WO2022269104A1 - Método y sistema de control para convertidores dc/ac - Google Patents
Método y sistema de control para convertidores dc/ac Download PDFInfo
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- WO2022269104A1 WO2022269104A1 PCT/ES2021/070463 ES2021070463W WO2022269104A1 WO 2022269104 A1 WO2022269104 A1 WO 2022269104A1 ES 2021070463 W ES2021070463 W ES 2021070463W WO 2022269104 A1 WO2022269104 A1 WO 2022269104A1
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- voltage
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Classifications
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
- H02M7/5387—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration
- H02M7/53871—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current
- H02M7/53875—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current with analogue control of three-phase output
Definitions
- the present invention belongs to the electrical grid sector, and in particular to that of electronic converters for connecting renewable energy generation sources to the electrical grid. More specifically, the invention relates to a control method and system for electronic converters.
- inverters have been connected to the grid controlled as a sinusoidal current source at fundamental frequency, so that they follow the voltage waveform at the connection point to deliver the desired active and reactive power.
- This control provides a correct behavior under the assumption of the availability of a robust voltage network.
- the growing penetration of renewable energy sources connected through electronic converters is causing a decrease in the power ratio of synchronous generators with respect to the total power of the system.
- maintaining the current control of electronic converters would compromise the quality and stability of the electrical network in the medium term. To avoid this, the electronic converters will have to provide the functionalities currently provided by the synchronous generator.
- a widespread strategy consists of implementing a cascade control with an external voltage loop and an internal current loop whose current references are saturated at the maximum current value allowed.
- An example of this method is shown in the document "L. Zhang, L. Harnefors, and H.-P. Nee, “Power-Synchronization Control of Grid-Connected Voltage-Source Converters,” IEEE Trans. Power Syst., vol. 25, no. 2, p. 809-820, May 2010”.
- This technique has the disadvantage that the operation of the current control in situations where it is not necessary to limit current causes a greater harmonic distortion of the generated voltage, in case harmonic current components are demanded from the electronic converter.
- the introduction of resonant drivers tuned to the typical frequencies at which these harmonics usually appear has been proposed.
- Another of the methods proposed with a single voltage loop and which, like the previous one, is also based on limiting the current by limiting the voltage generated by the inverter, consists in calculating the maximum amplitude of the voltage that could be generated by the electronic converter without risk of overcurrent.
- This maximum voltage is calculated from the voltage measurement at the connection point, the impedance from the electronic converter to the connection point, and the maximum current supported by the electronic converter.
- An example of this method is found in US7804184B2.
- the limitation of the open-loop voltage means that this method does not provide precision to limit the current, which reduces the robustness of the method.
- this technique also has the disadvantage that it is an RMS control, which is why it is slow and causes the appearance of overcurrent in the first moments of the faults or overloads, which can cause damage to the electronic converter.
- the present invention provides a method and a control system that try to solve the drawbacks of the methods and systems described in the state of the art. Specifically, a control method and system for an electronic converter as a voltage source is provided, which provide the electronic converter with the ability to limit the current in fault or overload situations.
- a first aspect of the invention refers to a control method for a DC/AC electronic converter, comprising, for at least one phase of the DC/AC electronic converter: calculating, by means of a voltage controller, a first reference voltage at starting from predefined voltage setpoints and a phase voltage; calculating, by means of a current controller, a second reference voltage as a function of a difference between a predefined upper current limit and the current of said at least one phase, and of the phase voltage; calculating, by means of the current controller, a third reference voltage as a function of a difference between a predefined current lower limit and the current of said at least one phase, and of the phase voltage; comparing the first reference voltage with the second reference voltage; selecting the lower reference voltage between the first reference voltage and the second reference voltage; comparing the selected reference voltage with the third reference voltage; selecting as the control voltage to be generated by the electronic DC/AC converter the highest reference voltage between the selected reference voltage and the third reference voltage; and applying the selected control voltage to the at least one phase of the electronic DC/AC converter.
- a control method and system have a stage executed by means of a voltage controller and a stage executed by means of a current controller.
- the method and system are applicable, among others, to DC/AC (direct current / alternating current, English Direct Current / Alternating Current) converters.
- the converters can be connected in parallel with the mains or to a system of loads isolated from the network, either independently or with several converters in parallel.
- the current control loop consists of two branches per phase, one to control the current to the maximum positive value and another to control it to the maximum negative value.
- the only difference between these two branches is the reference current, which in one case is the current maximum allowed current and in the other, in a more general case, its opposite (that is, the negative value of the maximum allowed current).
- the current of the phase (or of each phase) of the converter has been previously measured.
- the difference between a predefined upper (or lower, where appropriate) current limit and the current of said at least one phase is also called current error. This current error is used as the input of the current controller, which comprises previously determined parameters.
- the calculation of the first, second and third reference voltages is carried out in parallel, where parallel is understood to mean that the first, second and third reference voltages are calculated substantially simultaneously (as opposed to, for example, cascading, in in which case a first loop or external loop, of voltage, determines the reference of a second loop or internal loop, of current).
- the phase voltage is a voltage measured at some terminals of a capacitor of an output filter of the at least one phase.
- the phase voltage is a voltage measured at the output of the electronic converter.
- the output filter of at least one phase is an LC filter
- the voltage measured at the output of the electronic converter is the same as the voltage measured at the terminals of the output filter capacitor.
- the output filter of at least one phase is an LCL filter
- the voltage measured at the terminals of the capacitor is different from the voltage at the output of the electronic converter. In this case, any of the two voltages can be used as phase voltage.
- the phase voltage is a voltage obtained from a line voltage measurement.
- the control method is performed at a plurality of time instants.
- the cited instants of time refer, in the present description, to each sampling operation according to a frequency, that is to say, to the stroke of the clock.
- the sampling frequency falls within the usual ranges of controllers used in inverter control systems, for example, at the switching frequency of the converter or multiples or submultiples of it.
- the voltage controller calculates the reference voltage that should be generated in one phase (or each phase) by the electronic converter so that the corresponding phase behaves as an alternating voltage source with values of a given amplitude and phase.
- the current controller calculates two reference voltages that should be generated in one phase (or each phase) by the electronic converter-, so that the value of the current is between said upper current limit and said lower current limit.
- the step of calculating the second reference voltage comprises: providing as input to a first controller module the difference between the upper current limit and the current of the at least one phase; and adding the phase voltage to a voltage at the output of the first controller module, where the first controller module is a proportional regulator.
- the method comprises, before said phase voltage is added to the output voltage of the first driver module: filtering the phase voltage by means of a voltage filter; and leading the phase of the filtered phase voltage by means of a phase leading compensator.
- the step of calculating the third reference voltage comprises: providing as input to a second controller module the difference between the lower current limit and the phase current; and adding the phase voltage to a voltage at the output of the second controller module, where the second controller module is a proportional regulator, which can be equal to the first controller module.
- the method comprises, before said phase voltage is added to the output voltage of the second driver module: filtering the phase voltage by means of a voltage filter; and leading the phase of the filtered phase voltage by means of a phase leading compensator.
- any of the existing methods in the state of the art such as Grid-forming, can be used.
- control method is applied for each phase of the electronic DC/AC converter.
- the DC/AC electronic converter is a three-phase electronic converter, where the method of the first aspect of the invention is applied to each of the phases.
- an uncontrolled zero-sequence reference voltage is obtained for each phase from the selected control voltages to compensate for the effect of an uncontrolled zero-sequence component contained in the selected control voltages, and those non-controlled uncontrolled zero-sequence reference voltages are applied to the phases of the drive.
- the method comprises: calculating modulating ones from the uncontrolled zero-sequence reference voltages, and controlling some switches of the conversion stage of the DC/AC electronic converter based on said modulating ones.
- the method comprises: starting from the reference voltages without uncontrolled zero sequence, calculating modulating ones; introducing a desired or controlled homopolar component (such as, for example, a third harmonic) to said modulators, obtaining modulators with a homopolar component; and control some switches of the conversion stage of the DC/CA electronic converter from said modulating with zero-sequence component.
- a desired or controlled homopolar component such as, for example, a third harmonic
- a pulse width modulator uses said modulating or modulating with zero-sequence component to generate the switch-on commands.
- the method includes a step of reducing the predefined voltage setpoints if any of the control voltages are imposed by the current controller. For example, saturation techniques with anti-windup are applied.
- a second aspect of the invention relates to a control system for a DC/AA electronic converter that carries out the method described in the first aspect of the invention.
- the control system comprises: a voltage controller configured to, for at least one phase of the conversion stage of the DC/AC electronic converter, calculate a first reference voltage from predefined voltage setpoints and a phase voltage; a current controller configured to, for said at least one phase of the conversion stage of the DC/AC electronic converter, calculate a second reference voltage as a function of a difference between the upper current limit and the phase current, and the phase voltage and a third reference voltage as a function of a difference between the current lower limit and the phase current, and the phase voltage; a control unit configured to: compare the first reference voltage with the second reference voltage, select the lower reference voltage between the first reference voltage and the second reference voltage, compare the selected reference voltage with the third voltage reference voltage, and selecting as the control voltage to be generated by the conversion stage of the DC/AC electronic converter the highest reference voltage among the selected reference voltage and the third reference voltage; means for applying the selected
- control unit is further configured to obtain an uncontrolled zero-sequence reference voltage for each phase of the conversion stage of the electronic DC/AC converter from said selected control voltages to compensate for the effect of an uncontrolled zero-sequence component contained in at least one of the selected control voltages.
- the voltage controller further comprises a control loop to reduce predefined voltage setpoints if any of the control voltages are imposed by the current controller.
- the proposed method and control system require a simple calculation of the phase voltage and an implementation of the phase voltage that substantially immediately converges the phase current to values between an upper limit current and a current lower limit, so that neither the converter (also called inverter throughout this description), for example, the semiconductors thereof, nor the phases of the electric generator, are damaged by overheating.
- control method and system of the invention make it possible to detect both an intensity greater than a maximum intensity and an intensity less than a minimum intensity. It is not, as in other control systems of the state of the art, necessary to wait a certain time -for example, half a period- in order to compare the actual phase current against a maximum current again.
- the speed in the detection of overcurrents is of great importance due, for example, to the rapid heating suffered by semiconductors.
- the method and control system of the invention are applicable both to single-phase inverters and to each of the phases of a three-phase inverter.
- current control can cause asymmetry in phase voltages. This asymmetry is compensated according to certain embodiments of the invention by calculating a modulating for each phase of the electronic converter.
- the phase or, where appropriate, each of the phases of the electronic converter is controlled, independently, as a voltage source at times when there is no risk of overcurrent, that is, under normal operating conditions, while at those moments in which there is a risk of overcurrent in a phase, due to faults or overloads, it will be the current control loop that automatically takes control of the phase .
- the proposed method presents, among others, the following advantages: • Under normal operating conditions, functioning as a voltage source provides the inverter with all the features of the grid-forming mode: active power management, contribution of harmonics and unbalances, contribution of inertia and damping to the system, etc.
- Carrying out the current control with the instantaneous value provides the electronic converter with the capacity to limit overcurrents during the first moments of faults or overloads.
- the invention relates to a phase control method according to claim 1 and to a control system according to claim 22, capable of implementing said method.
- the dependent claims refer to different embodiments of the invention.
- Figure 1A shows a connection diagram of an electronic converter, whose input is a power source or a storage system and at its output it is connected to the main electrical network, to a load in the case of a single-phase converter or to several loads in the case of being a three-phase converter.
- the electronic converter has been represented as a conversion block followed by an output filter.
- Figure 1B shows a connection diagram of an electronic converter similar to that of Figure 1A, with the difference that the conversion block of the electronic converter in this figure is different from that of Figure 1A.
- Figure 2 shows a block diagram that generically represents the implementation of voltage control for the electronic converter to operate as a voltage source.
- Figure 3 shows a block diagram corresponding to the realization of the current control for the phase of a single-phase converter or for one of the phases of the three-phase electronic converter, which includes the loop for controlling the current to the maximum positive value and the loop for check the current at the maximum negative value and that it is analogous for the rest of the phases, if any.
- Figure 4 shows the implementation of the control proposed in this invention for the phase of a single-phase converter or one of the phases of the three-phase converter, which is analogous for the rest of the phases.
- Figure 5 shows the implementation in the form of a block diagram of the calculation of uncontrolled zero-sequence control voltages from the selected control voltages.
- Optional modulating calculation stages and controlled zero-sequence component introduction are also included.
- Figure 6 shows a block diagram corresponding to positive maximum current control for one phase of the electronic converter of a preferred embodiment of the method of the invention, which embodiment is analogous to negative maximum current control.
- Figure 7 shows the results of the simulation of the electronic converter with the proposed method against an overload of 20%.
- Figure 8 shows the results of the simulation of the electronic converter with the proposed method against the connection and start of an asynchronous machine.
- the control method of the invention is adapted to control a DC/AC electronic converter 1 as a voltage source, providing it with the capacity to limit the current in those situations in which overcurrents may occur, such as faults, overloads, short circuits or voltage dips.
- the electronic converter 1 may be working in parallel with other electronic converters and/or electrical generators.
- the electronic converter 1 can be connected at its output to the main electrical network, to a load (for example, in the case of a single-phase converter) or to a set of isolated loads (for example, in the case of a three-phase converter).
- the events that cause the appearance of overcurrents can be both symmetrical and asymmetrical.
- Figures 1A and 1B show the connection diagram of an electronic converter 1, specifically of a DC/AC electronic converter.
- the connection diagram of an electronic DC/AC converter 1 of figures 1A-1B refers both to the phase of a single-phase converter and to one of the phases of a three-phase converter.
- Input 2 of converter 1 can be a power source or a storage system.
- an energy source it can be of different types, such as a renewable generation source (solar or wind, for example).
- a storage system this can be a battery or a capacitor bank, for example.
- converter 1 can be connected to the main electrical network, to a load in the case of a single-phase converter or to several loads in the case of a three-phase converter (generally represented by reference 3).
- the electronic converter 1 has been schematically represented as two blocks 11, 12 (11', 12 in figure 1B).
- Block 11, 11' represents the conversion stage.
- Block 12 represents the output filter.
- Two possible conversion schemes 11, 11' are shown without limitation, but an expert will understand that any other conventional conversion step can be used.
- the output filter 12 in both figures an LCL filter has been used, but an LC filter or any other variant could alternatively be used.
- the output filter 12 is intended to filter the switching harmonics.
- the control method implements a control in the electronic converter 1, based on a control of an output voltage e (hereinafter called phase voltage) in one or more phases and a control of the current i of the converter (in general , of the current of at least one of its phases) that are executed at all times and in parallel. Specifically, the control method is applied to the phase (or in general, to one or more phases) of the conversion stage 11 , 11' from the converter.
- phase voltage an output voltage
- i of the converter in general , of the current of at least one of its phases
- the phase voltage can be either the voltage Ve measured across the capacitor of the output filter 12, or the voltage VPCC at the network or load (loads) 3.
- the output filter 12 of the phase (or phases) is an LC filter, not illustrated, the voltage measured at the output (in the network or load 3) is the same than the voltage measured across the capacitor of the LC filter. This voltage is then the phase voltage referred to in this description.
- the phase voltage can be calculated indirectly through the measurement of the line voltage, not illustrated (referring to the three-phase converter for example).
- the voltage control implemented in a voltage controller 21 shown for example in figure 2, calculates the reference voltages e r,v , es,v , e t,v that should be generated in each phase. (if the converter is three-phase) or in phase (if the converter is single-phase) by electronic converter 1 so that this phase behaves like an alternating voltage source with certain amplitude and phase values, that is, those desired in depending on the load, the loads or the network to which the converter will be connected.
- three reference voltages e r,v , es,v , et ,v corresponding to a three-phase system are shown.
- the current control loop implemented in a current controller 30 shown for example in figure 3, calculates the reference voltages ep ° s e 3 , ep ° s e 3 , ep ° s e 9 , which should be generated in each phase (if the converter is three-phase) or in the phase (if the converter is single-phase) by the electronic converter 1 so that the current does not exceed the defined maximum value.
- the phase or “each phase” it must be understood that it can be the only phase if the converter is single-phase or one or each of the three phases if the converter is three-phase.
- the reference voltages obtained according to the method described below are compared.
- the voltage generated by the inverter in each phase is equal to the reference voltage calculated by the output voltage control, that is, the electronic converter 1 generates the voltage commands 22 previously. calculated.
- the reference voltage of one or several phases
- the current control is more restrictive than that provided by the voltage control.
- the voltage generated by the electronic converter 1 is equal to the reference voltage provided by the current control, which ensures current control at a defined maximum value at the expense of a voltage reduction. output.
- voltage control can be represented, for example, by the diagram in figure 2.
- the current measurements i r , i s , i t (in the case of a three-phase converter with phases r, s, t) or, in general, the current i (see figures 1A-1B) of the electronic converter 1 and the phase voltages ve r , ve s , vc t at the output, for example, at the terminals of the output filter capacitors, are used to determine the voltage setpoints 22.
- these set points 22 are determined by a selected grid-forming method 20 .
- grid-forming methods 20 such as droop control and virtual synchronous machine, but their choice is outside the scope of the present invention.
- the voltage controller 21 From the voltage commands 22 and from said phase voltages ve r , ve s , vc t , the voltage controller 21 obtains the reference voltages e r,v , es,v , e t,v that it must generate the electronic converter 1 to function as a voltage source.
- the method carried out by the tension controller 21 is outside the scope of the present invention.
- the voltage controller 21 can calculate the reference voltages e r,v , es,v , et ,v by means of open-loop control of the voltage, control of the instantaneous value of the voltage in alpha axes and beta or in d and q axes, among others.
- Figure 3 shows a possible implementation of the current control 30.
- the proposed current control 30 consists of two closed control loops per phase, one to control the current to a maximum positive value Lax and another to control it to the maximum negative value - Lax. .
- the current control closed loop to control the current at a maximum positive value consists of a first adder 33 that has the reference current ax at its positive input and the phase current i r at its negative input. This current is the one that circulates through the corresponding phase of the converter. This intensity has been previously measured.
- the result of the sum is the current error, and it is the input of a controller C(s) 31 whose function is to generate a voltage value v ⁇ ° s , which is the positive input of a second adder 35 in which is added to the value of voltage v ⁇ ° s , in its other positive input, the value resulting from filtering the phase voltage ver r in a filter FT vc (s) 37, so that at the output of the second adder 35 the tension e ° s is obtained.
- the input to the filter 37 is the voltage vc r at the output of the corresponding phase, for example, across an output filter capacitor. It should be noted that, if the value of i r is greater than that of the reference current Lax, the resulting voltage e ° s of this closed current control loop will be less than the voltage value entered in the second adder 35.
- the current control closed loop to control the current at a maximum negative value consists of a third adder 34 (first adder of this closed loop) that has at its positive input the current of reference -Lax and in its negative input the phase current i r .
- the result of the sum is the current error of this loop, and it is the input of a controller C(s) 32 whose function is to generate a voltage value v 3 , which is the positive input of a fourth adder 36 (second adder of this closed loop), in which the value of voltage v 9 is added, in its other positive input, the value resulting from filtering phase voltage ver r in a filter FT vc (s) 38, so that in the output of the fourth adder 36 obtains the voltage e 3 .
- a controller C(s) 32 whose function is to generate a voltage value v 3 , which is the positive input of a fourth adder 36 (second adder of this closed loop), in which the value of voltage v 9 is added, in its other positive input, the value resulting from filtering phase voltage ver r in a filter FT vc (s) 38, so that in the output of the fourth adder 36 obtains the voltage e 3 .
- phase s For the phases s, t, not illustrated in figure 3, current control loops are used to control the current at a maximum positive value and a maximum negative value, respectively, similar to the two loops illustrated in figure 3.
- both the first adder 33 and the third adder 34 have the phase current i s at their negative input and the input to the filter 37 is the voltage vc s at the output of phase s.
- both the first adder 33 and the third adder 34 have the phase current i t at their negative input and the input to the filter 37 is the voltage ve t at the output of phase t.
- the two current control loops provide the reference voltages e 9 ° s e TM 9 .
- phase t the two current control loops provide the reference voltages e ° s e 3 .
- the Lax, -Lax current references can be configured dynamically for the development of tasks such as protection of the electronic converter 1 against overtemperatures or variation of the allowed current limit as a function of time during the fault to facilitate its dissipation, among others.
- Another possible application of the dynamic variation of the reference currents is, for example, the variation of the current range within which the reference voltage calculated by the voltage control is considered the optimum phase voltage.
- the references of the positive and negative maximum current controls can be modified according to profiles or calculations defined from predetermined objectives.
- control proposed in the present invention is applicable to the phase of a single-phase electronic converter or to each of the phases of a three-phase electronic converter and is shown in figure 4.
- figure 4 has been further developed in detail the control of phase r, but the development is analogous for phases s, t, as explained in relation to figure 3.
- these controls the voltage one (figure 2) and the two of current (carried out through the current control loops of figure 3 as described), are executed in parallel and each of them calculates, at each instant and for each phase, the necessary reference voltage to carry out your goal.
- a voltage is selected as the control voltage, from the three reference voltages (e r,v , e 9 ° s , e 9 in the case of phase r; e s,v , e 9 ° s , e si 9 in the case of phase s; e t,v , et vi , e ti 9 in the case of phase t), as described below.
- the selected control voltage is applied to the corresponding phase of the conversion stage 11, 11' of the converter 1 (the applied voltage is referenced as e in figure 1A). In this way, the current l r of that phase will be between the predefined upper current limit Lax and the lower predefined current limit -Lax.
- a voltage control 21 calculates reference voltages e r,v , es,v , e t,v (one per phase, in the case of a three-phase system) based on voltage references 22. These voltages are the desirable phase voltages in the event of normal operation of the converter 1, that is, in the absence of faults in the electrical system .
- Figure 4 illustrates how the choice of the desirable phase voltage is made in two stages. In a first stage, the reference voltage e r,v calculated by the voltage control 21 and that calculated e 9 ° s by the maximum positive current control loop are compared in a first comparator 41, the smaller of them being chosen.
- a second comparator 42 the reference voltage selected in the previous stage is compared, that is, the output of the first comparator 41, and that calculated e 9 by the maximum negative current control, and the highest e r is chosen, s .
- anti-windup saturation techniques are applied to those controllers in which the reference voltage they provide is not selected.
- the control scheme of figure 4 is applicable to a single-phase converter, taking into account that in a single-phase converter it is only necessary to generate a reference voltage by the voltage control 21.
- the selected control voltage can then be applied to the corresponding phase of the conversion stage 11 of the electronic DC/AC converter 1 , so that the current i r of that phase falls between the predefined upper current limit L ax and the -Lax current lower limit predefined.
- the reference voltages selected in all the phases in the case of a three-phase converter, or in one of the phases in the case of a single-phase converter are determined by the voltage control.
- the reference voltage provided by the positive maximum current control will be less than that provided by the voltage control and greater than that provided by the negative maximum current control, since the first adder 33 of the current control closed current loop to control the current to positive maximum value and the so-called third adder 34 (first to act in the current control closed current loop to control the current to negative maximum value), operate in the same instant in which the intensity with which the first and second comparators 41, 42 operate is the same, and the reference voltage selected in that phase will be that calculated by the maximum positive current control loop.
- the reference voltage provided by the negative maximum current control will be greater than that provided by the voltage control and less than that provided by the positive maximum current control, and the reference voltage selected in that phase will be the one calculated by the negative maximum current control loop.
- the measurements of current i r and voltage ve r are filtered.
- the filters H ⁇ (s) 70 and H v (s) 71 respectively, before considering them for the different calculations, in order to eliminate switching harmonics and high-frequency noise.
- the filter H ⁇ (s) 70 provides at its output a measure of filtered current i r, f .
- the filters used can be implemented both analogically and digitally, and can be, for example, low-pass or high-pass filters, or a combination of different types of filters.
- Figure 6 shows a possible implementation of the current control for the positive branch (current control closed loop to control the current at maximum positive value), which is analogous to that of the negative branch (current control closed loop to control the current at negative maximum value).
- the controller C(s) 31 of figures 3 and 4 has been implemented as a proportional controller K p 731.
- an integral proportional type controller (Pl) can be used as a maximum current controller 31, 32 .
- other elements can be added to the current control loops, such as phase delay compensators, phase advance compensators, or a combination of both.
- compensators can be added both in the direct chain and in the feedback of the voltage at the output of the controller C(s) 31 , 32 to improve the control performance. It is also possible to implement active damping from the capacitor current measurement or any other variable.
- figure 6 includes a phase lead compensator AF(s) 72 applied to the voltage measurement v r , which could previously be filtered with the filter H v (s) 71.
- An embodiment is shown in which both things are done (filtering and phase lead compensation), but only one of them can also be done.
- the output vc r,f of the phase ahead compensator 72 is summed (adder 735) to the output of the controller 731 of the maximum current control of each one of the phases to compensate the delays introduced, for example, by the digitalization and the voltage filter H v (s) 71 used in this embodiment.
- an algorithm or module 53 can be introduced for the calculation, for each phase r, s, t, of the electronic converter 1, of a voltage reference voltage without uncontrolled zero-sequence er , es , et , from the selected reference voltages er,s , es,s , et ,s .
- a voltage reference voltage without uncontrolled zero-sequence er es , et
- the uncontrolled zero-sequence component that contains the control voltages is canceled or corrected, obtaining the reference voltages that must be imposed in each phase of the electronic converter 1.
- the blocks 50, 51, 52 represent, for each phase of a three-phase converter, the stages 41, 42 (figure 4) of the control of the proposed invention, in which, from the three reference voltages, one of the three reference voltages is selected. them as selected control voltage.
- block 50 refers to phase r and represents stages 41, 42 in which, from the reference voltages e r,v , e 9 ° s , e 3 , one of them is chosen as selected control voltage e r,s .
- Block 50 also provides a signal indicating whether the chosen control voltage e r,s comes (“YES” at the output of block 50) or not (“NO” at the output of block 50) from current control (i.e. that is, if it corresponds with e 9 ° s or with Blocks 51, 52 work analogously, but in relation to phases s, t, respectively.
- the Module 53 provides, for each phase, an uncontrolled zero-sequence reference voltage e r , es , e t .
- This uncontrolled zero-sequence reference voltage er , es , et is the one that is applied or imposed on the corresponding phase of the conversion stage 11, 11' of the electronic converter 1.
- the module 53 does not make any changes. That is: er — e r,s > es — es , s > e t ⁇ e t , s
- module 53 calculates the following reference voltages without uncontrolled zero-sequence er , es , e t : a) If it is the phase r voltage that comes from the current control:
- phase r the selected reference voltage in phase r is maintained as selected, and the two reference voltages (phases s, t) coming from the voltage control are adapted. b) If it is the voltage of phase s that comes from the current control:
- phase s the selected reference voltage in phase s is maintained as selected, and the two reference voltages (phases r, t) coming from the voltage control are adapted. c) If it is the voltage of phase t that comes from the current control:
- the selected reference voltage in phase t is maintained as selected, and the two reference voltages (phases r, s) coming from the voltage control are adapted.
- the module 53 calculates the following uncontrolled zero-sequence reference voltages e r , es , e t : a) If the voltages of the phases r and s are the ones imposed by the current control: e — e rs ; es — ess ; — ( er e s , s ) b) If it is the phase voltages r and t that are imposed by the current control: er — e r,s > e t — e t ⁇ S ; e s — (e rs £t,s) c) If it is the phase voltages s and t that are imposed by the current control: es — e s,s > e t :
- the module 53 prioritizes limiting current in the two phases with the highest level current. That is, the reference voltages without uncontrolled zero-sequence are calculated as if two of the three selected reference voltages e r,s , es,s , e t,s are imposed by current control: a ) If phases r and s are the two phases with the highest current: er — e r,s> e s — es,s> e t ⁇ ⁇ (.
- phases r and t are the two phases with the highest current: er — e r,s> e t — et ,s> e s — — ( e r,s ⁇ e t,s ) c) If the two phases s and t are the two phases with higher current: es — es,s> e t — et ,s > e r — — (. es,s — e t , s )
- the voltage that is applied by the electronic converter 1 in that phase is the selected reference voltage (the one provided by the control current), while in the phase or phases in which the reference voltage is imposed by the voltage control, the voltage applied by the electronic converter 1 in that phase is modified with respect to the reference voltage to eliminate the component zero sequence introduced by the control of the present invention.
- the three reference voltages are imposed by the current control, in which key two of them must be prioritized.
- the uncontrolled zero-sequence component introduced by the proposed control is canceled or minimized, while ensuring that the generated voltage is equal to the reference voltage in the phases in which it comes from the current control.
- the reference voltages without uncontrolled zero-sequence er , es , et in addition to being imposed or applied to the corresponding phase of the electronic converter 1 , can also be used to calculate some modulating m r ,d, m s , d , m t ,d as indicated by block 54 of figure 5.
- the calculation of modulators 54 is conventional and falls outside the scope of the present invention.
- These modulators can be used, for example, to control switches of the converter 1, for example, according to a pulse width modulation (PWM) method. That is, a PWM modulator can use the modulators to generate the power-on orders of the switches that make up converter 1.
- PWM pulse width modulation
- a desired zero sequence component m 0 can be introduced to the modulating m r ,d, m s ,d, m t ,d.
- a desired zero sequence component m 0 can be introduced to the modulating m r ,d, m s ,d, m t ,d.
- some modulators with zero sequence component m r are obtained. , m s , m t .
- the calculation of modulating with zero-sequence component m r , m s , m t is conventional and is outside the scope of the present invention.
- These modulators can be used for the same purpose as the modulators m r ,d, m s ,d, m t ,d, that is, for example, to control some switches of the converter 1 , for example according to a modulation method of pulse width (PWM).
- PWM pulse width
- the three-phase implementation applies, for example, to an electronic converter 1 as illustrated in figure 1A or 1B, controlled as a voltage source and to whose input a battery is connected (as a storage system 2) and to its output is connected to a set of 3 isolated ac loads through an LC output filter and a transformer (not shown).
- the first graph shows the currents (Amps) exchanged by electronic converter 1 and the positive and negative current references (in Amps) defined for current control
- the second graph the phase voltages (in Volts) generated at the load terminals and in the third the reference voltages (in Volts) of phase r calculated in parallel by the voltage control and by the positive and negative branches of the current control.
- the reference voltage selected at each instant is the most restrictive, which corresponds to the one with an intermediate value among the 3 calculated by the control loops.
- Figure 7 identifies the reference voltage selected in phase r at each instant (e rv , e 3 ° s and e 3 ).
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AU2021452327A AU2021452327A1 (en) | 2021-06-22 | 2021-06-22 | Control method and system for dc/ac converters |
EP21801579.0A EP4362316A1 (en) | 2021-06-22 | 2021-06-22 | Control method and system for dc/ac converters |
PCT/ES2021/070463 WO2022269104A1 (es) | 2021-06-22 | 2021-06-22 | Método y sistema de control para convertidores dc/ac |
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US7804184B2 (en) | 2009-01-23 | 2010-09-28 | General Electric Company | System and method for control of a grid connected power generating system |
EP2469699A2 (en) * | 2010-12-23 | 2012-06-27 | Daniel Friedrichs | Electrosurgical generator controller for regulation of electrosurgical generator output power |
EP2930840A2 (en) * | 2014-03-28 | 2015-10-14 | Kabushiki Kaisha Toshiba | Power conversion device |
US10756536B2 (en) | 2014-10-29 | 2020-08-25 | Aggreko Deutschland Gmbh | System for handling short circuits on an electrical network |
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2021
- 2021-06-22 WO PCT/ES2021/070463 patent/WO2022269104A1/es active Application Filing
- 2021-06-22 EP EP21801579.0A patent/EP4362316A1/en active Pending
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Patent Citations (4)
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US7804184B2 (en) | 2009-01-23 | 2010-09-28 | General Electric Company | System and method for control of a grid connected power generating system |
EP2469699A2 (en) * | 2010-12-23 | 2012-06-27 | Daniel Friedrichs | Electrosurgical generator controller for regulation of electrosurgical generator output power |
EP2930840A2 (en) * | 2014-03-28 | 2015-10-14 | Kabushiki Kaisha Toshiba | Power conversion device |
US10756536B2 (en) | 2014-10-29 | 2020-08-25 | Aggreko Deutschland Gmbh | System for handling short circuits on an electrical network |
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L. ZHANGL. HARNEFORSH.-P. NEE: "Power-Synchronization Control of Grid-Connected Voltage-Source Converters", IEEE TRANS. POWER SYST., vol. 25, no. 2, May 2010 (2010-05-01), pages 809 - 820 |
X. PEIY. KANG: "Short-Circuit Fault Protection Strategy for High-Power Three-Phase Three-Wire Inverter", IEEE TRANS. IND. INFORMATICS, vol. 8, no. 3, August 2012 (2012-08-01), pages 545 - 553, XP011454350, DOI: 10.1109/TII.2012.2187913 |
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