Instantaneous Current Control Research Articles

A Simple Model Predictive Instantaneous Current Control for Single-Phase PWM Converters in Stationary Reference Frame

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.

Model Predictive Current Control with Fixed Switching Frequency and Dead-Time Compensation for Single-Phase PWM Rectifier

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.

PV-STATCOM in Photovoltaic Systems under Variable Solar Radiation and Variable Unbalanced Nonlinear Loads

The paper focuses on an efficient method to compensate the harmonics and zero-sequence component caused by the variable unbalanced nonlinear loads. The studied compensator is based on the conventional Static Compensator (STATCOM) which is supplied by a photovoltaic generator rather than the storage passive components. That constitutes a Photovoltaic Static Compensator (PV-STATCOM). In addition to the active power production, this PV-STATCOM will improve the quality of the electric grid highly disturbed without any additional devices and costs. The used control strategy is based on the instantaneous power method and current control. The obtained results show the benefits of the photovoltaic active filter compensator to improve the energy quality. Specially, the Total Harmonic Distortion (THD) is decreased from 28.80 % to 2.03 %. The zero-sequence component of the load currents is reduced from 31.50 % to 4.26 %. The results prove also a high stabilization and limitation of the harmful repercussions of the compensator on the photovoltaic station and an automatic adapting to the solar variable radiation and to the unbalanced nonlinear load variations.

Elimination of DC-Link Voltage Ripple in PMSM Drives With a DC-Split-Capacitor Converter

This article presents an electrolytic capacitorless (ECL) motor drive based on a dc-split-capacitor converter. In order to decrease the dc-link voltage ripple of ECL motor drive, an active power decoupling circuit (APDC) with a dc-split-capacitor is proposed. The APDC is composed of two converters, among which the boost converter is named the main converter and the buck-boost converter is named the auxiliary converter. The output capacitors of the two converters are connected in series to increase the dc-link voltage, which expands the speed range of the internal permanent magnet synchronous motor. When there is voltage ripple on the capacitor of the main converter, the auxiliary converter will produce complementary voltage on another capacitor. In addition, an instantaneous current control strategy is proposed in the auxiliary converter to reduce the voltage ripple, while the conventional control strategy is applied in the main converter. The main converter can achieve unity power factor, and the auxiliary converter is used to suppress the dc-link voltage ripple. Experiments are conducted, and the results verify the feasibility and effectiveness of the APDC.

Optimized Active Power Management in Solar PV-Fed Transformerless Grid-Connected System for Rural Electrified Microgrid

Dynamic voltage instability is one of the major issues faced by grid-connected renewable energy systems due to fluctuations in the generation and sudden variation in the loads. The primary objective of this paper is to propose a method for constant power consumption from the grid to maintain a stable DC-link voltage during peak and nonpeak hours. It can be achieved by implementing an optimized active power management (OAPM) scheme between the photovoltaic (PV) and the grid by enabling a battery energy storage system (BESS). The intelligent constant power balance (ICPB) algorithm and detailed control strategies for dual active bridge (DAB) isolated DC–DC converter and grid-connected voltage source inverter (VSI) are discussed in this paper. Moreover, the high-gain step-up DC–DC converter (HSDC) is utilized to perform maximum power point tracking (MPPT) operation and to meet the required DC-link voltage. The accuracy of power transmission of DAB gets improved by imposing a curve-fitting interpolation (CFI) approach, thereby maintaining a constant DC-link voltage. Furthermore, an instantaneous sinusoidal current control (ISCC) scheme assures the feeding of active power with better power quality. The measured results are obtained and verified under different dynamic conditions of load and generation. Based on the validation, we conclude that the proposed OAPM scheme is most suitable for grid-connected renewable energy systems in the rural electrified microgrid.

Instantaneous Flux and Current Control for a Three-Phase Dual-Active Bridge DC–DC Converter

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.

Design of Solar Pv Based Shunt Active Filter for Nonlineasr Load

Elevation of power electronics technology, converter are the main causes for power quality issues, because of their high switching characteristics.so to reduce the harmonics injected by the nonlinear load, the filters are play a major role to improve a power quality improvement, particularly shunt active filter is more reliable for reduce a harmonic in power system network. This novel technique proposed for design a shunt active filter with solar photovoltaic array integrated into nonlinear load using a Point of Common Coupling (PCC) technique. Zero crossing detection technique are used to extract the magnitude of a fundamental active components of distorted load currents. The estimation of harmonic isolator and current compensation are controlled by Field Programmable Gate Array (FPGA) controller, different types of compensation techniques are used in this work Synchronous reference frame theory, instantaneous reactive power theory (PQ) and hysteresis current control technique. These techniques enable extraction of active power, regulates a load voltage and maintain a phasor sequence at PCC under the voltage sag and swell. Simulation is carried out by MATLAB/SIMULINK for different compensations techniques and Total Harmonics Distortion (THD) values are tabulated.

Unified Control for Switched Reluctance Motors for Wide Speed Operation

In this paper, a unified controller for switched reluctance motors is proposed for wide speed operations. The proposed controller achieves minimum output torque ripple at low and medium speeds and operates in a single-pulse mode at high speeds. Overlapping regions between the phases are controlled such that direct instantaneous torque control (DITC) and current control (CC) can be implemented simultaneously on different phases. This simplifies the torque sharing during commutation and minimizes torque ripple due to imperfect current tracking and mutual torque. A demagnetization curve concept to demagnetize the phase currents at an optimum angle is introduced to ensure high torque per ampere and single-pulse mode operation. This results in extending low ripple operation to medium speed ranges. The seamless combination of DITC, CC, and the demagnetization curves leads to torque ripple minimization, automatic excitation angle control, and smooth operation over a wide speed range. The effectiveness of the proposed unified controller is verified through simulation and experimental studies.

Coordinate Control of Power/Current for Grid‐Connected Inverter Based on PCI Controller under Unbalanced Grid Conditions

The oscillations on output power and distortion of the inverter currents will occur in the case of unbalanced grid voltage faults. Constant output power and good current quality cannot be achieved simultaneously. Aiming at these problems, a coordinate control strategy for suppressing power fluctuations and current harmonics is proposed by analyzing instantaneous power control and current balance control. The proposed control is achieved by adjusting the weight coefficient of current reference values to change the current harmonic contents based on proportional complex integral (PCI) controller and proportional multiple complex integral (PMCI) controller. The control strategy with a simple control structure neither needs to detect harmonic components of the inverter currents, nor needs to separate the positive and negative components of voltage and current, which is easy to be realized. The feasibility and effectiveness of the proposed control are verified by the comparison and analysis of simulation.

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

Few papers concern about the instantaneous current control (ICC) scheme for single-phase converters under frequency variations. The inherent relations between inaccurate virtual current and the relevant dynamic and static performances of converters are rarely reported. To address the issue, the inherent relations among the DC error, double-line frequency error and inaccurate virtual current are discussed in the paper. An improved virtual current method is proposed to eliminate the DC error and double-line frequency error, which are caused by frequency variations. Based on this method, a new ICC scheme, which is immune to frequency variations, is presented in steady-state scenarios. The improved virtual current method and the proposed ICC scheme are validated in a single-phase converter. Simulation and experimental results show that a unity power factor under frequency variations and a fast dynamic response under load change and voltage sag can be achieved with the proposed ICC scheme.

Priority-based Energy Management Technique for Integration of Solar PV, Battery, and Fuel Cell Systems in an Autonomous DC Microgrid

Recent times have witnessed a significant positive trend in adoption of renewable energy sources and DC-based loads, which questions the efficiency and reliability of existing structure of electrical power system. DC microgrids are identified as potential solutions for addressing India's and other developing nations' rural electrification. This paper presents an energy management technique for isolated DC microgrids for academic readers, as well as provides an introduction to not-familiarized readers for understanding the common design challenges for implementing off-grid power systems. The principle of the proposed technique is based on law of energy conservation defined by the energy balance equation and is implemented by synthesizing the instantaneous current reference and hysteresis control with source priority, which was validated by rigors simulation studies in Matlab/Simulink. Furthermore, in order to demonstrate the modularity and scalability of the algorithm, it was tested on a prototype hardware test setup at the Solar Energy Research Centre, VIT University.

Power control in centralized distributed AC load for wind energy system

In electrical power systems, isolated energy system is a more challenging task to fulfill the active power demand as well as reactive power demand under the fluctuating wind at different load conditions. In this paper, a centralized AC load, centralized distributed hybrid system (CDHS), is analyzed. CDHS has the following features in place of the DC centralized grid system, which is focused on controlling of a permanent magnet synchronous generator, a bi-directional DC-AC converter (BDC) with battery energy storage, and a wind energy conversion system with a single-stage, 3-phase 4-wire AC-AC converter connected to a common AC bus. Non-isolation of the input terminals, multi-stage operation, size and cost of the circuits, and efficient working of the AC-AC converter has been resolved using a 3-phase 4-wire AC-AC converter. A specific triggering pattern of variable frequencies to a constant frequency has been generated for the switching devices in the AC-AC converter to achieve a desired polarity of the output voltage. A BDC connects the isolated load using a natural frame instantaneous current control technique to manage the active and reactive load power flow among the parallel connection AC hybrid systems. Different conditions such as a constant load and a variable load for variable source supplies are demonstrated for the architecture of CDHS in MATLAB/Simulink. The modelling of CDHS and performance analysis have been disseminated out that the proposed CDHS is capable of managing the active power demand with reactive power for voltage variations.

技術開発レポート：Refinement of Inverter Model Considering Dead-Time for Performance Improvement in Predictive Instantaneous Current Control

技術開発レポート：Refinement of Inverter Model Considering Dead-Time for Performance Improvement in Predictive Instantaneous Current Control

FPGA Based Speed Control of SRM with Optimized Switching Angles by Self Tuning

The electromagnetic torque and speed in Switched Reluctance Motor (SRM) greatly depend on the excitation parametersi.e. turn-on angle, turn-off angle, dwell angle and magnitude of the phase currents of its phases. At lower speeds, a change in the current contributes the torque requirement which can be achieved either by voltage control (pulse width modulation) or instantaneous current control techniques. At high speeds, due to high back EMF, the regulation of current is crucial and achieved with the control of switching angles of phases. This type of control is referred as average torque control, where the torque is averaged over one stroke (2π/Nr). With constant dwell angle, advancing the phase angle influences the current into the phase winding at minimum inductance position. It has more time to get the current out of the phase winding before the rotor reaches the negative inductance slope. To maintain the speed of the motor at different load conditions, the turn-on and turn-off angles are adaptively varied. The change in dwell angle may be required where the turn-on and turn-off angle may not be sufficient to reach the required speed. In this paper, a new algorithm is proposed for self tuning of switching parameters of SRM. The proposed algorithm is simulated in MATLAB-Simulink and experimentally validated with Field Programmable Gated Array (FPGA) using MATLAB- system generator environment.

Online open‐switch fault diagnosis method in single‐phase PWM rectifiers

On the basis of sampling theory, an online open-switch fault diagnosis and location method for single-phase pulse-width modulation rectifiers applied in electric railway traction is presented. First, on the basis of analysing the features of the post-fault line current under instantaneous current control strategy at low switching frequency, two specific pulse sequences for sampling line current are generated via the modulation. Then, the DC component of the sampled signal, which is easy to use for diagnostic decision, is obtained through filters. Experimental results are presented to illustrate the validity of the proposed scheme.

Double deadbeat‐loop control method for distribution static compensator

This study presents a double deadbeat-loop control method for distribution static compensator (DSTATCOM), which aims to simplify design of the controller for DSTATCOM and improve the dynamic performance of DSTATCOM. The proposed control method comprises of dc-link voltage deadbeat controller and the ac-side instantaneous current deadbeat controller, in which the dc-link voltage deadbeat control method is proposed for simplifying the design of the outer voltage controller of DSTATCOM. The output of the dc-link voltage deadbeat controller and the reactive current reference obtained from the load are imported into the ac-side instantaneous current controller based on the deadbeat current method. The parameters of the proposed control method can be directly calculated according to the parameters of the given circuit components, and the proposed control method is very easy to be realised in digital processor and with fast dynamic response. Finally, the feasibility of the proposed control method is validated through both simulation and experiment results.

Power Flow Control of a Power Conversion Circuit for Contactless Power Transformer Systems with Coil Misalignment

SUMMARYThe coupling coefficient between the coils of a noncontact power supply system is reduced by coil misalignment. This reduces the output voltage and the active power in the coils. To cope with these problems, an instantaneous current control method is applied to a single‐phase contactless power transformer system in order to apply the equivalent impedance of the PWM rectifier at the load side of the transformer. We propose a control method to supply power constantly to the load even when there is a misalignment in the receiving coils. The limit of the transferred power associated with the proposed control method is investigated. The proposed system, including the control method, is verified by experimental tests over a power range of several tens of watts.

Advanced compensation mode for cascade multilevel static synchronous compensator under unbalanced voltage

An improved control scheme for delta-connected cascade multilevel static synchronous compensator (STATCOM) operating under unbalanced conditions is proposed. The individual phase instantaneous current control is suitable for delta-connected cascade multilevel STATCOM which can be equivalent to three single-phase inverters. To compensate the system imbalance, the reactive control mode and the voltage control mode are studied, and the discrete current loop controller has been designed. Accordingly, the cascade multilevel STATCOM can maintain normal operation under unbalanced voltage by using the individual phase instantaneous current control strategy while the unbalanced system can be effectively compensated by the two modified compensation modes. The proposed control scheme has been verified by simulation and experimental results based on a three-phase 36-chain cascade multilevel STATCOM laboratory prototype are shown.

産業サーボドライブ用四相SRモータの瞬時電流波形制御

産業サーボドライブ用四相SRモータの瞬時電流波形制御

Development of Shunt-Type Three-Phase Active Power Filter with Novel Adaptive Control for Wind Generators.

This paper proposes a new adaptive filter for wind generators that combines instantaneous reactive power compensation technology and current prediction controller, and therefore this system is characterized by low harmonic distortion, high power factor, and small DC-link voltage variations during load disturbances. The performance of the system was first simulated using MATLAB/Simulink, and the possibility of an adaptive digital low-pass filter eliminating current harmonics was confirmed in steady and transient states. Subsequently, a digital signal processor was used to implement an active power filter. The experimental results indicate, that for the rated operation of 2 kVA, the system has a total harmonic distortion of current less than 5.0% and a power factor of 1.0 on the utility side. Thus, the transient performance of the adaptive filter is superior to the traditional digital low-pass filter and is more economical because of its short computation time compared with other types of adaptive filters.