Braking Chopper Research Articles

Fault ride through enhancement of large‐scale solar plants using distributed converters

AbstractThe grid‐connected photovoltaic plants (GCPVPs) encounter various types of anomalies during fault occurrence in the main grid. During a fault occurrence on the grid side, the voltage of the point of common coupling (PCC) drops, causing the DC connection voltage to become too high for power balancing. This high DC voltage may damage the inverter and DC link equipment, which necessitates a reliable control scheme with low voltage passage requirements. These requirements, which obligate the GCPVP to remain connected to the main grid during abnormal conditions are generally known as low voltage ride‐through (LVRT). Herein, a developed LVRT method in the control approach that injects maximum rated current during a sag is proposed to rectify the shortcomings in single and multi‐inverter grid topologies. The proposed approach utilizes a current limiter combined with a DC braking chopper to guarantee the GCPVP's continuous participation in the power supply. Different scenarios including low and high power generations as well as two‐phase and three‐phase severe faults to the ground are considered. The results show that the proposed approach not only improves the performance in the single‐inverter system but also remedies the defects aggravated in the case of a GCPVP with several inverters.

A multi‐objective low‐voltage ride‐through control strategy for three‐phase grid‐interfaced solar power plant during symmetrical and asymmetrical faults†

SummaryThis paper presents a low‐voltage ride‐through capability (LVRT) solution for the photovoltaic (PV) grid‐connected inverters compliant with the Indian grid code. The LVRT strategy ensures the uninterrupted connection of solar energy to the grid, safeguarding against system shutdown in the event of various grid faults. During this time, the inverter supplies reactive power to the utility grid, effectively utilizing converter capacity and aiding the restoration of the voltage profile at the point of common coupling (PCC). The system used in this study involves a two‐stage grid‐interfaced solar PV setup with a boost converter that tracks the maximum power point (MPP) and an inverter that maintains the DC‐link voltage. A modified dynamic braking chopper control (MDBCC) has also been implemented to minimize the DC‐link voltage oscillations during asymmetrical faults while simultaneously injecting the sinusoidal current into the grid. To improve grid synchronization in the presence of unbalanced abnormalities, a modified dual second‐order generalized integrator phase‐locked loop (DSOGI‐PLL) has been employed to track the grid voltage angle precisely. Furthermore, a new control system has been developed in conjunction with the LVRT approach. The suggested system is simulated in MATLAB/Simulink to validate the efficacy of the LVRT control method during symmetrical and asymmetrical faults using a 100‐kW two‐stage grid‐interfaced solar PV facility. Finally, for experimental validation, a real‐time test bench (RTS) OPAL‐RT 4510 is used to implement the setup with its control, and the practical results are compared with the simulation outcomes.

Zero-Voltage Ride-Through Scheme of PMSG Wind Power System Based on NLESO and GFTSMC

In this paper, a scheme for zero-voltage ride through of a permanent magnet synchronous generator wind power system is proposed. Maintaining the stability of DC-link voltage is the key to realizing zero-voltage ride through. A braking chopper is used to dissipate the active power to restrain the rise of DC-link voltage during a grid fault. However, the braking chopper-caused disturbance to the double closed-loop control of the grid side converter makes the control effect on DC-link voltage worse. Therefore, a robust current feedforward control, based on a nonlinear extended state observer and global fast terminal sliding mode control is proposed. A nonlinear extended state observer estimates the total disturbance in the system and compensates for the control law. Global fast terminal sliding mode control enables the system to reach the sliding mode surface in a finite time, and its control law is continuous without switching terms, thereby eliminating the chattering phenomenon. A nonlinear extended state observer and global fast terminal sliding mode control change the current feedforward control into a nonlinear robust current feedforward control. The control effect is improved, and the use of current transformers is reduced in practical applications, thereby reducing costs. The validity of this scheme has been verified by simulation.

Preliminary design of an OWC wave energy converter battery charger

This paper introduces a low-power off-grid oscillating water column wave energy converter with an internal battery bank. The research aims at the preliminary design and devising of the control strategy of a power electronics interface between the turbo generator and the battery bank. The converter comprises a spar buoy, a biradial turbine, a permanent magnet generator, a full-wave bridge rectifier, a braking chopper, a DC-to-DC step-down converter, and a lead-acid battery bank. The power-take-off system was modelled in Simulink/MATLAB, and its performance was assessed with steady-state simulations, considering a wave climate characteristic of Leixões, Portugal. The chamber pressure, the turbine, generator and rectifier performance were taken from experimental data sets. A simple battery model was derived from the manufacturer's datasheet. An ideal step-down DC-to-DC converter operating in discontinuous conduction mode regulates the battery charging current. This converter, in parallel with the braking chopper, adjusts the generator counter torque by regulating the current through the rectifier. Twelve system variables were recorded for selected pairs of input pressure and step-down converter design coefficient. The power at the rectifier's output terminals was mapped for the rotational speed and input pressure. The results show a system rating of 1.4 kW with 400 W of electrical power at 200 rad/s for the most frequent sea states. The range of the duty cycle, the inductance and the braking resistance were derived. Two closed-loop controllers were proposed for managing the step-down converter and the braking chopper. Their set points and saturation limits were derived from the simulation results.

Control method of an AC-AC MMC for open-end stator winding wind turbine generation system

With the increasing of power rating and voltage level of wind turbine, the traditaional low voltage converter is being replaced by multilevel converter. This paper proposes a new ac-ac modular multi-level converter (MMC) connecting the open-end stator winding permanent magnet synchronous generator (OW-PMSG) to AC power grid. The working principle of the proposed topology is analyzed. Under different grid conditions, a unified capacitor voltage balance control method and a current control method are proposed. Aiming at the low grid voltage ride through problem, a distributed braking chopper circuit and the corresponding control strategy is given. Simulation is conducted for verification. Compared with the back to back (BTB) MMC for OW-PMSG, the number of capacitors and arm inductors of the proposed topology are reduced by 43% and 33%. Moreover, the number of the state variables of the average capacitor voltages and currents of the proposed topology are reduced by 33% and 47%, reducing the control complexity. The proposed topology also has higher efficiency than the BTB MMC for OW-PMSG. Compared with the other ac-ac MMC topologies for OW-PMSG, the combined power rating of the power devices of the proposed topology is much lower and thus the proposed topology has higher power density.

Energy Efficiency Improvement with Reversible Substations for Electrified Transportation Systems

More and more often overall energy efficiency of an electrified transportation system appears as target of new constructions, sometimes with incomplete definitions of performance indexes to assess that target has been reached. A worked out example is based on the introduction of reversible substations. Reversible substations are a method to improve energy efficiency, whose application in an existing system can be progressive and does not require large traffic intensity to be effective. Their effectiveness depends on some system parameters (nominal catenary voltage in particular). A simulation model fed with experimental data from a line section of Metro de Madrid is used to demonstrate the operation and optimization of reversible substations. Background The ambitious reduction of CO2 greenhouse gas emission within 2050 declared by the European Commission also involves transportation systems. In this context an optimum recovery of the electric braking energy produced by railway vehicles is more and more relevant. Several strategies to completely recover the braking energy are being developed and applied. A methodology that allows the accurate determination of the amount of recovered energy in real operating conditions becomes then a valuable tool. Objective Reversible substations are one of the braking energy recovery methods that are widely applicable. Their effect is analyzed in a system perspective, considering them integrated in the transportation system with its dynamics and various operating points. The effectiveness and consequences of the operation of one or more reversible substations are evaluated by identifying relevant system conditions and scenarios. Methods An electric network model is provided, fed by measured timetable and traction current. Simulation results are analyzed and compared with some experimental results: simulation configurations will be selected to match those of the available experimental data. Results The selected substation no-load output voltage level has a significant effect on efficiency and performance of reversible substations. A reduction of 50 V, from 1700 V to 1650 V produces a decrease of the energy dissipated by the braking rheostat on-board trains of about 13%. The voltage increase caused during braking phases is kept under control better for track positions close to reversible substations: tests show that line voltage increase is 2.5% of nominal value with a reversible substation, and only 0.5% when it is operated. Trimming the thresholds that trigger the operation of the on-board braking chopper (intermingling regenerative and dissipative braking) has a dramatic effect on regenerability: a reduction of 50 V causes an improvement of 19%. Conclusion The paper presents a methodology that merges measurements and circuital model to investigate on the energy saving provided by reversible substations supplying railway system. The methodology has been applied to a real case. Preliminary results regarding the impact of supply voltage level, reversible module position and threshold levels of the braking chopper control system on the dissipated braking energy and power quality has been carried out.

Improved current control loops in wind side converter with the support of wild horse optimizer for enhancing the dynamic performance of PMSG-based wind generation system

ABSTRACT The creation of optimization methods is relatively common and popular today for solving issues in engineering areas. In this paper, a new wild horse optimizer (WHO) method is adopted to design an optimal controller for a permanent-magnet synchronous generator (PMSG)-based wind turbine system (WTS). A control method consisting of two current control loops of the optimized controller is proposed for the control of the machine-side converter. The dynamic performance of PMSG can be improved during the different normal and abnormal conditions through effective tuning of the PI controller gains which enhances the overall response of the system parameters. This enhancement consequently results in the realization of the maximal power tracking during wind speed changes and the fault ride-through capability during faults and large-signal events. Furthermore, the power fluctuations due to the incoming wind speed variants can be smoothed by using the suggested controller. In addition, the proposed controller system employs an optimal torque control method and braking chopper system to help in achieving such tasks. MATLAB simulations of a 1.5 MW PMSG-WTS have been carried out and compared with the Ziegler Nichols-based PI controller in order to validate the feasibility and efficacy of the proposed controller.

A simple and effective grid-supporting low voltage ride-through scheme for single-stage photovoltaic power plants

Due to the ever-increasing impact of grid-connected photovoltaic power plants (GCPPP), compliance with grid-code (GC) requirements has become inevitable. According to current GCs, not only a GCPPP needs to inject reactive current into the network with a drop in the grid’s voltage, but a necessity exists to inject active power into the network during grid fault occurrence and post-faults. This is because the power system faces stability issues in the case of either GCPPP being disconnected from the network or active power not being injected into the grid after fault clearance. In this paper, a braking chopper (BC) is installed and a controller has been designed to enable fulfillment of low voltage ride through (LVRT) criteria for single-stage grid-integrated PV systems. This method proves to be simple, inexpensive, and effective for a wide range of operating conditions and different types of grid-faults. Furthermore, a current limiter has been incorporated for the DC–AC converter that is compatible with the BC controller itself. A general guideline has been devised in this research to evaluate the proposed LVRT strategy for seamless operation of single-stage GCPPPs. Not only does the GCPPP remain connected to the network by adhering to relevant GCs, but it also tracks the maximum power point after fault clearance without any delays. The simulations are carried out in MATLAB/Simulink software and comparisons have been drawn with the conventional approach. The results indicate excellent improvement in transient and steady-state operation of the GCPPP.

Fault Ride Through Capability Enhancement of Permanent Magnet Synchronous Generator-based Wind Energy Conversion System

With the speedy increase of wind energy in electric networks, many important issues could emerge, where the most important matter is to maintain the connection of wind generators during fault conditions. With different faults in the electrical network, the voltage at the point of common coupling (PCC) decreases causing unwanted transients in the stator currents. This results in substantially increased fluctuations in the DC-link voltage (Vdc). To avoid this negative impact, it is a must to maintain the capability of wind generators to continue linked to the network during faults, which is depicted as low voltage ride through (LVRT) capability. This paper investigates the LVRT enhancement by two techniques, the first is based on Braking Chopper (BC) and the second method is based on electrical double-layer capacitors (EDLC), or Supercapacitor Energy Storage System (SCESS), under abnormal conditions. The full model of the permanent magnet synchronous generator (PMSG) system and FRT technique are performed in MATLAB/Simulink platform. As a consequence of the findings, both the BC and SCESS are capable to provide satisfactory performance with superior FRT capability for the SCESS compared to the BC.

Robust control scheme for the braking chopper of PMSG-based wind turbines–A comparative assessment

Despite the grid-integration of permanent magnet synchronous generator (PMSG) wind energy conversion systems (WECS), utilities are facing challenges that are hindering wind penetration growth. Grid-side voltage sags at the point of common coupling (PCC) are considered as one of such uncontested issues. Due to imbalance in back-to-back (BTB) converter’s dc-link input-output powers, its capacitor and power electronics are highly susceptible to PCC voltage sags. Hence, provision of wind farm grid-codes (GC) for supporting grid operations is imperative and development of strategies for realizing low-voltage ride-through capability in WECSs have emerged as an integral GC requirement. One strategy is to install a braking chopper (BC) across the dc-link. This study presents (a) an overview of conventional BC control methods, (b) design of a robust BC controller for PMSG-based WECSs, and (c) comparative performance assessment of (b) with (a) for PMSG-based WECS operations during normal and grid fault conditions. The robust BC controller takes advantage of the sliding mode method to control BC and to determine the grid-side converter active power reference set-point. This nonlinear control scheme ensures proper execution of GCs and offers reliable protection to the dc-link. Chattering phenomenon and reaching-time is reduced significantly, by further adoption of exponential reaching law. In addition to its robustness, a prominent feature of this BC controller is its applicability to present BTB control structures. The simulation results reflect on effectuality and robustness of the proposed BC controller in comparison to conventional BC control strategies.

An Enhanced Low Voltage Ride-Through Control Scheme of a DIFG based WTG Using Crowbar and Braking Chopper

The grid codes define low voltage ride-through (LVRT) as capability of wind turbine generator (WTG) to support the grid voltage by injecting reactive power and suppress the rise of DC-link voltage and inrush rotor current in the rotor side converter (RSC) of the doubly fed induction generator (DFIG) during a fault. Moreover, the rotor current increases significantly during severe disturbances if any protection schemes are not employed. Therefore, the protection schemes must be used to avoid the damage to the converter during a fault. This paper proposes an enhanced LVRT control scheme of a DFIG employing a crowbar in the RSC side and braking chopper across the DC-link capacitor. The DFIG is highly delicate to grid voltage fluctuation during a fault because the DFIG is directly linked to the grid via stator. During severe fault the crowbar regulates the rotor current within an acceptable range and the braking chopper discharges the DC-link capacitor via resistor within a safe limit. The proposed LVRT control scheme is performed for a 2.4-MW DFIG using a MATLAB/SIMULINK simulator. The results delineate that the proposed control scheme is able to rapidly decrease the rotor current and repress the escalation in DC-link voltage during a grid fault.

Design and implementation of FLC system for fault ride-through capability enhancement in PMSG-wind systems

Fault ride-through (FRT) capability enhancement for the growth of renewable energy generators has become a crucial issue for their incorporation into the electricity grid to provide secure, reliable, and efficient electricity. This paper presents a new FRT capability scheme for a permanent magnet synchronous generator (PMSG)-based wind energy generation system using a hybrid solution. The hybrid solution is a combination of a braking chopper (BC) and a fuzzy logic controller (FLC). All proportional-integral (PI) controllers which control the generator and grid side converters are replaced with FLC. Moreover, a BC system is connected to the dc link to improve the dynamic response of the PMSG during fault conditions. The PMSG was evaluated on a three-phase fault that occurs on an electrical network in three scenarios. In the first two scenarios, a BC is used with a PI controller and FLC respectively. While the third scenario uses only FLC without a BC. The obtained results showed that the suggested solution can not only enhance the FRT capability of the PMSG but also can diminish the occurrence of hardware systems and reduce their impact on the PMSG system. The simulation tests are performed using MATLAB/SIMULINK software.

Application of a Non-carrier-Based Modulation for Current Harmonics Spectrum Control during Regenerative Braking of the Electric Vehicle

The regenerative braking of railway vehicles is widely used in DC railway systems all over the world. This mode of operation provides an opportunity to reuse part of the energy consumed by vehicles, and makes the railway system more energy efficient. During regenerative braking, not only energy management is an issue, but also Electromagnetic Compatibility EMC issues, such as interference of generated current harmonics with a railway signaling system. In this paper, the selective harmonic elimination modulation technique (SHE-PWM) was introduced to the traction drive with a three-level inverter to reduce specific catenary current harmonics generated during regenerative braking. The simulation model of a traction drive appropriate for harmonics analysis was proposed and verified by the measurements in the low-power laboratory drive system. The model was re-scaled to the 3 kV DC system for further study. The model of an induction motor with electromotive force and the method of its calculation was proposed. Furthermore, an analysis of the braking chopper operation was carried out. The asymmetric control of braking chopper was proposed to reduce the current harmonics below limits during chopper operation.

Dynamic evaluation of optimization techniques–based proportional–integral controller for wind-driven permanent magnet synchronous generator

Converters of permanent magnet synchronous generator (PMSG), driven by wind turbines, are controlled by a classical proportional–integral controller. However, many research studies highlighted the challenge in PMSG due to the poor performance of the classical proportional–integral controller, especially in the event of faults or wind speed variations. This article proposes a solution for the limitations of the classical proportional–integral controller with PMSG driven by a wind turbine. The proposed solution includes two optimization techniques: gray wolf optimizer and whale optimizer algorithm. To ensure the effectiveness of the proposed techniques, step change and random variation of wind speed are studied. Moreover, fault ride-through capability of the PMSG is studied with gray wolf optimizer and whale optimizer algorithm techniques during the occurrence of a three-phase fault incident. In this case, a braking chopper controlled by a hysteresis controller is connected to the DC-link capacitor. The simulated results show that compared with the classical proportional–integral controller, gray wolf optimizer and whale optimizer algorithm techniques are greatly efficient in improving the dynamic behavior of the PMSG during wind speed variations. Moreover, gray wolf optimizer and whale optimizer algorithm techniques present their effectiveness during the fault incident by suppressing the transient variations of all the PMSG parameters, improving the fault ride-through capability, and decreasing the total harmonic distortion of the current waveforms. All simulations are performed with MATLAB/ Simulink program package.

Design and implementation of fuzzy logic based modified real-reactive power control of inverter for low voltage ride through enhancement in grid connected solar PV system

In a grid connected solar PV system, during grid faults, increase in grid current, dip in voltage at point of common coupling and overshoot in dc link voltage in the inverter side are observed. The solar PV system gets disconnected from the grid whenever the grid voltage goes below a certain nominal value in order to safeguard the cascaded power converter systems from high currents and over voltages. This paper proposes an intelligent fuzzy based real and reactive power control of inverter for effective Low Voltage Ride Through (LVRT) capability during grid faults. The proposed fuzzy logic based modified inverter real and reactive power control strategy, stabilizes the grid voltage by injecting reactive current and limits the grid over current by reducing active power flow into the grid. To regulate the overshoot in dc link voltage during grid faults, a braking chopper and dynamic braking resistor strategies are included in the proposed LVRT scheme. The performance of the proposed inverter control strategy is studied through simulation of 100 kW grid connected solar PV system in MATLAB/SIMULINK 2018a platform. The algorithm is validated in real time hardware of 1 kW grid connected solar PV system. The simulation and hardware results validate the superior performance of the proposed inverter LVRT control strategy in comparison with other conventional schemes during grid faults.

Enhancing the dynamic performance of a wind-driven PMSG implementing different optimization techniques

Quick transient and smooth stable-state output of permanent magnet synchronous generator (PMSGs) is crucial for sustained power generation and grid code fulfillment specifically the fault ride-through (FRT) capability. Optimization techniques such as gray wolf optimizer (GWO), particle swarm optimizer (PSO) and whale optimizer algorithm (WOA) are proposed to realize a fast transient response and smooth operation of the PMSG. The proposed algorithms for machine-side converter are used to get the optimum power generated. Braking chopper (BC) was chosen as a solution for achieving the FRT for PMSG. The studied cases are the three-step wind speed change and symmetrical fault contingencies. In the first case, PSO gives better performance compared with conventional proportional integral, while in the second case, GWO and WOA give a better performance than PSO. GWO delivers the best output in the case of symmetrical fault compared to the WOA. MATLAB/Simulink environment is used to demonstrate the effectiveness of the proposed GWO technique including BC for improving the PMSG dynamic performance.

Two-Stage Protection Circuit for a Multichanneled Power Electronic Converter Fed Large Asynchronous Hydrogenerating Unit

Reliable operation of multichannel power electronic converters in a large pumped storage power plant (PSPP) is a main concern among policymakers and/or hydropower project developers. This paper aims to design a two-stage protection circuit operation strategy for a large-rated doubly fed induction machine (DFIM) employed for variable-speed PSPPs. This paper initially studies the dynamic behavior of DFIM under symmetrical short-circuit faults in both the 400-kV power system and at stator terminal of the generating unit. Based on the fault analysis, a two-stage protection circuit (dc-link braking chopper circuit and crowbar protection circuit) operation strategy is designed in consideration of practical limitations. The designed operation strategy ensures the continuous operation of large-rated DFIM under marginal grid disturbances. To investigate the effective operation of a two-stage protection circuit, a 250-MW DFIM with multichannel power converters is implemented in MATLAB/Simulink tool. An experimental test is carried in a 2.2-kW DFIM laboratory prototype.

Low‐voltage ride‐through enhancement with the ω and T controls of PMSG in a grid‐integrated wind generation system

This study deals with the formulation of a simple control strategy for the enhancement of the low-voltage ride-through (LVRT) capability of the grid-integrated permanent magnet synchronous generator (PMSG)-based wind generation system (WGS). The control warrants satisfying minimum required reactive current support to the ac grid as first priority with minimum loss of generation and maximum utilisation of the converter current capacity during LVRT compliance as per E.ON Netz German grid code requirements. The reference control variables in coordinated control of the stator-side and grid-side converters are altered so as to support the reactive current to the ac grid and, to store the excess active power in the system inertia for keeping the dc-link capacitor voltage in the safe limit during voltage dips at the grid side. The investigations have been made on the proposed strategy of LVRT enhancement with the speed (ω) and torque (T) controls of the direct-drive PMSG in grid-integrated WGS exploiting commonly used tip-speed-ratio and optimum-torque control algorithms of peak power tracking, respectively. Simulation results have been presented to validate the proposed strategy. The performances of the proposed strategy of LVRT enhancement has also been compared to the conventional method like dc-link braking chopper.

Performance of a Distributed Dynamic Brake for an Induction Motor Fed by a Modular Multilevel DSCC Inverter

This paper provides an experimental and theoretical discussion on dynamic braking for a medium-voltage induction motor fed by a modular multilevel double-star chopper-cell (DSCC) inverter. It is intended to apply the motor drive to large-capacity fans and compressors with a large moment of inertia. Each chopper cell consists of a bidirectional chopper and a braking chopper connecting a single small-rated braking resistor in series with a single IGBT. This configuration results in a “distributed” dynamic brake that provides a distinctive welcomed side effect of protecting all the bidirectional-chopper cells against sudden overvoltage. An experimental system rated at 400 V and 15 kW is designed, constructed, and tested to verify operating performance of the distributed dynamic brake. Experimental waveforms, along with simulated waveforms, confirm firmly that the distributed dynamic brake is feasible and effective in an induction motor fed by a medium-voltage high-power DSCC inverter for fans and compressors. Finally, this paper gives a design example of a distributed dynamic-braking resistor for the 11-kV, 12-MW induction motor driving a large-capacity fan equipped with a large moment of inertia.

An internal model control for enhanced grid-connection of direct-driven PMSG-based wind generators

For Wind Energy Conversion Systems (WECS) based on Permanent Magnet Synchronous Generators (PMSG) with back-to-back converters, some strategies have been employed aiming safe and reliable grid-connection, among them the grid-side control in coordination with the braking chopper. Conventionally, the grid-side control is of the Proportional-Integral (PI) type, however, due to the presence of cross-coupling terms between the dq currents delivered to the grid, PI does not ensure null steady-state error resulting in an inappropriate power delivery. Moreover, during voltage sags at the connection point, the chopper turning on is often commanded based on the DC-link voltage increase, however, a more suitable trigger signal should be based on the current delivered to the grid. Seeking to improve the grid-connection issue, in this work a new control is presented, which is based on Internal Model State Feedback Control (IMSFC) in order to eliminate dq current steady-state error and whose the control design is achieved through Linear Quadratic Regulator (LQR). Besides, the chopper trigger signal is based on the current delivered to the grid, ensuring safe Low-Voltage Ride-Through (LVRT). The proposed control and the conventional PI have been discretized and implemented to interact with a suitable model of grid-connected PMSG WECS in MatLab/Simulink. The proposed control performance has overcome the conventional both for steady-state and low-voltage conditions.