Search

This study proposes a voltage-oriented control scheme for four-quadrant grid-tie of a single-phase bidirectional direct current/alternating current (AC) voltage-sourced converter (VSC) to operate smartly at modes of unity power factor (PF) rectifier (UPFR), inverter or static var compensator. Given the possible harmonic-distorted AC grid voltage, the proposed scheme follows or filters the grid voltage to generate the appropriate current command template for minimising the harmonic current while synchronising with the grid. The following template is for the UPFR mode, whereas the filtered template is for the other modes. The scheme proposes a unique band-pass filter (BPF) to proceed with direct component generation for the filtered template. The proposed scheme further unifies the grid-tie inductor current-to-voltage conversion for the following emplate and the quadrature component generation for the filtered template into a differentiator. The control laws under the filtered and following templates are derived. The BPF and differentiator designs are introduced. Simulations and experiments are conducted with a one-cycle control full-bridge VSC to verify the proposed grid-tie control scheme and evaluate its performance.

This paper presents rehabilitation robot with torque control with impedance scheme for post-stroke patients in the upper limb of the shoulder. This impedance scheme consists of external force input and impedance value. The external force input comes from the load cell at the end of the robot (the end effector), which is generated by the patient's force. The input force consists of two Cartesian directions, which will affect the robot dynamic torque for the X-axis and Y-axis. Meanwhile, the value of the impedance in the robotic system is provided by the therapist who handles the stroke patients. The amount of impedance in the robotic system can be adjusted according to the patient's condition. In this paper, we used 3 DOF (Degree of Freedom) self-produced robots. The rehabilitation trajectory consists of two parameters, the position parameter, and the torque control parameter in the impedance system. The impedance scheme in the robotic system use impedance characteristics and Proportional Integral (PI) controller. Proportional Integral (PI) controller is used as a simulation control in tracking errors of position and the torque impedance of the robot. With a simple controller, the characteristics relationship between the changes in the magnitude of the external force produced by the patient and the change in impedance values given to the robot system are obtained. By knowing these characteristics, robots can interact with various types of stroke patients.

A differential boost inverter (DBI) consists of two bidirectional boost converters and has a differential sinusoidal output voltage. This output voltage is obtained because each bidirectional boost converters generates a dc-biased sinusoidal voltage. Owing to this characteristic, this inverter topology requires a controller that can track a dc-biased sinusoidal voltage as the control reference. One cycle control (OCC) is a non-linear control approach that can meet the requirements and be easily implemented in a simple circuit with constant switching frequency. The controller must be capable of achieving a unity power factor (PF) because the inverter is designed to deliver maximum active power to the grid. Therefore, the sinusoidal reference signal of the OCC is formed by the scaled grid voltage and its derivation. Given this reference signal, the inverter output voltage represents the grid voltage with a small variation phase and amplitude. Furthermore, this strategy will guarantee that the output current and the grid voltage are in phase. An experimental prototype of DBI is implemented to verify that the control approach can achieve PF close to unity such that the maximum active power can be delivered to the grid with minimum current total harmonic distortion.

In a grid-connected photovoltaic (PV) system, an inverter should have a capability not only to track the maximum power of PV module but also to synchronize the output current to the grid. In the previous work, a grid-connected single-stage inverter based on differential topology with an analog one-cycle controller (OCC) has been proposed. However, the inverter lacks PV power tracking capability. In this paper, a simple maximum power point tracking (MPPT) technique is studied to be integrated to the proposed inverter. The MPPT technique is based on the inverter output current adjusting. The simulation results verify that the designed MPPT can extract the power maximum of PV module and the inverter can maximally deliver the photovoltaic power to the grid.

This paper presents a one-cycle controller of buck inverter with a current limiter. In some applications, a buck inverter is widely used to convert a higher input DC voltage to a lower output AC voltage. There are some types of buck inverter such as full-bridge, half-bridge, differential, and so on. For a buck inverter with differential type, one-cycle control (OCC) can be easily implemented because it has a simple design. It has also another advantage including an ability of disturbance rejection. Since OCC is designed to work in voltage mode, it has no capability to control the output current. Therefore, a current limiter is important to be integrated to the controller. The simulation verification shows that by integrating the current limiter to the controller, overshoot of output current can be limited to the certain value without decreasing the controller performance.

One-cycle control (OCC) is widely used in many power converter topologies because of its advantages. However, in the control process, OCC uses integration of chopped diode voltage to control the output voltage of the converter where, in the case of the dc-dc buck converter, the chopped diode voltage represents only the input voltage. Thus, it will lead to the nonzero steady state error of the output voltage. Moreover, the output disturbance will have more effect to the converter performance. In this paper, a type-III compensator is designed for improving the performance of one-cycle controlled buck converter. Furthermore, the controller can eliminate both input and output disturbance with zero steady-state error. The simulation results verify the performance of the designed controller.

This paper presents a photovoltaic (PV) system parallel connected to an electric power grid with a power factor corrector (PFC) for supplying the DC loads. The operation principles and design considerations for the presented PV system are analyzed and discussed. The balanced distribution of the power flows between the utility and the PV panels is achieved automatically by regulating the output DC voltage of the PFC. Experimental results are shown to verify the feasibility of the proposed topology, which can effectively transfer the tracked maximum power from the PV system to the DC load, while the unity power factor is obtained at the utility side.

This paper presents a DSP-based differential boost inverter (DBI) with maximum power point tracking (MPPT) for photovoltaic (PV) applications. In a conventional DC/AC MPPT system, power of photovoltaic is delivered into two stages, they are DC/DC boost converter and buck type DC/AC inverter. A DC link capacitor appears between these two stages. Furthermore the system has higher complexity and costly than that of DC/AC MPPT system with a single stage boost inverter. Here, a single stage differential boost inverter is implemented. Since it can produce a sinusoidal output voltage higher than its DC voltage input, it is not only able to reduce the stage number of DC/AC MPPT system but also able to eliminate the DC link capacitor. The MPPT method employed in this study is P&O method. This technique is widely used due to its easy implementation, and unimportant extreme weather change consideration. To implement this technique, a digital signal processor (DSP) was used. In this paper, a review of DBI and MPPT implementation are presented. Finally a 400 W laboratory prototype has been built. The result shows that the P&O MPPT method has been successfully implemented for various PV power and it can reach 95% maximum MPPT accuracy. In addition, the DBI is able to produce a sinusoidal output voltage at the various PV power conditions.

Conventional maximum power point tracking (MPPT) method, e.g. perturbation and observation (P&O) and incremental conductance (INC), have the drawbacks such as oscillation at the MPP during power fast tracking and power divergence under rapidly changing atmospheric condition. Thus, a fuzzy logic controller (FLC) is implemented in the PV system to avoid the conventional problem. FLC method has not only fast response under rapidly changing atmospheric conditions but also small oscillation at the maximum power point (MPP). However, FLC presents tuning difficulty of membership function, scaling factor and control rules. The FLC disadvantages can be reduced using single-fuzzy logic controller (S-FLC) without degrading its performance. The experiment results are shown to verify the studied S-FLC MPPT method.