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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.

This paper presents systems and algorithms for the low-voltage ride-through control of wind power systems. The low-voltage ride-through (LVRT) requirement which is included in the grid-code regulates wind power systems to maintain their operation and supply reactive power during grid fault. When the grid fault arises some problems occur in wind power systems, such as over voltage and over current by transient conditions or surplus power. This paper proposes the LVRT strategy for a stable operation of wind power systems under the grid-fault condition. Proposed LVRT methods include a fault detection method, a design of dynamic braking resistor, and a flexible power control under various fault conditions. The simulation results show a validity of the proposed LVRT strategy with a 2-MW wind power system model.

This paper proposes an output current ripple reduction algorithm using a proportional-integral (PI) controller for an energy storage system (ESS). In single-phase systems, the DC/AC inverter has a second-order harmonic at twice the grid frequency of a DC-link voltage caused by pulsation of the DC-link voltage. The output current of a DC/DC converter has a ripple component because of the ripple of the DC-link voltage. The second-order harmonic adversely affects the battery lifetime. The proposed algorithm has an advantage of reducing the second-order harmonic of the output current in the variable frequency system. The proposed algorithm is verified from the PSIM simulation and experiment with the 3 kW ESS model.

This paper proposes a new design for quick battery charger systems for electric vehicles that consists of a three-phase inverter and a full-bridge converter which use the phase-shift method. The 3-phase inverter controls the input and DC-link voltage by use of a current controller and a voltage controller. The full-bridge converter transfers the DC-link voltage to a fixed output voltage. Designs for the output-side converter and controller for improved performance are proposed in this paper. Design schemes for the filter and controller of an input-side inverter are also presented. Furthermore, the paper proposes a compensation method for the offset current that is caused by switch failure and circuit problems. Simulations and experiments have been performed on a 50kW-battery charger system that is suitable for vehicles. The presented results verify the validity of the proposed method and the superiority of the system over conventional methods.

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.

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.

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.

This paper proposes a second-order harmonic reduction technique using a proportional-resonant (PR) controller for a photovoltaic (PV) power conditioning system (PCS). In a grid-connected single-phase system, inverters create a second-order harmonic at twice the fundamental frequency. A ripple component unsettles the operating points of the PV array and deteriorates the operation of the maximum power point tracking (MPPT) technique. The second-order harmonic component in PV PCS is analyzed using an equivalent circuit of the DC/DC converter and the DC/AC inverter. A new feed-forward compensation technique using a PR controller for ripple reduction is proposed. The proposed algorithm is advantageous in that additional devices are not required and complex calculations are unnecessary. Therefore, this method is cost-effective and simple to implement. The proposed feed-forward compensation technique is verified by simulation and experimental results.

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.

This paper proposes an improved maximum power point tracking (MPPT) method for wind power systems. The proposed method combines hysteresis control with tip speed ratio (TSR) control using a power coefficient curve. It has fast dynamic characteristics with the TSR control using data obtained from an anemometer. Moreover it can track the maximum power point (MPP) with hysteresis control even when there is incomplete data. Since the proposed method selects the operating mode according to the operation state of the generator of three control modes, the controllers do not interfere with each other and they provide excellent performance. The effectiveness of the proposed algorithm is verified by simulation and experiments based on a 3 kW wind turbine system.

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.

This paper proposes a performance improvement of a grid-connected wind turbine using sliding-mode based direct power control under an unbalanced grid fault. The proposed control method has some advantages for grid connected control. At first, it doesn't need the synchronous phase angle of the grid voltage. It has also fast dynamic characteristics compared with a conventional current controller. In addition, it is suitable for an unbalance compensation control. The effectiveness and robustness of the proposed algorithm are verified by simulations and experiments.

This paper proposes an output current ripple reduction algorithm using model-based predictive control (MPC) for an energy storage system (ESS). In single-phase systems, the DC/AC inverter has a second-order harmonic at twice the grid frequency of a DC-link voltage caused by pulsation of the DC-link voltage. The output current of a DC/DC converter has a ripple component because of the ripple of the DC-link voltage. The second-order harmonic adversely affects the battery lifetime. The MPC predicts the output current of next state from a converter model. The optimal duty is determined by minimizing the error between the reference and the predicted current. Due to the calculated optimal duty, the dynamic response is fast. The proposed algorithm has an advantage of reducing the second-order harmonic of the output current in the variable frequency system. The proposed algorithm is verified from the PSIM simulation with the 3 kW ESS model.

This paper proposes a fault diagnosis and tolerant method for switched reluctance motor (SRM) drives. In many industrial applications, the reliability of the power transistor of the power converter is the main problem. In this paper, two types of faults (short and open) are analyzed through the current pattern of the power converter for SRM drives. The fault is detected when the measured amplitude of the current differs from the normal state. The fault tolerant scheme is applied according to each fault type. Simulations have been performed in the 1.5kW SRM drive and their results are presented to verify the validity of the proposed method.

This paper proposes a control scheme of the low voltage ride through (LVRT) in wind turbines (WTs). The LVRT requirement which is included in the grid-code regulates WTs to maintain their operation and supply reactive power during grid fault. If the systems do not have solutions for the LVRT control, the WTs cannot maintain operation under LVRT condition or the faults can be generated in the system. This paper proposes a detection method of grid faults and control strategy for flexible power control under LVRT condition. In addition, the control scheme using a direct power control based on a sliding mode control (DPC-SMC) improves a performance of the LVRT control. The simulation results verify the validity of a proposed control scheme.

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

This paper proposes a controller design of quick battery chargers for electric vehicles with a current offset. The quick charger consists of a three-phase grid connected inverter and a full-bridge converter which use the phase-shift switching method. The 3-phase inverter controls the input and DC-link voltage by use of a current controller and a DC-link voltage controller. The full-bridge converter transfers the DC-link voltage to a fixed output voltage. The system and controller design of the quick charger are proposed in this paper. Furthermore, the paper proposes a compensation method for the offset current that is caused by switch failure and circuit problems. Simulations have been performed on a 50kW-battery charger system that is suitable for vehicles. The presented results verify the validity of the proposed method.

This paper proposes a neutral-point voltage balancing method for a grid-connected NPC inverter system. The proposed method is achieved by adding the time-offset to three phase turn-on times of switches. The proper time-offset is simply obtained through the proposed time-offset variant estimating. By using the proposed method, it is possible to balance the neutral-point voltage without additional hardware, complex calculation and analysis. Simulations are carried out to confirm the effectiveness of the proposed method.

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.

A fault detection method for the switch devices of three-parallel power converters in a wind turbine system is presented. The proposed method utilizes the measured 3-phase currents which were already used for controlling the converters. Additional current and voltage sensors are thus not necessary. Consequently, this particular feature potentially cuts costs to apply the detection algorithm. The 3-phase currents are transformed to a stationary reference frame. This reference frame possesses specific patterns in accordance to the conditions of the switch devices in the converter. Open faulty switches can be detected by analyzing the obtained pattern. The reliability of the proposed fault detection method was proven by simulation results.