Performance improvement of resonant multi-loop controller with odd harmonic injection for standalone three-phase inverter

In this paper, a novel control system structure is introduced for generating a sinusoidal wave on the differential boost inverter terminals using inverse model approach. To address the high-frequency resonance issues, an active damping technique is proposed. Proportional-resonant controllers are designed for tracking and harmonic rejection. Pulling direct and constant current from photovoltaic panels as the DC source is essential in maximum power point tracking. Therefore, a decoupling controller is utilised to suppress current oscillations. An innovative combination of tracking controller, harmonic rejector, and decoupling controller is proposed in order to provide a sinusoidal voltage output for linear and nonlinear loads with low total harmonic distortion. The proposed method reduces the number of controllers by half compare to conventional methods. In addition to simulation, experimental results show the effectiveness of the proposed method.

Integration of photovoltaic (PV) power to the grid is achieved using three-phase inverters with high-quality current waveforms. The new grid codes impose a limit on the total harmonic distortion (THD) value of the inverter’s current waveforms. Due to simple structure and ease of design, proportional integral (PI) controllers are the most widely adopted methods to control three-phase grid-connected inverters; however under abnormal grid conditions, PI controllers may suffer from instability problems. To address the aforementioned problem, this article proposes an expert knowledge-based proportional resonant (PR) control for the integration of PV power to the grid under abnormal grid conditions. The proposed control method adjusts the control parameters based on rules generated from expert knowledge. Initially, parameters of the proposed control methods are optimized using particle swarm optimization (PSO) method. The proposed control is tested with a 100 kW grid-tied three-phase inverter unit under normal and abnormal grid conditions and its performance are compared with PI and fixed gain PR control methods. Moreover, the proposed control is tested experimentally with a scaled down 300 W grid-tied inverter lab prototype module. From the simulation and experimental results, it is verified that the proposed adaptive PR control technique is capable of providing low THD in the injected current under abnormal grid conditions compared with fixed gained PR controllers.

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.

In recent years, the research on control strategy of three-phase grid-connected inverter has attracted significant attention. Proportion integration (PI) control method is widely utilized to control the grid-connected inverter. However, coordinate transformation is an essential and complex step during the design process of the conventional PI controller. It is difficult to implement in practice due to the complex coordinate transformation. The proportional-resonant (PR) control method of the three-phase grid-connected inverter is proposed, where the conventional PI controller is replaced by PR controller. PR controller has a simple structure as the complex coordinate transformation can be neglected. In order to improve the power factor and the stability of the system, double closed loop structure is also introduced in the proposed control strategy. In the end, simulation software is developed, and the simulation results confirm the effectiveness of the proposed control method.

Recent technological advances in power electronics has led to a substantial increase in nonlinear loads. This has led to deterioration in quality of power in distribution networks and sparked interest in power quality issues and its solutions. This paper discusses the issue of harmonics, which is a power quality problem: their estimation and subsequent control and mitigation using a shunt compensator. The control of shunt compensator using proportional-resonant (PR) controllers has been designed and implemented. Literature review presents a wide range of control techniques and proportional-integral (PI) controllers are the simplest and most commonly used in industries. Recently introduced PR controllers have been presented as an alternative to PI controllers. These controllers are believed to overcome the shortcomings of the conventional PI controller, which include the presence of steady-state errors and the need for transformation in three-phase systems using the synchronous dq frame. The added advantages of PR controllers include the possibility of implementation for simultaneous detection and extraction of harmonic components without requiring excessive computational efforts. This paper highlights the application of PR controller for harmonic estimation and their reduction in the utility grid using shunt compensator. Closed loop control using PR controllers as filters has been demonstrated using simulation as well as experimental results. Extensive results are presented for different loading conditions, and they demonstrate the application of PR controllers in grid-interfaced converter for power quality improvement.

This paper addresses two types of additional losses in induction motors. One is stray load loss resulting from loss segregation when induction motors operate from a sinusoidal supply voltage and the other is harmonic loss when induction motors operate from inverter-fed supply voltage. Both losses are of concern in machine design and operation but they are difficult to predict accurately without the use of empirical factors. This is due to their complex loss mechanisms and small magnitudes in most cases. Investigation into the correlation of the two loss components could enable effective quality control of the manufacturing of machines for use on inverter supplies. With the availability of advanced calorimetric and harmonic injection techniques, it becomes possible for these small loss components to be measured with precision. In this paper, seven induction motors ranging in power through 1.1, 7.5, 15 to 30 kW are tested for experimental comparison. Among these are four 7.5 kW machines. Test results suggest there is a need for induction motors designed specifically for inverter-fed operation.

Harmonic injection matrix converter (HIMC) achieves direct AC‐AC power conversion with maximum voltage transfer and reduced transistor capacity. However, the existing open‐loop current control method for HIMC may bring in low‐order harmonics if the injected harmonic current deviates from its desired value. To address this issue, this paper proposes a closed‐loop input current control strategy based on the waveform similarity index (WSI) for these emerging MC topologies. The WSIs are defined as the ratios of the corresponding input currents against the maximum and minimum input voltages. Multi resonant controllers are adopted to regulate the WSI difference so that its low‐order harmonics are eliminated, which generate an additional signal to correct the injected harmonic current. By adopting the proposed current control strategy, the 5th and 7th harmonics are suppressed to lower than 1.0% under the sinusoidal input voltages and nominal load scenario. Even with inaccuracies in the reference harmonic current generation, the proposed strategy enables the input currents to approach sinusoidal waveforms with significantly reduced WSIs difference, thus enhancing the input power factor over the conventional open‐loop method. Besides, the proposed method is effective under unbalanced and distorted conditions through the experimental verification.

The proportional–integral (PI) control is usually applied in synchronous reference frame to regulate the output voltage of three-phase voltage source inverter (VSI). However, the PI controller is constrained by the capability of suppressing harmonic and negative sequence components; besides, its direct application in single-phase VSI is limited. While the proportional–resonant (PR) control can track ac reference and achieve harmonic suppression in stationary frame for both single-phase and three-phase VSI. Due to the high order of the resonant controller, lots of efforts are needed during the parameter design to get a satisfactory performance, such as trial-and-error. In this article, the way to approximately reduce the order of the resonant controller in the discrete time domain is presented, and then a method of selective pole placement and cancellation for the PR control design used in VSI is proposed. With the proposed method, the closed-loop pole-zero distribution of the PR control structure used in the VSI is well handled, and the parameters of the feedback controller and the reference feedforward controller are directly calculated by placing the selected poles and zeros in desired positions. The procedure of the parameter design is facilitated, and the performance of the VSI with PR control is improved.

This paper highlights the power quality issues and explains the remedial measures taken by means of hybrid front-end third harmonic current injection rectifiers. Here, a zig-zag transformer is used as the current injection device so that the advantages pertaining to the zig-zag transformer are effectively utilized. The third harmonic current injection device along with three-level boost converter at the output stage will increase the dc-link voltage. With less boost inductance, generally half of the conventional boost converter inductance is sufficient to implement the proposed converter structure resulting in reduced ripple current and also the device rating is reduced by half of the output voltage. Moreover, the power quality is well improved using third harmonic current modulated front-end structure, which is well appropriate for medium/higher power applications. The experimental prototype of hybrid front-end converter is developed in the laboratory to validate the MATLAB simulation results.

The single-phase inverters with higher-order filters are popular for grid interface of photovoltaic (PV) systems. Increasing penetration of these systems coupled with nonlinear loads impact grid voltage quality. The grid code restricts the injection of harmonic currents into the grid. To reduce the harmonic distortions in the current that is fed to the grid, this article presents a Proportional-Resonant (PR) controller for a HERIC inverter topology with an integrated input side dc-dc converter. The traditional controllers cannot restrict the injected current harmonic content when the grid voltage is polluted. To solve this problem a PR controller with Harmonic Compensators (HC) has been presented to limit the harmonic distortions. A 1.5kVA single-phase grid-tied inverter with an LCL filter on the output side has been simulated in MATLAB. Simulation studies on a grid-tied PV inverter have been carried out, and performance has been investigated and compared with other controllers for different levels of the injected grid current. The developed grid-tied inverter with a PR controller with HC is suitable for achieving low total harmonic distortion which guarantees that the system provides satisfactory performance according to the grid standards.

This paper presents the study, development and application of new control techniques for photovoltaic power generation systems, connected to single-phase power grid in order to improve the efficiency of these systems in relation to control methods typically used. The work is divided into two main parts, which are related to tracking the maximum power point (Maximum Power Point Tracking - MPPT) and then the internal controller of boost quadratic converters - side of the photovoltaic panels - as well as the controllers the voltage inverter, the side of the single-phase mains. The first part of the work is the development of a heuristic goal algorithm for MPPT, which is based on the method of simulated annealing (Simulated Annealing - SA) and aims at determining the overall maximum point, seeking out solutions in a close vicinity, so as to prevent the docking local maxima in the curve of power output of the photovoltaic array, thereby improving the utilization of energy in partial shading situations. The second part presents the design of controllers based on internal model (Internal Model Control - IMC) with 1 degree of freedom (1 Degree of Freedom - 1 DOF) applied, first, the DC-DC Boost Quadratic converter, used for MPPT, and thereafter, a voltage inverter with LCL filter connected to the single phase power supply operating in current injection mode. A mathematical modeling of both converters and analyzed the compensation of internal feedback to the voltage inverter system corresponding to the disconnection of the mains voltage through the power strategy a head (feedforward). A basis of comparison for the performance analysis of IMC-1DOF converter is aiming at, is also applied to the current injection system, Proportional-Resonant Controller (P + Res). They are presented computer simulation and experimental results of both controllers, which allow you to check the system performance in low and non-linear local load network situation.

Over recent years, the output power of micro-inverters [module-incorporated inverter (MIC)] is progressively pushed to higher levels, following the current photovoltaic (PV) modules market trends. The interleaved Flyback inverter—under discontinuous conduction mode of operation (DCM)—is an appealing solution for PV applications which are based on MIC technology. This topology provides increased power level for distributed PV generation exploitation with simple control configuration, high efficiency, and reduced filter size. In this paper, the harmonic injection capability is incorporated into the interleaved Flyback inverter for the implementation of an active anti-islanding scheme. A suitable technical solution is proposed that bypasses the unfolding H-bridge, without affecting the active power generation of the inverter and without requiring any hardware modification. In addition, a mathematical model based on the instantaneous power balance theory is presented, being a powerful analysis tool for inverters operating under complete magnetic discharge such as the Flyback inverter (either conventional or interleaved) under DCM or boundary conduction mode of operation. The proposed model predicts accurately the steady-state operational behavior of the Flyback inverter under current harmonic injection, either in grid-tied or islanding operation. The proposed technical implementation method and mathematical model are verified through simulation and experimental results. Finally, an anti-islanding set-up based on the proposed harmonic injection technique is presented and implemented into the Flyback micro-inverter. The proposed set-up is verified through experimental results on various quality factor values, as well as for weak grid conditions.

Light load efficiency and total harmonic distortion (THD) of AC-DC converters is of increasing importance when considering the increase in non-linear electronic loads on the modern grid. Efficiency and THD standards are becoming stricter in their requirements to account for this increase in non-linear loads. To address the increasing requirements for higher efficiency and lower THD without increasing the cost or complexity of the design, a Line Cycle Skipping (LCS) method is proposed and its digital control implementation presented. A 100W universal line input voltage PFC boost converter prototype is built to demonstrate the effectiveness of the proposed control method.

This paper presents a closed loop controller for bidirectional high-frequency link inverter. Deadbeat control is adopted to achieve fast dynamic response. The controller consists of inner current loop and outer voltage loop. To improve overall performance of the system, additional decoupling networks are employed. Output voltage decoupling network is included to improve the response of current loop; while load current decoupling network is used to increase the robustness of the inverter towards load variation. Simulation results are presented for the closed loop system under linear and nonlinear loads. It is shown that the control method provides good dynamic response with low total harmonic distortion, even under full-bridge rectifier loads.

Solar photovoltaics (PV) is one of the popular renewable energy sources in tropical countries like India which can help in supplementing the rising demand of electrical energy. DC input from solar PV strings needs to be converted into AC component both for ON and for OFF grid applications. Three-phase inverters are used for the above inversion when power levels are high. In OFF grid applications, task of maintaining stable terminal voltage across the loads lies with the inverter in the absence of utility grid. It also has to supply variety of balanced and unbalanced loads. In this paper, cascaded voltage control scheme, for a three-phase four-leg inverter, is developed. Parameters of the proportional resonant controllers (PR) are tuned using bode plot techniques. Simulations results are presented for operation under different loading conditions.