• Journal of Power Electronics
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• v.17 no.1
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• pp.222-231
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• 2017

In this paper, a new architecture for a cost-effective power conditioning systems (PCS) using a single-sourced asymmetric cascaded H-bridge multilevel inverter (MLI) for photovoltaic (PV) applications is proposed. The asymmetric MLI topology has a reduced number of parts compared to the symmetrical type for the same number of voltage level. However, the modulation index threshold related to the drop in the number of levels of the inverter output is higher than that of the symmetrical MLI. This problem results in a modulation index limitation which is relatively higher than that of the symmetrical MLI. Hence, an extra voltage pre-regulator becomes a necessary component in the PCS under a wide operating bias variation. In addition to pre-stage voltage regulation for the constant MLI dc-links, another auxiliary pre-regulator should provide isolation and voltage balance among the multiple H-bridge cells in the asymmetrical MLI as well as the symmetrical ones. The proposed PCS uses a single-ended DC-DC converter topology with a coupled inductor and charge-pump circuit to satisfy all of the aforementioned requirements. Since the proposed integrated-type voltage pre-regulator circuit uses only a single MOSFET switch and a single magnetic component, the size and cost of the PCS is an optimal trade-off. In addition, the voltage balance between the separate H-bridge cells is automatically maintained by the number of turns in the coupled inductor transformer regardless of the duty cycle, which eliminates the need for an extra voltage regulator for the auxiliary H-bridge in MLIs. The voltage balance is also maintained under the discontinuous conduction mode (DCM). Thus, the PCS is also operational during light load conditions. The proposed architecture can apply the module-integrated converter (MIC) concept to perform distributed MPPT. The proposed architecture is analyzed and verified for a 7-level asymmetric MLI, using simulation results and a hardware implementation.

• Proceedings of the KIEE Conference
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• 1996.11a
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• pp.370-372
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• 1996

A control scheme for the Voltage-sourced PWM converter based on space vector equations is introduced. The main advantages of this new control scheme are that sinusoidal line currents with nearly unity power factor, ripple-free DC voltage output are achevied without current sensors. The dynamical equations with battery model is derived. The proposed scheme is verified by computer simulation.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.9
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• pp.1221-1225
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• 2012

This paper describes CSC(Current Sourced Converters)-based HVDC operational strategy for voltage stability enhancement in the power system. In case of CSC-based HVDC system, rectifier and inverter consume reactive power up to about 60% of converter rating. Therefore, CSC-based HVDC is basically not useful system for voltage stability even if AC filters and shunt capacitors are attached. But, If the particular power system condition is fulfilled, CSC-based HVDC also can be the rapid reactive power source for voltage stability enhancement using a cooperative control with converter and AC filters/Shunt Capacitors. In this paper, the cooperative control algorithm is presented and simulated to ${\pm}80kV$ 60MW HVDC system in Jeju island.

• Proceedings of the KIEE Conference
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• 1997.07f
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• pp.2210-2212
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• 1997

A sensorless input current controller for three phase PWM converter is proposed. A merit of this controller is that sinusoidal input line current, unity power factor, and ripple-free DC voltage can be achieved with low-cost. The paper describes the proposed control strategy and its implementation. Simulation result for the proposed controller is compared with that of the sensor based version.

• Journal of Power Electronics
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• v.15 no.5
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• pp.1367-1379
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• 2015

A hybrid HVDC system that is composed of line commutated converter (LCC) at the rectifier side and voltage source converter (VSC) in series with LCC at the inverter side is studied in this paper. The start-up strategy, DC fault ride-through capability, and fault recovery strategy for the hybrid HVDC system are proposed. The steady state and dynamic performances under start-up, AC fault, and DC fault scenarios are analyzed based on a bipolar hybrid HVDC system. Furthermore, the immunity of the LCC inverter in hybrid HVDC to commutation failure is investigated. The simulation results in PSCAD/EMTDC show that the hybrid HVDC system exhibits favorable steady state and dynamic performances, in particular, low susceptibility to commutation failure, excellent DC fault ride-through, and fast fault recovery capability. Results also indicate that the hybrid HVDC system can be a good alternative for large-capacity power transmission over a long distance byoverhead line.

• Journal of Power Electronics
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• v.16 no.6
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• pp.2272-2283
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• 2016

This paper proposes a power conditioning system (PCS) for distributed photovoltaic (PV) applications using an asymmetric cascaded multilevel inverter with a single PV source. One of the main disadvantages of the cascaded multilevel inverters in PV systems is the requirement of multiple isolated DC sources. Using multiple PV strings leads to a compromise in either the voltage balance of individual H-bridge cells or the maximum power point tracking (MPPT) operation due to localized variations in atmospheric conditions. The proposed PCS uses a single PV source with a flyback DC-DC converter to facilitate a reduction of the required DC sources and to maintain the voltage balance during MPPT operation. The flyback converter is used to provide input for low-voltage H-bridge cells which processes only 20% of the total power. This helps to minimize the losses occurring in the proposed PCS. Furthermore, transient analyses and controller design for the proposed PCS in both the stand-alone mode and the grid-connection mode are presented. The feasibility of the proposed PCS and its control scheme have been tested using a 1kW hardware prototype and the obtained results are presented.

• Proceedings of the KIPE Conference
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• 2015.07a
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• pp.323-324
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• 2015

Recently, asymmetrical cascaded H-bridge multilevel inverter started to be highlighted as an alternative for the symmetrical cascaded H-bridge. The topology has a small number of part count compared to the symmetrical with higher number of levels. However, it has a drawback of the modulation index limitation which is relatively higher than its symmetrical counterpart, which causes a necessity of an extra voltage pre-regulator. In this paper, the single-sourced pre-regulator is unified with an inner single switch DC/DC converter isolated by coupled inductor. It leads to cost and size reduction. The proposed topology is verified using simulation results.

• Proceedings of the KIEE Conference
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• 2015.07a
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• pp.237-238
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• 2015

This paper analyzed the impact of Voltage Sourced Converter High Voltage Direct Current(VSC HVDC) connected an offshore wind power on the Jeju Island electrical power system. Wind power output fluctuates with the changing of wind speed. By changing wind power output occupancy into 100%, 60%, 10% respectively, we can understand the bus voltage distribution controlled by VSC HVDC. PSS/E is used to analyze steady-state simulation results which show effectiveness of the VSC HVDC for Jeju Island power system.

• Progress in Superconductivity and Cryogenics
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• v.20 no.4
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• pp.55-59
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• 2018

Currently, the development of industry makes needs larger electric supply. Providers must consider the efficiency about losses and reliability of the system. In this case, DC power system can save electrical energy; long-distance transmission line losses. Relevance to switch technology with a voltage-source converter (VSC) in AC-DC conversion system have been researched. But, protection device of DC-link against fault current is still needed to study much. VSC DC power system is vulnerable to DC-cable short-circuit and ground faults, because DC-link has a huge size of capacitor filter which releases extremely large current during DC faults. Furthermore, DC has a fatal flaw that current zero crossing is nonexistence. To interrupt the DC, several methods which make a zero crossing is used; parallel connecting self-excited series LC circuit with main switch, LC circuit with power electronic device called hybrid DC circuit breaker. Meanwhile, self-excited oscillator needs a huge size capacitor that produces big oscillation current which makes zero crossing. This capacitor has a quite effective on the price of DCCB. In this paper, hybrid self-excited type superconducting DCCB which are using AC circuit breaker system is studied by simulation tool PSCAD/EMTDC.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.274-275
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• 2011

Fault current problems is considered a serious issue in the power system because large fault currents not only cause many side effects to the equipments of power system but also lead to severe problems, such as blackouts. This paper deals with the structural analysis and 3-phase fault current stability of the future Seoul metropolitan power system. The simulation composition and analysis are performed with the 4th KEPCO power supply planning data using PSS/e. Through the results of the simulations, it can be observed that the future Seoul metropolitan system results in a fault current which exceeds the circuit breaker (CB) rate. This unremovable fault current can cause critical damage to power system. To resolve the problem, the algorithm for the application of Voltage Sourced Converter Back-to-Back High Voltage Direct Current (VSC BTB HVDC) is being proposed. where the most suitable location for solving fault current problem in Seoul metropolitan area is being implemented.