Power Compensation Research Articles

Voltage Modulated DPC Strategy of DFIG Using Extended Power Theory under Unbalanced Grid Voltage Conditions

This paper develops a voltage modulated direct power control (VM-DPC) strategy of a doubly fed induction generator (DFIG) using extended power theory under unbalanced grid voltage conditions. By introducing the modulated voltage of the active and reactive powers and the non-linear VM controller, the proposed VM-DPC strategy enables the generator dynamics to change from the time-varying differential equations into the time-invariant ones. Then, in order to deal with the voltage unbalance, three available power feedbacks, a combination of real active power and extended reactive power, a combination of extended active power and real reactive power, a combination of extended active power and extended reactive power, are developed. Together with a conventional controller (PI + R and feedforwards) and a non-linear VM controller, the power feedbacks are well controlled to track their references with the achievement of the constant active power, the constant reactive power and the balanced stator current. The main advantage of the VM-DPC strategy is the introduction of the modulated voltage and the non-linear VM controller making the generator dynamics time-invariant, which is easy for applying various control methods. Furthermore, the application of extended power can avoid the sequence extractions and the power compensations under unbalanced grid voltage. Finally, the simulation results demonstrate the effectiveness of the developed VM-DPC strategy.

Mathematical modeling start-up and steady state modes of asynchronous motors operation with capacitive compensation of reactive power

Mathematical modeling start-up and steady state modes of asynchronous motors operation with capacitive compensation of reactive power

Bidirectional DC–DC Converter with Coupled Inductor Fordc-Bus Regulation in Microgrid Applications


 This paper presents a theoretical analysis and the experimental results of the bidirectional coupled inductor dc-dc converter for dc-bus voltage regulation and power compensation in dc-microgrid applications. In dc-microgrids, a power distribution system requires a bidirectional converter to control the power flow between dc-bus and batteries. Furthermore, the dc-bus needs to be kept stabilized within certain limits and the converter handles a large range of voltage variation in the accumulators. The proposed topology is also relatively feasible for low-input-voltage applications for interfacing energy storage elements, such as batteries, ultracapacitors with the high voltage dc-bus in electric vehicles. The converter allows greater voltage gain compared to classic non-isolated topologies and can better deal with the wide range of voltage variation imposed by the source/load. The operation principles, the DC voltage gain, the design of the filters, the voltage/current stresses and a comparison are discussed. The experimental results confirmed and validated the theoretical study as well as the converter performance so that the measurements performed obtained from a 600 W laboratory prototype.

Novel PAPR reduction scheme based on continuous nonlinear piecewise companding transform for OFDM systems

In this paper, a novel efficient continuous piecewise nonlinear companding scheme is proposed for reducing the peak-to-average power ratio (PAPR) of orthogonal frequency division multiplexing (OFDM) systems. In the proposed companding transform, signal samples with large amplitudes is clipped for peak power reduction, and the signal samples with medium amplitudes is nonlinear transformed with power compensation. While the signal samples with small amplitudes remain unchanged. The whole companding function is continuous and smooth in the range of positive numbers, which is beneficial for guaranteeing the bit error rate (BER) and power spectral density (PSD) performance. This scheme can achieve a significant reduction in PAPR. And at the same time, it cause little increment in BER and PSD performance. Simulation results indicate the superiority of the proposed scheme over existing companding schemes.

Development of Smart Grid technology for maintaining the functioning of a biogas cogeneration system

The integrated Smart Grid System of harmonization of production and consumption of electric power and heat with the use of heat-pumping power supply of the biogas plant, which uses fermented wort as a low-potential source of power, was developed. A change in the power factor of the cogeneration system, the temperature of local water is predicted by measuring the voltage at the inlet to the inverter, at the outlet from the inverter and voltage frequency. In the engine cooling circuit, the temperature of cooling water at the inlet to the heat exchanger, at the outlet from the heat exchanger, and the return water temperature are measured. It was proposed to estimate a change in the ratio of voltage at the inlet to the inverter and at the outlet from the inverter. Making forestalling decisions to change the power of the heat pump and the number of plates in the heat exchanger of the engine cooling circuit makes it possible to maintain the voltage at the entrance to the inverter and the temperature of the heated local water. The complex mathematical and logical modeling of the cogeneration system, based on the mathematical substantiation of the architecture of the cogeneration system and mathematical substantiation of the maintenance of functioning of the cogeneration system, was performed. Time constants and coefficients of the mathematical models of dynamics regarding the estimation of a change in the power factor of the cogeneration system, temperature of local water, were determined. Functional estimation of a change in power factor of the cogeneration system in the range of 85–95 %, temperature of local water in the range of 30–55 °С at the compensation of reactive power of up to 40 % was obtained. Determining final functional information provides an opportunity to make forestalling decisions on a change in the power of a heat pump and a change in the number of plates in the heat exchanger of the engine cooling circuit to maintain the functioning of the cogeneration system

Steady-State Characteristics of a Line-Commutated Converter-Based High-Voltage Direct Current Transmission System for Series-Connected Wind Power Plants

A line-commutated converter-based (LCC) high-voltage direct current (HVdc) transmission system without ac harmonic filters for series-connected wind power plants has been proposed. This type of wind power plant is expected as a next-generation offshore wind power plant due to offshore substation free. In the LCC-HVdc system, power compensators are connected to each receiving-end circuit instead of the conventional ac harmonic filters and static var compensators (SVC). In this article, steady-state characteristics of the system are investigated through theoretical and experimental investigations. A set of steady-state equations for the system is derived first. The steady-state characteristics of the system for changes in wind speed are discussed using experimental setup built in our laboratory, and the validity of the derived equations is confirmed. Also, it is shown that the output active power and reactive power of the system can be controlled independently. Finally, the steady-state characteristics of a practical-scale system are investigated using the steady-state equations.

Control of a BDFIG Based on Current and Sliding Mode Predictive Approaches

The Brushless Doubly Fed Induction Generator (BDFIG) is a great attraction nowadays thanks to its high reliability and high low voltage ride-through capability. In variable speed generation systems, the most used control techniques are the vector control, direct torque/power control. Vector control is highly sensitive to parameters variations, while the two others offer high amount of ripples reducing power quality. This paper therefore proposes a Sliding Mode Power Predictive Control (SMPPC) and an Indirect Model Power Predictive Control (I-MPPC) for a simple and efficient power control of the BDFIG. The SMPPC takes current components in the αβ frame as sliding surfaces derived from the I-MPPC based on current predictions to track the desired active and reactive powers in the BDFIG. A cost function defined as currents’ quadratic errors is used to choose the appropriate voltage vector for control winding supply, and the Particle Swarm Optimization algorithm is used to determine the optimal gain for the SMPPC. Simulations on MATLAB/Simulink are carried out to show the effectiveness of the control schemes as well as their robustness to some parameters variations. More so, power compensation is used to improve the capability of the control strategy to provide sinusoidal and balanced currents under unbalanced grid conditions. The proposed methods compared to direct power control show good performances in terms of total harmonic distortion reduction, low ripples and robustness, strengthening the idea of using the BDFIG as an alternative to new generation of wind energy conversion systems.

Frequency-Adaptive Virtual Flux Estimator-Based Predictive Power Control With Suppression of Dc Voltage Ripples Under Unbalanced Network

This article presents a closed-loop virtual-flux (VF) estimator for grid voltage sensorless control of pulsewidth modulation (PWM) rectifier under unbalanced network. Compared with the prior open-loop VF estimator, the proposed method shows better filtering capability and improved robustness against load variation. Considering the grid frequency may deviate from the nominal value in practical application, an adaptive method is further developed for online frequency estimation. Additionally, the finite control set-model predictive power control with power compensation is implemented based on the proposed VF estimator to attenuate dc voltage ripples under unbalanced network. Theoretical analysis show that the twice-grid-frequency ripple component in the dc voltage can be effectively suppressed even with inductance mismatches. Experimental tests on a two-level PWM rectifier confirm the effectiveness of the proposed method.

An analog photonic down-conversion link with simultaneous IMD3 distortion suppression and dispersion-induced power fading compensation

A novel analog photonic down-conversion link based on a polarization modulator and a phase modulator with simultaneous linear optimization and chromatic dispersion-induced power fading compensation is proposed and experimentally demonstrated. By introducing an appropriate phase shift to the optical sidebands, chromatic dispersion-induced power fading is compensated, and third-order intermodulation distortion terms are eliminated in the same time. The scheme exhibits wide operating frequency range due to its no use of filters and frequency-dependent electrical or optical devices. The scheme is robust, as the operation of the polarization modulator and the phase modulator are independent of signal amplitude and bias voltage. Experimental results show that, for a 25-km transmission link, an improvement of more than 15.5 dB in spurious-free dynamic range is achieved and the dispersion-induced power fading is compensated at the same time. In addition, benefiting from the power compensation and significant suppression of IMD3, a 16QAM vector signal is demonstrated to have a good demodulation performance.

Integrated configuration and control strategy of PV generation in railway traction power supply system

Recently, electric railways have experienced a rapid development with an increasing power demand. Due to the flexible installation at trackside land along railways, photovoltaic (PV) generation is suggested to extend to the traction power supply system (TPSS) in railway. Firstly, this paper proposes a three-phase integrated configuration for PV generation connected to two-phase traction network and on-site consumption of solar resource alongside railways. In this configuration, another inverse V/V transformer is used to maintain a balanced three-phase low voltage (LV) ac bus from two-phase traction network. It is more convenient to access more PV generation units. Then, in order to mitigate the negative sequence currents caused by electric trains, an individual phase current (IPC) control strategy for PV converters is developed for power quality improvement. It can not only supply the locomotive with asymmetrical currents but also feed back to the grid with symmetrical currents. All the implementation and calculations are conducted in the three-phase stationary reference frame without any sequence extracting and power compensations. Finally, simulation results are presented to validate the effectiveness of the proposed IPC control strategy.

Design and Analysis of an Equivalent Load Power-Stability Control Circuit for Cabled Underwater Information Networks

Cabled underwater information networks (CUINs) have evolved over the last decade to provide abundant power and broad bandwidth communication to enable marine science. To ensure reliable operation of the CUINs, the stability of the remote power supply system, a key component of underwater power facilities, is essential. To avoid instability and collapse of the power system caused by rapid changes in load, we propose an equivalent load power-stability control circuit suited for an underwater constant current power supply system. This circuit can change its own working state according to the size of the load and play a role in power compensation. In order to prove the feasibility of the converter design, the working state of the circuit under different load values was analyzed and the performance of circuit was verified through simulation and experiments. The results show that when the load resistance changes within a large range (including when the load has an open circuit or short circuit fault), the equivalent load is basically unchanged or changed within a very small range for the constant current source, causing the constant current source to maintain stable output voltage and output power. Thus, the influence of the branch line cable on the trunk line cable is reduced, and the reliability of the underwater constant current power supply system is improved. Furthermore, the equivalent load power-stability control circuit would facilitate live equipment replacement and maintenance for CUINs.

Design and implementation of an optical module based on an improved incremental proportional integral differential algorithm

This article discusses the design and implementation of a 100 G tunable laser optical module, and briefly introduces the functions of each module in the MCU. The main technologies involve TEC control, wavelength locking, wavelength tuning, and power compensation. By analyzing the traditional positional proportional integral and differential algorithm, improving the proportional integral and differential algorithm, and using the algorithm to achieve wavelength locking, this can prevent the wavelength drift or even the lock due to the overload of the adjustment during the system adjustment process.

Study of compensation of reactive power of short-circuited rotor of asynchronous motor

This paper provides an overview of the current state of reactive power compensation technologies. Principles of operation, design characteristics are presented. One of the basic questions connected with improvement of quality of the electric power in branches which will be solved both at a design stage and at the stages of functioning of industrial systems of electrical supply is the compensation of jet capacity, including a choice of corresponding sources, calculation and regulation of their capacity, placing of sources in the power supply system. Rational coverage of reactive power in industrial electrical networks involves many problems aimed at increasing the efficiency of electrical installations.

The impact of motor starting on the quality of the industrial electricity network

The use of electric motors in the industrial sector has become increasingly important, especially with the development of power electronics. However, the use of these motors poses many problems, including the starting problem. Our work focuses on the study of the impact of the starting of electric motors on the quality of the industrial electricity grid, such as voltage drops during and after the starting, increasing the starting current to exorbitant values, and the starting time becoming too long. Besides, we propose solutions for these problems, such as compensation of the reactive power, insertion of VFD, and lag in the starting time of the motors. In the end, do a comparative study between these different solutions to justify the choice that is the insertion of VFD.

Quality management of electric energy and compensation of reactive power in the electric power system by means of stimulating tariffs

The article noted that feed-in tariffs are effective enough to attract consumers to participate in the process of improving power quality and reactive power compensation. It is shown that the application of premiums and discounts must not modify the revenues of the budget of ESO. Otherwise there is a contradiction to the principles of state regulation of tariffs for services of natural monopolies. In this case, legal barriers do not allow to use the model in practice. The proposed criteria that must be considered in the development and approval of the scale of discounts and allowances to ensure the legal purity of the incentive rate, to avoid its cancellation, as it was in 2000. Then, the proposed mechanism of discounts and allowances with the support of the Antimonopoly service and the Ministry of justice of the Russian Federation was cancelled as violating the principles of state regulation of tariffs in the conditions of the natural monopoly position of the network organization.

Improving the efficiency of oilfield electric power distribution

The issues of increasing the efficiency of electricity transmission to consumers with different nature of their load are considered. The dependence of the efficiency of the electric network of the oil field, consisting of a power line and a step-down transformer, on the total load power at various ratios between the active and reactive components of the power is analyzed, and the conditions under which the maximum transmission efficiency can be ensured are determined. It is shown by examples that the power transmission efficiency depends not only on the active load, but also largely on its reactive load. In the presence of a constant reactive load and an increase in active load, the total power increases and the power transmission efficiency decreases. In the low-load mode, the schedule for changing the power transmission efficiency approaches a parabolic form, since the influence of the active load on the amount of active power loss decreases, and their value will mainly depend on reactive load, which remains unchanged. The efficiency reaches its maximum value provided that the active and reactive components of the power are equal. In the case of a different ratio between them, the efficiency decreases. With a simultaneous increase in active and reactive loads and a constant value of the power factor, the power transmission efficiency is significantly reduced due to an increase in losses. With a constant active load and an increase in reactive load, efficiency of power transmission decreases, since with an increase in reactive load, losses of active power increase, while the active power remains unchanged. The second condition, under which the line efficiency will be maximum, is full compensation of reactive power. Therefore, in order to increase the efficiency of power transmission, it is necessary to compensate for the reactive load, which can reduce the loss of electricity and the cost of its payment and improve the quality of electricity. Other methods are also proposed to increase the efficiency of power transmission by regulating the voltage level in the power center, reducing the equivalent resistance of the line wires, optimizing the loading of the transformers of the step-down substations and ensuring the economic modes of their operation.

Compensation of Reactive Power and Unbalanced Power in Three-Phase Three-Wire Systems Connected to an Infinite Power Network

The compensation of an electrical system from passive compensators mainly focuses on linear systems where the consumption of charges does not vary significantly over time. In three-phase three-wire systems, when the network voltages are unbalanced, negative-sequence voltages and currents appear, which can significantly increase the total apparent power supplied by the network. This also increases the network losses. This paper presents a method for calculating the compensation of the positive-sequence reactive power and unbalanced powers caused by the negative-sequence line currents using reactive elements (coils and/or capacitors). The compensation is applied to three-phase three-wire linear systems with unbalanced voltages and loads, which are connected to an infinite power network. The method is independent of the load characteristics, where only the line-to-line voltages and line currents, at the point where compensation is desired, need to be known in advance. The solution obtained is optimal, and the system observed from the network behaves as one that only consumes the active power required by a load with a fully balanced current system. To understand the proposed method and demonstrate its validity, a case study of a three-phase three-wire linear system connected to an infinite power network with unbalanced voltages and currents is conducted.

Optimization of the Size of Dstatcom System Based on Data – Driven Control Design

This paper elaborates on a Distributed Static Synchronous Compensator (DSTATCOM). It renders a setup of hardware which provides compensation of power along with the optimization of the size of DSTATCOM set up. This DSTATCOM hardware set up reduces the power loss through compensation of power, regulates the voltage profile and increases the power factor. The performance of the DSTATCOM for linear and nonlinear loads was simulated.

WAY OF CONNECTION OF A THREE-PHASE MOTOR TO A SINGLE-PHASE NETWORK VIA RESONANCE EFFECT

In this paper, we propose a method to connect a three-phase motor, with windings connected by a star and a phase-shifting capacitor as the third contact, to a single-phase network, with efficient use of electrical energy due to compensation of reactive power and due to effective distribution of the voltage in front of the motor’s oscillating circuit. A resonance phenomenon in an oscillating circuit of the motor is used to compensate for reactive power, i.e. to increase the active power coefficient to the maximum value. A capacitor bank in front of the circuit is used to effectively distribute the voltage at the input of the motor circuit in order to increase the motor voltage from the mains value of 220 V to the nominal value of a three-phase motor of 380 V. A special installation was created for experimental studies. The results of experimental studies, theoretical calculations of the electrical circuit of the installation, as well as the voltage vector diagram of the motor circuit show that the case when voltages on the motor are U = 380 B (UL= UC5= 325.4 B) and U = 392 B (UL= UC5= 375.6 B) most closely corresponds to the resonant state of the motor oscillating circuit. The proposed method was introduced into the educational process as a laboratory work for students of technical specialties of the Almaty University of Energy and Communications, and can be used by designers, inventors, scientists and specialists interested in similar issues to create devices that connect a three-phase star-connected motor to a single-phase network.

Design and Simulation of a Unified Power Quality Conditioner by Fuzzy Logic for Egyptian Power Grid Connected to Zafarana Egypt Wind System

Wind energy system is lately receiving a lot of attention, because they are cost inexpensive, environmental safe and clean renewable energy source, as compared with nuclear and fossil fuel power generation. The operational characteristics of wind electric turbines has considerable dissatisfaction and stress on the quality of electric power system. Harmonics, variations of voltage and reactive power are most of power quality issues for grid connected with wind turbine. This paper introduces a design and simulation of unified power quality conditioner using a fuzzy controller to improve the power quality for Egyptian power grid connected to Zafarana Egypt wind system. The proposed performance of the unified power quality conditioner system is verified by simulating the model using MATLAB/SIMULINK environment. The simulation results showed that the proposed unified power quality conditioner provide efficient cancellation of both load current harmonics and supply voltage sag in addition to compensation of reactive power, and thus making the electrical grid connected wind energy system more efficient by improving the quality of power.