domination and administration of converter

View Original This paper presents a voltage-power droop/frequency-reactive power boost (VPD/FQB) control scheme that permits multiple voltage source converters (VSCs)to operate in parallel during a VSC fed microgrid. Each current-contained VSC in such a microgrid has its own VPD/FQB auditor that sets its current allusion to manage the voltage and frequency of a standard microgrid bus. By dropping the voltage reference of every controller against its real power output, multiple VPD/FQB controllers jointly regulate the microgrid voltage while sharing a requirement converters load power in distribution toa pre-determined ratio. equivalently, by promising the prevalence insinuation of every controller against its reactive power output, multiple VPD/FQB controllers jointly regulate the microgrid frequency while sharing the reactive load in proportion to predetermine the ratio. The proposed control scheme also can operate in grid-connected mode. Experimental results are provided to validate the VPD/FQB control scheme

INTRODUCTION

A section of the majority power grid with distributed power sources could also be called a microgrid if it’s capable of operating as one controllable system . Many new distributed power sources, like turbine generators, microturbines, and fuel cells, don’t generate 60 Hz ac voltage and thus require voltage source converters (VSCs) as a part of the circuitry to interface them with the microgrid. Thus, a contemporary microgrid typically includes a network of VSCs that operate in parallel to provide a standard load. it’s desirable that a microgrid, which is generally connected to the majority power grid, continues to work when it becomes islanded. Some important requirements for reliable islanded operation of a VSC fed microgrid are:1) VSCs must jointly regulate the microgrid bus voltage and frequency.2) VSCs must share a standard load in proportion to a pre-determined ratio no matter plant parameters.3) VSC control must be achieved using converters locally measured feedback signals only. Furthermore, it’s desirable to use an equivalent VSC topology and controls in both grid-connected and islanded operation and to avoid undesirable interactions between the VSCs and therefore the distribution network [2]. Low voltage ride-through (LVRT)is also a requirement for distributed power sources.

THE MULTI-VSC-FED MICROGRID

A simplified microgrid with multiple VSCs is shown in Fig.1. The microgrid consists of a collector bus, a bus capacitor, CB, a motor load, and a static load, which is represented as a parallel combination of resistance R and inductance L. The motor may be a three-phase, wound rotor machine. it’s assumed that the load is balanced which the road impedance between the collector bus and therefore the load is little. The microgrid could also be connected to the majority power grid through breaker S.The VSCs employ high bandwidth current controllers, consequently, the VSCs alongside their interface inductors are modeled as current sources. Converter currents are assumed adequate to their current controller reference values. The model is an extension of the only VSC fed microgrid.

REVIEW OF VP/FQ CONTROL SCHEME

The VP/FQ control scheme, presented in [10], has been developed for a microgrid fed by one VSC. The control design is predicated on the linearized microgrid model shown inFig. 2, for the case n = 1. The VP/FQ control consists of voltage and frequency control loops to manage bus voltage,vB, and converters frequency, ωB. A voltage control loop is meant to support the nominal transfer function relating d-axis VSC current to the microgrid bus voltage control loop, which is shown in . Many new distributed power sources, like turbine generators, microturbines, and fuel cells, don’t generate 60 Hz ac voltage and thus require voltage source converters (VSCs) as a part of the circuitry to interface them with the microgrid. Thus, a contemporary microgrid typically includes a network of VSCs that operate in parallel to provide a standard load. it’s desirable that a microgrid, which is generally connected to the majority power grid, continues to work when it becomes islanded. Some important requirements for reliable islanded operation of a VSC fed microgrid are:1) VSCs must jointly regulate the microgrid bus voltage and frequency.2) VSCs must share a standard load in proportion to a pre-determined ratio no matter plant parameters.3) VSC control must be achieved using locally measured feedback signals only. Furthermore, it’s desirable to use an equivalent VSC topology and controls in both grid-connected and islanded operation and to avoid undesirable interactions between the VSCs and therefore the distribution network, employs a PI compensator to manage vB to the voltage reference v∗B. it’s demonstrated in [10] that the resulting system is strong under all loading conditions. A frequency control loop, shown in Fig. 3(b), is meant to support the transfer function relating q-axis VSC current to the microgrid bus frequency, given by (10). thanks to cross-coupling, the dynamics of the inner voltage control loop must be included during this transfer function to make sure overall system stability [10]. A diagram representation of the whole closed loop.

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THE VPD/FQB CONTROL SCHEME

The VPD/FQB Control scheme is proposed for multi-VSC-fed microgrids. To simplify the analysis, a microgrid with only2 VSCs are going to be analyzed (n = 2). Each VSC has its own VPD/FQB controller. These VPD/FQB controllers operate in parallel to jointly regulate the voltage and frequency of the microgrid as shown in Fig. 6. supported the observation that experimentally obtained step response of the voltage and frequency loops of the VP/FQ control scheme. only inputs i1dand i2 dinfluence vBd which i1qand i2qare the remaining inputs available for regulating ωB, these VPN/FQB controllers set i1dand i2dto to manage brand seti1qand i2qto regulate ωB. almost like parallel operating generators that can’t use speed governors with fixed speed references [11], the VPN/FQB controllers cannot use fixed references to manage the microgrid voltage and frequency. An analysis of the droop characteristic of two parallel operating generators is presented to justify the drooped voltage and frequency references of the VPD/FQB controllers. A simplified microgrid is about up within the laboratory to validate the control scheme of section IV. The schematic diagram of the microgrid and its controls are shown in Fig. 8. The ratings and parameters of the microgrid are listed in Table II. Note that resistances R1and R2represent conduction losses of the converters and their interface inductorsThis experiment validates joint microgrid control and cargo sharing of controllers C1 and C2 by activating C2 while VSC1(with controller C1) is feeding the islanded microgrid as its sole power source. Table III lists the parameters of C1. C2 is just like C1. before activating.

CONCLUSION 

This paper proposes the VPD/FQB control scheme that permits multiple VSCs with standard inductor interfaces and-frame current controls to work in parallel during a VSC fed microgrid. This control scheme operates in both grid-connected and islanded modes and it’s independent of the islanding detection circuitry. Moreover, the control scheme provides voltage and frequency regulation of the microgrid in islanded mode, provides inherent over-current protection of the VSC, and requires just one 3-phase inductor within the VSC output interface. . Many new distributed power sources, like turbine generators, microturbines, and fuel cells, don’t generate 60 Hz ac voltage and thus require voltage source converters (VSCs) as a part of the circuitry to interface them with the microgrid. Thus, a contemporary microgrid typically includes a network of VSCs that operate in parallel to provide a standard load. it’s desirable that a microgrid, which is generally connected to the majority power grid, continues to work when it becomes islanded. Some important requirements for reliable islanded operation of a VSC fed microgrid are:1) VSCs must jointly regulate the microgrid bus voltage and frequency.2) VSCs must share a standard load in proportion to a pre-determined ratio no matter plant parameters.3) VSC control must be achieved using locally measured feedback signals only. Furthermore, it’s desirable to use an equivalent VSC topology and controls in both grid-connected and islanded operation and to avoid undesirable interactions between the VSCs and therefore the distribution network In islanded mode, the VPD/FQB controllers set the present references of the VSCs to jointly regulate the voltage and frequency of a standard microgrid bus. to form joint intensity control imaginable the voltage reference of every VPD/FQB investigator is imaginable against the d-axis current, and hence the paramount power output, of the comparable VSC. Such a droop idiosyncratic also ensures that the VSCs share a standard real load in proportion to their voltage droop coefficients. Real power allocation among the VSCs is therefore achieved without control interconnections by drooping the voltage reference. this is often in stark contrast to synchronous generators which autonomously share a standard load by drooping their frequency references against the mechanical power of the corresponding turbine. Joint regulation of a standard frequency by multiple VSCsand autonomous reactive load sharing is achieved by dropping the frequency reference on each VPD/FQB controller against the q-axis current of the corresponding VSC. this is often like boosting the frequency reference against the reactive power output of the VSC. the utilization of drooped references also allowVSCs with VPD/FQB controllers to work in grid-connected microgrids since during this case the bus voltage and frequency are dictated by the majority power grid. it’s been demonstrated that the proposed control scheme is strong to both grid connection and islanding transients.

Prepared By

ABHIRAJ JPS

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