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

This paper proposes a straightforward control method for voltage control of a three-phase transformer-based inverter in uninterruptible power supplies or distributed generation systems. The approach offers a dual-loop design consisting inner current control loop and outer voltage loop. Sliding mode current controller provides desired bandwidth for voltage controller which consists of a state feedback term for stabilization and resonant term for harmonic damping. The proposed scheme provides fast dynamic response and low total harmonic distortion even for high power inverters with the limitations of switching frequency and LC filter components. Experimental studies for 2KVA linear and nonlinear loads using digital signal processors validate excellent performance of the proposed method.

This paper presents a novel digital control scheme for the regulation of single-phase voltage source pulse width modulation (PWM) inverters used in AC power sources. The proposed scheme adopts two deadbeat controllers to regulate the inner current loop and the outer voltage loop of the PWM inverter. For the overhead of digital processing, the change of duty of PWM lags one carrier period behind the sampling signal, which is modeled as a first-order lag unit in a discrete domain. Based on this precise modeling, the deadbeat controllers make the inverter get a fast dynamic response, so that the inverter’s output voltage is obtained with a very low total harmonic distortion (THD), even when the load is fluctuating. The parameter sensitivity of the deadbeat control was analyzed, which shows that the proposed deadbeat control system can operate stably when the LC filter’s parameters vary within the range allowed. The experimental results of a 2kW inverter prototype show that the THD of the output voltage is less than 3% under resistive and rectifier loads, which verifies the feasibility of the proposed scheme. An additional advantage of the proposed scheme is that the parameter design of the controller can be fully programmed without the experience of a designer.

In the present scenario, renewable energy source like solar power is the more convenient source of energy. Sustaining a steady DC link voltage and regulation of grid-current are challenging task in grid-tied photovoltaic (PV) system. These issues are overcome by designing a dual-loop control schemes; outer dc-link voltage loop which generates the reference signal for the inner current loop. The grid-tried inverter is used in photovoltaic (PV) system to inject the current with low total harmonic distortion (THD) into the utility grid by designing the efficient current controller. Generally, proportional-integral (PI) controller, proportional-resonant (PR) controller, dead-beat controller and hysteresis current controller are used in PV system to regulate the grid-current. These controllers are implemented in any one of the reference frames like; synchronous (d-q), stationary (α-β) or natural (a-b-c) reference frame. In this paper, the above-mentioned grid-current controllers are employed in all three reference frames and evaluate the steady-state performance of the controllers in terms of THD. The advantages and disadvantages of all grid-current controllers in each reference frames are briefly discussed and compared. This paper provides the best possible grid-current controller in three different reference frames. Finally, the simulation results from a two-stage 5.5 kW, 440 V (L-L), three-phase grid-tied PV system are provided to confirm the theoretical analysis and effectiveness of the control schemes.

Purpose This paper aims to investigate an improved control method and digital signal processor-based (DSP-based) digital implementation of three-phase standalone inverter. The proposed method is performance developed of the proportional-resonant controller (PRC) with harmonic injection technique, aiming to improve load voltages quality under different loads, especially nonlinear loads. The advanced proposed multi-loop controller is consisted of current harmonic loops for suppressing odd harmonic, which are analyzed in discrete-time domain. Besides, the voltage loop is also used to compensate the output capacitor voltage. Design/methodology/approach The proposed method can effectively enlarge output voltage stability with low total harmonics distortion and improve the dynamic transient response. The other advantage of the proposed PRC is the injection of the selective harmonic without any additional calculation compensator. Findings The method is given the opportunity to be controlled exactly all harmful outputs with high-quality voltage referenced of the standalone inverter. The proposed method is implemented using a DSP processor (TMS320F28335) and is verified on the 10 kVA three-phase standalone inverter prototype. Originality/value The proposed method is performance developed of the PRC with harmonic injection technique, aiming to improve load voltages quality under different loads, especially nonlinear loads.

This paper presents a nested loop control strategy for a bidirectional Cuk inverter. The Cuk converter is a high order, non-linear power converter and as such, controlling the converter to achieve good and dynamically robust behavior can be difficult. Existing solutions to this problem include sliding mode and current control strategies; although these solutions work, they suffer from complexity in design, implementation and limited compensation. The solution presented in this paper analyses the coupling capacitor, as the primary energy transfer element, and uses its power transfer during the different states of the converter, to decouple the control loop into a nested current loop and outer voltage loop; with low order, linear plants that can be compensated for using classical control theory. This also solves the non-linearity due to the duty cycle without deriving an average model. The control will be shown to cope with both AC and DC reference voltages with variable point operation. As illustrated by the simulated and experimental results, the control strategy can compensate for sudden load changes, short circuits and non-linear loads – changes that sliding mode and current control cannot compensate for.

The voltage closed-loop field-weakening scheme (VCFS) is an effective method to achieve the maximum output torque for induction motor high-speed drives. However, the cross-coupling between the inner current and outer voltage loops leads to system performance deterioration. To address this problem, this article proposed a unified complex vector field-weakening control. First, the inherent coupling problem in VCFS is analyzed based on the double closed-loop structure. On this basis, a complex vector structure is designed to unify the inner current and outer voltage loops, following with a decoupled criterion for controller coefficient selection. Compared with the conventional VCFS, the studied scheme can eliminate the natural complex vector zero in the voltage loop, leading to current ripple and voltage overshoot reduction. The experimental results confirm the effectiveness of the investigated scheme.

The controller design with on-line scheme for an active boost power-factor-correction (PFC) converter is proposed to comply with the international harmonic current standards. The average current-mode control (ACC) is used for the PFC boost converter. The ACC-controlled boost converter includes a fast inner current loop and a slow outer voltage loop. The current loop regulates the input current such that input average current follows the input voltage waveform to achieve high power factor. The outer voltage loop maintains the output voltage at a reference level against load variation and line voltage fluctuation. To optimize the control systems, a hybrid particle swarm optimization (HPSO) algorithm is used to determine the optimal controllers for both of the inner and outer loops. A 450 W converter prototype is built to validate the effectiveness of the approach. The experimental results show the proposed controllers can provide better performance in load regulation and line regulation than the conventional controller design.

This paper presents the proposed control structure of Duty phase control (DPC) for single-phase boost-type switching mode rectifier having only one voltage loop which shapes the input current and regulates the output voltage instead of conventional multi-loop control structure with inner current loop and outer voltage loop. The closed loop simulation results are presented using Matlab simulink. The spectrum for the output voltage is also presented and open loop Hardware implementation has done using Microcontroller (8051).

The double closed loops control strategy composed of inner current loop and outer voltage loop in the d-q synchronous frame is a relatively common control strategy of the three-phase voltage-sourced PWM rectifier. The system can not be completely decoupled because of the variable inductance in the actual system. And for simple, the decoupled part of the controller is usually ignored. What's more, the equation of the outer voltage loop is nonlinear. According to the analysis of the model of the rectifier, a novel double closed loops control strategy composed of inner current loop in the complex vector and outer square of the voltage loop, is proposed. The inner current loop using the mentioned control strategy can be completely decoupled without the exact value of the boost inductance, and the equation of the outer square of the voltage loop is linear. From the results of the simulation, the mentioned control strategy can greatly improve the dynamic and static of the system.

A novel control technique optimized for digital power factor correction (DPFC), which consists of two loops: "outer voltage loop" and "inner current loop", is presented. The current loop employs predictive dead beat (PDB) technique to boost the switching frequency. The voltage loop employs "voltage sensor-less technique", which senses in an interleaving manner the inductor current and derives information regarding the input and output voltages for use in output-voltage feedback and input-voltage feed-forward compensation. This control technique saves the DSP resources and alleviates itself from the limitation of the DSP processing speed. Also, it works for a wide range of input voltages with the addition of input-voltage feed-forward compensation. A boost controller is presented to demonstrate the applicability of this technique in a DPFC

This paper describes the detailed design of a singlephase multi-level single-phase shunt current injection converter based on cascaded H-bridge topology. The shunt current injection converter can inject an arbitrary current perturbation at three-phase power system interfaces, in order to identify small-signal dq impedances. Special attention is given toward the selection of inductors and capacitors, trying to optimize the selected component values. The proposed control is extensively treated and inner current and outer voltage loops are completely analyzed. Furthermore, voltage balancing is included into the control to assure dc voltage control for each H-bridge module. Analytical expressions, which describe the design procedure, are derived and verified to be accurate. The designed converter is simulated using detailed switching simulation model and excellent agreement between theory and simulation results are obtained. The proposed multi-level single-phase converter is a natural solution for single-phase shunt current injection with the following properties: modular design, capacitor energy distribution, reactive element minimization, higher equivalent switching frequency, capability to inject higher frequency signals, suitable to perturb higher voltage power systems and capable of generating cleaner injection signals.

Sequences having the minimum peak aperiodic autocorrelation sidelobe level one (1) are called Barker Sequences. Such sequences have been used in numerous real-world applications such as channel estimation, radar and spread spectrum communication etc. Unfortunately, the longest known biphase and quadriphase Barker sequences are of lengths 13 and 15 respectively. In this paper Modified Simulated Annealing Algorithm (MSAA) is used to design thirty-two phase sequences, which have good autocorrelation properties. Some of the synthesized results are presented here. The properties of the sequences up to length 24 have Barker properties which were not reported in literature earlier. The sequences of lengths from 4 to 289 have autocorrelation properties better than Frank codes. The synthesized 32-phase sequence sets are promising for practical application to radar and spread spectrum communication systems.

This paper presents a control of a three-phase, twolevel Voltage Source Converter (VSC) operating as a regulated rectifier for grid-connected applications. VSC-based rectifiers are increasingly employed in modern power networks due to their ability to provide superior controllability, lower harmonic distortion, and unity power factor compared to conventional linecommutated rectifiers. The rectifier is modeled in the synchronous $d q$ reference frame, allowing the dynamics of AC-side currents and the DC-link voltage to be explicitly derived and used in controller design. A cascaded control strategy is implemented, consisting of an outer DC voltage loop and an inner current loop, coordinated through a Phase-Locked Loop (PLL) for grid synchronization and Sinusoidal Pulse Width Modulation (SPWM) for switching signal generation. This approach ensures robust DC-link voltage regulation, effective current control, and reduced harmonic distortion even under operating disturbances. Simulation studies in MATLAB/Simulink confirm that the proposed VSC-based rectifier maintains stability during DC voltage reference changes and load variations. These results validate the robustness of the cascaded control strategy and highlight its applicability to modern power conversion systems such as renewable energy integration, HVDC transmission, and flexible AC-DC interfaces.

Predictive Control for AC-Drives

PREDICTIVE CONTROL FOR AC-DRIVES