Current mode control of switching regulators

This paper presents a novel current mode control technique using an Adaptive Neuro Fuzzy Inference system (ANFIS) for single phase power factor correction (PFC) with DC- DC Single Ended Primary Inductance converter (SEPIC). The proposed system uses cascade control strategy which comprises of outer voltage PI controller and an inner current controller. The outer PI controller coefficients are determined by appropriate tuning and inner current control is implemented with AnFIS. The performance of the proposed system is analysed using Matlab/Simulink based simulation studies. In order to ensure the robustness of the proposed controller the performance parameters such as Percentage Total Harmonic Distortion(%THD), Power factor (PF),%Voltage regulation, %Efficiency are analyzed. From the simulation results, it is inferred that the proposed method provides efficient tracking of output voltage and source current for step load, set point and line variations.

Microgrids are distributed generation structures that link groups of Distributed Generators (DGs) to either connect to the utility grid, or to operate as a standalone (islanded) system. However, the injected power from each DG must be carefully controlled to ensure reliable power distribution, balanced modular operation, and regulated voltages across the microgrid. It is commonly accepted that DG units cannot operate in current-control mode when islanded, because there is no stiff grid voltage available. Consequently they are usually operated in voltage control mode, with individual droop controllers regulating the inverter voltage magnitude and frequency to share active and reactive power. This paper presents a new approach to operate islanded microgrid DG units in current control mode, by combining linear current regulators with predictive voltage control. The result achieves a rapid load response while still maintaining well regulated voltage levels. A current magnitude droop controller is also proposed to maintain equal power sharing between the current controlled DG units.

To realize accurate current control for a boost converter, a precise measurement of the inductor current is required to achieve high resolution current regulating. Current sensors are widely used to measure the inductor current. However, the current sensors and their processing circuits significantly contribute extra hardware cost, delay and noise to the system. They can also harm the system reliability. Therefore, current sensorless control techniques can bring cost effective and reliable solutions for various boost converter applications. According to the derived accurate model, which contains a number of parasitics, the boost converter is a nonlinear system. An Extended Kalman Filter (EKF) is proposed for inductor current estimation and output voltage filtering. With this approach, the system can have the same advantages as sensored current control mode. To implement EKF, the load value is necessary. However, the load may vary from time to time. This can lead to errors of current estimation and filtered output voltage. To solve this issue, a load variation elimination effect elimination (LVEE) module is added. In addition, a predictive average current controller is used to regulate the current. Compared with conventional voltage controlled system, the transient response is greatly improved since it only takes two switching cycles for the current to reach its reference. Finally, experimental results are presented to verify the stable operation and output tracking capability for large-signal transients of the proposed algorithm.

This paper presents the principles and performance of peak current mode control applied to active clamp forward converter in comparison to the conventional voltage mode control. There is a clamp circuit comprising one auxiliary switch and one clamp capacitor, used in the forward converter to recycle the energy stored in the transformer. Due to presence of clamp circuit the active clamp forward converter with center tapped secondary exhibits fourth order power stage dynamics. When conventional voltage mode control is adapted, the forth order power stage dynamics imposes limitations on the closed loop performance of the converter. It is demonstrated that current mode control can be adapted to enhance the closed loop performance of active clamp forward converter. Different transfer functions are derived using state space average model. The peak current mode control is applied and simulation results are presented.

This chapter contains sections titled: Sampling Effects of Current Mode Control Expressions for s-Domain Model for Current Mode Control New Control Design Procedures for Current Mode Control Off-Line Flyback Converter with Optocoupler-Isolated Current Mode Control Summary ]]>

Traditional multi-input converters have simpler configuration, but they have some disadvantages like multiple primary winding, high voltage stresses across the switches and also transfer of energy to the load occurs only from anyone of the input sources. This article proposes an isolated converter with reduced number of primary winding, and the load can be supplied by the sources either individually or simultaneously. The main objective of this work is to inject power into the grid using a three input single output Fly back DC–DC converter with closed loop control using one cycle controller (OCC) and PI controller. For power management, the inductor current is measured and the duty ratios of respective sources are controlled in such a manner that the average current flowing through the switch is proportional to power delivered by respective sources. In order to maintain the output voltage to be constant, the duty ratio of any one source is to be controlled by using outer voltage controller and inner current controller. Here, the duty ratios of first two sources are controlled by current mode control using OCC and the duty ratio of third source is controlled by using voltage controller with inner OCC current control. Since OCC is a nonlinear technique, only one PI controller is needed by the system. The system has only two sensors, one for measuring the output voltage and one for measuring the inductor current.

This paper presents the control to output transfer function, principles and performance of peak current mode-controlled active clamp forward converter with centre-tap transformer. There is a clamp circuit comprising of one auxiliary switch and one clamp capacitor, which is used in the forward converter to recycle the energy stored in the magnetising inductor. Due to presence of clamp circuit, the active clamp forward converter with centre tap transformer exhibits fourth-order power stage dynamics. The current mode control is implemented to enhance the performance of the converter by sensing the main switch current. It is demonstrated that current loop gain splits not only the complex-conjugate pole of the output filter but also the complex-conjugate pole pair formed by clamp circuit into real poles. Different transfer functions are derived using state space average model. The peak current mode control is implemented experimentally using controller IC, UCC2891D, and the simulation results are verified with the experimental setup.

Normalized small signal model of switching DC-DC converter with voltage mode control, current mode control, V2 control and V2C control technique is derived, analyzed and compared in the present paper. It is shown that the transient response character of V2 control and V2C control is better than voltage mode control and current mode control, with the transient response character of V2C control the best. The experiment study performed on buck converter verifies our studies.

A boost converter-based LED driver is predominantly used in portable display devices, where the high voltage gain makes it difficult to achieve fast start-up and dimming performance, because of the detrimental effect of the right-half-plane (RHP) zero. In the majority of commercial products, a fixed-frequency current mode control (CMC) technique is used. This requires an over-compensated ramp for current-loop stability, which would tend to degrade the phase margin using a type-II compensator. Constant off-time (COFT) CMC may not require any ramp compensation and can achieve superior performance. However, suitable design methods are not readily available to identify performance limits using fixed-frequency and COFT CMC architectures. This paper presents the small-signal design and performance limitations of a type-II controller in CMC architectures. Thereafter, a trajectory-based design approach is developed to identify critical performance limits using a resettable PI controller, which can achieve near time-optimal performance with and without a peak current limit. Start-up performance is shown to be further improved by using a low voltage LED string, however, at the cost of an increasing pin count. Finally, a method is identified to achieve smooth controller transitions in a peak current-based constant on/off-time multi-mode controller. Experimental results of a few commercial LED drivers with their performance limits are presented, and for the same specs, the performance improvement using the proposed design framework is demonstrated using simulation results.

Impact of distributed generation on power systems has caused considerable recent research interest. Development of distributed generation sources, usually uses renewable energy, associate with power electronics in field of development invertors. Consequently, much research in recent years has focused on improving invertors and their control systems. Actual task is to forming information and control signals for invertor current mode controller, according to results of stability evaluation algorithm. This algorithm aimed on provides stable operation of power system. In addition, it should be proposed supplements to logic of current mode controller into invertor. Our results focus on improving of invertor performance, consist of control systems dexterity extension. Results are propose procedure of creating control signals, aimed on provide stable operation of electrical network. Suggestions on development module of stability estimation and forming control signals are made. Our results have potential on dexterity extension of current mode controller operation, therefore, total performance of invertor.

Shunt active power filter is a complete current source which can provide a effective and adjustable solution for elimination of harmonic currents in power system. Its performance, depends on strategy employed in reference current generation, control technique and topology of inverter used in the design. In this study, fuzzy logic current control technique was presented for generation of pulse for PWM current control of the three phase inverter. A band pass filter was used in synchronous reference frame algorithm (SRF) for harmonics extraction. The shunt active power filter performance was evaluated with MATLAB/SIMULINK under balanced voltage condition. The result obtained gives good and satisfactory response to mitigate the harmonics in the system.

Grid-forming converters (GFMs) are faced with the threat of inrush current and sever transient instability issues during grid faults, which calls for fault ride through (FRT) capability. Several FRT control strategies are proposed for single GFM connected to grid system in existing literatures while transient interaction mechanism among paralleled GFMs still remain unrevealed and corresponding FRT control are rarely discussed. To fill this gap, coordinated FRT control based on mode-switching is proposed for paralleled GFMs in this article. The proposed FRT control would turn GFMs into current control mode during grid fault periods and return to voltage control mode after fault clearance, which enables current control flexibility during grid fault. To guarantee stable operation throughout fault period, transient interaction models in current control mode and voltage control mode are established respectively. Then, design-oriented transient stability analysis is carried out using equal area criterion (EAC) theory. Finally, detailed simulation results based on PSCAD/EMTDC and experimental results are provided to validate the effectiveness of proposed method.

Minimization of Torque Ripple Content for BLDC Motor by Current Controller using MLI

Current mode control (CMC) though offers improved line regulation, phase margin and high bandwidth suffers from high output impedance. Although load regulation can be improved by incorporating an integral gain, it reduces the phase margin and increases the overshoot. The objective of this paper is to achieve improved output impedance without using an integral controller. Incorporating a high pass filter in series with the current sensor in CMC, the closed loop DC gain of a CCM buck converter is shown to be almost independent of the load resistance, thus improving load regulation using a proportional controller only. Improved features of CMC are also retained. Following VMC modeling approach, we develop a method to obtain the small signal model of the proposed scheme, and extended to CMC with an accurate low frequency characterisation. The proposed scheme is implemented on a buck converter, and the theoretical results are validated by experiments.

A new all-digital current control technique is presented in this paper. The current control is based on Ramptime current control technique, where multisampling is chosen as the sampling strategy due to its ability to provide higher accuracy. The resultant current control is called Digital Ramptime current control. The performance of the new current control is compared with the original Ramptime in an active power filter experiment. Results show that with sufficient sampling, the performance of Digital Ramptime is satisfactory.