Power Injection Control Research Articles

Direct maximum power injection control of grid-connected PV micro-inverter systems connected to the grid

The increasing use of fossil fuels such as gas and oil has caused many environmental problems, including air pollution, depletion of underground resources, the destructive phenomenon of global warming, destruction of the ozone layer, and many other problems for the environment. Photovoltaic systems are one of the most promising solutions to overcome these problems. Due to the low voltage of solar panels and the higher controllability of photovoltaic systems against changes in sunlight intensity during the day, DC-DC power converters are required. In this project, the aim is to design and build a DC-DC converter with the ability to provide high voltage gain at a suitable efficiency for a 1-string photovoltaic system with the ability to track the maximum power point 2. The designed converter is designed and analyzed with the ability to provide a voltage gain of 5/6 at the critical operating point, a minimum efficiency of 94%, and a power of 500 watts. This converter uses classical soft switching, so the switching losses are reduced, which in turn increases the efficiency of the converter. This converter has a lower voltage stress on the switch (4/0) than the existing techniques. On the other hand, while new converters use a large number of switches and magnetic cores in the cell to provide high gain, this converter uses the least number of switches and magnetic cores to achieve high gain. Also, the passive elements of this converter, such as inductor and capacitor, are in the order of a few microhenries and farads, and therefore the size of these components is also reduced. In addition, due to the high gain provided in lower duty cycles, the efficiency of the switch is increased, and therefore cheaper switches can be used. Also, due to the reduction in the size of passive elements, the size of the magnetic core is also reduced, which in turn optimizes the converter economically.

Service Restoration of AC–DC Distribution Grids Based on Multiple-Criteria Decision Analysis

Modern distribution grids are transforming due to the increasing amount of load and generation based on DC technologies, whose interconnection is facilitated by the upcoming AC-DC distribution networks. Their fault management is challenged by new issues related to the power transferred among AC and DC sub-networks. In light of this, the present paper proposes a novel Service Restoration (SR) algorithm, specifically tailored for AC-DC distribution grids, that optimizes the re-energization by establishing priorities of disconnected bus groups and computing, as candidate solutions, hierarchical combinations of normally open and normally closed switches. To overcome the limitations of existing approaches, a Multiple Criteria Decision Analysis (MCDA) is proposed to combine and objectively prioritize different SR goals (i.e., the use of telecontrolled switches, the minimization of power losses, and the applicability of the proposed solutions in a defined time horizon), and ultimately make the grid operator benefit from the possibility to flexibly tune different operational objectives. The proposed algorithm allows to effectively discriminating competing solutions, i.e. whence and how to re-energize disconnected buses, and complies with the time requirements for field implementation. The results prove the crucial role of DC sub-networks, associated to the control of power injection from AC-DC converters, in enhancing the SR by improving its targets and increasing the number of re-energized loads. Ultimately, the effect of MCDA comparison parameters on the SR outcomes is quantitatively investigated via global sensitivity analysis, whose adoption is recommended for supporting the grid operator in the algorithm implementation.

A Flexible Reactive Power Injection Method for DC-Link Capacitors Voltage Balancing in Back-to-Back Multilevel Converters

The dc-link capacitor voltage drift is the key technical problem of the converters with multi-intermediate nodes. The back-to-back (BTB) configuration with voltage balancing control can achieve a certain operation range. Nevertheless, the challenge of voltage drift still remains, especially when both sides operate at high but different modulation indexes and high power factors. This article focuses on a BTB seven-level V-clamp multilevel converter (VMC). The balanced operation limits are presented, and the effect of the power factor on balancing capability is analyzed. To maintain the voltage balancing of the dc-link capacitor under different operation conditions of the load (inverter side), a reactive power injection control is proposed in this article. Suitable reactive power is injected into the rectifier according to the balancing situation. The proposed control method can actively adjust the power factor of the rectifier to provide the required balancing capability. In this way, the dc-link capacitor voltage balancing is maintained within a larger operation range. In this article, a 10-kVA laboratory prototype of BTB seven-level VMC is set up to verify the effectiveness of the proposed control.

Implementation of a Photovoltaic Inverter with Modified Automatic Voltage Regulator Control Designed to Mitigate Momentary Voltage Dip

The main objective of this research is to propose an active and reactive power injection control in order to mitigate voltage sags. The proposed control strategy works in conjunction with a modified version of an automatic voltage regulator (AVR), where it will act on the active and reactive powers injected by the inverter to reduce the effects of voltage sags. In this way, the control will avoid possible shutdowns and damage to the equipment connected to the grid. The voltage improvement can be perceived for consumers connected to the power system. Modifications in AVR model and parameters are performed to speed up its performance, thus identifying the short-duration voltage variations (SDVV) and, consequently, the control acts to alter the powers, decreasing the active power injection and increasing the reactive power based on inverter capacity during the momentary voltage dip (MVD). Finally, when the fault is cleared, all values return to the pre-fault condition, so that the inverter only operates with active power. A 75 kW three-phase grid-connected photovoltaic system (GCPVS) equipped with the proposed control was inserted in a distribution grid of the city of Palmas, state of Tocantins, Brazil, and all of the computer simulations were performed on the Matlab/Simulink®.

DG integration to distribution system with active power injection control

Conventional methodology for electrical power generation is vulnerable due to environmental limitations and the availability of fuel. Distributed generation, offering virtuous benefits to the market partakers, is trending in electrical power system in modern era. This paper presents the distributed generation integration to grid with active power injection control. Distributed generation source delivers DC power which is processed through square wave inverter. Inverter circuit is controlled using a simple control technique to match grid code. Fixing the current reference and varying the same, analysis is carried out for grid integration scheme of distributed generation injecting active power to grid. Simulation work is carried out and results are shown using MATLAB/SIMULINK software.

Effective sensitivity-based method for N-1 contingency analysis of VSC-based MTDC power grids considering power generation droop speed controls

This paper introduces a sensitivity-based approach for the efficient calculation of the post-disturbance, steady-state conditions in VSC-based MTDC power grids subject to generation outages and VSC disconnections. This approach is useful for the N-1 contingency analysis, a crucial tool in power system control centres. In order to maintain a high degree of fidelity, the approach considers state-of-the-art VSC control strategies: converters with DC voltage regulation, power-injection control, DC voltage/power droop control, and converters imposing frequency regulation on passive grids. The speed-governing response of power plants is also considered, enabling accurate calculations of AC/DC power flows and AC system frequencies. Indeed, the derived sensitivity factors permit the primary frequency response of the AC systems and DC grid to be efficiently assessed, something that would require several hours of simulation by standard electromagnetic transient (EMT) simulators. Evidently, this novel approach allows a much faster calculation of the AC/DC network’s post-disturbance conditions than is possible with dynamic simulation tools. A formulation with such modelling versatility and practicality does not currently exist elsewhere.The usefulness of this novel formulation has been confirmed using an MTDC system comprising six VSC-connected AC grids and a 13-bus DC grid. The disconnections of VSC units and power plants have also been evaluated. The study shows that the post-disturbance, steady-state conditions computed by the sensitivity-based approach agree well with those obtained by full dynamic simulations, because the relative errors between the two fundamentally different methods are smaller than 0.1% for the AC system frequencies and smaller than 4% for the AC and DC transmission line power flows.

Voltage sag influence on controlled three‐phase grid‐connected inverters according to the Spanish grid code

To ensure the safe operation of the grid, there are some requirements to be taken into consideration to connect power converters. During abnormal conditions – e.g. during voltage sags –, the control of the converters is a very important key to guarantee power quality and good behaviour of the distributed generation system. The aim of this study is to employ two possible control strategies for a grid-connected inverter according to the Spanish grid code, and to analyse the behaviour of the output voltages during both symmetrical and unsymmetrical voltage sags. The analytical development shows the sag influence on currents, voltages, active and reactive powers. These influences are explained through Ku transformation in the synchronous reference frame, thus giving a representation for electrical variables easiest to analyse. The results show how control strategies affect the converter behaviour and how they can support the main grid during faults through the control of active and reactive power injection. Sags with different durations and depths have been taken into account, which can provoke critical values for electrical magnitudes and can lead to the violation of the grid code. The proposed control strategies study has been validated by means of both simulations in Matlab TM –Simulink and experimental results.

FAPI Controller for Frequency Support in Low-Inertia Power Systems

This paper presents different forms of Fast Active Power Injection (FAPI) control schemes for the analysis and development of different mitigation measures to address the frequency stability problem due to the growth of the penetration level of the Power Electronic Interfaced Generation (PEIG) in sustainable interconnected energy systems. Among the studied FAPI control schemes, two different approaches in the form of a derivative-based control and a virtual synchronous power (VSP) based control for wind turbine applications are also proposed. All schemes are attached to the PEIG represented by a generic model of wind turbines type 4. The derivative-based FAPI control is applied as an extension of the droop based control scheme, which is dependent on the measurement of the network frequency. By contrast, the proposed VSP-based FAPI is fed by the measurement of the active power deviation. Additionally, unlike existing approaches for virtual synchronous machines, which are characterized by high-order transfer functions, the proposed VSP-based FAPI is defined by a second-order transfer function, which can contribute to fast mitigation of the system primary frequency deviations during containment period. The Great Britain (GB) test system, for the Gone-Green planning scenario for the year 2030 (GG2030), is used to evaluate the effects of the proposed FAPI controllers on the dynamics of the system frequency within the frequency containment period. Thanks to proposed FAPI controllers, it is possible to reach up to 70% for the share of wind power generation without violating the threshold limits for frequency stability. For verification purposes, a full-scale wind turbine facilitated with each FAPI controller is tested in EMT real-time simulation environment.

Static voltage stability improvement with battery energy storage considering optimal control of active and reactive power injection

Voltage stability analysis and improvement remain a major concern of power system operators due to the recurrent risk of voltage collapse. Many approaches have been used to analyze voltage stability but an approach that can directly indicate the closeness of power system to voltage collapse can be used to optimally plan for the improvement of the power system voltage stability condition when compensation devices are to be deployed. In this study, optimal active and reactive power compensation was performed on a continuously loaded power system, using the battery energy storage system (BESS). In order to achieve this, a voltage stability evaluation model which contains information concerning the active and reactive power flow along the transmission line was adopted. The BESS is considered as a combination of storage units and voltage source converter (VSC) in order to facilitate independent control of both the active and reactive injection to the grid. The optimal control of the output of the BESS minimizes its installed capacity and consequently, reduced the cost as shown by simulation on the IEEE 14 bus system.

An Efficient Reactive Power Control Method for Power Network Systems with Solar Photovoltaic Generators Using Sparse Optimization

With the incremental introduction of solar photovoltaic (PV) generators into existing power systems, and their fast-growing share in the gross electricity generation, system voltage stability has become a critical issue. One of the major concerns is voltage fluctuation, due to large and random penetration of solar PV generators. To suppress severe system voltage deviation, reactive power control of the photovoltaic system inverter has been widely proposed in recent works; however, excessive use of reactive power control would increase both initial and operating costs. In this paper, a method for efficient allocation and control of reactive power injection using the sparse optimization technique is proposed. Based on a constrained linearized model describing the influence of reactive power injection on voltage magnitude change, the objective of this study is formulated as an optimization problem, which aims to find the best reactive power injection that minimizes the whole system voltage variation. Two types of formulations are compared: the first one is the conventional least-square optimization, while the second one is adopted from a sparse optimization technique, called the constrained least absolute shrinkage and selection operator (LASSO) method. The constrained LASSO method adds ℓ 1 -norm penalty to the total reactive power injection, which contributes to the suppression of the number of control nodes with non-zero reactive power injection. The authors analyzed the effectiveness of the constrained LASSO method using the IEEE 39-bus and 57-bus power network as benchmark examples, under various PV power generation and allocation patterns. The simulation results show that the constrained LASSO method automatically selects the minimum number of inverters required for voltage regulation at the current operating point.

Active Power Injection Control for Power Converters Connected to the Grid Through an L Filter

ABSTRACTThis paper presents the design, implementation, and evaluation of a model-based controller for a general scheme of transformerless power converters connected to the grid through an L filter. The proposed controller is aimed at active power injection, and consists of a damping term over the current error in addition to a filter parameter estimation scheme. The latter provides estimates of the filter internal resistance and inductance values. It involves the fundamental and quadrature components of the grid voltage to asymptotically compensate for current harmonic peturbations. As a result, the closed-loop system fulfills the active power injection objective. The proposed controller is tested in an experimental setup and its performance is compared to that of the Proportional-Resonant controller. Experimental results are presented for a single-phase H-bridge inverter; however, the control scheme can be used in several other H-bridge based inverter topologies such as H5 and HERIC.

Coordination Control Strategy for AC/DC Hybrid Microgrids in Stand-Alone Mode

Interest in DC microgrids is rapidly increasing along with the improvement of DC power technology because of its advantages. To support the integration process of DC microgrids with the existing AC utility grids, the form of hybrid AC/DC microgrids is considered for higher power conversion efficiency, lower component cost and better power quality. In the system, AC and DC portions are connected through interlink bidirectional AC/DC converters (IC) with a proper control system and power management. In the stand-alone operation mode of AC/DC hybrid microgrids, the control of power injection through the IC is crucial in order to maintain the system security. This paper mainly deals with a coordination control strategy of IC and a battery energy storage system (BESS) converter under stand-alone operation. A coordinated control strategy for the IC, which considers the state of charge (SOC) level of BESS and the load shedding scheme as the last resort, is proposed to obtain better power sharing between AC and DC subgrids. The scheme will be tested with a hybrid AC/DC microgrid, using the tool of the PSCAD/EMTDC software.

Integrated voltage regulation in distribution grids with photovoltaic distribution generation assisted by telecommunication infrastructure

Massive penetration of Distributed Generation Photovoltaic Systems – DGPV – connected to the power distribution grid through electronic inverters can contribute, in an aggregate scenario, to the performance of several power system control functions, notably in voltage regulation along a distribution feeder. In this context, the supervision and control of these generating units through a standardized, flexible and capillary communication infrastructure becomes a key factor in enabling large-scale integration. Present voltage regulation methods adopted in distribution grids using DGPV units are based on the local interaction of each source with the power grid, without exploiting the potential benefits of a wide integration among them. This paper proposes the use of an optimization method for voltage regulation, focused on reactive power injection control, based on a communication architecture model that coordinates the interaction among the inverters of DGPV units. This architecture enables each distributed source to perform in accordance with its operational characteristics and location, while dynamically coordinated by a DGMS (Distributed Generation Management System). The proposed communication infrastructure is based on the connectivity and interoperability requirements established by the international standard IEC 61850 and the IEEE 2030 reference model. A sensitivity analysis regarding the performance of voltage regulation and communication infrastructure, based on a co-simulation of PSCAD and MatLab, shows the effectiveness of the proposed optimization method. This work analyses the impact of communication network delay and unavailability in voltage regulation process.

A novel structure proposal for distributed generation using SMES and PV system with relative controllers design

A combined power source including superconductor magnetic energy storage system (SMES) and photovoltaic (PV) systems has been considered for distributed generation system as a hybrid power source in this research. Both power sources have been connected to power grid and some controllers have been designed for power injection control. The SMES system can be in charging mode via PV system and power grid. Moreover, power injection controller has been designed for tuning of produced power of PV and SMES system. For this aim, a DC/DC converter has been connected to PV system and a bi-directional-three-level chopper has been used for SMES. PV power control has been based on the DC/DC converter control and the chopper control has been used for SMES power control. On the other hands, inverter control has been confirmed for injection of active/reactive power from distributed generation system to power grid. Proposal of a new scheme and design of a novel controller, are the advantages of this research. Finally, a series of simulation results have been shown.

Development of a quasi-direct temperature control system of modulated induction thermal plasmas for advanced materials processing

A new modulated induction thermal plasma system, called a feedback control type of modulated induction thermal plasma system, was developed for quasi-direct control of thermal plasma temperature for advanced materials processing. The system is based on the arbitrary-waveform modulation induction thermal plasma system developed previously in our work, and a real-time spectroscopic observation system. The Ar excitation temperature was measured in real time using a spectroscopic observation technique. Its time evolution was controlled to trace externally given waveform periodical signals between 6000 and 8000 K such as rectangular, triangular and sawtooth waveforms. In addition, the developed system was confirmed to adopt an automatic power injection control, synchronized with gas injection as a disturbance.

Options for Control of Reactive Power by Distributed Photovoltaic Generators

High-penetration levels of distributed photovoltaic (PV) generation on an electrical distribution circuit present several challenges and opportunities for distribution utilities. Rapidly varying irradiance conditions may cause voltage sags and swells that cannot be compensated by slowly responding utility equipment resulting in a degradation of power quality. Although not permitted under current standards for interconnection of distributed generation, fast-reacting, VAR-capable PV inverters may provide the necessary reactive power injection or consumption to maintain voltage regulation under difficult transient conditions. As side benefit, the control of reactive power injection at each PV inverter provides an opportunity and a new tool for distribution utilities to optimize the performance of distribution circuits, e.g., by minimizing thermal losses. We discuss and compare via simulation various design options for control systems to manage the reactive power generated by these inverters. An important design decision that weighs on the speed and quality of communication required is whether the control should be centralized or distributed (i.e., local). In general, we find that local control schemes are able to maintain voltage within acceptable bounds. We consider the benefits of choosing different local variables on which to control and how the control system can be continuously tuned between robust voltage control, suitable for daytime operation when circuit conditions can change rapidly, and loss minimization better suited for nighttime operation.

Harmonic and reactive power compensation as ancillary services in inverter-based distributed generation

The introduction of distributed generation, DG, into low-voltage (LV) networks opens up the possibility of supplying ancillary services to aid network management and to maintain power quality. DG itself can cause voltage magnitude difficulties when injecting real power into networks with high R/X ratios, but control of reactive power injection can help overcome this. Continuous control and support only at the voltage limit conditions (to avoid unnecessary reactive power flows in normal conditions) are explored. Relatively high-impedance LV networks are prone to harmonic distortion from nonlinear loads. A variety of control methods that emphasise either harmonic-line flows or local-voltage distortion are examined, and a compromise method based on resistance emulation is shown to be effective. Experimental results from a single-phase laboratory network and 2 kVA inverter are used to illustrate how these additional control functions can be integrated into the existing control scheme for real-power management. Decomposition of observed voltages and currents into harmonic terms that are phasesynchronised to the grid voltage is a challenge in real-time systems. Kalman observers are used to achieve this with an additional advantage of avoiding explicit phase-locking while producing quadrature components useful in instantaneous calculation of reactive power and in providing feed-forward compensation terms

Control strategy for dynamic voltage restorers to achieve minimum power injection without introducing sudden phase shift

A power injection control strategy is proposed for dynamic voltage restorers (DVR) under voltage sag or swell conditions. Under such a strategy, the error between the voltage of the energy storage capacitor in the DVR and a given reference voltage is extracted to control the injected power such that during an upstream voltage disturbance, zero or minimum power injection can be achieved automatically, while sudden phase jump of the load-side voltage can also be avoided. The proposed control strategy is analysed in detail and numerical examples are provided to demonstrate the effectiveness of the scheme.

Dynamic maximum power injection control of AC photovoltaic modules using current-mode control

Maximum power point tracking (MPPT) strategies are an essential part of photovoltaic (PV) power converters' control. These algorithms maintain the operation of the PV panel at the optimal point for maximum performance. In addition, the power converter must synchronise with the electricity grid and inject the power extracted from the PV panel. These two tasks are executed by the controller in the power conditioning unit. This, however, results in complicated control loops. Moreover, the interaction with the grid may cause stability problems in the power converter during voltage disturbances. The dynamic control of PV modules connected to the electricity supply presented by the authors provides a substantial improvement in power converter stability and ease of implementation. This strategy combines grid power injection control and PV MPPT into a single control block. The first objective is achieved using current-mode control to shape the current injection whereas the latter objective exploits the dynamic behaviour of the PV panel to determine changes in the grid current magnitude. An implemented prototype system shows the performance of the proposed strategy and the results are compared against commercially available inverters.