Dynamic Voltage Compensation Research Articles

A Cascaded Multilevel Battery Energy Storage Based Parallel Dynamic Voltage Compensator for Medium Voltage Industrial Distribution Systems

This paper proposes a cascaded multilevel battery energy storage based parallel dynamic voltage compensator (DVC) for medium voltage industrial distribution systems. In this parallel DVC, fast switch is series-connected for voltage sag detection, and cascaded multilevel battery energy storage is parallel-connected for voltage support during the voltage sag period. According to the grid-side voltage sags or not, corresponding circuits and three-layer control strategies are developed. While the feedforward proportional–integral (PI) control method is adopted in the outer layer to track the ideal compensation voltage when the grid-side voltage sags, the ideal compensation current when the grid-side voltage does not sag is obtained through battery charging current as well as reactive power, harmonics, and negative sequence load current components. In order to cope with parameter differences in cascaded multilevel battery energy storage, the middle layer interphase and the inner layer intermodular state of charge (SOC) equalization control are adopted in two scenarios. Furthermore, the parallel DVC is quantitatively compared with series DVC in the aspect of required battery capacity, and their advantages and disadvantages are systematically analyzed. Case studies are performed to verify the effectiveness and superiority of the proposed methodology on voltage support.

A Centralized Battery Energy Storage-Based Medium-Voltage Multiwinding DVC for Balance and Unbalance Operations

This paper proposes a centralized battery energy storage based medium-voltage multi-winding dynamic voltage compensator (DVC) for balance and unbalance operations. In this topology, the compensation voltage is added to the grid side through the transformer, and the primary side of the transformer is shunted by multiple windings to support the voltage sag on the medium-voltage distribution systems. According to the symmetrical and asymmetrical grid-side voltage sags, the positive and negative sequence mathematical models of DVC as well as their voltage-current double closed-loop control strategies are developed. As for the DC bias caused by circulating current between the primary windings of each phase of the multi-winding transformer, circulating current suppression algorithm is added to the positive and negative sequence inner current loops. Simulation and experiments results are performed to verify the effectiveness and superiority of the proposed methodology on voltage support.

Suppression Strategy of Subsynchronous Oscillation Based on Dynamic Voltage Compensation Control for Grid-Forming D-PMSG in Weak Grid

The virtual impedance can suppress the low-frequency oscillation effectively caused by the power coupling effect for the grid-forming direct-drive permanent magnet synchronous generator (D-PMSG). However, there are few studies on the influence of virtual impedance on the subsynchronous oscillation caused by the interaction between the grid-forming D-PMSG and the weak grid. In this paper, the mechanism of virtual impedance improving the stability of virtual synchronous generator (VSG) control for the converter is revealed from the perspective of power coupling, and the influence of virtual impedance on the system stability in subsynchronous frequency range was analysed based on the sequence impedance model. The analysis results show that the virtual inductance cannot effectively improve the oscillation suppression effect, but the virtual resistance can greatly improve the damping characteristics of the system which has a good oscillation suppression effect. However, excessive increase in virtual resistance will cause power coupling oscillation, even subsynchronous oscillation, which shows limitations in subsynchronous oscillation suppression. To solve the problem, a dynamic voltage compensation control method based on active disturbance rejection control (ADRC) was proposed, and the parameters are designed by bandwidth method. The method can suppress the subsynchronous oscillation effectively in a certain frequency range under different grid strength and disturbance conditions. And it shows strong adaptability and good system robustness in weak grid. Finally, the effectiveness of the proposed oscillation suppression strategy was verified by time domain simulation.

Dynamic Compensation Strategy With Dual Closed-Loop Control for Voltage Drift and Torque Ripple in TPFSI-Fed PMSM Drives

Aiming at capacitor voltage offset (CVO) in permanent magnet synchronous motor (PMSM) driven by three-phase four-switch inverter (TPFSI), the paper proposes a strategy to resist voltage drift with dynamic voltage compensation. A correction factor is introduced to adjust the capacitor voltage applied to Space Vector Pulse Width Modulation (SVPWM). Then, the additionally superimposed component controlled by the correction factor will be injected into the component of the actual output voltage vector on the α-axis. The additionally superimposed component is adjusted by setting the appropriate correction factor to cancel the CVO on the α-axis. By setting a controllable variable correction factor, its anti-offset characteristics can ensure the continuous and stable operation of the system. However, the scheme introduces torque ripple. The strategy adopts double closed-loop control. Experimental results on a 1 kW PMSM prototype show that the proposed scheme can effectively suppress CVO and torque ripple.

Adaptive Single Carrier Modulation scheme based MLI supported TDVC for Voltage Quality enhancement

Abstract In this article, An Adaptive Single Carrier Modulation (ASCM) scheme based Multilevel Inverter (MLI) is proposed for the Transformerless Dynamic Voltage Compensator (ASCM-MLITDVC) to enhance the load Voltage Quality (VQ). The enhancement of VQ includes voltage sag, swell, unbalance and reducing Total Harmonic Distortion (THD). The Pulse Generation Unit (PGU) require more Carrier Waves (CW) for higher levels of MLI with respect to the number of switches used. This made the PGU complex, hence a carrier wave modulation scheme is proposed which can use it for n number of levels. The Position of CW is altered automatically with respect to the amplitude of Reference Staircase Waveform (RSW). The RSW is created by utilizing the Half Height Method and optimized NLM scheme which makes the least possible output THD is achieved. This scheme is implemented utilizing a real-time simulator OP4500. The results are obtained by conducting Power Hardware in Loop (P-HIL) test method to prove ASCM-MLITDVC can enhance load VQ with reduced THD.

간단한 듀티비 제어 기법에 의한 quasi Z-소스 동적전압보상기

The quasi Z-source dynamic voltage restorer using the conventional switching scheme was able to obtain only the compensation voltage in the out of phase buck-boost mode for voltage swell compensation of the power source and the in-phase boost mode compensation voltage for more than 50% voltage sag compensation. Since this method cannot compensate for the voltage sag of 1-50%, which mainly occurs in industrial fields, a method of connecting additional quasi Z source converter in series and parallel was studied. In this study, a simple duty ratio scheme was proposed which is can be operated as an out of phase buck boost mode to compensate for swell, an in-phase boost mode to compensate for sag of 50% or more and an in-phase buck mode to compensate for sag of 1-50%. In order to prove the validity of this study, PSIM simulation and DSP based experiment were performed. As a result, by the proposed duty ratio control scheme, it was possible to compensate both the in-phase buck boost mode and the out of phase buck boost mode for sag and swell with a single quasi Z-source dynamic voltage compensator. Finally, for each load of 50Ω and 100Ω even if the voltage sag and swell were generated step by step by 10%, the voltage compensation rate remained almost 1, and the THD of the voltage was all good at 5% or less.

A Dynamic Series Voltage Compensator for the Mitigation of LCC-HVDC Commutation Failure

To effectively mitigate the commutation failure (CF) of the line-commutated converter high-voltage direct current (LCC-HVDC) transmission system, a dynamic series voltage compensator (DSVC) scheme is proposed. The DSVC consists of three integrated gate-commutated thyristor (IGCT)-based full-bridge submodule (FBSM) chains to match the bulk power transmission of the LCC-HVDC. Inserted between the transformer and the AC port of the inverter, the DSVC assists the commutation process by superposing the transient voltage to the AC line voltage and increasing the commutation margin of the inverter valve. Operation and control strategies, which are two critical techniques for the DSVC, are designed based on the working states of the FBSMs, assisting the commutation process and balancing the DSVC capacitor dynamic voltages. The CF detection method is another critical technique of the DSVC control and is improved considering the reverse time of the LCC-HVDC thyristors. Compared with the topologies proposed in existing literature, the DSVC has better performances in safe and stable operation due to the urgent control strategy considering situations beyond its ability. A detailed EMT simulation shows that the DSVC can respond quickly to mitigate CFs and validate the effectiveness of the overall design and key techniques. Furthermore, the operation and control strategy can limit the current stress once it is beyond the capability of the DSVC, which guarantees its feasibility and practicability.

Voltage Quality Enrichment using Transformerless Dynamic Voltage Compensator based on Asymmetrical Multilevel Inverter

In this article, Asymmetrical voltage source Multilevel Inverter based Transformerless Dynamic Voltage Compensator (ASMLI-TDVC) for load Voltage Quality (VQ) enrichment is proposed. The ASMLI-TDVC is controlled such that it compensates different levels of VQ problems with lesser Total Harmonic Distortion (THD). Synchronized voltage injection achieved through series transformer from traditional DVC leads to rise in the size of DVC and make system cumbersome. ASMLI based on less switch count topology is utilized for TDVC to overcome these aforementioned issues. Simulation studies of ASMLI-TDVC are carried out using Matlab Simulink software. Further, an experimental model is developed and tested in real-time using OP4500. Results prove that dynamic compensation for VQ improvement is achieved by ASMLI-TDVC.

Minimizing Capacitance Value of Interleaved Power Factor Corrected Boost Converter for Battery Charger in Electric Vehicles

A dynamic voltage compensator (DVC) technique is presented for the minimizing of the capacitance value of the interleaved power factor corrected (PFC) boost converter for the battery charger in electric vehicles. This technique is based on eliminating the ripple on the capacitor by creating a voltage in the opposite direction as well as the amount of ripple on the capacitor. With the proposed method, the capacitance value is reduced by approximately five times. Reducing the size of the capacitor also provides the use of film-capacitors with a longer life. The other contribution of this study is designing a faster and more stable fully-digital control system, instead of the commonly used analogue controller of interleaved PFC boost converter. A 3.3 kW interleaved PFC boost converter is designed to verify the effect of the designed dynamic voltage compensator and digital controller.

Adaptive Active Power Sharing Techniques for DC and AC Voltage Control in a Hybrid DC/AC Microgrid

This paper deals with the ac and dc dynamic voltage control in a hybrid dc/ac microgrid (MG) with central and distributed battery energy storage systems (BESSs), applying a power sharing mechanism between the different devices in the MG. The MG is composed by a multiport transformation center and two fixed frequency three phase ac nanogrids (NGs) coupled to a dc bus through three-phase power electronic converters. The system pursues to minimize the dependence on the utility grid and the stress in the MGs central BESS, while increasing the power handling capability and the overall system stability during islanding condition. In order to approach the proposed aim, two main concerns are studied in this paper: An adaptive power sharing mechanism between the dc bus and the ac NGs for dc voltage control, and the design and implementation of an ac dynamic local voltage compensator based on distributed energy storage system. The proposed techniques are validated through simulations and experimental results.

The Design of Filter Parameters of Dynamic Voltage Restorer in Medium Voltage Network

Dynamic Voltage Compensator (DVR) is able to handle the dynamic power quality problems in distribution network, such as voltage sags and voltage unbalance, and the parameters of the output filter will have important affect on the compensation results. In this paper, the parameter design method of the output filter of a cascaded H-bridge based DVR applied in medium-voltage distribution grid is studied. Through the analysis of the case when filter inductor current has the maximum value, the theoretical expression of the relationship between the low limit of the value of filter inductor and the capability of voltage compensation and power factor is derived. Meanwhile, the method of selecting the filter capacitor value is ​​obtained. The realization of the proposed method are given by taking an engineering project as an example, the correctness and validity of the design method of filter parameters proposed in this paper are verified by simulation.

A Dynamic Voltage Compensation Method for Improving Weighing Accuracy

In order to eliminate the measurement error caused by working voltage fluctuation of weighing sensor, a dynamic voltage compensation method for improving the weighing accuracy was proposed in the paper. The method takes strain gauge type pressure sensor as the weighing sensor and corrects Wheatstone bridge circuit. By synchronously detecting output voltage signal and working voltage of the weighing sensor, the method dynamically compensates the working voltage fluctuation of the weighing sensor, corrects the measurement error caused by the voltage fluctuation of external source and calculates the weight in real time. A weighing system based on the digital signal processor (DSP) was designed. Results of simulation experiment verify the feasibility of the proposed method.

Voltage optimization

This paper deals with the voltage unbalance in three-phase circuits which introduces additional losses and reduces the stability of the 600 V distribution system. For automatic voltage regulation, there are methods of voltage-level optimization available that will compensate for voltage changes. These generally involve a tap-changing transformer in combination with an automatic voltage regulator. To mitigate voltage unbalance autotransformer with a delta winding and a buck boost transformer with dynamic voltage compensation can be used. To mitigate voltage harmonics active filters that cancel harmonic current distortion can be used

Analysis of a Dynamic Voltage Compensator With Reduced Switch-Count and Absence of Energy Storage System

The utilization of dynamic voltage restorers to protect sensitive loads against short-term voltage disturbances has been proven to be a competitive solution in medium- and high-power applications. For low-power applications further cost reductions are required to make the technology even more competitive, although just a few numbers of studies have already been conducted in this area. This paper discusses the design and operation of a three-phase dynamic voltage compensator, including control strategies for the converters. The proposed topology and control strategies are evaluated through simulation studies based on measured data, selected by the IEEE Power Quality Task Force for the characterization of power quality events and device performance evaluation, along with disturbances recorded in a steel plant, in Minas Gerais State, Brazil. An experimental implementation of the compensator is developed to allow a better evaluation of specific and critical operating modes, such as the forced commutation of the bypass thyristors and inverter operation.

A combined uninterruptible power supply and dynamic voltage compensator using a flywheel energy storage system

Due to technological advancements, the flywheel energy storage system is becoming a viable alternative to electrochemical batteries. Two potential applications of flywheel systems are for voltage support and as an uninterruptible power supply. The two applications are both useful to protect critical loads on distribution feeders. Therefore, it may be useful to look at the possibility of combining both functions into one system. This paper considers a flywheel energy storage system which performs both functions and presents a novel control scheme using both sinusoidal pulse width modulation as well as a boost converter to regulate the critical load voltage on the feeder. Dynamic voltage compensation is achieved by injecting voltage through series transformers rather than by connecting the system in shunt, to minimize the amount of kVA required by the flywheel system. Simulations are provided using the Electromagnetic Transients Program to validate the concept.

Dynamic voltage compensation on distribution feeders using flywheel energy storage

Advancements in power electronics, bearings and materials have made flywheel energy storage systems a viable alternative to electrochemical batteries. A future application of such a device is as an uninterruptible power supply for critical loads on a distribution feeder. However, the same power electronics and flywheel system could also be used for dynamic voltage compensation. A comparison is made between series and parallel connection of such dynamic compensation techniques used to maintain rated load voltage on distribution feeders when there are momentary dips in the supply voltage. For each case a mathematical model is presented and analyzed. The two cases are compared and the series compensation technique is more effective.

Microprocessor controlled reactive power compensator for loss reduction in radial distribution feeders

A new real-time reactive power compensation scheme for distribution feeders is proposed. A network of data acquisition interfaces and microcontrolled fixed capacitor biased thyristor controlled reactors measures the reactive component of the load current at each feeder node and injects optimal levels of leading compensation current. The degree of compensation is determined by a dynamic approach, optimizing the total dollar savings which result for VAr compensation. Load currents are sampled every 3 s and compensation currents every 5 s and recalculated every 10 min. System response time is rapid enough to react to real-time load variations and closed loop control of thyristor firing angles enables adjustment for dynamic voltage fluctuations and compensator dissimilarities. A model compensation network was constructed and successfully tested in a laboratory environment.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Laboratory Test and Feasibility Study of Two Countermeasures to Subsynchronous Resonance

This paper presents two countermeasures to subsynchronous resonance. One is a dynamic resistor which is controlled by thyristor switches based on shaft torsional oscillations. The other is a new dynamic compensator. Two types, called a dynamic current compensator and a dynamic voltage compensator, have been developed. Laboratory tests were conducted to investigate their damping forces against subsynchronous resonance. Results indicate that they can damp torsional interactions sufficiently; especially, a dynamic resistor has an excellent damping force. Analytical studies suggest that dynamic compensators can also stabilize induction generator effects. Stability analysis and transient simulations have good agreement with tested results.