Soft-switching T-type three-level inverter, its modulation method and controller

Abstract

This invention discloses a soft-switching T-type three-level inverter, its modulation method, and controller, belonging to the field of power electronic conversion and control technology. This inverter removes the performance limit of a single switching device through parallel connection, increasing the availability of the switching device in high-power applications. Furthermore, by adding a pair of differential-mode inductors with low inductance to each phase, it achieves ZVS soft switching of the soft-switching T-type three-level inverter at a lower power density cost. In addition, by adopting independent modulation methods for the parallel bridge arms, and changing the current direction of the two differential-mode inductors connected to the first and second three-level bridge arms, the current flow direction when the switching transistors are turned on is changed, enabling each switching transistor in the inverter to achieve ZVS soft switching conditions, reducing system losses under specific operating conditions. Moreover, this modulation method is universal and can be applied to three-phase and single-phase systems, without being constrained by device type or converter type, exhibiting strong versatility.

Description

Technical Field

[0001] This invention belongs to the field of power electronic conversion and control technology, and more specifically, relates to a soft-switching T-type three-level inverter and its modulation method and controller. Background Technology

[0002] T-type three-level inverters, as power conversion devices, are widely used in AC photovoltaic, energy storage, and other DC units connected to AC loads or the power grid. With the increasing penetration rate of new energy sources in the power grid, the complexity of AC loads is increasing, requiring inverters to have higher control bandwidth. From the perspective of inverter equipment components, this means a higher switching frequency is needed. Therefore, some equipment manufacturers are now introducing SiC MOSFETs (Silicon Carbide Metal-Oxide-Semiconductor Field-Effect Transistors) into inverters, replacing traditional Si IGBTs (Silicon Insulated Gate Bipolar Transistors). Although the superior switching characteristics of SiC MOSFETs can increase the switching frequency, their current device losses still limit their application potential.

[0003] For SiC MOSFET devices, turn-on losses are much higher than turn-off losses. If turn-on losses can be eliminated through zero-voltage switching (ZVS) technology, there is great potential for frequency increase. In addition, it can also suppress the high dv / dt and di / dt caused by hard switching.

[0004] Therefore, this paper proposes a T-type three-level inverter suitable for ZVS soft switching and studies its ZVS soft switching modulation method for the T-type three-level inverter. This approach can provide potential for improving its switching frequency and is of great significance for improving the system's conversion efficiency, power density, and control capability. Summary of the Invention

[0005] In view of the above-mentioned defects or improvement needs of the existing technology, the present invention provides a soft-switching T-type three-level inverter and its modulation method and controller, thereby solving the technical problem of how to reduce system losses, improve system efficiency under all operating conditions, and further improve the power density of the entire system in high-power and high-frequency applications.

[0006] To achieve the above objectives, according to a first aspect of the present invention, a soft-switching T-type three-level inverter is provided, comprising: Three-phase parallel T-type three-level bridge arms and three AC output filter inductors; The three-phase parallel T-type three-level bridge arm includes three pairs of three-level bridge arms and three pairs of differential-mode inductors. One pair of three-level bridge arms and one pair of differential-mode inductors form a phase T-type three-level bridge arm. In a phase T-type three-level bridge arm, the output terminal of each three-level bridge arm is connected to the first terminal of a differential-mode inductor, the second terminals of two differential-mode inductors are connected, and the connection terminal between the two differential-mode inductors serves as the output terminal of a phase T-type three-level bridge arm. The output terminal of a phase T-type three-level bridge arm is connected to an AC output filter inductor.

[0007] According to the above soft-switching T-type three-level inverter, the switching transistors used in the three-phase parallel T-type three-level bridge arms are IGBTs or MOSFETs.

[0008] According to a second aspect of the present invention, a modulation method for a soft-switching T-type three-level inverter as described in the first aspect is provided, comprising: In the soft-switching T-type three-level inverter, the three-phase T-type three-level bridge arms are independently modulated; Modulation methods for any phase T-type three-level bridge arm include: Generate driving signals corresponding to the first three-level bridge arm and the second three-level bridge arm in any phase T-type three-level bridge arm, so as to drive the first three-level bridge arm and the second three-level bridge arm to operate based on the driving signals corresponding to the first three-level bridge arm and the second three-level bridge arm respectively, so as to achieve the zero-voltage turn-on soft-switching condition of the soft-switching T-type three-level inverter. The driving signals corresponding to the first three-level bridge arm and the second three-level bridge arm respectively enable the action of the second three-level bridge arm to always be delayed compared to the first three-level bridge arm, resulting in the current direction of the two differential mode inductors connected to the first three-level bridge arm and the second three-level bridge arm changing alternately.

[0009] According to the above modulation method, generating driving signals corresponding to the first and second three-level bridge arms in any phase T-type three-level bridge arm, and driving the first and second three-level bridge arms to operate based on the driving signals corresponding to the first and second three-level bridge arms respectively, specifically includes: Obtain the current of the differential mode inductor connected to the first three-level bridge arm and the second three-level bridge arm in any phase T-type three-level bridge arm, and the current of the AC output filter inductor connected to the output terminal of any phase T-type three-level bridge arm; A sinusoidal modulation wave is generated based on the current of the AC output filter inductor connected to the output terminal of any of the phase T-type three-level bridge arms, and a drive signal corresponding to the first three-level bridge arm is generated based on the sinusoidal modulation wave using a carrier-based pulse width modulation method.

[0010] According to the above modulation method, generating driving signals corresponding to the first and second three-level bridge arms in any phase T-type three-level bridge arm, and driving the first and second three-level bridge arms to operate based on the driving signals corresponding to the first and second three-level bridge arms respectively, specifically includes: Within one switching cycle corresponding to the sinusoidal modulation wave, the first three-level bridge arm is driven to operate first based on the drive signal corresponding to the first three-level bridge arm, so that there is a level difference between the first three-level bridge arm and the second three-level bridge arm. Under the influence of the level difference, the current of the differential mode inductor connected to the two three-level bridge arms drops from the peak value to zero and rises from zero to the peak value, respectively. After the current exchange of the differential mode inductor connected to the two three-level bridge arms is completed, the level of the drive signal corresponding to the second three-level bridge arm is switched.

[0011] According to the above modulation method, after the current exchange of the differential mode inductors connected to the two three-level bridge arms is completed, switching the level of the drive signal corresponding to the second three-level bridge arm specifically includes: Within one switching cycle corresponding to the sinusoidal modulation wave, when the sinusoidal modulation wave is in the positive half-cycle, if the trigger condition i is satisfied... Lx1 >i Lx2 And i Lx2 <-I ZVS Then, the level of the drive signal corresponding to the second three-level bridge arm is set to +1. If the trigger condition i is met... Lx1 Lx2 And i Lx1 <-I ZVS Then, the level of the driving signal corresponding to the second three-level bridge arm is set to 0; when the sinusoidal modulation wave is in the negative half-cycle, if the trigger condition i is met... Lx1 Lx2 And i Lx2 >I ZVS Then, the level of the drive signal corresponding to the second three-level bridge arm is set to -1. If the trigger condition i is met... Lx1 >i Lx2 And i Lx1 >I ZVS Then the level of the drive signal corresponding to the second three-level bridge arm is set to 0; Among them, i Lx1 i is the current of the differential mode inductor connected to the first three-level bridge arm. Lx2 For the current of the differential mode inductor connected to the second three-level bridge arm, I ZVS To meet the minimum reverse current required for the complete charging and discharging of the output capacitor of the switching transistor.

[0012] ​​According to a third aspect of the invention, a controller is provided for performing the modulation method as described in the second aspect.

[0013] According to a fourth aspect of the present invention, an electronic device is provided, comprising: a computer-readable storage medium and a processor; The computer-readable storage medium is used to store executable instructions; The processor is configured to read executable instructions stored in the computer-readable storage medium and execute the method as described in the second aspect.

[0014] According to a fifth aspect of the invention, a computer-readable storage medium is provided, the computer-readable storage medium storing computer instructions for causing a processor to perform the method as described in the second aspect.

[0015] In summary, compared with the prior art, the above-described technical solutions conceived by this invention can achieve the following beneficial effects: This invention provides a soft-switching T-type three-level inverter suitable for ZVS soft switching. By using parallel connection, the performance limit of a single switching device is removed, increasing the availability of the switching device in high-power applications. Furthermore, by adding a pair of differential-mode inductors with small inductance to each phase, ZVS soft switching of the T-type three-level inverter is achieved at a lower power density cost. Furthermore, the ZVS soft-switching modulation method for the aforementioned T-type three-level inverter provided by this invention adopts an independent and differentiated modulation method for the parallel bridge arms. By generating drive signals corresponding to the first and second three-level bridge arms respectively, the operation of the second three-level bridge arm is always delayed compared to the first three-level bridge arm. This causes the current direction of the two differential-mode inductors connected to the first and second three-level bridge arms to change alternately, thereby changing the current flow direction when the switching transistor is turned on. This allows each switching transistor in the inverter to achieve the ZVS soft-switching condition, reducing system losses under specific operating conditions. Moreover, the modulation method of this invention is universal, and the switching devices used can be IGBTs or MOSFETs. The modulation method can be applied to three-phase and single-phase systems, and is not limited by device type or converter type, thus exhibiting strong versatility. Attached Figure Description

[0016] Figure 1 This is a topology diagram of a soft-switching T-type three-level inverter provided in an embodiment of the present invention; Figure 2 The waveform diagram of a certain switching cycle of phase a when using the soft-switching modulation method provided in the embodiments of the present invention; Figure 3 The working principle diagram of the inverter when using the soft-switching modulation method provided in the embodiments of the present invention; Figure 4The waveforms of the differential mode inductor current and the AC filter inductor current during a certain power frequency cycle of phase a when using the soft-switching modulation method provided in this embodiment of the invention; Figure 5 The waveforms of the differential-mode inductor current and the AC filter inductor current during a certain power frequency cycle of phase a when using the traditional hard-switching modulation method are shown. Figure 6 The power loss histogram generated during the operation of the soft-switching modulation method provided in the embodiments of the present invention and the traditional hard-switching modulation method. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0018] This invention provides a soft-switching T-type three-level inverter, such as... Figure 1 As shown, it includes: Three-phase parallel T-type three-level bridge arm 110 and three AC output filter inductors 120; The three-phase parallel T-type three-level bridge arm includes three pairs of three-level bridge arms and three pairs of differential-mode inductors, and one pair of three-level bridge arms (e.g., as shown in the figure). Figure 1 The bridge arm 1 and bridge arm 2 of phase a are shown, and a pair of differential mode inductors (e.g., ... Figure 1 The L phase shown is a a1 and L a2 This forms a single-phase T-type three-level bridge arm. In a single-phase T-type three-level bridge arm, the output terminal of each three-level bridge arm is connected to the first terminal of a differential-mode inductor, and the second terminals of two differential-mode inductors are connected together. The connection between the two differential-mode inductors serves as the output terminal of the single-phase T-type three-level bridge arm, and the output terminal of the single-phase T-type three-level bridge arm is connected to an AC output filter inductor L. fx Connected.

[0019] In some embodiments, the switching transistors used in the three-level bridge arm can be IGBTs or MOSFETs.

[0020] In other embodiments, Figure 1 The relevant parameters of the topology shown are: rated capacity S =15kVA; DC input voltage V dc =800V; AC output voltage V o =220V(RMS); Output frequency f o=50Hz; Switching frequency f s =200kHz; AC output filter inductor L fx =75μH.

[0021] Preferably, the differential mode inductance value is... L x1 = L x2 =5μH, which is sufficient to complete the commutation between parallel bridge arms within the duration of one +1, 0, -1 level, so that the source-drain (or collector-emitter) current direction is changed before the switch is turned on, so as to complete ZVS soft switching.

[0022] As can be seen, the embodiments of the present invention provide a soft-switching T-type three-level inverter suitable for ZVS soft switching. By connecting in parallel, the performance limit of a single switching device is removed, increasing the availability of the switching device in high-power applications. Furthermore, by adding a pair of differential-mode inductors with small inductance to each phase, ZVS soft switching of the soft-switching T-type three-level inverter is achieved at a lower power density cost.

[0023] Based on the above-mentioned soft-switching T-type three-level inverter, this embodiment of the invention also provides a modulation method applicable to the above-mentioned soft-switching T-type three-level inverter, wherein the three-phase T-type three-level bridge arms in the soft-switching T-type three-level inverter are independently modulated, and each single-phase T-type three-level bridge arm can be modulated using the modulation method provided in this embodiment of the invention.

[0024] Specifically, the modulation methods for any phase T-type three-level bridge arm include: Generate corresponding drive signals for the first and second three-level bridge arms in the T-type three-level bridge arm of the phase, so as to drive the first and second three-level bridge arms to operate based on the corresponding drive signals, so as to achieve the zero-voltage turn-on soft-switching condition of the soft-switching T-type three-level inverter.

[0025] The driving signals corresponding to the first and second three-level bridge arms respectively enable the action of the second three-level bridge arm to always be delayed compared to the first three-level bridge arm, resulting in the alternating change of the current direction of the two differential mode inductors connected to the first and second three-level bridge arms.

[0026] Specifically, such as Figure 2 As shown, the waveform of phase a during a certain switching cycle is given when the above modulation method is used. The figure shows the switching modes of the first and second three-level bridge arms. At this time, it is in the positive half-cycle of the modulation wave, and the output levels of the two bridge arms switch between +1 and 0. i La1 ,i La2 These are the differential mode inductor currents connected to the first and second three-level bridge arms, respectively. i Lfa This refers to the current of the AC output filter inductor connected to this phase. t 1. t 3. t At time 5, based on the modulation wave information, the first three-level bridge arm actively switches the output level; t 2. t 4. t At time 6, the second three-level bridge arm switches its output level slightly later than the first three-level bridge arm. Through the above modulation method, at the moment the switching transistor is turned on, the current in the AC output filter inductor connected to this phase is greater than the minimum reverse current I required to fully charge and discharge the output capacitor of the switching transistor. ZVS Therefore, it can achieve the zero-voltage turn-on soft-switching condition of a soft-switching T-type three-level inverter.

[0027] In some embodiments, such as Figure 3 As shown, for the first three-level bridge arm (i.e. Figure 3 In the three-level bridge arm 1 of the phase, to generate the drive signal corresponding to the first three-level bridge arm, and to drive the first three-level bridge arm based on the drive signal corresponding to the first three-level bridge arm, the current of the differential-mode inductor connected to the first and second three-level bridge arms and the current of the AC filter inductor connected to the output terminal of the phase T-type three-level bridge arm can be obtained. Subsequently, a sinusoidal modulation wave is generated based on the current of the AC filter inductor connected to the output terminal of the phase T-type three-level bridge arm, and the drive signal corresponding to the first three-level bridge arm is generated using a carrier-based pulse width modulation method for the sinusoidal modulation wave. Specifically, the currents of the two differential-mode inductors in the phase can be obtained. i Lx1 , i Lx2 (like Figure 3 The differential mode inductor current of phase a shown i La1 , i La2 and AC output filter inductor current i Lfx ( i Lfx = i Lx1 + i Lx2 ), the measured i Lfx With a pre-given reference current i refx Calculate the difference and send the difference value to the corresponding PR controller G. ix(s) The controller outputs a sinusoidal modulated wave. v mx The sinusoidal modulated wave v mx Intersecting with the positive and negative triangular carriers output by the carrier generator, a drive signal corresponding to the first three-level bridge arm is generated to drive the first three-level bridge arm.

[0028] In other embodiments, for the second three-level bridge arm (i.e. Figure 3 The three-level bridge arm 2 in the sinusoidal modulation wave v mx Within a corresponding switching cycle, the first three-level bridge arm is driven by the drive signal corresponding to it, causing it to operate first and creating a level difference between it and the second three-level bridge arm. Under this level difference, the currents of the differential-mode inductors connected to the two three-level bridge arms decrease from their peak value to zero and rise from zero to their peak value, respectively. After the current exchange between the differential-mode inductors connected to the two three-level bridge arms is complete—that is, when the current of one differential-mode inductor has decreased to zero and the current of the other has risen to its peak value—the level of the drive signal corresponding to the second three-level bridge arm is switched, generating a signal as follows: Figure 2 The drive signal shown.

[0029] Furthermore, in sinusoidal modulated waves v mx Within a corresponding switching cycle, when the sinusoidal modulation wave v mx When in the positive half-cycle, if the triggering condition i is met Lx1 >i Lx2 And i Lx2 <-I ZVS Then, the level of the drive signal corresponding to the second three-level bridge arm is set to +1. If the trigger condition i is met... Lx1 Lx2 And i Lx1 <-I ZVS Then, the level of the drive signal corresponding to the second three-level bridge arm is set to 0; when the sinusoidal modulation wave v mx When in the negative half-cycle, if the trigger condition i is met... Lx1 Lx2 And i Lx2 >I ZVS Then, the level of the drive signal corresponding to the second three-level bridge arm is set to -1. If the trigger condition i is met... Lx1 >i Lx2 And i Lx1 >I ZVS Then the level of the drive signal corresponding to the second three-level bridge arm will be set to 0.

[0030] Figure 4 ,​​ Figure 5 The waveforms of the differential-mode inductor current and AC filter inductor current in phase a during a certain power frequency cycle are shown when the above modulation method and the traditional hard-switching modulation method are used separately. As can be seen from the figure, the differential-mode inductor current waveform of the proposed modulation method differs from that of the traditional hard-switching method, but both exhibit high sinusoidal characteristics in the AC filter inductor current. The ZVS soft-switching modulation strategy provided in this embodiment of the invention can operate independently and is feasible.

[0031] Figure 6 The power loss generated when using the above modulation method and the traditional hard-switching modulation method separately is shown. The soft-switching modulation strategy provided in this embodiment of the invention generates lower losses and is more effective; within the rated capacity... S =15kVA, DC input voltage V dc =800V, AC output voltage V o =220V(RMS), Output Frequency f o =50Hz, switching frequency f s =200kHz, AC output filter inductor L fx Under the condition of 75μH, the loss is reduced by 25.6% compared with traditional hard-switching modulation.

[0032] In summary, the ZVS soft-switching modulation method for soft-switching T-type three-level inverters provided by this invention adopts independent modulation methods for the parallel bridge arms. By generating drive signals corresponding to the first and second three-level bridge arms respectively, the operation of the second three-level bridge arm is always delayed compared to the first three-level bridge arm. This causes the current direction of the two differential-mode inductors connected to the first and second three-level bridge arms to change alternately, thereby changing the current flow direction when the switching transistor is turned on. This allows each switching transistor in the inverter to achieve the ZVS soft-switching condition, reducing system losses under specific operating conditions. Furthermore, the modulation method of this invention is universal and can be applied to three-phase and single-phase systems, without being constrained by device type or converter type, thus exhibiting strong versatility.

[0033] Furthermore, embodiments of the present invention also provide a controller for executing the modulation method provided in any of the above embodiments.

[0034] This invention provides an electronic device, including: a computer-readable storage medium and a processor; The computer-readable storage medium is used to store executable instructions; The processor is configured to read executable instructions stored in the computer-readable storage medium and execute the method as described in any of the above embodiments.

[0035] This invention provides a computer-readable storage medium storing computer instructions that cause a processor to perform the method described in any of the above embodiments.

[0036] This invention provides a computer program product, including a computer program or instructions, which, when executed by a processor, implement the method described in any of the above embodiments.

[0037] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A modulation method for a soft-switching T-type three-level inverter, characterized in that, The soft-switching T-type three-level inverter includes three-phase parallel T-type three-level bridge arms and three AC output filter inductors. Each three-phase parallel T-type three-level bridge arm comprises three pairs of three-level bridge arms and three pairs of differential-mode inductors. One pair of three-level bridge arms and one pair of differential-mode inductors constitute one phase T-type three-level bridge arm. In one phase T-type three-level bridge arm, the output terminal of each three-level bridge arm is connected to the first terminal of one differential-mode inductor, and the second terminals of two differential-mode inductors are connected. The connection between the two differential-mode inductors serves as the output terminal of one phase T-type three-level bridge arm, and the output terminal of one phase T-type three-level bridge arm is connected to one AC output filter inductor. The three phase T-type three-level bridge arms in the soft-switching T-type three-level inverter are independently modulated. Modulation methods for any phase T-type three-level bridge arm include: Generate driving signals corresponding to the first three-level bridge arm and the second three-level bridge arm in any phase T-type three-level bridge arm, so as to drive the first three-level bridge arm and the second three-level bridge arm to operate based on the driving signals corresponding to the first three-level bridge arm and the second three-level bridge arm respectively, so as to achieve the zero-voltage turn-on soft-switching condition of the soft-switching T-type three-level inverter. The driving signals corresponding to the first three-level bridge arm and the second three-level bridge arm respectively enable the action of the second three-level bridge arm to always be delayed compared to the first three-level bridge arm, resulting in the current direction of the two differential mode inductors connected to the first three-level bridge arm and the second three-level bridge arm changing alternately.

2. The modulation method as described in claim 1, characterized in that, The switching transistors used in the three-phase parallel T-type three-level bridge arm are IGBTs or MOSFETs.

3. The modulation method as described in claim 1, characterized in that, The step of generating driving signals corresponding to the first and second three-level bridge arms in any phase T-type three-level bridge arm, and driving the first and second three-level bridge arms to operate based on the driving signals corresponding to the first and second three-level bridge arms respectively, specifically includes: Obtain the current of the differential mode inductor connected to the first three-level bridge arm and the second three-level bridge arm in any phase T-type three-level bridge arm, and the current of the AC output filter inductor connected to the output terminal of any phase T-type three-level bridge arm; A sinusoidal modulation wave is generated based on the current of the AC output filter inductor connected to the output terminal of any of the phase T-type three-level bridge arms, and a drive signal corresponding to the first three-level bridge arm is generated based on the sinusoidal modulation wave using a carrier-based pulse width modulation method.

4. The modulation method as described in claim 3, characterized in that, The step of generating driving signals corresponding to the first and second three-level bridge arms in any phase T-type three-level bridge arm, and driving the first and second three-level bridge arms to operate based on the driving signals corresponding to the first and second three-level bridge arms respectively, specifically includes: Within one switching cycle corresponding to the sinusoidal modulation wave, the first three-level bridge arm is driven to operate first based on the drive signal corresponding to the first three-level bridge arm, so that there is a level difference between the first three-level bridge arm and the second three-level bridge arm. Under the influence of the level difference, the current of the differential mode inductor connected to the two three-level bridge arms drops from the peak value to zero and rises from zero to the peak value, respectively. After the current exchange of the differential mode inductor connected to the two three-level bridge arms is completed, the level of the drive signal corresponding to the second three-level bridge arm is switched.

5. The modulation method as described in claim 4, characterized in that, After the current exchange with the differential mode inductor connected to the two three-level bridge arms is completed, the level of the drive signal corresponding to the second three-level bridge arm is switched, specifically including: Within one switching cycle corresponding to the sinusoidal modulation wave, when the sinusoidal modulation wave is in the positive half-cycle, if the trigger condition i is satisfied... Lx1 >i Lx2 And i Lx2 <-I ZVS Then, the level of the drive signal corresponding to the second three-level bridge arm is set to +1. If the trigger condition i is met... Lx1 Lx2 And i Lx1 <-I ZVS Then, the level of the driving signal corresponding to the second three-level bridge arm is set to 0; when the sinusoidal modulation wave is in the negative half-cycle, if the trigger condition i is met... Lx1 Lx2 And i Lx2 >I ZVS Then, the level of the drive signal corresponding to the second three-level bridge arm is set to -1. If the trigger condition i is met... Lx1 >i Lx2 And i Lx1 >I ZVS Then the level of the drive signal corresponding to the second three-level bridge arm is set to 0;​​ Among them, i Lx1 i is the current of the differential mode inductor connected to the first three-level bridge arm. Lx2 For the current of the differential mode inductor connected to the second three-level bridge arm, I ZVS To meet the minimum reverse current required for the complete charging and discharging of the output capacitor of the switching transistor.

6. A controller, characterized in that, Used to perform the modulation method as described in any one of claims 1-5.

7. An electronic device, characterized in that, include: Computer-readable storage media and processors; The computer-readable storage medium is used to store executable instructions; The processor is configured to read executable instructions stored in the computer-readable storage medium and execute the modulation method as described in any one of claims 1-5.

8. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores computer instructions for causing a processor to perform the modulation method as described in any one of claims 1-5.

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