Grid-connected power converter with controller and method for the same

Abstract

A grid-connected power converter with a controller configured to be connected to a grid and to handle faults in the grid by detecting that a fault has occurred and in response thereto generate an output voltage,V d , with specific frequency components and voltage amplitudes, where the grid-connected power converter controller includes a current control circuit and an extremum seeking control actuation circuit. The extremum seeking control actuation circuit is configured to determine a phase-angle offset of a main component of the power converter output voltage,V d , being the grid voltage amplitude,V pCC , and capacitor leg voltage amplitude,V C , to be maximized. The grid-connected power converter controller is configured to maintain synchronism with the grid and support the grid, when the fault mode is activated.

Description

[0001]GRID-CONNECTED POWER CONVERTER WITH CONTROLLER AND METHOD FOR THE SAME TECHNICAL FIELD The present disclosure relates generally to the field of power systems; and more specifically, to a grid-connected power converter with a controller and a method for the grid-connected power converter with the controller. BACKGROUND Modern power systems rely extensively on inverters to convert direct current (DC) obtained from renewable energy sources,such as photovoltaic (PV) systems, into alternating current (AC), and hence, suitable for grid integration. While inverters playa significant role in sustainable energy generation, they are more susceptible to abnormal operations which may compromisethe stability of the grid (or power grid). The abnormal operations means that the voltage and frequency are deviated from theirnominal values. The abnormal operations may occur during the inverter operation and may destabilize the grid. The abnormal operations may include power grid faults, which are defined as physical conditions that cause a circuit element not to perform according to the requirement. The power grid faults may include physical short circuits, open circuits, device failures, poweroverload, and the like. Furthermore, the power grid faults can be classified as 1-phase faults, 2-phase faults and 3-phase faultsdepending on the number of phases affected. Moreover, the structure of the fault as well as the grid is unknown. The gridstructure may be more resistive or inductive or capacitive. Also, the final impedance and its composition is also unknown.The inverter control technique can be classified in two main groups, grid following (GFL) and grid forming (GFM). The GFLtechnique usually relies on a synchronization unit, usually a phase locked loop (PLL) algorithm within the controller. On theother hand, the GFM technique does not need it. It generates its own frequency and angle using an algorithm which relies on the power exchange. In terms of behaviour, GFL acts like a current source and GFM acts like a voltage source. When a 3-phasefault is faced e.g., a strong voltage dip, both of them present limitations. Firstly, GFL synchronization unit is very sensitive tovoltage variations, leading to strong oscillation or even the loss of synchronism, especially in a weak grid environment.Secondly, as already mentioned, the grid structure is unknown, therefore, it is technically challenging to set the correct referenceto support the grid in a deterministic way. On the other hand, GFM also presents several problems. The stiff voltage source behaviour leads the system to current saturation due to the strong voltage dip. This saturation creates that the power injected decreases a lot respect to the reference value, leading to a frequency variation, which increases the power angle, and, eventually,it reaches the loss of synchronism. Moreover, the current saturation makes that current is the driving variable leading to currentsource behaviour. This can be solved applying a synchronization unit, however, GFL problems arise. Focusing on PV systems,most of them operate in maximum power point tracking (MPPT). The MPPT means that the controller optimizes the power extracted from the PV panel. For that, there are many optimization techniques. One of them is called extremum seeking (ES).This technique was not used before to synchronize with the grid. Thus, there exists a technical problem of loss of synchronismof the inverter respect to the grid when the power fault occurs on the grid side during the inverter operation.Therefore, in light of the foregoing discussion, there exists a need to overcome the aforementioned drawbacks associated withthe conventional ways of achieving the grid synchronization with the inverter using the GFM or the GFL techniques.SUMMARYThe present disclosure provides a grid-connected power converter with a controller and a method for the grid-connected powerconverter with the controller. The present disclosure provides a solution to the existing problem of loss of synchronism of theinverter respect to the grid when the power fault occurs on the grid side during the inverter operation. An aim of the presentdisclosure is to provide a solution that overcomes at least partially the problems encountered in prior art, and provide an improved grid-connected power converter with a controller and an improved method for the grid-connected power converter with the controller. The object of the present disclosure is achieved by the solutions provided in the enclosed independent claims. Advantageous implementations of the present disclosure are further defined in the dependent claims.In one aspect, the present disclosure provides a grid-connected power converter with a controller configured to be connectedto a grid and to handle faults in the grid by detecting that a fault has occurred and in response thereto generate an output voltage,^^, with specific frequency components and voltage amplitudes, where the grid-connected power converter controllercomprises a current control circuit and an extremum seeking control actuation circuit. The extremum seeking control actuationcircuit is configured to determine a phase-angle offset of the main component of the power converter output voltage, ^^, beingthe grid voltage amplitude, ^^^^ , and capacitor leg voltage amplitude, ^^, to be maximized.The disclosed grid-connected power converter with the controller maintains synchronization with the grid when the fault occurson the grid side during the power converter (e.g., inverter) operation. More specifically, the grid-connected power convertercontroller maintains synchronism with the grid when the fault has occurred on the grid side by virtue of the extremum seekingcontrol actuation circuit. The performance of the grid-connected power converter with the controller is independent of the gridconfiguration. Alternatively stated, the configuration of the grid whether inductive or resistive, weak or strong does not have any effect on the performance of the grid-connected power converter with the controller. The power converter with thecontroller can be connected to the grid using either GFM or GFL technique during normal operation. In case of use of the GFLtechnique, the grid-connected power converter controller removes the PLL and its induced instability and configured to injectthe optimal current during the fault. Moreover, the grid-connected power converter controller provides the GFM features duringthe fault period. In the case of use of the GFM technique, the system remains synchronized and it still support the grid by setting the closest value to the nominal one during the fault.In an implementation form, the extremum seeking control actuation circuit is configured to determine a phase-angle offset ofthe main component of the power converter output voltage, ^^, based on the phase at a time when the fault is detected and thefrequency at a time when the fault is detected. The use of the phase and frequency at the time when the fault is detected leads to optimization of the grid voltage amplitude,^^^^ , and capacitor leg voltage amplitude, ^^.In a further implementation form, the extremum seeking control actuation circuit is configured to determine a phase-angleoffset plus the phase at a time when the fault is detected and the integral of the frequency at a time when the fault is detected,given the main component of the power converter output voltage angle, ^^.This is advantageous for a reliable determination of the phase-angle offset of the main component of the power converter output voltage angle, ^^. In a further implementation form, the grid-connected power converter controller further comprises a fault detector circuit configured to detect a fault and in response thereto cause the extremum seeking control actuation circuit to determine the phase- angle offset.The use of the fault detector circuit and the extremum seeking control actuation circuit comprised by the grid-connected powerconverter controller leads to a seamless operation of the grid connected with the power converter, during the fault. In another aspect, the present disclosure provides a method for a grid-connected power converter controller configured to be connected to a grid. The method comprises detecting a fault and in response thereto determining the main component of thepower converter output voltage, ^^, angle based on the grid values at a time when the fault is detected utilizing an extremumseeking algorithm, and obtaining a maximum voltage of the grid, ^^^^ , and capacitor leg voltage amplitude, ^^, through thephase-angle offset.The method manifests all the advantages and technical effects of the grid-connected power converter controller of the presentdisclosure. It is to be appreciated that all the aforementioned implementation forms can be combined. It has to be noted that all devices, elements, circuitry, units and means described in the present application could be implemented in the software or hardware elements or any kind of combination thereof. All steps which are performed by the various entities described in the present application as well as the functionalities described to be performed by the various entities are intended to mean that the respective entity is adapted to or configured to perform the respective steps and functionalities. Even if, in the following description of specific embodiments, a specific functionality or step to be performed by external entities is not reflected in the description of a specific detailed element of that entity which performs that specific step or functionality, it should be clear for a skilled person that these methods and functionalities can be implemented in respective software or hardware elements, or any kind of combination thereof. It will be appreciated that features of the present disclosure are susceptible to being combined in various combinations without departing from the scope of the present disclosure as defined by the appended claims. Additional aspects, advantages, features and objects of the present disclosure would be made apparent from the drawings and the detailed description of the illustrative implementations construed in conjunction with the appended claims that follow. BRIEF DESCRIPTION OF THE DRAWINGS The summary above, as well as the following detailed description of illustrative embodiments, is better understood when readin conjunction with the appended drawings. For the purpose of illustrating the present disclosure, exemplary constructions ofthe disclosure are shown in the drawings. However, the present disclosure is not limited to specific methods andinstrumentalities disclosed herein. Moreover, those skilled in the art will understand that the drawings are not to scale. Whereverpossible, like elements have been indicated by identical numbers. Embodiments of the present disclosure will now be described, by way of example only, with reference to the following diagrams wherein:FIG. 1 is a block diagram that illustrates various exemplary components of a grid-connected power converter controller, inaccordance with an embodiment of the present disclosure;FIG. 2 is a circuit diagram of a grid-connected power converter with a controller, in accordance with an embodiment of the present disclosure; FIG.3 is schematic diagram of a grid-connected power converter controller operating in a fault mode, in accordance with an embodiment of the present disclosure; FIG. 4 illustrates functioning of an extremum seeking control actuation circuit, in accordance with an embodiment of the present disclosure;FIG. 5A is a graphical representation that illustrates variation of voltage with time for an inductive fault, in accordance with anembodiment of the present disclosure; FIG.5B is a graphical representation that illustrates variation of voltage with time for a resistive fault, in accordance with an embodiment of the present disclosure; andFIG.6 is a flowchart of a method for a grid-connected power converter controller, in accordance with an embodiment of the present disclosure. In the accompanying drawings, an underlined number is employed to represent an item over which the underlined number is positioned or an item to which the underlined number is adjacent. A non-underlined number relates to an item identified by a line linking the non-underlined number to the item. When a number is non-underlined and accompanied by an associated arrow, the non-underlined number is used to identify a general item at which the arrow is pointing. DETAILED DESCRIPTION OF EMBODIMENTS The following detailed description illustrates embodiments of the present disclosure and ways in which they can beimplemented. Although some modes of carrying out the present disclosure have been disclosed, those skilled in the art wouldrecognize that other embodiments for carrying out or practicing the present disclosure are also possible.FIG. 1 is a block diagram that illustrates various exemplary components of a grid-connected power converter controller, inaccordance with an embodiment of the present disclosure. With reference to FIG.1, there is shown a block diagram 100 of agrid-connected power converter controller 102. The grid-connected power converter controller 102 comprises a current controlcircuit 106, an extremum seeking control actuation circuit 108 and a fault detector circuit 110. There is further shown a powerconverter 112 which is connected to the grid-connected power converter controller 102 and the grid 104, and which will be measured.In operation, a grid-connected power converter (e.g., the power converter 112) with a controller (e.g., the grid-connected powerconverter controller 102) configured to be connected to the grid (G) 104 and to handle faults in the grid 104 by detecting thata fault has occurred and in response thereto generate an output voltage, ^^, with specific frequency components and voltageamplitudes, where the grid-connected power converter controller 102 comprises the current control circuit 106 and theextremum seeking control actuation circuit 108. The extremum seeking control actuation circuit 108 is configured to determinea phase-angle offset of the main component of the power converter output voltage, ^^, being the grid voltage amplitude, ^^^^ ,and capacitor leg voltage amplitude, ^^, to be maximized. The grid-connected power converter may also be referred to as agrid-tied inverter. The grid-connected power converter (e.g., the power converter 112) with the controller (e.g., the grid-connected power converter controller 102) is configured to detect the fault when the fault has occurred in the grid 104. Thegrid-connected power converter controller 102 is configured to connect to the grid 104 either through an inductor-capacitor(LC) or inductor-capacitor-inductor (LCL) or inductor (L) filter during the fault, as shown, for example, in FIG. 2. Duringnormal operation of the gird 104, the filter (e.g., LC or LCL or L) does not change. In response of detecting the fault in the grid104, the grid-connected power converter controller 102 is configured to generate its own frequency in order to maintain thesynchronization with the grid 104. More specifically, the grid-connected power converter (e.g., the power converter 112) isconfigured to generate the output voltage, ^^, with specific frequency components and voltage amplitudes. The grid-connectedpower converter controller 102 comprises the current control circuit 106 that is referred to as an inner current control loop. The current control circuit 106 is configured to track the current reference signal. The grid-connected power converter controller102 incorporates the current control circuit 106 even when operating in the normal operation mode. Any structure can be usedas the current control circuit 106 that can track the current reference signal, for instance, a proportional-integral (PI) controller in dq frame, where dq frame is typically a current control technique for 3-phase AC currents, which uses a rotating referenceframe. The rotating reference frame rotates at the frequency of the grid-connected power converter controller 102. The grid-connected power converter controller 102 also comprises the extremum seeking control actuation circuit 108, which isconfigured to provide the frequency and angle to optimize the voltage in order to obtain the maximum possible voltage at themeasured point and phase considering a constant current injection (e.g., the maximum current). Moreover, the extremumseeking control actuation circuit 108 is configured for functioning when the fault has occurred in the grid 104 or the fault mode is activated. In order to maintain a smooth functioning of the grid 104 when the fault mode is activated, the initialization values(e.g., the phase and the frequency at a time when the fault is detected) are obtained either from a frequency generator, orfrequency measurements or frequency estimation at the moment the fault mode is detected. The structure of the extremumseeking control actuation circuit 108 is described in more detail, for example, in FIG. 4. Moreover, an input to the extremumseeking control actuation circuit 108 is a voltage signal, that is the voltage to maximize, the voltage across the grid, ^^^^ , (i.e.,the voltage across the point of common coupling) or the capacitor leg voltage amplitude, ^^. The first one in case of gridconnection through the L filter, the second one in case of grid connection through the LC or LCL filter.FIG. 2 is a circuit diagram of a grid-connected power converter with a controller, in accordance with an embodiment of the present disclosure. FIG. 2 is described in conjunction with elements from FIG. 1. With reference to FIG. 2, there is shown acircuit diagram 200 of the power converter 112 connected with the controller (e.g., the grid-connected power convertercontroller 102) and the grid 104. In the circuit diagram 200, this is shown that the power converter 112 (e.g., the inverter) withthe controller (e.g., the grid-connected power converter controller 102) is connected to the grid 104 and a load 204 through theLCL filter (may also be represented as ^^^^). The load 204 is used to emulate a fault (e.g., a 3-phase fault), which has occurredin the grid 104. The grid 104 encompasses the load 204. Moreover, the grid 104 is represented by a Thevenin equivalent (e.g.,a voltage source ^^in series with an inductor ^^). The power converter 112 (e.g., the inverter) is fed by a photovoltaic (PV) system 202 which provides a DC voltage, represented as VDC. The power converter 112 (e.g., the inverter) is controlled by thecontroller (e.g., the grid-connected power converter controller 102). Furthermore, there is shown a point of common coupling(PCC) 206 between the load 204 and the grid 104.The controller (e.g., the grid-connected power converter controller 102) defines the behaviour of the power converter 112 whichuses one of the control techniques, such as the GFM or GFL and sets either a voltage or current source behaviour. Thereafter,the controller (e.g., the grid-connected power converter controller 102) can be connected to any power converter (e.g., theinverter). However, the power converter 112 becomes the GFM power converter when the fault occurs in the grid 104. The execution of the grid-connected power converter controller 102 is described in the following way: Initially, the grid 104 connected with the power converter 112 (e.g., the inverter) and the controller (e.g., the grid-connected power converter controller 102) is running in a normal operation mode. Thereafter, a fault occurs in the grid 104 and in response of the fault, the fault detector circuit 110 (of FIG.1) comprised by the grid-connected power converter controller 102 is configured to detect the fault and initiate a fault mode signal. The fault detector circuit 110 is configured to detect the current saturation situation,or current threshold value or a voltage drop on the grid 104 side. As soon as, the fault on the grid 104 side is detected, the lastfrequency and angle, which come from the normal operation controller, are frozen. The extremum seeking control actuation circuit 108 is configured to start operating with these initial values (e.g., the frozen frequency and angle). All the loops which are external to the current control circuit 106 (e.g., the inner current loop) are disabled. The current control circuit 106 (e.g., the inner current loop) and the extremum seeking control actuation circuit 108 keep functioning. An input signal to the current control circuit 106 (e.g., the inner current loop) is the maximum current that is allowed by hardware components comprised bythe current control circuit 106. The phase angle and the frequency are provided by the extremum seeking control actuationcircuit 108. The extremum seeking control actuation circuit 108 keeps functioning and generating the frequency and anglevalues, iteratively. Finally, the maximum voltage in the measured point and phase is achieved. When the fault is cleared, the fault mode signal is disabled and the grid 104 connected with the power converter 112 (e.g., the inverter) and the controller(e.g., the grid-connected power converter controller 102) returns to the normal operation mode.In accordance with an embodiment, the extremum seeking control actuation circuit 108 is configured to determine a phase-angle offset of the main component of the power converter output voltage, ^^, based on the phase at a time when the fault isdetected and the frequency at a time when the fault is detected. Initially, the grid 104 connected with the power converter 112(e.g., the inverter) and the controller (e.g., the grid-connected power converter controller 102) is operating in the normaloperation mode. When the fault occurs on the grid 104, the controller (e.g., the grid-connected power converter controller 102)is configured to operate in the fault mode. Furthermore, the extremum seeking control actuation circuit 108 is configured touse the phase and frequency at the time when the fault is detected in the grid 104. Alternatively stated, the phase and frequencycorrespond to the last phase and frequency supported by the grid 104 when the normal operation mode of the grid 104 ends, onoccurrence of the fault and the fault mode signal is activated. The extremum seeking control actuation circuit 108 is configured to use aforementioned phase and frequency in determination of the phase-angle offset of the power converter output voltage,^^. Alternatively stated, the extremum seeking control actuation circuit 108 is configured to modify the angle of the frequencymeasured at the time when the fault is detected and use this angle to determine the phase-angle offset of the main component of the power converter output voltage, ^^. In accordance with an embodiment, the extremum seeking control actuation circuit 108 is configured to determine a phase-angle offset of the main component of the power converter output voltage, ^^, based on the optimization of the grid voltageamplitude, ^^^^ . When the fault mode signal is activated, the extremum seeking control actuation circuit 108 is configured tooptimize the grid voltage amplitude, ^^^^ , for determining the phase-angle offset of the power converter output voltage, ^^.In accordance with an embodiment, the extremum seeking control actuation circuit 108 is configured to determine a phase- angle offset of the main component of the power converter output voltage, ^^, based on the optimization of the capacitor leg voltage amplitude, ^^. When the fault mode signal is activated, the extremum seeking control actuation circuit 108 is configured to optimize the capacitor leg voltage amplitude, ^^for determining the phase-angle offset of the power converter output voltage,^^. In the considered implementation scenario, as shown in FIG. 2, when either the LC or LCL filter is used between the grid-connected power converter controller 102 and the grid 104, the capacitor leg voltage amplitude, ^^ is optimized. In anotherimplementation scenario, when only L filter is used between the grid-connected power converter controller 102 and the grid104, the grid voltage amplitude ^^^^ is optimized.In accordance with an embodiment, the maximum voltage reached is the maximum possible voltage of the grid, ^^^^ . In animplementation, the extremum seeking control actuation circuit 108 is configured to maximize the grid voltage amplitude ^^^^.In accordance with an embodiment, the maximum voltage reached is the capacitor leg voltage amplitude, ^^. In animplementation, the extremum seeking control actuation circuit 108 is configured to maximize the capacitor leg voltage amplitude, ^^.FIG. 3 is schematic diagram of a grid-connected power converter controller operating in a fault mode, in accordance with anembodiment of the present disclosure. FIG.3 is described in conjunction with elements from FIGs.1 and 2. With reference toFIG. 3, there is shown a schematic diagram 300 of the grid-connected power converter controller 102 comprising the currentcontrol circuit 106, the extremum seeking control actuation circuit 108 and the fault detector circuit 110.In accordance with an embodiment, the grid-connected power converter controller 102 further comprises the fault detector circuit 110 configured to detect a fault and in response thereto cause the extremum seeking control actuation circuit 108 todetermine the phase-angle offset. On occurrence of the fault on the grid 104, the fault detector circuit 110 is configured todetect the fault and trigger the grid-connected power converter controller 102 to operate in the fault mode. In response of detecting the fault, the fault detector circuit 110 is configured to cause the extremum seeking control actuation circuit 108 to determine the phase-angle offset of the main component of the power converter output voltage, ^^, based on optimization of the grid voltage amplitude, ^^^^and the capacitor leg voltage amplitude, ^^. In accordance with an embodiment, the fault detector circuit 110 is configured to detect the fault based on a Point of CommonCoupling, PCC, voltage for the grid 104. As shown in FIG. 3, the fault detector circuit 110 is configured to detect the faultbased on the PCC voltage (e.g., ^^^^) for the grid 104. In accordance with an embodiment, the fault detector circuit 110 is further configured to switch an input to the current controlcircuit 106 from a reference current ^^^^^^ to a default current amplitude On detection of the fault, the input to thecurrent control circuit 106 is switched from the reference current ^^^^^^ to the default current amplitude The outputfrom the current control circuit 106 is used as an input to a pulse width modulator (PWM).In accordance with an embodiment, the default current amplitude ^^^^^^ is a maximum current amplitude (^^^^). As shown inthe FIG. 3, the default current amplitude ^^^^^^ is the maximum current amplitude (^^^^).In accordance with an embodiment, the fault detector circuit 110 is further configured to disable outer loops. Furthermore, thefault detector circuit 110 is configured to the disable outer loops, such as GFM, GFL or outer voltage controller.FIG. 4 illustrates functioning of an extremum seeking control actuation circuit, in accordance with an embodiment of thepresent disclosure. FIG.4 is described in conjunction with elements from FIGs.1, 2, and 3. With reference to FIG.4, there is shown a diagram 400 that illustrates functioning of the extremum seeking control actuation circuit 108 (of FIG.1). In accordance with an embodiment, the extremum seeking control actuation circuit 108 is configured to determine a phase- angle offset plus the phase at a time when the fault is detected and the integral of the frequency at a time when the fault isdetected, given the main component of the power converter output voltage angle, ^^. As shown in the FIG. 4, the extremumseeking control actuation circuit 108 is configured to determine the phase-angle offset (represented as ^^^) plus the phase atthe time when the fault is detected (e.g., ^^^ = and the integral of the frequency represented as ^^, given the maincomponent of the power converter output voltage ^^angle. Instead of the integrator as shown in FIG.4, a proportional-integral(PI) filter may be used. Also, low-pass or high pass filters, which are 1st order filter, can be modified by other filters, fordetermination of the phase-angle offset (e.g., ^^^).The power converter 112 (e.g., the inverter) with the controller (e.g., the grid-connected power converter controller 102) canbe connected to the grid 104 using different control techniques, such as a GFL technique, a GFM technique, and the like.In an implementation scenario, the power converter 112 (e.g., the inverter) with the controller (e.g., the grid-connected powerconverter controller 102) connected with the grid 104 is configured to operate in the normal operation mode based on the GFLtechnique. This means that there is a synchronization unit, such as a phased locked loop (PLL), which measures or estimatesthe frequency. In the GFL technique, the controlled variable is the current. Because of the current reference generation, thefault detector circuit 110 is configured to measure the voltage drop below a threshold value. Once the fault is detected in thegrid 104, the controller (e.g., the grid-connected power converter controller 102) is configured to perform as mentioned inFIGs. 1, 2, 3, and 4. In such implementation scenario, the GFL is usually applied to non-dispatchable energy sources, such asPV system (as shown in FIG. 2), when the fault is detected on the grid 104. When the fault occurs, the voltage across the grid104 drops therefore, the injected power is less than the generated one. Consequently, the power converter 112 with the controller(e.g., the grid-connected power converter controller 102) connected with the grid 104 starts operating according to the GFMtechnique. The GFM technique supports the grid 104 that is the GFM technique maintains the frequency and increases thevoltage to the maximum value (e.g., the closest possible value to the normal operation value). The reason (that allows thetransition from non-dispatchable GFL source to non-dispatchable GFM source) is that the power generation is not the limitingfactor but the maximum current that can be injected to the controller. Moreover, if the grid 104 weakens, the controller (e.g.,the grid-connected power converter controller 102) is configured to generate the required frequency. In such condition, thePLL may oscillate and even, may lose the synchronism. Also, the GFM performance is becoming demanded by grid codes.This may help to keep GFL inverters operating on the grid 104. Conventionally, a power converter connected to a grid based on the GFL technique does not provide any support to the grid due to the current reference generation, which usually depends on the power injection. Therefore, this is technically challenging to focus on increasing the voltage of the grid through the current source behaviour of the power converter without knowing thegrid structure. In contrast to the conventional way of using the GFL technique for connecting the power converter with the gridduring the fault, the power converter 112 with the controller (e.g., the grid-connected power converter controller 102) connectedwith the grid 104 is able to remain synchronized with the grid 104 and support the grid 104 by maximizing the voltage that isby optimizing the power converter 112 (e.g., the inverter) performance.In another implementation scenario, the power converter 112 (e.g., the inverter) with the controller (e.g., the grid-connectedpower converter controller 102) connected with the grid 104 is configured to operate in the normal operation mode based onthe GFM performance. Typically, the GFM technique does not require the synchronization unit (e.g., the PLL) to measure orestimate the frequency. This means that the frequency is generated by an external loop, which is replaced by the extremumseeking control actuation circuit 108 when the fault mode is activated. The fault detection depends mainly on the current. Whenthe current exceeds a threshold value, the fault mode is activated. After the detection of the fault on the grid 104, the controller(e.g., the grid-connected power converter controller 102) is configured to perform, as mentioned in FIGs. 1, 2, 3, and 4.Conventionally, a power converter connected to a grid based on the GFM technique is not able to maintain the synchronism with the grid after occurrence of the fault on the grid due to current saturation. The power converter with the grid is synchronized by virtue of the power measurements and operate as a voltage source but during the fault, the current saturation situation isreached. Thereafter, the voltage drops, which in turn reduces the injected power and disrupts the frequency of synchronism.The power converter tries to inject more current to increase the voltage, but the current saturation blocks the more currentinjection. Consequently, the injected power continues to drop, further reducing the frequency until the angle difference between the grid and the power converter becomes too large and de-synchronism occurs. In contrast to the GFM synchronism with thegrid during the fault, the power converter 112 with the controller (e.g., the grid-connected power converter controller 102)connected with the grid 104 is able to remain synchronized with the grid 104 during the fault and supports the grid 104 bymaintaining the maximum voltage across the point of common coupling. Moreover, the power converter 112 with the controller(e.g., the grid-connected power converter controller 102) is configured for grid forming with the grid 104 with non-dispatchableenergy sources (e.g., PV systems) during voltage dips when the fault is detected on the grid 104.Thus, use of the controller (e.g., the grid-connected power converter controller 102) with the power converter 112 (e.g., theinverter) connected with the grid 104 enables the power converter 112 to maintain the synchronism with the grid 104 when the fault occurs on the grid 104 side. The performance of the power converter 112 (e.g., the inverter) with the controller (e.g., thegrid-connected power converter controller 102) is independent of the grid 104 configuration. Alternatively stated, theconfiguration of the grid 104 whether inductive or resistive, weak or strong does not have any effect on the performance of thepower converter 112 (e.g., the inverter) with the controller (e.g., the grid-connected power converter controller 102) connectedwith the grid 104. The maximum performance of the grid-connected power converter controller 102 is obtained, if the maximumcurrent allowed by the hardware components, is injected into the controller. Moreover, the grid-connected power convertercontroller 102 is configured to maintain the synchronism with the grid 104 when the fault has occurred on the grid 104 side byvirtue of the extremum seeking control actuation circuit 108. The power converter 112 is connected to the grid 104 using eitherGFM or GFL technique. In case of use of the GFL technique, the grid-connected power converter controller 102 removes the PLL and its induced instability and configured to inject the optimal current. Moreover, the grid-connected power convertercontroller 102 provides the GFM features during fault periods. The grid-connected power converter controller 102 is configuredto generate the frequency and maintain the synchronism and optimize the voltage to the maximum value (considering thehardware capabilities) in order to support the grid 104. In this way, the grid 104 is fully supported under the most challengingconditions, that is during occurrence of faults on the grid 104 side. The power converter 112 with the controller (e.g., the grid-connected power converter controller 102) supports the grid 104 during fault on the grid 104 side when the power converter112 is connected to either dispatchable or non-dispatchable energy source.FIG. 5A is a graphical representation that illustrates variation of voltage with time for an inductive fault, in accordance with anembodiment of the present disclosure. FIG. 5A is described in conjunction with elements from FIGs. 1, 2, 3, and 4. Withreference to FIG. 5A, there is shown a graphical representation 500A illustrates variation of voltage with time for an inductivefault which has occurred on a grid side (e.g., the grid 104 side). The graphical representation 500A includes an X-axis 502 thatrepresents time in seconds (s) and a Y-axis 504 that represents voltage in volts (V).With reference to the graphical representation 500A, there is shown a first curve 506, a second curve 508 and a third curve 510.The first curve 506 and the second curve 508 are obtained by use of conventional methods, such as PLL and frozen frequency,respectively. The first curve 506 is obtained by considering ^^ = 0^ and ^^ = −500^. Similarly, the second curve 508 isobtained by considering ^^ = 500^ and ^^ = 0^. However, the third curve 510 is obtained by use an extremum seekingalgorithm, described in detail, for example, in FIGs. 1, 2, 3, and 4. The third curve 510 is obtained by considering ^^ = 500^and ^^ = 0^. The third curve 510 illustrates that the power converter 112 (e.g., the inverter) with the controller (e.g., the grid-connected power converter controller 102) supports the grid 104 when the fault (e.g., the inductive fault) is detected on the grid104 side. FIG.5B is a graphical representation that illustrates variation of voltage with time for a resistive fault, in accordance with an embodiment of the present disclosure. FIG.5B is described in conjunction with elements from FIGs.1, 2, 3, 4, and 5A. Withreference to FIG. 5B, there is shown a graphical representation 500B illustrates variation of voltage with time for a resistivefault which has occurred on a grid side (e.g., the grid 104 side). The graphical representation 500B includes an X-axis 502 thatrepresents time in seconds (s) and a Y-axis 504 that represents voltage in volts (V).With reference to the graphical representation 500B, there is shown a first curve 512, a second curve 514 and a third curve 516.The first curve 512 and the second curve 514 are obtained by use of conventional methods, such as PLL and frozen frequency,respectively. The first curve 512 is obtained by considering ^^ = 0^ and ^^ = −500^. Similarly, the second curve 514 isobtained by considering ^^ = 500^ and ^^ = 0^. However, the third curve 516 is obtained by use an extremum seekingalgorithm, described in detail, for example, in FIGs. 1, 2, 3, and 4. The third curve 516 is obtained by considering ^^ = 500^and ^^ = 0^. The third curve 516 illustrates that the power converter 112 (e.g., the inverter) with the controller (e.g., the grid-connected power converter controller 102) supports the grid 104 when the fault (e.g., the resistive fault) is detected on the grid104 side.FIG. 6 is a flowchart of a method for a grid-connected power converter controller, in accordance with an embodiment of thepresent disclosure. FIG. 6 is described in conjunction with elements from FIGs. 1, 2, 3, 4, and 5. With reference to FIG. 6, thereis shown a method 600 for the grid-connected power converter controller 102 (of FIG.1). The method 600 includes steps 602to 606. The method 600 is executed by the grid-connected power converter controller 102.There is provided the method 600 for the grid-connected power converter controller 102. The method 600 applies an extremumseeking optimization technique to generate an internal frequency and to keep synchronized with a grid (e.g., the grid 104, ofFIG.1) when the fault appears on the grid side and offers support to the grid by maximizing the voltage.At step 602, the method 600 comprises detecting a fault. Initially, the fault is detected on the grid side.At step 604, in response of detecting the fault, the method 600 further comprises determining a phase angle offset of the maincomponent of the power converter output voltage, ^^, angle based on the grid values at a time when the fault is detected utilizingan extremum seeking algorithm. In response of detecting the fault, the power converter (e.g., the power converter 112) outputvoltage, ^^, is generated. Thereafter, the extremum seeking algorithm is applied to determine a phase angle offset of the maincomponent of the power converter output voltage, ^^, using the phase and frequency at the time when the fault is detected onthe grid 104 side.At step 606, the method 600 further comprises obtaining a maximum voltage of the grid, ^^^^ , and capacitor leg voltageamplitude, ^^, through the phase-angle offset. The determined phase angle offset is used in order to maximize the voltageacross the point of common coupling, ^^^^ , and the capacitor leg voltage amplitude, ^^.The steps 602 to 606 are only illustrative and other alternatives can also be provided where one or more steps are added, oneor more steps are removed, or one or more steps are provided in a different sequence without departing from the scope of the claims herein.In one aspect, the present disclosure provides a computer program product comprising program instructions for performing themethod 600, when executed by one or more controllers (e.g., the grid-connected power converter controller 102). In a yet another aspect, the present disclosure provides a computer-readable storage medium comprising instructions which, when executed by a computer, cause the computer to carry out the method 600 for the grid-connected power converter controller 102. Modifications to embodiments of the present disclosure described in the foregoing are possible without departing from the scope of the present disclosure as defined by the accompanying claims. Expressions such as "including", "comprising","incorporating", "have", "is" used to describe and claim the present disclosure are intended to be construed in a non-exclusivemanner, namely allowing for items, components or elements not explicitly described also to be present. Reference to the singular is also to be construed to relate to the plural. The word "exemplary" is used herein to mean "serving as an example, instance or illustration". Any embodiment described as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments and / or to exclude the incorporation of features from other embodiments. The word "optionally" is used herein to mean "is provided in some embodiments and not provided in other embodiments". It is appreciatedthat certain features of the present disclosure, which are, for clarity, described in the context of separate embodiments, mayalso be provided in combination in a single embodiment. Conversely, various features of the present disclosure, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable combination or as suitable in any other described embodiment of the disclosure.

Claims

CLAIMS1. A grid-connected power converter with a controller configured to be connected to a grid (104) and to handle faults in thegrid (104) by detecting that a fault has occurred and in response thereto generate an output voltage, ^^, with specific frequencycomponents and voltage amplitudes, wherein the grid-connected power converter controller (102) comprises:a current control circuit (106) andan extremum seeking control actuation circuit (108), whereinthe extremum seeking control actuation circuit (108) is configured to determine a phase-angle offset of a maincomponent of the power converter output voltage, ^^, beinggrid voltage amplitude, ^^^^, and capacitor leg voltage amplitude, ^^, to be maximized.

2. The grid-connected power converter controller (102) according to claim 1, wherein the extremum seeking control actuationcircuit (108) is configured to determine a phase-angle offset of the main component of the power converter output voltage, ^^,based on optimization of the grid voltage amplitude, ^^^^.

3. The grid-connected power converter controller (102) according to claim 1 or 2, wherein the extremum seeking controlactuation circuit (108) is configured to determine a phase-angle offset of the main component of the power converter outputvoltage, ^^, based on optimization of the capacitor leg voltage amplitude, ^^.

4. The grid-connected power converter controller (102) according to any of the claims 1 to 3, wherein the extremum seekingcontrol actuation circuit (108) is configured to determine a phase-angle offset of the main component of the power converteroutput voltage, ^^, based on a phase at a time when the fault is detected and a frequency at a time when the fault is detected.

5. The grid-connected power converter controller (102) according to claim 4, wherein the extremum seeking control actuationcircuit (108) is configured to determine a phase-angle offset plus the phase at a time when the fault is detected and the integralof the frequency at a time when the fault is detected, given the main component of the power converter output voltage angle,^6. The grid-connected power converter controller (102) according to any preceding claim, wherein the maximum voltagereached is the maximum possible voltage of the grid, ^^^^.7 The grid-connected power converter controller (102) according to any preceding claim, wherein the maximum voltagereached is the capacitor leg voltage amplitude, ^^.

8. The grid-connected power converter controller (102) according to any preceding claim, wherein the fault detector circuit(110) is configured to detect the fault based on a Point of Common Coupling, PCC, voltage for the grid (104).

9. The grid-connected power converter controller (102) according to any preceding claim, further comprising a fault detectorcircuit (110) configured to detect a fault and in response thereto cause the extremum seeking control actuation circuit (108) todetermine the phase-angle offset.

10. The grid-connected power converter controller (102) according to claim 9, wherein the fault detector circuit (110) is furtherconfigured to switch an input to the current control circuit (106) from a reference current ^^^^^^ to a default current amplitude11. The grid-connected power converter controller (102) according to claim 10, wherein the default current amplitude ^^^^^^is a maximum current amplitude (^^^^).

12. The grid-connected power converter controller (102) according to claim 9 or 10, wherein the fault detector circuit (110) isfurther configured to disable outer loops.

13. A method (600) for a grid-connected power converter controller (102) configured to be connected to a grid (104), themethod (600) comprising:detecting a fault and in response thereto, determining a phase-angle offset of a main component of the power converter output voltage, ^^, angle based on gridvalues at a time when the fault is detected utilizing an extremum seeking algorithm, and obtaining a maximum voltage of the grid, ^^^^ , and capacitor leg voltage amplitude, ^^, through the phase-angle offset.

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