Model predictive control for current balancing in a four-phase buck converter

Multiphase buck topology offers smaller ripple current and lower component ratings. This, however, compromises unbalanced output current between each phase of an inductor which leads to over-current and inductor saturation issues. Often when discussing the linear control schemes, it involves the use of superposition theorem to understand the system’s response. However, the limitation of superposition theorem in this application is that it assumes the circuit to be completely linear. For components with nonlinear behaviour such as power switches and diodes, the analytical results may not be accurate resulting to unexpected behaviour as the algorithm is implemented on a real system. Hence, the use of a more advanced control scheme is necessary to improve a system with a non-linear characteristic. This paper proposes a current limit control (CLC) consists of MPC for inner loop control and PID for outer loop control for phase current balancing in a four-phase buck converter. The controller is designed to achieve balanced current for each phase with acceptable response time. The proposed system is designed using MATLAB/Simulink simulation software and verified by a laboratory prototype with a TMS320F28335 as the main controller. Simulation and experimental results are provided to validate the system performance

Improvement of speed response in four-phase DC–DC converter switching using two shunt voltage-source

This study proposes a technique that is able to improve the speed response of a four-phase DC–DC converter switching. The basic concept of the proposed technique is the inclusion of two shunt-connected voltage sources in series to the converter system. Using a higher input voltage to drive the load, a higher current per microsecond output system will be obtained and reverts to its nominal input upon obtaining desired references. Thus, the transient response observed when using this proposed technique is found to be much faster when compared to the conventional converter. Moreover, this technique is easily implemented as it requires only an additional voltage source, power switch, and power diode. The integrated model of the two shunt voltage-source in a four-phase DC–DC converter was simulated in MATLAB/Simulink and validated against the experimental results of a laboratory prototype, 600 W four-phase DC–DC converter. The novelty of this proposed technique is its ability to provide faster operations for critical loads applications, lower output capacitor and lower operating frequency

Switching speed improvements in multiphase buck converter via two-shunt voltage-sources

Multiphase Buck converters are well known for their smaller ripple current, smaller filter design and smaller component ratings. The converter operating responses however depend on the value of inductor and load resistance. Increasing the switching frequency can improve the transient responses. However, it reduces the system efficiency and controlling the current response can be complex. This paper proposes an improved multiphase buck converter for a lithium-ion battery charging applications. The proposed system is based on the ‘Bi-level drives’ concept, which requires two input voltage in which one is higher than the other input and is connected in series to the system. By driving the load with a higher input voltage, the transient response is observed to be much faster. Upon reaching the desired reference output, the system will revert to a lower input voltage, thus, the efficiency of the system will not be affected. This scheme requires additional two power switches and a power diode. The operation and the switching scheme will be discussed in this paper

Experimental implementation controlled SPWM inverter based harmony search algorithm

An optimum PI controller using harmony search optimization algorithm (HS) is utilized in this research for the single-phase bipolar SPWM inverter. The aim of this algorithm is to avoid the conventional trial and error procedure which is usually applied in finding the PI coefficients in order to obtain the desired performance. Then, the control algorithm of the inverter prototype is experimentally implemented using the eZdsp F28355 board along with the bipolar sinusoidal pulse width modulation (SPWM) to control the output voltage drop under different load conditions. The proposed overall inverter design and the control algorithm are modelled using MATLAB environment (Simulink/m-file Code). The mean absolute error (MAE) formula is used as an objective function with the HS algorithm in finding the adaptive values of  and  parameters to minimize the error of the inverter output voltage. Based on the output results, the proposed voltage controller using HS algorithm based PI (HS-PI) showed that the inverter output performance is improved in terms of voltage amplitude, robustness, and convergence rate speed as compared to PSO algorithm based PI (PSO-PI). This is to say that the proposed controller provides a good dynamic responses in both cases; transient and steady-state. Finally, the experimental setup result of the inverter controller is verified to validate the simulation results

Global economic burden of unmet surgical need for appendicitis

Background: There is a substantial gap in provision of adequate surgical care in many low-and middle-income countries. This study aimed to identify the economic burden of unmet surgical need for the common condition of appendicitis. Methods: Data on the incidence of appendicitis from 170 countries and two different approaches were used to estimate numbers of patients who do not receive surgery: as a fixed proportion of the total unmet surgical need per country (approach 1); and based on country income status (approach 2). Indirect costs with current levels of access and local quality, and those if quality were at the standards of high-income countries, were estimated. A human capital approach was applied, focusing on the economic burden resulting from premature death and absenteeism. Results: Excess mortality was 4185 per 100 000 cases of appendicitis using approach 1 and 3448 per 100 000 using approach 2. The economic burden of continuing current levels of access and local quality was US $92 492 million using approach 1 and$73 141 million using approach 2. The economic burden of not providing surgical care to the standards of high-income countries was $95 004 million using approach 1 and$75 666 million using approach 2. The largest share of these costs resulted from premature death (97.7 per cent) and lack of access (97.0 per cent) in contrast to lack of quality. Conclusion: For a comparatively non-complex emergency condition such as appendicitis, increasing access to care should be prioritized. Although improving quality of care should not be neglected, increasing provision of care at current standards could reduce societal costs substantially