An improved virtual current method for single-phase converters under frequency variations

The three-phase dual-active bridge converter is a promising topology for the high-power high-frequency dc–dc conversion, due to the soft-switching capability and inherent galvanic isolation. With the state-of-the-art instantaneous current control (ICC) based on the single phase-shift (SPS) operation, a bidirectional power flow can be controlled dynamically between two dc ports without inducing overshoots in the transformer currents. However, a transient dc-bias flux may still occur in the transformer, which may cause the transformer core saturation in the dynamic operation such as start-up, power- off , and abrupt load changes. To analyze and address this issue, this paper presents a set of model-based methods to avoid inducing the dc-bias flux in various transient situations. The proposed double-side SPS operation could nullify the dc-bias flux in abrupt load changes and even instant power-flow reversals. Furthermore, the soft-magnetizing and soft-demagnetizing techniques are presented to eliminate the initial and residual dc-bias flux during start-up and power- off instantly. The proposed flux control method can be integrated with the ICC. Thus, the transformer magnetizing flux and the winding currents can be controlled simultaneously and instantaneously in transient situations. Simulations and experiments on a down-scaled hardware prototype validate the effectiveness of the proposed methods.

The traditional proportional–integral (PI) based current control for single-phase pulsewidth-modulation (PWM) converters in railway traction applications either has a steady-state error or a poor dynamic response. Deadbeat instantaneous current control (ICC) cannot eliminate the steady-state error due to approximation errors of the linear extrapolation. Compared with PI-based direct current control, continuous-control-set (CCS) model predictive control (MPC) implemented in a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d-q</i> frame offers better performance, but its dynamic response is still slower than ICC. To solve these problems, a simple model predictive (MP) ICC scheme for single-phase PWM converters is proposed in this article. The optimal modulation function is calculated in the stationary reference frame by the CCS-MPC principle without <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">β</i> -axis current estimation and reference frame transformation. The proposed MP-ICC scheme can keep the fast dynamic response characteristics of ICC and achieve zero steady-state error. In addition, it has the advantages of low current harmonics and low computational complexity. The influence of the inductance parameter mismatch on the current loop is analyzed in detail, and a phasor-method-based inductance parameter online estimation is developed. This solution can be executed during the idle time of the digital processor without making the control delay longer. Finally, a comprehensive experimental comparison with four existing current control schemes is conducted to verify the feasibility and effectiveness of the proposed scheme.

For better performance, different current control schemes are used in LCL-type grid-connected converters. However, these schemes are mostly used in three-phase grid-connected converters and multiple current sensors are needed. To address these issues, a current decoupling control scheme for single-phase grid-connected converters in rotating reference frame is proposed in the paper. Because an extended state observer is adopted in the control scheme, only one current sensor is needed and the complicated coupling relationships between the $d$ axis components and $q$ axis components can be eliminated completely. Moreover, to improve the dynamic and steady-state performance of converters, a state feedback closed-loop system structure and nonlinear controllers are adopted. The current decoupling control scheme is validated in an LCL-type single-phase grid-connected converter. The experimental results show that a fast-dynamic response under load change and voltage sag can be achieved besides preferable static performances with the proposed control scheme.

Power quality and voltage stability are the main indicators of customer satisfaction because it influences business operations. Based on the results of the 2016 customer satisfaction survey by Markplus.inc, some industrial customers complain of voltage stability, especially related to dip voltage. Industrial customers complained about this dip voltage due to the loss of the company's operational tools. Dip voltage is a problem that must be resolved by industrial customers and electric utility companies. For electric utility companies, dip voltage greatly affects the sale of electricity that is not optimal because the dip voltage has an impact on the operation failure in industrial machinery. In addition, the dip voltage also has a negative effect on the service image of the electric utility company on the priority customer side. For this reason, the voltage dip needs to be handled seriously. According to IEEE 1159-1995, Dip voltage of 20 kV is a decrease in AC voltage of 2 kV up to 18 kV for 0.01 seconds until 60 seconds (for a frequency of 50 Hz). This dip voltage is caused by lightning, network interference, the effect of switching, motor operation, and sudden load changes. Dip voltage causes a huge financial impact on industrial consumers. In this paper, a dip voltage case study will be evaluated at The Food and Beverage Industry in East Java. The financial loss of industrial customers reaches 328,000 USD or 4.7 billion Rupiah in one dip voltage event. This is because customers have suffered a production failure so they have to restart their production process. They also have to dispose of large quantities of raw materials due to product failure due to the dip voltage. For this reason, it is necessary to formulate a proposed management model in solving this dip voltage problem. This paper also offers proposed steps that can be taken by electric utility companies in suppressing the amount of dip voltage so that the electricity supply becomes more qualified. In accordance with the evaluation of priority and risk management matrices, the results show that the steps are appropriate and can be implemented in reducing the number of dip voltages.

The research object of this paper is single-phase PWM rectifier, the purpose is to reduce the total harmonic distortion (THD) of the grid-side current. A model predictive current control (MPCC) with fixed switching frequency and dead-time compensation is proposed. First, a combination of an effective vector and two zero vectors is used to fix the switching frequency, and a current prediction equation based on the effective vector’s optimal action time is derived. The optimal action time is resolved from the cost function. Furthermore, in order to perfect the established prediction model and suppress the current waveform distortion as a consequence of the dead-time effect, the dead-time’s influence on the switching vector’s action time is analyzed, and the current prediction equation is revised. According to the experimental results, the conclusion is that, firstly, compared with finite-control-set model predictive control, proportional-integral-based instantaneous current control (PI-ICC) scheme and model predictive direct power control (MP-DPC), the proposed MPCC has the lowest current THD. In addition, the proposed MPCC has a shorter execution time than MP-DPC and has fewer adjusted parameters than PI-ICC. In addition, the dead-time compensation scheme successfully suppresses the zero-current clamping effects, and reduce the current THD.

Custom Power Devices like the dynamic voltage restorer have been applied for voltage dip mitigation in the last years. These electronic equipments need fast and reliable voltage dip detection algorithms. Such detection methodologies must be able to detect a voltage dip as fast as possible and be immune to other types of perturbations. In this paper we address the problem of voltage dip estimation by using different advanced signal processing methods such as Kalman filtering, Fourier based algorithms and Wavelet processing. The three algorithms have been tested under different conditions: voltage dip with phase jump, noise, frequency variations. The final implementation on a Texas Instrument DSP TMS320F2812DSP has been done.

The increase of sustainable energy sources and integration with the power distribution grid produced power quality (PQ) problems such as voltage sag and voltage swell. These problems are produced in the power distribution systems due to multiple reasons that affect sensitive loads. Voltage sag and voltage swell mostly occurring Power quality complications in the power system. These power quality issues in the power distribution system can be mitigated by using custom power devices, Dynamic Voltage Restorer (DVR) is the newly introduced device. Different techniques and algorithms have been used to mitigate these problems. In this research work, an ultra-capacitor-based DVR and a super-twisting sliding mode controller are used for the said problem. The addition of energy storage, such as an ultra-capacitor, to a dynamic voltage restorer, creates a voltage that can alleviate voltage issues such as sag and swell. For both the voltage sags and voltage swells, a high voltage is necessary for a short spell. A dynamic voltage restorer is an apparatus that is linked between the voltage source and the load side using an injection transformer to input voltage into the power distribution side to remedy a problem that has a significant impact on the load voltage. With the inclusion of a dynamic voltage restorer and sliding mode controller, the system will be able to fix PQ issues such as voltage sag and swell on its own, rather than relying on the grid as in past years. MATLAB/Simulink R2018a has been used to conduct simulation studies. Simulation studies have demonstrated that the proposed scheme is more effective, simple, robust, and more flexible and has a better mitigation time of 2.5 milliseconds and a total harmonic distortion of less than 5% as per IEEE standards.

Existing standards use information of the residual voltage magnitude and duration to characterize voltage dips severity. In reality, these two-dimensions of voltage dips may not always indicate the actual impact on customers and the published indices can lead to misleading information. This paper describes a new approach of estimating the impact of voltage dips on aggregated customers and the correlation with several voltage dip parameters. The method uses information of active-powers of aggregated customers of each feeder connected to the primary substations of MV-networks to estimate the change in load or generation. To study the applicability of the methodology in utilities, a dataset of voltage dips monitored from six Dutch substations for four years is used. The type and severity of voltage dips are compared with the changes in load and generation in the network. The approach can fill the gap in the standards, and help in setting the limit for voltage dips in the distribution networks which are not regulated in most countries.

The analysis and design of a nearly unity power-factor and fast dynamic response of the modular three-phase AC to DC converter with minimized DC bus capacitor is discussed. The proposed system significantly improves the dynamic response of the converter to load steps with minimized DC bus capacitor. It chooses output capacitor according to the output voltage droop and overshoot. This is confirmed by 600 W prototype modular three-phase AC to DC converter comprising three 200 W single-phase SEPIC rectifier modules with dc bus output capacitor 470 muF and experimental implementation.

High-frequency bidirectional dual-bridge series-resonant dc–dc converters have been attracted more attention in power electronic transformer (PET) due to high power density and efficiency. In this article, a model predictive power control method with phase shift modulation is proposed, to improve the dynamic response and robustness of the converter without load current sensor. In addition, the proposed method is insensitive to the resonant parameters in the adopted converter and can keep excellent dynamic characteristics even if the resonant parameter deviates from the desired operating point, which indicates good robustness. Effectiveness of the proposed control is verified on a 400-W scale-down experimental prototype with resistance load and inverter load, respectively. Compared with traditional voltage loop control and model predictive voltage control schemes, the proposed scheme can achieve a faster dynamic response of the output voltage in load and input voltage step change.

This paper presents an implementation methodology for a current harmonic compensation technique of three-phase grid-connected voltage-source converter (VSC), which was applied under the grid voltage distortion and frequency variation. The proportional-integral plus multi-resonant controllers (PIMR) were used to mitigate the high order harmonic current. The PIMR controller was transformed to the discrete-time domain and implemented on a TMS320F28379D digital signal processor. The proposed control scheme was validated with a hardware in the loop (HiL) and with a 5 kW three-phase LCL-filtered grid-connected VSC. The harmonic compensators were used in the dq-frame at harmonic orders 6 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> and 12 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> for suppression of the grid voltage harmonic orders 5 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> , 7 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> , 11 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> , and 13 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> . Results from MATLAB/Simulink simulation and experiments with HiL and hardware implementations were found to be in close agreement. The experimental grid current exhibited excellent harmonic rejection with a total harmonic distortion close to 1% and complied with the IEEE 1547 standard. The grid current can tracked the reference command with a fast dynamic response.

Harmonics pollution is very dangerous in medium power applications. Generally, harmonics are produced in the system due to the connection of nonlinear loads. This article presents a novel load voltage and current harmonic compensation, voltage sag and swells compensation approach using hybrid UPQC. The proposed synchronous reference controller uses the Carrier Pulse Width Modulation (CPWM) technique for the proper control of UPQC. The simulations are carried on Matlab/Simulink platform. The output results present the proposed hybrid UPQC compensates the load current harmonics, voltage sag and swell effectively. The load voltage harmonics are reduced from 11.65% to 1.53% and the current harmonics are reduced from 30.97% to 2.24% respectively. https://dorl.net/dor/20.1001.1.13090127.2021.11.2.6.5

This paper deals with the modified kernel least mean square (KLMS) control strategy in double-stage, solar photovoltaic (PV) grid tied system to enhance the power quality at common coupling point (CCP). This proposed control algorithm has less oscillations, fast convergence, fast dynamic response and good steady state performance. A control strategy is used to extract the fundamental active current component of load and generates reference grid current for a DC-AC converter. The proposed modified KLMS control mitigates multiple power quality concerns such as harmonics reduction, unity power factor and load balancing. The dynamic performance of proposed system is confirmed into the MATLAB\Simulink environment. Test results on hardware implementation are presented at varying solar irradiation levels and load unbalancing. Test results are found satisfactory and total harmonic distortion (THD) of the grid currents are observed well within the IEEE-519 standard.

This paper presents a design and simulation of a controller circuit for Power Factor Correction applied to BLDC Motor Control. To achieve accurate and dynamic performance from a BLDC motor, it is usually fed from a Voltage Source Inverter (VSI). Such drives have to deal with problems in power quality and poor power factor at AC mains input as they include a diode bridge rectifier. To overcome such problems and provide faster dynamic performance a power factor correction One Cycle Controlled Cuk converter is proposed to feed the Voltage Source Inverter based BLDC motors. The Cuk PFC converter inherits many advantages like low output current and voltage ripple, near unity power factor with simple control. The One Cycle technique provides excellent power source disturbance rejection, fast dynamic response, automatic switching error correction and robust performance.

This paper presents a smart DC network formed by a multi-terminal VSC-HVDC connecting various micro-grids, independent power generation stations, and passive loads. The corresponding deadbeat current control scheme based on coordinated strategy for multi-terminal VSC-HVDC systems is proposed. The current control scheme is easy to design, implement and has good dynamic response. the case of four-terminal VSC-HVDC interconnected with AC grids, wind farms, and passive loads is developed in MATLAB/Simulink to demonstrate the validity of the proposed control scheme and the united system. Simulation results have demonstrated that the proposed scheme enables optimal operation under conditions of voltage dip, power flow and load changes when used for a large DC smart network.