Method for controlling the switches of a multi-active-bridge converter
The method optimizes phase shift values in MAB converters by minimizing reactive power exchange and total losses, enhancing efficiency and reducing RMS currents, addressing inefficiencies at low power levels.
Patent Information
- Application Number
- FR2024006122
- Authority / Receiving Office
- FR · FR
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-06-10
- Publication Date
- 2025-12-12
AI Technical Summary
Existing methods for controlling multi-port active-bridge converters (MAB) are inefficient at low power levels and do not determine optimal phase shift values in real-time, leading to suboptimal performance and increased losses.
A method that iteratively calculates internal and external phase shifts by minimizing reactive power exchange and optimizing total losses or ZVS conditions, using a generalized harmonic approximation model to determine optimal phase shift values for each port.
The method significantly reduces total system losses and improves efficiency across the entire operating range, particularly at low power levels, while maintaining ZVS conditions and reducing RMS currents.
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Abstract
Description
Title of the invention: Method for controlling the switches of a multi-bridge active converter. Technical field
[0001] The invention lies in the field of power electronics, and in particular in the field of DC / DC conversion. The invention relates to a method for controlling the switches of a multi-port active-bridge converter (also called a MAB converter for Multi-port Active-Bridge).
[0002] A MAB converter is an energy concentrator topology that has emerged in recent years. This multiport structure has recently attracted considerable attention, particularly for applications using renewable energy sources and energy storage systems.
[0003] Fig. 1 illustrates an example of an MAB converter 1 connecting several sources (electrical grid 2, photovoltaic panel 3), loads 4 and electrical energy storage system (accumulator 5) to a multi-winding transformer 6 through a plurality of DC / AC converters 7. Electricity consumption, production and storage take place in one location, and with few conversion stages.
[0004] Fig. 2 illustrates in more detail the topology of the MAB converter.
[0005] Each port (Prtb Prt2, ..., Prt1, ..., Prt2) consists of a voltage source (Vb V2 , ..., Vi, ..., Vn), which represents either a real power supply or a load behaving like a voltage source, and an H-bridge (Pntb Pnt2, ..., Put, ..., Pntn) whose operation is known to those skilled in the art. Each H-bridge Put consists of four transistors (Tu, Ti2, Ti3, Ti4).
[0006] U represents the leakage inductance of the transformer winding of the Prf port, which can be connected to an external series inductance.
[0007] The MAB converter enables bidirectional power transfer, high efficiency and intrinsic electrical isolation.
[0008] The principle of controlling an MAB converter consists of supplying each port Prb with the active power P; which it needs at each instant.
[0009] The control system of an n-port MAB converter requires n control outputs, which are the n active powers. To vary these outputs, the control inputs must be adjusted. As is known, an MAB converter has two types of control inputs: internal phase shifts ai and external phase shifts ^i. The inputs and outputs of the control system are illustrated in [Fig. 3].
[0010] The power of the reference port is not controlled because it is determined by the law of conservation of power: the sum of the powers entering the MAB converter is equal to the sum of the powers leaving it. Therefore, the number of control outputs becomes (n-1) for an MAB with n ports.
[0011] Figure 4 illustrates the AC voltages at a reference port, for example the first port Prti, and at a port Prt;, over a switching period Ts, with the internal and external phase shifts.
[0012] By convention, the external phase shift of a so-called reference port is considered to be zero. All other ports are therefore offset relative to this port. The vl — / The external phase shift between port Prt; and port Prt; is noted ~ 'P; " (Pj. The internal phase shift of a port Prt; is noted ai.
[0013] It can be demonstrated that the switching instants of a port Prt, can be expressed as a function of its internal and external phase shifts with the following relationship:
[0014] T + T i\~ \ ( P }i + 2
[0015] r L2 “ 2 + [ <PÜ 2}-2st
[0016] Ts corresponds to the switching period of the converter | / y j.
[0017] Thus, by determining the internal phase shift and the external phase shift of a port, it is possible to calculate the switching times of the switches of each port.
[0018] Determining the internal phase shift ai and the external phase shift for each port amounts to solving a system of (n-1) equations with (2n-l) unknowns, which generates an infinite number of solutions.
[0019] A first technique for determining the control signal in a MAB converter consists of applying the so-called EPS (External Phase Shift) modulation, described in particular in the article by [Galeshi], in which the internal phase shift ai is considered to be zero for all ports. This technique has the advantage of offering a single solution (system of n equations with n unknowns); it is efficient when the converter operates at its rated power. However, the efficiency is not optimal at low power.
[0020] A second technique for determining the control signal in a MAB converter, described in particular in the article by [Hebala], consists of varying the internal phase shift ai and detecting a local minimum of the RMS current in the transformer ("disturb and observe"). The disturbance is performed on the converter in real time, without the need to study a mathematical model. This technique is simple to implement, and adding ports does not increase the complexity or computation time. However, only RMS currents are taken into consideration; thus, this This technique only considers the system's conduction losses. More generally, stopping at the first local minimum does not offer an optimized solution.
[0021] A third technique for determining the control signal in a MAB converter, described in particular in [Dey's] article, consists of creating a generic mathematical model that takes into account all the system variables. This technique requires significant computing power. The modeling is performed "offline" (upstream of the conversion), and then the optimal values of the internal and external phase shifts are stored in a table. During the conversion, the closest points are extracted from the table in real time. Under real-world conditions, it is not possible to store all the points, so the extraction is performed on values close to the actual points; thus, the values of the internal and external phase shifts may be suboptimal.
[0022] There is therefore a need to provide a method for controlling a MAB converter that maintains high efficiency at low power, and that can determine optimal phase shift values in real time. Summary of the invention
[0023] An object of the invention is therefore a method for controlling the switches of a converter with multiple active bridges and comprising n ports, the method comprising the steps of:
[0024] a) perform a sweep between 0 and n of the value of the internal phase shift of a so-called reference port, and, for each value of the internal phase shift of the reference port, the following sub-steps:
[0025] al) for each of the n-1 different ports of the reference port, calculate the internal phase shift by applying a condition for eliminating reactive power exchange between the ports, from the voltage measured across the ports;
[0026] a2) for each of the n-1 different ports of the reference port, calculate the phase shift external based on constraints on desired power values at each of the said n-1 ports different from the reference port;
[0027] a3) calculate a set of at least one power parameter comprising the total converter losses and, optionally, the number of converter switches in ZVS condition;
[0028] a4) determine an optimized value for the internal phase shift of the reference port, said optimized value corresponding to a global extremum of the set of at least one power parameter;
[0029] b) updating the switching commands of the switches according to the optimized values of the internal phase shift and the external phase shift of all ports, the optimized values of the internal phase shift and the external phase shift / \ being '^OPT / calculated from the optimized value of the internal phase shift of the reference port.
[0030] Advantageously, the total losses of the converter correspond to the sum of the conduction losses on all ports of the converter and the switching losses on all ports of the converter.
[0031] Advantageously, the set of at least one power parameter corresponds only to the total losses of the converter, the optimized value of the internal phase shift of the reference port corresponds to a local minimum of the total losses of the converter.
[0032] Advantageously, the set of at least one power parameter corresponds to the total losses of the converter and the number of switches of the converter in ZVS condition, the optimized value of the internal phase shift of the reference port corresponds to a maximum of the number of switches of the converter in ZVS condition.
[0033] Advantageously, if there are at least two maxima of the number of switches of the converter in ZVS condition, the optimized value of the internal phase shift of the reference port corresponds to a local minimum of the total losses of the converter among the at least two maxima of the number of switches of the converter in ZVS condition.
[0034] Advantageously, the method includes, between substeps a2) and a3), a substep a21) comprising the detection of at least one external phase shift having a value strictly greater than 37°, the method not comprising a step of updating the switching instants of the switches if at least one external phase shift having a value strictly greater than 37° is detected.
[0035] Advantageously, the method includes a step aO) of initializing to zero the value of the internal phase shift of all ports, and of assigning an external phase shift value which is calculated by external phase shift modulation.
[0036] Advantageously, the optimized values of the external phase shift are transmitted to a proportional-integral controller before step b).
[0037] Advantageously, the condition for eliminating reactive power exchange between two ports is defined by the following formula: [°°38i
[0039] Vj and V j correspond respectively to the DC voltage across the terminals of ports i and j;
[0040] ai and aj correspond respectively to the internal phase shift of ports i and j;
[0041] nü and nii correspond respectively to the turns ratio between port i and the reference port, and to the turns ratio between port j and the reference port.
[0042] Advantageously, the update of the switching commands of the switches is carried out provided that a change in voltage or desired power value across the terminals of at least one of the ports has been detected.
[0043] Advantageously, the desired power values are determined from a generalized harmonic approximation model of order k, and in which k=7 for the calculation of the total losses of the converter, and k=101 for the calculation of the number of switches of the converter in ZVS condition.
[0044] The invention also relates to a control device for the switches of a multi-bridge active converter comprising n ports, the device being configured to:
[0045] a) perform a sweep between 0 and ~ of the value of the internal phase shift of a so-called reference port, and, for each value of the internal phase shift of the reference port:
[0046] al) for each of the n-1 different ports of the reference port, calculate the internal phase shift by applying a condition for eliminating reactive power exchange between the ports, from the voltage measured across the ports;
[0047] a2) for each of the n-1 different ports of the reference port, calculate the phase shift external based on constraints on desired power values at each of the said n-1 ports different from the reference port;
[0048] a3) calculate a set of at least one power parameter corresponding to the total converter losses and, optionally, the number of converter switches in ZVS condition;
[0049] a4) determine an optimized value for the internal phase shift of the reference port, said optimized value corresponding to a global extremum of the set of at least one power parameter;
[0050] b) update switching commands of the switches according to the optimized values of the internal phase shift and the external phase shift of all ports, the optimized values of the internal phase shift and the external phase shift being calculated from the optimized value of the internal phase shift of the reference port.
[0051] The invention also relates to a conversion system, comprising an active multi-bridge converter comprising n ports, and further comprising a control device as mentioned above. Description of the figures
[0052] Other features, details and advantages of the invention will become apparent from the description made with reference to the accompanying drawings given by way of example.
[0053] Fig. 1, already described, illustrates an example of an MAB converter connected to different sources.
[0054] Fig. 2, already described, illustrates a topology of MAB converter.
[0055] Fig. 3, already described, illustrates the inputs and outputs of the MAB converter control.
[0056] Figure 4, already described, illustrates the AC voltage across the terminals of a port.
[0057] Fig. 5 and Fig. 6 illustrate two flowcharts of the process according to the invention.
[0058] Figure 7 illustrates the determination of an optimized value of the internal phase shift aWPT according to a first embodiment
[0059] Fig. 8 illustrates a Thevenin equivalent circuit of a port.
[0060] Figure 9 illustrates the determination of an optimized value for the internal phase shift aWPT according to a second embodiment
[0061] Figure 10 illustrates a diagram of the system capable of implementing the method according to the invention.
[0062] Fig. 11, Fig. 12, Fig. 13, Fig. 14 and Fig. 15 illustrate experimental results of the process according to the invention. Detailed description
[0063] The method according to the invention is based on scanning between 0 and 77 the value of the internal phase shift ai of a so-called reference port, for example the port Prti (any other port can be defined as a reference port). The method is iterated for a plurality of values of the internal phase shift aK. The iteration step can be predetermined and adjustable by the user, depending on the desired degree of accuracy.
[0064] For each value of the internal phase shift ai of the reference port Prti, the internal phase shift ^mps of the other ports is calculated, by applying a condition for eliminating reactive power exchange between the ports, from the voltage measured across the ports.
[0065] According to one embodiment, the condition for eliminating reactive power exchange between the ports can be determined as follows.
[0066] Using the first harmonic approximation of the alternating signals of an MAB converter, it can be determined that the reactive power Q.. exchanged between A port Prti and a port Prtj are equal to:
[0068] Vj corresponds to the DC voltage of the Prti port
[0069] ws = 2æf and fs is the switching frequency of the converter.
[0070] f not applicable, Yi = j
[0071] L^Li!w2 corresponds to the leakage inductance of a port Prt; with respect to the reference port Prti, and corresponds to the ratio of the number of turns between the port Prt; and the reference port Prti.
[0072] When reactive power flows through a converter, the circulating currents increase, as do the system losses. Therefore, minimizing reactive power exchange between ports increases system efficiency at certain operating points, particularly under light loads, because the ratio of reactive power to total apparent power is higher when active power is low. From equation #(1), we can deduce that eliminating reactive power exchange between ports can be achieved by realizing the following equality: vt / «i \ vi ( aj 1 6,1 7^.COS(- ) = TT".COS\~ ) #
[0073] Obtaining equality #(1) also implies that the RMS values of the first harmonics of the AC voltage of ports Prt; and Prtj are equal, which can be of interest when there are voltage offsets, because the variations in DC voltages are thus compensated, and smooth switching can thus be restored.
[0074] From equation #(2), we can deduce the internal phase shifts of the other ports, from the value of the internal phase shift ai of the reference port Prti:
[0075] o / C / «) \ \ = 2arccos —Ji xi £os ( — ) j
[0076] DC voltages can be measured by measuring devices known to those skilled in the art.
[0077] Similarly, for each value of the internal phase shift j of the reference port, and after calculating the internal phase shifts of the other ports using the previous expression, the external phase shifts of the non-reference ports are calculated from the constraints on the desired power values P, using the following expression derived from the generalized harmonic approximation model:
[0078] jri
[0079] Given that:
[0080] p._ _4_£ k=1 j_ ^_Lcos(kÇ)>Cos(k7)
[0081] 11 is the total number of ports of the MAB and h is the harmonic order.
[0082] The method also includes a substep of calculating a set of at least one power parameter corresponding to the total losses of the converter / p \ and, optionally, to the number of switches of the converter in 'total lossesjVIPS / ZVS condition, for each value of the internal phase shift of the reference port Prti
[0083] Thus, two embodiments can be envisaged.
[0084] According to a first embodiment, only the total losses of the converter are taken into consideration.
[0085] The total losses of the MAB converter are considered to be equal to the sum of the conduction losses Pamdi and the switching losses Pswi of all its ports. Other losses, such as iron losses, are neglected. The total losses P total lasses can therefore be calculated as follows:
[0086] p = yn p.yn p. 1 total losses condj^ W
[0087] The conduction losses Pcandi of a port Prt; can be calculated as follows:
[0088] p ..= (K. + 2Ra 2 * condi \ ' ^^ds^n- / irms
[0089] Ri corresponds to the series resistance at port Prt; and Rdspn corresponds to the resistance of an activated switch, such that a maximum of two switches are activated at a time in each port. Iij-ms is the RMS (Root Mean Square) value of the alternating current flowing through port Prt; the expression for which is defined by the following formula:
[0090] 2__Lfr'- 2, 'ij-ms ~ Ts J o
[0091] The expression for the total iFi current from port Prt to the other ports, referred to its own side of the transformer, can be defined as follows: [009211^)=^
[0093] with
[0094] . . xf . <z , -z x x j = L"-’o( (O )dt
[0095] = __^cos(^ ).cvs(k\wst- <p}.) ) +^cosUy ) ]
[0096] with / bare
[0097] The switching losses Pswj of a port Prt allow the soft switching loss of the switches on each port to be quantified. The switching losses PSwt are calculated by first determining whether at > 0 or si = 0.
[0098] If = 0, the switching losses P are calculated as follows:
[0099] PSWi = 2.VD(Til).ID(TiA).fs.[tON.(l-ZVSü) +tOFF] + 4J1^(^i)
[0100] With the following variables:
[0101] VD(Tik)=Vi
[0102]
[0103]
[0104] h)(Tik ) ~ Vu(Tik) I
[0105]
[0106]
[0107]
[0108]
[0109]
[0110] [YES]
[0112]
[0113]
[0114]
[0115] Lthf are respectively the voltage and inductance of the Thevenin equivalent circuit of a port Prt; (cf figure 9). An and Sjisont are real constants calculated from the initial conditions of the switching instant (0)=^(^-]) and vx ( 0 ) = 0) and Wr = 2æ f with fr the resonance frequency of the LC circuit composed of the Thevenin inductance L® and the parasitic capacitances. The loss caused by the charging / discharging of the parasitic capacitance of a switch is calculated as follows: corresponds to the parasitic capacity At the end of a switching instant, the final value of the voltage V cÜSS,final of the The parasitic capacitance Coss at power-up is therefore defined as follows: Vc^final ~ (0 in case of soft switching (ZVS) Vj in case of hard switching AV in case of incomplete soft switching Incomplete soft switching occurs when the capacitance of a port switch is not fully discharged when activated, leaving a residual AV voltage whose calculation is not detailed in this description. If O / > 0, the switching losses PSwi are calculated as follows: P™i = l[PoN( Al) +POFf( Al) +Pon(tI2) + PoFf(tî2) ] + 2-P^(Al) +2-Pc„s(Ti2) Put another way:
[0116] ^0(^1)-(^1)- / ,-(^--(1-^5^) + <off] +^0(^)-^0(^)- / / (^-(1-^¾) +tOFP} + 2Pc„(rn) +2Pc^Ta)
[0117] The switching instants Ta and rî2 have been defined previously, with reference to the [Fig.4]
[0118] Once the total converter losses have been calculated, the value of the internal phase shift aWPT qu reference port is determined for which the total converter losses are minimal. [Fig. 7] illustrates the total converter losses as a function of different values of the internal phase shift of the reference port at 60% of its rated power.
[0119] The simulation results in Figures 7 and 9 were obtained with a four-port MAB converter and the following parameters:
[0120] V^200V
[0121] V2=180V
[0122] V3=160V
[0123] F4 = 240V
[0124] 4 = 40½
[0125] Rated power of each port = 5001V
[0126] In the example of Figure 7, it appears that the losses are minimal for 04 = 1.8 rad. This value is the optimized value aWPT of the internal phase shift of the reference port.
[0127] The external phase shift of the reference port, and the internal and external phase shifts of the other ports are calculated from the optimized value of the internal phase shift of the reference port, from the formulas described above.
[0128] Thus, the number of degrees of freedom for controlling the MAB converter is reduced to n, where n is the total number of ports. The remaining control parameters are the (n-1) external phase shifts of the ports other than the reference port and the internal phase shift of the reference port. Therefore, the control method reduces to a system of (n-1) equations with n unknowns, which can be executed in real time.
[0129] For this first embodiment, it is advantageous to set k=7 for the generalized harmonic approximation of order k, for the calculation of the RMS current and conduction losses. This value offers a good compromise between accuracy and computation time.
[0130] According to a second embodiment, a set of at least one power parameter corresponding to the total losses of the converter and the number of switches of the converter in ZVS condition is calculated.
[0131] Thus, at each iteration of the internal phase shift ai of the reference port, the number of switches of the converter in ZVS condition and the total losses of the converter are recorded.
[0132] The calculation of the total losses of the converter is identical to the previous embodiment.
[0133] The determination of the soft switching condition (ZVS condition) is described in the table above described in relation to the first embodiment.
[0134] In the second embodiment, the choice of the optimal internal phase shift aims to maximize the number of switches in ZVS while reducing total losses as much as possible, whereas, in the first embodiment, the aim is only to minimize total losses, even if this leads to a smaller number of switches in ZVS.
[0135] It should be noted that a switch is zero-voltage activated (ZVS) if its drain current is negative during its switching instant. This negative current flows through its antiparallel diode, turning it on, hence the voltage drop across the switch. Therefore, in an ideal case, the ZVS operation of a switch depends solely on the direction of its current.
[0136] However, this condition is not sufficient in a practical converter. Indeed, the parasitic capacitance Cuss between the drain and source of the switch requires that a minimum amount of energy flow through it during the switching instant to charge or discharge. Consequently, a minimum current must flow through each port during its switching instants, assuming that the imposed dead time is long enough for the energy exchange to take place completely. This energy value can be calculated using the Thévenin equivalent circuit of a port Prt, shown in [Fig. 8].
[0137] The voltage source Vthi and the inductance Ltiû replace the remaining ports of the MAB converter and are calculated from the following formulas: 101381
[0139] ,z
[0140] For each port, there are four switching instants in a switching period Ts. These instants are shown in Figure 4. Since the current in each port is symmetrical from one half-cycle to the other, only two switching instants need to be studied for each port (Ai and Tty).
[0141] At each of these instants, one switch is turned on and another switch is turned off. The switch that is turned on is the switch on which the ZVS conditions are examined. Smooth switching (ZVS) will result in almost zero switching losses.
[0142] In [Fig.4], it is recalled that the switching times of a port can be expressed as a function of its phase shifts as follows:
[0143] _ _ (m
[0144] _ + ( m LJ ri2~ 2 + 2 )-2;t
[0145] With reference to the table above described for the first embodiment, to determine the condition of ZVS, a distinction is made depending on the case (¾ > 0 or ai - 0.
[0146] Thus, at each iteration of the process, that is to say for each value of the internal phase shift °h of the reference port, the number of transistors in soft switching condition is determined.
[0147] Figure 9 illustrates the evolution of the number of transistors in soft switching condition as a function of the value of the internal phase shift ai, for a given operating point where the power is equal to 60% of the rated power. The value of the internal phase shift exhibiting the maximum number of transistors in soft switching is considered to be the optimal value of the internal phase shift a^pp reference port (between 0.8 and 1.5 rad in [Fig. 9]).
[0148] For this second embodiment, it is advantageous to fix k=101 (in the generalized harmonic approximation of order k), for the calculation of the number of switches of the converter in ZVS condition.
[0149] This value also presents a good compromise between accuracy and computation time. Greater accuracy is required for calculating an instantaneous current than an RMS current, which explains why the optimal value of k is different compared to the first embodiment.
[0150] If several values of the optimal value of the internal phase shift aWPT have the same maximum of transistors in soft switching condition, a second test consists of determining, among the first set of values, the one for which the total losses are minimal.
[0151] For ports other than the reference port, the optimized values of the internal phase shift ai.OPT and the external phase shift ^lopt are determined from the optimized value of the internal phase shift of the reference port ^opt, according to the formulas previously introduced.
[0152] The method includes a final step which consists of updating switching commands of the switches according to the optimized values of the internal phase shift ai.OPT and the external phase shift ^opt of all ports.
[0153] To this end, and in a manner known to those skilled in the art, a microcontroller produces PWM control signals which are phase-shifted relative to each other according to the optimal values obtained from the internal and external phase shifts.
[0154] The choice of the first (minimizing losses) or the second (maximizing switches in ZVS) depends on the priorities set by the user.
[0155] If the priority is to maximize system efficiency, even if non-ZVS switching may occur on some switches, then the user may choose the first embodiment, i.e., seek to have minimal total losses.
[0156] Conversely, if electromagnetic compatibility is the priority, it is It is rather relevant to implement the second method of implementation.
[0157] It may be advantageous, when calculating the external phase shift, to detect, at each iteration of the internal phase shift ai of the reference port, whether the phase shift external angle has a value strictly greater than 37°. Indeed, beyond 37°, the difference between • / \ and becomes too important, and the approximation • / \ _ , sin\ipj Slnvp J — (p. The method used to calculate the output power of each port is no longer considered valid (see [Galeshi]). If the external phase shift of one of the ports has a value strictly greater than 37°, the current increases non-linearly in the MAB converter.
[0158] In this case, the method does not include a step of updating the converter control.
[0159] According to another advantageous embodiment, the method includes a step of initializing the total loss values of the Ptotai converter, the internal phase shift aï and the external phase shift of each port.
[0160] The initial values can be determined using EPS (Extreme Phase Shift) modulation, in which the internal phase shift ai is considered to be zero for all ports.
[0161] It may also be advantageous to implement the converter control update process provided that a change in voltage across at least one of the ports has been detected, which avoids a permanent strain on the computational resources of the converter control update device.
[0162] Figure 10 illustrates a block diagram of the control device 8 for the switches of a multi-active bridge converter 1 according to the invention. The control device 8 transmits the internal phase shift values ai,OPT to the MAB converter 1.
[0163] The control device 8 also allows the dynamic control of the different ports to be decoupled.
[0164] The power levels are measured at the different ports, and a closed loop with PI 9 (Proportional-Integral) controllers is added to correct the steady-state error due to the uncertainty of the mathematical model and the parameter values of the actual converter. The Proportional-Integral type control is at preferred because of its simplicity, but other controllers can be considered, provided they can also correct the static error.
[0165] Figure 11 and Figure 12 illustrate the total losses of the converter as a function of the value of the internal phase shift ai of the reference port, with a four-port MAB converter at different power levels.
[0166] Figure 11 shows that the method used according to the invention reduces the total system losses with respect to EPS modulation over its entire operating range, particularly at low power. Furthermore, for each operating point, there is a value of the internal phase shift ai of the reference port where these losses reach an overall minimum.
[0167] The presence of local minima in the total loss curve is caused by the saturation of certain internal phase shifts of ports other than the reference ports. These values cannot be negative or greater than ir in radians. The existence of local minima demonstrates that a "Perturb and Observe" type algorithm cannot achieve optimal operation, as it would stop at the first local minimum.
[0168] Figure 12 illustrates the number of switches in ZVS with the method according to the invention, compared to the number of switches in ZVS with an EPS modulation technique. The method according to the invention demonstrates that it also allows the restoration of the ZVS condition at certain switches. Furthermore, at all power levels, the ZVS condition is achieved on all port switches at certain values of the internal phase shift ai.
[0169] Figure 13 illustrates, on its left side, the experimental waveforms of the AC current and AC voltage at each port of a four-port MAB converter operating at 8% of its rated power, with a known prior art EPS modulation. Figure 13 illustrates, on its right side, the same data with the method according to the invention.
[0170] In the simulation of Figure 13, the average effective current flowing through each port at the chosen operating point is = 1.1 A when EPS modulation is applied, and is reduced to Irmsj = 462.5 mA using the method according to the invention.
[0171] In other words, the RMS current is reduced by approximately 58% with the method according to the invention at this operating point studied. Furthermore, it can be seen in [Fig. 13] that the ZVS condition is restored at ports 3 and 4, and that ZCS (zero-current switching) occurs at the stop switches with the method according to the invention. Peak AC currents are also reduced, resulting in less iron loss in the transformer and the inductors of the MAB converter.
[0172] Figures 14 and 15 illustrate, respectively, the experimental efficiency and loss curves obtained with a four-port MAB converter at different power levels. We can deduce that the proposed control strategy significantly reduces the total system losses, resulting in an increase in the overall efficiency of the MAB converter over its entire operating range. This gain is particularly noticeable at operating points where low power flows through the QAB converter.
[0173] References cited
[0174] [Galeshi] Soleiman Galeshi, David Frey, Yves Lembeye, “Efficient and scalable power control in multi-port active-bridge converters”, The 22nd European Conference on Power Electronics and Applications EPE'20 ECCE Europe, Sep 2020, Lyon, France. 10.23919 / EPE20ECCEEurope43536.2020.9215905, hal-03145571
[0175] [Hebala] O. M. Hebala, A. A. Aboushady, K. H. Ahmed, and I. Abdelsalam, « Generalized Active Power Flow Controller for Multiactive Bridge DC-DC Converters With Minimum-Current-Point-Tracking Algorithm, » IEEE Trans. Ind. Electron., vol. 69, no. 4, pp. 3764-3775, Apr. 2022, doi: 10.1109 / TIE.2021.3071681.
[0176] [Dey] S. Dey, A. Mallik, and A. Akturk, « Investigation of ZVS Criteria and Optimization of Switching Loss in a Triple Active Bridge Converter Using Penta-Phase-Shift Modulation, » IEEE J. Emerg. Sel. Topics Power Electron., vol. 10, no. 6, pp. 7014-7028, Dec. 2022, doi: 10.1109 / JESTPE.2022.3191987.
Claims
Demands
1. A method for controlling the switches of a converter with multiple active bridges and comprising n ports, the method comprising the steps of: - a) performing a sweep between 0 and 77 of the value of the internal phase shift fj of a so-called reference port, and, for each value ^1 / of the internal phase shift / \ of the reference port, the following substeps: — a1) for each of the n-1 ports different from the reference port, calculating the internal phase shift j by applying a condition for eliminating reactive power exchange between the ports, from the voltage measured across the ports; — a2) for each of the n-1 ports different from the reference port, calculating the external phase shift j from constraints on desired power values (p) at each of said n-1 ports different from the reference port;— a3) calculate a set of at least one power parameter including the total losses of the converter [pj] and, optionally, the number of converter switches in ZVS condition, the ZVS condition being defined by switching the switch at zero voltage; — a4) determine an optimized value of the internal phase shift / j of the reference port, said optimized value corresponding to a global extremum of the set of at least one power parameter; — b) update the switching commands of the switches as a function of the optimized values of the internal phase shift / j and the external phase shift / i,OPT / of all ports, the optimized values ^^OPT / of the internal phase shift / j and the external phase shift / i,OPT / being ^i,OPT / Wi,OPT / calculated from the optimized value of the internal phase shift of the reference port / j. LO PT J;
2. A method according to claim 1, wherein the total converter losses / p 1 correspond to the sum of the total losses / p / on all converter ports and the switching losses / p / on all converter ports.
3. A method according to any one of the preceding claims, wherein the set of at least one power parameter corresponds solely to the total losses of the converter / p Y the 'total losses / optimized value of the internal phase shift / \ of the reference port \a]OPT) corresponds to a local minimum of the total losses of the converter (P ,, )• x total losses /
4. A method according to any one of claims 1 or 2, wherein, the set of at least one power parameter corresponds to the total losses of the converter [p \ and the number ' total losses / of converter switches in ZVS condition, the optimized value of the internal phase shift / 1 of the reference port \<\OPT} corresponds to a maximum of the number of converter switches in ZVS condition.
5. A method according to claim 4, wherein, if there are at least two maxima of the number of switches of the converter in ZVS condition, the optimized value of the internal phase shift / j \aloPT} of the reference port corresponds to a local minimum of the total losses of the converter / p Y among the at least two maxima total losses / of the number of switches of the converter in ZVS condition.
6. A method according to any one of the preceding claims, comprising, between substeps a2) and a3), a substep a21) comprising the detection of at least one external phase shift / \ having a ^iMPS / value strictly greater than 37°, the method not comprising a step for updating the switching instants of the switches if at least one external phase shift j having a value strictly A temperature above 37° is detected.
7. A method according to any one of the preceding claims, comprising a step aO) of initializing to zero the value of the internal phase shift ) of all ports, and of assigning an external phase shift value which is calculated by external phase shift modulation.
8. A method according to any one of the preceding claims, wherein the optimized values of the external phase shift / \ are transmitted to a ^.OPT / proportional integral controller (9) before step b).
9. A method according to any one of the preceding claims, wherein the condition for eliminating reactive power exchange between two ports is defined by the following formula: V; ! ai\ Vi ( aj fn .-COSt ? ) — zïv.COS[ 2 / Vi and Vj correspond respectively to the DC voltage across ports * and j; aî and aj correspond respectively to the internal phase shift of ports 1 and . / ; nv and niJ correspond respectively to the turns ratio between port 1 and the reference port, and to the turns ratio between port j and the reference port.
10. A method according to any one of the preceding claims, wherein the update of the switching commands of the switches is performed subject to the condition that a change in voltage or desired power value across the terminals of at least one of the ports has been detected.
11. 1 A method according to any one of the preceding claims, wherein the desired power values [p 1 are determined from a k-order generalized harmonic approximation model, and wherein k=7 for the calculation of the total losses of the converter [p 1, and k= 101 for the calculation of the number of switches of the total losses / converter in ZVS condition.
12. 2. A control device for the switches of a multi-active-bridge converter comprising n ports, the device being configured to: - a) perform a sweep between 0 and Φ of the value of the internal phase shift of a so-called reference port, and, for each value of the internal phase shift j of the reference port, : — a1) for each of the n-1 different ports of the reference port, calculate the internal phase shift ) by applying a condition for eliminating reactive power exchange between the ports, from the voltage measured across the ports; — a2) for each of the n-1 different ports of the reference port, calculate the external phase shift from constraints on desired power values (pj) at each of said n-1 different ports of the reference port; — a3) calculate a set of at least one power parameter corresponding to the total losses of the converter / pj and, optionally, to the number of switches of the converter in ZVS condition; — a4) determine an optimized value of the internal phase shift / ) of the reference port, said optimized value corresponding to a global extremum of the set of at least one power parameter;- b) update switching commands of the switches based on the optimized values of the internal phase shift / \ and the external phase shift / \ of all ports, the optimized values ^.OPT / of the internal phase shift / ) and of the external phase shift / \ being ^iOPT / “PlOPT / calculated from the optimized value of the internal phase shift of the reference port / V\OPTJ;
13. Conversion system, comprising an active multi-bridge converter and comprising n ports, and further comprising a control device according to claim 12.