Performance Improvement of Brushless Generator Voltage Regulation by Using a Controlled Non Linear Discharge Resistor

Synchronous generators (SG) are key electromechanical converters widely used in power plants, where precise excitation control is crucial for maintaining voltage regulation and stability. The main limitation of the conventional brushless excitation (CBE) system is its inability to supply negative voltages to the field winding, which limits fast de-excitation during sudden load rejection and causes terminal-voltage overshoots. To address this issue, this paper proposes an advanced fuzzy brushless excitation (FABE) system integrating fuzzy logic control (FLC) with H∞ control to enhance the transient and steady-state performance of synchronous generators. The H∞ controller ensures robustness against disturbances, parameter uncertainties, and nonlinearities, while the FLC improves adaptability and dynamic response. The proposed hybrid approach enables faster de-excitation, reduced voltage peaks, and improved damping of oscillations. Simulation results demonstrate that the FABE system clearly outperforms the conventional excitation method in terms of voltage stability, dynamic response, and overall control performance under various operating conditions.

• The paper focuses on optimising Virtual Synchronous Generator (VSG) control in Modular Multilevel Converter (MMC)-based HVDC systems to enhance power system stability and oscillation damping. • It introduces virtual inertia and damping to mimic synchronous generator behaviour, improving frequency and voltage regulation. • The proposed control strategy ensures smooth transitions between grid-connected and islanded modes, suppresses harmonics, and addresses challenges like low inertia and weak grid conditions. • Simulation results validate the effectiveness of the VSG-controlled MMC in maintaining stability during dynamic and transient events, making it suitable for future power systems with high renewable energy integration. This paper discusses the development of a Virtual Synchronous Generator utilizing a Modular Multilevel Converter. The control system employs an internal simulation of the electromechanical swing equation to replicate the inertia and damping characteristics of a synchronous generator, enabling the generation of the necessary frequency and phase angle for MMC control as a VSG. The ac-side management involves cascaded voltage and current controllers operating within a synchronous reference frame defined by the virtual swing equation. Simulation findings validate the performance of the VSG-controlled MMC when connected to an external AC grid and in islanded mode with a resistive load. This paper validates, through experimentation, the effectiveness of controlling a Modular Multilevel Converter (MMC) as a Virtual Synchronous Generator (VSG) designed to deliver virtual inertia and robust frequency stabilization in power systems with low physical inertia. The proposed control structure incorporates a virtual swing equation, cascaded voltage and current regulation loops, reactive power control, and emulated impedance. A 60 kVA MMC model was employed to demonstrate the system’s capabilities. During frequency disturbances such as a drop from 50 Hz to 49.8 Hz, the controller facilitated dynamic power injection up to approximately 35 kW while capping peak currents at 100 A. Frequency deviations were mitigated within 300 milliseconds, and the converter exhibited seamless transitions to islanded operation along with reliable voltage control during load variations. These findings confirm the proposed controller’s effectiveness in maintaining grid stability under diverse operating conditions.

This paper deals with the design of an adaptive and robust control scheme to achieve the rotor speed stability enhancement and the terminal voltage regulation through the excitation control of a single synchronous generator connected to an infinite bus through a transmission line. A comprehensive 10th‐order plant model of the plant is provided, including the exciter system dynamics, under the condition that all model parameters are completely unknown. The scheme design is developed based on a combination of modified adaptive backstepping, second‐order constrained SM, and fuzzy logic methods. Based on the stator currents and the rotor angle‐speed sensors data and the plant model structure, an adaptive sliding mode observer is designed to estimate the unmeasured rotor flux. Using the estimated rotor flux to overcome the uncertainty in the plant model, two sliding surfaces on which the rotor speed and terminal voltage errors asymptotically tend to zero are formulated. With only one excitation control input, a discontinuous control algorithm is proposed in combination with fuzzy logic to achieve finite‐time convergence of the closed‐loop system state to the intersection of the two designed sliding surfaces. The effectiveness of the proposed control scheme is confirmed by simulation.

– This paper presents a successful stand-alone pico-hydro generation system using a high-efficiency interior permanent-magnet (IPM) synchronous generator. A 1-kW 4-pole V-type IPM generator with low voltage regulation is used for laboratory test in stand-alone hydro energy conversion system. It has been found from experimental results that the constant output voltage is supplied stably by the proposed system under wide speed range. Keywords : Hydro g eneration system, IPM generator, Automatic voltage regulation 1. Introduction Recently, global warming has become an important problem. In Japan, there has been a power-shortage problem because of the shutdown of the nuclear power reaction by the Great East Japan Earthquake on March 11, 2011. In such situation, the territorially distributed energy generation using wind or water power attracts attention. The development of permanent-magnet (PM) synchronous generators has progressed rapidly due in part to emergence of the high energy rare-earth magnets like neodymium-iron-boron (Nd-Fe-B) and many designs of PM rotors have been presented in recent years [1]-[6]. However, rare-earth materials such as neodymium and dysprosium are expensive and depend on China for 90% or more of the world share [7]. Therefore, the research for the substitution of Nd-Fe-B to Ferrite magnets has been reported [8]. However, it is considered that the downsizing of the generator needs the high energy rare-earth magnets in stand-alone small power generation system still now. Small wind or water power generation systems have been presented in recent years, for example, [9]-[12]. This paper presents a successful automatic voltage regulation of high-efficiency IPM synchronous generators for stand-alone pico-hydro power generation system. A 1-kW 4-pole V-type IPM generator with low voltage regulation [13] is used for laboratory test in hydro energy conversion system.

Some communities in Thailand located on Island with high wind velocities but an unreliable utility supply, will typically install diesel powered generators and wind generators to form a microgrid. Microgrid projects have been developed in many parts of the world, and commercial solutions have started to appear. Such systems face specific design issues, especially when the wind penetration is high enough to affect the operation of the diesel plant. The dynamic behavior of a medium penetration hybrid microgrid is investigated. It consists of a diesel generator set, a wind power generator and several loads. The diesel engine drives a 3x2,000 kW synchronous generator with excitation control. The wind turbine drives a 6x800 kW (full power converter) synchronous generator. The total load of the microgrid is about 4 MW which varies during the day. The excitation controller and speed controller for the diesel’s synchronous generator are designed, as well as the power control of the wind turbine. The system is modeled and simulated using software DIgSILENT PowerFactory. The study evaluates how the power generation is shared between the diesel generator set and the wind generator, the voltage regulation during load connections, and discusses the need of battery energy storage, the system ride-through-fault capability and frequency control. The results of several case studies are presented. The results have shown that the systems are stable under various ratio of PWIND / PLOAD from 10% to 100%, except ratio of PWIND / PLOAD from 110%.

This paper proposes a nonlinear control strategy for a hybrid PV-battery system insuring frequency and voltage support of the power system. The hybrid system includes a PV panel and battery connected to three-phase DC-AC inverter via DC-DC boost converter and bidirectional DC-DC boost converter. A synchronous generator represents the power grid. The voltage regulators control DC-DC boost converter and DC-AC inverter while the frequency regulator controls the bidirectional DC-DC boost converter. A conventional MPPT is used to adjust the reference for nonlinear PV voltage regulator. The voltage regulator is designed based on multi-input multi-output exact feedback linearization technique. It consists of a module that uses the terminal voltage deviation to generate q-axis voltage component. A module that maintains the DC-link voltage is also added to generate d-axis voltage component as well. The proposed frequency regulator includes a module that changes the reference signal of a battery current control module when the frequency deviation is significant. The battery current regulator is designed based on partial input-output feedback linearization strategy. The proposed control system is evaluated in simulation. The results reveal that with the proposed control scheme, the PV-battery generator reacts like a conventional synchronous generator when the grid frequency changes considerably.

Synchronous generators (SGs) are the major contributors in maintaining the stability of power systems. As SGs are displaced by electronically-coupled distributed energy resources (DERs), the dynamic behaviour of these new generation technologies will become critical in ensuring grid stability. One method of ensuring continued provision of voltage and frequency regulation is to have these new devices emulate the response of traditional SGs. Achieving the desired emulation behaviour requires fast, robust control of DERs to track the rapid changes in current injections that arise when SGs are subjecting to changing grid conditions. Hence, this paper focuses on the feasibility of controlling a voltage source converter to emulate the behaviour of a SG during both steady-state and transient periods. Two types of hysteresis current controllers (HCCs)—standard and space vector based—are considered for tracking the current injections of a virtual SG in real-time. Through simulation, it is demonstrated that both HCCs provide robust, fast tracking that enables the desired emulation, but they exhibit a wide range of variations in switching frequencies. Hence, this paper proposes a dead-time control method and demonstrates that the switching frequencies can be limited while maintaining the quality of voltages and currents that are compatible to the IEEE 1547 standard.

In modern aviation power systems, the dynamic stability of power generation systems has become a major challenge. To tackle issues such as slow response, poor voltage stability, and voltage oscillations in aircraft synchronous generators under sudden load changes, a Proportional-Integral-Derivative (PID) voltage regulator modified using the Differential Evolution (DE) algorithm has been developed. Additionally, the DE algorithm’s convergence speed and robustness are enhanced through the incorporation of directional search strategies and adaptive control parameters. Simulation results demonstrate that the optimized regulator delivers rapid response and minimal overshoot, thereby improving the accuracy and dynamic performance of the voltage regulator. The modified DE algorithm notably accelerates convergence compared to the traditional DE algorithm.

In a power system, voltage is a quantity that has a narrow range of permissible variations under normal operating conditions. The upper and lower limits most often vary from ±5% to ±10%, depending on the voltage level which is being observed. This ensures voltage stability and reliable power transfer in the power systems. Reactive power is a quantity directly linked to voltage and responsible for its regulation. Most grid codes in the world define reactive power capability requirements at the connection point which power plants must comply with in both inductive and capacitive regimes. In traditional power systems, voltage regulation was carried out mainly by synchronous generators. The increase in penetration, and in certain power systems, the dominance of renewable energy sources has caused a change to the sources and the methods carrying out voltage regulation. Solar and wind power plants are nowadays being developed and implemented with the ability to independently regulate reactive power and voltage conditions at the connection point. To help inverter-based resources meet the reactive power requirements, the capability of power plants can be enhanced by adding specialized devices such as capacitor banks or STATCOMs. The aim of this paper is to assess the capability of a large PV plant (750MW) connected to a 132kV transmission system to meet the reactive power requirements at the connection point under various operating conditions. Base case will represent the assessment of P-Q characteristics of the PV plant at ambient temperature characteristic for the observed geographical region (46°C), assuming the voltage of the inverters can be at the maximum values guaranteed by the equipment manufacturer (1.1pu). Sensitivity analysis will be carried out in two cases: in other ambient conditions (outdoor temperature of 52°C) and for the inverter voltage lower than maximum (1.05pu). For each of the three cases mentioned above both inductive and capacitive operating modes will be considered at nominal and extreme voltage values at the connection point. The analysis will be conducted in the DIgSILENT PowerFactory software tool, including the detailed modeling of the observed PV plant and its elements. The results will give an assessment of the reactive power capabilities of a large PV plant to support the power system in critical operating regimes. The influence of ambient conditions on the inverters’ power production will also be assessed, as well as the impact of limiting the inverter voltage to values less than the maximum in order to extend the lifetime of the observed equipment.

The brushless excitation system of aircraft AC generator is a strong coupled and nonlinearity dynamic system which is often being subjected to disturbances. Therefore, the conventional PID controller is unable to meet the brushless excitation system control requirements of More Electric Aircraft (MEA) or All Electric Aircraft (AEA). A new brushless excitation compound control controller (RBFPID) is proposed in this paper based on radical basis function (RBF) neural networks and the conventional PID control. Because the new brushless excitation compound controller (RBFPID) has a number of mutually coupled parameters that needs to be set, the improved adaptive particle swarm optimization (APSO) algorithm is used to optimize mutually coupled PID parameters Kp , Ki , Kd and RBF parameters ! , ! , m , n on line. In order to validate performances of the new brushless excitation compound controller based on multi-parameter op- timization by the improved APSO, the simulation model of the aircraft brushless excitation system is implemented in MATLAB/SIMULINK according to differential equations of each component of brushless excitation system. The simula- tion results show that the optimized adaptive compound excitation controller (APSORBFPID) exhibits quick response speed, short adjustment time and high steady state accuracy.

A low quiescent current digital low-dropout (D-LDO) voltage regulator with fast-transient response time is proposed for self-powered wireless sensor applications operating at near/subthreshold supply voltage. The D-LDO regulator incorporates both hill-climbing and binary search algorithms (HCBS) in the control logic, thus leveraging on each other's strengths to minimize the output voltage's ripple and the quiescent current during the steady-state period as well as output voltage's spike and response time during the transition period. Additional features such as hysteresis mode control and freeze mode control are incorporated into the system to improve the performance of the D-LDO regulator. A dynamic comparator is proposed for the near/subthreshold supply voltage operation, which minimizes the voltage error and improves the maximum operating frequency. Fabricated in 130-nm CMOS technology, the D-LDO regulator regulates the output voltage ${V}_{{\rm OUT}}$ from 350 to 1150 mV, while the input supply voltage ${V}_{\text{IN}}$ ranges from 450 to 1200 mV. At a ${V}_{{\rm OUT}}$ of 450 mV, ${V}_{{\rm IN}}$ of 500 mV and an operating frequency of 10 MHz, the regulator delivers 1500- ${\mu }$ A load current with $I_{\text{QUIESCENT}}$ of 8.9 ${\mu }$ A and a transient response time of 1.6 ${\mu }$ s. The maximum current and power efficiencies reach 99.9% and 89.9%, respectively. The measured line regulation and load regulation are 1.6 and 0.6 mV/mA, respectively.

A brief review of permanent magnet (PM) synchronous generators with hybrid field excitation systems and output voltage regulation capabilities has been presented. Both series and parallel hybrid field excitation systems have been discussed. The review emphasizes the construction, advantages, drawbacks and basic characteristics of PM synchronous generators with additional field excitation winding placed either on the stator or rotor.

This paper presents an in-depth analysis of the primary causes and mechanisms of damage in 200 MW synchronous generator units. Particular attention is given to assessing how deviations in key controlled operational parameters influence the technical condition, stability, and reliability of the generator during various load conditions. The study examines abnormal thermal regimes, insulation degradation, rotor imbalance, excitation irregularities, and cooling system inefficiencies that can lead to progressive deterioration or sudden failures. To systematically identify and classify potential faults, detailed fault trees were developed for both the stator and rotor of the TG (TНН-200) generator. The stator fault tree includes branching scenarios related to insulation wear, partial discharges, overheating zones, mechanical deformation of windings, and electrical asymmetries. The rotor fault tree incorporates failure modes such as excitation winding breakdown, interturn short circuits, mechanical fatigue, and deviations in magnetic flux distribution. In addition, separate fault trees were constructed for the cooling system and the excitation system, emphasizing their critical influence on the overall reliability of synchronous generators. Cooling system faults were modeled through scenarios involving insufficient coolant flow, clogging of channels, pump failures, and sensor malfunction. The excitation system model includes voltage instability, rectifier faults, regulator misoperation, and disturbances in control circuits. Combining these subsystem analyses, a comprehensive unified fault tree for the TНН-200 generator was developed. This integrated diagnostic structure provides a complete representation of interdependencies between components, enabling more accurate fault localization and prioritization of maintenance actions. The resulting model enhances the quality of technical diagnostics, supports predictive maintenance, and contributes to increasing the operational reliability and lifespan of 200 MW synchronous generator units.

The operational characteristics of a stand-alone hybrid-powered system are investigated. The sources are conventionally powered synchronous generator and photovoltaic (PV) array. The voltage of the common coupling point is controlled by the automatic voltage regulator of the synchronous generator via which the maximum power point (MPP) of the PV generator is tracked using the open-circuit voltage method. Numerical simulations based on the non-linear dynamical model in dq stationary reference frame are conducted. Power control unit is incorporated to control the driving torque of the synchronous generator once the PV generator becomes unable to meet the requirements of the motor because of reduction of the solar irradiance and/or increase of the load. The analysis includes the response of the system after step changes in the load coupled to the motor and after step changes in the levels of the solar irradiance. The steady-state characteristics of the induction motor in case of hybridisation at various solar intensities are presented and compared with the case when the motor is powered by fixed terminal voltage. It is concluded that the proposed system can run at wide range of operating conditions and robust enough to withstand system parameters step changes.

Large-scale renewable energy bases increasingly employ automatic voltage control (AVC) to coordinate heterogeneous reactive-power resources. The resulting voltage regulation process inherently involves sampling, communication delay, and nonlinear device characteristics, which may induce nontraditional voltage oscillations and stability degradation that cannot be adequately captured by conventional continuous-time or small-signal analysis. This paper proposes a discrete-time nonlinear voltage stability analysis framework for renewable energy bases with multi-reactive-power-resource coupling under AVC-based coordinated control. The voltage regulation dynamics are formulated as a discrete-time nonlinear closed-loop system by incorporating sampled AVC actions, delayed voltage feedback, and nonlinear voltage–reactive-power coupling. An incremental system representation is constructed, and a strong-contraction-based stability criterion is derived using sector-bounded nonlinearity descriptions and linear matrix inequalities, providing a sufficient condition for global voltage convergence without local linearization. Extensive numerical studies are conducted on a representative renewable energy base with parallel and series coupling topologies. A total of 2916 randomized configurations are evaluated. The proposed criterion achieves consistency rates exceeding 96% for the parallel topology and 99% for the series topology when compared with time-domain simulations, while the probability of dangerous misjudgment remains below 1%. Scenario-based simulations further demonstrate that coupling topology plays a critical role in shaping voltage stability behaviors, and state-space analysis further supports the observed stability behaviors. These results indicate that nonlinear strong contraction offers an effective and practical stability notion for AVC-based voltage regulation in renewable energy bases.