Conventional Direct Power Control Research Articles

Application of DPC to improve the integration of DFIG into wind energy conversion systems using FOPI controller

While the direct power control (DPC) approach has proven effective in improving the efficiency of wind energy conversion systems (WECS) using doubly fed induction generators (DFIG), its applicability is currently confined to a single usage and has not been extended to meet numerous applications. This work aimed to modify the implementation of DPC in WECS-DFIG for several objectives. This is accomplished by updating the reference power of the conventional DPC method into an adapted one to achieve two goals independently. The first objective is to track the maximum power during wind speed variations. This tracking is performed by updating the reference power to match the maximum available power at the current wind speed. The second purpose is to ensure that the WECS remains connected to the grid and continues to operate smoothly even in the event of faults; supporting fault-ride through (FRT) capability. That is achieved by reducing the reference power during these faults. The discrimination between these two objectives is based on the voltage level at the point of connecting WECS to the grid. The controller provided is an improved fractional order PI controller developed using arithmetic optimization technique (AOA). A comparison between the AOA and cuckoo search is presented. The results demonstrate the efficacy of the suggested configuration and regulator in enhancing the performance of integrating DFIG into the WECS in the presence of wind fluctuations and short circuit faults occurring. It is worth noting that AOA is better than cuckoo search in fine-tuning the settings of the FOPI controller.

Improvement of power quality in WT-DFIG systems using novel direct power control based on fuzzy logic control under randomness conditions

ABSTRACT In this paper, a novel direct power control technique founded on fuzzy logic controller (FLC-DPC) is selected to master and control the DFIG for wind energy conversion system (WECS). The fuzzy logic controller replaces both hysteresis regulators and the switching table in the proposed strategy. Seeking to enhance the control and overcome the defects associated with the conventional DPC (C-DPC) technique, this control depends on the errors of both active and reactive powers. The suitable rotor voltage vector for the inverter is obtained by FLC-DPC. The proposed control strategy is applied to the WT-DFIG system, in order to study its effectiveness. To reflect a real WECS operation, this study considers the wind’s random behaviour in successive and continuous ways throughout all WT-DFIG operating modes. Also, it takes into consideration all compensated local reactive power modes. The studied system and the proposed control were tested under MATLAB/Simulink environment. The obtained results showed the high effectiveness of the proposed control in terms of response time, robustness and ease. Consequently, C-DPC’s drawbacks are eliminated, and the ripples in compensated local reactive and produced active powers are reduced. Additionally, the total harmonic distortions (THDs) of injected currents are reduced, which improves their quality.

Stability analysis of VSC-HVDC system based on new phase-locked-loop less voltage oriented control method

Voltage Source Converters-based High Voltage Direct Current (VSC-HVDC) systems are generally implemented to transmit power across long distances due to their low cost and flexibility. This paper will discuss a new simple and low-computational-burden phase-locked loop less voltage-oriented control strategy (PLL-less-VOC strategy) for controlling and synchronizing a VSC-HVDC system in a synchronous rotating frame (dq frame). The proposed method is used not only to control the VSC-HVDC but also to obtain the mathematical model of both VSCs-based HVDC systems in the dq frame using the basics of the direct instantaneous power control theory (DPC) without using PLL and Park transformations. The proposed PLL-less-VOC strategy is equivalent to the conventional VOC strategy for steady-state stability, but it has the benefit of both conventional VOC and DPC, better transient stability performance, and low computational burden in the implementation. The experimental tests using STM32F407G microcontroller demonstrate that the proposed control strategy has better dynamic stability under certain exceptional conditions such as step changes on DC-link voltage change, powers change, and three-phase fault.

An efficient scanning algorithm for photovoltaic systems under partial shading

<span lang="EN-US">This paper proposes a new technique of maximum power point tracking (MPPT) for a photovoltaic (PV) system connected to three phase grids under partial shading condition (PSC), based on a new combined perturb and observe (P&O) with scanning algorithm. This new algorithm main advantages are the high-speed tracking compared to existing algorithms, high accuracy and simplicity which makes it ideal for hardware implementation. Simulation was carried on MATLAB/Simulink. Results showed the effectiveness in speed and accuracy of our algorithm over the existing ones either during standard condition (STC) or PSC. Furthermore, conventional direct power control (DPC) was applied to synchronize successfully the injected power with the grid, which makes our algorithm global and works efficiently under severe conditions.</span>

Hybrid Renewable Energy System Controlled with Intelligent Direct Power Control

The paper suggests a novel DPC approach to ameliorate the management and HRES “hybrid renewable energy system” control composed of photovoltaic and wind systems. In the conventional DPC technique, the “switching table” is founded on a “hysteresis comparator”, which poses the problem of fluctuations on the HRES various output variables. The approach proposed here is based on an FLC and shown to diminish the ripples in the “active” and “reactive” powers waveforms. The comprehensive HRES and the advised “control schemes” are implemented using “MATLAB/Simulink” and the results indicate that the advised method had preferable performance over the conventional DPC.

Predictive-DPC Based on Duty Cycle Control of PWM Rectifier under Unbalanced Network

This work proposes a predictive direct power control (P-DPC) technique of a PWM rectifier, based on a duty cycle control method, using a new definition of the instantaneous reactive power in the predefined cost function, able to operate under balanced and unbalanced grid voltages. In conventional DPC, the use of a single voltage vector during a control period leads to high power ripples and variable switching frequency. To overcome these problems, a duty cycle control is introduced in P-DPC to achieve performance improvement in terms of power ripple reduction, dynamic response and robustness against unbalanced grid voltages. Its main characteristic is the use of several voltage vectors applied during a control period. In effect, the duration of the selected vector is determined by minimizing the active power ripple during a control period. Simulation results are presented to confirm the theoretical study developed.

New application of artificial neural network-based direct power control for permanent magnet synchronous generator

Purpose. This article proposes a new strategy for Direct Power Control (DPC) based on the use of Artificial Neural Networks (ANN-DPC). The proposed ANN-DPC scheme is based on the replacement of PI and hysteresis regulators by neural regulators. Simulation results for a 1 kW system are provided to demonstrate the efficiency and robustness of the proposed control strategy during variations in active and reactive power and in DC bus voltage. Methodology. Our strategy is based on direct control of instant active and reactive powers. The voltage regulator and hysteresis are replaced by more efficient and robust artificial neuron networks. The proposed control technique strategy is validated using MATLAB / Simulink software to analysis the working performances. Results. The results obtained clearly show that neuronal regulators have good dynamic performances compared to conventional regulators (minimum response time, without overshoots). Originality. Regulation of continuous bus voltage and sinusoidal currents on the network side by using artificial neuron networks. Practical value. The work concerns the comparative study and the application of DPC based on ANN techniques to achieve a good performance control system of the permanent magnet synchronous generator. This article presents a comparative study between the conventional DPC control and the ANN-DPC control. The first strategy based on the use of a PI controller for the control of the continuous bus voltage and hysteresis regulators for the instantaneous powers control. In the second technique, the PI and hysteresis regulators are replaced by more efficient neuronal controllers more robust for the system parameters variation. The study is validated by the simulation results based on MATLAB / Simulink software.

A 24-sectors direct power control-feedforward neural network method of DFIG integrated to dual-rotor wind turbine

<p class="Abstract">In this work, a 24-sector direct power control (24-sector DPC) of a doubly-fed induction generator (DFIG) based dual-rotor wind turbine (DRWT) is studied. The major disadvantage of the 24-DPC control is the steady-state ripples in reactive and active powers. The use of 24 sectors of rotor flux, a feedforward neural network (FNN) algorithm is proposed to improve traditional 24-sector DPC performance and minimize significantly harmonic distortion (THD) of stator current and reactive/active power ripple. The proposed method is modeled and simulated by using MATLAB/Simulink software under different tests and compared with conventional 24-sector DPC.</p>

An advanced virtual flux integrated multifold table‐based direct power control with delay compensation for active front‐end rectifiers

Direct power control (DPC) technique for the control of ac–dc converters projects many advantages over conventional techniques. Even after the advent of upgraded DPC techniques, the conventional switching table-based DPC is preferred where a simple control structure with less computational burden is the design requirement. During the real-time implementation of any ac-dc converter or vice versa, the PWM signal for the converter/inverter operation is applied after a delay of one sampling time period to allow some computational time for the operating processor. In the literature, only the predictive group of controllers is seen to provide a restitution for the inaccuracy caused by this control delay. This group of controllers involves a complex vector selection process that needs to evaluate many expressions in order to find the correct switching voltage vector. In this work, an effort has been made to apply for the delay compensation in the conventional DPC techniques, which has much less complexity in the vector selection algorithm. Hence to obtain better performance at lower computational burden, the delay compensation is used with a multifold table-based DPC. The hysteresis band and lookup tables are designed based upon standardized parameters so that the control is unaffected even when the load is changed. For real-time application, the proposed control technique's feasibility and applicability are validated in simulation and an experimental setup for an ideal as well as nonideal grid.

Direct active damping control for grid‐connected AC/DC converter with LCL filter using augmented look‐up table

This paper presents a novel approach to adapt the conventional direct power control (DPC) methods that are applied to ac/dc converters with an inductive capacitive inductive (LCL) filter. These new solutions improved the conventional DPC with an active damping algorithm via multi-variable constraint adjustment, which is based on an augmented look-up table and multi-variable comparators. The novel look-up table proposed for the active damping algorithm of the LCL filter allows an optimal voltage vector assignment to be chosen using differences in converter-side current and capacitor voltage. This method is also compared with the DPC method with active damping via the addition of a virtual damping resistor and a harmonic rejection loop. The steady-state (total harmonic distortion of the grid current) and dynamic performances (response time on step changes of the set current), as well as the immunity under distorted grid voltage conditions of the proposed system, are verified through simulation results and experimental measurements.

Modeling and Predictive Control of Shipboard Hybrid DC Power Systems

Although onboard dc power systems bring values for the power and propulsion system of the future hybrid ships, the main barrier for the development of such systems for large-scale vessels is the technical operational issues, such as stability and power quality and how to satisfy the related standards and regulations. In the advanced ship power systems, the conventional diode rectifiers are being replaced with active front-end (AFE) rectifiers providing the control flexibility but at a higher cost. However, to make such devices more profitable, the ship control system can be reconfigured to unlock the potentials of AFEs for the general system stability. This article is dealing with the stability issue of hybrid dc power systems proposing a predictive control approach to improve the voltage regulation and better use of converters. The proposed method replaces the conventional direct power control (DPC) of AFE rectifiers with a model predictive control (MPC) and integrates the dc-dc converters in the same control platform. In this method, optimal control commands for the rectifiers and the dc-dc converter are calculated by the predictive control to minimize the dc bus voltage fluctuations, especially under the fast load changes. The controller is then extended to regulate the load sharing between the different energy units. The effectiveness of the proposed method is evaluated in simulation with a typical shipload profile, as well as a real ship profile, which has several operating modes, such as steep load increase & decrease, high speed, and maneuvering operation. The performance of the proposed control strategy is compared with conventional controllers, and the results show that the new method can provide significant advantages in terms of fast and stable control performance, as well as the steady-state voltage regulation and enhancing the power smoothing function of the battery. Laboratory experimental data are also used for validation.

Novel model predictive direct power control strategy for grid‐connected three‐level inverters

Conventional switching table-based direct power control (DPC) usually suffers from higher power ripples due to the heuristic nature of the switching table. This study presents a novel model predictive DPC (MPDPC) strategy for grid-connected three-level inverters. In the proposed MPDPC strategy, a new synchronous frame-based predictive model is first developed and the conjugate of the complex power is then chosen as the control variable to simplify the analysis. Based on the newly developed predictive model, new principles of the voltage vector selection are further derived with the strict analytical proof to match all the control requirements, including the active and reactive power control, neutral point potential balance control, as well as the avoidance of the high voltage jumps. Finally, experimental results are provided to support the theoretical study and confirm the effectiveness of the proposed MPDPC strategy, as well as to demonstrate better performance in both steady-state and dynamic responses over the conventional DPC.

Analysis of direct power control AC-DC converter under unbalance voltage supply for steady-state and dynamic response

This paper presents an analysis of Direct Power Control (DPC) technique for the Three-Phase Pulse Width Modulation (PWM) AC-DC converter under unbalanced supply condition. Unbalance condition will cause the presence of unbalanced current and voltages thus produce the negative components on the grid voltage as well as severe performance degradation of a grid connected Voltage Source Inverter (VSI). The input structures for conventional DPC has been modified with a three simpler sequence networks instead of coupled by a detailed Three-Phase system method. The imbalance voltage can be resolved by separating from the individual elements of voltage and current into symmetrical components called Sequence Network. Consequently, the input power relatively improved during unbalanced condition almost 70% through the measurement of Total Harmonic Distortion (THD) from the conventional Direct Power Control (DPC) in individual elements which is higher compared to separate components. Hence, several analyses are performed in order to analyze the steady state and dynamic performance of the converter, particularly during the load and DC voltage output reference variations.

Model predictive power control for grid‐connected ac–dc converters with trajectory optimisation of the modulated voltage vector

As a classical control algorithm for grid-connected ac–dc converters, the conventional proportional–integral (PI) based direct power control (DPC) has several disadvantages, including the complexity of tuning PI parameters and poor dynamic performance. To tackle those drawbacks, this study presents a simple model predictive power control (MPPC) scheme with pulse-width modulation stage for single-phase ac–dc converters. Distinct from previous MPPC schemes, the proposed approach is formulated in terms of the terminal trajectory of modulated voltage vector, which is defined as an elliptic region. From the elliptical trajectory point of view, the proposed approach applies a cost function to predict an optimal radius of elliptic trajectory instead of the outputs of inner-loop PI controllers in PI-based DPC. To solve the parameter sensitiveness problem of MPPC schemes, a quantitative relationship between the predicted powers and their references considering inductance mismatch is analysed in detail. Then, an inductance estimation method is developed according to the analysis. A comprehensive experimental comparison with conventional PI-based DPC, and finite-control-set MPPC schemes have been conducted to verify the effectiveness of the proposed scheme.

Direct Power Control of Shunt Active Power Filter Using Space Vector Modulation Based on Supertwisting Sliding Mode Control

This article proposes direct power control (DPC) associated with space vector modulation (SVM) for a shunt active power filter (SAPF). This control is suggested in order to overcome the drawbacks of the conventional DPC, where the SVM is able to decrease the high active and reactive power ripples maintaining a fixed switching frequency. In addition, the performance of the proposed scheme is improved by replacing PI controllers with supertwisting second-order sliding mode controllers (ST-SMCs) in the active and reactive power control loops. This technique provides high robustness and dynamics for external perturbations. The proposed control DPC-SVM based on ST-SMC is investigated by simulation and practical implementation using MATLAB/Simulink with a real-time interface based on a dSPACE 1104 board.

Coordinate strategy of dual-pulse-width-modulation converter based on direct power control with load power feed-forward

The common dual-pulse-width-modulation converter adopts the independent method to control the rectifier and inverter, which has the defects including direct current voltage fluctuation, slow system response and so on. A coordinate strategy of dual-pulse-width modulation based on direct power control with load power feed-forward is proposed in this paper. The fixed switching frequency method with space vector pulse width modulation is provided to overcome the instability of power devices, caused by the hysteresis comparators in the conventional direct power control. With the analysis on the dynamic performance of load power feed-forward coordination, the principle of load power feed-forward is introduced to control the dual-pulse-width-modulation converter. According to the state variable of the alternating current motor, the load power is estimated to construct the feed-forward channel. The experimental results show that the proposed coordinate control method has rapid response, direct current bus voltage fluctuation minimization, lower capacity and unit power factor.

Fuzzy logic-based instantaneous power ripple minimization for direct power control applied in a shunt active power filter

The high presence of instantaneous active and reactive power ripples when using the direct power control (DPC) strategy in power converters represents a serious issue, especially when used in active power filters (APFs) to compensate harmonics; those ripples are due to the presence of hysteresis controllers and the rigidity of the conventional switching table, and they cause serious limitations in the filtering capabilities of APFs. Many attempts had been proposed to solve this problem, but at the expense of over-complicating the DPC. In this paper, we tackle this problem by shifting toward a fuzzy logic paradigm and creating a fuzzy inference system that replaces the hysteresis controllers and the switching table, and the goal is to reduce the rigidity of the conventional DPC and build a smoother alternative, which will result in less power ripples. The proposed strategy is tested using MATLAB simulations and experimentally validated using an FPGA-based laboratory setup during both steady-state and transient conditions.

Online Inductance Identification of a PWM Rectifier under Unbalanced and Distorted Grid Voltages

Direct power control (DPC) works well under ideal grid voltage conditions with accurate parameters. However, under unbalanced and distorted network conditions, significant power ripples and current harmonics arise in conventional DPC if no special measures are taken. Furthermore, the system performance further deteriorates if the inductance value differs from the actual value. To cope with the problems above, this article proposes an online inductance identification method for the DPC of a PWM rectifier under unbalanced and distorted network conditions. It is shown that the proposed method can guarantee sinusoidal characteristics of the grid current and reduce power ripples under unbalanced and distorted network conditions when the identification algorithm is enabled. The presented simulated and experimental results confirm the effectiveness of the proposed method.

Direct Power Control of PWM Rectifiers With Online Inductance Identification Under Unbalanced and Distorted Network Conditions

In the conventional direct power control (DPC) methods, the grid currents are highly distorted, and substantial ripple is present in the dc-bus voltage under unbalanced and distorted grid conditions. Various improved DPC methods have been proposed to address these problems, but these methods are generally complicated and not easy to use because of the complex controlling structures, need for considerable tuning, and so on. This paper proposes an improved DPC method obtained by simply adding a compensation term to the original power references. The compensation power is obtained by analyzing the power ripple in the input line inductance based on extended power theory. The reference voltage vector is subsequently calculated from the new power reference and synthesized by space vector modulation. To improve the robustness of the proposed DPC against inductance variations, an online inductance identification technique based on the gradient correction method is proposed and combined with the proposed DPC. The presented simulation and experimental results demonstrate that the proposed method can achieve sinusoidal grid currents and significantly reduce the dc-voltage ripple even with mismatched inductance under unbalanced and distorted grid conditions.

Robust DPC-SVM control strategy for shunt active power filter based on H∞ regulators

This paper proposes an improved direct power control (DPC) strategy for shunt active power filter (SAPF). The conventional DPC control suffers from variable switching frequency and high-power ripples due to hysteresis comparators used. In order to overcome the drawbacks and to ensure a fast response, a perfect reference tracking with required dynamic behavior and low power ripple level, a direct power control combined with space vector modulation DPC-SVM is proposed. An H∞ regulator is considered for the closed loop active and reactive power. The effectiveness of the proposed DPC-SVM control based on H∞ regulator is examined by simulation and experimental validation using Matlab/Simulink software with a real-time interface based on dSPACE 1104 under different loading conditions.