Input Reactive Power Research Articles

Input Reactive Power Control of Bidirectional WPT to Improve System Efficiency

Input Reactive Power Control of Bidirectional WPT to Improve System Efficiency

A Matrix-Type Back-to-Back Converter With Single-Arm Current Injection

A matrix-type back-to-back converter (MT-BBC) with single-arm current injection, consisting of a three-phase rectifier with a small film dc-link capacitor and a three-phase inverter, is proposed in this paper. A clamped modulation strategy is applied to the rectifier, which is featured by only one high-frequency switching bridge arm, reduced switching losses, and enhanced input reactive power control range. By controlling and injecting the quasi-third harmonic current into the phase with a high-frequency switching bridge arm of the rectifier, sinusoidal input currents and controllable input power factor are achieved. A carrier modulation strategy with variable carrier is applied to the inverter to compensate for the time-varying six-pulse dc-link voltage. The presented converter inherits the advantages of both the conventional voltage-source back-to-back converter (V-BBC) and the matrix converter (MC) including simple main circuit structure, sinusoidal inputs and outputs, bidirectional power flow capability, potentially high power density, high reliability, high efficiency, and direct ac-ac conversion. Additionally, the input reactive power control range is extended significantly. The effectiveness of the proposed methods is verified by a 6-kW experimental prototype.

Mains Current Distortion Analysis and Suppression Method for Third-Harmonic Injection Two-Stage Matrix Converter

Compared with the direct matrix converter and the two-stage matrix converter (TSMC), the third-harmonic injection TSMC (3TSMC) has significant advantages in the input reactive power control range and the maximum linear voltage transfer ratio. However, for nonunity input power factor operations and high-mains-frequency applications, there are input current distortions in the 3TSMC. Further analysis reveals that the actual injection current cannot track the reference without error in the conventional harmonic current injection circuit, resulting in the current distortions. Therefore, an improved circuit is proposed, which is based on the asymmetric H-bridge and does not need extra energy storage components or current sensors. The injection current in the improved circuit can follow the reference without error by injection current modulation, which means that the input current distortions are suppressed significantly. All theoretical considerations are verified by experimental results taken on a 3-kVA prototype.

Advanced Vector Controller for a Four-Switch Three-Phase Rectifier under Unbalanced Grid Voltage

One of the main challenges of a four-switch three-phase rectifier (FSTPR) is a DC imbalance in capacitor voltages. On the other hand, under unbalanced grid voltage conditions, unbalanced three-phase input current and the DC-link voltage affect the performance of the FSTPR. Although many papers focus on designing a controller to balance DC-link capacitor voltage, a few papers are available to cope with the imbalance of DC-link capacitor voltages and input current simultaneously under unbalanced grid voltage. In this paper, first, the operation of the FSTPR under unbalanced grid voltage conditions is investigated. It can be seen that under these conditions, the oscillatory parts of the active and reactive input power, i.e., sin and cos components, are the leading cause of the problems that can severely degrade the FSTPR performance of the controller. Therefore, this paper presents a promising control technique to eliminate the mentioned oscillation components. Aiming at this purpose, the current control loops in the dq axis are divided into two positive and negative sequences, i.e., idq+ and idq−. Simulation results in MATLAB/SimPowerSystem™ show that the proposed controller can reduce the output voltage ripple, the total harmonic distortion, and the unbalancing of input current compared to a conventional controller. Under these conditions, the DC-link capacitor voltages are more balanced, significantly reducing the voltage limiter of the FSTPR.

Switching State Selection for Model Predictive Control Based on Genetic Algorithm Solution in an Indirect Matrix Converter

Model predictive control (MPC) has emerged as a promising control scheme for power converters and motor drives. One of the major advantages of MPC is the possibility to control several system objectives with a single control law (cost function). However, the minimization selection of the cost function and its corresponding switching state is often achieved by using the enumeration method based on a simple element comparison that can lead to a local optimum solution and is time-consuming. In this article, a genetic algorithm (GA) optimum technique is applied to enable a global optimal solution to the cost function and its corresponding switching state in parallel implementation of MPC that ensures good performance in terms of the input reactive power and output current in an indirect matrix converter (IMC). Moreover, a performance comparison between using a GA and a conventional enumeration method is described. Meanwhile, a hybrid weighting factor searching method combining branch and bound algorithms with a strategy of precise searching over a small weighting range is proposed. Finally, the operation principles and validity of the proposed algorithm are analyzed and verified by using simulation and experimental results.

Improved Third-Harmonic Injection Two-Stage Matrix Converter Topology Based on Decomposition Control of Injection Current

In this article, an improved topology of the third-harmonic injection two-stage matrix converter (3TSMC) is proposed, which not only ensures that the input reactive power control capability is independent of the voltage transfer ratio (VTR) and the load conditions but also achieves high-quality mains current waveforms. To solve the problem of injection current control error in nonunit input power factor operation of 3TSMC, the third-harmonic injection current is decomposed into the active and reactive components, which are, respectively, controlled by the original injection current control bridge arm and an additional bridge arm named reactive power control bridge arm (RB). The maximum current of the inductor of RB is equal to the absolute value of the required input reactive current amplitude and will not increase with the increase of the VTR. The design criteria of the inductor of RB are discussed. To ensure the closed-loop stability under two injection directions, the controller of the injection current reactive component is designed. The effectiveness of the proposed topology and control strategy is verified by the experimental results.

CVR Study and Active Power Loss Estimation Based on Analytical and ANN Method

Conservation through voltage reduction (CVR) aims to reduce the peak load and energy savings in electric power systems and is being deployed at various utilities. The effectiveness of the CVR program depends on the load characteristics, i.e., the sensitivity of the load to voltage variation, and voltage regulation device settings. In the current literature, there is a lack of discussion on the CVR factor calculation using different measurements, and there is a lack of method for active power loss estimation using substation measurements. This paper provides insights into CVR factor calculation based on the measurements captured at the substation and those at the load location. This paper also proposes a new method based on curve fitting and artificial neural network to estimate the active power loss using input active power, input reactive power and input voltage at the substation. The CVR comparison study conducted in this paper helps in understanding the factors affecting CVR factor and may provide guidance in CVR implementation and impact assessment. The proposed loss estimation method sheds light on the impacts of CVR in terms of load and loss reduction. The results based on simulation studies using the IEEE 13-bus and 34-bus systems are reported in this paper, noting that the proposed methods are applicable to larger systems, as long as the required measurements at the substation are available. Future research includes testing and refining the methods using large IEEE and utility distribution systems and considering the stochastic nature of the CVR factor with changing load and voltage regulator control schemes.

Simplified predictive current controller for three-to-five-phase direct matrix converter

PurposePredictive current control (PCC) of three-to-five-phase direct matrix converters (DMCs) is computationally expensive. For this reason, this study aims to consider a reduced number of switching states of DMC in PCC algorithm to predict the control objectives, such as output current control and input reactive power control.Design/methodology/approachThe switching sequences which yield the voltage vectors of variable amplitude at a constant frequency in space are considered for the prediction and optimization step of PCC algorithm. For the selected voltage vectors, the phase angles of the output vectors are independent on the phase angles of the input vectors. In a three-to-five-phase DMC, there are 243 valid switching states. Among the switching states, only 91 states are considered using the aforementioned concept of variable amplitude output at a constant frequency. This reduced number of switching states simplifies the computational complexity of MPC based current control of three-to-five-phase DMC.FindingsThe computational complexity of the proposed PCC based DMC is lower than the all 243 vectors based PCC. The current total harmonic distortion, transient current response and input reactive power control for the simplified 91 vector based PCC are similar to the all 243 vectors based PCC.Originality/valueA reduced number of switching sequence is considered for the prediction and optimization step of PCC algorithm. Hence, PCC algorithm can be sampled at a high frequency in real-time applications. Then, the performance of the PCC will be improved.

Voltage-Sourced Converter Fed High-Speed Switched Reluctance Motor Drive System With Energy Feedback and Near-Unity Power Factor

The diode bridge rectifier fed asymmetric half-bridge converter (AHBC) is conventionally employed to drive switched reluctance motors (SRMs), which leads to poor grid-side power quality. In the proposed system, a topology made up of a voltage-sourced converter and an AHBC is employed to drive the high-speed SRM. Stable SRM operation can be obtained by manipulating the active power flowing to motor side, and on the basis of that, the grid-side power quality is enhanced by directly manipulating input reactive power. Predictive deadbeat control with disturbance observer is employed to follow the power references, thereby achieving controllable speed, energy feedback, near-unity grid-side power factor, and low grid-side current distortion simultaneously. Additionally, an improved asymmetric modulation method is developed for switching frequency reduction. Experiments are carried out to test the proposed drive system in steady and dynamic conditions. Performance comparisons validate the improvement of the proposed high-speed SRM drive system.

Analysis of harmonic characteristics based on improved double-LCC compensation network structure

The article firstly analyzes the filtering characteristics of double-LCC circuit in wireless power transfer (WPT) system. By defining voltage interference ratio (VIR), the harmonic interference introduced by inverter output voltage square waveform is represented. The ability of suppressing harmonic voltage source interference with different frequency of each branch of compensation network is obtained by analyzing VIR. In order to further reduce the harmonic content of each branch of circuit and decrease the harmonic introduction from the input-side, the article adopts an LC-double-LCC topology circuit. That is, an LC resonant part is connected in series at the input-side of circuit. The VIR of both double-LCC and new structure are compared by building mathematical model, and it is proved that the new structure has better ability to restrain interference. The total harmonic distortion (THD) of input-side current is calculated and the relation between the values of LC part, coupling coefficient, load and THD is quantitatively expressed. The sensitivity analysis in detuning condition of two structures is conducted. When the frequency offset becomes larger, the new topology shows better effect on inhibiting the increase of capacitive and inductive degree of the input impedance angle. The efficiency of WPT system with LC-double-LCC structure is analyzed, and reactive power of input-side is expressed by the value of LC part. With the parameters selected in this article, the input reactive power decreases 55.6% and power factor increases 0.68% after adding LC part. The results of simulation and calculation show that the LC-double-LCC structure has higher efficiency and larger power factor. An experimental platform is built and the theoretical results are verified.

Optimisation of the FE Model Based on the No-Load Test Measurement for Estimating Electromagnetic Parameters of an Induction Motor Equivalent Circuit Including the Rotor Deep-Bar Effect

The various measurement procedures for determination of electromagnetic parameters for the induction motor (IM) equivalent circuits including the rotor deep-bar effect were proposed in the literature. One of them is the procedure based on the load curve test (LCT). Since the execution of the LCT can pose some difficulties, especially in industrial conditions, as an alternative, the finite element method (FEM) can be employed to simulate the IM operation under the LCT. In this work we developed the optimisation technique for the finite element (FE) model. This technique is performed with the use of the stator current space-vector components which determine the IM input active and reactive power consumption during no-load operation. Relying on the LCT simulation carried out with the optimised FE model the inductance frequency characteristic can be determined and then used as the reference characteristic in the electromagnetic parameter estimation for the IM equivalent circuit including the rotor deep-bar effect. The presented research results demonstrate proper conformity between the inductance frequency characteristics obtained from the LCT performed experimentally and determined by means of the optimised FE model. Satisfactory conformity is also achieved in the case of the torque-versus-slip frequency curves acquired from the measurement and calculated by the IM space-vector model with estimated electromagnetic parameters. All of this validates the effectiveness of the proposed technique for the FE-model optimisation and the usefulness of the presented approach using the FEM in the electromagnetic parameter estimation for the IM equivalent circuit including the rotor deep-bar effect.

Modulation Technique for a $3 \times 5$ Matrix Converter Achieving a Maximum Input Reactive Power Range Based on Load Information

In this article, a load information-based modulation algorithm is proposed for a three-input five-output matrix converter (3 ×5 MC) to achieve a maximum input reactive power, whose superiority can be illustrated visually through a 2-D modulation graph. This article first derives the modulation matrix and its inherent constraints in the framework of duty-cycle calculation. After that, a constrained optimization problem for maximizing the reactive power is formulated; with the aforementioned constraints mapped to the 2-D modulation graph, the solution can be obtained without a substantial computational burden. The main contribution of this article is the adoption of a 2-D modulation graph to solve the constrained optimization problem for maximizing the input reactive power of a 3 ×5 MC, which presents a new viewpoint by employing load information in modulation constraints. Finally, experiment results are presented for assessing the performance of the proposed modulation algorithm.

Continuous Control Set Model Predictive Control for an Indirect Matrix Converter

A continuous control set model predictive power control strategy for an indirect matrix converter is proposed in this paper. The load reactive power, the load active power, and the input reactive power are controlled simultaneously. This control strategy can obtain output waveforms with fixed switching frequency. Additionally, an optimal switching sequence is proposed to simplify the commutations of the indirect matrix converter. To suppress the input filter resonance, an active damping method is proposed. Experimental results prove that the proposed method features controllable input reactive power, controllable load active and reactive power, fixed switching frequency output waveforms, zero-current switching operations, and effectively suppresses input filter resonance.

Mains Current Distortion Suppression for Third-Harmonic Injection Two-Stage Matrix Converter

The third-harmonic injection two-stage matrix converter (3TSMC) not only possesses the advantages of a TSMC, but also enhances the input reactive power control capability. Due to the input current deviation caused by the voltage ripple across the input filter capacitors, the mains currents of the 3TSMC are distorted at sector boundaries. To improve mains current quality, this article proposes a mains current distortion suppression method for a 3TSMC, which adds a prefilter to the output side of the input voltage selector to reduce the input current harmonics. As a result, the input filter capacitor voltage ripple and the input current deviation are reduced. The details of design of the prefilter are explained mathematically. To compensate for the dc-link voltage variation after topology improvement, an algorithm based on calculation of the voltage drops across the prefilter inductors is proposed, which can further improve the mains current performance. The feasibility of the proposed method is verified by simulation and experimental results.

A strategy based on the strain‐to‐kinetic energy ratio to ensure stability and convergence in topology optimization of globally resonating one‐material structures

SummaryThe authors propose a new formulation of SIMP‐based topology optimization problems aiming to obtain resonating one‐material structures through a stable maximization process. The new formulation is capable of achieving globally resonant lightly damped “0‐1” structures for frequencies close to those of interest. The proposed strategy successfully deals with known issues like design “degeneration” and instability of the gradient‐based optimization process around the resonance frequency (which is a local maximum when maximizing vibration responses) at which harmonic excitation forces shall be applied. In this work, the authors use the concept of complex input power to overcome the mentioned issues. It is proposed a topology optimization procedure where a weighted sum between the active input power (real part of the complex input power) and the static compliance is minimized with a constraint on the reactive input power (imaginary part of the complex input power), which is converted to a ratio between the time‐averaged potential and kinetic energies of the system named quotient R. By this way, it is possible to ensure viability to the procedure by preventing the resonance frequency from reaching exactly the excitation frequency throughout the process, which otherwise causes difficulties on convergence. The process achieves resonance frequencies very close to given values of interest by keeping the “side” of R<1 or R>1. Several examples are presented to illustrate the potential of the proposed method.

Improved power system state estimator with preprocessing based on the modified intersection of confidence intervals

Abstract The paper proposes a power system state estimator upgraded by the improved relative intersection of confidence intervals (RICI) algorithm combined with the local polynomial approximation (LPA). In the proposed approach, a novel LPA-RICI denoising technique is utilized to preprocess the input measurements. The accuracy of the adaptive, data-driven LPA-RICI based state estimator was tested on the IEEE test systems with 14 and 30 buses, as well as on a model of the real-life Croatian transmission power system. Due to its adaptivity to high transitions in measurement series achieved by varying filter support size, the LPA-RICI based state estimator enhanced the estimation accuracy for all tested power systems, and at the same time reduced the number of iterations required for the estimator to converge when compared to the classical weighted least squares (WLS) based estimator. Namely, improvement when using the proposed preprocessor was obtained in estimation of the input voltage magnitudes, active and reactive power flows and injections for the Croatian transmission power system by up to 29.3% and 19.4% in terms of the reduction of the mean squared error (MSE) and mean absolute error (MAE), respectively. Furthermore, the LPA-RICI based estimator resulted in an overall estimation quality enhancement for the Croatian transmission power system by up to 13.3%, 12.3%, and 3.7%, in terms of the objective function, variance of the estimated states, and average time for the state estimator to converge, respectively.

Reactive Power Transfer via Matrix Converter Controlled by the “One Periodical” Algorithm

The article describes the application of a straight forward energy converter, a multiphase matrix converter (MC), as part of a device, connected parallel to the power grid, and able to supply variable reactive power flow to the power system. The research performed by authors included the development of control procedures for a multiphase MC, based on a new approach and power system (application) requirements. The multiphase MC structure (6 × 6, 12 × 12) was used since the proposed control procedure creates output as the combination of input voltages. The increased number of phases decreases the order of harmonics in the MC converter similarly as in multilevel converters. This manuscript concentrates on the mathematical analysis of MC work under the “one periodical” algorithm and links it introduces in the power system. The previously developed, spatial-temporal mathematical model of the MC was limited to the dominant (first) harmonic and applied between the grid and reactive load. The results obtained from the analysis of the model showed that, for the applied control procedure (one periodical algorithm), the output voltage is built only from positive or negative sequences of input voltage. Three cases were recognized where the sign input power factor depends on input voltage and control sequence as well as on the value of control frequency. The effects of the model simulation were compared to those obtained from the MATLAB simulation and from the real laboratory 30 kVA-rated model. The main factors analyzed during this research include the expected value and distortion of input current and sign of reactive input power.

Seamless Dynamics for Wild-Frequency Active Rectifiers in More Electric Aircraft

In this article, a seamless dynamics controller for wild-frequency active rectifiers in more electric aircraft (MEA) is presented. The novelty of the proposed control scheme resides in its ability to seamlessly regulate the output dc-bus voltage and input reactive power in the presence of rapid frequency changes. These smooth dynamics are achieved through a multivariable direct model reference adaptive control (MRAC) formulation, which allows the gains of the controller to adjust themselves to the wild-frequency operation of the MEA power generation. The validity and performance effectiveness of the proposed seamless dynamics control scheme is verified experimentally through a laboratory-scaled three-phase 1.5-kW 270-V SiC two-level voltage-source-converter using a variable-frequency programmable grid emulator. Moreover, a traditional proportional-integral controller is implemented experimentally with the same converter as a benchmark to highlight the merits of the proposed MRAC.

On the use of active and reactive input power in topology optimization of one-material structures considering steady-state forced vibration problems

As studied by the authors in a previous work, applying topology optimization to minimize overall dynamic response of structures under time-harmonic loads may present serious drawbacks. It happens e.g. for an excitation frequency above the first resonance of the initial design, especially when the objective is to obtain one-material structures. Essential part of these drawbacks is due to the use of dynamic quantities that present strong influence of local responses, with antiresonances in their frequency spectrum, as is the case of the dynamic compliance. When minimizing for dynamic compliance, density-based topology optimization may present early convergence to designs filled predominantly with intermediate artificial densities. In this article, the authors present their studies on how to overcome these drawbacks by using a better objective function for the problem. The active input power (real part of complex input power) is proportional to time-averaged strain energy and/or to kinetic energy, being a global measure of vibration. Furthermore, it does not have antiresonances in its spectrum. It is illustrated that its minimization produces in most of the cases well defined structures consisting of practically only one material, with reduction of overall vibration at frequencies of interest, even above the first resonance of the initial design. In this work, the authors also show that the application of a constraint on the reactive input power (imaginary part of complex input power) allows to introduce displacement antiresonances for the excitation region at frequencies of interest. Several examples are presented to illustrate the physical issues and the effectiveness of the use of complex input power in topological optimization procedures for overall and local vibration reduction considering harmonic problems.

Input Reactive Power Controller With a Novel Active Damping Strategy for a Matrix Converter Fed Direct Torque Controlled DFIG for Wind Power Generation

The LC filter at the matrix converter (MC) input, excited by the PWM MC input current, introduces unwanted resonance oscillations in the input line current. The problem is more severe with a direct torque controlled (DTC) MC due to variable switching frequency operation. Active damping of this oscillation is preferred as it eliminates the power loss in the damping resistance. However, no such active damping strategy for a DTC-controlled MC-fed system has been reported in the literature so far. This article presents an input reactive power controller and a novel active damping strategy to improve the input filter current quality of an MC-fed doubly fed induction generator (DFIG) for variable speed constant frequency wind power generation. For the MC input reactive power control, superior performance of a multi-loop control structure over single-loop is established by experimental results. Stability analysis of the closed-loop input filter system using a small-signal model reveals that the system damping is the lowest in the sub-synchronous generating mode with unity DFIG stator power factor and can be improved by proper selection of the active damping controller parameters. Effects of these parameters on the system damping are predicted from the small-signal model and verified experimentally.