Digital Hysteresis Current Control Research Articles

VOT and VFT-Based hybrid digital hysteresis control for UPS inverter

When the digital hysteresis current control (DHCC) strategy is applied to control the uninterruptible power supply (UPS) inverter, here are some issues such as large hysteresis tracking error caused by sampling interval and severe switching frequency swing caused by rapid change rate of inductor current. To address these issues, this paper presents a digital control strategy based on the hybrid digital hysteresis current control (HDHCC) of variable opening time (VOT) and variable falling time (VFT) for UPS inverter. Firstly, the HDHCC structure is established and the working principle of the inverter system is described in detail. Then, the tracking error and switching frequency error of the DHCC are derived. Based on the performance requirement of quasi-constant frequency control of UPS inverter, VOT and VFT control criteria without the dependency of circuit parameters are given. The experimental results demonstrate that the hybrid digital hysteresis control strategy based on VOT and VFT has the advantages of high current tracking accuracy, accurate switching frequency control, small output voltage waveform distortion, and simple implementation.

Optimal Real Power Penetration to Solar PV-Fed Double Boost Integrated Multilevel Converter with Improved Power Quality

In grid-connected solar PV system, power quality gets affected seriously due to the variable real power penetration. The transformer is mandatory to integrate and isolate the solar PV and powered network. However, due to presence of this transformer, size and cost of the entire solar PV station get increased and it requires more space while supplying poor quality of power. In order to overcome this drawback, this paper proposes a double boost integrated multilevel inverter to inject the power into utility grid. In addition, the optimal control strategy is used to tap maximum power generation from solar PV and injected into grid with improved power quality. This paper presents an adaptive digital hysteresis current control approach to penetrate optimal power into grid. To validate the proposed work, the simulation results are carried out using PSCAD/EMDTC software. Furthermore, to confirm theoretical study and simulation study, the experimental test was performed and detailed results with validation were presented in this paper.

A Digital Hysteresis Current Control for Half-Bridge Inverters with Constrained Switching Frequency

This paper proposes a new robustly adaptive hysteresis current digital control algorithm for half-bridge inverters, which plays an important role in electric power, and in various applications in electronic systems. The proposed control algorithm is assumed to be implemented on a high-speed Field Programmable Gate Array (FPGA) circuit, using measured data with high sampling frequency. The hysteresis current band is computed in each switching modulation period based on both the current error and the negative half switching period during the previous modulation period, in addition to the conventionally used voltages measured at computation instants. The proposed control algorithm is derived by solving the optimization problem—where the switching frequency is always constrained at below the desired constant frequency—which is not guaranteed by the conventional method. The optimization problem also keeps the output current stable around the reference, and minimizes power loss. Simulation results show good performances of the proposed algorithm compared with the conventional one.

Research and Simulation of Two-Phase Interleaving Boost Converter

本文介绍了交错并联技术的基本原理及其优点，详细分析两相交错并联Boost变换器基本原理，分别采用PI控制和数字电流滞环控制方法，简单叙述了两种控制方法的原理并进行优缺点的分析与对比。使用MATLAB仿真，结果显示采用交错并联技术能在很大程度上减小流过开关管的电流，降低开关损耗和输出电压、输出电流纹波；相对于PI控制，采用数字电流滞环的控制方法使得整个电路的性能得到提升。 This paper introduces the basic principle and unique advantages of interleaving technology, and analyzes the efficacy of the two-phase interleaved boost converter in detail. In the control part of the circuit, a PI control strategy and digital hysteresis current control strategy are respectively adopted for the sake of comparison. Via MATLAB simulation, interleaving technology is shown to possess a number of important advantages compared to other methods, such as high frequency output voltage ripple with lower switching frequency, reducing current flowing through the switch tube, reducing switching loss, decreasing output voltage ripple, and output current ripple. Compared to the PI control method, the digital hysteresis current control method makes the performance of whole circuit is improved.

A Digital Hysteresis Current Controller for Three-Level Neural-Point-Clamped Inverter With Mixed-Levels and Prediction-Based Sampling

For a grid-tied three-level neural-point-clamped (NPC) inverter, fully digital hysteresis controller with simple variable hysteresis band is insufficient to stabilize switching frequency ( fs ). The challenge mainly comes from the restriction of analogue-to-digital converter (ADC) sampling frequency, which leads to inaccurate current-boundary-touching capture. As a result, $f_{s}$ jitter appears. This phenomena becomes much more serious around grid voltage zero-crossing points due to zero-approaching hysteresis band, where obvious $f_{s}$ variation happens. To stabilize $f_{s}$ in a fully digital manner, two techniques are proposed in this paper: the mixed-level scheme and the prediction-based sampling method. The former one is used to cope with the obvious $f_{s}$ variation around grid voltage zero-crossing points. It switches operating status from three-level state into two-level state around grid voltage zero-crossing points to enlarge the hysteresis band for digital implementation. The latter one is used to resolve $f_{s}$ jitter. It makes the sampling and switching to happen at the moment of current boundary-touching to achieve the most effective boundary-comparing with the lowest ADC sampling frequency. With these two techniques, $f_{s}$ of the grid-tied three-level NPC inverter could be well stabilized with a fully digital hysteresis controller, and therefore, high-quality grid-side could be achieved.

Sampling period online adjusting-based hysteresis current control without band with constant switching frequency

In this paper, a simple digital hysteresis current control (DHCC) with quasi-constant switching frequency (SF) for the current control of a single-phase grid-connected inverter (SPGI) is proposed. The hysteresis band is cancelled, and the SF is fixed by online adjusting the sampling period. The principle of the DHCC with constant sampling period is analyzed, and the distribution of the switching period (SP) corresponding to the phase angle of the grid is derived. The rule of online adjusting the sampling period to fix SF is then determined according to the former theoretical analysis results. Furthermore, the effect of variation of the filter inductor on the SP is analyzed. An online estimation of the filter inductor based on the linear model of the current increment within one switching cycle is developed to eliminate this kind of effect. The proposed scheme shows the features of simple control, easy implementation in a digital way, robust to the filter inductor, and excellent steady and dynamic performance. The detailed simulation and experimental results verify its accuracy and feasibility.

DSP-based flexible digital hysteresis in switched capacitor active power filter

This paper proposes implementation of digital signal processor (DSP) to perform flexible-band digital hysteresis current control in a switched capacitor active power filter (SCAPF). By integrating hysteresis current control with digital-based neural network harmonic detection, the proposed SCAPF forces the supply current to be sinusoidal, to have low current harmonics, and to be in phase with the line voltage. Simulation on MATLAB Simulink verified the controller's algorithm design, and a purpose-built laboratory SCAPF system tested its feasibility.

A fully digital hysteresis current controller for an active power filter

An active power filter is used to eliminate current harmonics produced by nonlinear loads. This paper discusses a fully digital method of controlling a power inverter used to inject the active filter compensating currents into the power system. A digital signal processor performs the harmonic isolation and generates a digital reference current. A hysteresis current controller has been implemented in a field programmable gate array that generates the inverter switching signals using this reference. This reduces the analogue circuitry and enhances the system's immunity to electromagnetic interference. The performance of a small-scale inverter under completely digital control is presented and discussed.