Mohd. Zulkifli Ramli

A simple energy recovery scheme to harvest the energy from shaded photovoltaic modules during partial shading

This paper proposes a simple circuit to recover the energy that otherwise would be lost due to the partial shadings on photovoltaic (PV) modules. Since the circuit can be readily retrofitted to an existing PV system, no modification on the central inverter is required. The main idea of the scheme is that, during partial shading, parts of the current from the nonshaded modules are harvested by an energy recovery circuit using power electronic switches and storage components. In doing so, the current of the PV string is maintained at the level generated by the shaded module. There is no need for the shaded module to be short-circuited; as a result, it can still actively produce output power (despite being partially shaded). To investigate the idea, the proposed circuit is retrofitted to a prototype PV system using eight modules. The partial shading conditions are emulated using a solar simulator with a controllable irradiance capability. The results are validated by a good agreement between the experimental and simulation works.

A bidirectional high-frequency link inverter using center-tapped transformer

In this paper, a bidirectional high-frequency link inverter is proposed. The main feature of the inverter is that the electrical isolation is provided by a high-frequency center-tapped transformer. Furthermore, the sinusoidal pulse width modulation method is modified so that the transformer can be utilized near to its full potential. As a result, the power switches count is reduced, and the efficiency increased. A 1 kW prototype inverter is built and typical results are presented.

High-Frequency Transformer-Link Inverter with Regenerative Snubber

This work proposes a bidirectional high-frequency link inverter using center-tapped high-frequency transformer. The topology also incorporates a regenerative snubber to clamp the high voltage spikes due to the leakage inductance of the transformer. The closed-loop control method used is deadbeat control, which provides fast response and low harmonic distortion, even under nonlinear loads. A 1 kVA prototype inverter is built and the workability of the system is experimentally verified

Hardware Implementation of the High Frequency Link Inveter Using the dSPACE DS1104 Digital Signal Processing Board

In this paper, a detail description of a highly efficient and compact high frequency link inverter is given. The focus will be on the deadbeat controller implementation using the dSPACE DS1104 digital signal processing (DSP) board. In addition, other hardware components such as the gate drives, power circuit, control signals generation, signal conditioning and test-load banks is also described. Selected results from the experimental prototype will be presented.

An Improved `DC-DC Type' High Frequency Transformer-Link Inverter by Employing Regenerative Snubber Circuit

This work proposes a bidirectional high frequency (HF) link inverter using center-tapped high frequency transformer. The main advantage of this topology is the reduced size of the converter. However the utilization of the high frequency transformer results in the occurrence of high voltage spike at its secondary. To solve this problem, we incorporate a regenerative snubber to clamp the spike and subsequently feed the energy back to the power circuit. The inverter also utilizes less number of switches, which results in lower conduction and switching losses. This paper describes some of the important aspects of the snubber design. It is verified with a 1 kW inverter prototype.

A bidirectional inverter with high frequency isolated transformer

There is a growing interest to develop renewable energy, particularly the solar energy to meet the growing energy demand. In this paper, a bidirectional photovoltaic (PV) inverter using high frequency (HF) transformer is proposed. The HF transformer provides electrical isolation between the DC supply and AC output. Besides, by using minimum power switches at the active rectifier on the secondary side of HF transformer, the system has low switching losses. Therefore, the proposed inverter has advantages of reliable, lightweight, low cost and increased efficiency. A prototype inverter is implemented using a low cost microcontroller and laboratory experiments are carried out to verify the system viability.

A low cost solar array simulator using halogen tungsten bulb with temperature control capability

This paper proposes a configuration of a low cost solar module simulator (SAS), suitable for basic studies on PV systems. The utilizes the halogen tungsten bulbs as the light source. Furthermore, water tank is placed in between the bulbs and the PV module to control the rise in temperature. The halogen tungsten bulb is powered by DC voltage rectified from a three phase supply. Its light intensity is control by IGBT using high frequency switching. The SAS is capable of generating 1000W/m2 of irradiation. During the experiment the PV modules temperature dropped about half to 53°C after using water filters in 15 minutes exposure to the 1000W/m2 irradiation. To test the capability of the SAS, a case study involving PV system under partial shading is carried out.

AC Voltage Regulation of a Bidirectional High-Frequency Link Converter Using a Deadbeat Controller

This paper presents a digital controller for ac voltage regulation of a bidirectional high-frequency link (BHFL) inverter using deadbeat control. The proposed controller consists of inner current loop, outer voltage loop and a feed-forward controller, which imposes a gain scheduling effect according to the reference signal to compensate the steady-state error of the system. The main property of the proposed controller is that the current- and the voltage-loop controllers have the same structure, and use the same sampling period. This simplifies the design and implementation processes. To improve the overall performance of the system, additional disturbance decoupling networks are employed. This takes into account the model discretization effect. Therefore, accurate disturbance decoupling can be achieved, and the system robustness towards load variations is increased. To avoid transformer saturation due to low frequency voltage envelopes, an equalized pulse width modulation (PWM) technique has been introduced. The proposed controller has been realized using the DS1104 digital signal processor (DSP) from dSPACE. Its performances have been tested on a one kVA prototype inverter. Experimental results showed that the proposed controller has very fast dynamic and good steady-state responses even under highly nonlinear loads

Analysis and design of a closed loop controller for bidirectional high-frequency link inverter

This paper presents a closed loop controller for bidirectional high-frequency link inverter. Deadbeat control is adopted to achieve fast dynamic response. The controller consists of inner current loop and outer voltage loop. To improve overall performance of the system, additional decoupling networks are employed. Output voltage decoupling network is included to improve the response of current loop; while load current decoupling network is used to increase the robustness of the inverter towards load variation. Simulation results are presented for the closed loop system under linear and nonlinear loads. It is shown that the control method provides good dynamic response with low total harmonic distortion, even under full-bridge rectifier loads.