Design and development of digital Ramptime current control technique

Mathematical modeling and analysis of converters is an essential and critical phase in the design stage of the system. High current switching and inductor ripple causes electromagnetic interference in the system. Paralleling of the converters and smart switching control will reduce the stress on the converter switches. Substantial ripple reduction in the source and load current can be achieved by optimally choosing the transfer ratio. Multiphase technique increases the ripple frequency resulting in lesser filter requirements. A two phase bidirectional converter operating in continuous current conduction mode is modeled and digital average current mode control technique is proposed to regulate the output voltage. A 700 watt system is designed and the simulation and experimental results are presented.

The digital double loop current control become the promising technique for digital switching DC-DC converters. In this paper a novel current control technique, named cycle-borrow control is proposed and studied, which has faster loop transient response than the time delay control, and its requirement to loop processing speed can be relaxed as compared with the deadbeat current control. The cycle-borrow valley current control laws of buck DC-DC converters with four different pulse width modulations are derived, and their stabilities are analyzed. A simple digital slope compensation (DSC) method which doesn't need any extra slope compensation circuit is proposed to eliminate the sub-harmonic oscillations of cycle-borrow control. The simulation results show that, the transient response performance of dual-edge modulations is better than that of single-edge modulations. The cycle-borrow control technique is especially benefit to high-frequency digitally controlled switching DC-DC converters.

Performance of conventional digital current controllers is constrained by transport delays within the feedback acquisition chain, as well as by delays inherent to the pulse width modulation. In this paper, we introduce a novel current controller which provides a very high closed-loop bandwidth, improves the robustness and disturbance rejection, and eliminates the noise and sampling errors in the feedback path. In order to achieve these goals, we suppress the transport delays by introducing an improved execution schedule of the control interrupt and by inserting a cascaded multiplier of differential character. With the novel gain setting rule, the closed-loop bandwidth reaches 17% of the sampling frequency, disturbance rejection capability is doubled, the step response has a negligible overshoot, and the robustness is characterized by the vector margin of 0.65. Experimental verification is performed using an experimental setup with a three-phase inverter, digital controller, and a permanent magnet synchronous motor.

This paper presents an advanced current controller for grid-connected bidirectional ac/dc converters used for energy storage systems (ESSs). The proposed control scheme is designed to incorporate both the time-domain and frequency-domain dynamics to achieve superior transient and steady-state performance. The advanced current controller can overcome the various challenges faced by the conventional current controllers used in this application, which lead to sluggish transients and steady-state errors when tracking the sinusoidal reference for the grid current. Combining the time-domain dynamics with the frequency-domain dynamics creates a more intelligent controller compared to existing methods, which only consider the dynamics of one domain. The proposed controller is able to eliminate steady-state error by adaptively changing the controller coefficients in the frequency domain according to the current error. In the time domain, the control scheme minimizes the derivative of a defined energy function in order to optimize the transient performance. Simulation and experimental results obtained from a 3.3-kW grid-connected ac/dc converter demonstrate its superior performance.

A novel fully digital FPGA-based current controller for switched reluctance machines is presented in this paper. The digital current controller provides PWM and hysteresis band modulation in a seamless way and allows complex rotor position based shaping of the phase currents to optimize torque ripple and acoustic behavior. Arbitrary phase current waveforms can be stored in a position-addressed memory. The FPGA based implementation ensures flexible scaling and adaptation to various machine designs and inverter topologies. Experimental results prove the feasibility and performance of the chosen approach.

A novel digital current control strategy for digitally controlled DC-DC switching converters, referred to as Adjacent Cycle Sampling (ACS), is proposed in this paper. For the ACS current control strategy, the available time interval from sampling the current to updating the duty ratio, is approximately one switching cycle. In addition, it is independent of the duty ratio. As a result, the contradiction between the processing speed of the hardware and the transient response speed can be effectively relaxed by using the ACS current control strategy. For digitally controlled buck DC-DC switching converters with trailing-edge modulation, digital current control algorithms with the ACS control strategy are derived for three different control objectives. These objectives are the valley, average, and peak inductor currents. In addition, the sub-harmonic oscillations of the above current control algorithms are analyzed and eliminated by using the digital slope compensation (DSC) method. Experimental results based on a FPGA are given, which verify the theoretical analysis results very well. It can be concluded that the ACS control has a faster transient response speed than the time delay control, and that its requirements for hardware processing speed can be reduced when compared with the deadbeat control. Therefore, it promises to be one of the key technologies for high-frequency DC-DC switching converters.

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.

This paper compares two types of current control techniques with a view to the problem of switching ripples in the supply current caused by switching of an active power filter (APF). A closed loop control scheme of a three-phase APF is implemented using a TMS320C31 DSP for direct and indirect current control techniques. A current controlled voltage source inverter (CC-VSI) is used as an APF. A three-phase diode bridge rectifier with R-L load is taken as a nonlinear load. Experimental results for both the techniques of current control are compared and the capability of the indirect current control technique towards the elimination of switching ripples is established.

In this paper, a novel current control technique is proposed to control both active and reactive power flow from a renewable energy source feeding a microgrid system through a single-phase parallel-connected inverter. The parallel-connected inverter ensures active and reactive power flow from the grid with low-current total harmonic distortion even in the presence of nonlinear load. A p-q theory-based approach is used to find the reference current of the parallel-connected converter to ensure desired operating conditions at the grid terminal. The proposed current controller is simple to implement and gives superior performance over the conventional current controllers, such as rotating frame proportional-integral controller or stationary frame proportional resonant controller. The stability of the proposed controller is ensured by direct Lyapunov method. A new technique based on the spatial repetitive controller is also proposed to improve the performance of the current controller by estimating the grid and other periodic disturbances. Detailed experimental results are presented to show the efficacy of the proposed current control scheme along with the proposed nonlinear controller to control the active and reactive power flow in a single-phase microgrid under different operating conditions.

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.

By adapting the forward converter range of switching regulators to include an additional current-controlled feedback loop, derived from either the secondary or primary power circuit, an improvement in the closed-loop performance of the switching regulator can be obtained. The basic analysis work examines the simple single-ended forward converter, with d.c. plus a.c. current control, derived from the secondary power circuit. An additional fixed voltage ramp is also included in the control loop to provide `feedforward? compensation for input voltage disturbances, and also to extend the maximum duty cycle from 50% up to 100%. Using this circuit configuration a simple small signal equivalent circuit for the current-controlled switching regulator can be obtained, enabling the performance of practical designs to be predicted. Practical implementation of the current mode control technique using a standard large-scale integrated circuit together with a number of applications is also given.

This paper deals with the harmonic mitigation and reactive power compensation using Shunt Active filter. The performance of the Shunt active filter depends on the design and current control technique for generating a reference current. The design of the filter involves the iterative procedure for choosing the filter components so that it compensates the harmonics and reactive power for maximum load condition. The current controller method adopted for indirect current control technique where the reference signal is similar to the supply current signal. The Adaptive filter used in current controller mitigates harmonics and reactive power and voltage control loop of SAF balancing the active power between the load and supply unit. The learning rate is fixed by repeated simulation. The SAF active filter is tested in four load condition ie., nonlinear load(37% Total Harmonic Distortion(THD)),highly nonlinear load(>100% THD), linear load(<8% THD, power factor(pf) <0.5) and both nonlinear and linear load(37% THD and 0.7 pf). The study is carried out in MATLAB Simulink and the results are presented.

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

Since parabolic current control has fast transient response and high control precision with constant switching frequency, it is an attractive current control strategy for voltage source inverters. The employment of parabolic current control delivers great performance on current waveform control or voltage waveform control. The implementation of parabolic current control usually requires high speed digital-to-analog converters (DACs) to generate a pair of parabolic carriers as the control band. With increases in switching frequency, this requirement becomes more critical because the speed of DAC limits the update rates of the parabolic carriers. This impacts the smoothness and punctuality of the parabolic control band. To solve this issue, a parabolic current control based digital current control strategy is proposed in this paper. The proposed method uses the sensed current of the output inductor to calculate the next duty-cycle. To improve the transient response speed, a duty-cycle adjustment is presented. The performance of the proposed digital control method is verified in simulation.

From the cost-effective product point of view, it is very important to design a current controller with the highest utilization factor of current capacity of power devices. This can be accomplished by a current controller without overshoot irrespective of the varying bounds of control voltage in PWM power converters. This paper suggests a novel digital current controller which has a deadbeat current control response without steady state errors and deals with the design method of the controller for PWM power converters. The superior performance of the suggested controller is verified through extensive digital simulations performed by SIMULINK/MATLAB and is compared with those of a state deadbeat controller and a tracking anti-windup PI controller. Simulation results show that the suggested controller guarantees the full utilization of current capacity of power devices.