrid

Wang, Yi,Jiang, Hanhong,Xing, Pengxiang The Korean Institute of Power Electronics 2018 JOURNAL OF POWER ELECTRONICS Vol.18 No.1

To enable a master-slave control independent microgrid system (MSCIMGS) to supply electricity continuously, the microgrid inverter should perform mode transfer between grid-connected and islanding operations. Transient oscillations should be reduced during transfer to effectively conduct a seamless mode transfer. This study uses a typical MSCIMGS as an example and improves the mode transfer strategy in three aspects: (1) adopts a status-tracking algorithm to improve the switching strategy of the outer loop, (2) uses the voltage magnitude and phase pre-synchronization algorithm to reduce transient shock at the time of grid connection, and (3) applies the hybrid-sensitivity $H_{\infty}$ robust controller instead of the current inner loop to improve the robustness of the controller. Simulations and experiments show that the proposed strategy is more practical than the traditional proportional-derivative control mode transfer and effective in reducing voltage and current oscillations during the transfer period.

Strategy for the Seamless Mode Transfer of an Inverter in a Master–Slave Control Independent Microgrid

Yi Wang,Hanhong Jiang,Pengxiang Xing 전력전자학회 2018 JOURNAL OF POWER ELECTRONICS Vol.18 No.1

To enable a master–slave control independent microgrid system (MSCIMGS) to supply electricity continuously, the microgrid inverter should perform mode transfer between grid-connected and islanding operations. Transient oscillations should be reduced during transfer to effectively conduct a seamless mode transfer. This study uses a typical MSCIMGS as an example and improves the mode transfer strategy in three aspects: (1) adopts a status-tracking algorithm to improve the switching strategy of the outer loop, (2) uses the voltage magnitude and phase pre-synchronization algorithm to reduce transient shock at the time of grid connection, and (3) applies the hybrid-sensitivity H∞ robust controller instead of the current inner loop to improve the robustness of the controller. Simulations and experiments show that the proposed strategy is more practical than the traditional proportional–derivative control mode transfer and effective in reducing voltage and current oscillations during the transfer period.

Seamless Transfer를 위한 계통연계형 인버터의 간접전류 제어기법

유태식(Taesik Yu),최세완(Sewan Choi),김효성(Hyosung Kim) 전력전자학회 2005 전력전자학술대회 논문집 Vol.- No.-

Distributed generation (DG) systems fall in islanding operation when they still in operation even when the main grid is out of electric power. Islanding operation is further classified into intentional islanding and unintentional islanding operations. In intentional islanding operation, the DG backs up critical loads while it separates from the main grid on islanding detection. Intentional islanding operation increases utilization of the DG system during the islanding operation. This paper proposes reasonal inverter topology and its control algorithm for seamless transfer of DG systems in intentional islanding operation.

Research of Seamless Transfer Control Strategy of Microgrid System

M.J. Yang,F. Zhuo,X.W. Wang,H.P. Guo,Y.J. Zhou 전력전자학회 2011 ICPE(ISPE)논문집 Vol.2011 No.5

Microgrid has two typical working modes: grid-connected mode and islanded mode. The transfer between these two modes should be seamless. In a microgrid that uses master-slave strategy to avoid circumfluence in the islanded mode, to control the master converter’s voltage is to control the microgrid voltage. Considering this, the master converter in this paper works as a voltage-controlled inverter when the microgrid is disconnecting from the utility grid while working as a current-controlled rectifier when the microgrid is in the grid-connected mode. Besides, by gradually adjusting the master converter’s output voltage to equal that of the utility grid when the microgrid is going to connect the utility grid and by setting an appropriate initial phase of the converter voltage when the microgrid needs to work alone, the seamless transfers between these two modes are accomplished. Experiment has been done to validate the accuracy, rapidity and reliability of this strategy.

Cost-Effective APF/UPS System with Seamless Mode Transfer

이우철 대한전기학회 2015 Journal of Electrical Engineering & Technology Vol.10 No.1

In this paper, the development of a cost-effective active power filter/uninterruptible powersupply (APF/UPS) system with seamless mode transfer is described. The proposed scheme employs apulse-width-modulation (PWM) voltage-source inverter and has two operational modes. First, whenthe source voltage is normal, the system operates as an APF, which compensates for the harmonics andpower factor while boosting the DC-link voltage to be ready for the disturbance, without an additionalDC charging circuit. A simple algorithm to detect the load current harmonics is also proposed. Second,when the source voltage is out of the normal range (owing to sag, swell, or outage), it operates a UPS,which controls the output voltage constantly by discharging the DC-link capacitor. Furthermore, aseamless transfer method for the single-phase inverter between the APF mode and the UPS mode isalso proposed, in which an IGBT switch with diodes is used as a static bypass switch. Dissimilar to aconventional SCR switch, the IGBT switch can implement a seamless mode transfer. During the UPSoperation, when the source voltage returns to the normal range, the system operates as an APF. Theproposed system has good transient and steady-state response characteristics. The APF, chargingcircuit, and UPS systems are implemented in one inverter system. Finally, the validity of the proposedscheme is investigated with simulated and experimental results for a prototype APF/UPS system ratedat 3 kVA.

간접전류제어방식 병렬형 계통연계 인버터의 무순단 모드절환

송인종,최준수,임경배,최재호 전력전자학회 2019 전력전자학회 논문지 Vol.24 No.5

This study proposes the control strategy for the seamless mode transfer of indirect current controlled parallel grid-connected inverters. Under the abnormal grid condition, the grid-connected inverter can convert the operation mode from grid-connected to stand-alone mode to supply power to the local load. For a seamless mode transfer, the time delay problems caused by the accumulated control variable error must be solved, and the indirect current control method has been applied as one of the solutions. In this study, the design of control parameters for the proportional-resonant-based triple-loop indirect current controller and the control strategy for the seamless mode transfer of parallel grid-connected inverters are described and analyzed. The validity of the proposed mode transfer method is verified by the PSiM simulation results.

Seamless Mode Transfer of Utility Interactive Inverters Based on Indirect Current Control

Kyungbae Lim,Injong Song,Jaeho Choi,Hyeong-Jun Yoo,Hak-Man Kim 전력전자학회 2019 JOURNAL OF POWER ELECTRONICS Vol.19 No.1

This paper proposes an indirect current control technique based on a proportional resonant (PR) approach for the seamless mode transfer of utility interactive inverters. Direct-current and voltage hybrid control methods have been used for inverter control under grid-connected and islanded modes. A large bandwidth can be selected due to the structure of single-loop control. However, this results in poor dynamic transients due to sudden changes of the controller during mode changes. Therefore, inverter control based on indirect current is proposed to improve the dynamic transients by consistently controlling the output voltage under all of the operation modes. A PR-based indirect current control topology is used in this study to maintain the load voltage quality under all of the modes. The design processes of the PR-based triple loop are analyzed in detail while considering the system stability and dynamic transients. The mode transfer techniques are described in detail for both sudden unintentional islanding and islanded mode voltage quality improvements. In addition, they are described using the proposed indirect control structure. The proposed method is verified by the PSiM simulations and laboratory-scale VDER-HILS experiments.

태양광 발전 시스템의 무순단 MPPT 운전 모드 절체 기법

박종화(Jong-Hwa Park),조종민(Jongmin Jo),안현성(Hyunsung An),차한주(Hanju Cha) 대한전기학회 2018 전기학회논문지 Vol.67 No.2

This paper proposes a seamless MPPT operation mode transfer method of photovoltaic system. The photovoltaic system consists of a DC-DC boost converter, a DC-Link, and a 3-level neutral point clamp (NPC) type inverter. The PV voltage fluctuates due to the output characteristics of the solar pane1 depending on the irradiation amount and the temperature. The photovoltaic system requires seamless MPPT mode transfer method that the discontinuity does not occur in order to supply the stable power to system without affecting the fluctuation of the PV voltage. MPPT operation is divided into two modes by the voltage reference. Under the condition that the PV voltage is below 650V, the DC-DC boost converter performs MPPT through duty control based on perturb & observe (P&O) method, and the inverter conducts DC-link voltage and grid current controls in synchronous reference frame. On the other hand, when the PV voltage exceeds above 650V, inverter performs MPPT in accordance with the variation of DC-link voltage control while the converter stops operating. Two MPPT operation modes is smoothly transferred through the proposed method that DC-link voltage or grid current commands are appropriately adjusted from the certain criteria. The feasibility of the MPPT operation mode transfer method is verified using a 10kW solar photovoltaic system, experimental results have good performances that the fluctuation of PV current is reduced to 100%.