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To meet the augmented load power demand, the doubly-fed induction generator (DFIG) based wind electrical power conversion system (WECS) is a better alternative. Further, to enhance the power flow capability and raise security margin in the power system, the STATCOM type FACTS devices can be adopted as an external reactive power source. In this paper, a three-level STATCOM coordinates the system with its dc terminal voltage is connected to the common back-to-back converters. Hence, a lookup table-based control scheme in the outer control loops is adopted in the Rotor Side Converter (RSC) and the grid side converter (GSC) of DFIG to improve power flow transfer and better dynamic as well as transient stability. Moreover, the DC capacitor bank of the STATCOM and DFIG converters connected to a common dc point. The main objectives of the work are to improve voltage mitigation, operation of DFIG during symmetrical and asymmetrical faults, and limit surge currents. The DFIG parameters like winding currents, torque, rotor speed are examined at 50%, 80% and 100% comparing with earlier works. Further, we studied the DFIG system performance at 30%, 60%, and 80% symmetrical voltage dip. Zero-voltage fault ride through is investigated with proposed technique under symmetrical and asymmetrical LG fault for super-synchronous (1.2 p.u.) speed and sub-synchronous (0.8 p.u.) rotor speed. Finally, the DFIG system performance is studied with different phases to ground faults with and without a three-level STATCOM.

DC Transformer (DCX) is widely used because of its high efficiency and tight conversion ratio. Although the traditional cascade converter can regulated output voltage, it causes a huge loss (over 10% efficiency). The proposed topology outputs regulated voltage with high efficiency and wide input voltage. It consists of a push-pull DCX converter in parallel with a voltage compensation circuit. The compensation circuit only processes part of input power with low stress and low loss; thus, the total efficiency is improved. Two compensation circuits are compared and discussed, then the small-signal model and the control-to-output transfer function are derived. A design example is presented, and the simulation and calculation results verify the theory. The results show that the secondary-side compensation circuit has high efficiency (92.5%), wide input voltage range (±43%), and the efficiency penalty caused by voltage compensation is less than 2.5%.

In this paper, a composite speed control strategy is proposed to achieve a smooth speed response for the PMSM which is running at the low-speed range with a low encoder resolution. Under these preconditions, the encoder pulses may not exist in each sampling period. Therefore, there is a large lagging between instantaneous speed and measured speed. An extended state observer is designed to estimate the instantaneous speed. To improve the anti-disturbance ability and get a stable speed performance, a generalized model predictive speed control was applied. Based on the predict speed, a cost function is designed, and the q-axis is derived through minimizing the cost function. Considering the dead-time effect under low current amplitude, the parasitic capacitance cannot be ignored. Therefore, a voltage compensation model is re-established in this paper. The proposed control algorithm is verified through simulation and experimental results.

This paper presents the design of an All-Digital-Temperature Sensor (ADTS) with low power supply sensitivity (PSS). In this architecture, the delay cell-based ring-oscillator acts like a temperature sensor. The delay cells have been designed featuring the voltage compensation technique. This paper demonstrates the improvement over the conventional Current Starved Ring Oscillator (CSRO), and Voltage Compensated Ring Oscillator (VCRO) based temperature sensor. The proposed design consumes only 180μW power, exhibits PSS of 0.034°C/mV (i.e., 6-12%) and generates an error of only -0.4°C to +0.8°C across process comers and over the temperature range -40°C to 150°C and supply range of 1.8V +/-10%.

Featured with the characteristics of expandable modular structure, no need for line-frequency transformer directly connected to medium voltage grid and the same active power of each phase, three-phase common dc-bus cascaded H-bridge multilevel inverter has great advantages in high-voltage and high-power photovoltaic (PV) power generation application. However, if the number of modules in three phases is different, the active power of each module in the phase with fewer modules will be higher, and the active power transmitted by each module in the phase with more modules will be lower. Unbalanced active powers among modules lead to different heat dissipation requirements, which does not contribute to the modular design of the system. Aiming at this problem, this paper proposes an active power equalization control strategy based on zero-sequence voltage compensation. According to the actual number of modules in three phases and power factor of inverter, the compensated zero-sequence voltage can be calculated, by which all modules are capable of transmitting the almost same active power no matter whether the number of modules in three phases are same or not, and whether the inverter operates at unit power factor or not. The effectiveness of the proposed strategy is verified by simulation and experimental results.

Multi-terminal High Voltage Direct Current (MTDC) with modular multilevel converter (MMC) is a promising technology, because it integrates diverse energy resources. However, there is still a risk for transient stability of a system with MMC in the case of communication delay. In order to improve the transient stability of hybrid AC/DC networks, the point of common coupling (PCC) voltage compensation scheme is proposed for MMC-MTDC to maintain stable operation when communication delay occurs. Based on the established closed-loop network control system (NCS) which the MMC-MTDC participates in, the proposed control strategy utilizes the multi-layer control according to the dynamic characteristic of MMC-MTDC, and compensates the PCC voltage in the controller input signal to reduce inaccuracy case by time delay, thus offset the negative effect of communication delay on power system transient stability. The proposed control method is fully investigated in a MMC-MTDC model based on 4-generator 10-node system model and the simulation results clearly indicate the proposed strategy can effectively enhance transient stability of system.

This paper proposes a new control strategy to improve the effective voltage compensation range of electric springs (ES) under reactive compensation modes. The influence of line impedance, including its resistive part and inductive part, on ES regulation ability is analyzed, which shows that the compensation range of ES is more sensitive to the inductive part of the transmission line impedance than the resistive part. Through the introduction of a fixed series compensation (FSC) device, only the reactance of the transmission line impedance is changed without changing the line voltage level and topology structure, thus the improvement of ES voltage regulating capacity is realized. Simulation results are provided to verify the correctness of the analysis and the proposed control strategy.

The ever-increasing levels of distributed energy resources (DERs), especially solar photovoltaics (PV) tend to detrimentally affect the operation of the distribution systems on which they are installed, causing issues like voltage violations, excessive voltage regulator operations, voltage flicker, etc. Recent improvements in power electronics have led to an increase in the proliferation of power electronics based voltage regulators that are capable of fast voltage compensation. However, being a recent addition, very few studies exist that quantify the benefits of such devices on a distribution system. This work uses a case study to quantify the main benefits of a power electronics assisted voltage regulator (PEVR) in mitigating the impacts of high penetration PV using a supervisory control scheme for the PEVR. This study considers high resolution (1 second) PV and load profiles to capture the accurate operation of the step voltage regulator (SVR) and PEVR. The results from this case study highlight the effectiveness of a PEVR in mitigating excessive voltage variation and tap operations due to high penetration PV. The results also illustrate the trade-off between converter capacity and benefits.

In recent times, interior permanent magnet synchronous motors (IPMSMs) with high efficiency have been used in various applications. However, IPMSMs generate torque ripple and acoustic noise due to a radial electromagnetic force. In particular, the acoustic noise needs to be suppressed in applications where low noise levels are required. In this paper, the suppression of the 6th‐ and 12th-order radial electromagnetic forces, which contribute significantly to acoustic noise, is discussed. The relationship among the armature current, the permanent magnet of the rotor, and the radial electromagnetic force of the IPMSM is clarified. Moreover, the compensation current required to suppress the 6th‐ and 12th-order radial electromagnetic forces is derived. In addition, a method to suppress the 6th‐ and 12th-order radial electromagnetic forces is proposed through the feedforward addition of the compensation voltage calculated from the compensation current to the voltage command of the drive system based on a sinusoidal current tracking control. By setting the gain of the sinusoidal current tracking control as low as possible, the voltage command produced by the current control system is maintained low, and a margin is provided for adding a compensation voltage to suppress the radial electromagnetic forces. The effectiveness of the proposed feedforward voltage compensation method is verified by the results of frequency analysis of the sound produced by an IPMSM. In addition, the superiority of the proposed sinusoidal current tracking control is confirmed by comparison with the frequency analysis of the sound produced by a $d-q$ axis current controlled motor.

With the rapid development of the photovoltaic (PV), making full use of the spare capacity of PV converters to remedy the unbalanced voltage problem is becoming a promising idea. In this paper, a dual-module based asymmetrical voltage compensation strategy is developed for PV converters to utilize the spare converter capacity as needed. By means of the positive/negative-sequence dual-module design, the proposed control strategy can mitigate the negative voltage and provide the reactive power to improve the overall PCC voltage. A power constraint factor based on the instantaneous power theory is introduced to flexibly adjust the converter power within the converter capacity. Effectiveness of the proposed strategy is verified by simulations on PSCAD/EMTDC platform.

In order to reduce the probability of commutation failure in HVDC weak receiving system, and improve the recovery characteristics of the DC system after a fault, an interactive control strategy of STATCOM and VDCOL (Voltage Dependent Current Order Limiter) was proposed. AC voltage compensation was derived based on the Current -time Area, and added to the STATCOM constant AC voltage control of outer loop to adjust the reactive power of the STATCOM output. Meanwhile, an additional DC current control functions was applied to LCC-HVDC system VDCOL. Simulation in PSCAD/EMTDC showed that the proposed interactive control strategy can restrain commutation failure effectively when the short-circuit fault occurs in the AC bus of the weak receiving system, and the improved VDCOL can strengthen the ability of the DC system to resume stable operation as soon as possible.

Induction motor is robust and simple in construction; it can operate in any environment condition so induction motor is a reliable choice in industry for electromechanical device. They found a wide range of application due to its durable design, low maintenance cost and wide range of load carrying capacity. As the application of induction motor in industry is increasingly widespread, it is very important to use floating H Bridge convertors to challenge and solve the problem related grid connected induction motor. Textile mills, compressors and hundreds of fans are common industrial applications of induction motor. Motor starting on heavy load or poor grid system can causes damage to induction motor as well as fluctuation of voltage. Under no load condition or steady operating condition induction motor draws reactive lagging current which varies the grid voltage that reduces motor operating efficiency. This paper contains floating capacitor H bridge convertor as series voltage compensation to improve steady state operation as well as efficiency of induction motor by controlling the motor voltage above and below the grid voltage so it is possible to achieve improved operating lifetime expectancy. In simulation, proposed method is introduced and experimental results are presented.

The voltage variations in weak low-voltage distribution systems are a common practice as these systems are prone to faults and other events. In order to compensate for the voltage variations in such systems, one popular solution is to use power-electronic based series voltage compensation devices, such as the dynamic voltage restorer (DVR). A five-level cross-switched multilevel inverter (5LCSMLI) based DVR is presented in this paper. The lower AC filter requirement is achieved as a result of using the multilevel inverter. Also, the proposed DVR uses lower number of power-electronic switches compared to the conventional symmetric cascaded B-bridge (CHB) multilevel inverter-based DVR. Simulation studies are carried out to evaluate the performance of the 5LCSMLI-based DVR.

This paper proposes a control scheme for stabilization and voltage regulation of a continuous conduction mode (CCM) flyback converter supplying constant power loads (CPL)s. A two-stage controller is proposed for the non-linear system. The first stage involves inserting a virtual resistor in series with the primary winding of the flyback transformer. The virtual resistance, inserted through control action damps limit cycle oscillations due to CPL. This stage is referred to as active damping stage. The second stage enables voltage restoration and performs voltage regulation in the event of source and load variations. This stage is referred to as voltage compensation stage. Stability conditions are derived for equilibrium points. A method to choose one of the control parameters to minimize the output capacitance of the converter is proposed. Simulation results are presented using both averaged and switched models to verify the proposed control scheme.

Renewable energy system at a low power level is of utmost significance since the area of the distributed power system is growing rapidly. DC-DC converters which can step up and step down voltage levels are extensively researched for the control and regulation of power and voltage of these types of system. Zeta converter, one of the promising DC-DC converter topology has advantages of low ripple output current over the conventional buck-boost converters and hence is considered in this paper. Zeta converter can operate in both excessive and deficit power modes while providing better load voltage regulation. This makes it a good candidate for PV based applications whose output power is intermittent in nature. Hybrid Energy Storage System (HESS) are increasingly becoming popular as energy storage devices since it inherits the quality of reducing fast and slow transients. Integration of zeta converter and such an energy storage system will provide optimal power transfer between the load and storage along with the load side regulation. State Space averaging technique is one of the modeling approach where in the parasitic resistances can be included so that the small signal behavior is captured and analyzed. For the control of small signal response, state feedback is implemented so that the optimal current flows in the energy storage system along with the HESS component voltage compensation. In the work presented in this paper, state space modeling is used to analyze the converter properties and feedback is appropriately ensued such that there is a seamless transfer of power to the load and HESS while keeping the steady state voltage error at the minimum.

In low-voltage AC microgrid, the different distance between distributed generation units (DGs) and common bus leads to the mismatch of feeder impedance, which results in the error of output power sharing. In order to realize the accurate power sharing and maintain the stability of the AC bus voltage, this paper proposes an improved resistive droop control strategy based on adaptive virtual impedance, which introduces dynamic dominant resistance and negative inductance to diminish the impact caused by different feeder impedance. Furthermore, a voltage compensation stage is added to maintain the bus voltage at a satisfactory value by mitigating the voltage drop caused by the virtual impedance. The effectiveness of the proposed control strategy has been demonstrated by various simulation cases. The results show that the proposed control strategy can deal with conditions of dynamic and nonlinear load without the information of accurate feeder parameters.

Due to the influence of motor body factors such as air gap magnetic field distortion, as well as external motor factors such as inverter circuit dead time and on-voltage drop, the stator phase current of the permanent magnet synchronous motor (PMSM) under traditional control strategy has harmonics, which leads to current distortion. A large number of current harmonics cause torque ripple of PMSM during operation, which affects the motor performance. To solve this problem, this paper proposes an effective suppression control strategy by voltage compensation. Firstly, the harmonic mathematical model of PMSM was established and the harmonic disturbance was analyzed. The results show that the specific harmonic current will affect the operation of PMSM. Then, the harmonic suppression loop was added to the PMSM vector control system. This paper proposed a novel harmonic current extraction method, which can extract the total harmonic current based on the real-time PMSM speed. The harmonic current and torque ripple can be suppressed by compensating the appropriate voltage to the control system. Finally, the simulation experiment was carried out under Matlab /Simulink software. By analyzing the PMSM current waveform and electromagnetic torque waveform with or without harmonic suppression strategy, the effectiveness of the control strategy was verified.

Energy storage device can provide the support to the DC microgrid to resist the disturbance from the distributed new-energy source and load. However, the energy storage device with a lower or higher initial State Of Charge (SOC) among multiple energy storage devices may delay or advance the discharge or charge due to the uneven power distribution, which affects the system stability. This paper proposes an adaptive droop control by relating the droop coefficient of the energy storage devices to a arccotangent function of the battery SOC, so as to achieve the dynamic equalization of SOCs. Accordingly, the charge and discharge speed of the energy storage device are adaptively changed. However, SOC equalization speed decreases when the SOC difference between energy storage devices is small. This paper further proposes a variable-factor droop control by further adjusting the factor in the arccotangent function dynamicly according to the SOC. Compared with the droop control with the fixed factors in the arccotangent function, the SOC equalization speed can be maintained as the SOC difference between energy storage devices continues to decrease. In addition, a voltage compensation link is added into the droop control to compensate the DC-bus voltage drop caused by the changed droop coefficient. Finally, the variable-factor droop control simulation model with the voltage compensation is established. It is verified by simulation results that the proposed adaptive droop control can realize the dynamic SOC equalization of multiple energy storage devices and the dynamic SOC adjustment speed. And the DC-bus voltage is stable during during all the charging or discharging periods of the energy storage device.

In this paper, a simple and fast open-phase fault (OPF) detection and fault tolerant control method is proposed for three-phase induction machine. Instead of using integrators or low pass filter, this method utilizes the phase current magnitude and trajectory to detect open phase fault in three-phase motor drive. This significantly increases the speed of fault detection, allowing an OPF to be detected and compensated within several sampling cycles, which is advantageous for safety-critical applications. In addition, a double synchronous reference frame PI (DSRF-PI) controller method is adopted as the fault tolerant controller. Compared to previous methods that utilizes feedforward voltage compensation, the DSRF-PI does not require prior knowledge on the machine parameters and operating condition, and therefore is easier to implement. The proposed fault detection and fault tolerant control method are simulated using MATLAB Simulink simulation where the results confirms the high speed and robustness of the proposed methods.

As an inevitable issue, voltage unbalancing can have some adverse effects on the power systems equipment. This paper investigates a double synchronous reference frame-based control method to compensate unbalanced voltage, helping to properly active and reactive power-sharing. This approach controls the positive and negative components of the voltage separately, which can be implemented in the primary and secondary control levels of islanded AC microgrids. The secondary control is based on the dynamic consensus algorithm that helps restore deviated voltage and frequency induced by the primary control, but it also improves the proposed control scheme performance. The proposed control strategy’s effectiveness is investigated based on some simulations in the MATLAB Sim/Powersystem environment.

Fault-tolerant (FT) ability is a significant distinctive feature of any drive-in applications such as in aerospace and automotive fields. An FT drive is intelligent to function even in faulty environments, promising service continuousness of a drive, partly or completely fulfilling the performance necessities. A fault can occur in converter, such as an short/open circuit of converter switches and failing in the gate pulse of a switch. Whereas faults that can occur in the motor windings, as an open/short circuit of the stator windings also. To overcome the irregular condition, the fault must be punctually recognized, secluded and appropriate drive reconfiguration is essential. The difficulties which generally happen owing to fault in a phase or switch are namely: torque fluctuations, imbalance in the voltages and alterations in the currents of a phase windings which affects the consistency and efficacy of a drive. In case of field-oriented control (FOC) technique to overcome the defective state suitable combinations of the remaining healthy reference currents/amendment of the pulse width modulation methods can be used. Some of the solutions when Faults occurs due to Phases are: FOC with Appropriate Reference Frame Transformation; Midpoint DC Link Voltage Control; Combination of Reconfigurable Voltages; Independent Control of Phases; Decomposition of Space Vectors; Compensated Voltage Control. In case, when Faults occurs due to Switch of an inverter the solutions could be: Multiphase multilevel inverters fed drives using multiple SVM techniques and decomposition of space vectors, Voltage compensation-based fault tolerant control, Hysteresis Current Controller (HCC). The whole system is established in MATLAB software atmosphere and analyzed for different load and speed conditions using Maximum Torque per Ampere (MTPA) with HCC.

This paper presents a cyber physical system implementation of an improved distributed secondary control (IDSC) scheme of islanded dc microgrid (DCMG). The IDSC scheme mitigates the hidden issues of primary control with included droop technique for the distributed generation unit (DGU) in a DCMG by providing the adjustable voltage compensation, improves voltage regulation and enhances the current sharing of all DGUs. The voltage compensation of IDSC is the resultant of two voltage components, i.e., average distributed integral voltage controller and average current controller. The dynamic consensus algorithm is used to obtain the global average values in the for distributed secondary controlusing relatively low bandwidth communication. The impact of communication time delay on the stability in IDSC based DCMG with two DGUs is presented. The performance of IDSC scheme is validated on a microgrid scenario, which includes parallel connection of four DGUs and common load. The real-time cyber physical system of DCMG is implemented on OP AL-RT test platform that combines the device layer on FPGA, control and cyber layers on CPU of OP5700 by using eFPGASim and RT-LAB.

This paper shows the current and torque performance of a 750 W induction motor with a voltage unbalance compensator (VUC) when a DC link voltage is boosted using simulation. The VUC consists of a diode bridge, an inverter, and a voltage booster, however, DC voltage source was used in the simulation simply instead of the diode bridge and voltage booster. The VUC is connected to both of the power grid lines and the induction motor windings. It supplies compensating voltage and keep the terminal voltage balanced of the induction motor when the voltage unbalances occur on the power grid. It was cleared that the compensable range was expanded by boosting the DC link voltage of the VUC in the simulation. Besides, pulsation torque was also suppressed by voltage compensation enhancement. The current and torque waveforms were compered under three conditions such as without the VUC, with the VUC without boosted voltage, and with the VUC with boosted voltage. As a result, we clarified that the current and torque performance of the induction motor with the VUC is improved by the voltage booster even if the voltage unbalances factor increases., 23rd International Conference on Electrical Machines and Systems (ICEMS2020), November 24-27, 2020, Hamamatsu, Japan （新型コロナ感染拡大に伴い、オンライン開催に変更）

In a weak grid environment, at renewable energy integration, the harmonics and unbalance issues are very frequent due to nonlinear loads. In this regard, achieving unbalance compensation involves two control targets, which are harmonics compensation and then unbalance compensation. Under nonlinear loads, in a weak grid environment, voltage compensation or current compensation alone not sufficient to improve power quality. To overcome the aforementioned drawback, a flexible compensation strategy is proposed for a current-controlled inverter connected to an unbalanced-distorted weak grid under nonlinear load conditions. The proposed compensation strategy uses harmonic components of nonlinear load current, and harmonic components of voltage are the feedback variables. This compensation strategy performs both voltage and nonlinear current compensation simultaneously with seamless interaction between voltage harmonic components and current harmonics components. The proposed compensation strategy achieves unbalance compensation and harmonics compensation simultaneously in a weak grid environment without stability issues. Further, to improve the performance of the proposed compensation strategy, individual phase compensation of the current controllers is included, and the effectiveness and superiority of the proposed strategy are validated through various test cases.

Dispersed rural renewable energy systems (RRESs) are often located near the end of long distribution feeders. The RRESs connected to weak distribution network, cause voltage regulation issue at its point of common intersection with local loads. The erratic nature of renewable sources like wind and solar, renders use of fixed-step line voltage regulators, impractical. Corrective voltage compensation for RRES, through an additional distribution static synchronous compensator (DSTATCOM) yields better performance, however, with increased cost. This paper deals with the operation of a wind-solar based RRES with integrated DSTATCOM capabilities. The grid side power converter control for RRES is configured to tackle voltage disturbances caused due to renewable power variations and unbalanced and/or non-sinusoidal load currents. An improved recursive least squares (IRLS) algorithm is utilized for estimation of reference grid currents. This control scheme for voltage regulation in RRES fed by a weak grid is validated through simulations in Matlab platform.

A capacitorless based drive system has the advantages of lower cost and longer lifetimes. However, a resonance phenomenon occurs when it is operated with the unbalance between grid input power and inverter output power. A high frequency resonance voltage is imposed on the dc-link capacitor. In order to suppress the voltage oscillation, a reliable method is the active damping technique. Conventional methods utilize the harmonic component of the dc-link current or voltage to compensate the currents or voltages in dq-axes. For current compensation based-methods, the compensated current is in either d-axis or q-axis not a vector component, which leads to the current commands are not optimal. For conventional voltage compensation based-methods, a large component of compensated voltage would cause a disturbance to current regulator seriously. This paper proposes a voltage vector compensation method which uses the information of limited dc-link voltage and currents to predict the modified voltages. The superiority of the proposed method was experimentally justified.

This paper presents a control strategy of series APF for harmonic suppression and dynamic voltage compensation. The harmonic current through the primary winding of transformer and the voltage swell or sag of power supply voltage are extracted. After these two signals are controlled and combined as a reference signal, VSI connected in parallel with the secondary side of transformer would present a controllable voltage characteristic. And the control parameter of harmonic currents can make the transformer show a large controllable impedance to harmonics so as to isolate harmonics. Besides, VSI can compensate the system voltage deviation by detecting voltage drop. Finally, the simulation model was established to prove that the series APF based on the control strategy can isolate harmonics, and effectively compensate the voltage deviation.

Dynamic Voltage Restorer (DVR) is an increasingly popular voltage compensator mainly used for mitigating voltage sags through the series-connected transformer that connects electric distribution system and AC sub-system or load. The high response speed required for voltage compensation makes DC magnetic bias and magnetic saturation apt to occur when series-connected transformer in DVR outputs voltages, which may cause the waveform distortion of output offset voltages, or even worse, the failure to compensate. In consequence, observations and suppression of transformer magnetic saturation and magnetizing inrush current are imperative during voltage compensation. To realize that purpose, this paper proposes a method by which the flux linkage of the transformer that is regarded as a state variable can be directly controlled, and then verifies it through co-simulation by using the software Ansys Simplorer, Matlab and Ansys Maxwell from three parts.

This paper proposes an improved compensation strategy for dynamic voltage restorers (DVR) to solve the voltage sag problem of different duration. Based on the detailed analysis of the traditional compensation strategies, an improved compensation strategy adapting to voltage sags is proposed, which can gradually switch from pre-sag voltage compensation strategy to minimum energy compensation strategy. This proposed strategy not only avoids the impact of phase angle jumps on sensitive loads, but also achieves long-term voltage compensation. In addition, to further reduce the energy consumption during the compensation process, the load reference voltage is appropriately reduced considering the voltage sag tolerance of loads. The simulation experiment results prove the effectiveness of this strategy in reducing the phase angle jump and extending the compensation time.

This article presents a robust nonlinear control scheme applied for voltage regulation in a node of an electrical distribution network through power electronic converters. It is achieved utilizing a series of nested control loops that are based on sliding mode control. In the event of voltage variations in the common coupling point (PCC), the proposed control scheme drives the power converter to inject the necessary power to the grid node to perform voltage compensation. It is worth mentioning that this control scheme can be applied to control distributed generation systems that can provide auxiliary services to the electrical network in terms of voltage regulation. Simulation results demonstrate the effectiveness of the present control scheme.

Energy Storage Systems (ESS) are vital to improving the reliability of an islanded Micro-grid (MG). In this paper, a distributed control strategy integrated with multi-agent-based average consensus algorithm is presented for the Distributed Energy Storage Systems (DESS) in islanded AC micro-grid. A hierarchical control structure is implemented that consists of three control levels, i.e.: inner controls, primary controls, and secondary controls. The secondary control layer consists of estimators for injected power, SoC, and system frequency. Power sharing is achieved with SoC based adaptive droop control. The multi-agent based average consensus algorithm is implemented to obtain average estimate of SoC, frequency and active power. A voltage compensation method is given to ensure that the voltage of PCC is within the acceptable range. The simulation studies carried out, verify that the proposed control strategy can ensure accurate power sharing among DESS and restore voltage and frequency to a nominal accepted range.

The droop control strategy is widely used in parallel inverter systems. However, when the line impedance of each inverter is not matched, it will result in the reactive power sharing error. At the same time, due to the droop characteristics, the output voltage accuracy will be reduced. Aiming at the reactive power sharing error and voltage control accuracy in droop control, an improved droop control scheme is proposed. First, the principle of droop control is introduced, and the power sharing model is established. Secondly, a multidimensional adaptive droop control strategy is proposed to achieve better reactive power sharing performance. Then, the frequency and voltage compensation control is added to improve the accuracy of PCC voltage. Finally, a simulation model of the parallel inverter system is built to illustrate the effectiveness of the proposed scheme.

Large-scale wind power access to the power grid poses great challenges to the safe operation and management of the power grid. The new power grid guidelines require that wind turbines should be equipped with low voltage ride through (LVRT) capabilities. Considering that the dynamic voltage restorer (DVR) has the advantage of being able to quickly and accurately perform voltage compensation in a short time, this paper proposes a fault ride-through scheme for doubly-fed wind turbine based on the dynamic voltage restorer. Aiming at the detection delay and attenuation caused by the filter in DVR, an integral detection method based on the theory of instantaneous reactive power is adopted to reduce the influence of the filter. According to the control characteristics of DVR, a DVR control algorithm based on the double Q-P theory of coordinate transformation is proposed, which can compensate the transient voltage disturbance and effectively improve the compensation performance of the dynamic voltage restorer. Using PSCAD / EMTDC simulation software to establish a simulation platform, the simulation results show that when a serious short-circuit fault occurs during the transmission of electrical energy from the wind farm to the grid, the DVR can quickly detect voltage changes and accurately compensate for the required voltage to obtain the ideal transient characteristics Improves the low voltage ridethrough performance of wind turbines.

In this paper, an improved topology for unified power quality conditioner (UPQC) is proposed. By adding a coupling capacitor to the LC filter branch in series side of UPQC, the improved topology can reduce the output voltage of the inverter, and provide a large part of the load-reactive power, thereby effectively reducing the overall capacity and dc-link voltage level of the UPQC system. Because of these prominent characteristics, the overall utilization and the cost performance of the device can be improved. Firstly, the circuit topology and working principle of the proposed UPQC are introduced. Secondly, the two working modes of UPQC under different working conditions are introduced in detail, including: power regulation mode under the normal steady-state condition and voltage compensation mode under the voltage sag condition. Then, the proposed topology is compared with other topologies to show its advantages in reducing overall capacity. Finally, the validity and feasibility of the proposed topology are verified by experimental results.

Aiming at improving the voltage-based power quality issues and maximizing the utilization of renewable generation (RG) simultaneously, this paper proposes a microgrid multifunctional dynamic voltage restorer (MFDVR). Whether the grid voltage disturbances (such as sag, swell) happen or not, the MFDVR can always work by adopting vector control. Based on it, MFDVR realizes the full utilization of RG when the normal grid voltage happens, and it can utilize RG along with ensuring the stability for the voltage of critical loads during grid voltage disturbances, both of which expand the function of device. In addition, the constraint problem between output power and output voltage of the inverter can be solved by adding a series coupling capacitor in structure. This method, which can apparently reduce the output voltage of inverter combining the multifunctional method mentioned above, thereby reduce the voltage demand of DC side and the voltage stress of switch. All of those broaden the operating range and improve the performance of device effectively. The operating principle of the proposed MFDVR, power flow under different conditions and the optimization mechanism of the coupling capacitor are analyzed in detail. Simulation results verify the effectiveness of the proposed topology and control strategy.