Hae-Gwang Jeong

Method for Detecting an Open-Switch Fault in a Grid-Connected NPC Inverter System

This paper proposes a fault-detection method for an open-switch fault in the switches of grid-connected neutral-point-clamped inverter systems. The proposed method can not only detect the fault condition but also identify the location of the faulty switch. In the proposed method, which is designed by incorporating a simple switching control in the conventional method, the fault condition is detected on the basis of the radius of the Concordia current pattern, and the location of the faulty switch can be identified. By using the proposed method, it is possible to detect the open-switch fault and identify the faulty switch within two fundamental periods, without using additional sensors or performing complex calculations. Simulations and experiments are carried out to confirm the reliability of the proposed fault-detection method.

Tolerant Control for Power Transistor Faults in Switched Reluctance Motor Drives

This paper presents a fault identification and tolerant method for switched reluctance motor (SRM) drives. The reliability of a power transistor in a power converter is the source of most problems in several industrial applications. It is critical to correctly diagnosis the faults occurring in a drive system to avoid harmful accidents and to ensure continuity of operation. In this paper, two types of faults, namely, short- and open-circuit faults, are analyzed on the basis of the current patterns of the power transistors of SRM drives. A fault is detected when the measured amplitude of the current differs from that of the normal-state current. A fault-tolerant scheme is applied according to the type of fault. Simulations and experiments are performed on a 1.0-kW SRM drive. The results are presented to verify the validity of the proposed method.

Design of an LCL-Filter for Three-Parallel Operation of Power Converters in Wind Turbines

This paper proposes a design scheme for an LCL-filter used for the three-parallel operation of the power converters in high-capacity wind turbines. The designs of the power devices and grid connected filter are difficult due to the high level voltages and currents in huge-capacity wind turbines. To solve these problem, this paper presents three-parallel operation and LCL-filter design techniques optimized by parallel operation. Furthermore, the design of an inverter side inductance of the LCL-filter is discussed in detail considering the switching modulation method. Simulation and experimental results demonstrate the validity of the designed filter and wind turbines.

Active Damping for Wind Power Systems with LCL Filters Using a DFT

This paper proposes a simple active damping algorithm for small-scale wind power systems with an LCL filter. Compared to an L filter or an LC filter, an LCL filter can decrease the harmonics induced by low switching frequencies and produce a satisfactory grid-side current using a comparatively low inductance. Additional active damping of the filter resonance is necessary when an LCL filter is used. This paper introduces an active damping method using a Discrete Fourier Transform (DFT) filter to improve performance without additional sensors or complexity. Experimental results are shown to verify the validity of the proposed algorithm as an active damping method.

A 2 nd Order Harmonic Compensation Method for Wind Power System Using a PR Controller

This paper proposes a compensation method for the 2 nd -order harmonic of single-phase grid-connected wind power generation systems. Theoretically, a single-phase grid-connected inverter system has no choice but to cause the 2 nd -order harmonic to DC-link voltage. The reference active current is affected by the DC-link voltage. The output current from the reference active current is distorted by the 1 st and 3 rd -order harmonic. The proposed method can compensate, conveniently, the reference active current with the 2 nd -order harmonic. To reduce the 2 nd -order ripple in the reference active current, proposed method takes a PR controller as a feed-forward compensator. PR controllers can implement selective harmonic compensation without excessive computational requirements; the use of these controllers simplifies the method. Both the simulation and experimental results agree well with the theoretical analysis.

Performance Improvement of Grid-Connected Inverter Systems under Unbalanced and Distorted Grid Voltage by Using a PR Controller

This paper proposes a control method for grid-connected inverter systems under unbalanced and distorted grid voltage. The proposed method can reduce the power ripple caused by the unbalanced condition and compensate for the low-order harmonics of the output currents caused by the distortion of grid voltage. To reduce the power ripple, our method replaces the two conventional PI controllers with one PR controllers in the stationary frame. PR controllers can implement selective harmonic compensation without excessive computational requirements; the use of these controllers simplifies the method. Both the simulated and experimental results agree well with the theoretical analysis.

Control strategies for wind power systems to meet grid code requirements

This paper proposes LVRT (low voltage ride through) control strategies for wind power systems. According to the grid requirements, wind turbines should continue to operate during a grid voltage fault. LVRT control must guarantee stability under an unbalanced grid-fault condition, because a single-phase ground fault or two-phase short-circuit leads to an unbalanced voltage. This paper proposes LVRT control strategies that satisfy grid requirements under unbalanced conditions. These strategies include dynamic breaking resistor operation, detection of grid faults, and the power flow for each grid-voltage condition. Simulation results show that the proposed control strategies are effective for the LVRT control of wind power systems.

Torque Ripple Minimization Scheme Using Torque Sharing Function Based Fuzzy Logic Control for a Switched Reluctance Motor

This paper presents an advanced torque ripple minimization method of a switched reluctance motor (SRM) using torque sharing function (TSF). Generally, TSF is applied into the torque control. However, the conventional TSF cannot follow the expected torque well because of the nonlinear characteristics of the SRM. Moreover, the tail current that is generated at a high speed motor drive makes unexpected torque ripples. The proposed method combined TSF with fuzzy logic control (FLC). The advantage of this method is that the torque can be controlled unity at any conditions. In addition, the controller can track the torque under the condition of the wrong TSF. The effectiveness of the proposed algorithm is verified by the simulations and experiments.

Torque ripple minimization of switched reluctance motors based on fuzzy logic and sliding mode control

The torque ripple reduction control of the switched reluctance motor (SRM) is generally implemented by current control, turn-on and turn-off control based on the inductance profile. Turn-off angle control, as a complex relation between motor speed and current, is required for a wide range of operating speeds. However, these methods show limited performance. This paper presents a fuzzy logic turn-off angle control scheme with a sliding mode torque control considering complex and nonlinear characteristics of SRM. Since a turn-off angle controller cannot reduce torque ripple satisfactorily in commutation region, this paper additionally applies a sliding mode torque controller. The proposed control strategy combines fuzzy logic turn-off angle control and sliding mode torque control which does not require a complex look-up table and allows a wide speed range operation. Simulation results are presented to verify the effectiveness of the proposed torque ripple minimization technique.

A Controller Design for a Stability Improvement of an On-Board Battery Charger

This paper proposes the controller design for a stability improvement of an on-board battery charger. The system is comprised of a power factor correction (PFC) circuit and phase shift full-bridge DC-DC converter. The PFC circuit performs the control of the DC-link voltage and the input power factor. The DC-DC converter regulates the voltage and the current in the battery using the DC-link voltage. This paper proposes the design method of PI controller for the PFC circuit using a small signal model. The analysis and design of a type-three controller for the DC-DC converter is also presented. A simulation and experiment has been performed on the on-board battery charger and their results are presented to verify the validity of the proposed system.